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Sample records for ion chamber response

  1. Response of large cavity ion chambers to space protons

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Khandelwal, G. S.

    1981-01-01

    The assumption that spherical-shell ion chamber rssponse is equal to the dose in the center of the cavity is found to be a poor approximation for ion chambers used for area monitoring in the space program. The dose response is calculated using the appropriate areal density distribution function. Effects of nuclear reaction are evaluated using proton buildup factors. Errors of up to 100% are found for some components of the space radiation environments.

  2. Response of air-filled ion chambers to high-intensity radiation pulses

    SciTech Connect

    Plum, M.; Brown, D.

    1993-06-01

    Ion chambers are one of the most popular types of detectors used for beam loss-monitor systems. To provide a foundation for the development of future loss-monitor systems, and to fully characterize the ion chambers in use at LAMPF, we have studied the response of air-filled cylindrical ion chambers to high-intensity, short-duration radiation pulses. The most intense pulses were about 180 rad in 250 ns (the equivalent steady-state dose rate was about 700 Mrad/h). We filled our chambers with nitrogen gas at 760 Torr and air at 600 Torr. The ion chambers were driven into extreme nonlinear response. We hope these data will be used to design loss-monitor systems based on air-filled ion chambers, thus eliminating the need for gas-flow systems and/or airtight ion chambers.

  3. Response of air-filled ion chambers to high-intensity radiation pulses

    SciTech Connect

    Plum, M.; Brown, D.

    1993-01-01

    Ion chambers are one of the most popular types of detectors used for beam loss-monitor systems. To provide a foundation for the development of future loss-monitor systems, and to fully characterize the ion chambers in use at LAMPF, we have studied the response of air-filled cylindrical ion chambers to high-intensity, short-duration radiation pulses. The most intense pulses were about 180 rad in 250 ns (the equivalent steady-state dose rate was about 700 Mrad/h). We filled our chambers with nitrogen gas at 760 Torr and air at 600 Torr. The ion chambers were driven into extreme nonlinear response. We hope these data will be used to design loss-monitor systems based on air-filled ion chambers, thus eliminating the need for gas-flow systems and/or airtight ion chambers.

  4. Influence of ion chamber response on in-air profile measurements in megavoltage photon beams.

    PubMed

    Tonkopi, E; McEwen, M R; Walters, B R B; Kawrakow, I

    2005-09-01

    This article presents an investigation of the influence of the ion chamber response, including buildup caps, on the measurement of in-air off-axis ratio (OAR) profiles in megavoltage photon beams using Monte Carlo simulations with the EGSnrc system. Two new techniques for the calculation of OAR profiles are presented. Results of the Monte Carlo simulations are compared to measurements performed in 6, 10 and 25 MV photon beams produced by an Elekta Precise linac and shown to agree within the experimental and simulation uncertainties. Comparisons with calculated in-air kerma profiles demonstrate that using a plastic mini phantom gives more accurate air-kerma measurements than using high-Z material buildup caps and that the variation of chamber response with distance from the central axis must be taken into account.

  5. Three chamber negative ion source

    DOEpatents

    Leung, Ka-Ngo; Ehlers, Kenneth W.; Hiskes, John R.

    1985-01-01

    A negative ion vessel is divided into an excitation chamber, a negative ionization chamber and an extraction chamber by two magnetic filters. Input means introduces neutral molecules into a first chamber where a first electron discharge means vibrationally excites the molecules which migrate to a second chamber. In the second chamber a second electron discharge means ionizes the molecules, producing negative ions which are extracted into or by a third chamber. A first magnetic filter prevents high energy electrons from entering the negative ionization chamber from the excitation chamber. A second magnetic filter prevents high energy electrons from entering the extraction chamber from the negative ionizing chamber. An extraction grid at the end of the negative ion vessel attracts negative ions into the third chamber and accelerates them. Another grid, located adjacent to the extraction grid, carries a small positive voltage in order to inhibit positive ions from migrating into the extraction chamber and contour the plasma potential. Additional electrons can be suppressed from the output flux using ExB forces provided by magnetic field means and the extractor grid electric potential.

  6. SU-F-303-15: Ion Chamber Dose Response in Magnetic Fields as a Function of Incident Photon Energy

    SciTech Connect

    Malkov, V. N.; Rogers, D. W. O.

    2015-06-15

    Purpose: In considering the continued development of synergetic MRI-radiation therapy machines, we seek to quantify the variability of ion chamber response per unit dose in the presence of magnetic fields of varying strength as a function of incident photon beam quality and geometric configuration. Methods: To account for the effect of magnetic fields on the trajectory of charged particles a new algorithm was introduced into the EGSnrc Monte Carlo code. In the egs-chamber user code the dose to the cavity of an NE2571 ion chamber is calculated in two configurations, in 0 to 2 T magnetic fields, with an incoming parallel 10×10 cm{sup 2} photon beam with energies ranging between 0.5 MeV and 8 MeV. In the first, the photon beam is incident on the long-axis of the ion chamber (config-1), and in the second the beam is parallel to the long-axis and incident from the conical end of the chamber (config-2). For both, the magnetic field is perpendicular to the direction of the beam and the long axis of the chamber. Results: The ion chamber response per unit dose to water at the same point is determined as a function of magnetic field and is normalized to the 0T case for each of incoming photon energies. For both configurations, accurate modeling of the ion chamber yielded closer agreement with the experimental results obtained by Meijsing et. al (2009). Config-1 yields a gradual increase in response with increasing field strength to a maximum of 13.4% and 1.4% for 1 MeV and 8 MeV photon beams, respectively. Config-2 produced a decrease in response of up to 6% and 13% for 0.5 MeV and 8 MeV beams, respectively. Conclusion: These results provide further support for ion chamber calibration in MRI-radiotherapy coupled systems and demonstrates noticeable energy dependence for clinically relevant fields.

  7. Ion chamber based neutron detectors

    DOEpatents

    Derzon, Mark S; Galambos, Paul C; Renzi, Ronald F

    2014-12-16

    A neutron detector with monolithically integrated readout circuitry, including: a bonded semiconductor die; an ion chamber formed in the bonded semiconductor die; a first electrode and a second electrode formed in the ion chamber; a neutron absorbing material filling the ion chamber; and the readout circuitry which is electrically coupled to the first and second electrodes. The bonded semiconductor die includes an etched semiconductor substrate bonded to an active semiconductor substrate. The readout circuitry is formed in a portion of the active semiconductor substrate. The ion chamber has a substantially planar first surface on which the first electrode is formed and a substantially planar second surface, parallel to the first surface, on which the second electrode is formed. The distance between the first electrode and the second electrode may be equal to or less than the 50% attenuation length for neutrons in the neutron absorbing material filling the ion chamber.

  8. Response to high-energy photons of PTW31014 PinPoint ion chamber with a central aluminum electrode.

    PubMed

    Agostinelli, S; Garelli, S; Piergentili, M; Foppiano, F

    2008-07-01

    Since its introduction the PinPoint (PTW-Freiburg) micro-ionization chamber has been proposed for relative dosimetry (output factors, depth dose curves, and beam profiles) as well as for determination of absolute dose of small high-energy photon beams. This paper investigates the dosimetric performance of a new design (type 31014) of the PinPoint ion chamber with a central aluminum electrode. The study included characterization of inherent and radiation-induced leakage, ion collection efficiency and polarity effect, relative response of the chamber, measurement of beam profiles, and depth dose curves. The 6 and 15 MV photon beams of a Varian 2100 C/D were considered. At the nominal operating voltage of 400 V the PinPoint type 31014 chamber was found to present a strong field size dependence of the polarity correction factor and an excess of the collected charge, which can lead to an underestimation of the collection efficiency if determined with the conventional "two-voltage" method. In comparison to the original PinPoint design (type 31006) the authors found for type 31014 chamber no overresponse to large-area fields if polarity correction is applied. If no correction is taken into consideration, the authors found the chamber's output to be inaccurate for large-area fields (0.5% accuracy limited up to the 12 x 12 and 20 x 20 cm2 field for the 6 and 15 MV beams, respectively), which is a direct consequence of the stem and polarity effects due to the chamber's very small sensitive volume (0.015 cc) and cable irradiation. Beam profiles and depth dose curves measured with type 31014 PinPoint chamber for small and medium size fields were compared to data measured with a 0.125 cc ion chamber and with high-resolution Kodak EDR2 films. Analysis of the penumbra (80%-20% distance) showed that the spatial resolution of type 31014 PinPoint ion chamber approaches (penumbra broadening < or = 0.6 mm) EDR2 film results.

  9. Response to high-energy photons of PTW31014 PinPoint ion chamber with a central aluminum electrode.

    PubMed

    Agostinelli, S; Garelli, S; Piergentili, M; Foppiano, F

    2008-07-01

    Since its introduction the PinPoint (PTW-Freiburg) micro-ionization chamber has been proposed for relative dosimetry (output factors, depth dose curves, and beam profiles) as well as for determination of absolute dose of small high-energy photon beams. This paper investigates the dosimetric performance of a new design (type 31014) of the PinPoint ion chamber with a central aluminum electrode. The study included characterization of inherent and radiation-induced leakage, ion collection efficiency and polarity effect, relative response of the chamber, measurement of beam profiles, and depth dose curves. The 6 and 15 MV photon beams of a Varian 2100 C/D were considered. At the nominal operating voltage of 400 V the PinPoint type 31014 chamber was found to present a strong field size dependence of the polarity correction factor and an excess of the collected charge, which can lead to an underestimation of the collection efficiency if determined with the conventional "two-voltage" method. In comparison to the original PinPoint design (type 31006) the authors found for type 31014 chamber no overresponse to large-area fields if polarity correction is applied. If no correction is taken into consideration, the authors found the chamber's output to be inaccurate for large-area fields (0.5% accuracy limited up to the 12×12 and 20×20 cm2 field for the 6 and 15 MV beams, respectively), which is a direct consequence of the stem and polarity effects due to the chamber's very small sensitive volume (0.015 cc) and cable irradiation. Beam profiles and depth dose curves measured with type 31014 PinPoint chamber for small and medium size fields were compared to data measured with a 0.125 cc ion chamber and with high-resolution Kodak EDR2 films. Analysis of the penumbra (80%-20% distance) showed that the spatial resolution of type 31014 PinPoint ion chamber approaches (penumbra broadening ≤0.6 mm) EDR2 film results. © 2008 American Association of Physicists in Medicine.

  10. Measurement of surface alpha contamination using electret ion chambers.

    PubMed

    Dua, S K; Biswas, S K; Szerszen, P; Boudreaux, J; Ebadian, M A

    1999-06-01

    Electret ion chambers are inexpensive, light-weight, commercially available, passive charge-integrating devices for accurate measurement of different radiations. Performance of electret ion chambers for surface alpha contamination measurement was evaluated. Ion chambers of two types and electrets of three thicknesses were used for the study. Calibration of the electret ion chambers was performed using reference alpha standards of different energies and radioactivities. Effects of various parameters such as chamber dimensions, electret thickness, alpha particle energy, position of alpha source from the chamber centerline, source localized or uniformly distributed, level of alpha contamination, Mylar window covering the chamber, and ambient radon and gamma radiation on the response of the electret ion chambers were determined. Suitable combinations of chambers and electrets to measure surface alpha contamination were determined.

  11. Compact ion chamber based neutron detector

    DOEpatents

    Derzon, Mark S.; Galambos, Paul C.; Renzi, Ronald F.

    2015-10-27

    A directional neutron detector has an ion chamber formed in a dielectric material; a signal electrode and a ground electrode formed in the ion chamber; a neutron absorbing material filling the ion chamber; readout circuitry which is electrically coupled to the signal and ground electrodes; and a signal processor electrically coupled to the readout circuitry. The ion chamber has a pair of substantially planar electrode surfaces. The chamber pressure of the neutron absorbing material is selected such that the reaction particle ion trail length for neutrons absorbed by the neutron absorbing material is equal to or less than the distance between the electrode surfaces. The signal processor is adapted to determine a path angle for each absorbed neutron based on the rise time of the corresponding pulse in a time-varying detector signal.

  12. Monte Carlo modeling of ion chamber performance using MCNP.

    PubMed

    Wallace, J D

    2012-12-01

    Ion Chambers have a generally flat energy response with some deviations at very low (<100 keV) and very high (>2 MeV) energies. Some improvements in the low energy response can be achieved through use of high atomic number gases, such as argon and xenon, and higher chamber pressures. This work looks at the energy response of high pressure xenon-filled ion chambers using the MCNP Monte Carlo package to develop geometric models of a commercially available high pressure ion chamber (HPIC). The use of the F6 tally as an estimator of the energy deposited in a region of interest per unit mass, and the underlying assumptions associated with its use are described. The effect of gas composition, chamber gas pressure, chamber wall thickness, and chamber holder wall thicknesses on energy response are investigated and reported. The predicted energy response curve for the HPIC was found to be similar to that reported by other investigators. These investigations indicate that improvements to flatten the overall energy response of the HPIC down to 70 keV could be achieved through use of 3 mm-thick stainless steel walls for the ion chamber.

  13. Fast-response cloud chamber

    NASA Technical Reports Server (NTRS)

    Fogal, G. L.

    1977-01-01

    Wall structure keeps chambers at constant, uniform temperature, yet allows them to be cooled rapidly if necessary. Wall structure, used in fast-response cloud chamber, has surface heater and coolant shell separated by foam insulation. It is lightweight and requires relatively little power.

  14. Three chamber negative ion source

    DOEpatents

    Leung, K.N.; Ehlers, K.W.; Hiskes, J.R.

    1983-11-10

    It is an object of this invention provide a negative ion source which efficiently provides a large flux of negatively ionized particles. This invention provides a volume source of negative ions which has a current density sufficient for magnetic fusion applications and has electrons suppressed from the output. It is still another object of this invention to provide a volume source of negative ions which can be electrostatically accelerated to high energies and subsequently neutralized to form a high energy neutral beam for use with a magnetically confined plasma.

  15. Chamber transport for heavy ion fusion

    NASA Astrophysics Data System (ADS)

    Olson, Craig L.

    2014-01-01

    A brief review is given of research on chamber transport for HIF (heavy ion fusion) dating from the first HIF Workshop in 1976 to the present. Chamber transport modes are categorized into ballistic transport modes and channel-like modes. Four major HIF reactor studies are summarized (HIBALL-II, HYLIFE-II, Prometheus-H, OSIRIS), with emphasis on the chamber transport environment. In general, many beams are used to provide the required symmetry and to permit focusing to the required small spots. Target parameters are then discussed, with a summary of the individual heavy ion beam parameters required for HIF. The beam parameters are then classified as to their line charge density and perveance, with special emphasis on the perveance limits for radial space charge spreading, for the space charge limiting current, and for the magnetic (Alfven) limiting current. The major experiments on ballistic transport (SFFE, Sabre beamlets, GAMBLE II, NTX, NDCX) are summarized, with specific reference to the axial electron trapping limit for charge neutralization. The major experiments on channel-like transport (GAMBLE II channel, GAMBLE II self-pinch, LBNL channels, GSI channels) are discussed. The status of current research on HIF chamber transport is summarized, and the value of future NDCX-II transport experiments for the future of HIF is noted.

  16. Recombination characteristics of therapeutic ion beams on ion chamber dosimetry

    NASA Astrophysics Data System (ADS)

    Matsufuji, Naruhiro; Matsuyama, Tetsuharu; Sato, Shinji; Kohno, Toshiyuki

    2016-09-01

    In heavy ion radiotherapy, ionization chambers are regarded as a standard for determining the absorbed dose given to patients. In ion dosimetry, it is necessary to correct the radiation quality, which depends on the initial recombination effect. This study reveals for the radiation quality dependence of the initial recombination in air in ion dosimetry. Ionization charge was measured for the beams of protons at 40-160 MeV, carbon at 21-400 MeV/n, and iron at 23.5-500 MeV/n using two identical parallel-plate ionization chambers placed in series along the beam axis. The downstream chamber was used as a monitor operated with a constant applied voltage, while the other chamber was used for recombination measurement by changing the voltage. The ratio of the ionization charge measured by the two ionization chambers showed a linear relationship with the inverse of the voltage in the high-voltage region. The initial recombination factor was estimated by extrapolating the obtained linear relationship to infinite voltage. The extent of the initial recombination was found to increase with decreasing incident energy or increasing atomic number of the beam. This behavior can be explained with an amorphous track structure model: the increase of ionization density in the core region of the track due to decreasing kinetic energy or increasing atomic number leads to denser initial ion production and results in a higher recombination probability. For therapeutic carbon ion beams, the extent of the initial recombination was not constant but changed by 0.6% even in the target region. This tendency was quantitatively well reproduced with the track-structure based on the initial recombination model; however, the transitional change in the track structure is considered to play an important role in further understanding of the characteristics of the initial recombination.

  17. Vacuum chamber for ion manipulation device

    SciTech Connect

    Chen, Tsung-Chi; Tang, Keqi; Ibrahim, Yehia M; Smith, Richard D; Anderson, Gordon A; Baker, Erin M

    2014-12-09

    An ion manipulation method and device is disclosed. The device includes a pair of substantially parallel surfaces. An array of inner electrodes is contained within, and extends substantially along the length of, each parallel surface. The device includes a first outer array of electrodes and a second outer array of electrodes. Each outer array of electrodes is positioned on either side of the inner electrodes, and is contained within and extends substantially along the length of each parallel surface. A DC voltage is applied to the first and second outer array of electrodes. A RF voltage, with a superimposed electric field, is applied to the inner electrodes by applying the DC voltages to each electrode. Ions either move between the parallel surfaces within an ion confinement area or along paths in the direction of the electric field, or can be trapped in the ion confinement area. A predetermined number of pairs of surfaces are disposed in one or more chambers, forming a multiple-layer ion mobility cyclotron device.

  18. Polarity effects and apparent ion recombination in microionization chambers.

    PubMed

    Miller, Jessica R; Hooten, Brian D; Micka, John A; DeWerd, Larry A

    2016-05-01

    Microchambers demonstrate anomalous voltage-dependent polarity effects. Existing polarity and ion recombination correction factors do not account for these effects. As a result, many commercial microchamber models do not meet the specification of a reference-class ionization chamber as defined by the American Association of Physicists in Medicine. The purpose of this investigation is to determine the cause of these voltage-dependent polarity effects. A series of microchamber prototypes were produced to isolate the source of the voltage-dependent polarity effects. Parameters including ionization-chamber collecting-volume size, stem and cable irradiation, chamber assembly, contaminants, high-Z materials, and individual chamber components were investigated. Measurements were performed with electrodes coated with graphite to isolate electrode conductivity. Chamber response was measured as the potential bias of the guard electrode was altered with respect to the collecting electrode, through the integration of additional power supplies. Ionization chamber models were also simulated using comsol Multiphysics software to investigate the effect of a potential difference between electrodes on electric field lines and collecting volume definition. Investigations with microchamber prototypes demonstrated that the significant source of the voltage-dependent polarity effects was a potential difference between the guard and collecting electrodes of the chambers. The voltage-dependent polarity effects for each prototype were primarily isolated to either the guard or collecting electrode. Polarity effects were reduced by coating the isolated electrode with a conductive layer of graphite. Polarity effects were increased by introducing a potential difference between the electrodes. comsol simulations further demonstrated that for a given potential difference between electrodes, the collecting volume of the chamber changed as the applied voltage was altered, producing voltage

  19. Polarity effects and apparent ion recombination in microionization chambers

    SciTech Connect

    Miller, Jessica R.; Hooten, Brian D.; Micka, John A.; DeWerd, Larry A.

    2016-05-15

    Purpose: Microchambers demonstrate anomalous voltage-dependent polarity effects. Existing polarity and ion recombination correction factors do not account for these effects. As a result, many commercial microchamber models do not meet the specification of a reference-class ionization chamber as defined by the American Association of Physicists in Medicine. The purpose of this investigation is to determine the cause of these voltage-dependent polarity effects. Methods: A series of microchamber prototypes were produced to isolate the source of the voltage-dependent polarity effects. Parameters including ionization-chamber collecting-volume size, stem and cable irradiation, chamber assembly, contaminants, high-Z materials, and individual chamber components were investigated. Measurements were performed with electrodes coated with graphite to isolate electrode conductivity. Chamber response was measured as the potential bias of the guard electrode was altered with respect to the collecting electrode, through the integration of additional power supplies. Ionization chamber models were also simulated using COMSOL Multiphysics software to investigate the effect of a potential difference between electrodes on electric field lines and collecting volume definition. Results: Investigations with microchamber prototypes demonstrated that the significant source of the voltage-dependent polarity effects was a potential difference between the guard and collecting electrodes of the chambers. The voltage-dependent polarity effects for each prototype were primarily isolated to either the guard or collecting electrode. Polarity effects were reduced by coating the isolated electrode with a conductive layer of graphite. Polarity effects were increased by introducing a potential difference between the electrodes. COMSOL simulations further demonstrated that for a given potential difference between electrodes, the collecting volume of the chamber changed as the applied voltage was altered

  20. Measurement of alpha particle energy using windowless electret ion chambers.

    PubMed

    Dua, S K; Kotrappa, P; Srivastava, R; Ebadian, M A; Stieff, L R

    2002-10-01

    Electret ion chambers are inexpensive, lightweight, robust, commercially available, passive, charge-integrating devices for accurate measurement of different ionizing radiations. In an earlier work a chamber of dimensions larger than the range of alpha particles having aluminized Mylar windows of different thickness was used for measurement of alpha radiation. Correlation between electret mid-point voltage, alpha particle energy, and response was developed and it was shown that this chamber could be used for estimating the effective energy of an unknown alpha source. In the present study, the electret ion chamber is used in the windowless mode so that the alpha particles dissipate their entire energy inside the volume, and the alpha particle energy is determined from the first principles. This requires that alpha disintegration rate be accurately known or measured by an alternate method. The measured energies were within 1 to 4% of the true values for different sources (230Th, 237Np, 239Pu, 241Am, and 224Cm). This method finds application in quantitative determination of alpha energy absorbed in thin membrane and, hence, the absorbed dose.

  1. Accuracy of EGSnrc calculations at 60Co energies for the response of ion chambers configured with various wall materials and cavity dimensions.

    PubMed

    La Russa, Daniel J; Rogers, D W O

    2008-12-01

    In this investigation, five experimental data sets are used to evaluate the ability of the EGSnrc Monte Carlo code to calculate the change in chamber response associated with changes in wall material and cavity dimension at 60Co energies. Calculations of the ratios of response per unit mass of air as a function of cavity volume for walls ranging from polystyrene to lead are generally within 1%-3% of experiments. A few exceptions, which are discussed, include 20%-30% discrepancies with experiments involving lead-walled chambers used by Attix et al. [J. Res. Natl. Bur. Stand. 60, 235-243 (1958)] and Cormack and Johns [Radiat. Res. 1, 133-157 (1954)], and 5% discrepancies for the graphite chamber of Attix et al. (relative to data for other wall materials). Simulations of the experiment by Whyte [Radiat. Res. 6, 371-379 (1957)], which varied cavity air pressure in a large cylindrical chamber, are generally within 0.5% (wall/electrode materials ranging from beryllium to copper). In all cases, the agreement between measurements and EGSnrc calculations is much better when the response as a function of cavity height or air pressure is considered for each wall material individually. High-precision measurements [Burns et al., Phys. Med. Biol. 52, 7125-7135 (2007)] of the response per unit mass as a function of cavity height for a graphite chamber are also accurately reproduced, and validate previous tests of the transport mechanics of EGSnrc. Based on the general agreement found in this work between corresponding experimental results and EGSnrc calculations it can be concluded that EGSnrc can reliably be used to calculate changes in response with changes in various wall materials and cavity dimensions at 60Co energies within a accuracy of a few percent or less.

  2. SU-C-304-01: Investigation of Various Detector Response Functions and Their Geometry Dependence in a Novel Method to Address Ion Chamber Volume Averaging Effect

    SciTech Connect

    Barraclough, B; Lebron, S; Li, J; Fan, Qiyong; Liu, C; Yan, G

    2015-06-15

    Purpose: A novel convolution-based approach has been proposed to address ion chamber (IC) volume averaging effect (VAE) for the commissioning of commercial treatment planning systems (TPS). We investigate the use of various convolution kernels and its impact on the accuracy of beam models. Methods: Our approach simulates the VAE by iteratively convolving the calculated beam profiles with a detector response function (DRF) while optimizing the beam model. At convergence, the convolved profiles match the measured profiles, indicating the calculated profiles match the “true” beam profiles. To validate the approach, beam profiles of an Elekta LINAC were repeatedly collected with ICs of various volumes (CC04, CC13 and SNC 125) to obtain clinically acceptable beam models. The TPS-calculated profiles were convolved externally with the DRF of respective IC. The beam model parameters were reoptimized using Nelder-Mead method by forcing the convolved profiles to match the measured profiles. We evaluated three types of DRFs (Gaussian, Lorentzian, and parabolic) and the impact of kernel dependence on field geometry (depth and field size). The profiles calculated with beam models were compared with SNC EDGE diode-measured profiles. Results: The method was successfully implemented with Pinnacle Scripting and Matlab. The reoptimization converged in ∼10 minutes. For all tested ICs and DRFs, penumbra widths of the TPS-calculated profiles and diode-measured profiles were within 1.0 mm. Gaussian function had the best performance with mean penumbra width difference within 0.5 mm. The use of geometry dependent DRFs showed marginal improvement, reducing the penumbra width differences to less than 0.3 mm. Significant increase in IMRT QA passing rates was achieved with the optimized beam model. Conclusion: The proposed approach significantly improved the accuracy of the TPS beam model. Gaussian functions as the convolution kernel performed consistently better than Lorentzian and

  3. Polarity and ion recombination corrections in continuous and pulsed beams for ionization chambers with high Z chamber walls.

    PubMed

    Aldosary, Ghada; Safigholi, Habib; Song, William; Seuntjens, Jan; Sarfehnia, Arman

    2017-03-01

    In this work, the response of Farmer-type ionization chambers fitted with high atomic number (Z) walls is studied, and results of the effects of such walls on polarity and ion recombination correction factors in both continuous and pulsed beams are presented. Measurements were made in a continuous Co-60 beam and a pulsed 6MV linac beam using an Exradin-A12 ionization chamber fitted with the manufacturer's C-552 plastic wall, as well as geometrically identical walls made from aluminum, copper and molybdenum. The bias voltage was changed between 10values (range: +50 to +560V). Ion recombination was determined from Jaffé plots and by using the "two-voltage technique". The saturation charge measured with each chamber wall was extrapolated from Jaffé plots. Additionally, the effect of different wall materials on chamber response was studied using MCNP simulations. Results showed that the polarity correction factor is not significantly affected by changes in chamber wall material (within 0.1%). Furthermore, although the saturation charges greatly vary with each chamber wall material, and charge multiplication increases for higher atomic number wall materials, the standard methods of calculating ion recombination yielded results that differed by only 0.2%. Therefore, polarity and ion recombination correction factors are not greatly affected by the chamber wall material. The experimental saturation charges for all the different wall materials agreed well within the uncertainty with MCNP simulations. The breakdown of the linear relationship in Jaffé plots that was previously reported to exist for conventional chamber walls was also observed with the different wall materials. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  4. Technical Note: Impact of the geometry dependence of the ion chamber detector response function on a convolution-based method to address the volume averaging effect.

    PubMed

    Barraclough, Brendan; Li, Jonathan G; Lebron, Sharon; Fan, Qiyong; Liu, Chihray; Yan, Guanghua

    2016-05-01

    To investigate the geometry dependence of the detector response function (DRF) of three commonly used scanning ionization chambers and its impact on a convolution-based method to address the volume averaging effect (VAE). A convolution-based approach has been proposed recently to address the ionization chamber VAE. It simulates the VAE in the treatment planning system (TPS) by iteratively convolving the calculated beam profiles with the DRF while optimizing the beam model. Since the convolved and the measured profiles are subject to the same VAE, the calculated profiles match the implicit "real" ones when the optimization converges. Three DRFs (Gaussian, Lorentzian, and parabolic function) were used for three ionization chambers (CC04, CC13, and SNC125c) in this study. Geometry dependent/independent DRFs were obtained by minimizing the difference between the ionization chamber-measured profiles and the diode-measured profiles convolved with the DRFs. These DRFs were used to obtain eighteen beam models for a commercial TPS. Accuracy of the beam models were evaluated by assessing the 20%-80% penumbra width difference (PWD) between the computed and diode-measured beam profiles. The convolution-based approach was found to be effective for all three ionization chambers with significant improvement for all beam models. Up to 17% geometry dependence of the three DRFs was observed for the studied ionization chambers. With geometry dependent DRFs, the PWD was within 0.80 mm for the parabolic function and CC04 combination and within 0.50 mm for other combinations; with geometry independent DRFs, the PWD was within 1.00 mm for all cases. When using the Gaussian function as the DRF, accounting for geometry dependence led to marginal improvement (PWD < 0.20 mm) for CC04; the improvement ranged from 0.38 to 0.65 mm for CC13; for SNC125c, the improvement was slightly above 0.50 mm. Although all three DRFs were found adequate to represent the response of the studied ionization

  5. Technical Note: Impact of the geometry dependence of the ion chamber detector response function on a convolution-based method to address the volume averaging effect

    SciTech Connect

    Barraclough, Brendan; Lebron, Sharon; Li, Jonathan G.; Fan, Qiyong; Liu, Chihray; Yan, Guanghua

    2016-05-15

    Purpose: To investigate the geometry dependence of the detector response function (DRF) of three commonly used scanning ionization chambers and its impact on a convolution-based method to address the volume averaging effect (VAE). Methods: A convolution-based approach has been proposed recently to address the ionization chamber VAE. It simulates the VAE in the treatment planning system (TPS) by iteratively convolving the calculated beam profiles with the DRF while optimizing the beam model. Since the convolved and the measured profiles are subject to the same VAE, the calculated profiles match the implicit “real” ones when the optimization converges. Three DRFs (Gaussian, Lorentzian, and parabolic function) were used for three ionization chambers (CC04, CC13, and SNC125c) in this study. Geometry dependent/independent DRFs were obtained by minimizing the difference between the ionization chamber-measured profiles and the diode-measured profiles convolved with the DRFs. These DRFs were used to obtain eighteen beam models for a commercial TPS. Accuracy of the beam models were evaluated by assessing the 20%–80% penumbra width difference (PWD) between the computed and diode-measured beam profiles. Results: The convolution-based approach was found to be effective for all three ionization chambers with significant improvement for all beam models. Up to 17% geometry dependence of the three DRFs was observed for the studied ionization chambers. With geometry dependent DRFs, the PWD was within 0.80 mm for the parabolic function and CC04 combination and within 0.50 mm for other combinations; with geometry independent DRFs, the PWD was within 1.00 mm for all cases. When using the Gaussian function as the DRF, accounting for geometry dependence led to marginal improvement (PWD < 0.20 mm) for CC04; the improvement ranged from 0.38 to 0.65 mm for CC13; for SNC125c, the improvement was slightly above 0.50 mm. Conclusions: Although all three DRFs were found adequate to

  6. Calibration of the borated ion chamber at NIST reactor thermal column.

    PubMed

    Wang, Z; Hertel, N E; Lennox, A

    2007-01-01

    In boron neutron capture therapy and boron neutron capture enhanced fast neutron therapy, the absorbed dose of tissue due to the boron neutron capture reaction is difficult to measure directly. This dose can be computed from the measured thermal neutron fluence rate and the (10)B concentration at the site of interest. A borated tissue-equivalent (TE) ion chamber can be used to directly measure the boron dose in a phantom under irradiation by a neutron beam. Fermilab has two Exradin 0.5 cm(3) Spokas thimble TE ion chambers, one loaded with boron, available for such measurements. At the Fermilab Neutron Therapy Facility, these ion chambers are generally used with air as the filling gas. Since alpha particles and lithium ions from the (10)B(n,alpha)(7)Li reactions have very short ranges in air, the Bragg-Gray principle may not be satisfied for the borated TE ion chamber. A calibration method is described in this paper for the determination of boron capture dose using paired ion chambers. The two TE ion chambers were calibrated in the thermal column of the National Institute of Standards and Technology (NIST) research reactor. The borated TE ion chamber is loaded with 1,000 ppm of natural boron (184 ppm of (10)B). The NIST thermal column has a cadmium ratio of greater than 400 as determined by gold activation. The thermal neutron fluence rate during the calibration was determined using a NIST fission chamber to an accuracy of 5.1%. The chambers were calibrated at two different thermal neutron fluence rates: 5.11 x 10(6) and 4.46 x 10(7)n cm(-2) s(-1). The non-borated ion chamber reading was used to subtract collected charge not due to boron neutron capture reactions. An optically thick lithium slab was used to attenuate the thermal neutrons from the neutron beam port so the responses of the chambers could be corrected for fast neutrons and gamma rays in the beam. The calibration factor of the borated ion chamber was determined to be 1.83 x 10(9) +/- 5.5% (+/- 1sigma) n

  7. Chamber transport of ''foot'' pulses for heavy-ion fusion

    SciTech Connect

    Sharp, W.M.; Callahan-Miller, D.A.; Tabak, M.; Yu, S.S.; Peterson, P.F.

    2002-02-20

    Indirect-drive targets for heavy-ion fusion must initially be heated by ''foot'' pulses that precede the main heating pulses by tens of nanoseconds. These pulses typically have a lower energy and perveance than the main pulses, and the fusion-chamber environment is different from that seen by later pulses. The preliminary particle-in-cell simulations of foot pulses here examine the sensitivity of the beam focusing to ion-beam perveance, background-gas density, and pre-neutralization by a plasma near the chamber entry port.

  8. Realistic modeling of chamber transport for heavy-ion fusion

    SciTech Connect

    Sharp, W.M.; Grote, D.P.; Callahan, D.A.; Tabak, M.; Henestroza, E.; Yu, S.S.; Peterson, P.F.; Welch, D.R.; Rose, D.V.

    2003-05-01

    Transport of intense heavy-ion beams to an inertial-fusion target after final focus is simulated here using a realistic computer model. It is found that passing the beam through a rarefied plasma layer before it enters the fusion chamber can largely neutralize the beam space charge and lead to a usable focal spot for a range of ion species and input conditions.

  9. Modeling Chamber Transport for Heavy-Ion Fusion

    SciTech Connect

    Sharp, W M; Niller, D A C; Tabak, M; Yu, S S; Peterson, P F; Welch, D R; Rose, D V; Olson, C L

    2002-08-02

    In a typical thick-liquid-wall scenario for heavy-ion fusion (HIF), between seventy and two hundred high-current beams enter the target chamber through ports and propagate about three meters to the target. Since molten-salt jets are planned to protect the chamber wall, the beams move through vapor from the jets, and collisions between beam ions and this background gas both strip the ions and ionize the gas molecules. Radiation from the preheated target causes further beam stripping and gas ionization. Due to this stripping, beams for heavy-ion fusion are expected to require substantial neutralization in a target chamber. Much recent research has, therefore, focused on beam neutralization by electron sources that were neglected in earlier simulations, including emission from walls and the target, photoionization by the target radiation, and pre-neutralization by a plasma generated along the beam path. When these effects are included in simulations with practicable beam and chamber parameters, the resulting focal spot is approximately the size required by a distributed radiator target.

  10. Modeling chamber transport for heavy-ion fusion

    SciTech Connect

    Sharp, W.M.; Callahan, D.A.; Tabak, M.; Yu, S.S.; Peterson, P.F.; Welch, D.R.; Rose, D.V.; Olson, C.L.

    2002-10-01

    In a typical thick-liquid-wall scenario for heavy-ion fusion (HIF), between seventy and two hundred high-current beams enter the target chamber through ports and propagate about three meters to the target. Since molten-salt jets are planned to protect the chamber wall, the beams move through vapor from the jets, and collisions between beam ions and this background gas both strip the ions and ionize the gas molecules. Radiation from the preheated target causes further beam stripping and gas ionization. Due to this stripping, beams for heavy-ion fusion are expected to require substantial neutralization in a target chamber. Much recent research has, therefore, focused on beam neutralization by electron sources that were neglected in earlier simulations, including emission from walls and the target, photoionization by the target radiation, and pre-neutralization by a plasma generated along the beam path. When these effects are included in simulations with practicable beam and chamber parameters, the resulting focal spot is approximately the size required by a distributed radiator target.

  11. Characterization of a multi-axis ion chamber array.

    PubMed

    Simon, Thomas A; Kozelka, Jakub; Simon, William E; Kahler, Darren; Li, Jonathan; Liu, Chihray

    2010-11-01

    The aim of this work was to characterize a multi-axis ion chamber array (IC PROFILER; Sun Nuclear Corporation, Melbourne, FL, USA) that has the potential to simplify the acquisition of LINAC beam data. The IC PROFILER (or panel) measurement response was characterized with respect to radiation beam properties, including dose, dose per pulse, pulse rate frequency (PRF), and energy. Panel properties were also studied, including detector-calibration stability, power-on time, backscatter dependence, and the panel's agreement with water tank measurements [profiles, fractional depth dose (FDD), and output factors]. The panel's relative deviation was typically within (+/-) 1% of an independent (or nominal) response for all properties that were tested. Notable results were (a) a detectable relative field shape change of approximately 1% with linear accelerator PRF changes; (b) a large range in backscatter thickness had a minimal effect on the measured dose distribution (typically less than 1%); (c) the error spread in profile comparison between the panel and scanning water tank (Blue Phantom, CC13; IBA Schwarzenbruck, DE) was approximately (+/-) 0.75%. The ability of the panel to accurately reproduce water tank profiles, FDDs, and output factors is an indication of its abilities as a dosimetry system. The benefits of using the panel versus a scanning water tank are less setup time and less error susceptibility. The same measurements (including device setup and breakdown) for both systems took 180 min with the water tank versus 30 min with the panel. The time-savings increase as the measurement load is increased.

  12. Leakage correction estimate for electret ion chamber dielectric material used for long-term environmental gamma monitoring.

    PubMed

    Jones, David F; Paulus, L R

    2008-05-01

    The Idaho Department of Environmental Quality INL Oversight Program (DEQ-INL) operates an environmental gamma radiation detection network consisting of a series of high-pressure ion chambers to provide real-time ambient radiation measurements and a series of passive environmental electret ion chambers to increase coverage area and measure cumulative dose over a calendar quarter. DEQ-INL has identified a consistent over-response of approximately 40% by the electret ion chambers with respect to co-located high-pressure ion chambers since 1998. DEQ-INL conducted a series of three investigations to quantify this over-response. The over-response is likely attributable to a number of factors, including inherent voltage loss by the electret material not due to ionization within the chamber. One aspect of the investigation verified the manufacturer's calibration factor used to convert decrease in voltage to exposure. Additional investigations were performed that identified an average electret voltage loss of 0.2 V d(-1). When this voltage correction was applied to historical environmental data, electret ion chamber response was within 10% of the co-located high-pressure ion chamber response.

  13. Charges and current induced by moving ions in multiwire chambers

    NASA Astrophysics Data System (ADS)

    Erskine, G. A.

    1982-07-01

    A method for calculating the charges induced on the grid wires, and on cathode strips parallel to the grid wires, by a point charge in a multiwire chamber is described. The method is applied to the calculation, as a function of time, of the charge and current induced by a small group of positive ions moving in accordance with the drift equation v= μE where v is the velocity. An appendix lists a number of formulae relating to the electrostatic field of a multiwire chamber.

  14. Investigation of thermal and temporal responses of ionization chambers in radiation dosimetry.

    PubMed

    AlMasri, Hussein; Funyu, Akira; Kakinohana, Yasumasa; Murayama, Sadayuki

    2012-07-01

    The ionization chamber is a primary dosimeter that is used in radiation dosimetry. Generally, the ion chamber response requires temperature/pressure correction according to the ideal gas law. However, this correction does not consider the thermal volume effect of chambers. The temporal and thermal volume effects of various chambers (CC01, CC13, NACP parallel-plate, PTW) with different wall and electrode materials have been studied in a water phantom. Measurements were done after heating the water with a suitable heating system, and chambers were submerged for a sufficient time to allow for temperature equilibrium. Temporal results show that all chambers equilibrate quickly in water. The equilibration time was between 3 and 5 min for all chambers. Thermal results show that all chambers expanded in response to heating except for the PTW, which contracted. This might be explained by the differences in the volumes of all chambers and also by the difference in wall material composition of PTW from the other chambers. It was found that the smallest chamber, CC01, showed the greatest expansion. The magnitude of the expansion was ~1, 0.8, and 0.9% for CC01, CC13, and parallel-plate chambers, respectively, in the temperature range of 295-320 K. The magnitude of the detected contraction was <0.3% for PTW in the same temperature range. For absolute dosimetry, it is necessary to make corrections for the ion chamber response, especially for small ion chambers like the CC01. Otherwise, room and water phantom temperatures should remain within a close range.

  15. Beam loss ion chamber system upgrade for experimental halls

    SciTech Connect

    D. Dotson; D. Seidman

    2005-08-01

    The Beam loss Ion Chamber System (BLICS) was developed to protect Jefferson Labs transport lines, targets and beam dumps from a catastrophic ''burn through''. Range changes and testing was accomplished manually requiring the experiment to be shut down. The new upgraded system is based around an ''off the shelf'' Programmable Logic Controller located in a single control box supporting up to ten individual detectors. All functions that formerly required an entry into the experimental hall and manual adjustment can be accomplished from the Machine Control Center (MCC). A further innovation was the addition of a High Voltage ''Brick'' at the detector location. A single cable supplies the required voltage for the Brick and a return line for the ion chamber signal. The read back screens display range, trip point, and accumulated dose for each location. The new system is very cost effective and significantly reduces the amount of lost experimental time.

  16. Beam Loss Ion Chamber System Upgrade for Experimental Halls

    SciTech Connect

    D.W. Dotson; D.J. Seidman

    2005-05-16

    The Beam loss Ion Chamber System (BLICS) was developed to protect Jefferson Labs transport lines, targets and beam dumps from a catastrophic ''burn through''. Range changes and testing was accomplished manually requiring the experiment to be shut down. The new upgraded system is based around an ''off the shelf'' Programmable Logic Controller located in a single control box supporting up to ten individual detectors. All functions that formerly required an entry into the experimental hall and manual adjustment can be accomplished from the Machine Control Center (MCC). A further innovation was the addition of a High Voltage ''Brick'' at the detector location. A single cable supplies the required voltage for the Brick and a return line for the ion chamber signal. The read back screens display range, trip point, and accumulated dose for each location. The new system is very cost effective and significantly reduces the amount of lost experimental time.

  17. Commissioning of a large segmented ion chamber for the FMA

    SciTech Connect

    Lister, C.J.; Davids, C.N.; Blumenthal, D.J.

    1995-08-01

    A large-area sectored ion chamber was built by a Yale-Daresbury (U.K.) - ANL collaboration to allow extensions of studies of N = Z (T = 0) nuclei. The ion chamber is a conventional DE-DE-E detector which is 20-cm deep, but each anode is segmented into eight pads to allow high count-rate capability and ray-trace reconstruction. With suitable electronics, the detector can become eight close-packed ion chambers, considerably reducing the count rate in each. A position-wire plane allows further raytracing which should permit the rejection of anomalous trajectories and improve Z-separation. A brief test run was scheduled shortly after delivery. Performance appeared promising, but issues of gain matching and cross talk need further exploration. We will study these features {open_quotes}off line{close_quotes} and hope to perform a full experiment on selenium isotopes in the summer. This detector appears to have many uses and is potentially more useful than previous detectors of its type. Similar detectors are being built for the HHRF at Oak Ridge and for Texas A&M University.

  18. Particle based plasma simulation for an ion engine discharge chamber

    NASA Astrophysics Data System (ADS)

    Mahalingam, Sudhakar

    Design of the next generation of ion engines can benefit from detailed computer simulations of the plasma in the discharge chamber. In this work a complete particle based approach has been taken to model the discharge chamber plasma. This is the first time that simplifying continuum assumptions on the particle motion have not been made in a discharge chamber model. Because of the long mean free paths of the particles in the discharge chamber continuum models are questionable. The PIC-MCC model developed in this work tracks following particles: neutrals, singly charged ions, doubly charged ions, secondary electrons, and primary electrons. The trajectories of these particles are determined using the Newton-Lorentz's equation of motion including the effects of magnetic and electric fields. Particle collisions are determined using an MCC statistical technique. A large number of collision processes and particle wall interactions are included in the model. The magnetic fields produced by the permanent magnets are determined using Maxwell's equations. The electric fields are determined using an approximate input electric field coupled with a dynamic determination of the electric fields caused by the charged particles. In this work inclusion of the dynamic electric field calculation is made possible by using an inflated plasma permittivity value in the Poisson solver. This allows dynamic electric field calculation with minimal computational requirements in terms of both computer memory and run time. In addition, a number of other numerical procedures such as parallel processing have been implemented to shorten the computational time. The primary results are those modeling the discharge chamber of NASA's NSTAR ion engine at its full operating power. Convergence of numerical results such as total number of particles inside the discharge chamber, average energy of the plasma particles, discharge current, beam current and beam efficiency are obtained. Steady state results for

  19. Monte Carlo calculations of electron beam quality conversion factors for several ion chamber types

    SciTech Connect

    Muir, B. R.; Rogers, D. W. O.

    2014-11-01

    Purpose: To provide a comprehensive investigation of electron beam reference dosimetry using Monte Carlo simulations of the response of 10 plane-parallel and 18 cylindrical ion chamber types. Specific emphasis is placed on the determination of the optimal shift of the chambers’ effective point of measurement (EPOM) and beam quality conversion factors. Methods: The EGSnrc system is used for calculations of the absorbed dose to gas in ion chamber models and the absorbed dose to water as a function of depth in a water phantom on which cobalt-60 and several electron beam source models are incident. The optimal EPOM shifts of the ion chambers are determined by comparing calculations of R{sub 50} converted from I{sub 50} (calculated using ion chamber simulations in phantom) to R{sub 50} calculated using simulations of the absorbed dose to water vs depth in water. Beam quality conversion factors are determined as the calculated ratio of the absorbed dose to water to the absorbed dose to air in the ion chamber at the reference depth in a cobalt-60 beam to that in electron beams. Results: For most plane-parallel chambers, the optimal EPOM shift is inside of the active cavity but different from the shift determined with water-equivalent scaling of the front window of the chamber. These optimal shifts for plane-parallel chambers also reduce the scatter of beam quality conversion factors, k{sub Q}, as a function of R{sub 50}. The optimal shift of cylindrical chambers is found to be less than the 0.5 r{sub cav} recommended by current dosimetry protocols. In most cases, the values of the optimal shift are close to 0.3 r{sub cav}. Values of k{sub ecal} are calculated and compared to those from the TG-51 protocol and differences are explained using accurate individual correction factors for a subset of ion chambers investigated. High-precision fits to beam quality conversion factors normalized to unity in a beam with R{sub 50} = 7.5 cm (k{sub Q}{sup ′}) are provided. These

  20. Characterization of a multi-axis ion chamber array

    SciTech Connect

    Simon, Thomas A.; Kozelka, Jakub; Simon, William E.; Kahler, Darren; Li, Jonathan; Liu, Chihray

    2010-11-15

    Purpose: The aim of this work was to characterize a multi-axis ion chamber array (IC PROFILER; Sun Nuclear Corporation, Melbourne, FL USA) that has the potential to simplify the acquisition of LINAC beam data. Methods: The IC PROFILER (or panel) measurement response was characterized with respect to radiation beam properties, including dose, dose per pulse, pulse rate frequency (PRF), and energy. Panel properties were also studied, including detector-calibration stability, power-on time, backscatter dependence, and the panel's agreement with water tank measurements [profiles, fractional depth dose (FDD), and output factors]. Results: The panel's relative deviation was typically within ({+-}) 1% of an independent (or nominal) response for all properties that were tested. Notable results were (a) a detectable relative field shape change of {approx}1% with linear accelerator PRF changes; (b) a large range in backscatter thickness had a minimal effect on the measured dose distribution (typically less than 1%); (c) the error spread in profile comparison between the panel and scanning water tank (Blue Phantom, CC13; IBA Schwarzenbruck, DE) was approximately ({+-}) 0.75%. Conclusions: The ability of the panel to accurately reproduce water tank profiles, FDDs, and output factors is an indication of its abilities as a dosimetry system. The benefits of using the panel versus a scanning water tank are less setup time and less error susceptibility. The same measurements (including device setup and breakdown) for both systems took 180 min with the water tank versus 30 min with the panel. The time-savings increase as the measurement load is increased.

  1. Technical Note: Ion chamber angular dependence in a magnetic field.

    PubMed

    Reynolds, Michael; Rathee, Satyapal; Fallone, B Gino

    2017-08-01

    There have been several studies investigating dose deposition effects within radiation detectors in the presence of a magnetic field. However, to date there has only been a passing investigation which explicitly investigates detector dose-response as a function of detector orientation. Herein we will investigate the dose-response as a function angular orientation of a PR06C ionization chamber. We will also benchmark the Monte Carlo code PENELOPE with the newly developed magnetic field Fano test. The PENELOPE Monte Carlo package was used to simulate a PR06C ionization chamber in 0.35 T through 1.5 T magnetic fields oriented either parallel or orthogonal to an incident 6 MV radiation beam. The ionization chamber was rotated through a number of polar and azimuthal angles. The dose deposited within the chamber at each angular position and magnetic field strength was scored then normalized to that deposited in the same orientation with no magnetic field. The simulation was also benchmarked via a Fano test in magnetic field. The Fano test yielded a 0.4% difference between simulation and expected result, which is similar to previous findings and sufficient for the purposes of this study. The angular dose-response map in all cases where the magnetic field is oriented orthogonal to the radiation beam is quite varied and can range from 0.89 to 1.08. Angular deviations as small as 3° can lead to dose-response changes in excess of 1%. When the magnetic field is parallel to the photon beam, the angular dose-response map is homogeneous and less than 1% below 1.0 T. Within a magnetic field-oriented orthogonal to the radiation beam, the ionization chamber dose-response fluctuates greatly as a function of polar and azimuthal angle, where a parallel field yields a more homogeneous dose-response. © 2017 American Association of Physicists in Medicine.

  2. MEASUREMENT OF SURFACE ALPHA CONTAMINATION USING ELECTRET ION CHAMBERS

    SciTech Connect

    M.A. Ebadian, Ph.D.

    1999-01-01

    Electret ion chambers (EICs) are known to be inexpensive, reliable, passive, integrating devices used for measurement of ionizing radiation. Their application for measurement of alpha contamination on surfaces was recently realized. This two-year project deals with the evaluation of electret ion chambers with different types of electrets and chambers for measurement of surface alpha contamination, their demonstration at U.S. Department of Energy (DOE) sites, a cost-benefit comparison with the existing methods, and the potential deployment at DOE sites. During the first year (FY98) of the project, evaluation of the EICS was completed. It was observed that EICS could be used for measurement of free release level of alpha contamination for transuranics (100 dpm/100 cm{sup 2} fixed). DOE sites, where demonstration of EIC technology for surface alpha contamination measurements could be performed, were also identified. During FY99, demonstration and deployment of EICS at DOE sites are planned. A cost-benefit analysis of the EIC for surface alpha contamination measurement will also be performed.

  3. Self-pinched chamber transport of heavy ion beams

    NASA Astrophysics Data System (ADS)

    Rose, D. V.; Welch, D. R.; Oliver, B. V.; Yu, S. S.; Olson, C. L.

    2001-10-01

    Self-pinched heavy ion beams are being examined as a chamber transport scheme for heavy-ion-driven inertial confinement fusion. In this scheme, beam-impact-ionization of a low-density background gas provides neutralizing electrons. For certain ranges of background gas pressures the beam is essentially charge-neutralized but incomplete current-neutralization allows the self-magnetic field of the beam to act as a pinch force, confining the beam divergence. Equilibrium transport modes for a Pb^+65 ion beam propagating through low density Xe gas are being studied with particle-in-cell simulations using the LSP code [1]. Time dependent evolution of the beam net current and pinched beam radius as a function of Xe chamber pressure from the simulations is examined. [1] T. P. Hughes, R. E. Clark, and S. S. Yu, Phys. Rev. ST-AB 2, 110401 (1999); D. R. Welch, D. V. Rose, B. V. Oliver, and R. E. Clark, Nucl. Inst. Meth. Phys. Res. A 242, 134 (2001).

  4. Long ion chamber systems for the SLC (Stanford Linear Collider)

    SciTech Connect

    Rolfe, J.; Gearhart, R.; Jacobsen, R.; Jenkins, T.; McComick, D.; Nelson, R.; Reagan, D.; Ross, M.

    1989-03-01

    A Panofsky Long Ion Chamber (PLIC) is essentially a gas-filled coaxial cable, and has been used to protect the Stanford Linear Accelerator from damage caused by its electron beam, and as a sensitive diagnostic tool. This old technology has been updated and has found renewed use in the SLC. PLIC systems have been installed as beam steering aids in most parts of the SLC and are a part of the system that protects the SLC from damage by errant beams in several places. 5 refs., 3 figs., 1 tab.

  5. Paired Ion Chamber Constants for Fission Gamma-Neutron Fields

    DTIC Science & Technology

    1984-12-01

    energy E. For neutrons with energies distributed over a spectrum, the above theory must be extended to define a spectrum-averaged neutron W-value...733, 1979. 21. DLC-31/(DPL-1/FEWG1), 37- neutrOn , 21-gamma ray coupled, P3, multigroup library in ANISN Format. ORNL/TM-4840. Oak Ridge National...ragMD©/^ ^i[p@^¥ Paired ion chamber constants for fission gamma- neutron fields G. H.Zeman K. P. Ferlic DEFENSE NUCLEAR AGENCY ARMED FORCES

  6. Ion recombination correction factor in scanned light-ion beams for absolute dose measurement using plane-parallel ionisation chambers

    NASA Astrophysics Data System (ADS)

    Rossomme, S.; Horn, J.; Brons, S.; Jäkel, O.; Mairani, A.; Ciocca, M.; Floquet, V.; Romano, F.; Rodriguez Garcia, D.; Vynckier, S.; Palmans, H.

    2017-07-01

    Based on international reference dosimetry protocols for light-ion beams, a correction factor (k s) has to be applied to the response of a plane-parallel ionisation chamber, to account for recombination of negative and positive charges in its air cavity before these charges can be collected on the electrodes. In this work, k s for IBA PPC40 Roos-type chambers is investigated in four scanned light-ion beams (proton, helium, carbon and oxygen). To take into account the high dose-rates used with scanned beams and LET-values, experimental results are compared to a model combining two theories. One theory, developed by Jaffé, describes the variation of k s with the ionization density within the ion track (initial recombination) and the other theory, developed by Boag, describes the variation of k s with the dose rate (volume recombination). Excellent agreement is found between experimental and theoretical k s-values. All results confirm that k s cannot be neglected. The solution to minimise k s is to use the ionisation chamber at high voltage. However, one must be aware that charge multiplication may complicate the interpretation of the measurement. For the chamber tested, it was found that a voltage of 300 V can be used without further complication. As the initial recombination has a logarithmic variation as a function of 1/V, the two-voltage method is not applicable to these scanned beams.

  7. Chamber design for the LIBRA light ion beam fusion reactor

    SciTech Connect

    Sawan, M.E.; Sviatoslavsky, I.N.; Wittenberg, L.J.; Lovell, E.G.; Engelstad, R.L.

    1989-03-01

    Scoping analysis was performed for LIBRA to determine the blanket design options that satisfy the tritium breeding and wall protection requirements. The blanket is made of banks of INPORT tubes of porous SiC and Li/sub 17/Pb/sub 83/ flowing in them. The reference design utilizes a 1.35 m thick blanket region backed by a 0.5 m thick HT-9 reflector. The lithium in the blanket and reflector is enriched to 90% /sup 6/Li. This design leads to the shortest possible beam propagation channel. The TBR is 1.5 and the end-of-life dpa in the chamber wall is 200 dpa. In this paper the authors describe the design and configuration of the chamber as well as the tritium fueling and the response to the target explosion.

  8. Discharge Chamber Performance of the NEXIS Ion Thruster

    NASA Technical Reports Server (NTRS)

    Goebel, Dan M.; Polk, James; Sengupta, Anita

    2004-01-01

    The Nuclear-Electric Xenon Ion System (NEXIS) thruster was designed to produce greater than or equal to 70% efficiency at ISPs in excess of 6500 sec and total power levels in excess of 15 kW. In order to achieve this performance, the thruster requires a large area plasma generator capable of high propellant utilimtion efficiency and low discharge loss while producing a very flat, uniform beam profile. Fortunately, larger thrusters can be made more uniform and efficient due to the higher volume to surface ratio, provided that the magnetic cusp confinement is designed properly and the thruster length to diameter ratio is adequate. This paper describes the discharge chamber performance of the NEXIS Laboratory Model (LM) thruster. The LM discharge chamber is 65 cm in diameter at the grid plane and uses 6 ring-cusps to provide magnetic confinement of the plasma. The thruster was tested with flat carbon-carbon composite grids with the hole pattern masked to 57 cm in diameter and a conventional Type-B "1/2" diameter hollow cathode. During the preliminary "discharge only" tests, the LM thruster demonstrated profile factors of 0.84 and a discharge loss of about 160 eV/ion at 25 V discharge voltage and over 90% propellant utilization efficiency in simulated beam extraction experiments at 3.9 A of beam current. Analysis of the data from these tests used the discharge-only model developed by Brophy. Subsequent beam extraction experiments validated the key variables used in the model to predict the performance from the discharge-only data, and demonstrated 3.9 A of beam current at over 90% propellant utilization efficiency with a flatness parameter of better than 0.8 and a discharge loss of about 185 eV/ion. The slightly higher discharge loss measured during beam extractions was found to be due to a lower screen transparency in the as-manufactured LM grid set. Plasma measurements with a scanning probe internal to the thruster near the screen grid showed plasma densities over l

  9. Plasma generation near an Ion thruster disharge chamber hollow cathode

    NASA Technical Reports Server (NTRS)

    Katz, Ira; Anderson, John R.; Goebel, Dan M.; Wirz, Richard; Sengupta, Anita

    2003-01-01

    In gridded electrostatic thrusters, ions are produced by electron bombardment in the discharge chamber. In most of these thrusters, a single, centrally located hollow cathode supplies the ionizing electrons. An applied magnetic field in the discharge chamber restricts the electrons leaving the hollow cathode to a very narrow channel. In this channel, the high electron current density ionizes both propellant gas flowing from the hollow cathode, and other neutrals from the main propellant flow from the plenum. The processes that occur just past the hollow cathode exit are very important. In recent engine tests, several cases of discharge cathode orifice place and keeper erosion have been reported. In this paper we present results from a new 1-D, variable area model of the plasma processes in the magnetized channel just downstream of the hollow cathode keeper. The model predicts plasma densities, and temperatures consistent with those reported in the literature for the NSTAR engine, and preliminary results from the model show a potential maximum just downstream of the cathode.

  10. Plasma generation near an Ion thruster disharge chamber hollow cathode

    NASA Technical Reports Server (NTRS)

    Katz, Ira; Anderson, John R.; Goebel, Dan M.; Wirz, Richard; Sengupta, Anita

    2003-01-01

    In gridded electrostatic thrusters, ions are produced by electron bombardment in the discharge chamber. In most of these thrusters, a single, centrally located hollow cathode supplies the ionizing electrons. An applied magnetic field in the discharge chamber restricts the electrons leaving the hollow cathode to a very narrow channel. In this channel, the high electron current density ionizes both propellant gas flowing from the hollow cathode, and other neutrals from the main propellant flow from the plenum. The processes that occur just past the hollow cathode exit are very important. In recent engine tests, several cases of discharge cathode orifice place and keeper erosion have been reported. In this paper we present results from a new 1-D, variable area model of the plasma processes in the magnetized channel just downstream of the hollow cathode keeper. The model predicts plasma densities, and temperatures consistent with those reported in the literature for the NSTAR engine, and preliminary results from the model show a potential maximum just downstream of the cathode.

  11. Simple ``Package Design'' Ion Chamber Monitors for TRIUMF's Proton Beamlines

    NASA Astrophysics Data System (ADS)

    Gray, Daniel; Minato, Brian

    2002-12-01

    In the beam line designed to supply 100 μA of 500 MeV protons to the two ISAC production targets at TRIUMF, 13 profile monitor stations were required. The design allows each station to be fitted with either an air driven wire scanner module for high currents or an ionization chamber for low currents. Ring shaped multilayer G10 circuit boards were designed for the latter to enable a simple modular "gas package" that is easily serviced and aligned. These gas packages have only five basic parts, two outer window frames with 0.010 in. thick E-beam welded Al windows, two ring shaped circuit boards with 2 mm wire spacing and edge card connectors (X and Y use the same design of board) and one center frame for mounting to the inserting mechanism and holding a .001 in. Al foil. The circuit boards are critical components due to the necessity to hold vacuum along their edges. Signal traces pass from the inner part of the ring that is gas filled to the outside of the ring that is in vacuum. The windows and center foil frame are at -300 V bias. This gas package design led to a similar design used to upgrade the existing (1970's vintage) proton beamline ion chamber monitors.

  12. A model for electron/ion recombination in ionization chambers

    SciTech Connect

    Sailor, W.C.

    1988-05-01

    The recombination of free electrons and positive ions along charged particle tracks in gases has been modeled using electron tranport equations, which assume homogeneous distribution in the vicinity of the tracks. The equations include space charge terms, which have been negelected in previous models. A formula for the electron yield as a function of detector applied potential is obtained from a perturbation solution valid when the ratio of the Debye length to the charge column radius is larger then unity. When this ratio is very large, the formula reduces to that of previous models. Pulse height measurements in a /sup 3/He ionization chamber indicate 2% to 30% losses to recombination which vary with applied field, particle type, and energy. Using reasonable values for the electron transport coefficients, the calculated loss of signal to recommendation is generally in agreement with experiment, but the variation with applied bias is stronger in the experiment.

  13. Extraction characteristics of a low-energy ion beam system with a remote plasma chamber

    SciTech Connect

    Vasquez, M. R.; Wada, M.

    2016-02-15

    Low-energy argon beams were extracted from a dual-chamber ion source system. The first chamber is a quartz cylinder where dense inductively coupled plasmas were produced using 13.56 MHz radio frequency (rf) power. The discharge was driven into an adjacent chamber which acts as a reservoir for ion beam extraction using a dual-electrode extractor configuration. Extraction of ions from the second chamber with energies in the 100 eV range was achieved while minimizing fluctuations induced by the rf signal. A custom-built retarding potential analyzer was used to analyze the effectiveness of ion beam transport using the remote plasma chamber. Well-defined beams were extracted between 60 and 100 V extraction potentials at 50–100 W rf powers. An increase in rf power resulted in an increase in average ion energy, increase in ion current density while the energy spread remains constant.

  14. Development of a novel reaction chamber for ion beam analysis of large samples

    NASA Astrophysics Data System (ADS)

    Kakuee, O. R.; Fathollahi, V.; Agha-Aligol, D.; Farmahini-Farahani, M.; Oliaiy, P.; Lamehi-Rachti, M.

    2008-04-01

    A novel vacuum chamber for ion beam analysis of large-size industrial samples - whose analysis are not feasible in conventional ion beam analysis reaction chambers - has been designed, fabricated and successfully tested. Using the newly developed chamber, both PIXE and RBS analyses could be carried out at the same time and on the same point of the samples. Ion beam analysis using this novel chamber lacks the disadvantages of external beam analysis and benefits the advantages of in-vacuum analysis. This has been achieved by designing a tiny open port in the wall of the reaction chamber to be sealed with a small flat area of sample body where its analysis is of interest. As a case study, two samples of gas turbine blades, a corroded one at highly corrosive environment and a refurbished one after application of certain coatings are analysed using the novel chamber. Experimental results confirm the performance and capability of the reaction chamber.

  15. A Current Mode Ion Chamber for the n+p->D+gamma Parity Violation Experiment

    NASA Astrophysics Data System (ADS)

    Snow, William

    2001-04-01

    We have developed and tested a current-mode 3He-based ion chamber for the measurement of the neutron time-of-flight spectrum from a pulsed cold neutron source on a pulse-by-pulse basis. Such a device is required in the n+p->D+gamma experiment for general diagnostic purposes and for monitoring the ortho-para ratio in the liquid hydrogen target by neutron transmission. This detector was tested in the fall of 2000 at the LANSCE pulsed cold neutron source. The chamber operates with a mixture gas of 0.5 atm 3He and 3 atm H2 and possesses segmentation along the neutron beam. The design is similar to that of Penn et al [1] which was used for a neutron-4He parity violation experiment, but with modifications to the time response and the dynamic range in neutron energy required for operation at a pulsed neutron source. The relevant technical characteristics of the ion chamber (time response, sensitivity to Mev gammas, noise, efficiency, neutron energy dynamic range, linearity) will be described. [1] S. Penn et.al., submitted to NIM (2000)

  16. Ionization chamber radial response deconvolution in megavoltage photon beam

    NASA Astrophysics Data System (ADS)

    Kulmala, A.; Tenhunen, M.

    2017-09-01

    The aim of this paper is to study a radial response model as a method, to correct output factor results gathered with ionization chambers of different size and shape in cone collimated RT fields. An enhanced version of a non-parametric super-resolution deconvolution method able to model a radial response function of a small cylinder symmetric ionization chamber is described and demonstrated. The radial response of four ionization chambers with different geometry and radius are estimated using 6 MV photon beam in water at the isocentre plane. Finally the validity of the estimates is tested by applying the response functions to the output factor measurements of 4–20 mm conical collimators. The enhanced method is demonstrated by obtaining the response function characteristics with a spatial uncertainty smaller than 0.1 mm when the distance from chamber axis is larger than 0.5 mm. In all studied ionization chambers, a significant local response maximum is found close to the air cavity boundary. The agreement between the output factor results of different chambers is promising, the largest difference (max—min) in output factor is 4% obtained for the smallest 4 mm cone size.

  17. Post-flight Analysis of the Argon Filled Ion Chamber

    NASA Technical Reports Server (NTRS)

    Tai, H.; Goldhagen, P.; Jones, I. W.; Wilson, J. W.; Maiden, D. L.; Shinn, J. L.

    2003-01-01

    Atmospheric ionizing radiation is a complex mixture of primary galactic and solar cosmic rays and a multitude of secondary particles produced in collision with air nuclei. The first series of Atmospheric Ionizing Radiation (AIR) measurement flights on the NASA research aircraft ER-2 took place in June 1997. The ER-2 flight package consisted of fifteen instruments from six countries and were chosen to provide varying sensitivity to specific components. These AIR ER-2 flight measurements are to characterize the AIR environment during solar minimum to allow the continued development of environmental models of this complex mixture of ionizing radiation. This will enable scientists to study the ionizing radiation health hazard associated with the high-altitude operation of a commercial supersonic transport and to allow estimates of single event upsets for advanced avionics systems design. The argon filled ion chamber representing about 40 percent of the contributions to radiation risks are analyzed herein and model discrepancies for solar minimum environment are on the order of 5 percent and less. Other biologically significant components remain to be analyzed.

  18. Ion-chamber-based loss monitor system for the Los Alamos Meson Physics Facility

    SciTech Connect

    Plum, M.A.; Brown, D.; Browman, A.; Macek, R.J.

    1995-05-01

    A new loss monitor system has been designed and installed at the Los Alamos Meson Physics Facility (LAMPF). The detectors are ion chambers filled with N{sub 2} gas. The electronics modules have a threshold range of 1:100, and they can resolve changes in beam loss of about 2% of the threshold settings. They can generate a trip signal in 2 {mu}s if the beam loss is large enough; if the response time of the Fast Protect System is included the beam will be shut off in about 37 {mu}s.

  19. Modelling ionization chamber response to nonstandard beam configurations

    NASA Astrophysics Data System (ADS)

    Tantot, L.; Seuntjens, J.

    2008-02-01

    Novel technologies aiming at improving target dose coverage while minimising dose to organs at risk use delivery of radiation fields that significantly deviate from reference conditions defined in protocols such as TG-51 and TRS-398. The use of ionization chambers for patient-specific quality assurance of these new delivery procedures calibrated in reference conditions increases the uncertainties on dose delivery. The conversion of the dose to the chamber cavity to the dose to water becomes uncertain; and the geometrical details of the chamber, as well as the details of the delivery, are expected to be significant. In this study, a realistic model of the Exradin® A12 Farmer chamber is simulated. A framework is applied for the calculation of ionization chamber response to arbitrarily modulated fields as a summation of responses to pencil beams. This approach is used with the chamber model and tested against measurements in static open fields and dynamic MLC IMRT fields. As a benchmark test of the model, quality conversion factors values calculated by Monte-Carlo simulation with the chamber model are in agreement within 0.1 % and 0.4 % with those in the AAPM TG-51, for 6 MV and 18 MV photon beams, respectively. Pencil-beam kernels show a strong dependence on the geometrical details of the chamber. Kernel summations with open fields show a relative agreement within 4.0 % with experimental data; the agreement is within 2.0 % for dynamic MLC IMRT beams. Simulations show a strong sensitivity of chamber response on positioning uncertainties, sometimes leading to dose uncertainties of 15 %.

  20. An experimental and computational investigation of the standard temperature-pressure correction factor for ion chambers in kilovoltage x rays.

    PubMed

    La Russa, Daniel J; McEwen, Malcolm; Rogers, D W O

    2007-12-01

    For ion chambers with cavities open to the surrounding atmosphere, the response measured at a given temperature and pressure must be corrected using the standard temperature-pressure correction factor (P(TP)). A previous paper based solely on Monte Carlo simulations [D. J. La Russa and D. W. O. Rogers, Med. Phys. 33, 4590-4599 (2006)] pointed out the shortcomings of the P(TP) correction factor when used to correct the response of non-air-equivalent chambers for low-energy x-ray beams. This work presents the results of several experiments that corroborate these calculations for a number of ion chambers. Monte Carlo simulations of the experimental setup revealed additional insight into the various factors affecting the extent of the breakdown of P(TP), including the effect of impurities and the sensitivity to chamber dimensions. For an unfiltered 60 kV beam, the P(TP)-corrected response of an NE 2571 ion chamber measured at 0.7 atm was 2.5% below the response measured at reference conditions. In general, Monte Carlo simulations of the experimental setup using EGSnrc were within 0.5% of measured values. EGSnrc-calculated values of air kerma calibration coefficients (N(K)) at low x-ray energies are also provided as a means of estimating the level of impurities in the chambers investigated. Calculated values of N(K) normalized to the value measured for a 250 kV beam were obtained for three chambers and were within 1% of experiment with one exception, the Exradin A12 in a 50 kV beam.

  1. Dose verification with different ion chambers for SRT/SBRT plans

    NASA Astrophysics Data System (ADS)

    Durmus, I. F.; Tas, B.; Okumus, A.; Uzel, O. E.

    2017-02-01

    Verification of patient plan is very important in stereotactic treatments. VMAT plans were prepared with 6MV-FFF or 10MV-FFF energies for 25 intracranial and extracranial stereotactic patients. Absolute dose was measured for dose verification in each plans. Iba® CC01, Iba® CC04, Iba® CC13 ion chambers placed at a depth of 5cm in solid phantom (RW3). Also we scanned this phantom with ion chambers by Siemens® Biograph mCT. QA plans were prepared by transferring twenty five patient plans to phantom assemblies for three ion chambers. All plans were performed separately for three ion chambers at Elekta® Versa HD linear accelerator. Statistical analysis of results were made by Wilcoxon signed-rank test. Difference between dose values were determined %1.84±3.4 (p: 0.001) with Iba CC13 ion chamber, %1.80±3.4 (p: 0.002) with Iba CC04 ion chamber and %0.29±4.6 (p: 0.667) with Iba CC01 ion chamber. In stereotactic treatments, dosimetric uncertainty increases in small areas. We determined more accurate results with small sized detectors. Difference between TPS calculations and all measurements were founded lower than %2.

  2. High-intensity positive beams extracted from a compact double-chamber ion source

    SciTech Connect

    Huck, H.; Somacal, H.; Di Gregorio, D.E.; Fernandez Niello, J.O.; Igarzabal, M.; Di Paolo, H.; Reinoso, M.

    2005-06-15

    This work presents the design and development of a simple ion source, the associated ion extraction optics, and the beam transport of a low-energy and high-current proton accelerator. In its actual version, the ion source can deliver positive proton currents up to 100 mA. This rather high beam current is achieved by adding a small ionization chamber between the discharge chamber containing the filament and the extraction electrode of the ion source. Different parameters of the ion source and the injection beam line are evaluated by means of computer simulations to optimize the beam production and transmission.

  3. Improved diffusion chamber cultures for cytokinetic analysis of antibody response

    PubMed Central

    Nettesheim, P.; Makinodan, T.; Chadwick, Carol J.

    1966-01-01

    Diffusion chambers (3×10 mm) constructed with 0.1 μ porosity filters, but not with 0.45 μ or greater porosity filters, were found to be consistently cell impermeable, with use of acryloid as the glueing agent. The filters permit free diffusion of 19S and 7S antibodies into `empty' chambers in vivo and in vitro. Pronase treatment of the chamber dissolves the clot and frees cells attached to the inner surfaces. This permits almost complete recovery of the chamber culture cells. Chamber cultures can be readily transferred from one host to another and kept in vitro at room temperature for at least 6 hours without any loss of activity. In vivo diffusion problems arise after 1 month of culture, most probably due to excessive growth of peritoneal cells on the outer surface of the filters; this limitation can be overcome by serial in vivo transfer of the chamber and wiping the outer surface at the time of transfer. The diffusion chamber culture method as described here fulfills all the prerequisites of an assay system with which one can perform precise cytokinetic analysis of antibody response. ImagesFIG. 3 PMID:5926065

  4. An Egsnrc investigation of the P(TP) correction factor for ion chambers in kilovoltage X rays.

    PubMed

    La Russa, Daniel J; Rogers, D W O

    2006-12-01

    As part of the standard practice for obtaining consistent ion chamber measurements with cavities open to the surrounding atmosphere, the raw measured response is corrected to the response at a reference temperature and pressure using the standard temperature-pressure correction factor (P(TP)). In this study, the EGSnrc Monte Carlo code was used to investigate the validity of the P(TP) correction factor for kilovoltage x rays incident on various geometrically distinct ion chambers. The calculated P(TP)-corrected chamber response deviated by over 2% relative to expected values for a 40 kV spectrum incident on a graphite thimble chamber at an air density typical of Mexico City. The relative deviation from the expected response was much worse for a large spherical graphite chamber, exceeding 16% at an air density of 0.6 kg/m3 (approximately 0.5 atm at 22 degrees C) for the same beam energy. The breakdown of the P(TP) correction factor was also observed for a 26 kV mammography spectrum incident on two mammography chambers. For 60Co beams, the P(TP) correction factor behaved as expected. For day-to-day variations in pressure, only a negligible of the P(TP) correction factor was observed with low x-ray energies. Factors contributing to the breakdown of the P(TP) correction factor at low x-ray energies and large pressure variations, such as the range of electrons, the material of the wall, the chamber dimensions and air-photon interactions, are discussed in depth.

  5. Effective point of measurement of thimble ion chambers in megavoltage photon beams.

    PubMed

    Tessier, Frédéric; Kawrakow, Iwan

    2010-01-01

    Determine the effective point of measurement (EPOM) of 12 thimble ion chambers, including miniature chambers and three models widely used for clinical reference dosimetry. The EPOM is the point at which the measured dose would arise in the measurement medium in the absence of the probe: For cylindrical chambers, it is shifted upstream relative to the central axis of the chamber. Although current dosimetry protocols prescribe a blanket upstream EPOM shift of 0.6r, with r as the chamber cavity radius, it has been shown in recent years that the EPOM does, in fact, depend on every detail of the chamber design and on the beam characteristics. In the wake of this finding, the authors undertake a comprehensive study of the EPOM for a series of chambers in water. This work relies on EGSnrc Monte Carlo calculations for the central axis depth dose in a water phantom and in ion chambers. They use a full Elekta Precise linac treatment head simulation to generate realistic photon beams with nominal energies of 6 and 25 MV and fields sizes of 10 x 10 and 40 x 40 cm2. The correct EPOM shift for the 12 ion chambers, modeled in realistic detail, is taken as the one minimizing the deviation of the ratio between the dose to water and the dose to the gas of the chamber cavity, according to a method proposed and validated in previous work. The analysis reveals that the actual EPOM shift is significantly smaller than the recommended value in current dosimetry protocols, by up to 25% for reference-class chambers and 80% for miniature chambers. The location of the EPOM also depends on the characteristics of the incident beam and varies in a well-defined way with the cavity length, the central electrode radius, and the thimble wall thickness. The authors confirm that an upstream EPOM shift of 0.6r is too large for thimble ion chambers in high energy photon beams. Proper values for the EPOM shift could be tabulated per beam and per chamber, but they envisage that a single shift for all

  6. Determination of relative ion chamber calibration coefficients from depth-ionization measurements in clinical electron beams

    NASA Astrophysics Data System (ADS)

    Muir, B. R.; McEwen, M. R.; Rogers, D. W. O.

    2014-10-01

    A method is presented to obtain ion chamber calibration coefficients relative to secondary standard reference chambers in electron beams using depth-ionization measurements. Results are obtained as a function of depth and average electron energy at depth in 4, 8, 12 and 18 MeV electron beams from the NRC Elekta Precise linac. The PTW Roos, Scanditronix NACP-02, PTW Advanced Markus and NE 2571 ion chambers are investigated. The challenges and limitations of the method are discussed. The proposed method produces useful data at shallow depths. At depths past the reference depth, small shifts in positioning or drifts in the incident beam energy affect the results, thereby providing a built-in test of incident electron energy drifts and/or chamber set-up. Polarity corrections for ion chambers as a function of average electron energy at depth agree with literature data. The proposed method produces results consistent with those obtained using the conventional calibration procedure while gaining much more information about the behavior of the ion chamber with similar data acquisition time. Measurement uncertainties in calibration coefficients obtained with this method are estimated to be less than 0.5%. These results open up the possibility of using depth-ionization measurements to yield chamber ratios which may be suitable for primary standards-level dissemination.

  7. Investigation of correction factors for non-reference conditions in ion chamber photon dosimetry with Monte-Carlo simulations.

    PubMed

    Wulff, Jörg; Heverhagen, Johannes T; Karle, Heiko; Zink, Klemens

    2010-01-01

    Current dosimetry protocols require geometrical reference conditions for the determination of absorbed dose in external radiotherapy. Whenever these geometrical conditions cannot be maintained the application of additional corrections becomes necessary, in principle. The current DIN6800-2 protocol includes a corresponding factor k(NR), but numerical values are lacking and no definite information about the magnitude of this correction is available yet. This study presents Monte-Carlo based calculations within the 6 MV-X photon field of a linear accelerator for a common used ion chamber (PTW31010) employing the EGSnrc code system. The linear accelerator model was matched to measurements, showing good agreement and is used as a realistic source. The individual perturbation correction factors as well as the resulting correction factor k(NR) were calculated as a function of depth for three field sizes, as a function of central axis distance for the largest field and within the build-up region. The behaviour of the ion chamber was further investigated for an idealized hypothetical field boundary. Within the field of the linear accelerator where charged particle equilibrium is achieved the factor k(NR) was generally below approximately 0.5%. In the build-up region a depth dependent correction of up to 2% was calculated when positioning the chamber according to DIN6800-2. Minimizing the depth dependence of the corrections in the build-up region lead to a slightly different positioning of the ion chamber as currently recommended. In regions of the hypothetical field boundary with missing charged particle equilibrium and high dose gradients, the ion chamber response changed by up to approximately 40%, caused by the comparatively large volume (0.125 cm(3)) of the investigated chamber. Copyright 2010. Published by Elsevier GmbH.

  8. [Clinical calibration dosimetry in JSMP-01: measurements using plane-parallel ion chambers.].

    PubMed

    Araki, Fujio; Kumagai, Kozo; Yoshiura, Takao; Oura, Hiroki; Tachibana, Masayuki; Moribe, Nobuyuki; Tajima, Hidetaka; Yoshida, Atsushi; Kido, Tetsuo

    2005-01-01

    The Japan Society of Medical Physics (JSMP) Task Group published Standard dosimetry of absorbed dose in external beam radiotherapy (Standard dosimetry 01) as a new high-energy photon and electron dosimetry protocol in 2002. In this study, we present Standard dosimetry 01 as the JSMP-01 protocol for the convenience of users. This protocol is based on using an ion chamber having a (60)Co absorbed dose to water calibration coefficient, N(D,w), which is calculated from a (60)Co exposure calibration coefficient, N(c). We present dose comparisons between a reference chamber and various plane-parallel chambers. The absorbed dose to water was compared at the calibration depth of 5 cm for a (60)Co beam and d(c) = 0.6R(50) - 0.1 (cm) for electron beams according to JSMP-01. The absorbed dose to water calibration coefficients, [N(D,w)](Co) and [N(D,w)](18E), for the plane-parallel chambers were also determined by (60)Co and electron beam cross-calibrations using a reference chamber. The dose for the plane-parallel chambers derived from [N(D,w)](Co) and [N(D,w)](18E) was compared to that for the reference chamber using electron beams. The JARP chamber in the Kyushu Regional Center which meets third-order standards in Japan was used as the reference chamber. The doses for the plane-parallel chambers determined according to JSMP-01 agreed with that for the JARP chamber within 1% and 2% for (60)Co and electron beams, respectively. For electron beams, the doses for the plane-parallel chambers calculated from [N(D,w)](Co) and [N(D,w)](18E) were within 1.5% and 1.0% compared to those for the JARP chamber, respectively, except for the Exradin A10 chamber.

  9. A method to enhance 2D ion chamber array patient specific quality assurance for IMRT.

    PubMed

    Diaz Moreno, Rogelio Manuel; Venencia, Daniel; Garrigo, Edgardo; Pipman, Yakov

    2016-11-21

    Gamma index comparison has been established as a method for patient specific quality assurance in IMRT. Detector arrays can replace radiographic film systems to record 2D dose distributions and fulfill quality assurance requirements. These electronic devices present spatial resolution disadvantages with respect to films. This handicap can be partially overcome with a multiple acquisition sequence of adjacent 2D dose distributions. The detector spatial response influence can also be taken into account through the convolution of the calculated dose with the detector spatial response. A methodology that employs both approaches could allow for enhancements of the quality assurance procedure. 35 beams from different step and shoot IMRT plans were delivered on a phantom. 2D dose distributions were recorded with a PTW-729 ion chamber array for individual beams, following the multiple acquisition methodology. 2D dose distributions were also recorded on radiographic films. Measured dose distributions with films and with the PTW-729 array were processed with the software RITv5.2 for Gamma index comparison with calculated doses. Calculated dose was also convolved with the ion chamber 2D response and the Gamma index comparisons with the 2D dose distribution measured with the PTW-729 array was repeated. 3.7 ± 2.7% of points surpassed the accepted Gamma index when using radiographic films compared with calculated dose, with a minimum of 0.67 and a maximum of 13.27. With the PTW-729 multiple acquisition methodology compared with calculated dose, 4.1 ± 1.3% of points surpassed the accepted Gamma index, with a minimum of 1.44 and a maximum of 11.26. With the PTW- multiple acquisition methodology compared with convolved calculated dose, 2.7 ± 1.3% of points surpassed the accepted Gamma index, with a minimum of 0.42 and a maximum of 5.75. The results obtained in this work suggest that the comparison of merged adjacent dose distributions with convolved calculated dose

  10. Heavy ion beam studies and imaging with a multiplane multiwire proportional chamber

    SciTech Connect

    Chu, W.T.; Alonso, J.R.; Tobias, C.A.

    1981-03-01

    A 16-plane multiwire proportional chamber is used to accurately measure intensity profiles of heavy ion beams at the Bevalac. An imaging capability has now been developed for the system, allowing for reconstruction of 3-dimensional representation of radiological objects using heavy ion beams.

  11. Imaging with a multiplane multiwire proportional chamber using heavy ion beams

    SciTech Connect

    Chu, W.T.; Alonso, J.R.; Tobias, C.A.

    1982-01-01

    A 16-plane multiwire proportional chamber has been developed to accurately map intensity profiles of heavy ion beams at the Bevalac. The imaging capability of the system has been tested for reconstruction of 3-dimensional representation of a canine thorax region using heavy ion beams.

  12. Effects of discharge chamber length on the negative ion generation in volume-produced negative hydrogen ion source

    SciTech Connect

    Chung, Kyoung-Jae; Jung, Bong-Ki; An, YoungHwa; Dang, Jeong-Jeung; Hwang, Y. S.

    2014-02-15

    In a volume-produced negative hydrogen ion source, control of electron temperature is essential due to its close correlation with the generation of highly vibrationally excited hydrogen molecules in the heating region as well as the generation of negative hydrogen ions by dissociative attachment in the extraction region. In this study, geometric effects of the cylindrical discharge chamber on negative ion generation via electron temperature changes are investigated in two discharge chambers with different lengths of 7.5 cm and 11 cm. Measurements with a radio-frequency-compensated Langmuir probe show that the electron temperature in the heating region is significantly increased by reducing the length of the discharge chamber due to the reduced effective plasma size. A particle balance model which is modified to consider the effects of discharge chamber configuration on the plasma parameters explains the variation of the electron temperature with the chamber geometry and gas pressure quite well. Accordingly, H{sup −} ion density measurement with laser photo-detachment in the short chamber shows a few times increase compared to the longer one at the same heating power depending on gas pressure. However, the increase drops significantly as operating gas pressure decreases, indicating increased electron temperatures in the extraction region degrade dissociative attachment significantly especially in the low pressure regime. It is concluded that the increase of electron temperature by adjusting the discharge chamber geometry is efficient to increase H{sup −} ion production as long as low electron temperatures are maintained in the extraction region in volume-produced negative hydrogen ion sources.

  13. Shielding analysis for a heavy ion beam chamber with plasma channels for ion transport

    SciTech Connect

    Sawan, M.E.; Peterson, R.R.; Yu, S.

    2000-06-28

    Neutronics analysis has been performed to assess the shielding requirements for the insulators and final focusing magnets in a modified HYLIFE-II target chamber that utilizes pre-formed plasma channels for heavy ion beam transport. Using 65 cm thick Flibe jet assemblies provides adequate shielding for the electrical insulator units. Additional shielding is needed in front of the final focusing superconducting quadrupole magnets. A shield with a thickness varying between 45 and 90 cm needs to be provided in front of the quadrupole unit. The final laser mirrors located along the channel axis are in the direct line-of-sight of source neutrons. Neutronics calculations were performed to determine the constraints on the placement of these mirrors to be lifetime components.

  14. Convert Ten Foot Environmental Test Chamber into an Ion Engine Test Chamber

    NASA Technical Reports Server (NTRS)

    VanVelzer, Paul

    2006-01-01

    The 10 Foot Space Simulator at the Jet Propulsion Laboratory has been used for the last 40 years to test numerous spacecraft, including the Ranger series, several Mariner class, among many others and finally, the Spirit and Opportunity Mars Rovers. The request was made to convert this facility to an Ion Engine test facility, with a possible long term life test. The Ion engine was to propel the Prometheus spacecraft to Jupiter's moons. This paper discusses the challenges that were met, both from a procedural and physical standpoint. The converted facility must operate unattended, support a 30 Kw Ion Engine, operate economically, and be easily converted back to former operation as a spacecraft test facility.

  15. Convert Ten Foot Environmental Test Chamber into an Ion Engine Test Chamber

    NASA Technical Reports Server (NTRS)

    VanVelzer, Paul

    2006-01-01

    The 10 Foot Space Simulator at the Jet Propulsion Laboratory has been used for the last 40 years to test numerous spacecraft, including the Ranger series, several Mariner class, among many others and finally, the Spirit and Opportunity Mars Rovers. The request was made to convert this facility to an Ion Engine test facility, with a possible long term life test. The Ion engine was to propel the Prometheus spacecraft to Jupiter's moons. This paper discusses the challenges that were met, both from a procedural and physical standpoint. The converted facility must operate unattended, support a 30 Kw Ion Engine, operate economically, and be easily converted back to former operation as a spacecraft test facility.

  16. Estimation of absorbed dose in clinical radiotherapy linear accelerator beams: Effect of ion chamber calibration and long-term stability.

    PubMed

    Ravichandran, Ramamoorthy; Binukumar, Johnson Pichy; Davis, Cheriyathmanjiyil Antony

    2013-10-01

    The measured dose in water at reference point in phantom is a primary parameter for planning the treatment monitor units (MU); both in conventional and intensity modulated/image guided treatments. Traceability of dose accuracy therefore still depends mainly on the calibration factor of the ion chamber/dosimeter provided by the accredited Secondary Standard Dosimetry Laboratories (SSDLs), under International Atomic Energy Agency (IAEA) network of laboratories. The data related to Nd,water calibrations, thermoluminescent dosimetry (TLD) postal dose validation, inter-comparison of different dosimeter/electrometers, and validity of Nd,water calibrations obtained from different calibration laboratories were analyzed to find out the extent of accuracy achievable. Nd,w factors in Gray/Coulomb calibrated at IBA, GmBH, Germany showed a mean variation of about 0.2% increase per year in three Farmer chambers, in three subsequent calibrations. Another ion chamber calibrated in different accredited laboratory (PTW, Germany) showed consistent Nd,w for 9 years period. The Strontium-90 beta check source response indicated long-term stability of the ion chambers within 1% for three chambers. Results of IAEA postal TL "dose intercomparison" for three photon beams, 6 MV (two) and 15 MV (one), agreed well within our reported doses, with mean deviation of 0.03% (SD 0.87%) (n = 9). All the chamber/electrometer calibrated by a single SSDL realized absorbed doses in water within 0.13% standard deviations. However, about 1-2% differences in absorbed dose estimates observed when dosimeters calibrated from different calibration laboratories are compared in solid phantoms. Our data therefore imply that the dosimetry level maintained for clinical use of linear accelerator photon beams are within recommended levels of accuracy, and uncertainties are within reported values.

  17. Impact of beam transport method on chamber and driver design for heavy ion inertial fusion energy

    SciTech Connect

    Rose, D.V.; Welch, D.R.; Olson, C.L.; Yu, S.S.; Neff, S.; Sharp, W.M.

    2002-12-01

    In heavy ion inertial fusion energy systems, intense beams of ions must be transported from the exit of the final focus magnet system through the target chamber to hit millimeter spot sizes on the target. In this paper, we examine three different modes of beam propagation: neutralized ballistic transport, assisted pinched transport, and self-pinched transport. The status of our understanding of these three modes is summarized, and the constraints imposed by beam propagation upon the chamber environment, as well as their compatibility with various chamber and target concepts, are considered. We conclude that, on the basis of our present understanding, there is a reasonable range of parameter space where beams can propagate in thick-liquid wall, wetted-wall, and dry-wall chambers.

  18. Computational Model Tracking Primary Electrons, Secondary Electrons, and Ions in the Discharge Chamber of an Ion Engine

    NASA Technical Reports Server (NTRS)

    Mahalingam, Sudhakar; Menart, James A.

    2005-01-01

    Computational modeling of the plasma located in the discharge chamber of an ion engine is an important activity so that the development and design of the next generation of ion engines may be enhanced. In this work a computational tool called XOOPIC is used to model the primary electrons, secondary electrons, and ions inside the discharge chamber. The details of this computational tool are discussed in this paper. Preliminary results from XOOPIC are presented. The results presented include particle number density distributions for the primary electrons, the secondary electrons, and the ions. In addition the total number of a particular particle in the discharge chamber as a function of time, electric potential maps and magnetic field maps are presented. A primary electron number density plot from PRIMA is given in this paper so that the results of XOOPIC can be compared to it. PRIMA is a computer code that the present investigators have used in much of their previous work that provides results that compare well to experimental results. PRIMA only models the primary electrons in the discharge chamber. Modeling ions and secondary electrons, as well as the primary electrons, will greatly increase our ability to predict different characteristics of the plasma discharge used in an ion engine.

  19. Backscatter towards the monitor ion chamber in high-energy photon and electron beams: charge integration versus Monte Carlo simulation.

    PubMed

    Verhaegen, F; Symonds-Tayler, R; Liu, H H; Nahum, A E

    2000-11-01

    In some linear accelerators, the charge collected by the monitor ion chamber is partly caused by backscattered particles from accelerator components downstream from the chamber. This influences the output of the accelerator and also has to be taken into account when output factors are derived from Monte Carlo simulations. In this work, the contribution of backscattered particles to the monitor ion chamber response of a Varian 2100C linac was determined for photon beams (6, 10 MV) and for electron beams (6, 12, 20 MeV). The experimental procedure consisted of charge integration from the target in a photon beam or from the monitor ion chamber in electron beams. The Monte Carlo code EGS4/BEAM was used to study the contribution of backscattered particles to the dose deposited in the monitor ion chamber. Both measurements and simulations showed a linear increase in backscatter fraction with decreasing field size for photon and electron beams. For 6 MV and 10 MV photon beams, a 2-3% increase in backscatter was obtained for a 0.5 x 0.5 cm2 field compared to a 40 x 40 cm2 field. The results for the 6 MV beam were slightly higher than for the 10 MV beam. For electron beams (6, 12, 20 MeV), an increase of similar magnitude was obtained from measurements and simulations for 6 MeV electrons. For higher energy electron beams a smaller increase in backscatter fraction was found. The problem is of less importance for electron beams since large variations of field size for a single electron energy usually do not occur.

  20. Distributed drift chamber design for rare particle detection in relativistic heavy ion collisions

    SciTech Connect

    Bellwied, R.; Bennett, M.J.; Bernardo, V.; Caines, H.; Christie, W.; Costa, S.; Crawford, H.J.; Cronqvist, M.; Debbe, R.; Dinnwiddie, R.; Engelage, J.; Flores, I.; Fuzesy, R.; Greiner, L.; Hallman, T.; Hoffmann, G.; Huang, H.Z.; Jensen, P.; Judd, E.G.; Kainz, K.; Kaplan, M.; Kelly, S.; Lindstrom, P.J; Llope, W.J.; LoCurto, G.; Longacre, R.; Milosevich, Z.; Mitchell, J.T.; Mitchell, J.W.; Mogavero, E.; Mutchler, G.; Paganis, S.; Platner, E.; Potenza, R.; Rotondo, F.; Russ, D.; Sakrejda, I.; Saulys, A.; Schambach, J.; Sheen, J.; Smirnoff, N.; Stokeley, C.; Tang, J.; Trattner, A.L.; Trentalange, S.; Visser, G.; Whitfield, J.P.; Witharm, F.; Witharm, R.; Wright, M.

    2001-10-02

    This report describes a multi-plane drift chamber that was designed and constructed to function as a topological detector for the BNL AGSE896 rare particle experiment. The chamber was optimized for good spatial resolution, two track separation, and a high uniform efficiency while operating in a 1.6 Tesla magnetic field and subjected to long term exposure from a 11.6 GeV/nucleon beam of 10**6 Au ions per second.

  1. Ring cusp/hollow cathode discharge chamber performance studies. [ion propulsion

    NASA Technical Reports Server (NTRS)

    Vaughn, J. A.; Wilbur, Paul J.

    1988-01-01

    An experimental study was performed to determine the effects of hollow cathode position, anode position, and ring cusp magnetic field configuration and strength on discharge chamber performance. The results are presented in terms of comparative plasma ion energy cost, extracted ion fraction, and beam profile data. Such comparisons are used to demonstrate whether changes in performance are caused by changes in the loss rate of primary electrons to the anode or the loss rate of ions to discharge chamber walls or cathode and anode surfaces. Results show: (1) the rate of primary electron loss to the anode decreases as the anode is moved downstream of the ring cusp toward the screen grid; (2) the loss rate of ions to hollow cathode surfaces are excessive if the cathode is located upstream of a point of peak magnetic flux density at the discharge chamber centerline; and (3) the fraction of the ions produced that are lost to discharge chamber walls and ring magnet surfaces is reduced by positioning of the magnet rings so the plasma density is uniform over the grid surface, and adjusting their strength to a level where it is sufficient to prevent excessive ion losses by Bohm diffusion.

  2. SU-E-T-198: Comparison Between a PTW MicroDiamond Dosimeter and a Markus Chamber in a 62 MeV/n Carbon Ion Beam

    SciTech Connect

    Rossomme, S; Hopfgartner, J; Delor, A; Vynckier, S; Palmans, H

    2015-06-15

    Purpose: To investigate the linear energy transfer (LET) dependence of a PTW Freiburg microDiamond dosimeter, we compared its response to the response of a plane-parallel Markus chamber in a 62 MeV/n mono-energetic carbon ion beam. Methods: The response of both detectors has been studied as a function of depth in graphite by adding or removing graphite plates in front of the detectors. To account for fluctuations of the beam, we used two setups with different monitor chambers. The depth of the effective point of measurement of both detectors has been converted into a graphite equivalent depth using ICRU Report 73 data. As recommended by IAEA TRS-398, the response of the Markus chamber has been corrected for temperature, pressure, polarity effects and ion recombination. The latter required an additional experiment; to quantify the effect of volume recombination and initial recombination, measurements have been performed at different voltages and different dose rates. Results: As expected, the dominant process leading to ion recombination for carbon ion beam is the initial recombination. At the entrance, the ion recombination correction equals 1.1% and the value is approximately constant in the plateau region. Due to the increase of the LET in the Bragg peak region, we observe a strong increase of the ion recombination correction, up to 6.1% at the distal edge. Comparison between the microDiamond response and the Markus chamber response shows good agreement in the plateau region. However, we observe a 13.6% under response of the microDiamond in the Bragg peak. Conclusion: Increasing between 1% and 6%, the depth dependent ion recombination correction has to be applied to the Markus response. The comparison between the microDiamond and the Markus chamber indicates that there is an under-response of the microDiamond in the vicinity of the Bragg peak due to the increased LET.

  3. Retention of Sputtered Molybdenum on Ion Engine Discharge Chamber Surfaces

    NASA Technical Reports Server (NTRS)

    Sovey, James S.; Dever, Joyce A.; Power, John L.

    2001-01-01

    Grit-blasted anode surfaces are commonly used in ion engines to ensure adherence of sputtered coatings. Next generation ion engines will require higher power levels, longer operating times, and thus there will likely be thicker sputtered coatings on their anode surfaces than observed to date on 2.3 kW-class xenon ion engines. The thickness of coatings on the anode of a 10 kW, 40-centimeter diameter thruster, for example, may be 22 micrometers or more after extended operation. Grit-blasted wire mesh, titanium, and aluminum coupons were coated with molybdenum at accelerated rates to establish coating stability after the deposition process and after thermal cycling tests. These accelerated deposition rates are roughly three orders of magnitude more rapid than the rates at which the screen grid is sputtered in a 2.3 kW-class, 30-centimeter diameter ion engine. Using both RF and DC sputtering processes, the molybdenum coating thicknesses ranged from 8 to 130 micrometers, and deposition rates from 1.8 micrometers per hour to 5.1 micrometers per hour. In all cases, the molybdenum coatings were stable after the deposition process, and there was no evidence of spalling of the coatings after 20 cycles from about -60 to +320 C. The stable, 130 micrometer molybdenum coating on wire mesh is 26 times thicker than the thickest coating found on the anode of a 2.3 kW, xenon ion engine that was tested for 8200 hr. Additionally, this coating on wire mesh coupon is estimated to be a factor of greater than 4 thicker than one would expect to obtain on the anode of the next generation ion engine which may have xenon throughputs as high as 550 kg.

  4. Efficiency improvements for ion chamber calculations in high energy photon beams.

    PubMed

    Wulff, J; Zink, K; Kawrakow, I

    2008-04-01

    This article presents the implementation of several variance reduction techniques that dramatically improve the simulation efficiency of ion chamber dose and perturbation factor calculations. The cavity user code for the EGSnrc Monte Carlo code system is extended by photon cross-section enhancement (XCSE), an intermediate phase-space storage (IPSS) technique, and a correlated sampling (CS) scheme. XCSE increases the density of photon interaction sites inside and in the vicinity of the chamber and results-in combination with a Russian Roulette game for electrons that cannot reach the cavity volume-in an increased efficiency of up to a factor of 350 for calculating dose in a Farmer type chamber placed at 10 cm depth in a water phantom. In combination with the IPSS and CS techniques, the efficiency for the calculation of the central electrode perturbation factor Pcel can be increased by up to three orders of magnitude for a single chamber location and by nearly four orders of magnitude when considering the Pcel variation with depth or with distance from the central axis in a large field photon beam. The intermediate storage of the phase-space properties of particles entering a volume that contains many possible chamber locations leads to efficiency improvements by a factor larger than 500 when computing a profile of chamber doses in the field of a linear accelerator photon beam. All techniques are combined in a new EGSnrc user code egs_chamber. Optimum settings for the variance reduction parameters are investigated and are reported for a Farmer type ion chamber. A few example calculations illustrating the capabilities of the egs_chamber code are presented.

  5. Efficiency improvements for ion chamber calculations in high energy photon beams

    SciTech Connect

    Wulff, J.; Zink, K.; Kawrakow, I.

    2008-04-15

    This article presents the implementation of several variance reduction techniques that dramatically improve the simulation efficiency of ion chamber dose and perturbation factor calculations. The cavity user code for the EGSnrc Monte Carlo code system is extended by photon cross-section enhancement (XCSE), an intermediate phase-space storage (IPSS) technique, and a correlated sampling (CS) scheme. XCSE increases the density of photon interaction sites inside and in the vicinity of the chamber and results - in combination with a Russian Roulette game for electrons that cannot reach the cavity volume - in an increased efficiency of up to a factor of 350 for calculating dose in a Farmer type chamber placed at 10 cm depth in a water phantom. In combination with the IPSS and CS techniques, the efficiency for the calculation of the central electrode perturbation factor P{sub cel} can be increased by up to three orders of magnitude for a single chamber location and by nearly four orders of magnitude when considering the P{sub cel} variation with depth or with distance from the central axis in a large field photon beam. The intermediate storage of the phase-space properties of particles entering a volume that contains many possible chamber locations leads to efficiency improvements by a factor larger than 500 when computing a profile of chamber doses in the field of a linear accelerator photon beam. All techniques are combined in a new EGSnrc user code egs{sub c}hamber. Optimum settings for the variance reduction parameters are investigated and are reported for a Farmer type ion chamber. A few example calculations illustrating the capabilities of the egs{sub c}hamber code are presented.

  6. Comparison of dose measurements in CT using a novel semiconductor detector and a small ion chamber

    SciTech Connect

    Paschoal, Cinthia M. M.; Ferreira, Fernanda Carla L.; Santos, Luiz A. P.; Souza, Divanizia N.

    2015-07-01

    The advance of multislice computed tomography (CT) has become inadequate the currently dosimetric protocol used in CT. Instead of dosimetry based on the measurement of CTDI using a pencil ion chamber of 100 m of length, it was proposed the use of a small ion chamber (IC) and the calculating the dose equilibrium (Deq) at the location of the chamber. The objective of this work was to compare the performance of a short IC and a commercial photodiode to measure the accumulated dose at the center of the scan length L, DL(0), and to obtain the equilibrium dose Deq using the two detectors. The result for L=100 mm was compared with the result of a pencil chamber. The results indicate that the commercial photodiode is suitable to measure the accumulated dose at the center of the scan length L as compared with the ion chambers. This methodology allows measurements of the accumulated dose for any desired scan length, allowing measuring the equilibrium dose Deq if the phantom is long enough to allow it. (authors)

  7. Experimental analysis of general ion recombination in a liquid-filled ionization chamber in high-energy photon beams

    SciTech Connect

    Chung, Eunah; Seuntjens, Jan; Davis, Stephen

    2013-06-15

    Purpose: To study experimentally the general ion recombination effect in a liquid-filled ionization chamber (LIC) in high-energy photon beams. Methods: The general ion recombination effect on the response of a micro liquid ion chamber (microLion) was investigated with a 6 MV photon beam in normal and SRS modes produced from a Varian{sup Registered-Sign} Novalis Tx{sup TM} linear accelerator. Dose rates of the linear accelerator were set to 100, 400, and 1000 MU/min, which correspond to pulse repetition frequencies of 60, 240, and 600 Hz, respectively. Polarization voltages applied to the microLion were +800 and +400 V. The relative collection efficiency of the microLion response as a function of dose per pulse was experimentally measured with changing polarization voltage and pulse repetition frequencies and was compared with the theoretically calculated value. Results: For the 60 Hz pulse repetition frequency, the experimental relative collection efficiency was not different from the theoretical one for a pulsed beam more than 0.3% for both polarization voltages. For a pulsed radiation beam with a higher pulse repetition frequency, the experimental relative collection efficiency converged to the theoretically calculated efficiency for continuous beams. This result indicates that the response of the microLion tends toward the response to a continuous beam with increasing pulse repetition frequency of a pulsed beam because of low ion mobility in the liquid. Conclusions: This work suggests an empirical method to correct for differences in general ion recombination of a LIC between different radiation fields. More work is needed to quantitatively explain the LIC general ion recombination behavior in pulsed beams generated from linear accelerators.

  8. Experimental analysis of general ion recombination in a liquid-filled ionization chamber in high-energy photon beams.

    PubMed

    Chung, Eunah; Davis, Stephen; Seuntjens, Jan

    2013-06-01

    To study experimentally the general ion recombination effect in a liquid-filled ionization chamber (LIC) in high-energy photon beams. The general ion recombination effect on the response of a micro liquid ion chamber (microLion) was investigated with a 6 MV photon beam in normal and SRS modes produced from a Varian(®) Novalis Tx(TM) linear accelerator. Dose rates of the linear accelerator were set to 100, 400, and 1000 MU∕min, which correspond to pulse repetition frequencies of 60, 240, and 600 Hz, respectively. Polarization voltages applied to the microLion were +800 and +400 V. The relative collection efficiency of the microLion response as a function of dose per pulse was experimentally measured with changing polarization voltage and pulse repetition frequencies and was compared with the theoretically calculated value. For the 60 Hz pulse repetition frequency, the experimental relative collection efficiency was not different from the theoretical one for a pulsed beam more than 0.3% for both polarization voltages. For a pulsed radiation beam with a higher pulse repetition frequency, the experimental relative collection efficiency converged to the theoretically calculated efficiency for continuous beams. This result indicates that the response of the microLion tends toward the response to a continuous beam with increasing pulse repetition frequency of a pulsed beam because of low ion mobility in the liquid. This work suggests an empirical method to correct for differences in general ion recombination of a LIC between different radiation fields. More work is needed to quantitatively explain the LIC general ion recombination behavior in pulsed beams generated from linear accelerators.

  9. High-resolution ion pulse ionization chamber with air filling for the 222Rn decays detection

    NASA Astrophysics Data System (ADS)

    Gavrilyuk, Yu. M.; Gangapshev, A. M.; Gezhaev, A. M.; Etezov, R. A.; Kazalov, V. V.; Kuzminov, V. V.; Panasenko, S. I.; Ratkevich, S. S.; Tekueva, D. A.; Yakimenko, S. P.

    2015-11-01

    The construction and characteristics of the cylindrical ion pulse ionization chamber (CIPIC) with a working volume of 3.2 L are described. The chamber is intended to register α-particles from the 222Rn and its daughter's decays in the filled air sample. The detector is less sensitive to electromagnetic pick-ups and mechanical noises. The digital pulse processing method is proposed to improve the energy resolution of the ion pulse ionization chamber. An energy resolution of 1.6% has been achieved for the 5.49 MeV α-line. The dependence of the energy resolution on high voltage and working media pressure has been investigated and the results are presented.

  10. Determination of ion recombination correction factors for a liquid ionization chamber in megavoltage photon beams

    NASA Astrophysics Data System (ADS)

    Choi, Sang Hyoun; Kim, Kum-Bae; Ji, Young Hoon; Kim, Chan Hyeong; Kim, Seonghoon; Huh, Hyun Do

    2015-05-01

    The aim of this study is to determine the ion recombination correction factor for a liquid ionization chamber in a high energy photon beam by using our experimental method. The ion recombination correction factors were determined by using our experimental method and were compared with theoretical and experimental methods proposed by using the theoretical method (Greening, Johansson) and the two-dose rate method in a cobalt beam and a high energy photon beam. In order to apply the liquid ionization chamber in a reference and small field dosimetry, we acquired the absorbed dose to water correction coefficient, the beam quality correction factor, and the influence quantities for the microLion chamber according to the TRS-398 protocol and applied the results to a high energy photon beam used in clinical fields. As a result, our experimental method for ion recombination in a cobalt beam agreed with the results from the heoretical method (Greening theory) better than it did with the results from the two-dose rate method. For high energy photon beams, the two-dose rate and our experimental methods were in good agreement, less than 2% deviation, while the theoretical general collection efficiency (Johansson et al.) deviated greatly from the experimental values. When we applied the factors for the absorbed dose to water measurement, the absorbed dose to water for the microLion chamber was in good agreement, within 1%, compared with the values for the PTW 30013 chamber in 6 and 10 MV Clinac iX and 6 and 15 MV Oncor impression. With these results, not only can the microLion ionization chamber be used to measure the absorbed dose to water in a reference condition, it can also be used to a the chamber for small, non-standard field dosimetry.

  11. A general algorithm for calculation of recombination losses in ionization chambers exposed to ion beams.

    PubMed

    Christensen, Jeppe Brage; Tölli, Heikki; Bassler, Niels

    2016-10-01

    Dosimetry with ionization chambers in clinical ion beams for radiation therapy requires correction for recombination effects. However, common radiation protocols discriminate between initial and general recombination and provide no universal correction method for the presence of both recombination types in ion beams of charged particles heavier than protons. The advent of multiple field optimization in ion beams, allowing for complex patterns of dose delivery in both temporal and spatial domains, results in new challenges for recombination correction where the resulting recombination depends on the plan delivered. Here, the authors present the open source code IonTracks version 1.0, where the combined initial and general recombination effects in principle can be predicted for any ion beam with arbitrary particle-energy spectrum and temporal structure. IonTracks uses track structure theory to distribute the charge carriers in ion tracks. The charge carrier movements are governed by a pair of coupled differential equations, based on fundamental physical properties as charge carrier drift, diffusion, and recombination, which are solved numerically while the initial and general charge carrier recombination is computed. A space charge screening of the electric field is taken into account and the algorithm furthermore allows an inclusion of a free-electron component. The algorithm is numerically stable and in accordance with experimentally validated theories for initial recombination in heavy ion tracks and general recombination in a proton beam. Given IonTracks' ability to handle arbitrary inputs, IonTracks can in principle be applied to any complex particle field in the spatial and temporal domain. IonTracks is validated against the Jaffé's and Boag's theory of recombination in pulsed beams of multiple ion species. IonTracks is able to calculate the correction factor for initial and general recombination losses in parallel-plate ionization chambers. Even if only few

  12. High spatial resolution dosimetric response maps for radiotherapy ionization chambers measured using kilovoltage synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Butler, D. J.; Stevenson, A. W.; Wright, T. E.; Harty, P. D.; Lehmann, J.; Livingstone, J.; Crosbie, J. C.

    2015-11-01

    Small circular beams of synchrotron radiation (0.1 mm and 0.4 mm in diameter) were used to irradiate ionization chambers of the types commonly used in radiotherapy. By scanning the chamber through the beam and measuring the ionization current, a spatial map of the dosimetric response of the chamber was recorded. The technique is able to distinguish contributions to the large-field ionization current from the chamber walls, central electrode and chamber stem. Scans were recorded for the NE 2571 Farmer chamber, the PTW 30013, IBA FC65-G Farmer-type chambers, the NE 2611A and IBA CC13 thimble chambers, the PTW 31006 and 31014 pinpoint chambers, the PTW Roos and Advanced Markus plane-parallel chambers, and the PTW 23342 thin-window soft x-ray chamber. In all cases, large contributions to the response arise from areas where the incident beam grazes the cavity surfaces. Quantitative as well as qualitative information about the relative chamber response was extracted from the maps, including the relative contribution of the central electrode. Line scans using monochromatic beams show the effect of the photon energy on the chamber response. For Farmer-type chambers, a simple Monte Carlo model was in good agreement with the measured response.

  13. High resolution ion chamber array delivery quality assurance for robotic radiosurgery: Commissioning and validation.

    PubMed

    Blanck, Oliver; Masi, Laura; Chan, Mark K H; Adamczyk, Sebastian; Albrecht, Christian; Damme, Marie-Christin; Loutfi-Krauss, Britta; Alraun, Manfred; Fehr, Roman; Ramm, Ulla; Siebert, Frank-Andre; Stelljes, Tenzin Sonam; Poppinga, Daniela; Poppe, Björn

    2016-06-01

    High precision radiosurgery demands comprehensive delivery-quality-assurance techniques. The use of a liquid-filled ion-chamber-array for robotic-radiosurgery delivery-quality-assurance was investigated and validated using several test scenarios and routine patient plans. Preliminary evaluation consisted of beam profile validation and analysis of source-detector-distance and beam-incidence-angle response dependence. The delivery-quality-assurance analysis is performed in four steps: (1) Array-to-plan registration, (2) Evaluation with standard Gamma-Index criteria (local-dose-difference⩽2%, distance-to-agreement⩽2mm, pass-rate⩾90%), (3) Dose profile alignment and dose distribution shift until maximum pass-rate is found, and (4) Final evaluation with 1mm distance-to-agreement criterion. Test scenarios consisted of intended phantom misalignments, dose miscalibrations, and undelivered Monitor Units. Preliminary method validation was performed on 55 clinical plans in five institutions. The 1000SRS profile measurements showed sufficient agreement compared with a microDiamond detector for all collimator sizes. The relative response changes can be up to 2.2% per 10cm source-detector-distance change, but remains within 1% for the clinically relevant source-detector-distance range. Planned and measured dose under different beam-incidence-angles showed deviations below 1% for angles between 0° and 80°. Small-intended errors were detected by 1mm distance-to-agreement criterion while 2mm criteria failed to reveal some of these deviations. All analyzed delivery-quality-assurance clinical patient plans were within our tight tolerance criteria. We demonstrated that a high-resolution liquid-filled ion-chamber-array can be suitable for robotic radiosurgery delivery-quality-assurance and that small errors can be detected with tight distance-to-agreement criterion. Further improvement may come from beam specific correction for incidence angle and source

  14. SU-E-T-172: Evaluation of the Exradin A26 Ion Chamber in Megavoltage Photon Beams as a Reference Class Instrument

    SciTech Connect

    McEwen, M

    2014-06-01

    Purpose: The Exradin A26 is a new design of micro-ionization ion chamber that externally resembles the Exradin A16 model but has significant internal changes to address measurement issues reported in the literature for the A16. This project involved the characterization of two versions of the A26 chamber in high energy x-rays with particular reference to the performance specification laid out in the imminent Addendum to TG-51. Methods: The Exradin A26 was investigated in a range of megavoltage photon beams (6–25 MV). Investigations looked at chamber settling, ion recombination and polarity. Since it has been previously shown that non-ideal performance is most easily identified through ion recombination measurements, the focus was on the determination of Pion. Results: i) Chamber settling - the chamber response stabilizes very quickly (within 3 minutes), even after a large change in the polarizing voltage.ii) The polarity correction was found to be small (within 0.2% of unity)iii) The chamber showed linear behavior for a Jaffe plot (1/reading vs 1/polarizing voltage) for applied voltages ≤ 200 V.iv) The recombination correction showed a linear variation with the doseper- pulse, was not significantly dependent on the polarity of the collecting voltage and was consistent with the chamber dimensions (i.e. agreed with Boag theory). Conclusion: An initial investigation of the Exradin A26 micro chamber suggests that although its performance exceeds the AAPM specification for a reference-class ion chamber for use in megavoltage photon beams it is a significant improvement over the previous A16 design. Further work is required to evaluate long-term stability and determine kQ factors.

  15. Plasma Emission Characteristics from a High Current Hollow Cathode in an Ion Thruster Discharge Chamber

    NASA Technical Reports Server (NTRS)

    Foster, John E.; Patterson, Michael J.

    2002-01-01

    The presence of energetic ions produced by a hollow cathodes operating at high emission currents (greater than 5A) has been documented in the literature. In order to further elucidate these findings, an investigation of a high current cathode operating in an ion thruster discharge chamber has been undertaken. Using Langmuir probes, a low energy charged particle analyzer and emission spectroscopy, the behavior of the near-cathode plasma and the emitted ion energy distribution was characterized. The presence of energetic ions was confirmed. It was observed that these ions had energies in excess of the discharge voltage and thus cannot be simply explained by ions falling out of plasma through a potential difference of this order. Additionally, evidence provided by Langmuir probes suggests the existence of a double layer essentially separating the hollow cathode plasma column from the main discharge. The radial potential difference associated with this double layer was measured to be of order the ionization potential.

  16. Plasma Emission Characteristics From a High Current Hollow Cathode in an Ion Thruster Discharge Chamber

    NASA Astrophysics Data System (ADS)

    Foster, John E.; Patterson, Michael J.

    2002-11-01

    The presence of energetic ions produced by a hollow cathodes operating at high emission currents (greater than 5A) has been documented in the literature. In order to further elucidate these findings, an investigation of a high current cathode operating in an ion thruster discharge chamber has been undertaken. Using Langmuir probes, a low energy charged particle analyzer and emission spectroscopy, the behavior of the near-cathode plasma and the emitted ion energy distribution was characterized. The presence of energetic ions was confirmed. It was observed that these ions had energies in excess of the discharge voltage and thus cannot be simply explained by ions falling out of plasma through a potential difference of this order. Additionally, evidence provided by Langmuir probes suggests the existence of a double layer essentially separating the hollow cathode plasma column from the main discharge. The radial potential difference associated with this double layer was measured to be of order the ionization potential.

  17. TH-C-19A-08: PDD Discrepancies at Opposite Biases From Very Small Volume Ion Chambers When Using Water Scanners

    SciTech Connect

    Sarkar, V; Zhao, H; Rassiah-Szegedi, P; Huang, Y; Szegedi, M; Huang, L; Salter, B; Wang, B; James, J; McCullough, K; Lynch, B

    2014-06-15

    Purpose: As more so-called micro ion chambers become commercially available, medical physicists may be inclined to use them during the linear accelerator commissioning process, in an attempt to better characterize the beam in steep dose gradient areas. The purpose of this work is to inform the medical physics community of a non-trivial, anomalous behavior observed when very small chambers are used in certain beam scanning configurations. Methods: A total of six ion chambers (0.007cc to 0.6cc) were used to scan PDDs from a 10×10cm2 field at both +300V and −300V biases. PDDs were scanned using three different water tank scanning systems to determine whether different scanners exhibit the same abnormality. Finally, PDDs were sampled using an external electrometer to bypass the internal electrometer of the scanner to determine the potential contributions of the scanner electronics to the abnormality observed. Results: We observed a reproducible, significant difference (over-response with depth) in PDDs acquired when using very small ion chambers with certain bias and watertank combinations, on the order of 3–5% at a depth of 25 cm in water. This difference was not observed when the PDDs were sampled using the ion chambers in conjunction with an external electrometer. This suggests a contribution of interference produced by the controller box and scanning system, which becomes significant for the very small signals collected by very small ion chambers, especially at depth, as the signal level is reduced even further. Conclusion: Based on the results observed here, if currently available very small ion chambers are used with specific bias and scanning water-tank combinations, erroneous PDD data may be collected. If this data is used as input to the Treatment Planning System, systematic errors on the order of 3%–5% may be introduced into the treatment planning process.

  18. Ion recombination for ionization chamber dosimetry in a helical tomotherapy unit.

    PubMed

    Palmans, H; Thomas, R A S; Duane, S; Sterpin, E; Vynckier, S

    2010-06-01

    Ion recombination for ionization chambers in pulsed high-energy photon beams is a well-studied phenomenon. Despite this, the correction for ion recombination is often determined inaccurately due to the inappropriate combination of using a high polarizing voltage and the simple two-voltage method. An additional complication arises in new treatment modalities such as IMRT and tomotherapy, where the dosimetry of a superposition of many constituting fields becomes more relevant than of single static fields. For these treatment modalities, the irradiation of the ion chamber geometry can be instantaneously inhomogeneous and time dependent. This article presents a study of ion recombination in ionization chambers used for dosimetry in a helical tomotherapy beam. Models are presented for studying the recombination correction factors in a continuous beam, in pulsed large and small fields, and in helical fields. Measurements using Exradin A1SL, NE2571, and NE2611 type chambers and Monte Carlo simulations usingPENELOPE are performed in support of these models. Initial recombination and charge multiplication are found to be the same in C60o and in the pulsed high-energy photon beam for the chambers and operating voltages used in this study. Applying the two-voltage technique for the A1SL chamber at its recommended operating voltage of 300 V leads to an overestimation of the recombination. Operating at a voltage of 100 V yields larger but more accurate values for the recombination correction. The recombination correction measured for this chamber in the TomoTherapy HiArt unit is lower than the 1% applied in the routine dosimetry for this treatment unit. For a helical dose delivery with a small slice width, lateral electron scatter in the cavity makes that the recombination is smaller than for an open beam delivering the same total dose. In a Farmer type chamber, a helical delivery with a 1 cm slice field results in a time and spatially integrated volume recombination of 55% of

  19. Ion recombination for ionization chamber dosimetry in a helical tomotherapy unit.

    PubMed

    Palmans, H; Thomas, R A S; Duane, S; Sterpin, E; Vynckier, S

    2010-06-01

    Ion recombination for ionization chambers in pulsed high-energy photon beams is a well-studied phenomenon. Despite this, the correction for ion recombination is often determined inaccurately due to the inappropriate combination of using a high polarizing voltage and the simple two-voltage method. An additional complication arises in new treatment modalities such as IMRT and tomotherapy, where the dosimetry of a superposition of many constituting fields becomes more relevant than of single static fields. For these treatment modalities, the irradiation of the ion chamber geometry can be instantaneously inhomogeneous and time dependent. This article presents a study of ion recombination in ionization chambers used for dosimetry in a helical tomotherapy beam. Models are presented for studying the recombination correction factors in a continuous beam, in pulsed large and small fields, and in helical fields. Measurements using Exradin A1SL, NE2571, and NE2611 type chambers and Monte Carlo simulations using PENELOPE are performed in support of these models. Initial recombination and charge multiplication are found to be the same in 60Co and in the pulsed high-energy photon beam for the chambers and operating voltages used in this study. Applying the two-voltage technique for the A1SL chamber at its recommended operating voltage of 300 V leads to an overestimation of the recombination. Operating at a voltage of 100 V yields larger but more accurate values for the recombination correction. The recombination correction measured for this chamber in the TomoTherapy HiArt unit is lower than the 1% applied in the routine dosimetry for this treatment unit. For a helical dose delivery with a small slice width, lateral electron scatter in the cavity makes that the recombination is smaller than for an open beam delivering the same total dose. In a Farmer type chamber, a helical delivery with a 1 cm slice field results in a time and spatially integrated volume recombination of 55% of

  20. [Clinical calibration dosimetry in JSMP-01: measurements using Farmer-type cylindrical ion chambers.].

    PubMed

    Araki, Fujio; Kumagai, Kozo; Yoshiura, Takao; Oura, Hiroki; Tachibana, Masayuki; Moribe, Nobuyuki; Tajima, Hidetaka; Yoshida, Atsushi; Kido, Tetsuo

    2005-01-01

    The Japan Society of Medical Physics (JSMP) Task Group published Standard dosimetry of absorbed dose in external beam radiotherapy (Standard dosimetry 01) as a new high-energy photon and electron dosimetry protocol in 2002. In this study, we present Standard dosimetry 01 as the JSMP-01 protocol for the convenience of users. This protocol is based on using an ion chamber having a (60)Co absorbed dose to water calibration coefficient, N(D,w), which is calculated from a (60)Co exposure calibration coefficient, N(c). We present dose comparisons between a reference chamber and various Farmer-type cylindrical chambers with different wall materials. The absorbed dose to water was compared at the calibration depths of 5 cm for a (60)Co beam, 10 cm for photons, and d(c) = 0.6 R(50) - 0.1 (cm) for electrons according to JSMP-01. The JARP chamber in the Kyushu Regional Center which meets third-order standards in Japan was used as the reference chamber. The absorbed dose to water for the Farmer-type chambers determined according to JSMP-01 agreed with that for the JARP chamber within 1% for photon and electron beams. The doses obtained by JSMP-01 and the Japan Association of Radiological Physics protocol (JARP-86) were also compared for photon and electron beams. For the Farmer-type chambers with photon beams, JSMP-01 results were up to 1.5% higher than JARP-86 results. For electron beams JSMP-01 results were higher than JARP-86 results by 1.3-2.8%.

  1. Computational Study of Primary Electrons in the Cusp Region of an Ion Engine's Discharge Chamber

    NASA Technical Reports Server (NTRS)

    Stueber, Thomas J. (Technical Monitor); Deshpande, Shirin S.; Mahalingam, Sudhakar; Menart, James A.

    2004-01-01

    In this work a computer code called PRIMA is used to study the motion of primary electrons in the magnetic cusp region of the discharge chamber of an ion engine. Even though the amount of wall area covered by the cusps is very small, the cusp regions are important because prior computational analyses have indicated that most primary electrons leave the discharge chamber through the cusps. The analysis presented here focuses on the cusp region only. The affects of the shape and size of the cusp region on primary electron travel are studied as well as the angle and location at which the electron enters the cusp region. These affects are quantified using the confinement length and the number density distributions of the primary electrons. In addition to these results comparisons of the results from PRIMA are made to experimental results for a cylindrical discharge chamber with two magnetic rings. These comparisons indicate the validity of the computer code called PRIMA.

  2. Design of a prototype tri-electrode ion-chamber for megavoltage X-ray imaging

    NASA Astrophysics Data System (ADS)

    Samant, Sanjiv S.; Gopal, Arun; Jain, Jinesh; Xia, Junyi; DiBianca, Frank A.

    2007-04-01

    High-energy (megavoltage) X-ray imaging is widely used in industry (e.g., aerospace, construction, material sciences) as well as in health care (radiation therapy). One of the fundamental problems with megavoltage imaging is poor contrast and spatial resolution in the detected images due to the dominance of Compton scattering at megavoltage X-ray energies. Therefore, although megavoltage X-rays can be used to image highly attenuating objects that cannot be imaged at kilovoltage energies, the former does not provide the high image quality that is associated with the latter. A high contrast and spatial resolution detector for high-energy X-ray fields called the kinestatic charge detector (KCD) is presented here. The KCD is a tri-electrode ion-chamber based on highly pressurized noble gas. The KCD operates in conjunction with a strip-collimated X-ray beam (for high scatter rejection) to scan across the imaging field. Its thick detector design and unique operating principle provides enhanced charge signal integration for high quality imaging (quantum efficiency ˜50%) despite the unfavorable implications of high-energy X-ray interactions on image quality. The proposed design for a large-field prototype KCD includes a cylindrical pressure chamber along with 576 signal-collecting electrodes capable of resolving at 2 mm -1. The collecting electrodes are routed out of the chamber through the flat end-cap, thereby optimizing the mechanical strength of the chamber. This article highlights the simplified design of the chamber using minimal components for simple assembly. In addition, fundamental imaging measurements and estimates of ion recombination that were performed on a proof-of-principle test chamber are presented. The imaging performance of the prototype KCD was found to be an order-of-magnitude greater than commercial phosphor screen based flat-panel systems, demonstrating the potential for high-quality megavoltage imaging for a variety of industrial applications.

  3. Characterization and use of a 2D-array of ion chambers for brachytherapy dosimetric quality assurance

    SciTech Connect

    Yewondwossen, Mammo

    2012-10-01

    The two-dimensional (2D) ionization chamber array MatriXX Evolution is one of the 2D ionization chamber arrays developed by IBA Dosimetry (IBA Dosimetry, Germany) for megavoltage real-time absolute 2D dosimetry and verification of intensity-modulated radiation therapy (IMRT). The purpose of this study was to (1) evaluate the performance of ion chamber array for submegavoltage range brachytherapy beam dose verification and quality assurance (QA) and (2) use the end-to-end dosimetric evaluation that mimics a patient treatment procedure and confirm the primary source strength calibration agrees in both the treatment planning system (TPS) and treatment delivery console computers. The dose linearity and energy dependence of the 2D ion chamber array was studied using kilovoltage X-ray beams (100, 180 and 300 kVp). The detector calibration factor was determined using 300 kVp X-ray beams so that we can use the same calibration factor for dosimetric verification of high-dose-rate (HDR) brachytherapy. The phantom used for this measurement consists of multiple catheters, the IBA MatriXX detector, and water-equivalent slab of RW3 to provide full scattering conditions. The treatment planning system (TPS) (Oncentra brachy version 3.3, Nucletron BV, Veenendaal, the Netherlands) dose distribution was calculated on the computed tomography (CT) scan of this phantom. The measured and TPS calculated distributions were compared in IBA Dosimetry OmniPro-I'mRT software. The quality of agreement was quantified by the gamma ({gamma}) index (with 3% delta dose and distance criterion of 2 mm) for 9 sets of plans. Using a dedicated phantom capable of receiving 5 brachytherapy intralumenal catheters a QA procedure was developed for end-to-end dosimetric evaluation for routine QA checks. The 2D ion chamber array dose dependence was found to be linear for 100-300 kVp and the detector response (k{sub user}) showed strong energy dependence for 100-300 kVp energy range. For the Ir-192 brachytherapy

  4. Characterization and use of a 2D-array of ion chambers for brachytherapy dosimetric quality assurance.

    PubMed

    Yewondwossen, Mammo

    2012-01-01

    The two-dimensional (2D) ionization chamber array MatriXX Evolution is one of the 2D ionization chamber arrays developed by IBA Dosimetry (IBA Dosimetry, Germany) for megavoltage real-time absolute 2D dosimetry and verification of intensity-modulated radiation therapy (IMRT). The purpose of this study was to (1) evaluate the performance of ion chamber array for submegavoltage range brachytherapy beam dose verification and quality assurance (QA) and (2) use the end-to-end dosimetric evaluation that mimics a patient treatment procedure and confirm the primary source strength calibration agrees in both the treatment planning system (TPS) and treatment delivery console computers. The dose linearity and energy dependence of the 2D ion chamber array was studied using kilovoltage X-ray beams (100, 180 and 300 kVp). The detector calibration factor was determined using 300 kVp X-ray beams so that we can use the same calibration factor for dosimetric verification of high-dose-rate (HDR) brachytherapy. The phantom used for this measurement consists of multiple catheters, the IBA MatriXX detector, and water-equivalent slab of RW3 to provide full scattering conditions. The treatment planning system (TPS) (Oncentra brachy version 3.3, Nucletron BV, Veenendaal, the Netherlands) dose distribution was calculated on the computed tomography (CT) scan of this phantom. The measured and TPS calculated distributions were compared in IBA Dosimetry OmniPro-I'mRT software. The quality of agreement was quantified by the gamma (γ) index (with 3% delta dose and distance criterion of 2 mm) for 9 sets of plans. Using a dedicated phantom capable of receiving 5 brachytherapy intralumenal catheters a QA procedure was developed for end-to-end dosimetric evaluation for routine QA checks. The 2D ion chamber array dose dependence was found to be linear for 100-300 kVp and the detector response (k(user)) showed strong energy dependence for 100-300 kVp energy range. For the Ir-192 brachytherapy HDR

  5. Design and Installation of a Field Ionization Test Chamber for Ion Thrusters

    DTIC Science & Technology

    2011-12-01

    2011 3. REPORT TYPE AND DATES COVERED Master’s Thesis 4. TITLE AND SUBTITLE Design and Installation of a Field Ionization Test Chamber for Ion...Meter MS Mass Spectrometry MWNT Multi-Walled Carbon Nanotube MUF Mass Utilization Factor NASA National Aeronautics and Space Administration NPS...has a mass range of 1–10kg [1]. In comparison, the National Aeronautics and Space Administration ( NASA ) Solar Electric Propulsion Technology

  6. Methods and apparatus for cleaning objects in a chamber of an optical instrument by generating reactive ions using photon radiation

    DOEpatents

    Klebanoff, Leonard E.; Delgado, Gildardo R.; Hollenshead, Jeromy T.; Umstadter, Karl R.; Starodub, Elena; Zhuang, Guorong V.

    2015-10-13

    An optical instrument, including a chamber, an object exposed to an interior of the chamber, a source of low-pressure gas, the gas comprising at least one of low-pressure molecular hydrogen gas, low-pressure molecular oxygen and a low-pressure noble gas, the source of low pressure gas being fluidly coupled to the chamber, a low voltage source electrically coupled between the object and a remaining portion of the instrument that is exposed to the interior of the chamber so as to maintain the object at a low voltage relative to the remaining portion, and an EUV/VUV light source adapted to direct EUV/VUV light through the low pressure gas in the chamber onto the object. In such a system, when the EUV/VUV light source is activated ions of the low-pressure gas are formed and directed to the object. The ions may be ions of Hydrogen, Oxygen or a noble gas.

  7. Characterization of air temperature in modern ion chambers due to phantom geometry and ambient temperature changes.

    PubMed

    Saenz, Daniel L; Kirby, Neil; Gutiérrez, Alonso N

    2016-07-01

    Temperature and pressure corrections are necessary to account for the varying mass of air in the sensitive volume of a vented ionization chamber (IC) when performing absolute dose measurements. Locations commonly used to measure the presumed IC air temperature may not accurately represent the chamber cavity air temperature, and phantoms undergoing temperature changes further compound the problem. Prior studies have characterized thermal equilibrium in separate phantoms for Farmer chambers alone. However, the purpose of this study was to characterize the cavity air temperature dependence on changes in the ambient temperature and phantom geometry configuration for a wider and more modern variety of chambers to determine if previously published wait times apply to these chambers as well. Thermal conduction properties were experimentally investigated by modifying a PTW 0.3 cm(3) Semiflex IC with a thermocouple replacing the central electrode. Air cavity temperature versus time was recorded in three phantom geometries characteristic of common absolute dose measurements. The phantoms were (15 ± 1) °C before measurement with an IC at the treatment vault temperature of (21 ± 1) °C. Simulations were conducted to provide a theoretical basis for the measurements and to simulate temperature response of a PTW PinPoint® and Farmer chamber. The simulation methods were first validated by comparison with measured Semiflex chamber thermal response curves before extension to the other chambers. Two thermal equilibria curves were recorded on different time scales. IC temperature initially dropped to the colder phantom temperature but subsequently increased as the phantom itself equilibrated with the warmer room temperature. In a large phantom of dimensions (25.5 × 25.5 × 23.4) cm(3), 3 min was required before the IC temperature reached within 0.5 °C of its equilibrium within the phantom. Similarly, wait times of 2 min were needed for 7.5 and 2 cm slab phantoms. Recording

  8. Systematic uncertainties in the Monte Carlo calculation of ion chamber replacement correction factors.

    PubMed

    Wang, L L W; La Russa, D J; Rogers, D W O

    2009-05-01

    In a previous study [Med. Phys. 35, 1747-1755 (2008)], the authors proposed two direct methods of calculating the replacement correction factors (P(repl) or P(cav)P(dis)) for ion chambers by Monte Carlo calculation. By "direct" we meant the stopping-power ratio evaluation is not necessary. The two methods were named as the high-density air (HDA) and low-density water (LDW) methods. Although the accuracy of these methods was briefly discussed, it turns out that the assumption made regarding the dose in an HDA slab as a function of slab thickness is not correct. This issue is reinvestigated in the current study, and the accuracy of the LDW method applied to ion chambers in a 60Co photon beam is also studied. It is found that the two direct methods are in fact not completely independent of the stopping-power ratio of the two materials involved. There is an implicit dependence of the calculated P(repl) values upon the stopping-power ratio evaluation through the choice of an appropriate energy cutoff delta, which characterizes a cavity size in the Spencer-Attix cavity theory. Since the delta value is not accurately defined in the theory, this dependence on the stopping-power ratio results in a systematic uncertainty on the calculated P(repl) values. For phantom materials of similar effective atomic number to air, such as water and graphite, this systematic uncertainty is at most 0.2% for most commonly used chambers for either electron or photon beams. This uncertainty level is good enough for current ion chamber dosimetry, and the merits of the two direct methods of calculating P(repl) values are maintained, i.e., there is no need to do a separate stopping-power ratio calculation. For high-Z materials, the inherent uncertainty would make it practically impossible to calculate reliable P(repl) values using the two direct methods.

  9. Response to NAS Request for Information on Chamber Repetition Rate

    SciTech Connect

    Meier, Wayne R.

    2011-08-19

    This purpose of this report is to “Provide further information on the issues of repetition rates and chamber clearing issues for dry wall and liquid wall chamber concepts for IFE; namely what are the issues, possible solutions and needed R&D?”

  10. Monte Carlo calculations for reference dosimetry of electron beams with the PTW Roos and NE2571 ion chambers.

    PubMed

    Muir, B R; Rogers, D W O

    2013-12-01

    To investigate recommendations for reference dosimetry of electron beams and gradient effects for the NE2571 chamber and to provide beam quality conversion factors using Monte Carlo simulations of the PTW Roos and NE2571 ion chambers. The EGSnrc code system is used to calculate the absorbed dose-to-water and the dose to the gas in fully modeled ion chambers as a function of depth in water. Electron beams are modeled using realistic accelerator simulations as well as beams modeled as collimated point sources from realistic electron beam spectra or monoenergetic electrons. Beam quality conversion factors are calculated with ratios of the doses to water and to the air in the ion chamber in electron beams and a cobalt-60 reference field. The overall ion chamber correction factor is studied using calculations of water-to-air stopping power ratios. The use of an effective point of measurement shift of 1.55 mm from the front face of the PTW Roos chamber, which places the point of measurement inside the chamber cavity, minimizes the difference between R50, the beam quality specifier, calculated from chamber simulations compared to that obtained using depth-dose calculations in water. A similar shift minimizes the variation of the overall ion chamber correction factor with depth to the practical range and reduces the root-mean-square deviation of a fit to calculated beam quality conversion factors at the reference depth as a function of R50. Similarly, an upstream shift of 0.34 rcav allows a more accurate determination of R50 from NE2571 chamber calculations and reduces the variation of the overall ion chamber correction factor with depth. The determination of the gradient correction using a shift of 0.22 rcav optimizes the root-mean-square deviation of a fit to calculated beam quality conversion factors if all beams investigated are considered. However, if only clinical beams are considered, a good fit to results for beam quality conversion factors is obtained without

  11. Monte Carlo calculations for reference dosimetry of electron beams with the PTW Roos and NE2571 ion chambers

    SciTech Connect

    Muir, B. R. Rogers, D. W. O.

    2013-12-15

    Purpose: To investigate recommendations for reference dosimetry of electron beams and gradient effects for the NE2571 chamber and to provide beam quality conversion factors using Monte Carlo simulations of the PTW Roos and NE2571 ion chambers. Methods: The EGSnrc code system is used to calculate the absorbed dose-to-water and the dose to the gas in fully modeled ion chambers as a function of depth in water. Electron beams are modeled using realistic accelerator simulations as well as beams modeled as collimated point sources from realistic electron beam spectra or monoenergetic electrons. Beam quality conversion factors are calculated with ratios of the doses to water and to the air in the ion chamber in electron beams and a cobalt-60 reference field. The overall ion chamber correction factor is studied using calculations of water-to-air stopping power ratios. Results: The use of an effective point of measurement shift of 1.55 mm from the front face of the PTW Roos chamber, which places the point of measurement inside the chamber cavity, minimizes the difference betweenR{sub 50}, the beam quality specifier, calculated from chamber simulations compared to that obtained using depth-dose calculations in water. A similar shift minimizes the variation of the overall ion chamber correction factor with depth to the practical range and reduces the root-mean-square deviation of a fit to calculated beam quality conversion factors at the reference depth as a function of R{sub 50}. Similarly, an upstream shift of 0.34 r{sub cav} allows a more accurate determination of R{sub 50} from NE2571 chamber calculations and reduces the variation of the overall ion chamber correction factor with depth. The determination of the gradient correction using a shift of 0.22 r{sub cav} optimizes the root-mean-square deviation of a fit to calculated beam quality conversion factors if all beams investigated are considered. However, if only clinical beams are considered, a good fit to results for

  12. Heavy-ion inertial fusion: influence of target gain on accelerator parameters for vacuum-propagation regimes in reaction chambers

    SciTech Connect

    Mark, J.W.K.; Bangerter, R.O.; Barletta, W.A.; Fawley, W.M.; Judd, D.L.

    1982-03-04

    Target physics imposes requirements on the design of inertial fusion drivers. The influence of beam propagation in near vacuum fusion reaction chambers is evaluated for the relation between target gain and the phase-space requirements of heavy-ion accelerators. Initial results suggest that neutralization of the ion beam has a much greater positive effect than the deleterious one of beam stripping provided that the fusion chamber pressure is < 10/sup -3/ torr (of Li vapor or equivalent).

  13. Amendments to the theory underlying Ussing chamber data of chloride ion secretion after bacterial enterotoxin exposure.

    PubMed

    Lucas, M L

    2005-05-07

    Bacterial enterotoxins may cause life-threatening diarrhoeal fluid loss in part because they stimulate enterocytes to secrete fluid into the small intestine as well as preventing normal fluid uptake. Abnormal chloride ion secretion is believed to provide the osmotic driving force for the inappropriate fluid movement. Evidence for enhanced chloride secretion consists of isotopic flux measurements in Ussing chambers, the standard apparatus for permeation studies. Flux from the lumen of the intestine is assumed to be determined solely by absorptive processes and flux towards the lumen solely by secretory processes. Bacterial enterotoxin increased flux towards the lumen is taken as an evidence of enhanced secretion. Examination of the flux equation solutions shows that the existing theoretical treatment of the Ussing chamber consists of the super-imposition of two contradictory unidirectional models. In contrast, the present analysis shows that a measured 'unidirectional' flux contains information both about absorptive and secretory processes, regardless of which flux is measured. Reciprocity is predicted for the fluxes, as decreases in the absorptive processes will cause increases in apparent secretory flux. Data from the literature show that mucosal-to-serosal chloride ion flux in rabbit ileum after exposure to secretagogues correlates inversely and highly significantly (r=0.74, n=17, p<0.001) with increases in serosal-to-mucosal chloride ion flux. As a category of evidence, flux data do not provide conclusive evidence of enhanced chloride secretion after exposure to enterotoxins, since an apparently enhanced serosal-to-mucosal flux would also be noted after inhibition of the mucosal-to-serosal flux. As interruption of absorptive processes can be misinterpreted as enhanced secretion in the Ussing chamber, this is a serious deficiency in the evidence for direct enterotoxin enhancement of the intestinal chloride ion channel as a basis for diarrhoeal disease.

  14. Solutions for discharge chamber sputtering and anode deposit spalling in small mercury ion thrusters

    NASA Technical Reports Server (NTRS)

    Power, J. L.; Hiznay, D. J.

    1975-01-01

    Proposed solutions to the problems of sputter erosion and sputtered material spalling in the discharge chamber of small mercury ion thrusters are presented. The accelerated life test evaluated three such proposed solutions: (1) the use of tantalum as a single low sputter yield material for the exposed surfaces of the discharge chamber components subject to sputtering, (2) the use of a severely roughened anode surface to improve the adhesion of the sputter-deposited coating, and (3) the use of a wire cloth anode surface in order to limit the size of any coating flakes which might spall from it. Because of the promising results obtained in the accelerated life test with anode surfaces roughened by grit-blasting, experiments were carried out to optimize the grit-blasting procedure. The experimental results and an optimal grit-blasting procedure are presented.

  15. Dosimetry in MARS spectral CT: TOPAS Monte Carlo simulations and ion chamber measurements.

    PubMed

    Lu, Gray; Marsh, Steven; Damet, Jerome; Carbonez, Pierre; Laban, John; Bateman, Christopher; Butler, Anthony; Butler, Phil

    2017-06-01

    Spectral computed tomography (CT) is an up and coming imaging modality which shows great promise in revealing unique diagnostic information. Because this imaging modality is based on X-ray CT, it is of utmost importance to study the radiation dose aspects of its use. This study reports on the implementation and evaluation of a Monte Carlo simulation tool using TOPAS for estimating dose in a pre-clinical spectral CT scanner known as the MARS scanner. Simulated estimates were compared with measurements from an ionization chamber. For a typical MARS scan, TOPAS estimated for a 30 mm diameter cylindrical phantom a CT dose index (CTDI) of 29.7 mGy; CTDI was measured by ion chamber to within 3% of TOPAS estimates. Although further development is required, our investigation of TOPAS for estimating MARS scan dosimetry has shown its potential for further study of spectral scanning protocols and dose to scanned objects.

  16. Sputtering phenomena of discharge chamber components in a 30-cm diameter Hg ion thruster

    NASA Technical Reports Server (NTRS)

    Mantenieks, M. A.; Rawlin, V. K.

    1976-01-01

    Sputtering and deposition rates were measured for discharge chamber components of a 30-cm diameter mercury ion thruster. It was found that sputtering rates of the screen grid and cathode baffle were strongly affected by geometry of the baffle holder. Sputtering rates of the baffle and screen grid were reduced to 80 and 125 A/hr, respectively, by combination of appropriate geometry and materials selections. Sputtering rates such as these are commensurate with thruster lifetimes of 15,000 hours or more. A semiempirical sputtering model showed good agreement with the measured values.

  17. The response of a scintillation counter below an emulsion chamber to heavy nucleus interactions in the chamber

    NASA Technical Reports Server (NTRS)

    Burnett, T. H.; Dake, S.; Derrickson, J. H.; Fountain, W. F.; Fuki, M.; Gregory, J. C.; Hayashi, T.; Hayashi, T.; Holynski, R.; Iwai, J.; hide

    1985-01-01

    In 1982 a hybrid electronic counter-emulsion chamber experiment was flown on a balloon to study heavy nucleus interactions in the 20 to approximately 100 GeV/AMU energy range. A gas Cerenkov counter, two solid Cerenkov counters, and a proportional counter hodoscope gave the primary energy, the primary charge and the trajectory of the particles, respectively. Using the trajectory information cosmic ray nuclei of Z 10 were found reliably and efficiently, and interaction characteristics of the Fe group nuclei were measured in the chamber. A plastic scintillator below the emulsion chamber responded to showers resulting from interactions in the chamber and to noninteracting nuclei. Data on the response of the counter have been compared with simulations of hadronic-electromagnetic cascades to derive the average neutral energy fraction released by the heavy interactions, and to predict the performance of this kind of counter at higher energies. For the interacting events of highest produced particles multiplicity comparison between various simulations and the shower counter signal have been made.

  18. Formation of metal nanoparticles by short-distance sputter deposition in a reactive ion etching chamber

    SciTech Connect

    Nie Min; Meng, Dennis Desheng; Sun Kai

    2009-09-01

    A new method is reported to form metal nanoparticles by sputter deposition inside a reactive ion etching chamber with a very short target-substrate distance. The distribution and morphology of nanoparticles are found to be affected by the distance, the ion concentration, and the sputtering time. Densely distributed nanoparticles of various compositions were fabricated on the substrates that were kept at a distance of 130 mum or smaller from the target. When the distance was increased to 510 mum, island structures were formed, indicating the tendency to form continuous thin film with longer distance. The observed trend for nanoparticle formation is opposite to the previously reported mechanism for the formation of nanoparticles by sputtering. A new mechanism based on the seeding effect of the substrate is proposed to interpret the experimental results.

  19. Two-chamber configuration of Bio-Nano electron cyclotron resonance ion source for fullerene modification.

    PubMed

    Uchida, T; Rácz, R; Muramatsu, M; Kato, Y; Kitagawa, A; Biri, S; Yoshida, Y

    2016-02-01

    We report on the modification of fullerenes with iron and chlorine using two individually controllable plasmas in the Bio-Nano electron cyclotron resonance ion source (ECRIS). One of the plasmas is composed of fullerene and the other one is composed of iron and chlorine. The online ion beam analysis allows one to investigate the rate of the vapor-phase collisional modification process in the ECRIS, while the offline analyses (e.g., liquid chromatography-mass spectrometry) of the materials deposited on the plasma chamber can give information on the surface-type process. Both analytical methods show the presence of modified fullerenes such as fullerene-chlorine, fullerene-iron, and fullerene-chlorine-iron.

  20. Two-chamber configuration of Bio-Nano electron cyclotron resonance ion source for fullerene modification

    NASA Astrophysics Data System (ADS)

    Uchida, T.; Rácz, R.; Muramatsu, M.; Kato, Y.; Kitagawa, A.; Biri, S.; Yoshida, Y.

    2016-02-01

    We report on the modification of fullerenes with iron and chlorine using two individually controllable plasmas in the Bio-Nano electron cyclotron resonance ion source (ECRIS). One of the plasmas is composed of fullerene and the other one is composed of iron and chlorine. The online ion beam analysis allows one to investigate the rate of the vapor-phase collisional modification process in the ECRIS, while the offline analyses (e.g., liquid chromatography-mass spectrometry) of the materials deposited on the plasma chamber can give information on the surface-type process. Both analytical methods show the presence of modified fullerenes such as fullerene-chlorine, fullerene-iron, and fullerene-chlorine-iron.

  1. Two-chamber configuration of Bio-Nano electron cyclotron resonance ion source for fullerene modification

    SciTech Connect

    Uchida, T.; Rácz, R.; Biri, S.; Kato, Y.; Yoshida, Y.

    2016-02-15

    We report on the modification of fullerenes with iron and chlorine using two individually controllable plasmas in the Bio-Nano electron cyclotron resonance ion source (ECRIS). One of the plasmas is composed of fullerene and the other one is composed of iron and chlorine. The online ion beam analysis allows one to investigate the rate of the vapor-phase collisional modification process in the ECRIS, while the offline analyses (e.g., liquid chromatography-mass spectrometry) of the materials deposited on the plasma chamber can give information on the surface-type process. Both analytical methods show the presence of modified fullerenes such as fullerene-chlorine, fullerene-iron, and fullerene-chlorine-iron.

  2. An exposure chamber for studies on human perception of DC electric fields and ions

    SciTech Connect

    Nguyen, D.H.; Maruvada, P.S. )

    1994-10-01

    Direct current (DC) transmission lines are often used, for technical and economic reasons, as interconnections in modern high voltage power systems, which are essentially of the alternating current (AC) type. Significant differences exist, however, between the field effects produced in the vicinity of AC and DC transmission lines. DC electric fields induce charges, on the surface of a conducting body such as a human being and may therefore be ''perceived'' by humans due to hair stimulation and other sensations experienced by the skin. A human being exposed to the ionized field of a DC transmission line experiences not only surface charges but also the conducted ion currents. A systematic laboratory study has been undertaken by Hydro Quebec to investigate human perception, using well established psycho physical techniques, of DC electric fields and ions. The design, construction and operation of an exposure chamber for this purpose, in the high voltage laboratory of IREQ, are described in this paper.

  3. Diagnostics of discharge channels for neutralized chamber transport in heavy ion fusion

    NASA Astrophysics Data System (ADS)

    Niemann, C.; Penache, D.; Tauschwitz, A.; Rosmej, F. B.; Neff, S.; Birkner, R.; Constantin, C.; Knobloch, R.; Presura, R.; Yu, S. S.; Sharp, W. M.; Ponce, D. M.; Hoffmann, D. H. H.

    2003-01-01

    The final beam transport in the reactor chamber for heavy ion fusion in preformed plasma channels offers many attractive advantages compared to other transport modes. In the past few years, experiments at the Gesellschaft für Schwerionenforschung (GSI) accelerator facility have addressed the creation and investigation of discharge plasmas, designed for the transport of intense ion beams. Stable, self-standing channels of 50 cm length with currents up to 55 kA were initiated in low-pressure ammonia gas by a CO2-laser pulse along the channel axis before the discharge is triggered. The channels were characterized by several plasma diagnostics including interferometry and spectroscopy. We also present first experiments on laser-guided intersecting discharges.

  4. Electret ion chamber radon monitors measure dissolved 222Rn in water.

    PubMed

    Kotrappa, P; Jester, W A

    1993-04-01

    This paper describes a simple and relatively inexpensive method of determining the concentration of dissolved 222Rn in water. The method involves a recently developed electret-passive environmental radon monitor, which uses an electret ion chamber. The procedure consists of sealing a known volume of a carefully collected water sample with one of these monitors in an exposure container and determining the average equilibrium 222Rn gas concentration in the air phase during the exposure time period. This average concentration can then be used to calculate the 222Rn concentration in the original water sample. Identical samples were analyzed both by this new method and by a standard liquid scintillation method, and the results were compared over a wide range of 222Rn concentrations. There was good agreement except that the electret ion chamber method gave results that were consistently lower by about 15%. This bias in the results was attributed to both 222Rn losses during sample handling and possibly to some errors in the assumptions made in the theoretical model. A correction factor is recommended to bring the results of this technique into agreement with the standard method. The procedures are simple and economical and can be easily employed by many primary 222Rn-measuring laboratories currently using these monitors for measuring indoor 222Rn.

  5. Dosimetric verification of gated delivery of electron beams using a 2D ion chamber array.

    PubMed

    Yoganathan, S A; Das, K J Maria; Raj, D Gowtham; Kumar, Shaleen

    2015-01-01

    The purpose of this study was to compare the dosimetric characteristics; such as beam output, symmetry and flatness between gated and non-gated electron beams. Dosimetric verification of gated delivery was carried for all electron beams available on Varian CL 2100CD medical linear accelerator. Measurements were conducted for three dose rates (100 MU/min, 300 MU/min and 600 MU/min) and two respiratory motions (breathing period of 4s and 8s). Real-time position management (RPM) system was used for the gated deliveries. Flatness and symmetry values were measured using Imatrixx 2D ion chamber array device and the beam output was measured using plane parallel ion chamber. These detector systems were placed over QUASAR motion platform which was programmed to simulate the respiratory motion of target. The dosimetric characteristics of gated deliveries were compared with non-gated deliveries. The flatness and symmetry of all the evaluated electron energies did not differ by more than 0.7 % with respect to corresponding non-gated deliveries. The beam output variation of gated electron beam was less than 0.6 % for all electron energies except for 16 MeV (1.4 %). Based on the results of this study, it can be concluded that Varian CL2100 CD is well suitable for gated delivery of non-dynamic electron beams.

  6. Dosimetric verification of gated delivery of electron beams using a 2D ion chamber array

    PubMed Central

    Yoganathan, S. A.; Das, K. J. Maria; Raj, D. Gowtham; Kumar, Shaleen

    2015-01-01

    The purpose of this study was to compare the dosimetric characteristics; such as beam output, symmetry and flatness between gated and non-gated electron beams. Dosimetric verification of gated delivery was carried for all electron beams available on Varian CL 2100CD medical linear accelerator. Measurements were conducted for three dose rates (100 MU/min, 300 MU/min and 600 MU/min) and two respiratory motions (breathing period of 4s and 8s). Real-time position management (RPM) system was used for the gated deliveries. Flatness and symmetry values were measured using Imatrixx 2D ion chamber array device and the beam output was measured using plane parallel ion chamber. These detector systems were placed over QUASAR motion platform which was programmed to simulate the respiratory motion of target. The dosimetric characteristics of gated deliveries were compared with non-gated deliveries. The flatness and symmetry of all the evaluated electron energies did not differ by more than 0.7 % with respect to corresponding non-gated deliveries. The beam output variation of gated electron beam was less than 0.6 % for all electron energies except for 16 MeV (1.4 %). Based on the results of this study, it can be concluded that Varian CL2100 CD is well suitable for gated delivery of non-dynamic electron beams. PMID:26170552

  7. Characterization of Si distribution at the tungsten/titanium nitride interface using secondary ion mass spectrometry — an investigation of the dynamic response of a chemical vapor deposition chamber

    NASA Astrophysics Data System (ADS)

    Jones, Clive M.; Zhao, Jin; Yuan, Ting

    2000-09-01

    Secondary ion mass spectrometry (SIMS) was successfully used as an analytical method to characterize chemical vapor deposited (CVD) tungsten (W) processes. Blanket CVD tungsten film on titanium nitride (TiN) barrier layers generally begins with the deposition of a tungsten nucleation layer by silane (SiH 4) reduction of tungsten hexafluoride (WF 6), followed by hydrogen (H 2) reduction of WF 6 alone to form the bulk tungsten layer. In the present work, the tungsten nucleation layer was formed by simultaneous SiH 4 and H 2 reduction of WF 6. A two-step SiH 4 gas flow scheme was used to determine the effects of magnitude and duration of SiH 4 flow on the Si concentration at the W/TiN interface. SIMS was used to characterize the Si distribution at the CVD W/TiN interface. SIMS depth profiles indicate, with a constant SiH 4 flow time of 3 s, the Si concentration at W/TiN interface does not vary significantly with the increase of SiH 4 flow from 20 to 30 sccm. However, it increases dramatically with the increase of SiH 4 flow from 30 to 48 sccm. With a constant SiH 4 flow of 40 sccm, the Si concentration at the W/TiN interface increases linearly with the increase of the SiH 4 flow time. These results amply demonstrate that SIMS analysis can be used to evaluate the deposition process so as to meet the fill and barrier protection requirements for narrow trench or small via.

  8. Ion response in a weakly ionized plasma with ion flow

    SciTech Connect

    Kompaneets, Roman; Tyshetskiy, Yuriy O.; Vladimirov, Sergey V.

    2013-04-15

    We study the ion response to an initial perturbation in a weakly ionized plasma with ion flow driven by a dc electric field. The analysis is made by extending the classical Landau work [J. Phys. (USSR) 10, 25 (1946)] to the ion kinetic equation including ion-neutral collisions and a dc electric field. We show, in particular, that the complex frequencies of ion waves can be directly found from a known expression for the ion susceptibility [A. V. Ivlev et al., Phys. Rev. E 71, 016405 (2005); V. A. Schweigert, Phys. Rep. 27, 997 (2001)]; this is not obvious from its original derivation, because it only aims to describe the ion response for real frequencies.

  9. Performance of single chamber biocatalyzed electrolysis with different types of ion exchange membranes.

    PubMed

    Rozendal, René A; Hamelers, Hubertus V M; Molenkamp, Redmar J; Buisman, Cees J N

    2007-05-01

    In this paper hydrogen production through biocatalyzed electrolysis was studied for the first time in a single chamber configuration. Single chamber biocatalyzed electrolysis was tested in two configurations: (i) with a cation exchange membrane (CEM) and (ii) with an anion exchange membrane (AEM). Both configurations performed comparably and produced over 0.3 m3 H2/m3 reactor liquid volume/day at 1.0 V applied voltage (overall hydrogen efficiencies around 23%). Analysis of the water that permeated through the membrane revealed that a large part of potential losses in the system were associated with a pH gradient across the membrane (CEM DeltapH=6.4; AEM DeltapH=4.4). These pH gradient associated potential losses were lower in the AEM configuration (CEM 0.38 V; AEM 0.26 V) as a result of its alternative ion transport properties. This benefit of the AEM, however, was counteracted by the higher cathode overpotentials occurring in the AEM configuration (CEM 0.12 V at 2.39 A/m2; AEM 0.27 V at 2.15 A/m2) as a result of a less effective electroless plating method for the AEM membrane electrode assembly (MEA).

  10. Simulation of ion chamber signals in the n+3 He -> p + t experiment

    NASA Astrophysics Data System (ADS)

    Coppola, Christopher; n3He Collaboration

    2017-01-01

    The parity violating proton directional asymmetry from the capture of polarized neutrons on 3He was measured with a pulsed neutron beam at the Spallation Neutron Source at Oak Ridge National Laboratory. The target is an ion chamber with 3He at 0.476 atmosphere. Signal wires in the chamber have different sensitivities to the physics asymmetry, depdendent on their location and the configuration of the experiment. These geometry factors must be determined by simulation. In addition, simulation estimates the statistical precision of the experiment, optimizes configuration variables, and assists with systematic analysis. To achieve the most accurate simulation of the detector signals, a custom simulation was written in C++ using weighted variables and taking advantage of parallel execution. The phsyics inputs to the simulation came from measurements of the neutron phase space, ENDF cross sections, and PSTAR ionization data. A cell model was applied to combine this physics to produce an accurate simulation of the experimental data. This simulation can be used to calculate accurate and tunable geometry factors, and to produce desired quanities for use in optimization and analysis.

  11. Phantom dosimetric study of nondivergent aluminum tissue compensator using ion chamber, TLD, and gafchromic film.

    PubMed

    Kinhikar, Rajesh A; Tambe, Chandrashekhar M; Upreti, Ritu R; Patkar, Sachin; Patil, Kalpana; Deshpande, Deepak D

    2008-01-01

    Anatomic contour irregularity and tissue inhomogeneity in head-and-neck radiotherapy can lead to significant dose inhomogeneity due to the presence of hot and cold spots across the treatment volumes. Missing tissue compensators (TCs) can overcome this dose inhomogeneity. The current study examines the capacity of 2-dimensional (2D) custom aluminum TCs fabricated at our hospital to improve the dose homogeneity across the treatment volume. The dosimetry of the 2D custom TCs was carried out in a specially designed head-and-neck phantom for anterior-posterior (AP) and posterior-anterior (PA) fields with an ion chamber, thermoluminscence dosimeters (TLDs), and film. The results were compared for compensated and uncompensated plans generated from the Eclipse treatment planning system. On average, open-field plans contained peak doses of 117%, optimally wedged-plans contained peak doses of 113%, and custom-compensated plans contained peak doses of 105%. The dose variation between prescribed and measured dose at midplane of the phantom was observed as high as 17%, which was reduced to 3.2% for the customized TC during ionometric measurements. It was further confirmed with TLDs, in a sagittal plane, that the high-dose region of 13.3% was reduced to 2.3%. The measurements carried out with the ion chamber, TLDs, and film were found in good agreement with each other and with Eclipse. Thus, a custom-made 2D TC is capable of reducing hot spots to improve overall dose homogeneity across the treatment volume.

  12. SU-E-T-562: Scanned Percent Depth Dose Curve Discrepancy for Photon Beams with Physical Wedge in Place (Varian IX) Using Different Sensitive Volume Ion Chambers

    SciTech Connect

    Zhao, H; Sarkar, V; Rassiah-Szegedi, P; Huang, Y; Szegedi, M; Huang, L; Salter, B

    2014-06-01

    Purpose: To investigate and report the discrepancy of scanned percent depth dose (PDD) for photon beams with physical wedge in place when using ion chambers with different sensitive volumes. Methods/Materials: PDD curves of open fields and physical wedged fields (15, 30, 45, and 60 degree wedge) were scanned for photon beams (6MV and 10MV, Varian iX) with field size of 5x5 and 10x10 cm using three common scanning chambers with different sensitive volumes - PTW30013 (0.6cm3), PTW23323 (0.1cm3) and Exradin A16 (0.007cm3). The scanning system software used was OmniPro version 6.2, and the scanning water tank was the Scanditronix Wellhoffer RFA 300.The PDD curves from the three chambers were compared. Results: Scanned PDD curves of the same energy beams for open fields were almost identical between three chambers, but the wedged fields showed non-trivial differences. The largest differences were observed between chamber PTW30013 and Exradin A16. The differences increased as physical wedge angle increased. The differences also increased with depth, and were more pronounced for 6MV beam. Similar patterns were shown for both 5x5 and 10x10 cm field sizes. For open fields, all PDD values agreed with each other within 1% at 10cm depth and within 1.62% at 20 cm depth. For wedged fields, the difference of PDD values between PTW30013 and A16 reached 4.09% at 10cm depth, and 5.97% at 20 cm depth for 6MV with 60 degree physical wedge. Conclusion: We observed a significant difference in scanned PDD curves of photon beams with physical wedge in place obtained when using different sensitive volume ion chambers. The PDD curves scanned with the smallest sensitive volume ion chamber showed significant difference from larger chamber results, beyond 10cm depth. We believe this to be caused by varying response to beam hardening by the wedges.

  13. Influence of pressurized anode chamber on ion transports and power generation of UF membrane microbial fuel cells (UF-MFCs)

    NASA Astrophysics Data System (ADS)

    Kim, Kyoung-Yeol; Chae, Kyu-Jung; Yang, Euntae; Lee, Mi-Young; Kim, In S.

    2015-04-01

    Ultrafiltration membrane integrated microbial fuel cell (UF-MFC) has developed to produce high-quality effluents by integrating the membrane filtration process into the MFC system. During UF-MFC operation, however, unexpected power reductions were observed under different pressures that were applied in the anode chamber (22.0% and 25.5% at 0.7 bar and 2.1 bar, respectively). It was hypothesized that those of power reductions might occur due to the limitation of ion transport across the UF membrane- which could be caused by the pressurized anode chamber to filter the anode solution through the UF membrane. A test with a NaCl concentrated cathode solution showed few dissolved ions being transported from the cathode to anode chamber while the pressure was being applied in the anode chamber. This result clearly indicates that the limitation of ion transport from the cathode to the pressurized anode chamber is a significant factor affecting the power density of UF-MFCs, even more so than water permeation through the UF membrane.

  14. Integration of a broad beam ion source with a high-temperature x-ray diffraction vacuum chamber

    NASA Astrophysics Data System (ADS)

    Manova, D.; Bergmann, A.; Mändl, S.; Neumann, H.; Rauschenbach, B.

    2012-11-01

    Here, the integration of a low energy, linearly variable ion beam current density, mechanically in situ adjustable broad beam ion source with a high-temperature x-ray diffraction (XRD) vacuum chamber is reported. This allows in situ XRD investigation of phase formation and evolution processes induced by low energy ion implantation. Special care has been taken to an independent adjustment of the ion beam for geometrical directing towards the substrate, a 15 mm small ion source exit aperture to avoid a secondary sputter process of the chamber walls, linearly variable ion current density by using a pulse length modulation (PLM) for the accelerating voltages without changing the ion beam density profile, nearly homogeneous ion beam distribution over the x-ray footprint, together with easily replaceable Kapton® windows for x-rays entry and exit. By combining a position sensitive x-ray detector with this PLM-modulated ion beam, a fast and efficient time resolved investigation of low energy implantation processes is obtained in a compact experimental setup.

  15. Integration of a broad beam ion source with a high-temperature x-ray diffraction vacuum chamber.

    PubMed

    Manova, D; Bergmann, A; Mändl, S; Neumann, H; Rauschenbach, B

    2012-11-01

    Here, the integration of a low energy, linearly variable ion beam current density, mechanically in situ adjustable broad beam ion source with a high-temperature x-ray diffraction (XRD) vacuum chamber is reported. This allows in situ XRD investigation of phase formation and evolution processes induced by low energy ion implantation. Special care has been taken to an independent adjustment of the ion beam for geometrical directing towards the substrate, a 15 mm small ion source exit aperture to avoid a secondary sputter process of the chamber walls, linearly variable ion current density by using a pulse length modulation (PLM) for the accelerating voltages without changing the ion beam density profile, nearly homogeneous ion beam distribution over the x-ray footprint, together with easily replaceable Kapton(®) windows for x-rays entry and exit. By combining a position sensitive x-ray detector with this PLM-modulated ion beam, a fast and efficient time resolved investigation of low energy implantation processes is obtained in a compact experimental setup.

  16. Integration of a broad beam ion source with a high-temperature x-ray diffraction vacuum chamber

    SciTech Connect

    Manova, D.; Bergmann, A.; Maendl, S.; Neumann, H.; Rauschenbach, B.

    2012-11-15

    Here, the integration of a low energy, linearly variable ion beam current density, mechanically in situ adjustable broad beam ion source with a high-temperature x-ray diffraction (XRD) vacuum chamber is reported. This allows in situ XRD investigation of phase formation and evolution processes induced by low energy ion implantation. Special care has been taken to an independent adjustment of the ion beam for geometrical directing towards the substrate, a 15 mm small ion source exit aperture to avoid a secondary sputter process of the chamber walls, linearly variable ion current density by using a pulse length modulation (PLM) for the accelerating voltages without changing the ion beam density profile, nearly homogeneous ion beam distribution over the x-ray footprint, together with easily replaceable Kapton{sup Registered-Sign} windows for x-rays entry and exit. By combining a position sensitive x-ray detector with this PLM-modulated ion beam, a fast and efficient time resolved investigation of low energy implantation processes is obtained in a compact experimental setup.

  17. Heavy ion beam propagation through a gas-filled chamber for inertial confinement fusion

    SciTech Connect

    Barboza, Nigel Oswald

    1996-10-01

    The work presented here evaluates the dynamics of a beam of heavy ions propagating through a chamber filled with gas. The motivation for this research stems from the possibility of using heavy ion beams as a driver in inertial confinement fusion reactors for the purpose of generating electricity. Such a study is important in determining the constraints on the beam which limit its focus to the small radius necessary for the ignition of thermonuclear microexplosions which are the source of fusion energy. Nuclear fusion is the process of combining light nuclei to form heavier ones. One possible fusion reaction combines two isotopes of hydrogen, deuterium and tritium, to form an alpha particle and a neutron, with an accompanying release of ~17.6 MeV of energy. Generating electricity from fusion requires that we create such reactions in an efficient and controlled fashion, and harness the resulting energy. In the inertial confinement fusion (ICF) approach to energy production, a small spherical target, a few millimeters in radius, of deuterium and tritium fuel is compressed so that the density and temperature of the fuel are high enough, ~200 g/cm3 and ~20 keV, that a substantial number of fusion reactions occur; the pellet microexplosion typically releases ~350 MJ of energy in optimized power plant scenarios.

  18. Construction of a scattering chamber for ion-beam analysis of environmental materials in undergraduate physics research

    SciTech Connect

    LaBrake, Scott M.; Vineyard, Michael F.; Turley, Colin F.; Moore, Robert D.; Johnson, Christopher

    2013-04-19

    We have developed a new scattering chamber for ion-beam analysis of environmental materials with the 1.1-MV Pelletron accelerator at the Union College Ion-Beam Analysis Laboratory. The chamber was constructed from a ten-inch, Conflat, multi-port cross and includes a three-axis target manipulator and target ladder assembly, an eight-inch turbo pump, an Amptek X-ray detector, and multiple charged particle detectors. Recent projects performed by our undergraduate research team include proton induced X-ray emission (PIXE) and Rutherford backscattering (RBS) analyses of atmospheric aerosols collected with a nine-stage cascade impactor in Upstate New York. We will describe the construction of the chamber and discuss the results of some commissioning experiments.

  19. Ion-recombination correction for different ionization chambers in high dose rate flattening-filter-free photon beams.

    PubMed

    Lang, Stephanie; Hrbacek, Jan; Leong, Aidan; Klöck, Stephan

    2012-05-07

    Recently, there has been an increased interest in flattening-filter-free (FFF) linear accelerators. Removal of the filter results in available dose rates up to 24 Gy min(-1) (for nominal energy 10 MV in depth of maximum dose, a source-surface distance of 100 cm and a field size of 10×10 cm2). To guarantee accurate relative and reference dosimetry for the FFF beams, we investigated the charge collection efficiency of multiple air-vented and one liquid ionization chamber for dose rates up to 31.9 Gy min(-1). For flattened beams, the ion-collection efficiency of all air-vented ionization chambers (except for the PinPoint chamber) was above 0.995. By removing the flattening filter, we found a reduction in collection efficiency of approximately 0.5-0.9% for a 10 MV beam. For FFF beams, the Markus chamber showed the largest collection efficiency of 0.994. The observed collection efficiencies were dependent on dose per pulse, but independent of the pulse repetition frequency. Using the liquid ionization chamber, the ion-collection efficiency for flattened beams was above 0.990 for all dose rates. However, this chamber showed a low collection efficiency of 0.940 for the FFF 10 MV beam at a dose rate of 31.9 Gy min(-1). All investigated air-vented ionization chambers can be reliably used for relative dosimetry of FFF beams. The order of correction for reference dosimetry is given in the manuscript. Due to their increased saturation in high dose rate FFF beams, liquid ionization chambers appear to be unsuitable for dosimetry within these contexts.

  20. Ion-recombination correction for different ionization chambers in high dose rate flattening-filter-free photon beams

    NASA Astrophysics Data System (ADS)

    Lang, Stephanie; Hrbacek, Jan; Leong, Aidan; Klöck, Stephan

    2012-05-01

    Recently, there has been an increased interest in flattening-filter-free (FFF) linear accelerators. Removal of the filter results in available dose rates up to 24 Gy min-1 (for nominal energy 10 MV in depth of maximum dose, a source-surface distance of 100 cm and a field size of 10×10 cm2). To guarantee accurate relative and reference dosimetry for the FFF beams, we investigated the charge collection efficiency of multiple air-vented and one liquid ionization chamber for dose rates up to 31.9 Gy min-1. For flattened beams, the ion-collection efficiency of all air-vented ionization chambers (except for the PinPoint chamber) was above 0.995. By removing the flattening filter, we found a reduction in collection efficiency of approximately 0.5-0.9% for a 10 MV beam. For FFF beams, the Markus chamber showed the largest collection efficiency of 0.994. The observed collection efficiencies were dependent on dose per pulse, but independent of the pulse repetition frequency. Using the liquid ionization chamber, the ion-collection efficiency for flattened beams was above 0.990 for all dose rates. However, this chamber showed a low collection efficiency of 0.940 for the FFF 10 MV beam at a dose rate of 31.9 Gy min-1. All investigated air-vented ionization chambers can be reliably used for relative dosimetry of FFF beams. The order of correction for reference dosimetry is given in the manuscript. Due to their increased saturation in high dose rate FFF beams, liquid ionization chambers appear to be unsuitable for dosimetry within these contexts.

  1. Transplantation immunology of the anterior chamber of the eye. II. Immune response to allogeneic cells.

    PubMed

    Kaplan, H J; Streilein, J W; Stevens, T R

    1975-09-01

    The mechanism by which the anterior chamber of the eye extends immunologic privilege to allogeneic donor tissues has been studied in inbred rats. Inoculation of allogeneic lymphoid cells into the anterior chamber demonstrated that although the site lacks a lymphatic drainage, the afferent limb of the immunologic reflex arc is intact because the recipient can recognize and mount a specific immune response. In addition, host immunity was able to express itself within the anterior chamber when induced systemically, indicating that the efferent limb of the reflex arc is also intact. Therefore, it is suggested that the unique immunologic features of the anterior chamber may result from the obligate intravenous presentation of graft antigen to the host's systemic immunologic apparatus, a route that prejudices the host's response in the direction of tolerance and/or enhancement rather than cell-mediated, tissue destructive immunity.

  2. Development of a Novel Contamination Resistant Ion Chamber for Process Tritium Measurement and Use in the JET First Trace Tritium Experiment

    SciTech Connect

    Worth, L.B.C.; Pearce, R.J.H.; Bruce, J.; Banks, J.; Scales, S.

    2005-07-15

    The accuracy of process measurements of tritium with conventional ion chambers is often affected by surface tritium contamination. The measurement of tritium in the exhaust of the JET torus is particularly difficult due to surface contamination with highly tritiated hydrocarbons. JET's first unsuccessful attempt to overcome the contamination problem was to use an ion chamber, with a heating element as the chamber wall so that it could be periodically decontaminated by baking. The newly developed ion chamber works on the principle of minimising the surface area within the boundary of the anode and cathode.This paper details the design of the ion chamber, which utilises a grid of 50-micron tungsten wire to define the ion chamber wall and the collector electrode. The effective surface area which, by contamination, is able to effect the measurement of tritium within the process gas has been reduced by a factor of {approx}200 over a conventional ion chamber. It is concluded that the new process ion chamber enables sensitive accurate tritium measurements free from contamination issues. It will be a powerful new tool for future tritium experiments both to improve tritium tracking and to help in the understanding of tritium retention issues.

  3. Experimental validation of a versatile system of CT dosimetry using a conventional ion chamber: Beyond CTDI{sub 100}

    SciTech Connect

    Dixon, Robert L.; Ballard, Adam C.

    2007-08-15

    This article is an experimental demonstration and authentication of a new method of computed tomography dosimetry [R. L. Dixon, Med. Phys. 30, 1272-1280 (2003)], which utilizes a short, conventional ion chamber rather than a pencil chamber, and which is more versatile than the latter. The value of CTDI{sub 100} correctly predicts the accumulated dose only for a total scan length L equal to 100 mm and underestimates the limiting equilibrium dose approached for longer, clinically relevant body scan lengths [R. L. Dixon, Med. Phys. 30, 1272-1280 (2003); K. D. Nakonechny, B. G. Fallone, and S. Rathee, Med. Phys. 32, 98-109 (2005); S. Mori, M. Endo, K. Nishizawa, T. Tsunoo, T. Aoyama, H. Fujiwara, and K. Murase, Med. Phys. 32, 1061-1069 (2005); R. L. Dixon, M. T. Munley, and E. Bayram, Med. Phys. 32, 3712-3728 (2005); R. L. Dixon, Med. Phys. 33, 3973-3976 (2006)]. Dixon [Med. Phys. 30, 1272-1280 (2003)] originally proposed an alternative using a short ion chamber and a helical scan acquisition to collect the same integral for any scan length L (and not limited 100 mm). The primary purpose of this work is to demonstrate experimentally the implementation, robustness, and versatility of this small ion chamber method in measuring the accumulated dose in the body phantom for any desired scan length L (up to the available phantom length) including the limiting equilibrium dose (symbolically CTDI{sub {infinity}}), and validation of the method against the pencil chamber methodology. Additionally, a simple and robust method for independently verifying the active length of a pencil chamber is described. The results of measurements made in a 400 mm long, 32 cm diameter polymethylmethacrylate body phantom using a small Farmer-type ion chamber and two pencil chambers of lengths l=100 and 150 mm confirm that the two methodologies provide the same dose values at the corresponding scan lengths L=l. The measured equilibrium doses obtained for GE MDCT scanners at 120 kVp are CTDI

  4. Filifactor alocis Infection and Inflammatory Responses in the Mouse Subcutaneous Chamber Model

    PubMed Central

    Wang, Qian; Jotwani, Ravi; Le, Junyi; Krauss, Jennifer L.; Potempa, Jan; Coventry, Susan C.

    2014-01-01

    Recent microbiome studies have implicated a role for Filifactor alocis in periodontal disease. In this study, we investigated the colonization and survival properties of F. alocis in a mouse subcutaneous chamber model of infection and characterized host innate immune responses. An infection of 109 F. alocis successfully colonized all chambers; however, the infection was cleared after 72 h. F. alocis elicited a local inflammatory response with neutrophils recruited into the chambers at 2 h postinfection along with an increase in levels of the proinflammatory cytokines interleukin 1β (IL-1β), IL-6, and tumor necrosis factor (TNF). F. alocis also induced apoptosis in chamber epithelial cells and neutrophils. Consistent with resolution of infection, neutrophil numbers and cytokine levels returned to baseline by 72 h. Fluorescent in situ hybridization (FISH) and quantitative PCR demonstrated that F. alocis exited the chambers and spread to the spleen, liver, lung, and kidney. Massive neutrophil infiltration was observed in the spleen and lungs, and the recruited neutrophils were in close proximity to the infecting bacteria. Significant epithelial injury was observed in the kidneys. Infection of all tissues was resolved after 7 days. This first in vivo study of the pathogenicity of F. alocis shows that in the chamber model the organism can establish a proinflammatory, proapoptotic local infection which is rapidly resolved by the host concordant with neutrophil influx. Moreover, F. alocis can spread to, and transiently infect, remote tissues where neutrophils can also be recruited. PMID:24379289

  5. Monte Carlo calculated correction factors for diodes and ion chambers in small photon fields.

    PubMed

    Czarnecki, D; Zink, K

    2013-04-21

    The application of small photon fields in modern radiotherapy requires the determination of total scatter factors Scp or field factors Ω(f(clin), f(msr))(Q(clin), Q(msr)) with high precision. Both quantities require the knowledge of the field-size-dependent and detector-dependent correction factor k(f(clin), f(msr))(Q(clin), Q(msr)). The aim of this study is the determination of the correction factor k(f(clin), f(msr))(Q(clin), Q(msr)) for different types of detectors in a clinical 6 MV photon beam of a Siemens KD linear accelerator. The EGSnrc Monte Carlo code was used to calculate the dose to water and the dose to different detectors to determine the field factor as well as the mentioned correction factor for different small square field sizes. Besides this, the mean water to air stopping power ratio as well as the ratio of the mean energy absorption coefficients for the relevant materials was calculated for different small field sizes. As the beam source, a Monte Carlo based model of a Siemens KD linear accelerator was used. The results show that in the case of ionization chambers the detector volume has the largest impact on the correction factor k(f(clin), f(msr))(Q(clin), Q(msr)); this perturbation may contribute up to 50% to the correction factor. Field-dependent changes in stopping-power ratios are negligible. The magnitude of k(f(clin), f(msr))(Q(clin), Q(msr)) is of the order of 1.2 at a field size of 1 × 1 cm(2) for the large volume ion chamber PTW31010 and is still in the range of 1.05-1.07 for the PinPoint chambers PTW31014 and PTW31016. For the diode detectors included in this study (PTW60016, PTW 60017), the correction factor deviates no more than 2% from unity in field sizes between 10 × 10 and 1 × 1 cm(2), but below this field size there is a steep decrease of k(f(clin), f(msr))(Q(clin), Q(msr)) below unity, i.e. a strong overestimation of dose. Besides the field size and detector dependence, the results reveal a clear dependence of the

  6. Monte Carlo calculated correction factors for diodes and ion chambers in small photon fields

    NASA Astrophysics Data System (ADS)

    Czarnecki, D.; Zink, K.

    2013-04-01

    The application of small photon fields in modern radiotherapy requires the determination of total scatter factors Scp or field factors \\Omega ^{f_{clin} ,f_{msr}}_{Q_{clin} ,Q_{msr}} with high precision. Both quantities require the knowledge of the field-size-dependent and detector-dependent correction factor k^{f_{clin} ,f_{msr}}_{Q_{clin} ,Q_{msr}}. The aim of this study is the determination of the correction factor k^{f_{clin} ,f_{msr}}_{Q_{clin} ,Q_{msr}} for different types of detectors in a clinical 6 MV photon beam of a Siemens KD linear accelerator. The EGSnrc Monte Carlo code was used to calculate the dose to water and the dose to different detectors to determine the field factor as well as the mentioned correction factor for different small square field sizes. Besides this, the mean water to air stopping power ratio as well as the ratio of the mean energy absorption coefficients for the relevant materials was calculated for different small field sizes. As the beam source, a Monte Carlo based model of a Siemens KD linear accelerator was used. The results show that in the case of ionization chambers the detector volume has the largest impact on the correction factor k^{f_{clin} ,f_{msr}}_{Q_{clin} ,Q_{msr}}; this perturbation may contribute up to 50% to the correction factor. Field-dependent changes in stopping-power ratios are negligible. The magnitude of k^{f_{clin} ,f_{msr}}_{Q_{clin} ,Q_{msr}} is of the order of 1.2 at a field size of 1 × 1 cm2 for the large volume ion chamber PTW31010 and is still in the range of 1.05-1.07 for the PinPoint chambers PTW31014 and PTW31016. For the diode detectors included in this study (PTW60016, PTW 60017), the correction factor deviates no more than 2% from unity in field sizes between 10 × 10 and 1 × 1 cm2, but below this field size there is a steep decrease of k^{f_{clin} ,f_{msr}}_{Q_{clin} ,Q_{msr}} below unity, i.e. a strong overestimation of dose. Besides the field size and detector dependence, the results

  7. On-line quality assurance of rotational radiotherapy treatment delivery by means of a 2D ion chamber array and the Octavius phantom

    SciTech Connect

    Esch, Ann van; Clermont, Christian; Devillers, Magali; Iori, Mauro; Huyskens, Dominique P.

    2007-10-15

    For routine pretreatment verification of innovative treatment techniques such as (intensity modulated) dynamic arc therapy and helical TomoTherapy, an on-line and reliable method would be highly desirable. The present solution proposed by TomoTherapy, Inc. (Madison, WI) relies on film dosimetry in combination with up to two simultaneous ion chamber point dose measurements. A new method is proposed using a 2D ion chamber array (Seven29, PTW, Freiburg, Germany) inserted in a dedicated octagonal phantom, called Octavius. The octagonal shape allows easy positioning for measurements in multiple planes. The directional dependence of the response of the detector was primarily investigated on a dual energy (6 and 18 MV) Clinac 21EX (Varian Medical Systems, Palo Alto, CA) as no fixed angle incidences can be calculated in the Hi-Art TPS of TomoTherapy. The array was irradiated from different gantry angles and with different arc deliveries, and the dose distributions at the level of the detector were calculated with the AAA (Analytical Anisotropic Algorithm) photon dose calculation algorithm implemented in Eclipse (Varian). For validation on the 6 MV TomoTherapy unit, rotational treatments were generated, and dose distributions were calculated with the Hi-Art TPS. Multiple cylindrical ion chamber measurements were used to cross-check the dose calculation and dose delivery in Octavius in the absence of the 2D array. To compensate for the directional dependence of the 2D array, additional prototypes of Octavius were manufactured with built-in cylindrically symmetric compensation cavities. When using the Octavius phantom with a 2 cm compensation cavity, measurements with an accuracy comparable to that of single ion chambers can be achieved. The complete Octavius solution for quality assurance of rotational treatments consists of: The 2D array, two octagonal phantoms (with and without compensation layer), an insert for nine cylindrical ion chambers, and a set of inserts of

  8. On-line quality assurance of rotational radiotherapy treatment delivery by means of a 2D ion chamber array and the Octavius phantom.

    PubMed

    Van Esch, Ann; Clermont, Christian; Devillers, Magali; Iori, Mauro; Huyskens, Dominique P

    2007-10-01

    For routine pretreatment verification of innovative treatment techniques such as (intensity modulated) dynamic arc therapy and helical TomoTherapy, an on-line and reliable method would be highly desirable. The present solution proposed by TomoTherapy, Inc. (Madison, WI) relies on film dosimetry in combination with up to two simultaneous ion chamber point dose measurements. A new method is proposed using a 2D ion chamber array (Seven29, PTW, Freiburg, Germany) inserted in a dedicated octagonal phantom, called Octavius. The octagonal shape allows easy positioning for measurements in multiple planes. The directional dependence of the response of the detector was primarily investigated on a dual energy (6 and 18 MV) Clinac 21EX (Varian Medical Systems, Palo Alto, CA) as no fixed angle incidences can be calculated in the Hi-Art TPS of TomoTherapy. The array was irradiated from different gantry angles and with different arc deliveries, and the dose distributions at the level of the detector were calculated with the AAA (Analytical Anisotropic Algorithm) photon dose calculation algorithm implemented in Eclipse (Varian). For validation on the 6 MV TomoTherapy unit, rotational treatments were generated, and dose distributions were calculated with the Hi-Art TPS. Multiple cylindrical ion chamber measurements were used to cross-check the dose calculation and dose delivery in Octavius in the absence of the 2D array. To compensate for the directional dependence of the 2D array, additional prototypes of Octavius were manufactured with built-in cylindrically symmetric compensation cavities. When using the Octavius phantom with a 2 cm compensation cavity, measurements with an accuracy comparable to that of single ion chambers can be achieved. The complete Octavius solution for quality assurance of rotational treatments consists of: The 2D array, two octagonal phantoms (with and without compensation layer), an insert for nine cylindrical ion chambers, and a set of inserts of

  9. Electret ion chamber-based passive radon-thoron discriminative monitors.

    PubMed

    Kotrappa, P; Steck, D

    2010-10-01

    Electret ion chambers (EICs), commercially available under brand name E-PERM(®), are widely used for measuring indoor and outdoor (222)Rn concentrations in air. These are designed to respond only to (222)Rn and not to (220)Rn by restricting diffusional entry area. Such radon EIC (R EIC) monitors are modified by increasing the entry area to allow (220)Rn, in addition to (222)Rn. Such modified units are called RT EIC. When a set of R and RT EICs are collocated, it is possible to discriminate and measure both radon and thoron concentrations, using appropriate calibration factors (CFs) and algorithms. The EICs come in different volumes, providing different sensitivities. The thoron CFs for 58-, 210- and 960-ml volume R and RT pairs are, respectively, 2.8-, 18.7- and 89-V drop per (kBq m(-3) d ), respectively. These provide much wider sensitivities and ranges compared to alpha track-based passive radon-thoron discriminative monitors.

  10. Radon exhalation rates from building materials using electret ion chamber radon monitors in accumulators.

    PubMed

    Kotrappa, Payasada; Stieff, Frederick

    2009-08-01

    An electret ion chamber (EIC) radon monitor in a sealed accumulator measures the integrated average radon concentration at the end of the accumulation duration. Theoretical equations have been derived to relate such radon concentrations (Bq m(-3) ) to the radon emanation rate (Bq d(-1)) from building materials enclosed in the accumulator. As an illustration, a 4-L sealable glass jar has been used as an accumulator to calculate the radon emanation rate from different granite samples. The radon emanation rate was converted into radon flux (Bq mm(-2) d(-1)) by dividing the emanation rate by surface area of the sample. Fluxes measured on typical, commercially available granites ranged from 20-30 Bq m(-2) d(-1). These results are similar to the results reported in the literature. The lower limit of detection for a 2-d measurement works out to be 7 Bq m(-2) d(-1). Equations derived can also be used for other sealable accumulators and other integrating detectors, such as alpha track detectors.

  11. 3D dose reconstruction for narrow beams using ion chamber array measurements.

    PubMed

    Schombourg, Karin; Bochud, François O; Mirimanoff, René-Olivier; Moeckli, Raphaël

    2012-06-01

    3D dose reconstruction is a verification of the delivered absorbed dose. Our aim was to describe and evaluate a 3D dose reconstruction method applied to phantoms in the context of narrow beams. A solid water phantom and a phantom containing a bone-equivalent material were irradiated on a 6 MV linac. The transmitted dose was measured by using one array of a 2D ion chamber detector. The dose reconstruction was obtained by an iterative algorithm. A phantom set-up error and organ interfraction motion were simulated to test the algorithm sensitivity. In all configurations convergence was obtained within three iterations. A local reconstructed dose agreement of at least 3% / 3mm with respect to the planned dose was obtained, except in a few points of the penumbra. The reconstructed primary fluences were consistent with the planned ones, which validates the whole reconstruction process. The results validate our method in a simple geometry and for narrow beams. The method is sensitive to a set-up error of a heterogeneous phantom and interfraction heterogeneous organ motion. Copyright © 2011. Published by Elsevier GmbH.

  12. Enhanced thermal emittance of space radiators by ion-discharge chamber texturing

    NASA Technical Reports Server (NTRS)

    Mirtich, Michael J.; Kussmaul, Michael T.

    1987-01-01

    The discharge chamber of a 30-cm argon ion source was successfully used to texture potential space radiator materials for the purpose of obtaining values of thermal emittance greater than 0.85 at 700 and 900 K. Some samples were also treated in acid prior to texturing. To evaluate the durability of the textured materials to atomic oxygen, samples were exposed to an RF air plasma environment. The spectral emittance between 2.0 anf 15.0 microns was measured before and after the textured materials were exposed to the plasma asher. The results indicate that copper with extremely high values of emittance after texturing (0.978 and 0.983) at 700 and 900 K, respectively,did not change its values of emittance after ashing, whereas the emittance of stainless steel fell below 0.85 after ashing. These data, along with scanning electron photomicrographs, and the results of texturing and ashing titanium and Nb(1)Zr are presented .

  13. Response of Materials to Single Ion Events

    SciTech Connect

    Zhang, Yanwen; Weber, William J.

    2009-05-01

    Response of materials to single radiation events is fundamental to research and many technological applications that involve energetic particles. Ion-solid interactions lead to energy loss of ions, production of electron-hole pairs, and light emission from excitation-induced luminescence. Employing a unique time-of-flight system, material response to single ion irradiation has been utilized to measure electronic energy loss, and to evaluate materials performance for radiation detection. Measurements of electronic energy loss of single ions in a thin ZrO2 foil over a continuous energy range exhibit good agreement with SRIM predictions for He and Be ions. For O and F ions, slight over- and under-estimation of SRIM prediction is evident at energies around 250 (near the stopping maximum) and above 800 keV/nucleon, respectively. For a Si semiconductor detector, its response to single ion irradiation shows that pulse height defect is clear for elements heavier than Si, and nonlinear energy response is significant for all elements at energies below ~ 150 keV/nucleon. For a single crystal CsI:Tl scintillator, the response to H ion events is used to determine relative light yield and absolute energy resolution over a wide energy region, where energy resolution of ~ 5.3% is achieved at 2 MeV.

  14. Single-chamber, rate-responsive pacemaker-mediated tachycardia

    PubMed Central

    Bohm, Adam; Kiss, Robert; Dorian, Paul; Pinter, Arnold

    2010-01-01

    The case of a patient with a unipolar VVIR, who developed a sensor-driven increased pacing rate at rest following pulse generator replacement, is presented. The cause was pectoral muscle stimulation, which triggered a sensor-driven rate response in the supine position. The possible causes and management are discussed. PMID:21076726

  15. Early and Late Responses to Ion Irradiation

    NASA Astrophysics Data System (ADS)

    Schulte, Reinhard; Ling, Ted

    Early and late responses to ion beam therapy (IBT) are the result of complex interactions between host, dose volume, and radiobiological factors. Our understanding of these early and late tissue responses has improved greatly with the accumulation of laboratory and clinical experience with proton and heavy ion irradiation. With photon therapy becoming increasingly conformal, many concepts developed for 3D conformal radiotherapy and intensity modulated radiation therapy with photons are also applicable to IBT. This chapter reviews basic concepts and experimental data of early and late tissue responses to protons and ions.

  16. Configuration of the electron transport algorithm of PENELOPE to simulate ion chambers

    NASA Astrophysics Data System (ADS)

    Sempau, J.; Andreo, P.

    2006-07-01

    The stability of the electron transport algorithm implemented in the Monte Carlo code PENELOPE with respect to variations of its step length is analysed in the context of the simulation of ion chambers used in photon and electron dosimetry. More precisely, the degree of violation of the Fano theorem is quantified (to the 0.1% level) as a function of the simulation parameters that determine the step size. To meet the premises of the theorem, we define an infinite graphite phantom with a cavity delimited by two parallel planes (i.e., a slab) and filled with a 'gas' that has the same composition as graphite but a mass density a thousand-fold smaller. The cavity walls and the gas have identical cross sections, including the density effect associated with inelastic collisions. Electrons with initial kinetic energies equal to 0.01, 0.1, 1, 10 or 20 MeV are generated in the wall and in the gas with a uniform intensity per unit mass. Two configurations, motivated by the design of pancake- and thimble-type chambers, are considered, namely, with the initial direction of emission perpendicular or parallel to the gas-wall interface. This version of the Fano test avoids the need of photon regeneration and the calculation of photon energy absorption coefficients, two ingredients that are common to some alternative definitions of equivalent tests. In order to reduce the number of variables in the analysis, a global new simulation parameter, called the speedup parameter (a), is introduced. It is shown that setting a = 0.2, corresponding to values of the usual PENELOPE parameters of C1 = C2 = 0.02 and values of WCC and WCR that depend on the initial and absorption energies, is appropriate for maximum tolerances of the order of 0.2% with respect to an analogue, i.e., interaction-by-interaction, simulation of the same problem. The precise values of WCC and WCR do not seem to be critical to achieve this level of accuracy. The step-size dependence of the absorbed dose is explained in

  17. Configuration of the electron transport algorithm of PENELOPE to simulate ion chambers.

    PubMed

    Sempau, J; Andreo, P

    2006-07-21

    The stability of the electron transport algorithm implemented in the Monte Carlo code PENELOPE with respect to variations of its step length is analysed in the context of the simulation of ion chambers used in photon and electron dosimetry. More precisely, the degree of violation of the Fano theorem is quantified (to the 0.1% level) as a function of the simulation parameters that determine the step size. To meet the premises of the theorem, we define an infinite graphite phantom with a cavity delimited by two parallel planes (i.e., a slab) and filled with a 'gas' that has the same composition as graphite but a mass density a thousand-fold smaller. The cavity walls and the gas have identical cross sections, including the density effect associated with inelastic collisions. Electrons with initial kinetic energies equal to 0.01, 0.1, 1, 10 or 20 MeV are generated in the wall and in the gas with a uniform intensity per unit mass. Two configurations, motivated by the design of pancake- and thimble-type chambers, are considered, namely, with the initial direction of emission perpendicular or parallel to the gas-wall interface. This version of the Fano test avoids the need of photon regeneration and the calculation of photon energy absorption coefficients, two ingredients that are common to some alternative definitions of equivalent tests. In order to reduce the number of variables in the analysis, a global new simulation parameter, called the speedup parameter (a), is introduced. It is shown that setting a = 0.2, corresponding to values of the usual PENELOPE parameters of C1 = C2 = 0.02 and values of WCC and WCR that depend on the initial and absorption energies, is appropriate for maximum tolerances of the order of 0.2% with respect to an analogue, i.e., interaction-by-interaction, simulation of the same problem. The precise values of WCC and WCR do not seem to be critical to achieve this level of accuracy. The step-size dependence of the absorbed dose is explained in

  18. Response of thermal ions to electromagnetic ion cyclotron waves

    NASA Technical Reports Server (NTRS)

    Anderson, B. J.; Fuselier, S. A.

    1994-01-01

    Electromagnetic ion cyclotron waves generated by 10 - 50 keV protons in the Earth's equatorial magnetosphere will interact with the ambient low-energy ions also found in this region. We examine H(+) and He(+) distribution functions from approx. equals 1 to 160 eV using the Hot Plasma Composition Experiment instrument on AMPTE/CCE to investigate the thermal ion response to the waves. A total of 48 intervals were chosen on the basis of electromagnetic ion cyclotron (EMIC) wave activity: 24 with prevalent EMIC waves and 24 with no EMIC waves observed on the orbit. There is a close correlation between EMIC waves and perpendicular heated ion distributions. For protons the perpendicular temperature increase is modest, about 5 eV, and is always observed at 90 deg pitch angles. This is consistent with a nonresonant interaction near the equator. By contrast, He(+) temperatures during EMIC wave events averaged 35 eV and sometimes exceeded 100 eV, indicating stronger interaction with the waves. Furthermore, heated He(+) ions have X-type distributions with maximum fluxes occurring at pitch angles intermediate between field-aligned and perpendicular directions. The X-type He(+) distributions are consistent with a gyroresonant interaction off the equator. The concentration of He(+) relative to H(+) is found to correlate with EMIC wave activity, but it is suggested that the preferential heating of He(+) accounts for the apparent increase in relative He(+) concentration by increasing the proportion of He(+) detected by the ion instrument.

  19. Response of thermal ions to electromagnetic ion cyclotron waves

    NASA Astrophysics Data System (ADS)

    Anderson, B. J.; Fuselier, S. A.

    1994-10-01

    Electromagnetic ion cyclotron waves generated by 10 - 50 keV protons in the Earth's equatorial magnetosphere will interact with the ambient low-energy ions also found in this region. We examine H(+) and He(+) distribution functions from approx. equals 1 to 160 eV using the Hot Plasma Composition Experiment instrument on AMPTE/CCE to investigate the thermal ion response to the waves. A total of 48 intervals were chosen on the basis of electromagnetic ion cyclotron (EMIC) wave activity: 24 with prevalent EMIC waves and 24 with no EMIC waves observed on the orbit. There is a close correlation between EMIC waves and perpendicular heated ion distributions. For protons the perpendicular temperature increase is modest, about 5 eV, and is always observed at 90 deg pitch angles. This is consistent with a nonresonant interaction near the equator. By contrast, He(+) temperatures during EMIC wave events averaged 35 eV and sometimes exceeded 100 eV, indicating stronger interaction with the waves. Furthermore, heated He(+) ions have X-type distributions with maximum fluxes occurring at pitch angles intermediate between field-aligned and perpendicular directions. The X-type He(+) distributions are consistent with a gyroresonant interaction off the equator. The concentration of He(+) relative to H(+) is found to correlate with EMIC wave activity, but it is suggested that the preferential heating of He(+) accounts for the apparent increase in relative He(+) concentration by increasing the proportion of He(+) detected by the ion instrument.

  20. Response of thermal ions to electromagnetic ion cyclotron waves

    NASA Technical Reports Server (NTRS)

    Anderson, B. J.; Fuselier, S. A.

    1994-01-01

    Electromagnetic ion cyclotron waves generated by 10 - 50 keV protons in the Earth's equatorial magnetosphere will interact with the ambient low-energy ions also found in this region. We examine H(+) and He(+) distribution functions from approx. equals 1 to 160 eV using the Hot Plasma Composition Experiment instrument on AMPTE/CCE to investigate the thermal ion response to the waves. A total of 48 intervals were chosen on the basis of electromagnetic ion cyclotron (EMIC) wave activity: 24 with prevalent EMIC waves and 24 with no EMIC waves observed on the orbit. There is a close correlation between EMIC waves and perpendicular heated ion distributions. For protons the perpendicular temperature increase is modest, about 5 eV, and is always observed at 90 deg pitch angles. This is consistent with a nonresonant interaction near the equator. By contrast, He(+) temperatures during EMIC wave events averaged 35 eV and sometimes exceeded 100 eV, indicating stronger interaction with the waves. Furthermore, heated He(+) ions have X-type distributions with maximum fluxes occurring at pitch angles intermediate between field-aligned and perpendicular directions. The X-type He(+) distributions are consistent with a gyroresonant interaction off the equator. The concentration of He(+) relative to H(+) is found to correlate with EMIC wave activity, but it is suggested that the preferential heating of He(+) accounts for the apparent increase in relative He(+) concentration by increasing the proportion of He(+) detected by the ion instrument.

  1. Characterization of Downstream Ion Energy Distributions From a High Current Hollow Cathode in a Ring Cusp Discharge Chamber

    NASA Technical Reports Server (NTRS)

    Foster, John E.; Patterson, Michael J.

    2003-01-01

    The presence of energetic ions produced by a hollow cathodes operating at high emission currents (greater than 10 Angstroms) has been documented in the literature. As part of an ongoing effort to uncover the underlying physics of the formation of these ions, ion efflux from a high current hollow cathode operating in an ion thruster discharge chamber was investigated. Using a spherical sector electrostatic energy analyzer located downstream of the discharge cathode, the ion energy distribution over a 0 to 60 eV energy range was measured. The sensitivity of the ion energy distribution function to zenith angle was also assessed at 3 different positions: 0, 15, and 25 degrees. The measurements suggest that the majority of the ion current at the measuring point falls into the analyzer with an energy approximately equal to the discharge voltage. The ion distribution, however, was found to be quite broad. The high energy tail of the distribution function tended to grow with increasing discharge current. Sensitivity of the profiles to flow rate at fixed discharge current was also investigated. A simple model is presented that provides a potential mechanism for the production of ions with energies above the discharge voltage.

  2. Effective point of measurement for parallel plate and cylindrical ion chambers in megavoltage electron beams.

    PubMed

    von Voigts-Rhetz, Philip; Czarnecki, Damian; Zink, Klemens

    2014-09-01

    The presence of an air filled ionization chamber in a surrounding medium introduces several fluence perturbations in high energy photon and electron beams which have to be accounted for. One of these perturbations, the displacement effect, may be corrected in two different ways: by a correction factor pdis or by the application of the concept of the effective point of measurement (EPOM). The latter means, that the volume averaged ionization within the chamber is not reported to the chambers reference point but to a point within the air filled cavity. Within this study the EPOM was determined for four different parallel plate and two cylindrical chambers in megavoltage electron beams using Monte Carlo simulations. The positioning of the chambers with this EPOM at the depth of measurement results in a largely depth independent residual perturbation correction, which is determined within this study for the first time. For the parallel plate chambers the EPOM is independent of the energy of the primary electrons. Whereas for the Advanced Markus chamber the position of the EPOM coincides with the chambers reference point, it is shifted for the other parallel plate chambers several tenths of millimeters downstream the beam direction into the air filled cavity. For the cylindrical chambers there is an increasing shift of the EPOM with increasing electron energy. This shift is in upstream direction, i.e. away from the chambers reference point toward the focus. For the highest electron energy the position of the calculated EPOM is in fairly good agreement with the recommendation given in common dosimetry protocols, for the smallest energy, the calculated EPOM positions deviate about 30% from this recommendation. Copyright © 2014. Published by Elsevier GmbH.

  3. Physical and chemical analysis of lithium-ion battery cell-to-cell failure events inside custom fire chamber

    NASA Astrophysics Data System (ADS)

    Spinner, Neil S.; Field, Christopher R.; Hammond, Mark H.; Williams, Bradley A.; Myers, Kristina M.; Lubrano, Adam L.; Rose-Pehrsson, Susan L.; Tuttle, Steven G.

    2015-04-01

    A 5-cubic meter decompression chamber was re-purposed as a fire test chamber to conduct failure and abuse experiments on lithium-ion batteries. Various modifications were performed to enable remote control and monitoring of chamber functions, along with collection of data from instrumentation during tests including high speed and infrared cameras, a Fourier transform infrared spectrometer, real-time gas analyzers, and compact reconfigurable input and output devices. Single- and multi-cell packages of LiCoO2 chemistry 18650 lithium-ion batteries were constructed and data was obtained and analyzed for abuse and failure tests. Surrogate 18650 cells were designed and fabricated for multi-cell packages that mimicked the thermal behavior of real cells without using any active components, enabling internal temperature monitoring of cells adjacent to the active cell undergoing failure. Heat propagation and video recordings before, during, and after energetic failure events revealed a high degree of heterogeneity; some batteries exhibited short burst of sparks while others experienced a longer, sustained flame during failure. Carbon monoxide, carbon dioxide, methane, dimethyl carbonate, and ethylene carbonate were detected via gas analysis, and the presence of these species was consistent throughout all failure events. These results highlight the inherent danger in large format lithium-ion battery packs with regards to cell-to-cell failure, and illustrate the need for effective safety features.

  4. Monte Carlo-based correction factors for ion chamber dosimetry in heterogeneous phantoms for megavoltage photon beams.

    PubMed

    Araki, Fujio

    2012-11-21

    The purpose of this study was to investigate the perturbation correction factors and inhomogeneity correction factors (ICFs) for a thin-walled cylindrical ion chamber in a heterogeneous phantom including solid water, lung and bone plastic materials. The perturbation factors due to the replacement of the air cavity, non-water equivalence of the wall and the stem, non-air equivalence of the central electrode and the overall perturbation factor, P(Q), for a cylindrical chamber, in the heterogeneous phantom were calculated with the EGSnrc/Cavity Monte Carlo code for 6 and 15 MV photon beams. The PTW31010 (0.125 cm(3)) chamber was modeled with Monte Carlo simulations, and was used for measurements and calculations of percentage depth ionization (PDI) or percentage depth dose (PDD). ICFs were calculated from the ratio of the product of the stopping power ratios (SPRs) and P(Q) of lung or bone to solid water. Finally, the measured PDIs were converted to PDDs by using ICFs and were compared with those calculated by the Monte Carlo method. The perturbation effect for the ion chamber in lung material is insignificant at 5 × 5 and 10 × 10 cm(2) fields, but the effect needs to be considered under conditions of lateral electron disequilibrium with a 3 × 3 cm(2) field. ICFs in lung varied up to 2% and 4% depending on the field size for 6 and 15 MV, respectively. For bone material, the perturbation effects due to the chamber wall and the stem were more significant at up to 3.5% and 1.6% for 6 MV, respectively. ICFs for bone material were approximately 0.945 and 0.940 for 6 and 15 MV, respectively. The converted PDDs by using ICFs were in good agreement with Monte Carlo calculated PDDs. The chamber perturbation correction and SPRs should strictly be considered for ion chamber dosimetry in heterogeneous media. This is more important for small field dosimetry in lung and bone materials.

  5. Response to albuterol MDI delivered through an anti-static chamber during nocturnal bronchospasm.

    PubMed

    Prabhakaran, Sreekala; Shuster, Jonathan; Chesrown, Sarah; Hendeles, Leslie

    2012-08-01

    Decreasing electrostatic charge on valved holding chambers increases the amount of drug delivered. However, there are no data demonstrating that this increases bronchodilatation. To investigate the influence of reducing electrostatic charge on the bronchodilator response to albuterol inhaler during nocturnal bronchospasm. This randomized double-blind, double-dummy crossover study included subjects, 18-40 years old, with nocturnal bronchospasm (20% overnight decrease in peak flow on 3 of 7 nights during run-in), FEV(1) 60-80% predicted during the day, and ≥ 12% increase after albuterol. Subjects slept in the clinical research center up to 3 nights for each treatment. FEV(1) and heart rate were measured upon awakening spontaneously or at 4:00 am, and 15 min after each dose of 1, 2, and 4 cumulative puffs of albuterol via metered-dose inhaler. The drug was administered through an anti-static valved holding chamber (AeroChamber Plus Z-Stat) or a conventional valved holding chamber containing a static charge (AeroChamber Plus). Of 88 consented subjects, 11 were randomized and 7 completed the study. Most exclusions were due to lack of objective evidence of nocturnal bronchospasm. Upon awakening, FEV(1) was 44 ± 9% of predicted before the anti-static chamber and 48 ± 7% of predicted before the static chamber. The mean ± SD percent increase in FEV(1) after 1, 2, and 4 cumulative puffs using the anti-static versus the static chamber, respectively, were 52 ± 26% versus 30 ± 19%, 73 ± 28% versus 48 ± 26%, and 90 ± 34% versus 64 ± 35%. The point estimates for the differences (and 95% CIs) between the devices (anti-static vs static) were 21% (4-38%) (P = .03), 23% (6-41%) (P = .02), and 25% (7-42%) (P = .01) for 1, 2, and 4 cumulative puffs, respectively. There was no significant difference in heart rate between treatments. Delivery of albuterol through an anti-static chamber provides a clinically relevant improvement in bronchodilator response during acute

  6. The response of prototype plane-parallel ionization chambers in small megavoltage x-ray fields.

    PubMed

    McNiven, Andrea L; Mulligan, Matt; Kron, Tomas; Battista, Jerry J

    2006-11-01

    Accurate small-field dosimetry has become important with the use of multiple small fields in modern radiotherapy treatments such as IMRT and stereotactic radiosurgery. In this study, we investigate the response of a set of prototype plane-parallel ionization chambers, based upon the Exradin T11 chamber, with active volume diameters of 2, 4, 10, and 20 mm, exposed to 6 MV stereotactic radiotherapy x-ray fields. Our goal was to assess their usefulness for accurate small x-ray field dose measurements. The relative ionization response was measured in circular fields (0.5 to 4 cm diameter) as compared to a 10 x 10 cm2 reference field. A large discrepancy (approximately 40%) was found between the relative response in the smallest plane-parallel chamber and other small volume dosimeters (radiochromic film, micro-metal-oxide-semiconductor field-effect transistor and diode) used for comparison. Monte Carlo BEAMnrc simulations were used to simulate the experimental setup in order to investigate the cause of the under-response and to calculate appropriate correction factors that could be applied to experimental measurements. It was found that in small fields, the air cavity of these custom-made research chambers perturbed the secondary electron fluence profile significantly, resulting in decreased fluence within the active volume, which in turn produces a chamber under-response. It is demonstrated that a large correction to the p(fl) correction factor would be required to improve dosimetric accuracy in small fields, and that these factors could be derived using Monte Carlo simulations.

  7. Stability of A-150 plastic ionization chamber response over a ~30 year period

    SciTech Connect

    Kroc, Thomas K.; Lennox, Arlene J.; /Fermilab

    2007-08-01

    At the NIU Institute for Neutron Therapy at Fermilab, the clinical tissue-equivalent ionization chamber response is measured every treatment day using a cesium source that was configured to match readings obtained at the National Bureau of Standards. Daily measurements are performed in air using the air-to-tissue dose conversion factors given in AAPM Report no. 7. The measured exposure calibration factors have been tabulated and graphed as a function of time from 1978 to present. For A-150 plastic ionization chambers, these factors exhibit a sinusoidal variation with a period of approximately one year and amplitude of {+-} 1%. This variation, attributable to the hygroscopic nature of A-150 plastic, is correlated with the relative humidity of the facility, and is greater than the humidity corrections for gas described in the literature. Our data suggest that chamber calibration should be performed at least weekly to accommodate these variations.

  8. Monte Carlo calculation of the ionization chamber response to 60Co beam using PENELOPE.

    PubMed

    Yi, Chul-Young; Hah, Suck-Ho; Yeom, Min Sun

    2006-05-01

    The calculation of the ionization chamber response is one of key factors to develop a primary standard of air kerma. Using Monte Carlo code PENELOPE, we simulated the cavity response of the plane parallel ionization chamber to the monoenergetic 60Co beam incident normally on a flat surface of the chamber. Two simulation techniques, namely, the uniform interaction technique and the reentrance technique, were introduced. The effect of the input parameters such as C1 (average angular deflection in a single step between hard elastic events), C2 (maximum average fractional energy loss in a step), S(max) (maximum step length) and W(cc) (the lower energy of secondary electrons created as a result of a hard collision) on the simulated cavity dose was evaluated. We found that the simulated cavity response of the graphite and solid air chambers obtained by PENELOPE to the monoenergetic 60Co beam could be consistent with the value expected from the cross-sections of PENELOPE to within 0.2% (one standard deviation) when W(cc) and S(max) were selected carefully.

  9. Diamond detector versus silicon diode and ion chamber in photon beams of different energy and field size.

    PubMed

    Bucciolini, M; Buonamici, F Banci; Mazzocchi, S; De Angelis, C; Onori, S; Cirrone, G A P

    2003-08-01

    The aim of this work was to test the suitability of a PTW diamond detector for nonreference condition dosimetry in photon beams of different energy (6 and 25 MV) and field size (from 2.6 cm x 2.6 cm to 10 cm x 10 cm). Diamond behavior was compared to that of a Scanditronix p-type silicon diode and a Scanditronix RK ionization chamber. Measurements included output factors (OF). percentage depth doses (PDD) and dose profiles. OFs measured with diamond detector agreed within 1% with those measured with diode and RK chamber. Only at 25 MV, for the smallest field size, RK chamber underestimated OFs due to averaging effects in a pointed shaped beam profile. Agreement was found between PDDs measured with diamond detector and RK chamber for both 6 MV and 25 MV photons and down to 5 cm x 5 cm field size. For the 2.6 cm x 2.6 cm field size, at 25 MV, RK chamber underestimated doses at shallow depth and the difference progressively went to zero in the distal region. PDD curves measured with silicon diode and diamond detector agreed well for the 25 MV beam at all the field sizes. Conversely, the nontissue equivalence of silicon led, for the 6 MV beam, to a slight overestimation of the diode doses in the distal region, at all the field sizes. Penumbra and field width measurements gave values in agreement for all the detectors but with a systematic overestimate by RK measurements. The results obtained confirm that ion chamber is not a suitable detector when high spatial resolution is required. On the other hand, the small differences in the studied parameters, between diamond and silicon systems, do not lead to a significant advantage in the use of diamond detector for routine clinical dosimetry.

  10. Development of a root feeding system based on a fiber ion-exchange substrate for space plant growth chamber "Vitacycle".

    PubMed

    Berkovich, Yu A; Krivobok, N M; Krivobok, S M; Matusevich, V V; Soldatov, V S

    2003-01-01

    Selecting a plant root nutrient delivery system is one of the key aspects of designing root modules for space plant growth chambers. This article examines a number of the nutrient delivery systems and shows the most suitable technique for providing nutrients to roots in microgravity, which to date are ion-exchange artificial soils. In addition, this article characterizes the ion composition and hydrophysical parameters of a new Russian artificial ion charged fiber substrate, BIONA-V3. The BIONA-V3 substrate is comprised of ion-exchange resin fibers. The experimental data concerning the effects of anionic and cationic components on plant biomass is presented. Preliminary experiments with BIONA-V3 showed that 1 kg of dry BIONA-V3 produces up to 2.4 kg (fresh mass) of cabbage leaf or 180 g of dry plant mass per 1 dm3 of the substrate. Therefore, the root zone volume can be as small as 120 cm3 per plant. Further optimizing the nutrient composition of the resin fibers can increase space plant growth chamber productivity.

  11. The effect of ambient pressure on well chamber response: Monte Carlo calculated results for the HDR 1000 plus.

    PubMed

    Bohm, Tim D; Griffin, Sheridan L; DeLuca, Paul M; DeWerd, Larry A

    2005-04-01

    The determination of the air kerma strength of a brachytherapy seed is necessary for effective treatment planning. Well ionization chambers are used on site at therapy clinics to determine the air kerma strength of seeds. In this work, the response of the Standard Imaging HDR 1000 Plus well chamber to ambient pressure is examined using Monte Carlo calculations. The experimental work examining the response of this chamber as well as other chambers is presented in a companion paper. The Monte Carlo results show that for low-energy photon sources, the application of the standard temperature pressure PTP correction factor produces an over-response at the reduced air densities/pressures corresponding to high elevations. With photon sources of 20 to 40 keV, the normalized PTP corrected chamber response is as much as 10% to 20% over unity for air densities/pressures corresponding to an elevation of 3048 m (10000 ft) above sea level. At air densities corresponding to an elevation of 1524 m (5000 ft), the normalized PTP-corrected chamber response is 5% to 10% over unity for these photon sources. With higher-energy photon sources (>100 keV), the normalized PTP corrected chamber response is near unity. For low-energy beta sources of 0.25 to 0.50 MeV, the normalized PTP-corrected chamber response is as much as 4% to 12% over unity for air densities/pressures corresponding to an elevation of 3048 m (10000 ft) above sea level. Higher-energy beta sources (>0.75 MeV) have a normalized PTP corrected chamber response near unity. Comparing calculated and measured chamber responses for common 103Pd- and 125I-based brachytherapy seeds show agreement to within 2.7% and 1.9%, respectively. Comparing MCNP calculated chamber responses with EGSnrc calculated chamber responses show agreement to within 3.1% at photon energies of 20 to 40 keV. We conclude that Monte Carlo transport calculations accurately model the response of this well chamber. Further, applying the standard PTP correction

  12. The effect of ambient pressure on well chamber response: Monte Carlo calculated results for the HDR 1000 Plus

    SciTech Connect

    Bohm, Tim D.; Griffin, Sheridan L.; DeLuca, Paul M. Jr.; DeWerd, Larry A.

    2005-04-01

    The determination of the air kerma strength of a brachytherapy seed is necessary for effective treatment planning. Well ionization chambers are used on site at therapy clinics to determine the air kerma strength of seeds. In this work, the response of the Standard Imaging HDR 1000 Plus well chamber to ambient pressure is examined using Monte Carlo calculations. The experimental work examining the response of this chamber as well as other chambers is presented in a companion paper. The Monte Carlo results show that for low-energy photon sources, the application of the standard temperature pressure P{sub TP} correction factor produces an over-response at the reduced air densities/pressures corresponding to high elevations. With photon sources of 20 to 40 keV, the normalized P{sub TP} corrected chamber response is as much as 10% to 20% over unity for air densities/pressures corresponding to an elevation of 3048 m (10000 ft) above sea level. At air densities corresponding to an elevation of 1524 m (5000 ft), the normalized P{sub TP}-corrected chamber response is 5% to 10% over unity for these photon sources. With higher-energy photon sources (>100 keV), the normalized P{sub TP} corrected chamber response is near unity. For low-energy {beta} sources of 0.25 to 0.50 MeV, the normalized P{sub TP}-corrected chamber response is as much as 4% to 12% over unity for air densities/pressures corresponding to an elevation of 3048 m (10000 ft) above sea level. Higher-energy {beta} sources (>0.75 MeV) have a normalized P{sub TP} corrected chamber response near unity. Comparing calculated and measured chamber responses for common {sup 103}Pd- and {sup 125}I-based brachytherapy seeds show agreement to within 2.7% and 1.9%, respectively. Comparing MCNP calculated chamber responses with EGSnrc calculated chamber responses show agreement to within 3.1% at photon energies of 20 to 40 keV. We conclude that Monte Carlo transport calculations accurately model the response of this well

  13. Technical Note: Influence of Compton currents on profile measurements in small-volume ion chambers

    SciTech Connect

    Tanny, Sean; Sperling, Nicholas; Parsai, E. Ishmael; Holmes, Shannon

    2015-10-15

    Purpose: This work is to evaluate the effects of Compton current generation in three small-volume ionization chambers on measured beam characteristics for electron fields. Methods: Beam scans were performed using Exradin A16, A26, and PTW 31014 microchambers. Scans with varying chamber components shielded were performed. Static point measurements, output factors, and cable only irradiations were performed to determine the contribution of Compton currents to various components of the chamber. Monte Carlo simulations were performed to evaluate why one microchamber showed a significant reduction in Compton current generation. Results: Beam profiles demonstrated significant distortion for two of the three chambers when scanned parallel to the chamber axis, produced by electron deposition within the wire. Measurements of ionization produced within the cable identified Compton current generation as the cause of these distortions. The size of the central collecting wire was found to have the greatest influence on the magnitude of Compton current generation. Conclusions: Microchambers can demonstrate significant (>5%) deviations from properties as measured with larger volume chambers (0.125 cm{sup 3} and above). These deviations can be substantially reduced by averaging measurements conducted at opposite polarities.

  14. SU-E-T-118: Dose Verification for Accuboost Applicators Using TLD, Ion Chamber and Gafchromic Film Measurements

    SciTech Connect

    Chisela, W; Yao, R; Dorbu, G

    2014-06-01

    Purpose: To verify dose delivered with HDR Accuboost applicators using TLD, ion chamber and Gafchromic film measurements and to examine applicator leakage. Methods: A microSelectron HDR unit was used to deliver a dose of 50cGy to the mid-plane of a 62mm thick solid water phantom using dwell times from Monte Carlo pre-calculated nomograms for a 60mm, 70mm Round and 60mm Skin-Dose Optimized (SDO) applicators respectively. GafChromic EBT3+ film was embedded in the phantom midplane horizontally to measure dose distribution. Absolute dose was also measured with TLDs and an ADCL calibrated parallel-plate ion chamber placed in the film plane at field center for each applicator. The film was calibrated using 6MV x-ray beam. TLDs were calibrated in a Cs-137 source at UW-Madison calibration laboratory. Radiation leakage through the tungsten alloy shell was measured with a film wrapped around outside surface of a 60mm Round applicator. Results: Measured maximum doses at field center are consistently lower than predicated by 5.8% for TLD, 8.8% for ion chamber, and 2.6% for EBT3+ film on average, with measurement uncertainties of 2.2%, 0.3%, and 2.9% for TLD, chamber, film respectively. The total standard uncertainties for ion chamber and Gafchromic film measurement are 4.9% and 4.6% respectively[1]. The area defined by the applicator aperture was covered by 80% of maximum dose for 62mm compression thickness. When 100cGy is delivered to mid-plane with a 60mm Round applicator, surface dose ranges from 60cGy to a maximum of 145cGy, which occurs at source entrance to the applicator. Conclusion: Measured doses by all three techniques are consistently lower than predicted in our measurements. For a compression thickness of 62 mm, the field size defined by the applicator is only covered by 80% of prescribed dose. Radiation leakage of up to 145cGy was found at the source entrance of applicators.

  15. A zero-power warming chamber for investigating plant responses to rising temperature

    NASA Astrophysics Data System (ADS)

    Lewin, Keith F.; McMahon, Andrew M.; Ely, Kim S.; Serbin, Shawn P.; Rogers, Alistair

    2017-09-01

    Advances in understanding and model representation of plant and ecosystem responses to rising temperature have typically required temperature manipulation of research plots, particularly when considering warming scenarios that exceed current climate envelopes. In remote or logistically challenging locations, passive warming using solar radiation is often the only viable approach for temperature manipulation. However, current passive warming approaches are only able to elevate the mean daily air temperature by ˜ 1.5 °C. Motivated by our need to understand temperature acclimation in the Arctic, where warming has been markedly greater than the global average and where future warming is projected to be ˜ 2-3 °C by the middle of the century; we have developed an alternative approach to passive warming. Our zero-power warming (ZPW) chamber requires no electrical power for fully autonomous operation. It uses a novel system of internal and external heat exchangers that allow differential actuation of pistons in coupled cylinders to control chamber venting. This enables the ZPW chamber venting to respond to the difference between the external and internal air temperatures, thereby increasing the potential for warming and eliminating the risk of overheating. During the thaw season on the coastal tundra of northern Alaska our ZPW chamber was able to elevate the mean daily air temperature 2.6 °C above ambient, double the warming achieved by an adjacent passively warmed control chamber that lacked our hydraulic system. We describe the construction, evaluation and performance of our ZPW chamber and discuss the impact of potential artefacts associated with the design and its operation on the Arctic tundra. The approach we describe is highly flexible and tunable, enabling customization for use in many different environments where significantly greater temperature manipulation than that possible with existing passive warming approaches is desired.

  16. A zero-power warming chamber for investigating plant responses to rising temperature

    DOE PAGES

    Lewin, Keith F.; McMahon, Andrew M.; Ely, Kim S.; ...

    2017-09-19

    Advances in understanding and model representation of plant and ecosystem responses to rising temperature have typically required temperature manipulation of research plots, particularly when considering warming scenarios that exceed current climate envelopes. In remote or logistically challenging locations, passive warming using solar radiation is often the only viable approach for temperature manipulation. But, current passive warming approaches are only able to elevate the mean daily air temperature by ~1.5 °C. Motivated by our need to understand temperature acclimation in the Arctic, where warming has been markedly greater than the global average and where future warming is projected to be ~2–3more » °C by the middle of the century; we have developed an alternative approach to passive warming. Our zero-power warming (ZPW) chamber requires no electrical power for fully autonomous operation. It uses a novel system of internal and external heat exchangers that allow differential actuation of pistons in coupled cylinders to control chamber venting. This enables the ZPW chamber venting to respond to the difference between the external and internal air temperatures, thereby increasing the potential for warming and eliminating the risk of overheating. During the thaw season on the coastal tundra of northern Alaska our ZPW chamber was able to elevate the mean daily air temperature 2.6 °C above ambient, double the warming achieved by an adjacent passively warmed control chamber that lacked our hydraulic system. We describe the construction, evaluation and performance of our ZPW chamber and discuss the impact of potential artefacts associated with the design and its operation on the Arctic tundra. Our approach is highly flexible and tunable, enabling customization for use in many different environments where significantly greater temperature manipulation than that possible with existing passive warming approaches is desired.« less

  17. Consistency of absorbed dose to water measurements using 21 ion-chamber models following the AAPM TG51 and TG21 calibration protocols.

    PubMed

    Tailor, Ramesh C; Hanson, William F; Wells, Nathan; Ibbott, Geoffrey S

    2006-06-01

    In 1999, the AAPM introduced a reference dosimetry protocol, known as TG51, based on an absorbed dose standard. This replaced the previous protocol, known as TG21, which was based on an air kerma standard. A significant body of literature has emerged discussing the improved accuracy and robustness of the absorbed dose standard, and quantifying the changes in baseline dosimetry with the introduction of the absorbed dose protocol. A significant component playing a role in the overall accuracy of beam output determination is the variability due to the use of different dosimeters. This issue, not adequately addressed in the past, is the focus of the present study. This work provides a comparison of absorbed dose determinations using 21 different makes and models of ion chambers for low- and high-energy photon and electron beams. The study included 13 models of cylindrical ion chambers and eight models of plane-parallel chambers. A high degree of precision (<0.25%) resulted from measurements with all chambers in a single setting, a sufficient number of repeat readings, and the use of high quality ion chambers as external monitors. Cylindrical chambers in photon beams show an improvement in chamber-to-chamber consistency with TG51. For electron dosimetry with plane-parallel chambers, the parameters Ngas and the product ND,w x k(ecal) were each determined in two ways, based on (i) an ADCL calibration, and (ii) a cross comparison with an ADCL-calibrated cylindrical chamber in a high-energy electron beam. Plane-parallel chamber results, therefore, are presented for both methods of chamber calibration. Our electron results with technique (i) show that plane-parallel chambers, as a group, overestimate the beam output relative to cylindrical chambers by 1%-2% with either protocol. Technique (ii), by definition, normalizes the plane-parallel results to the cylindrical results. In all cases, the maximum spread in output from the various cylindrical chambers is <2% implying a

  18. A combined segmented anode gas ionization chamber and time-of-flight detector for heavy ion elastic recoil detection analysis

    NASA Astrophysics Data System (ADS)

    Ström, Petter; Petersson, Per; Rubel, Marek; Possnert, Göran

    2016-10-01

    A dedicated detector system for heavy ion elastic recoil detection analysis at the Tandem Laboratory of Uppsala University is presented. Benefits of combining a time-of-flight measurement with a segmented anode gas ionization chamber are demonstrated. The capability of ion species identification is improved with the present system, compared to that obtained when using a single solid state silicon detector for the full ion energy signal. The system enables separation of light elements, up to Neon, based on atomic number while signals from heavy elements such as molybdenum and tungsten are separated based on mass, to a sample depth on the order of 1 μm. The performance of the system is discussed and a selection of material analysis applications is given. Plasma-facing materials from fusion experiments, in particular metal mirrors, are used as a main example for the discussion. Marker experiments using nitrogen-15 or oxygen-18 are specific cases for which the described improved species separation and sensitivity are required. Resilience to radiation damage and significantly improved energy resolution for heavy elements at low energies are additional benefits of the gas ionization chamber over a solid state detector based system.

  19. A TPC (Time Projection Chamber) detector for the study of high multiplicity heavy ion collisions

    SciTech Connect

    Rai, G.; Arthur, A.; Bieser, F.; Harnden, C.W.; Jones, R.; Klienfelder, S.; Lee, K.; Matis, H.S.; Nakamura, M.; McParland, C.; Nesbitt, D.; Odyniec, G.; Olson, D.; Pugh, H.G.; Ritter, H.G.; Symons, T.J.M.; Wieman, H.; Wright, M.; Wright, R. ); Rudge, A. )

    1990-01-01

    The design of a Time Projection Chamber (TPC) detector with complete pad coverage is presented. The TPC will allow the measurements of high multiplicity ({approx} 200 tracks) relativistic nucleus-nucleus collisions initiated with the heaviest, most energetic projectiles available at the LBL BEVALAC accelerator facility. The front end electronics, composed of over 15,000 time sampling channels, will be located on the chamber. The highly integrated, custom designed, electronics and the VME based data acquisition system are described. 10 refs., 8 figs., 1 tab.

  20. Modeling of life limiting phenomena in the discharge chamber of an electron bombardment ion thruster

    NASA Technical Reports Server (NTRS)

    Handoo, Arvind K.; Ray, Pradosh K.

    1991-01-01

    An experimental facility to study the low energy sputtering of metal surfaces with ions produced by an ion gun is described. The energy of the ions ranged from 10 to 500 eV. Cesium ions with energies from 100 to 500 eV were used initially to characterize the operation of the ion gun. Next, argon and xenon ions were used to measure the sputtering yields of cobalt (Co), Cadmium (Cd), and Chromium (Cr) at an operating temperature of 2x10(exp -5) Torr. The ion current ranged from 0.0135 micro-A at 500 eV. The targets were electroplated on a copper substrate. The surface density of the electroplated material was approx. 50 micro-g/sq cm. The sputtered atoms were collected on an aluminum foil surrounding the target. Radioactive tracers were used to measure the sputtering yields. The sputtering yields of Cr were found to be much higher than those of Co and Cd. The yields of Co and Cd were comparable, with Co providing the higher yields. Co and Cd targets were observed to sputter at energies as low as 10 eV for both argon and xenon ions. The Cr yields could not be measured below 20 eV for argon ions and 15 eV for xenon ions. On a linear scale the yield energy curves near the threshold energies exhibit a concave nature.

  1. Response of synthetic diamond detectors in proton, carbon, and oxygen ion beams.

    PubMed

    Rossomme, Séverine; Marinelli, Marco; Verona-Rinati, Gianluca; Romano, Francesco; Cirrone, Pablo Antonio Giuseppe; Kacperek, Andrzej; Vynckier, Stefaan; Palmans, Hugo

    2017-07-15

    In this work, the LET-dependence of the response of synthetic diamond detectors is investigated in different particle beams. Measurements were performed in three nonmodulated particle beams (proton, carbon, and oxygen). The response of five synthetic diamond detectors was compared to the response of a Markus or an Advanced Markus ionization chamber. The synthetic diamond detectors were used with their axis parallel to the beam axis and without any bias voltage. A high bias voltage was applied to the ionization chambers, to minimize ion recombination, for which no correction is applied (+300 V and +400 V were applied to the Markus and Advanced Markus ionization chambers respectively). The ratio between the normalized response of the synthetic diamond detectors and the normalized response of the ionization chamber shows an under-response of the synthetic diamond detectors in carbon and oxygen ion beams. No under-response of the synthetic diamond detectors is observed in protons. For each beam, combining results obtained for the five synthetic diamond detectors and considering the uncertainties, a linear fit of the ratio between the normalized response of the synthetic diamond detectors and the normalized response of the ionization chamber is determined. The response of the synthetic diamond detectors can be described as a function of LET as (-6.22E-4 ± 3.17E-3) • LET + (0.99 ± 0.01) in proton beam, (-2.51E-4 ± 1.18E-4) • LET + (1.01 ± 0.01) in carbon ion beam and (-2.77E-4 ± 0.56E-4) • LET + (1.03 ± 0.01) in oxygen ion beam. Combining results obtained in carbon and oxygen ion beams, a LET dependence of about 0.026% (±0.013%) per keV/μm is estimated. Due to the high LET value, a LET dependence of the response of the synthetic diamond detector was observed in the case of carbon and oxygen beams. The effect was found to be negligible in proton beams, due to the low LET value. The under-response of the synthetic diamond detector may result from the

  2. Signal generator exciting an electromagnetic field for ion beam transport to the vacuum chamber of a mass spectrometer

    NASA Astrophysics Data System (ADS)

    Tubol'tsev, Yu. V.; Kogan, V. T.; Bogdanov, A. A.; Chichagov, Yu. V.; Antonov, A. S.

    2015-02-01

    A high-voltage high-frequency signal generator is described that excites an electric field for ion beam transport from an ion source to the vacuum chamber of a mass spectrometer. Excitation signals to the number of two are high-frequency sine-wave out-of-phase signals with the same amplitudes. The amplitude and phase of the signals vary from 20 to 100 V and from 10 kHz to 1 MHz, respectively. The generator also produces a controlled bias voltage in the interval 50-200 V. The frequency and amplitude of the signals, as well as the bias voltage, are computer-controlled via the USB interface.

  3. The Chamber for Studying Rice Response to Elevated Nighttime Temperature in Field

    PubMed Central

    Chen, Song; Zheng, Xi; Wang, Dangying; Xu, Chunmei; Laza, Ma. Rebecca C.; Zhang, Xiufu

    2013-01-01

    An in situ temperature-controlled field chamber was developed for studying a large population of rice plant under different nighttime temperature treatments while maintaining conditions similar to those in the field during daytime. The system consists of a pipe hoop shed-type chamber with manually removable covers manipulated to provide a natural environment at daytime and a relatively stable and accurate temperature at night. Average air temperatures of 22.4 ± 0.3°C at setting of 22°C, 27.6 ± 0.4°C at 27°C, and 23.8 ± 0.7°C ambient conditions were maintained with the system. No significant horizontal and vertical differences in temperature were found and only slight changes in water temperatures were observed between the chambers and ambient conditions at 36 days after transplanting. A slight variation in CO2 concentration was observed at the end of the treatment during the day, but the 10-μmol CO2 mol−1 difference was too small to alter plant response. The present utilitarian system, which only utilizes an air conditioner/heater, is suitable for studying the effect of nighttime temperature on plant physiological responses with minimal perturbation of other environmental factors. At the same time, it will enable in situ screening of many rice genotypes. PMID:24089603

  4. A pressurized ion chamber monitoring system for environmental radiation measurements utilizing a wide-range temperature-compensated electrometer

    SciTech Connect

    Stevenick, W. Van . Environmental Measurements Lab.)

    1994-08-01

    The performance of a complete pressurized ion chamber (PIC) radiation monitoring system is described. The design incorporates an improved temperature-compensated electrometer which is stable to [+-]3 [center dot] 10[sup [minus]16] A over the environmental range of temperature ([minus]40 to +40 C). Using a single 10[sup 11] [Omega] feed-back resistor, the electrometer accurately measures currents over a range from 3 [center dot] 10[sup [minus]15] A to 3 [center dot] 10[sup [minus]11] A. While retaining the sensitivity of the original PIC system (the instrument responds readily to small background fluctuations on the order of 0.1 [mu]R h[sup [minus]1]), the new system measures radiation levels up to the point where the collection efficiency of the ion chamber begins to drop off, typically [approximately]27 pA at 1 mR h[sup [minus]1]. A data recorder and system controller was designed using the Tattletale[trademark] Model 4A computer. Digital data is stored on removable solid-state, credit-card style memory cards.

  5. Measurement of changes in linear accelerator photon energy through flatness variation using an ion chamber array

    SciTech Connect

    Gao Song; Balter, Peter A.; Rose, Mark; Simon, William E.

    2013-04-15

    Purpose: To compare the use of flatness versus percent depth dose (PDD) for determining changes in photon beam energy for a megavoltage linear accelerator. Methods: Energy changes were accomplished by adjusting the bending magnet current by up to {+-}15% in 5% increments away from the value used clinically. Two metrics for flatness, relative flatness in the central 80% of the field (Flat) and average maximum dose along the diagonals normalized by central axis dose (F{sub DN}), were measured using a commercially available planner ionization chamber array. PDD was measured in water at depths of 5 and 10 cm in 3 Multiplication-Sign 3 cm{sup 2} and 10 Multiplication-Sign 10 cm{sup 2} fields using a cylindrical chamber. Results: PDD was more sensitive to changes in energy when the beam energy was increased than when it was decreased. For the 18-MV beam in particular, PDD was not sensitive to energy reductions below the nominal energy. The value of Flat was found to be more sensitive to decreases in energy than to increases, with little sensitivity to energy increases above the nominal energy for 18-MV beams. F{sub DN} was the only metric that was found to be sensitive to both increases and reductions of energy for both the 6- and 18-MV beams. Conclusions: Flatness based metrics were found to be more sensitive to energy changes than PDD, In particular, F{sub DN} was found to be the most sensitive metric to energy changes for photon beams of 6 and 18 MV. The ionization chamber array allows this metric to be conveniently measured as part of routine accelerator quality assurance.

  6. Measurement of changes in linear accelerator photon energy through flatness variation using an ion chamber array.

    PubMed

    Gao, Song; Balter, Peter A; Rose, Mark; Simon, William E

    2013-04-01

    To compare the use of flatness versus percent depth dose (PDD) for determining changes in photon beam energy for a megavoltage linear accelerator. Energy changes were accomplished by adjusting the bending magnet current by up to ± 15% in 5% increments away from the value used clinically. Two metrics for flatness, relative flatness in the central 80% of the field (Flat) and average maximum dose along the diagonals normalized by central axis dose (FDN), were measured using a commercially available planner ionization chamber array. PDD was measured in water at depths of 5 and 10 cm in 3 × 3 cm(2) and 10 × 10 cm(2) fields using a cylindrical chamber. PDD was more sensitive to changes in energy when the beam energy was increased than when it was decreased. For the 18-MV beam in particular, PDD was not sensitive to energy reductions below the nominal energy. The value of Flat was found to be more sensitive to decreases in energy than to increases, with little sensitivity to energy increases above the nominal energy for 18-MV beams. FDN was the only metric that was found to be sensitive to both increases and reductions of energy for both the 6- and 18-MV beams. Flatness based metrics were found to be more sensitive to energy changes than PDD, In particular, FDN was found to be the most sensitive metric to energy changes for photon beams of 6 and 18 MV. The ionization chamber array allows this metric to be conveniently measured as part of routine accelerator quality assurance.

  7. Accurate simulation of ionisation chamber response with the Monte Carlo code PENELOPE

    NASA Astrophysics Data System (ADS)

    Sempau, Josep; Andreo, Pedro

    2011-08-01

    Ionisation chambers (IC) are routinely used in hospitals for the dosimetry of the photon and electron beams used for radiotherapy treatments. The determination of absorbed dose to water from the absorbed dose to the air filling the cavity requires the introduction of stopping power ratios and perturbation factors, which account for the disturbance caused by the presence of the chamber. Although this may seem a problem readily amenable to Monte Carlo simulation, the fact is that the accurate determination of IC response has been, for various decades, one of the most important challenges of the simulation of electromagnetic showers. The main difficulty stems from the use of condensed history techniques for electron and positron transport. This approach, which involves grouping a large number of interactions into a single artificial event, is known to produce the so-called interface effects when particles travel across surfaces separating different media. These effects can be sizeable when the electron step length is not negligible compared to the size of the region being crossed, as it is the case with the cavity of an IC. The artefact, which becomes apparent when the chamber response shows a marked dependence on the adopted step size, can be palliated with the use of sophisticated electron transport algorithms. These topics are discussed in the context of the transport model implemented in the PENELOPE code. The degree of violation of the Fano theorem for a simple, planar geometry, is used as a measure of the stability of the algorithm with respect to variations of the electron step length, thus assessing the "quality" of its condensed history scheme. It is shown that, with a suitable choice of transport parameters, PENELOPE simulates IC response with an accuracy of the order of 0.1%.

  8. Dependence with air density of the response of the PTW SourceCheck ionization chamber for low energy brachytherapy sources.

    PubMed

    Tornero-López, Ana M; Guirado, Damián; Perez-Calatayud, Jose; Ruiz-Arrebola, Samuel; Simancas, Fernando; Gazdic-Santic, Maja; Lallena, Antonio M

    2013-12-01

    significant density corrections, and that effect should be taken into account. This effect is chamber-dependent, indicating that a specific calibration is necessary for each particular chamber. To our knowledge, this correction has not been considered so far for SourceCheck ionization chambers, but its magnitude cannot be neglected in clinical practice. The atmospheric pressure and temperature at which the chamber was calibrated need to be taken into account, and they should be reported in the calibration certificate. In addition, each institution should analyze the particular response of its SourceCheck ionization chamber and compute the adequate correction factors. In the absence of a suitable pressure chamber, a possibility for this assessment is to take measurements at different altitudes, spanning a wide enough air density range.

  9. Direct determination of k Q for Farmer-type ionization chambers in a clinical scanned carbon ion beam using water calorimetry.

    PubMed

    Osinga-Blättermann, J-M; Brons, S; Greilich, S; Jäkel, O; Krauss, A

    2017-03-21

    Until now, the dosimetry of carbon ions with ionization chambers has not reached the same level of accuracy as that of high-energy photons. This is mainly caused by the approximately threefold larger uncertainty of the k Q factor of ionization chambers, which, due to the lack of experimental data, is still derived by calculations. Measurements of absorbed dose to water, D w, by means of water calorimetry have now been performed in the entrance channel of a scanned 6 cm  ×  6 cm radiation field of 429 MeV/u carbon ions, allowing the direct calibration of ionization chambers and thus the experimental determination of k Q. Within this work, values for k Q have been determined for the Farmer-type ionization chambers FC65-G and TM30013. A detailed investigation of the radiation field enabled the accurate determination of correction factors needed for both calorimetric and ionometric measurements. Finally, a relative standard measurement uncertainty of 0.8% (k  =  1) could be achieved for the experimental k Q values. For both chambers, the experimental k Q factors were found to be about 1% larger than those tabulated in the German DIN 6801-1 protocol, whereas compared to the theoretical values stated in the TRS-398 protocol, the experimental k Q value agrees within 0.4% for the TM30013 chamber but is about 1% lower in the case of the FC65-G chamber.

  10. Direct determination of k Q for Farmer-type ionization chambers in a clinical scanned carbon ion beam using water calorimetry

    NASA Astrophysics Data System (ADS)

    Osinga-Blättermann, J.-M.; Brons, S.; Greilich, S.; Jäkel, O.; Krauss, A.

    2017-03-01

    Until now, the dosimetry of carbon ions with ionization chambers has not reached the same level of accuracy as that of high-energy photons. This is mainly caused by the approximately threefold larger uncertainty of the k Q factor of ionization chambers, which, due to the lack of experimental data, is still derived by calculations. Measurements of absorbed dose to water, D w, by means of water calorimetry have now been performed in the entrance channel of a scanned 6 cm  ×  6 cm radiation field of 429 MeV/u carbon ions, allowing the direct calibration of ionization chambers and thus the experimental determination of k Q. Within this work, values for k Q have been determined for the Farmer-type ionization chambers FC65-G and TM30013. A detailed investigation of the radiation field enabled the accurate determination of correction factors needed for both calorimetric and ionometric measurements. Finally, a relative standard measurement uncertainty of 0.8% (k  =  1) could be achieved for the experimental k Q values. For both chambers, the experimental k Q factors were found to be about 1% larger than those tabulated in the German DIN 6801-1 protocol, whereas compared to the theoretical values stated in the TRS-398 protocol, the experimental k Q value agrees within 0.4% for the TM30013 chamber but is about 1% lower in the case of the FC65-G chamber.

  11. Sputter erosion and deposition in the discharge chamber of a small mercury ion thruster

    NASA Technical Reports Server (NTRS)

    Power, J. L.

    1973-01-01

    A 5-cm diameter mercury ion thruster similar to one tested for 9715 hours was operated approximately 400 hrs each at discharge voltages of 36.6, 39.6, and 42.6 V, with corresponding discharge propellant utilizations of 58, 68, and 70 percent. The observed sputter erosion rates of the internal thruster parts and the anode weight gain rate all rose rapidly with discharge voltage and were roughly in the ratio of 1:3:5 for the three voltages. The combined weight loss of the internal thruster parts nearly balanced the anode weight gain. Hg+2 ions apparently caused most of the observed erosion.

  12. Sputter erosion and deposition in the discharge chamber of a small mercury ion thruster

    NASA Technical Reports Server (NTRS)

    Power, J. L.

    1973-01-01

    A 5 cm diameter mercury ion thruster similar to one tested for 9715 hours was operated approximately 400 hrs each at discharge voltages of 36.6, 39.6, and 42.6 V, with corresponding discharge propellant utilizations of 58, 68, and 70 percent. The observed sputter erosion rates of the internal thruster parts and the anode weight gain rate all rose rapidly with discharge voltage and were roughly in the ratio of 1:3:5 for the three voltages. The combined weight loss of the internal thruster parts nearly balanced the anode weight gain. Hg(+2) ion apparently caused most of the observed erosion.

  13. The Octavius1500 2D ion chamber array and its associated phantoms: Dosimetric characterization of a new prototype

    SciTech Connect

    Van Esch, Ann Huyskens, Dominique P.; Basta, Katarzyna; Evrard, Marie; Ghislain, Michel; Sergent, Francois

    2014-09-15

    Purpose: The purpose of the study is to characterize the prototype of the new Octavius1500 (PTW, Freiburg, Germany) 2D ion chamber array, covering its use in different phantom setups, from the most basic solid water sandwich setup to the more complex cylindrical Octavius{sup ®} 4D (Oct4D) (PTW) phantom/detector combination. The new detector houses nearly twice the amount of ion chambers as its predecessors (Seven29 and Octavius729), thereby tackling one of the most important limitations of ion chamber (or diode) arrays, namely the limited detector density. The 0.06 cm{sup 3} cubic ion chambers are now arranged in a checkerboard pattern, leaving no lines (neither longitudinally nor laterally) without detectors. Methods: All measurements were performed on a dual energy (6 MV and 18 MV) iX Clinac (Varian Medical Systems, Palo Alto, CA) and all calculations were done in the Eclipse treatment planning system (Varian) with the Anisotropic Analytical Algorithm. First, the basic characteristics of the 2D array, such as measurement stability, dose rate dependence and dose linearity were investigated in the solid water sandwich setup. Second, the directional dependence was assessed to allow the evaluation of the new Octavius2D phantom (Oct2D{sup 1500}) for planar verification measurements of composite plans. Third, measurements were performed in the Oct4D phantom to evaluate the impact of the increased detector density on the accuracy of the volumetric dose reconstruction. Results: While showing equally good dose linearity and dose rate independence, the Octavius1500 outperforms the previous models because of its instantaneous measurement stability and its twofold active area coverage. Orthogonal field-by-field measurements immediately benefit from the increased detector density. The 3.9 cm wide compensation cavity in the new Oct2D{sup 1500} phantom prototype adequately corrects for directional dependence from the rear, resulting in good agreement within the target dose

  14. The Octavius1500 2D ion chamber array and its associated phantoms: dosimetric characterization of a new prototype.

    PubMed

    Van Esch, Ann; Basta, Katarzyna; Evrard, Marie; Ghislain, Michel; Sergent, Francois; Huyskens, Dominique P

    2014-09-01

    The purpose of the study is to characterize the prototype of the new Octavius1500 (PTW, Freiburg, Germany) 2D ion chamber array, covering its use in different phantom setups, from the most basic solid water sandwich setup to the more complex cylindrical Octavius® 4D (Oct4D) (PTW) phantom/detector combination. The new detector houses nearly twice the amount of ion chambers as its predecessors (Seven29 and Octavius729), thereby tackling one of the most important limitations of ion chamber (or diode) arrays, namely the limited detector density. The 0.06 cm3 cubic ion chambers are now arranged in a checkerboard pattern, leaving no lines (neither longitudinally nor laterally) without detectors. All measurements were performed on a dual energy (6 MV and 18 MV) iX Clinac (Varian Medical Systems, Palo Alto, CA) and all calculations were done in the Eclipse treatment planning system (Varian) with the Anisotropic Analytical Algorithm. First, the basic characteristics of the 2D array, such as measurement stability, dose rate dependence and dose linearity were investigated in the solid water sandwich setup. Second, the directional dependence was assessed to allow the evaluation of the new Octavius2D phantom (Oct2D(1500)) for planar verification measurements of composite plans. Third, measurements were performed in the Oct4D phantom to evaluate the impact of the increased detector density on the accuracy of the volumetric dose reconstruction. While showing equally good dose linearity and dose rate independence, the Octavius1500 outperforms the previous models because of its instantaneous measurement stability and its twofold active area coverage. Orthogonal field-by-field measurements immediately benefit from the increased detector density. The 3.9 cm wide compensation cavity in the new Oct2D(1500) phantom prototype adequately corrects for directional dependence from the rear, resulting in good agreement within the target dose. Discrepancies may arise towards the sides of the

  15. SU-E-T-100: How to Improve the Dose Accuracy for Gantry Angle Dependent Patient Specific IMRT QA Using 2D Ion Chamber Array with Octavius Phantom.

    PubMed

    Choi, D; Nookala, P; Patyal, B

    2012-06-01

    To determine the cross calibration factors which can predict more accurate dose distribution for fixed beam IMRT QA using Octavius phantom. The ion chamber based Octavius 2D-array detector (PTW, Freiburg, Germany) is a step in the right direction to measure the absolute dose and dose distribution for patient specific IMRT QA. However, the directional dependency of this detector made it less than desirable for angle dependent IMRT QA. We evaluated the new Octavius system (PTW, Freiburg, Germany) for angle dependent IMRT QA which compensates the response due to directional dependency. The system is designed for full arc VMAT QA, but does not always work for the discrete angle IMRT QA due to non-averaging of errors caused by directional dependence of detectors. The proposed method uses correction factors for each gantry angle. The dose for a 10cm × 10cm open field for each gantry angle was calculated by treatment planning system and measured using the Octavius phantom. The correction factors were determined at each gantry angle and the dose distribution was renormalized at each angle using correction factors. The discrepancy between measured and planned dose per monitor unit depended on the gantry angle and were in the range of +-4% using the PTW method. Using our method, uncertainty due to the detector angle dependency was eliminated. The new method removes the angle dependency of ion chamber based 2D array detector for the fixed beam IMRT QA. It provides fast, accurate and more realistic results for angle dependent IMRT QA. © 2012 American Association of Physicists in Medicine.

  16. SU-E-T-392: Evaluation of Ion Chamber/film and Log File Based QA to Detect Delivery Errors

    SciTech Connect

    Nelson, C; Mason, B; Kirsner, S; Ohrt, J

    2015-06-15

    Purpose: Ion chamber and film (ICAF) is a method used to verify patient dose prior to treatment. More recently, log file based QA has been shown as an alternative for measurement based QA. In this study, we delivered VMAT plans with and without errors to determine if ICAF and/or log file based QA was able to detect the errors. Methods: Using two VMAT patients, the original treatment plan plus 7 additional plans with delivery errors introduced were generated and delivered. The erroneous plans had gantry, collimator, MLC, gantry and collimator, collimator and MLC, MLC and gantry, and gantry, collimator, and MLC errors. The gantry and collimator errors were off by 4{sup 0} for one of the two arcs. The MLC error introduced was one in which the opening aperture didn’t move throughout the delivery of the field. For each delivery, an ICAF measurement was made as well as a dose comparison based upon log files. Passing criteria to evaluate the plans were ion chamber less and 5% and film 90% of pixels pass the 3mm/3% gamma analysis(GA). For log file analysis 90% of voxels pass the 3mm/3% 3D GA and beam parameters match what was in the plan. Results: Two original plans were delivered and passed both ICAF and log file base QA. Both ICAF and log file QA met the dosimetry criteria on 4 of the 12 erroneous cases analyzed (2 cases were not analyzed). For the log file analysis, all 12 erroneous plans alerted a mismatch in delivery versus what was planned. The 8 plans that didn’t meet criteria all had MLC errors. Conclusion: Our study demonstrates that log file based pre-treatment QA was able to detect small errors that may not be detected using an ICAF and both methods of were able to detect larger delivery errors.

  17. Verification of patient-specific dose distributions in proton therapy using a commercial two-dimensional ion chamber array

    SciTech Connect

    Arjomandy, Bijan; Sahoo, Narayan; Ciangaru, George; Zhu, Ronald; Song Xiaofei; Gillin, Michael

    2010-11-15

    Purpose: The purpose of this study was to determine whether a two-dimensional (2D) ion chamber array detector quickly and accurately measures patient-specific dose distributions in treatment with passively scattered and spot scanning proton beams. Methods: The 2D ion chamber array detector MatriXX was used to measure the dose distributions in plastic water phantom from passively scattered and spot scanning proton beam fields planned for patient treatment. Planar dose distributions were measured using MatriXX, and the distributions were compared to those calculated using a treatment-planning system. The dose distributions generated by the treatment-planning system and a film dosimetry system were similarly compared. Results: For passively scattered proton beams, the gamma index for the dose-distribution comparison for treatment fields for three patients with prostate cancer and for one patient with lung cancer was less than 1.0 for 99% and 100% of pixels for a 3% dose tolerance and 3 mm distance-to-dose agreement, respectively. For spot scanning beams, the mean ({+-} standard deviation) percentages of pixels with gamma indices meeting the passing criteria were 97.1%{+-}1.4% and 98.8%{+-}1.4% for MatriXX and film dosimetry, respectively, for 20 fields used to treat patients with prostate cancer. Conclusions: Unlike film dosimetry, MatriXX provides not only 2D dose-distribution information but also absolute dosimetry in fractions of minutes with acceptable accuracy. The results of this study indicate that MatriXX can be used to verify patient-field specific dose distributions in proton therapy.

  18. An ion thruster internal discharge chamber electrostatic probe diagnostic technique using a high-speed probe positioning system.

    PubMed

    Herman, Daniel A; Gallimore, Alec D

    2008-01-01

    Extensive resources have been allocated to diagnose and minimize lifetime-limiting factors in gridded ion thrusters. While most of this effort has focused on grid erosion, results from wear tests indicate that discharge cathode erosion may also play an important role in limiting the lifetime of ring-cusp ion thrusters proposed for future large flagship missions. The detailed characterization of the near-cathode discharge plasma is essential for mitigating discharge cathode erosion. However, severe difficulty is encountered when attempting to measure internal discharge plasma parameters during thruster operation with conventional probing techniques. These difficulties stem from the high-voltage, high-density discharge cathode plume, which is a hostile environment for probes. A method for interrogating the discharge chamber plasma of a working ion thruster over a two-dimensional grid is demonstrated. The high-speed axial reciprocating probe positioning system is used to minimize thruster perturbation during probe insertion and to reduce heating of the probe. Electrostatic probe measurements from a symmetric double Langmuir probe are presented over a two-dimensional spatial array in the near-discharge cathode assembly region of a 30-cm-diameter ring-cusp ion thruster. Electron temperatures, 2-5 eV, and number density contours, with a maximum of 8 x 10(12) cm(-3) on centerline, are measured. These data provide detailed electron temperature and number density contours which, when combined with plasma potential measurements, may shed light on discharge cathode erosion processes and the effect of thruster operating conditions on erosion rates.

  19. Thermal characteristics of air flow cooling in the lithium ion batteries experimental chamber

    SciTech Connect

    Lukhanin A.; Rohatgi U.; Belyaev, A.; Fedorchenko, D.; Khazhmuradov, M.; Lukhanin, O; Rudychev, I.

    2012-07-08

    A battery pack prototype has been designed and built to evaluate various air cooling concepts for the thermal management of Li-ion batteries. The heat generation from the Li-Ion batteries was simulated with electrical heat generation devices with the same dimensions as the Li-Ion battery (200 mm x 150 mm x 12 mm). Each battery simulator generates up to 15W of heat. There are 20 temperature probes placed uniformly on the surface of the battery simulator, which can measure temperatures in the range from -40 C to +120 C. The prototype for the pack has up to 100 battery simulators and temperature probes are recorder using a PC based DAQ system. We can measure the average surface temperature of the simulator, temperature distribution on each surface and temperature distributions in the pack. The pack which holds the battery simulators is built as a crate, with adjustable gap (varies from 2mm to 5mm) between the simulators for air flow channel studies. The total system flow rate and the inlet flow temperature are controlled during the test. The cooling channel with various heat transfer enhancing devices can be installed between the simulators to investigate the cooling performance. The prototype was designed to configure the number of cooling channels from one to hundred Li-ion battery simulators. The pack is thermally isolated which prevents heat transfer from the pack to the surroundings. The flow device can provide the air flow rate in the gap of up to 5m/s velocity and air temperature in the range from -30 C to +50 C. Test results are compared with computational modeling of the test configurations. The present test set up will be used for future tests for developing and validating new cooling concepts such as surface conditions or heat pipes.

  20. A convolution model for obtaining the response of an ionization chamber in static non standard fields

    SciTech Connect

    Gonzalez-Castano, D. M.; Gonzalez, L. Brualla; Gago-Arias, M. A.; Pardo-Montero, J.; Gomez, F.; Luna-Vega, V.; Sanchez, M.; Lobato, R.

    2012-01-15

    Purpose: This work contains an alternative methodology for obtaining correction factors for ionization chamber (IC) dosimetry of small fields and composite fields such as IMRT. The method is based on the convolution/superposition (C/S) of an IC response function (RF) with the dose distribution in a certain plane which includes chamber position. This method is an alternative to the full Monte Carlo (MC) approach that has been used previously by many authors for the same objective. Methods: The readout of an IC at a point inside a phantom irradiated by a certain beam can be obtained as the convolution of the dose spatial distribution caused by the beam and the IC two-dimensional RF. The proposed methodology has been applied successfully to predict the response of a PTW 30013 IC when measuring different nonreference fields, namely: output factors of 6 MV small fields, beam profiles of cobalt 60 narrow fields and 6 MV radiosurgery segments. The two-dimensional RF of a PTW 30013 IC was obtained by MC simulation of the absorbed dose to cavity air when the IC was scanned by a 0.6 x 0.6 mm{sup 2} cross section parallel pencil beam at low depth in a water phantom. For each of the cases studied, the results of the IC direct measurement were compared with the corresponding obtained by the C/S method. Results: For all of the cases studied, the agreement between the IC direct measurement and the IC calculated response was excellent (better than 1.5%). Conclusions: This method could be implemented in TPS in order to calculate dosimetry correction factors when an experimental IMRT treatment verification with in-phantom ionization chamber is performed. The miss-response of the IC due to the nonreference conditions could be quickly corrected by this method rather than employing MC derived correction factors. This method can be considered as an alternative to the plan-class associated correction factors proposed recently as part of an IAEA work group on nonstandard field dosimetry.

  1. Investigating ion recombination effects in a liquid-filled ionization chamber array used for IMRT QA measurements

    SciTech Connect

    Knill, Cory Snyder, Michael; Rakowski, Joseph T.; Burmeister, Jay; Zhuang, Ling; Matuszak, Martha

    2016-05-15

    Purpose: PTW’s Octavius 1000 SRS array performs IMRT quality assurance (QA) measurements with liquid-filled ionization chambers (LICs) to allow closer detector spacing and higher resolution, compared to air-filled QA devices. However, reduced ion mobility in LICs relative to air leads to increased ion recombination effects and reduced collection efficiencies that are dependent on Linac pulse frequency and pulse dose. These pulse parameters are variable during an IMRT delivery, which affects QA results. In this study, (1) 1000 SRS collection efficiencies were measured as a function of pulse frequency and pulse dose, (2) two methods were developed to correct changes in collection efficiencies during IMRT QA measurements, and the effects of these corrections on QA pass rates were compared. Methods: To obtain collection efficiencies, the OCTAVIUS 1000 SRS was used to measure open fields of varying pulse frequency, pulse dose, and beam energy with results normalized to air-filled chamber measurements. Changes in ratios of 1000 SRS to chamber measured dose were attributed to changing collection efficiencies, which were then correlated to pulse parameters using regression analysis. The usefulness of the derived corrections was then evaluated using 6 MV and 10FFF SBRT RapidArc plans delivered to the OCTAVIUS 4D system using a TrueBeam (Varian Medical Systems) linear accelerator equipped with a high definition multileaf collimator. For the first correction, MATLAB software was developed that calculates pulse frequency and pulse dose for each detector, using measurement and DICOM RT Plan files. Pulse information is converted to collection efficiency, and measurements are corrected by multiplying detector dose by ratios of calibration to measured collection efficiencies. For the second correction the MU/min in the daily 1000 SRS calibration was chosen to match the average MU/min of the volumetric modulated arc therapy plan. Effects of the two corrections on QA results were

  2. Investigating ion recombination effects in a liquid-filled ionization chamber array used for IMRT QA measurements.

    PubMed

    Knill, Cory; Snyder, Michael; Rakowski, Joseph T; Zhuang, Ling; Matuszak, Martha; Burmeister, Jay

    2016-05-01

    PTW's Octavius 1000 SRS array performs IMRT quality assurance (QA) measurements with liquid-filled ionization chambers (LICs) to allow closer detector spacing and higher resolution, compared to air-filled QA devices. However, reduced ion mobility in LICs relative to air leads to increased ion recombination effects and reduced collection efficiencies that are dependent on Linac pulse frequency and pulse dose. These pulse parameters are variable during an IMRT delivery, which affects QA results. In this study, (1) 1000 SRS collection efficiencies were measured as a function of pulse frequency and pulse dose, (2) two methods were developed to correct changes in collection efficiencies during IMRT QA measurements, and the effects of these corrections on QA pass rates were compared. To obtain collection efficiencies, the OCTAVIUS 1000 SRS was used to measure open fields of varying pulse frequency, pulse dose, and beam energy with results normalized to air-filled chamber measurements. Changes in ratios of 1000 SRS to chamber measured dose were attributed to changing collection efficiencies, which were then correlated to pulse parameters using regression analysis. The usefulness of the derived corrections was then evaluated using 6 MV and 10FFF SBRT RapidArc plans delivered to the OCTAVIUS 4D system using a TrueBeam (Varian Medical Systems) linear accelerator equipped with a high definition multileaf collimator. For the first correction, matlab software was developed that calculates pulse frequency and pulse dose for each detector, using measurement and DICOM RT Plan files. Pulse information is converted to collection efficiency, and measurements are corrected by multiplying detector dose by ratios of calibration to measured collection efficiencies. For the second correction the MU/min in the daily 1000 SRS calibration was chosen to match the average MU/min of the volumetric modulated arc therapy plan. Effects of the two corrections on QA results were examined by

  3. Ion-driver fast ignition: Reducing heavy-ion fusion driver energy and cost, simplifying chamber design, target fab, tritium fueling and power conversion

    SciTech Connect

    Logan, G.; Callahan-Miller, D.; Perkins, J.; Caporaso, G.; Tabak, M.; Moir, R.; Meier, W.; Bangerter, Roger; Lee, Ed

    1998-04-01

    Ion fast ignition, like laser fast ignition, can potentially reduce driver energy for high target gain by an order of magnitude, while reducing fuel capsule implosion velocity, convergence ratio, and required precisions in target fabrication and illumination symmetry, all of which should further improve and simplify IFE power plants. From fast-ignition target requirements, we determine requirements for ion beam acceleration, pulse-compression, and final focus for advanced accelerators that must be developed for much shorter pulses and higher voltage gradients than today's accelerators, to deliver the petawatt peak powers and small focal spots ({approx}100 {micro}m) required. Although such peak powers and small focal spots are available today with lasers, development of such advanced accelerators is motivated by the greater likely efficiency of deep ion penetration and deposition into pre-compressed 1000x liquid density DT cores. Ion ignitor beam parameters for acceleration, pulse compression, and final focus are estimated for two examples based on a Dielectric Wall Accelerator; (1) a small target with {rho}r {approx} 2 g/cm{sup 2} for a small demo/pilot plant producing {approx}40 MJ of fusion yield per target, and (2) a large target with {rho}r {approx} 10 g/cm{sup 2} producing {approx}1 GJ yield for multi-unit electricity/hydrogen plants, allowing internal T-breeding with low T/D ratios, >75 % of the total fusion yield captured for plasma direct conversion, and simple liquid-protected chambers with gravity clearing. Key enabling development needs for ion fast ignition are found to be (1) ''Close-coupled'' target designs for single-ended illumination of both compressor and ignitor beams; (2) Development of high gradient (>25 MV/m) linacs with high charge-state (q {approx} 26) ion sources for short ({approx}5 ns) accelerator output pulses; (3) Small mm-scale laser-driven plasma lens of {approx}10 MG fields to provide steep focusing angles close-in to the target

  4. Discharge Chamber Plasma Structure of a 30-cm NSTAR-Type Ion Engine

    NASA Technical Reports Server (NTRS)

    Herman, Daniel A.; Gallimore, Alec D.

    2006-01-01

    Single Langmuir probe measurements are presented over a two-dimensional array of locations in the near Discharge Cathode Assembly (DCA) region of a 30-cm diameter ring cusp ion thruster over a range of thruster operating conditions encompassing the high-power half of the NASA throttling table. The Langmuir probe data were analyzed with two separate methods. All data were analyzed initially assuming an electron population consisting of Maxwellian electrons only. The on-axis data were then analyzed assuming both Maxwellian and primary electrons. Discharge plasma data taken with beam extraction exhibit a broadening of the higher electron temperature plume boundary compared to similar discharge conditions without beam extraction. The opposite effect is evident with the electron/ion number density as the data without began, extraction appears to be more collimated than the corresponding data with beam extraction. Primary electron energy and number densities are presented for one operating condition giving an order of magnitude of their value and the error associated with this calculation.

  5. Insulated Conducting Cantilevered Nanotips and Two-Chamber Recording System for High Resolution Ion Sensing AFM

    PubMed Central

    Meckes, Brian; Arce, Fernando Teran; Connelly, Laura S.; Lal, Ratnesh

    2014-01-01

    Biological membranes contain ion channels, which are nanoscale pores allowing controlled ionic transport and mediating key biological functions underlying normal/abnormal living. Synthetic membranes with defined pores are being developed to control various processes, including filtration of pollutants, charge transport for energy storage, and separation of fluids and molecules. Although ionic transport (currents) can be measured with single channel resolution, imaging their structure and ionic currents simultaneously is difficult. Atomic force microscopy enables high resolution imaging of nanoscale structures and can be modified to measure ionic currents simultaneously. Moreover, the ionic currents can also be used to image structures. A simple method for fabricating conducting AFM cantilevers to image pore structures at high resolution is reported. Tungsten microwires with nanoscale tips are insulated except at the apex. This allows simultaneous imaging via cantilever deflections in normal AFM force feedback mode as well as measuring localized ionic currents. These novel probes measure ionic currents as small as picoampere while providing nanoscale spatial resolution surface topography and is suitable for measuring ionic currents and conductance of biological ion channels. PMID:24663394

  6. SU-D-BRE-04: Evaluating the Dose Accuracy of a 2D Ion Chamber Array in High Dose Rate Pencil Beam Scanning Proton Beam

    SciTech Connect

    Perles, L; Mascia, A; Piskulich, F; Lepage, R; Zhang, Y; Giebeler, A; Dong, L

    2014-06-01

    Purpose: To evaluate the absolute dose accuracy of the PTW Octavius 729 XDR 2D ion chamber array at a high dose rate pencil beam scanning proton therapy facility. Methods: A set of 18 plans were created in our treatment planning system, each of which comprising a unique combination of field sizes (FS), length of spread out of Bragg peaks (SOBP) and depths. The parameters used were: FS of 5×5cm{sup 2}, 10×10cm{sup 2} and 15×15cm{sup 2}; flat SOBP of 5cm and 10cm; and isocenter depths of 10cm, 15cm and 20cm, which coincides with the center of the SOBP. The 2D array detector was positioned at the machine isocenter and the appropriate amount of solid water was used to match the planned depths of 10, 15 and 20 cm water equivalent depth. Subsequently, we measured the absolute dose at isocenter using a CC04 ion chamber in a 1D water tank. Both 2D array and CC04 were previously cross calibrated. We also collected the MU rates used by our proton machine from the log files. Results: The relative differences between the CC04 and the 2D array can be summarized into two groups, one with 5 cm SOBP and another with 10 cm SOBP. Plotting these datasets against FS shows that the 2D array response for high dose rate fields (FS of 5×5cm{sup 2} and 5cm SOBP) can be up to 2% lower. Similarly, plotting them against isocenter depths reveals the detector's response can be up to 2% lower for higher energy beams (about 200MeV nominal). The MU rate found in the machine log files for 5cm SOBP's were as high as twice the MU rate for the 10cm SOBP. Conclusion: The 2D array dose response showed a dose rate effect in scanning pencil beam delivery, which needs to be corrected to achieve a better dose accuracy.

  7. A 2D ion chamber array audit of wedged and asymmetric fields in an inhomogeneous lung phantom

    SciTech Connect

    Lye, Jessica; Dunn, Leon Alves, Andrew; Kenny, John; Lehmann, Joerg; Williams, Ivan; Kron, Tomas; Cole, Andrew

    2014-10-15

    Purpose: The Australian Clinical Dosimetry Service (ACDS) has implemented a new method of a nonreference condition Level II type dosimetric audit of radiotherapy services to increase measurement accuracy and patient safety within Australia. The aim of this work is to describe the methodology, tolerances, and outcomes from the new audit. Methods: The ACDS Level II audit measures the dose delivered in 2D planes using an ionization chamber based array positioned at multiple depths. Measurements are made in rectilinear homogeneous and inhomogeneous phantoms composed of slabs of solid water and lung. Computer generated computed tomography data sets of the rectilinear phantoms are supplied to the facility prior to audit for planning of a range of cases including reference fields, asymmetric fields, and wedged fields. The audit assesses 3D planning with 6 MV photons with a static (zero degree) gantry. Scoring is performed using local dose differences between the planned and measured dose within 80% of the field width. The overall audit result is determined by the maximum dose difference over all scoring points, cases, and planes. Pass (Optimal Level) is defined as maximum dose difference ≤3.3%, Pass (Action Level) is ≤5.0%, and Fail (Out of Tolerance) is >5.0%. Results: At close of 2013, the ACDS had performed 24 Level II audits. 63% of the audits passed, 33% failed, and the remaining audit was not assessable. Of the 15 audits that passed, 3 were at Pass (Action Level). The high fail rate is largely due to a systemic issue with modeling asymmetric 60° wedges which caused a delivered overdose of 5%–8%. Conclusions: The ACDS has implemented a nonreference condition Level II type audit, based on ion chamber 2D array measurements in an inhomogeneous slab phantom. The powerful diagnostic ability of this audit has allowed the ACDS to rigorously test the treatment planning systems implemented in Australian radiotherapy facilities. Recommendations from audits have led to

  8. A 2D ion chamber array audit of wedged and asymmetric fields in an inhomogeneous lung phantom.

    PubMed

    Lye, Jessica; Kenny, John; Lehmann, Joerg; Dunn, Leon; Kron, Tomas; Alves, Andrew; Cole, Andrew; Williams, Ivan

    2014-10-01

    The Australian Clinical Dosimetry Service (ACDS) has implemented a new method of a nonreference condition Level II type dosimetric audit of radiotherapy services to increase measurement accuracy and patient safety within Australia. The aim of this work is to describe the methodology, tolerances, and outcomes from the new audit. The ACDS Level II audit measures the dose delivered in 2D planes using an ionization chamber based array positioned at multiple depths. Measurements are made in rectilinear homogeneous and inhomogeneous phantoms composed of slabs of solid water and lung. Computer generated computed tomography data sets of the rectilinear phantoms are supplied to the facility prior to audit for planning of a range of cases including reference fields, asymmetric fields, and wedged fields. The audit assesses 3D planning with 6 MV photons with a static (zero degree) gantry. Scoring is performed using local dose differences between the planned and measured dose within 80% of the field width. The overall audit result is determined by the maximum dose difference over all scoring points, cases, and planes. Pass (Optimal Level) is defined as maximum dose difference ≤3.3%, Pass (Action Level) is ≤5.0%, and Fail (Out of Tolerance) is >5.0%. At close of 2013, the ACDS had performed 24 Level II audits. 63% of the audits passed, 33% failed, and the remaining audit was not assessable. Of the 15 audits that passed, 3 were at Pass (Action Level). The high fail rate is largely due to a systemic issue with modeling asymmetric 60° wedges which caused a delivered overdose of 5%-8%. The ACDS has implemented a nonreference condition Level II type audit, based on ion chamber 2D array measurements in an inhomogeneous slab phantom. The powerful diagnostic ability of this audit has allowed the ACDS to rigorously test the treatment planning systems implemented in Australian radiotherapy facilities. Recommendations from audits have led to facilities modifying clinical practice and

  9. Super-resolution non-parametric deconvolution in modelling the radial response function of a parallel plate ionization chamber.

    PubMed

    Kulmala, A; Tenhunen, M

    2012-11-07

    The signal of the dosimetric detector is generally dependent on the shape and size of the sensitive volume of the detector. In order to optimize the performance of the detector and reliability of the output signal the effect of the detector size should be corrected or, at least, taken into account. The response of the detector can be modelled using the convolution theorem that connects the system input (actual dose), output (measured result) and the effect of the detector (response function) by a linear convolution operator. We have developed the super-resolution and non-parametric deconvolution method for determination of the cylinder symmetric ionization chamber radial response function. We have demonstrated that the presented deconvolution method is able to determine the radial response for the Roos parallel plate ionization chamber with a better than 0.5 mm correspondence with the physical measures of the chamber. In addition, the performance of the method was proved by the excellent agreement between the output factors of the stereotactic conical collimators (4-20 mm diameter) measured by the Roos chamber, where the detector size is larger than the measured field, and the reference detector (diode). The presented deconvolution method has a potential in providing reference data for more accurate physical models of the ionization chamber as well as for improving and enhancing the performance of the detectors in specific dosimetric problems.

  10. Heavy ion beam degradation from stripping in near vacuum reactor chambers

    SciTech Connect

    Barletta, W.A.

    1981-07-21

    With the use of a particle simulation code we have investigated the ballistic transport of heavy ion beams through a gas-filled reactor for inertial confinement fusion. The background gas pressure has been taken to be 10/sup -4/ torr - 10/sup -3/ torr of Lithium vapor as is appropriate to the HYLIFE reactor concept. During transport to the pellet, Coulomb collisions of beam particles with the background gas will convert a fraction of the beam to charges states higher than the initial value. Collisons will also produce an associated swarm of knock-on electrons. As the beam approaches the pellet, anharmonic components of the space charges forces will lead to a distortion of the phase space of the beam and a consequent degradation of the focal properties of the beam. This degradation can be described in terms of an increase in the rms emittance of the beam. The degree of emittance growth depends sensitivity upon the initial spatial distribution of particles in the beam. For this study we have modified a single-disk particle simulation code, DESTIN (2), to follow two species of particles, the number of which varies in a prescribed fashion dependent upon reactor temperature as the beam converges toward the pellet.

  11. Monte Carlo correction factors for a Farmer 0.6 cm3 ion chamber dose measurement in the build-up region of the 6 MV clinical beam.

    PubMed

    Pena, J; Sánchez-Doblado, F; Capote, R; Terrón, J A; Gómez, F

    2006-03-21

    Reference dosimetry of photon fields is a well-established subject and currently available protocols (such as the IAEA TRS-398 and AAPM TG-51) provide methods for converting the ionization chamber (IC) reading into dose to water, provided reference conditions of charged particle equilibrium (CPE) are fulfilled. But these protocols cannot deal with the build-up region, where the lack of CPE limits the applicability of the cavity theorems and so the chamber correction factors become depth dependent. By explicitly including the IC geometry in the Monte Carlo simulations, depth-dependent dose correction factors are calculated for a PTW 30001 0.6 cm(3) ion chamber in the build-up region of the 6 MV photon beam. The corrected percentage depth dose (PDD) agrees within 2% with that measured using the NACP 02 plane-parallel ion chamber in the build-up region at depths greater than 0.4 cm, where the Farmer chamber wall reaches the phantom surface.

  12. Variation of spectral response curves of GaAs photocathodes in activation chamber

    NASA Astrophysics Data System (ADS)

    Zou, Jijun; Chang, Benkang; Yang, Zhi; Wang, Hui; Gao, Pin

    2006-09-01

    The spectral response curves of reflection-mode GaAs (100) photocathodes are measured in activation chamber by multi-information measurement system at RT, and by applying quantum efficiency formula, the variation of spectral response curves have been studied. Reflection-mode GaAs photocathodes materials are grown over GaAs wafer (100) by MBE with p-type beryllium doping, doping concentration is 1×10 19 cm -3 and the active layer thickness is 1.6μm. During the high-temperature activation process, the spectral response curves varied with activation time are measured. After the low-temperature activation, the photocathode is illuminated by a white light source, and the spectral response curves varied with illumination time are measured every other hour. Experimental results of both high-temperature and low-temperature activations show that the spectral response curve shape of photocathodes is a function of time. We use traditional quantum efficiency formulas of photocathodes, in which only the Γ photoemission is considered, to fit experimental spectral response curves, and find the theoretical curves are not in agreement with the experimental curves, the reason is other valley and hot-electron yields are necessary to be included in yields of reflection-mode photocathodes. Based on the two-minima diffusion model and the fit of escape probability, we modified the quantum efficiency formula of reflection-mode photocathodes, the modified formula can be used to explain the variation of yield curves of reflection-mode photocathodes very well.

  13. SU-E-T-382: Influence of Compton Currents On Profile Measurements in Small- Volume Ion Chambers

    SciTech Connect

    Tanny, S; Parsai, E; Holmes, S

    2014-06-01

    Purpose: Ionization chambers in electron radiation fields are known to exhibit polarity effects due to Compton currents. Previously we have presented a unique manifestation of this effect observed with a microionization chamber. We have expanded that investigation to include three micro-ionization chambers commonly used in radiation therapy. The purpose of this project is to determine what factors influence this polarity effect for micro-chambers and how it might be mitigated. Methods: Three chambers were utilized: a PTW 31016, an Exradin A-16, and an Exradin A- 26. Beam profile scans were obtained on a Varian TrueBeam linear accelerator in combination with a Wellhofer water phantom for 6, 9, and 12 MeV electrons. Profiles were obtained parallel and perpendicular to the chamber's long axis, with both positive and negative collecting bias. Profiles were obtained with various chamber components shielded by 5 mm of Pb at 6 MeV to determine their relative contributions to this polarity effect. Results: The polarity effect was observed for all three chambers, and the ratio of the polarity effect for the Exradin chambers is proportional to the ratio of chamber volumes. Shielding the stem of both Exradin chambers diminished, but did not remove the polarity effect. However, they demonstrated no out-of-field effect when the cable was shielded with Pb. The PTW chamber demonstrated a significantly reduced polarity effect without any shielding despite its comparable volume with the A-26. Conclusions: The sensitive volume of these micro-chambers is relatively insensitive to collecting polarity. However, charge deposition within the cable can dramatically alter measured ionization profiles. This is demonstrated by the removal of the out-of-field ionization when the cable is shielded for the Exradin chambers. We strongly recommend analyzing any polarity dependence for small-volume chambers used in characterization of electron fields.

  14. SU-F-BRA-08: An Investigation of Well-Chamber Responses for An Electronic Brachytherapy Source

    SciTech Connect

    Culberson, W; Micka, J

    2015-06-15

    Purpose: The aim of this study was to investigate the variation of well-type ionization chamber response between a Xoft Axxent™ electronic brachytherapy (EBT) source and a GE Oncoseed™ 6711 I-125 seed. Methods: A new EBT air-kerma standard has recently been introduced by the National Institute of Standards and Technology (NIST). Historically, the Axxent source strength has been based on a well chamber calibration from an I-125 brachytherapy source due to the lack of a primary standard. Xoft utilizes a calibration procedure that employs a GE 6711 seed calibration as a surrogate standard to represent the air-kerma strength of an Axxent source. This method is based on the premise that the energies of the two sources are similar and thus, a conversion factor would be a suitable interim solution until a NIST standard was established. For this investigation, a number of well chambers of the same model type and three different EBT sources were used to determine NIST-traceable calibration coefficients for both the GE 6711 seed and the Axxent source. The ratio of the two coefficients was analyzed for consistency and also to identify any possible correlations with chamber vintage or the sources themselves. Results: For all well chambers studied, the relative standard deviation of the ratio of calibration coefficients between the two standards is less than 1%. No specific trends were found with the well chamber vintage or between the three different EBT sources used. Conclusion: The variation of well chamber calibration coefficients between a Xoft Axxent™ EBT source versus a GE 6711 Oncoseed™ are consistent across well chamber vintage and between sources. The results of this investigation confirm the underlying assumptions and stability of the surrogate standard currently in use by Xoft, and establishes a migration path for future implementation of the new NIST air kerma standard. This research is supported in part by Xoft, a subsidiary of iCAD.

  15. Dose-response of EBT3 radiochromic films to proton and carbon ion clinical beams

    NASA Astrophysics Data System (ADS)

    Castriconi, Roberta; Ciocca, Mario; Mirandola, Alfredo; Sini, Carla; Broggi, Sara; Schwarz, Marco; Fracchiolla, Francesco; Martišíková, Mária; Aricò, Giulia; Mettivier, Giovanni; Russo, Paolo

    2017-01-01

    We investigated the dose-response of the external beam therapy 3 (EBT3) films for proton and carbon ion clinical beams, in comparison with conventional radiotherapy beams; we also measured the film response along the energy deposition-curve in water. We performed measurements at three hadrontherapy centres by delivering monoenergetic pencil beams (protons: 63-230 MeV; carbon ions: 115-400 MeV/u), at 0.4-20 Gy dose to water, in the plateau of the depth-dose curve. We also irradiated the films to clinical MV-photon and electron beams. We placed the EBT3 films in water along the whole depth-dose curve for 148.8 MeV protons and 398.9 MeV/u carbon ions, in comparison with measurements provided by a plane-parallel ionization chamber. For protons, the response of EBT3 in the plateau of the depth-dose curve is not different from that of photons, within experimental uncertainties. For carbon ions, we observed an energy dependent under-response of EBT3 film, from 16% to 29% with respect to photon beams. Moreover, we observed an under-response in the Bragg peak region of about 10% for 148.8 MeV protons and of about 42% for 398.9 MeV/u carbon ions. For proton and carbon ion clinical beams, an under-response occurs at the Bragg peak. For carbon ions, we also observed an under-response of the EBT3 in the plateau of the depth-dose curve. This effect is the highest at the lowest initial energy of the clinical beams, a phenomenon related to the corresponding higher LET in the film sensitive layer. This behavior should be properly modeled when using EBT3 films for accurate 3D dosimetry.

  16. Dose-response of EBT3 radiochromic films to proton and carbon ion clinical beams.

    PubMed

    Castriconi, Roberta; Ciocca, Mario; Mirandola, Alfredo; Sini, Carla; Broggi, Sara; Schwarz, Marco; Fracchiolla, Francesco; Martišíková, Mária; Aricò, Giulia; Mettivier, Giovanni; Russo, Paolo

    2017-01-21

    We investigated the dose-response of the external beam therapy 3 (EBT3) films for proton and carbon ion clinical beams, in comparison with conventional radiotherapy beams; we also measured the film response along the energy deposition-curve in water. We performed measurements at three hadrontherapy centres by delivering monoenergetic pencil beams (protons: 63-230 MeV; carbon ions: 115-400 MeV/u), at 0.4-20 Gy dose to water, in the plateau of the depth-dose curve. We also irradiated the films to clinical MV-photon and electron beams. We placed the EBT3 films in water along the whole depth-dose curve for 148.8 MeV protons and 398.9 MeV/u carbon ions, in comparison with measurements provided by a plane-parallel ionization chamber. For protons, the response of EBT3 in the plateau of the depth-dose curve is not different from that of photons, within experimental uncertainties. For carbon ions, we observed an energy dependent under-response of EBT3 film, from 16% to 29% with respect to photon beams. Moreover, we observed an under-response in the Bragg peak region of about 10% for 148.8 MeV protons and of about 42% for 398.9 MeV/u carbon ions. For proton and carbon ion clinical beams, an under-response occurs at the Bragg peak. For carbon ions, we also observed an under-response of the EBT3 in the plateau of the depth-dose curve. This effect is the highest at the lowest initial energy of the clinical beams, a phenomenon related to the corresponding higher LET in the film sensitive layer. This behavior should be properly modeled when using EBT3 films for accurate 3D dosimetry.

  17. Fusion studies with low-intensity radioactive ion beams using an active-target time projection chamber

    NASA Astrophysics Data System (ADS)

    Kolata, J. J.; Howard, A. M.; Mittig, W.; Ahn, T.; Bazin, D.; Becchetti, F. D.; Beceiro-Novo, S.; Chajecki, Z.; Febbrarro, M.; Fritsch, A.; Lynch, W. G.; Roberts, A.; Shore, A.; Torres-Isea, R. O.

    2016-09-01

    The total fusion excitation function for 10Be+40Ar has been measured over the center-of-momentum (c.m.) energy range from 12 to 24 MeV using a time-projection chamber (TPC). The main purpose of this experiment, which was carried out in a single run of duration 90 h using a ≈100 particle per second (pps) 10Be beam, was to demonstrate the capability of an active-target TPC to determine fusion excitation functions for extremely weak radioactive ion beams. Cross sections as low as 12 mb were measured with acceptable (50%) statistical accuracy. It also proved to be possible to separate events in which charged particles were emitted from the fusion residue from those in which only neutrons were evaporated. The method permits simultaneous measurement of incomplete fusion, break-up, scattering, and transfer reactions, and therefore fully exploits the opportunities presented by the very exotic beams that will be available from the new generation of radioactive beam facilities.

  18. Dependence with air density of the response of the PTW SourceCheck ionization chamber for low energy brachytherapy sources

    SciTech Connect

    Tornero-López, Ana M.; Guirado, Damián; Ruiz-Arrebola, Samuel; Perez-Calatayud, Jose; Simancas, Fernando; Lallena, Antonio M.; Gazdic-Santic, Maja

    2013-12-15

    changes in the weather conditions may produce significant density corrections, and that effect should be taken into account. This effect is chamber-dependent, indicating that a specific calibration is necessary for each particular chamber. To our knowledge, this correction has not been considered so far for SourceCheck ionization chambers, but its magnitude cannot be neglected in clinical practice. The atmospheric pressure and temperature at which the chamber was calibrated need to be taken into account, and they should be reported in the calibration certificate. In addition, each institution should analyze the particular response of its SourceCheck ionization chamber and compute the adequate correction factors. In the absence of a suitable pressure chamber, a possibility for this assessment is to take measurements at different altitudes, spanning a wide enough air density range.

  19. Flow chamber

    DOEpatents

    Morozov, Victor [Manassas, VA

    2011-01-18

    A flow chamber having a vacuum chamber and a specimen chamber. The specimen chamber may have an opening through which a fluid may be introduced and an opening through which the fluid may exit. The vacuum chamber may have an opening through which contents of the vacuum chamber may be evacuated. A portion of the flow chamber may be flexible, and a vacuum may be used to hold the components of the flow chamber together.

  20. Removal of nickel ion from electroplating wastewater using double chamber electrodeposition cell (DCEC) reactor partitioned with water hyacinth (Eichhornia crassipes) leaves

    NASA Astrophysics Data System (ADS)

    Djaenudin; Widyarani; Hariyadi, H. R.; Wulan, D. R.; Cahyaningsih, S.

    2017-03-01

    Nickel is a heavy metal present in many types of industrial wastewater, and its contamination to the water bodies should be prevented. The objective of this research was to study the performance of Double Chamber Electrodeposition Cell (DCEC) for nickel ion removal. Water hyacinth (Eichhornia crassipes) leaves were used to separate the two chambers. The experiment was performed with synthetic electroplating wastewater in a batch system for 72 h. Changes of pH, electric current, and nickel ion concentration in the catholyte were monitored. An experiment with Single Chamber Electrodeposition Cell (SCEC) was also performed as comparison. After 72 h operation of DCEC, nickel ion concentration in the catholyte decreased from 2200 g.m-3 to 0.4 g.m-3, equivalent to 99.98% removal. DCEC reactor performed better than the SCEC reactor that only achieved 59% removal. The results show that an almost-complete removal of nickel ion can be achieved with DCEC. Water hyacinth leaves can be used as low-cost alternatives for industrial membranes.

  1. Evaluation of the accuracy of 3DVH software estimates of dose to virtual ion chamber and film in composite IMRT QA

    SciTech Connect

    Olch, Arthur J.

    2012-01-15

    Purpose: A novel patient-specific intensity modulated radiation therapy (IMRT) QA system, 3DVH software and mapcheck 2, purports to be able to use diode array-measured beam doses and the patient's DICOM RT plan, structure set, and dose files to predict the delivered 3D dose distribution in the patient for comparison to the treatment planning system (TPS) calculated doses. In this study, the composite dose to an ion chamber and film in phantom predicted by the 3DVH and mapcheck 2 system is compared to the actual measured chamber and film doses. If validated in this context, then 3DVH can be used to perform an equivalent dose analysis as that obtained with film dosimetry and ion chamber-based composite IMRT QA. This is important for those losing their ability to perform film dosimetry for true composite IMRT QA and provides a measure of confidence in the accuracy of 3DVH 3D dose calculations which may replace phantom-based IMRT QA. Methods: The dosimetric results from 15 consecutive patient-specific IMRT QA tests performed by composite field irradiation of ion chamber and EDR2 film in a solid water phantom were compared to the predicted doses for those virtual detectors based on the calculated 3D dose by the 3DVH software using mapcheck 2 measured doses of each beam within each plan. For each of the 15 cases, immediately after performing the ion chamber plus film measurements, the mapcheck 2 was used to measure the dose for each beam of the plan. The dose to the volume of the virtual ion chamber and the dose distribution in the plane of the virtual film calculated by the 3DVH software was extracted. The ratio of the measured to 3DVH or eclipse-predicted ion chamber doses was calculated. The same plane in the phantom measured using film and calculated with eclipse was exported from 3DVH and the 2D gamma metric was used to compare the relationship between the film doses and the eclipse or 3DVH predicted planar doses. Also, the 3D gamma value was calculated in the 3DVH

  2. Ion recombination and polarity corrections for small-volume ionization chambers in high-dose-rate, flattening-filter-free pulsed photon beams.

    PubMed

    Hyun, Megan A; Miller, Jessica R; Micka, John A; DeWerd, Larry A

    2017-02-01

    To investigate ion recombination and polarity effects in scanning and microionization chambers when used with digital electrometers and high-dose-rate linac beams such as flattening-filter-free (FFF) fields, and to compare results against conventional pulsed and continuous photon beams. Saturation curves were obtained for one Farmer-type ionization chamber and eight small-volume chamber models with volumes ranging from 0.01 to 0.13 cm(3) using a Varian TrueBeam™ STx with FFF capability. Three beam modes (6 MV, 6 MV FFF, and 10 MV FFF) were investigated, with nominal dose-per-pulse values of 0.0278, 0.0648, and 0.111 cGy/pulse, respectively, at dmax . Saturation curves obtained using the Theratronics T1000 (60) Co unit at the UWADCL and a conventional linear accelerator (Varian Clinac iX) were used to establish baseline behavior. Jaffé plots were fitted to obtain Pion , accounting for exponential effects such as charge multiplication. These values were compared with the two-voltage technique recommended in TG-51, and were plotted as a function of dose-per-pulse to assess the ability of small-volume chambers to meet reference-class criteria in FFF beams. Jaffé- and two-voltage-determined Pion values measured for high-dose-rate beams agreed within 0.1% for the Farmer-type chamber and 1% for scanning and microionization chambers, with the exception of the CC01 which agreed within 2%. With respect to ion recombination and polarity effects, the Farmer-type chamber, scanning chambers and the Exradin A26 microchamber exhibited reference-class behavior in all beams investigated, with the exception of the IBA CC04 scanning chamber, which had an initial recombination correction that varied by 0.2% with polarity. All microchambers investigated, with the exception of the A26, exhibited anomalous polarity and ion recombination behaviors that make them unsuitable for reference dosimetry in conventional and high-dose-rate photon beams. The results of this work demonstrate that

  3. Characterization of a two-dimensional liquid-filled ion chamber detector array used for verification of the treatments in radiotherapy

    SciTech Connect

    Markovic, Miljenko Stathakis, Sotirios; Mavroidis, Panayiotis; Jurkovic, Ines-Ana; Papanikolaou, Nikos

    2014-05-15

    Purpose: The purpose of the study is to investigate the characteristics of a two-dimensional (2D) liquid-filled ion chamber detector array, which is used for the verification of radiotherapy treatment plans that use small field sizes of up to 10 × 10 cm. Methods: The device used in this study was Octavius 1000 SRS model (PTW, Freiburg, Germany). Its 2D array of detectors consists of 977 liquid-filled ion chambers arranged over an area of 11 × 11 cm. The size of the detectors is 2.3 × 2.3 × 0.5 mm (volume of 0.003 cm{sup 3}) and their spacing in the inner area of 5.5 × 5.5 cm is 2.5 mm center-to-center, whereas in the outer area it is 5 mm center-to-center. The detector reproducibility, dose linearity, and sensitivity to positional changes of the collimator were tested. Also, the output factors of field sizes ranging from 0.5 × 0.5 to 10 × 10 cm{sup 2} both for open and wedged fields have been measured and compared against those measured by a pin-point ionization chamber, liquid filled microchamber, SRS diode, and EDR2 film. Results: Its short-term reproducibility was within 0.2% and its medium and long-term reproducibility was within 0.5% (verified with air ionization chamber absolute dose measurements), which is an excellent result taking into account the daily fluctuation of the linear accelerator and the errors in the device setup reproducibility. The dose linearity and dose rate dependence were measured in the range of 0.5–85 Gy and 0.5–10 Gy min{sup −1}, respectively, and were verified with air ionization chamber absolute dose measurements was within 3%. The measurements of the sensitivity showed that the 2D Array could detect millimetric collimator positional changes. The measured output factors showed an agreement of better than 0.3% with the pinpoint chamber and microliquid filled chamber for the field sizes between 3 × 3 and 10 × 10 cm{sup 2}. For field sizes down to 1 × 1 cm{sup 2}, the agreement with SRS diode and microliquid filled

  4. Characterization of a two-dimensional liquid-filled ion chamber detector array used for verification of the treatments in radiotherapy.

    PubMed

    Markovic, Miljenko; Stathakis, Sotirios; Mavroidis, Panayiotis; Jurkovic, Ines-Ana; Papanikolaou, Nikos

    2014-05-01

    The purpose of the study is to investigate the characteristics of a two-dimensional (2D) liquid-filled ion chamber detector array, which is used for the verification of radiotherapy treatment plans that use small field sizes of up to 10 × 10 cm. The device used in this study was Octavius 1000 SRS model (PTW, Freiburg, Germany). Its 2D array of detectors consists of 977 liquid-filled ion chambers arranged over an area of 11 × 11 cm. The size of the detectors is 2.3 × 2.3 × 0.5 mm (volume of 0.003 cm(3)) and their spacing in the inner area of 5.5 × 5.5 cm is 2.5 mm center-to-center, whereas in the outer area it is 5 mm center-to-center. The detector reproducibility, dose linearity, and sensitivity to positional changes of the collimator were tested. Also, the output factors of field sizes ranging from 0.5 × 0.5 to 10 × 10 cm(2) both for open and wedged fields have been measured and compared against those measured by a pin-point ionization chamber, liquid filled microchamber, SRS diode, and EDR2 film. Its short-term reproducibility was within 0.2% and its medium and long-term reproducibility was within 0.5% (verified with air ionization chamber absolute dose measurements), which is an excellent result taking into account the daily fluctuation of the linear accelerator and the errors in the device setup reproducibility. The dose linearity and dose rate dependence were measured in the range of 0.5-85 Gy and 0.5-10 Gy min(-1), respectively, and were verified with air ionization chamber absolute dose measurements was within 3%. The measurements of the sensitivity showed that the 2D Array could detect millimetric collimator positional changes. The measured output factors showed an agreement of better than 0.3% with the pinpoint chamber and microliquid filled chamber for the field sizes between 3 × 3 and 10 × 10 cm(2). For field sizes down to 1 × 1 cm(2), the agreement with SRS diode and microliquid filled chamber is better than 2%. The measurements of open and

  5. THE PHYSIOLOGICAL RESPONSE OF PROSTATIC AND VESICULAR TRANSPLANTS IN THE ANTERIOR CHAMBER OF THE EYE

    PubMed Central

    Moore, Robert A.; Melchionna, Robert H.; Tolins, S. H.; Rosenblum, H. B.

    1937-01-01

    1. With a photographic method for the determination of the size of prostatic and vesicular transplants in the anterior chamber of the eye, it has been possible to follow continuously the response to an injection of a hormone. 2. The results may be briefly summarized as follows: (a) One injection of the gonadotropic substance of pregnancy urine produces a moderate increase in size; (b) subsequent injections of this same substance for a period of at least 3 months are without effect; (c) an alkaline extract of the whole anterior pituitary gland produces a similar increase; (d) all pituitary derivatives are ineffective in the castrated animal; (e) castration brings about a decrease in size that gradually loses velocity; (f) the male sex hormone produces a slight increase in intact, and a variable, at times conspicuous, increase in castrated animals; (g) the female sex hormone provokes a conspicuous increase in both intact and castrated animals; (h) the hormone of the corpus luteum has no effect; and (i) there is no evidence of synergism of the pituitary and male sex hormones nor of antagonism of the male and female sex hormones in adult rabbits. PMID:19870661

  6. Chamber transport

    SciTech Connect

    OLSON,CRAIG L.

    2000-05-17

    Heavy ion beam transport through the containment chamber plays a crucial role in all heavy ion fusion (HIF) scenarios. Here, several parameters are used to characterize the operating space for HIF beams; transport modes are assessed in relation to evolving target/accelerator requirements; results of recent relevant experiments and simulations of HIF transport are summarized; and relevant instabilities are reviewed. All transport options still exist, including (1) vacuum ballistic transport, (2) neutralized ballistic transport, and (3) channel-like transport. Presently, the European HIF program favors vacuum ballistic transport, while the US HIF program favors neutralized ballistic transport with channel-like transport as an alternate approach. Further transport research is needed to clearly guide selection of the most attractive, integrated HIF system.

  7. Note: Fabrication of a fast-response and user-friendly environmental chamber for atomic force microscopes

    SciTech Connect

    Ji, Yanfeng; Hui, Fei; Shi, Yuanyuan; Han, Tingting; Song, Xiaoxue; Pan, Chengbin; Lanza, Mario

    2015-10-15

    The atomic force microscope is one of the most widespread tools in science, but many suppliers do not provide a competitive solution to make experiments in controlled atmospheres. Here, we provide a solution to this problem by fabricating a fast-response and user-friendly environmental chamber. We corroborate the correct functioning of the chamber by studying the formation of local anodic oxidation on a silicon sample (biased under opposite polarities), an effect that can be suppressed by measuring in a dry nitrogen atmosphere. The usefulness of this chamber goes beyond the example here presented, and it could be used in many other fields of science, including physics, mechanics, microelectronics, nanotechnology, medicine, and biology.

  8. Note: Fabrication of a fast-response and user-friendly environmental chamber for atomic force microscopes

    NASA Astrophysics Data System (ADS)

    Ji, Yanfeng; Hui, Fei; Shi, Yuanyuan; Han, Tingting; Song, Xiaoxue; Pan, Chengbin; Lanza, Mario

    2015-10-01

    The atomic force microscope is one of the most widespread tools in science, but many suppliers do not provide a competitive solution to make experiments in controlled atmospheres. Here, we provide a solution to this problem by fabricating a fast-response and user-friendly environmental chamber. We corroborate the correct functioning of the chamber by studying the formation of local anodic oxidation on a silicon sample (biased under opposite polarities), an effect that can be suppressed by measuring in a dry nitrogen atmosphere. The usefulness of this chamber goes beyond the example here presented, and it could be used in many other fields of science, including physics, mechanics, microelectronics, nanotechnology, medicine, and biology.

  9. Note: Fabrication of a fast-response and user-friendly environmental chamber for atomic force microscopes.

    PubMed

    Ji, Yanfeng; Hui, Fei; Shi, Yuanyuan; Han, Tingting; Song, Xiaoxue; Pan, Chengbin; Lanza, Mario

    2015-10-01

    The atomic force microscope is one of the most widespread tools in science, but many suppliers do not provide a competitive solution to make experiments in controlled atmospheres. Here, we provide a solution to this problem by fabricating a fast-response and user-friendly environmental chamber. We corroborate the correct functioning of the chamber by studying the formation of local anodic oxidation on a silicon sample (biased under opposite polarities), an effect that can be suppressed by measuring in a dry nitrogen atmosphere. The usefulness of this chamber goes beyond the example here presented, and it could be used in many other fields of science, including physics, mechanics, microelectronics, nanotechnology, medicine, and biology.

  10. Temperature response in the pulpal chamber during ultrahigh-speed tooth preparation with diamond burs of different grit.

    PubMed

    Ottl, P; Lauer, H C

    1998-07-01

    Ultrahigh-speed tooth preparation can traumatize the hard dental tissues and the dental pulp. This in vitro study examined the relationship between different grits of diamond burs on the temperature response within a pulpal chamber during tooth preparation with a turbine. Newly extracted, undamaged third molars were secured by a rapid-tensioning device mounted on an air-supported slide. NiCrNi thermocouples were inserted apically and used to determine the temperature within a pulpal chamber. The grinding tests used cylindrical fine, coarse, and ultracoarse diamond burs. The maximal temperature elevation within the pulp was 3.2 degrees C, and the most pronounced rise in temperature occurred with ultracoarse burs. Temperature increases in the pulpal chambers and grinding times or temperatures of the cooling water were approximately proportional. Residual dentinal thickness was inversely proportional to temperature elevation within the pulpal chamber. This study demonstrated that coarse diamond burs resulted in more pronounced temperature increases within the pulpal chamber during tooth preparation. In addition, the benefit of short intervals between grinding steps and a cooling water temperature between 30 degrees C and 32 degrees C was confirmed. A cooling temperature of 38 degrees C to 43 degrees C did not afford actual cooling.

  11. The insulin secretion of a minced neonatal rat pancreas cultured in a pancreatic chamber, in response to various insulin secretagogues.

    PubMed

    Araki, Y; Yoshioka, K; Inoue, Y; Nakamura, Y; Nakamura, N; Nakano, K; Yoshida, T; Kondo, M

    1981-02-01

    The minced pancreas of the neonatal rat was cultured for 35 days in a pancreatic chamber which was constructed of a plastic tube and an ultrafiltration membrane. Insulin and amylase secreted from this pancreatic chamber into the culture medium were measured. During the experiment, the concentration of glucose in the culture medium was changed between 5.5 and 16.5 mM at 2-3 day intervals in order to determine the insulin secretory response of the pancreatic tissue. Insulin secretion was markedly increased in response to 16.5 mM glucose. The ratio of insulin secretion to amylase secretion in the culture medium increased with the advance of culture days although secretions of both insulin and amylase decreased individually. On the 7th culture day, short term incubations were performed to test with various insulin secretagogues; obvious insulin release into the incubation medium was observed. These results show that the pancreatic chamber also in vitro secretes insulin rapidly and significantly in response to various stimuli; that by longer culture of a neonatal rat pancreas in this device, insulin secretory cells without exocrine tissue would be obtained without using digestive enzymes; that application of a pancreatic chamber for a pancreatic transplantation may be feasible.

  12. A study of airborne radon levels in Paarl houses (South Africa) and associated source terms, using electret ion chambers and gamma-ray spectrometry.

    PubMed

    Lindsay, R; Newman, R T; Speelman, W J

    2008-11-01

    Indoor radon ((222)Rn) concentrations were measured in Paarl homes by means of electret ion chambers. The concentrations varied between 28 and 465 Bq m(-3). The average values (Bq m(-3)) found in houses on the west and east side of the Berg River, which bisects Paarl, were 132 (+/-11) and 37 (+/-3), respectively. Radiometric analyses of soils show that the mean (226)Ra activity concentration is three times higher on the west than on the east side of the Berg River.

  13. A new pressure chamber to study the biosynthetic response of articular cartilage to mechanical loading.

    PubMed

    Steinmeyer, J; Torzilli, P A; Burton-Wurster, N; Lust, G

    1993-01-01

    A prototype chamber was used to apply a precise cyclic or static load on articular cartilage explants under sterile conditions. A variable pressure, pneumatic controller was constructed to power the chamber's air cylinder, capable of applying, with a porous load platen, loads of up to 10 MPa at cycles ranging from 0 to 10 Hz. Pig articular cartilage explants were maintained successfully in this chamber for 2 days under cyclic mechanical loading of 0.5 Hz, 0.5 MPa. Explants remained sterile, viable and metabolically active. Cartilage responded to this load with a decreased synthesis of fibronectin and a small but statistically significant elevation in proteoglycan content. Similar but less extensive effects on fibronectin synthesis were observed with the small static load (0.016 MPa) inherent in the design of the chamber.

  14. Dermal exudate macrophages. Induction in dermal chambers and response to lymphokines.

    PubMed Central

    Goihman-Yahr, M; Ulrich, M; Noya-León, A; Rojas, A; Convit, J

    1975-01-01

    Chambers were implanted in the dorsum of guinea-pigs at the dermal-subcutaneous junction. Exudates were induced and harvested. Macrophages obtained were able to migrate in vitro. If procured from sensitized donors, macrophage migration was inhibited by the corresponding antigen. Dermal exudate macrophages are therefore subject to the effect of lymphokines. The chamber model may be useful for in vivo studies of cell to cell and cell-parasite interactions. PMID:1212821

  15. TH-E-BRE-03: A Novel Method to Account for Ion Chamber Volume Averaging Effect in a Commercial Treatment Planning System Through Convolution

    SciTech Connect

    Barraclough, B; Li, J; Liu, C; Yan, G

    2014-06-15

    Purpose: Fourier-based deconvolution approaches used to eliminate ion chamber volume averaging effect (VAE) suffer from measurement noise. This work aims to investigate a novel method to account for ion chamber VAE through convolution in a commercial treatment planning system (TPS). Methods: Beam profiles of various field sizes and depths of an Elekta Synergy were collected with a finite size ion chamber (CC13) to derive a clinically acceptable beam model for a commercial TPS (Pinnacle{sup 3}), following the vendor-recommended modeling process. The TPS-calculated profiles were then externally convolved with a Gaussian function representing the chamber (σ = chamber radius). The agreement between the convolved profiles and measured profiles was evaluated with a one dimensional Gamma analysis (1%/1mm) as an objective function for optimization. TPS beam model parameters for focal and extra-focal sources were optimized and loaded back into the TPS for new calculation. This process was repeated until the objective function converged using a Simplex optimization method. Planar dose of 30 IMRT beams were calculated with both the clinical and the re-optimized beam models and compared with MapCHEC™ measurements to evaluate the new beam model. Results: After re-optimization, the two orthogonal source sizes for the focal source reduced from 0.20/0.16 cm to 0.01/0.01 cm, which were the minimal allowed values in Pinnacle. No significant change in the parameters for the extra-focal source was observed. With the re-optimized beam model, average Gamma passing rate for the 30 IMRT beams increased from 92.1% to 99.5% with a 3%/3mm criterion and from 82.6% to 97.2% with a 2%/2mm criterion. Conclusion: We proposed a novel method to account for ion chamber VAE in a commercial TPS through convolution. The reoptimized beam model, with VAE accounted for through a reliable and easy-to-implement convolution and optimization approach, outperforms the original beam model in standard IMRT QA

  16. Robotic radiosurgery system patient-specific QA for extracranial treatments using the planar ion chamber array and the cylindrical diode array.

    PubMed

    Lin, Mu-Han; Veltchev, Iavor; Koren, Sion; Ma, Charlie; Li, Jinsgeng

    2015-07-08

    Robotic radiosurgery system has been increasingly employed for extracranial treatments. This work is aimed to study the feasibility of a cylindrical diode array and a planar ion chamber array for patient-specific QA with this robotic radiosurgery system and compare their performance. Fiducial markers were implanted in both systems to enable image-based setup. An in-house program was developed to postprocess the movie file of the measurements and apply the beam-by-beam angular corrections for both systems. The impact of noncoplanar delivery was then assessed by evaluating the angles created by the incident beams with respect to the two detector arrangements and cross-comparing the planned dose distribution to the measured ones with/without the angular corrections. The sensitivity of detecting the translational (1-3 mm) and the rotational (1°-3°) delivery errors were also evaluated for both systems. Six extracranial patient plans (PTV 7-137 cm³) were measured with these two systems and compared with the calculated doses. The plan dose distributions were calculated with ray-tracing and the Monte Carlo (MC) method, respectively. With 0.8 by 0.8 mm² diodes, the output factors measured with the cylindrical diode array agree better with the commissioning data. The maximum angular correction for a given beam is 8.2% for the planar ion chamber array and 2.4% for the cylindrical diode array. The two systems demonstrate a comparable sensitivity of detecting the translational targeting errors, while the cylindrical diode array is more sensitive to the rotational targeting error. The MC method is necessary for dose calculations in the cylindrical diode array phantom because the ray-tracing algorithm fails to handle the high-Z diodes and the acrylic phantom. For all the patient plans, the cylindrical diode array/ planar ion chamber array demonstrate 100% / > 92% (3%/3 mm) and > 96% / ~ 80% (2%/2 mm) passing rates. The feasibility of using both systems for robotic

  17. Robotic radiosurgery system patient-specific QA for extracranial treatments using the planar ion chamber array and the cylindrical diode array.

    PubMed

    Lin, Mu-Han; Veltchev, Iavor; Koren, Sion; Ma, Charlie; Li, Jinsgeng

    2015-07-01

    Robotic radiosurgery system has been increasingly employed for extracranial treatments. This work is aimed to study the feasibility of a cylindrical diode array and a planar ion chamber array for patient-specific QA with this robotic radiosurgery system and compare their performance. Fiducial markers were implanted in both systems to enable image-based setup. An in-house program was developed to postprocess the movie file of the measurements and apply the beam-by-beam angular corrections for both systems. The impact of noncoplanar delivery was then assessed by evaluating the angles created by the incident beams with respect to the two detector arrangements and cross-comparing the planned dose distribution to the measured ones with/without the angular corrections. The sensitivity of detecting the translational (1-3 mm) and the rotational (1°-3°) delivery errors were also evaluated for both systems. Six extracranial patient plans (PTV 7-137 cm(3)) were measured with these two systems and compared with the calculated doses. The plan dose distributions were calculated with ray-tracing and the Monte Carlo (MC) method, respectively. With 0.8 by 0.8 mm(2) diodes, the output factors measured with the cylindrical diode array agree better with the commissioning data. The maximum angular correction for a given beam is 8.2% for the planar ion chamber array and 2.4% for the cylindrical diode array. The two systems demonstrate a comparable sensitivity of detecting the translational targeting errors, while the cylindrical diode array is more sensitive to the rotational targeting error. The MC method is necessary for dose calculations in the cylindrical diode array phantom because the ray-tracing algorithm fails to handle the high-Z diodes and the acrylic phantom. For all the patient plans, the cylindrical diode array/ planar ion chamber array demonstrate 100%/>;92%(3%/3 mm) passing rates. The feasibility of using both systems for robotic radiosurgery system patient-specific QA

  18. Calculated absorbed-dose ratios, TG51/TG21, for most widely used cylindrical and parallel-plate ion chambers over a range of photon and electron energies.

    PubMed

    Tailor, R C; Hanson, W F

    2002-07-01

    Task Group 51 (TG51), of the Radiation Therapy Committee of the American Association of Physicists in Medicine (AAPM), has developed a calibration protocol for high-energy photon and electron therapy beams based on absorbed dose standards. This protocol is intended to replace the air-kerma based protocol developed by an earlier AAPM task group (TG21). Conversion to the newer protocol introduces a change in the determined absorbed dose. In this work, the change in dose is expressed as the ratio of the doses (TG51/TG21) based on the two protocols. Dose is compared at the TG-51 reference depths of 10 cm for photons and d(ref) for electrons. Dose ratios are presented for a variety of ion chambers over a range of photon and electron energies. The TG51/TG21 dose ratios presented here are based on the dosimetry factors provided by the two protocols and the chamber-specific absorbed dose and exposure calibration factors (N60Co(D,w) and Nx) provided by the Accredited Dosimetry Calibration Laboratory (ADCL) at The University of Texas, M. D. Anderson Cancer Center (MDACC). As such, the values presented here represent the expected discrepancies between the two protocols due only to changes in the dosimetry parameters and the differences in chamber-specific dose and air-kerma standards. These values are independent of factors such as measurement uncertainties, setup errors, and inconsistencies arising from the mix of different phantoms and ion chambers for the two protocols. Therefore, these ratios may serve as a guide for institutions performing measurements for the switch from TG21-to-TG51 based calibration. Any significant deviation in the ratio obtained from measurements versus those presented here should prompt a review to identify possible errors and inconsistencies. For all cylindrical chambers included here, the TG51/TG21 dose ratios are the same within +/-0.6%, irrespective of the make and model of the chamber, for each photon and electron beam included. Photon beams

  19. Responses to ragweed pollen in a pollen challenge chamber versus seasonal exposure identify allergic rhinoconjunctivitis endotypes.

    PubMed

    Jacobs, Robert L; Harper, Nathan; He, Weijing; Andrews, Charles P; Rather, Cynthia G; Ramirez, Daniel A; Ahuja, Sunil K

    2012-07-01

    The level of concordance between allergic symptoms induced on exposure to pollen in a pollen challenge chamber (PCC) versus the natural season is unknown. We sought to test the hypothesis that the symptom levels of allergic rhinoconjunctivitis elicited after out-of-season exposure to short ragweed in a PCC and during the natural season for giant ragweed pollen are highly correlated. Thirty-one ragweed-sensitive participants recorded symptoms for 15 days during the natural giant ragweed season in San Antonio, Texas. Twenty-six of these participants were challenged to short ragweed pollen in a PCC for 3 hours per day for up to 4 days. In the PCC participants were dichotomized into those in whom low versus high levels of symptoms developed slowly or rapidly (ie, slow/low vs rapid/high). Each successive exposure visit associated with a progressive increase in symptom levels that approximated those experienced during the natural season. Hierarchic clustering identified 3 endotypes: endotypes I and II reflected concordantly low (n= 7) versus high (n = 14) total symptom scores (TSSs) in both the natural season and the PCC, respectively. Accordingly, the correlation between the TSSs recorded in the natural season and in the PCC for these 21 participants was very high. Although participants with endotype III (n = 5) had greater TSSs in the natural season than in the PCC, the degree of correlation between the TSSs remained high. Our findings affirm our hypothesis, underscore the high cross-reactivity between distinct pollens, and highlight the utility of the PCC to identify novel allergy endotypes that might have contrasting mechanistic underpinnings and potentially therapeutic responses. Copyright © 2012 American Academy of Allergy, Asthma & Immunology. Published by Mosby, Inc. All rights reserved.

  20. SU-E-T-758: To Determine the Source Dwell Positions of HDR Brachytherapy Using 2D 729 Ion Chamber Array

    SciTech Connect

    Kumar, Syam; Sitha

    2015-06-15

    Purpose: Determination of source dwell positions of HDR brachytherapy using 2D 729 ion chamber array Methods: Nucletron microselectron HDR and PTW 2D array were used for the study. Different dwell positions were assigned in the HDR machine. Rigid interstitial needles and vaginal applicator were positioned on the 2D array. The 2D array was exposed for this programmed dwell positions. The positional accuracy of the source was analyzed after the irradiation of the 2D array. This was repeated for different dwell positions. Different test plans were transferred from the Oncentra planning system and irradiated with the same applicator position on the 2D array. The results were analyzed using the in house developed excel program. Results: Assigned dwell positions versus corresponding detector response were analyzed. The results show very good agreement with the film measurements. No significant variation found between the planned and measured dwell positions. Average dose response with 2D array between the planned and nearby dwell positions was found to be 0.0804 Gy for vaginal cylinder applicator and 0.1234 Gy for interstitial rigid needles. Standard deviation between the doses for all the measured dwell positions for interstitial rigid needle for 1 cm spaced positions were found to be 0.33 and 0.37 for 2cm spaced dwell positions. For intracavitory vaginal applicator this was found to be 0.21 for 1 cm spaced dwell positions and 0.06 for 2cm spaced dwell positions. Intracavitory test plans reproduced on the 2D array with the same applicator positions shows the ideal dose distribution with the TPS planned. Conclusion: 2D array is a good tool for determining the dwell position of HDR brachytherapy. With the in-house developed program in excel it is easy and accurate. The traditional way with film analysis can be replaced by this method, as the films will be more costly.

  1. Air density dependence of the response of the PTW SourceCheck 4pi ionization chamber for (125)I brachytherapy seeds.

    PubMed

    Torres Del Río, J; Tornero-López, A M; Guirado, D; Pérez-Calatayud, J; Lallena, A M

    2017-06-01

    To analyze the air density dependence of the response of the new SourceCheck 4pi ionization chamber, manufactured by PTW. The air density dependence of three different SourceCheck 4pi chambers was studied by measuring (125)I sources. Measurements were taken by varying the pressure from 746.6 to 986.6hPa in a pressure chamber. Three different HDR 1000 Plus ionization chambers were also analyzed under similar conditions. A linear and a potential-like function of the air density were fitted to experimental data and their achievement in describing them was analyzed. SourceCheck 4pi chamber response showed a residual dependence on the air density once the standard pressure and temperature factor was applied. The chamber response was overestimated when the air density was below that under normal atmospheric conditions. A similar dependence was found for the HDR 1000 Plus chambers analyzed. A linear function of the air density permitted a very good description of this residual dependence, better than with a potential function. No significant variability between the different specimens of the same chamber model studied was found. The effect of overestimation observed in the chamber responses once they are corrected for the standard pressure and temperature may represent a non-negligible ∼4% overestimation in high altitude cities as ours (700m AMSL). This overestimation behaves linearly with the air density in all cases analyzed. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  2. SU-E-T-242: Monte Carlo Simulations Used to Test the Perturbation of a Reference Ion Chamber Prototype Used for Small Fields

    SciTech Connect

    Vazquez Quino, L; Calvo, O; Huerta, C; DeWeese, M

    2014-06-01

    Purpose: To study the perturbation due to the use of a novel Reference Ion Chamber designed to measure small field dosimetry (KermaX Plus C by IBA). Methods: Using the Phase-space files for TrueBeam photon beams available by Varian in IAEA-compliant format for 6 and 15 MV. Monte Carlo simulations were performed using BEAMnrc and DOSXYZnrc to investigate the perturbation introduced by a reference chamber into the PDDs and profiles measured in water tank. Field sizes ranging from 1×1, 2×2,3×3, 5×5 cm2 were simulated for both energies with and without a 0.5 mm foil of Aluminum which is equivalent to the attenuation equivalent of the reference chamber specifications in a water phantom of 30×30×30 cm3 and a pixel resolution of 2 mm. The PDDs, profiles, and gamma analysis of the simulations were performed as well as a energy spectrum analysis of the phase-space files generated during the simulation. Results: Examination of the energy spectrum analysis performed shown a very small increment of the energy spectrum at the build-up region but no difference is appreciated after dmax. The PDD, profiles and gamma analysis had shown a very good agreement among the simulations with and without the Al foil, with a gamma analysis with a criterion of 2% and 2mm resulting in 99.9% of the points passing this criterion. Conclusion: This work indicates the potential benefits of using the KermaX Plus C as reference chamber in the measurement of PDD and Profiles for small fields since the perturbation due to in the presence of the chamber the perturbation is minimal and the chamber can be considered transparent to the photon beam.

  3. Temperature response of several scintillator materials to light ions

    NASA Astrophysics Data System (ADS)

    Rodríguez-Ramos, M.; Jiménez-Ramos, M. C.; García-Muñoz, M.; García López, J.

    2017-07-01

    Ion beam induced luminescence has been used to study the response of scintillator screens of Y2O3:Eu3+ (P56) and SrGa2S4:Eu2+ (TG-Green) when irradiated with light ions (protons, deuterium and helium particles). The absolute efficiency of the samples has been studied as a function of the ion energy (with energies up to 3.5 MeV), the beam current and the operating temperature. The evolution of the scintillator yield with ion fluence has been carried out for all the scintillators to estimate radiation damage. Finally, measurements of the decay time of these materials using a system of pulsed beam accelerated particles have been done. Among the screens under study, the TG-Green is the best suited material, in terms of absolute efficiency, temporal response and degradation with ion dose, for fast-ion loss detectors in fusion devices.

  4. Bakeout Chamber Within Vacuum Chamber

    NASA Technical Reports Server (NTRS)

    Taylor, Daniel M.; Soules, David M.; Barengoltz, Jack B.

    1995-01-01

    Vacuum-bakeout apparatus for decontaminating and measuring outgassing from pieces of equipment constructed by mounting bakeout chamber within conventional vacuum chamber. Upgrade cost effective: fabrication and installation of bakeout chamber simple, installation performed quickly and without major changes in older vacuum chamber, and provides quantitative data on outgassing from pieces of equipment placed in bakeout chamber.

  5. Bakeout Chamber Within Vacuum Chamber

    NASA Technical Reports Server (NTRS)

    Taylor, Daniel M.; Soules, David M.; Barengoltz, Jack B.

    1995-01-01

    Vacuum-bakeout apparatus for decontaminating and measuring outgassing from pieces of equipment constructed by mounting bakeout chamber within conventional vacuum chamber. Upgrade cost effective: fabrication and installation of bakeout chamber simple, installation performed quickly and without major changes in older vacuum chamber, and provides quantitative data on outgassing from pieces of equipment placed in bakeout chamber.

  6. Output current variation and polarity effect by electric field and ion-pair non-uniformity inside thimble-type ionization chamber

    NASA Astrophysics Data System (ADS)

    Kim, Jaecheon; Kim, Yong Kyun; Kim, Soon Young; Kim, Jong Kyung

    2007-09-01

    A new analytic approach considering both electric field and ion-pair non-uniformity has been proposed to accurately analyze the design characteristics of an ionization chamber and to interpret measurements. It is commonly assumed that ion-pairs are generated uniformly in the air volume, but such an assumption ignores various source and geometry conditions. The new approach was applied to angular dependence analysis and to polarity effect assessment in an ionization chamber. For the angular dependence analysis, whole, uniform, and non-uniform output currents were calculated as a function of the irradiation angle for an 241Am gamma-ray source. The non-uniform output current proposed in this paper was found to be closer to the measured one. This is because the non-uniform output current takes into account the ion-pair distribution in the air volume as well as the active volume determined by the electric field. For the polarity effect assessment, the amount of field distortion due to potential difference and actual current difference was calculated. Previous methods cannot appropriately estimate the variation of polarity effect because they ignore the influence of the ion-pair distribution. The polarity effect assessment using the non-uniform output current can be more useful for obtaining the practical current difference, because this assessment considers both the variation of active volume and the ion-pair non-uniformity according to source conditions such as the irradiation angle and the distance. It is important to precisely calculate not only the active volume, but also the variation in the ion-pair distribution.

  7. SU-E-T-137: Attenuation of Carbon Fiber IGRT Couch Top for SBRT By Using a MapCheck 2 and Ion Chamber

    SciTech Connect

    Dou, K; Li, B; Lerma, F; Sarfaraz, M; Jacobs, M; Laser, B

    2015-06-15

    Purpose: It is common to use posterior oblique beams in intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) for regular and stereotactic body radiotherapy (SBRT). Beam attenuation by the treatment couch is not negligible when the couch is in the beam portal. In this study, we have correlated relative dose versus beam angle through a MapCheck 2TM diode array and an ionization chamber measurement. Methods: A Varian TrueBeam linear accelerator equipped with the image-guided radiation therapy (IGRT) carbon fiber couch was used for delivery of radiation with different photon energies of 6MV, 15MV and 6MV FFF. A MapCHECK 2TM diode array with a MapPhan was employed for the measurement at three field sizes (3 by 3, 5 by 5, and 10 by 10 cm). The independent measurement was performed with an ionization chamber placed at the center of an acrylic cylindrical phantom at the isocenter. The measured data with the MapCHECK 2TM diode array were averaged over the central 2×2 cm diodes for each measurement. The couch attenuation was deduced from the angular dependence with and without the couch involvement. Results: For the MapCHECK 2TM with MapPhan used only the obvious attenuation was observed at the beam angle between 5 and 10 degree from the angular dependence using a 6MV photon beam. The similar Result was obtained for the MapCHECK 2TM /MapPhan with the couch involvement. The couch attenuation was then deduced from the difference of these two sets of data measurements. Maximum couch attenuation was found up to 4.2% which was verified with the ion chamber measurement. Conclusion: A maximum attenuation of 4.2% was found for the carbon fiber couch top using the MapCHECK 2TM/MapPhan, which is consistent with the ion chamber measurement.

  8. Response of the first wetted wall of an IFE reactor chamber to the energy release from a direct-drive DT capsule

    SciTech Connect

    Medin, Stanislav A.; Basko, Mikhail M.; Orlov, Yurii N.; Suslin, Victor M.

    2012-07-11

    Radiation hydrodynamics 1D simulations were performed with two concurrent codes, DEIRA and RAMPHY. The DEIRA code was used for DT capsule implosion and burn, and the RAMPHY code was used for computation of X-ray and fast ions deposition in the first wall liquid film of the reactor chamber. The simulations were run for 740 MJ direct drive DT capsule and Pb thin liquid wall reactor chamber of 10 m diameter. Temporal profiles for DT capsule leaking power of X-rays, neutrons and fast {sup 4}He ions were obtained and spatial profiles of the liquid film flow parameter were computed and analyzed.

  9. Response of the first wetted wall of an IFE reactor chamber to the energy release from a direct-drive DT capsule

    NASA Astrophysics Data System (ADS)

    Medin, Stanislav A.; Basko, Mikhail M.; Orlov, Yurii N.; Suslin, Victor M.

    2012-07-01

    Radiation hydrodynamics 1D simulations were performed with two concurrent codes, DEIRA and RAMPHY. The DEIRA code was used for DT capsule implosion and burn, and the RAMPHY code was used for computation of X-ray and fast ions deposition in the first wall liquid film of the reactor chamber. The simulations were run for 740 MJ direct drive DT capsule and Pb thin liquid wall reactor chamber of 10 m diameter. Temporal profiles for DT capsule leaking power of X-rays, neutrons and fast 4He ions were obtained and spatial profiles of the liquid film flow parameter were computed and analyzed.

  10. SU-E-T-82: A Study On Enhanced Dynamic Wedge (EDW) Dosimetry Using 2D Seven29 Ion Chamber Array Detector

    SciTech Connect

    Kumar, Syam; Aparna

    2015-06-15

    Purpose: To study the dosimetric properties of Enhanced Dynamic Wedge (EDW) using PTW Seven29 ion chamber array Methods: PTW Seven29 ion chamber array and Solid Water phantoms for different depths were used for the study. The study was carried out in Varian Clinac ix with photon energies, 6MV & 15MV. Primarily the solid water phantoms with the 2D array were scanned using a CT scanner (GE Optima 580) at different depths. These scanned images were used for EDW planning in an Eclipse treatment planning system (version 10). Planning was done for different wedge angles and for different depths for 6MV & 15MV. A dose of 100 CGy was delivered in each cases. For each delivery, calculated the Monitoring Unit (MU) required. Same set-up was created before delivering the plans in Varian Clinac-ix. For each clinically relevant depth and for different wedge angles, the same MU was delivered as calculated. Different wedged dose distributions where reconstructed from the measured 2D array data using the in-house developed excel program. Results: It is observed that the shoulder like region in the profile which reduces as depth increases. For the same depth and energy, the percentage difference between planned and measured dose is lesser than 3%. For smaller wedge angles, the percentage difference is found to be greater than 3% for the largest wedge angle. Standard deviation between measured doses at shoulder region for planned and measured profiles is 0.08 and 0.02 respectively. Standard deviations between planned and measured wedge factors for different depths (2.5cm, 5cm, 10cm, and 15cm) are (0.0021, 0.0007, 0.0050, 0.0001) for 6MV and (0.0024, 0.0191, 0.0013, 0.0005) for 15MV respectively. Conclusion: The 2D Seven29 ion chamber array is a good tool for the Enhanced Dynamic Wedge (EDW) dosimetry.

  11. Thermal conditions in freezing chambers and prediction of the thermophysiological responses of workers

    NASA Astrophysics Data System (ADS)

    Raimundo, A. M.; Oliveira, A. V. M.; Gaspar, A. R.; Quintela, D. A.

    2015-11-01

    The present work is dedicated to the assessment of the cold thermal strain of human beings working within freezing chambers. To obtain the present results, both field measurements and a numerical procedure based on a modified version of the Stolwijk thermoregulation model were used. Eighteen freezing chambers were considered. A wide range of physical parameters of the cold stores, the workers clothing insulation, and the working and recovering periods were observed. The combination of these environmental and individual parameters lead to different levels of thermal stress, which were grouped under three categories. Some good practices were observed in the field evaluations, namely situations with appropriate level of clothing protection and limited duration of exposure to cold avoiding unacceptable level of hypothermia. However, the clothing ensembles normally used by the workers do not provide the minimum required insulation, which suggests the possibility of the whole body cooling for levels higher than admissible. The numerical predictions corroborate the main conclusions of the field survey. The results obtained with both methodologies clearly show that, for the low temperature of the freezing chambers, the clothing insulation is insufficient, the exposure periods are too long, and the recovering periods are inadequate. Thus, high levels of physiological strain can indeed be reached by human beings under such working environments.

  12. Preliminary studies of a new monitor ionization chamber.

    PubMed

    Yoshizumi, Maíra T; Vivolo, Vitor; Caldas, Linda V E

    2010-01-01

    A new monitor ionization chamber was developed at Instituto de Pesquisas Energéticas e Nucleares (IPEN) in order to monitor X-ray beams. The main difference of this monitor ionization chamber in relation to other monitor chambers is its geometry, which consists of a ring-shaped sensitive volume. Because of this geometry, the monitor chamber has a central hole through which the direct radiation beam passes. The operational characteristics of the monitor chamber were evaluated: saturation, ion collection efficiency and polarity effect. Besides these tests, the short- and medium-term stabilities of its response were also evaluated. During the tests the leakage current was always negligible. All results showed values within those recommended internationally (IEC, 1997. Medical electrical equipment-dosimeters with ionization chambers and/or semi-conductor detectors as used in X-ray diagnostic imaging. IEC 61674. International Electrotechnical Commission, Genève). Copyright 2009 Elsevier Ltd. All rights reserved.

  13. Modeling ion recombination in liquid ionization chambers - Improvement and analysis of the two-dose-rate method.

    PubMed

    Andersson, Jonas; Tölli, Heikki

    2017-08-12

    The use of liquid ionization chambers can provide useful information to endeavors with radiation dosimetry for highly modulated beams. Liquid ionization chambers may be particularly suitable for computed tomography applications where conventional ionization chambers do not present a high enough sensitivity for the spatial resolution required to characterize common X-ray beams. Due to the sensitivity, which leads to high charge densities, liquid ionization chambers can suffer from large recombination losses leading to degradation in signal to dose rate linearity. To solve this problem, a two-dose-rate method for general recombination correction has been proposed for liquid ionization chambers. However, the valid range of recombination losses that the method can accurately account for has been found to vary depending on radiation quality. The present work provides an in-depth analysis of the performance of the two-dose-rate method. Furthermore, the soundness of applying gas theory to liquids is investigated by using the two-dose-rate method. In the present work, the two-dose-rate method for general recombination correction of liquid ionization chambers used in continuous beams is studied by employing theory for gas-filled ionization chambers. An approximate relation for the general collection efficiency containing a material-specific parameter that is traceable to liquids has been derived for theoretical and experimental investigation alongside existing theory. Furthermore, the disassociation between initial and general recombination in the method is analyzed both theoretically and experimentally. The results indicate that liquids and gases share general recombination characteristics, where the liquids investigated (isooctane and tetramethylsilane) to a large extent mimic the behavior theoretically expected in gases. Furthermore, it is shown that the disassociation between initial and general recombination in the two-dose-rate method is an approximation that depends

  14. Evaluation of the accuracy of 3DVH software estimates of dose to virtual ion chamber and film in composite IMRT QA.

    PubMed

    Olch, Arthur J

    2012-01-01

    A novel patient-specific intensity modulated radiation therapy (IMRT) QA system, 3DVH software and mapcheck 2, purports to be able to use diode array-measured beam doses and the patient's DICOM RT plan, structure set, and dose files to predict the delivered 3D dose distribution in the patient for comparison to the treatment planning system (TPS) calculated doses. In this study, the composite dose to an ion chamber and film in phantom predicted by the 3DVH and mapcheck 2 system is compared to the actual measured chamber and film doses. If validated in this context, then 3DVH can be used to perform an equivalent dose analysis as that obtained with film dosimetry and ion chamber-based composite IMRT QA. This is important for those losing their ability to perform film dosimetry for true composite IMRT QA and provides a measure of confidence in the accuracy of 3DVH 3D dose calculations which may replace phantom-based IMRT QA. The dosimetric results from 15 consecutive patient-specific IMRT QA tests performed by composite field irradiation of ion chamber and EDR2 film in a solid water phantom were compared to the predicted doses for those virtual detectors based on the calculated 3D dose by the 3DVH software using mapcheck 2 measured doses of each beam within each plan. For each of the 15 cases, immediately after performing the ion chamber plus film measurements, the mapcheck 2 was used to measure the dose for each beam of the plan. The dose to the volume of the virtual ion chamber and the dose distribution in the plane of the virtual film calculated by the 3DVH software was extracted. The ratio of the measured to 3DVH or eclipse-predicted ion chamber doses was calculated. The same plane in the phantom measured using film and calculated with eclipse was exported from 3DVH and the 2D gamma metric was used to compare the relationship between the film doses and the eclipse or 3DVH predicted planar doses. Also, the 3D gamma value was calculated in the 3DVH software which

  15. Detection of Amines and Ammonia with an Ambient Pressure Mass Spectrometer using a Corona Discharge Ion Source, in an Urban Atmosphere and in a Teflon Film Chamber

    NASA Astrophysics Data System (ADS)

    Alves, M.; Hanson, D. R.; Grieves, C.; Ortega, J. V.

    2015-12-01

    Amines and ammonia are an important group of molecules that can greatly affect atmospheric particle formation that can go on to impact cloud formation and their scattering of thermal and solar radiation, and as a result human health and ecosystems. In this study, an Ambient Pressure Mass Spectrometer (AmPMS) that is selective and sensitive to molecules with a high proton affinity, such as amines, was coupled with a newly built corona discharge ion source. AmPMS was used to monitor many different nitrogenous compound that are found in an urban atmosphere (July 2015, Minneapolis), down to the single digit pmol/mol level. Simultaneous to this, a proton transfer mass spectrometer also sampled the atmosphere through an inlet within 20 m of the AmPMS inlet. In another set of studies, a similar AmPMS was attached to a large Teflon film chamber at the Atmospheric Chemistry Division at NCAR (August 2015, Boulder). Exploratory studies are planned on the sticking of amines to the chamber walls as well as oxidizing the amine and monitoring products. Depending on the success of these studies, results will be presented on the reversability of amine partitioning and mass balance for these species in the chamber.

  16. Determination of PM10 and its ion composition emitted from biomass burning in the chamber for estimation of open burning emissions.

    PubMed

    Sillapapiromsuk, Sopittaporn; Chantara, Somporn; Tengjaroenkul, Urai; Prasitwattanaseree, Sukon; Prapamontol, Tippawan

    2013-11-01

    Biomass samples including agricultural waste (rice straw and maize residue) and forest leaf litter were collected from Chiang Mai Province, Thailand for the burning experiment in the self-designed stainless steel chamber to simulate the emissions of PM10. The burning of leaf litter emitted the highest PM10 (1.52±0.65 g kg(-1)). The PM10-bound ions emitted from the burning of rice straw and maize residue showed the same trend, which was K(+)>Cl(-)>SO4(2-)>NH4(+)>NO3(-). However, the emissions from maize residue burning were ~1.5-2.0 times higher than those from the rice straw burning. The ion content emitted from leaf litter burning was almost the same for all ion species. Noticeably, K(+) and Cl(-) concentrations were ~2-4 times lower than those emitted from agricultural waste burning. It can be deduced that K(+) and Cl(-) were highly emitted from agricultural waste burning due to the use of fertilizer and herbicides in the field, respectively. Based on emission values obtained from the chamber, the pollutant emission rate from open burning was calculated. Burned areas in Chiang Mai Province were 3510 and 866 km(2) in 2010 and 2011, respectively. Forest burning was 71-88%, while agricultural land burning accounted for 12-29% (rice field: crop field=1:3) of total burned area. Therefore, emissions of PM10 from open burning in Chiang Mai were 3051 ton (2010) and 705 ton (2011). Major ions emitted from agricultural waste burning were found to be K(+) and Cl(-), while those from forest burning were SO4(2-) and K(+).

  17. Verifying Sensor Response to Difficult Chemicals with a New Test Chamber Concept

    SciTech Connect

    Maughan, A. D.; Birnbaum, Jerome C.; Probasco, Kathleen M.

    2004-06-01

    In this article we discuss the application of technology innovations to optimize detection of hard-to-measure (less- or semi-volatile) compounds. These chemicals are found all around us: in pesticides and herbicides, the higher boiling polyaromatic hydrocarbons in diesel exhaust, and linked polyurethane foams in products ranging from hiking boots to acoustic ceilings. They appear in low concentrations and evaporate very slowly. These heavier chemicals are rarely measured accurately because they stick to surfaces and sampling equipment and, consequently, are not reliably sampled or delivered to analytical detectors. It’s like trying to identify cold, sticky honey by getting it to flow in through a sampling tube to a detector –it will hardly move. Honey generally coats out on surfaces and sample lines to the extent that even if it is detected, the amount present is vastly underestimated. Researchers at Pacific Northwest National Laboratory (PNNL) addressed the problem by developing a chamber facility with instrumentation that can overcome the under-reporting of these ubiquitous chemical compounds. The atmospheric chemistry chamber provides a controlled environment in which to certify the accuracy of and conditions under which sensors can best respond to volatile and semi-volatile chemicals. The facility is designed to handle and measure chemicals at the levels at which they are found in nature. Test environments can be created in which atmospheric concentrations are at low part-per-trillion concentrations. These concentrations are equivalent to an herbicide off-gassing from a commercially grown apple. The chamber can be set up to simulate releases ranging from industrial vents with high concentrations to releases from surfaces, soils, and/or vegetation where the concentrations are low.

  18. Monte Carlo computed machine-specific correction factors for reference dosimetry of TomoTherapy static beam for several ion chambers.

    PubMed

    Sterpin, E; Mackie, T R; Vynckier, S

    2012-07-01

    To determinekQmsr,Qofmsr,fo correction factors for machine-specific reference (msr) conditions by Monte Carlo (MC) simulations for reference dosimetry of TomoTherapy static beams for ion chambers Exradin A1SL, A12; PTW 30006, 31010 Semiflex, 31014 PinPoint, 31018 microLion; NE 2571. For the calibration of TomoTherapy units, reference conditions specified in current codes of practice like IAEA/TRS-398 and AAPM/TG-51 cannot be realized. To cope with this issue, Alfonso et al. [Med. Phys., - (2008)] described a new formalism introducing msr factors kQmsr,Qofmsr,fo for reference dosimetry, applicable to static TomoTherapy beams. In this study, those factors were computed directly using MC simulations for Q0 corresponding to a simplified (60) Co beam in TRS-398 reference conditions (at 10 cm depth). The msr conditions were a 10 × 5 cm(2) TomoTherapy beam, source-surface distance of 85 cm and 10 cm depth. The chambers were modeled according to technical drawings using the egs++ package and the MC simulations were run with the egs_chamber user code. Phase-space files used as the source input were produced using PENELOPE after simulation of a simplified (60) Co beam and the TomoTherapy treatment head modeled according to technical drawings. Correlated sampling, intermediate phase-space storage, and photon cross-section enhancement variance reduction techniques were used. The simulations were stopped when the combined standard uncertainty was below 0.2%. ComputedkQmsr,Qofmsr,fo values were all close to one, in a range from 0.991 for the PinPoint chamber to 1.000 for the Exradin A12 with a statistical uncertainty below 0.2%. Considering a beam quality Q defined as the TPR20,10 for a 6 MV Elekta photon beam (0.661), the additional correction kQmsr,Qfmsr,fref to kQ,Qo defined in Alfonso et al. [Med. Phys., - (2008)] formalism was in a range from 0.997 to 1.004. The MC computed factors in this study are in agreement with measured factors for chamber types already studied in

  19. Monte Carlo computed machine-specific correction factors for reference dosimetry of TomoTherapy static beam for several ion chambers.

    PubMed

    Sterpin, E; Mackie, T R; Vynckier, S

    2012-07-01

    To determine k(Q(msr),Q(o) ) (f(msr),f(o) ) correction factors for machine-specific reference (msr) conditions by Monte Carlo (MC) simulations for reference dosimetry of TomoTherapy static beams for ion chambers Exradin A1SL, A12; PTW 30006, 31010 Semiflex, 31014 PinPoint, 31018 microLion; NE 2571. For the calibration of TomoTherapy units, reference conditions specified in current codes of practice like IAEA∕TRS-398 and AAPM∕TG-51 cannot be realized. To cope with this issue, Alfonso et al. [Med. Phys. 35, 5179-5186 (2008)] described a new formalism introducing msr factors k(Q(msr),Q(o) ) (f(msr),f(o) ) for reference dosimetry, applicable to static TomoTherapy beams. In this study, those factors were computed directly using MC simulations for Q(0) corresponding to a simplified (60)Co beam in TRS-398 reference conditions (at 10 cm depth). The msr conditions were a 10 × 5 cm(2) TomoTherapy beam, source-surface distance of 85 cm and 10 cm depth. The chambers were modeled according to technical drawings using the egs++ package and the MC simulations were run with the egs_chamber user code. Phase-space files used as the source input were produced using PENELOPE after simulation of a simplified (60)Co beam and the TomoTherapy treatment head modeled according to technical drawings. Correlated sampling, intermediate phase-space storage, and photon cross-section enhancement variance reduction techniques were used. The simulations were stopped when the combined standard uncertainty was below 0.2%. Computed k(Q(msr),Q(o) ) (f(msr),f(o) ) values were all close to one, in a range from 0.991 for the PinPoint chamber to 1.000 for the Exradin A12 with a statistical uncertainty below 0.2%. Considering a beam quality Q defined as the TPR(20,10) for a 6 MV Elekta photon beam (0.661), the additional correction k(Q(msr,)Q) (f(msr,)f(ref) ) to k(Q,Q(o) ) defined in Alfonso et al. [Med. Phys. 35, 5179-5186 (2008)] formalism was in a range from 0.997 to 1.004. The MC computed factors

  20. Spectral differences in 6 MV beams with matched PDDs and the effect on chamber response

    NASA Astrophysics Data System (ADS)

    Lye, J. E.; Butler, D. J.; Ramanathan, G.; Franich, R. D.

    2012-11-01

    The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) has installed an Elekta Synergy platform linac to establish a direct megavoltage primary standard calibration service, instead of relying on calibrations derived from 60Co. One of the 6 MV beams of the ARPANSA linac has been approximately matched to the Varian high energy platform 6 MV photon beam. The electron beam energy was adjusted to match the percentage depth dose (PDD) curve and TPR20,10. This work calculates the error introduced when using a calibration factor from this Elekta Synergy Platform linac on a Varian high-energy platform beam at 6 MV. Monte Carlo models of the Varian and matched Elekta accelerator accurately predict the measured PDDs and profiles, but show significantly different energy spectra, resulting mainly from differences in target thickness between the two accelerators. Monte Carlo modelling of the energy correction factor kQ of a secondary standard NE2561 chamber shows a difference of 0.4% between the Varian and the Varian-matched Elekta beams. Although small, this is a significant discrepancy for primary standard calibrations. Similar variations are expected for chambers of similar construction, and additional variations may occur with other linac manufacturers. The work has also investigated the design of a custom flattening filter to precisely match the energy spectrum of the Varian beam on the Elekta platform.

  1. Exposure chamber

    DOEpatents

    Moss, Owen R.; Briant, James K.

    1983-01-01

    An exposure chamber includes an imperforate casing having a fluid inlet at the top and an outlet at the bottom. A single vertical series of imperforate trays is provided. Each tray is spaced on all sides from the chamber walls. Baffles adjacent some of the trays restrict and direct the flow to give partial flow back and forth across the chambers and downward flow past the lowermost pan adjacent a central plane of the chamber.

  2. Effect of a metal-dielectric structure introduced in the plasma chamber of the Frankfurt 14 GHz electron cyclotron resonance ion source

    NASA Astrophysics Data System (ADS)

    Schächter, L.; Stiebing, K. E.; Dobrescu, S.; Badescu-Singureanu, Al. I.; Schmidt, L.; Hohn, O.; Runkel, S.

    1999-02-01

    A new approach of the possibility to significantly increase the high charge state ion beams delivered by electron cyclotron resonance (ECR) ion sources by using metal-dielectric (MD) structures characterized by high secondary electron emission properties is presented. The intensities of argon ion beams extracted from the 14 GHz electron cyclotron resonance ion source of the Institut für Kernphysik (IKF) der Johann Wolfgang Goethe-Universität in Frankfurt/Main were measured when a 26 mm diam disk of a specially treated MD structure (Al-Al2O3) was introduced axially close to the ECR plasma. The Ar beam intensities and charge-state distributions obtained with this disk are compared to measurements with disks of iron and pure aluminum at the same position relative to the plasma. All measurements were performed with the disk at the plasma chamber potential. The results with the MD structure show a net shift of the beam intensity towards higher charge states as compared with the other disk materials. Enhancement factors of the beam current of up to 10 (for Ar12+) when using a MD disk compared to the output when using an aluminum disk and up to 40 (for Ar11+) when using an iron disk were measured.

  3. A comparison of linaclotide and lubiprostone dosing regimens on ion transport responses in human colonic mucosa

    PubMed Central

    Kang, Sang Bum; Marchelletta, Ronald R; Penrose, Harrison; Docherty, Michael J; McCole, Declan F

    2015-01-01

    Linaclotide, a synthetic guanylyl cyclase C (GC-C) agonist, and the prostone analog, Lubiprostone, are approved to manage chronic idiopathic constipation and constipation-predominant irritable bowel syndrome. Lubiprostone also protects intestinal mucosal barrier function in ischemia. GC-C signaling regulates local fluid balance and other components of intestinal mucosal homeostasis including epithelial barrier function. The aim of this study was to compare if select dosing regimens differentially affect linaclotide and lubiprostone modulation of ion transport and barrier properties of normal human colonic mucosa. Normal sigmoid colon biopsies from healthy subjects were mounted in Ussing chambers. Tissues were treated with linaclotide, lubiprostone, or vehicle to determine effects on short-circuit current (Isc). Subsequent Isc responses to the cAMP agonist, forskolin, and the calcium agonist, carbachol, were also measured to assess if either drug caused desensitization. Barrier properties were assessed by measuring transepithelial electrical resistance. Isc responses to linaclotide and lubiprostone were significantly higher than vehicle control when administered bilaterally or to the mucosal side only. Single versus cumulative concentrations of linaclotide showed differences in efficacy while cumulative but not single dosing caused desensitization to forskolin. Lubiprostone reduced forskolin responses under all conditions. Linaclotide and lubiprostone exerted a positive effect on TER that was dependent on the dosing regimen. Linaclotide and lubiprostone increase ion transport responses across normal human colon but linaclotide displays increased sensitivity to the dosing regimen used. These findings may have implications for dosing protocols of these agents in patients with constipation. PMID:26038704

  4. A comparison of linaclotide and lubiprostone dosing regimens on ion transport responses in human colonic mucosa.

    PubMed

    Kang, Sang Bum; Marchelletta, Ronald R; Penrose, Harrison; Docherty, Michael J; McCole, Declan F

    2015-03-01

    Linaclotide, a synthetic guanylyl cyclase C (GC-C) agonist, and the prostone analog, Lubiprostone, are approved to manage chronic idiopathic constipation and constipation-predominant irritable bowel syndrome. Lubiprostone also protects intestinal mucosal barrier function in ischemia. GC-C signaling regulates local fluid balance and other components of intestinal mucosal homeostasis including epithelial barrier function. The aim of this study was to compare if select dosing regimens differentially affect linaclotide and lubiprostone modulation of ion transport and barrier properties of normal human colonic mucosa. Normal sigmoid colon biopsies from healthy subjects were mounted in Ussing chambers. Tissues were treated with linaclotide, lubiprostone, or vehicle to determine effects on short-circuit current (I sc). Subsequent I sc responses to the cAMP agonist, forskolin, and the calcium agonist, carbachol, were also measured to assess if either drug caused desensitization. Barrier properties were assessed by measuring transepithelial electrical resistance. I sc responses to linaclotide and lubiprostone were significantly higher than vehicle control when administered bilaterally or to the mucosal side only. Single versus cumulative concentrations of linaclotide showed differences in efficacy while cumulative but not single dosing caused desensitization to forskolin. Lubiprostone reduced forskolin responses under all conditions. Linaclotide and lubiprostone exerted a positive effect on TER that was dependent on the dosing regimen. Linaclotide and lubiprostone increase ion transport responses across normal human colon but linaclotide displays increased sensitivity to the dosing regimen used. These findings may have implications for dosing protocols of these agents in patients with constipation.

  5. Liquid-filled ionization chamber temperature dependence

    NASA Astrophysics Data System (ADS)

    Franco, L.; Gómez, F.; Iglesias, A.; Pardo, J.; Pazos, A.; Pena, J.; Zapata, M.

    2006-05-01

    Temperature and pressure corrections of the read-out signal of ionization chambers have a crucial importance in order to perform high-precision absolute dose measurements. In the present work the temperature and pressure dependences of a sealed liquid isooctane filled ionization chamber (previously developed by the authors) for radiotherapy applications have been studied. We have analyzed the thermal response of the liquid ionization chamber in a ˜20C interval around room temperature. The temperature dependence of the signal can be considered linear, with a slope that depends on the chamber collection electric field. For example, a relative signal slope of 0.27×10-2 K-1 for an operation electric field of 1.67×106 V m-1 has been measured in our detector. On the other hand, ambient pressure dependence has been found negligible, as expected for liquid-filled chambers. The thermal dependence of the liquid ionization chamber signal can be parametrized within the Onsager theory on initial recombination. Considering that changes with temperature of the detector response are due to variations in the free ion yield, a parametrization of this dependence has been obtained. There is a good agreement between the experimental data and the theoretical model from the Onsager framework.

  6. Target chambers for gammashpere

    SciTech Connect

    Carpenter, M.P.; Falout, J.W.; Nardi, B.G.

    1995-08-01

    One of our responsibilities for Gammasphere, was designing and constructing two target chambers and associated beamlines to be used with the spectrometer. The first chamber was used with the early implementation phase of Gammasphere, and consisted of two spun-Al hemispheres welded together giving a wall thickness of 0.063 inches and a diameter of 12 inches.

  7. Nonlinear response and bistability of driven ion acoustic waves

    NASA Astrophysics Data System (ADS)

    Akbari-Moghanjoughi, M.

    2017-08-01

    The hydrodynamic model is used to obtain a generalized pseudoforce equation through which the nonlinear response of periodically driven ion acoustic waves is studied in an electron-ion plasma with isothermal and adiabatic ion fluids. The pseudotime series, corresponding to different driving frequencies, indicates that nonlinearity effects appear more strongly for smaller frequency values. The existence of extra harmonic resonances in the nonlinear amplitude spectrum is a clear indication of the interaction of an external force with harmonic components of the nonlinear ion acoustic waves. It is shown that many plasma parameters significantly and differently affect the nonlinear resonance spectrum of ion acoustic excitations. A heuristic but accurate model for the foldover effect is used which quite satisfactorily predicts the bistability of driven plasma oscillations. It is remarked that the characteristic resonance peak of isothermal ion plasma oscillations appears at lower frequencies but is stronger compared to that of adiabatic ions. Comparison of the exact numerical results for fully nonlinear and approximate (weakly nonlinear) models indicates that a weakly nonlinear model exaggerates the hysteresis and jump phenomenon for higher values of the external force amplitude.

  8. Investigation of the response variability of ionization chambers for the standard transfer of SIR-Spheres(®).

    PubMed

    Thiam, C; Bobin, C; Lourenço, V; Chisté, V; Amiot, M-N; Mougeot, X; Lacour, D; Rigoulay, F; Ferreux, L

    2016-03-01

    The present paper addresses the calibration of well-type ionization chambers (ICs) used at LNE-LNHB as standard transfer instruments to calibrate hospitals in the case of SIR-Spheres(®)(90)Y resin microspheres (Sirtex, Australia). Developed for interventional oncology, this radiopharmaceutical is directly injected in the liver for cancer treatment via a selective internal radiation therapy. The present work was carried out in the framework of the European project "Metrology for molecular radiotherapy" (MetroMRT). As commonly performed in radionuclide metrology for radiopharmaceuticals, the objective is to ensure the metrological traceability of SIR-Spheres(®) to hospitals. Preceding studies were focused on primary measurements of SIR-Spheres(®) based on the TDCR (Triple to Double Coincidence Ratio) method, applied after the dissolution of the (90)Y-labeled resin microspheres. As (90)Y is a high-energy β(-)-emitter, the IC response strongly depends on the transport of electrons in the radioactive solution and surroundings (vial, chamber liners and materials). The variability of the IC-response due to the geometry dependence is investigated by means of measurements and Monte Carlo simulations in the case of a Vinten IC. The aim of the present study was also to propose a reliable uncertainty for ICs calibrations for the standard transfer of SIR-Spheres(®) to hospitals. Copyright © 2015 Elsevier Ltd. All rights reserved.

  9. Indirect prediction of surface ozone concentration by plant growth responses in East Asia using mini-open top chambers.

    PubMed

    Kohno, Yoshihisa; Matsumura, Hideyuki; Miwa, Makoto; Yonekura, Tetsushi; Aihara, Keiji; Umponstira, Chanin; Le, Vo Thanh; Ngoc, Nguyen Thuy; Viet, Phanm Hung; Wei, Ma

    2013-03-01

    We developed small and mobile open top chambers (mini-OTC) measuring 0.6 m (W) × 0.6 m (D) × 1.2 m (H) with an air duct of 0.6 m (W) × 0.23 m (D) × 1.2 m (H). The air duct can be filled with activated charcoal to blow charcoal filtered air (CF) into the chamber, as opposed to non-filtered ambient air (NF). Ozone sensitive radish Raphanus sativus cv. Red Chime and rosette pakchoi Brassica campestris var. rosularis cv. ATU171 were exposed to NF and CF in mini-OTCs at different locations in East Asia. A total of 29 exposure experiments were conducted at nine locations, Shanghai, China, Ha Noi, Vietnam, Lampang, Phitsanulok and Pathumtani, Thailand, and Hiratsuka, Kisai, Abiko and Akagi, Japan. Although no significant relationships between the mean concentrations of ambient O(3) during the experimental period and the growth responses were observed for either species, multiple linear regression analysis suggested a good relationship between the biomass responses in each species and the O(3) concentration, temperature, and relative humidity. The cumulative daily mean O(3) (ppb/day) could be indirectly predicted by NF/CF based on the dry weight ratio of biomass, mean air temperature, and relative air humidity.

  10. Electrophysiological responses of the mouse retina to 12C ions.

    PubMed

    Sannita, Walter G; Peachey, Neal S; Strettoi, Enrica; Ball, Sherry L; Belli, Francesco; Bidoli, Vittorio; Carozzo, Simone; Casolino, Marco; Di Fino, Luca; Picozza, Piergiorgio; Pignatelli, Vincenzo; Rinaldi, Adele; Saturno, Moreno; Schardt, Dieter; Vazquez, Marcelo; Zaconte, Veronica; Narici, Livio

    2007-04-18

    Phosphenes ("light flashes") have been reported by most astronauts on space missions and by healthy subjects whose eyes were exposed to ionizing radiation in early experiments in particle accelerators. The conditions of occurrence suggested retinal effects of heavy ions. To develop an in vivo animal model, we irradiated the eyes of anesthetized wild-type mice with repeated bursts of 12C ions delivered under controlled conditions in accelerator. 12C ions evoked electrophysiological retinal mass responses and activated the visual system as indicated by responses recorded from the visual cortex. No retinal immunohistological damage was detected. Mice proved a suitable animal model to study radiation-induced phosphenes in vivo and our findings are consistent with an origin of phosphenes in radiation activating the retina.

  11. Development and application of a novel environmental preference chamber for assessing responses of laboratory mice to atmospheric ammonia.

    PubMed

    Green, Angela R; Wathes, Christopher M; Demmers, Theo G M; Clark, Judy MacArthur; Xin, Hongwei

    2008-03-01

    A novel environmental preference chamber (EPC) was developed and used to assess responses of laboratory mice to atmospheric ammonia. The EPC features 1) a test chamber with 4 individually ventilated, mutually accessible compartments; b) automated tracking of mouse movements by using paired infrared sensors; c) identification of individual mice by using photosensors; d) monitoring and regulation of the NH3 concentration in each compartment; and e) personal-computer-based data acquisition. In an initial preference study with the EPC, 4 groups of 4 laboratory mice (BALB/c/Bkl; body weight, 13.4 to 18.4 g) were each given a choice among 4 NH3 concentrations (mean +/- SE) of 4 +/- 2, 30 +/- 2, 56 +/- 4, and 110 +/- 6 ppm for 2 d after a 2-d familiarization period. Once trained to use the intercompartment tunnels, the mice made extensive use of the EPC, with each group making more than 2000 intercompartment movements during 48 h. Video recording verified the results of the automatic tracking system, which detected and correctly determined mouse location for 79% of the moves. The use of photosensors proved to be ineffective in recognizing individual mice. Although the EPC would benefit from refinement and further development, it simplified analysis of locomotion behavioral data. Results of the preference study indicated that the mice exhibited no clear preference for, or aversion to, any of the experimental concentrations of ammonia and that the mice clearly preferred the upper 2 compartments of the chamber over the lower 2 compartments. Further investigation should be conducted to verify these preliminary results and explore other preferences of laboratory mice for environmental conditions and resources.

  12. Smart responsive microcapsules capable of recognizing heavy metal ions.

    PubMed

    Pi, Shuo-Wei; Ju, Xiao-Jie; Wu, Han-Guang; Xie, Rui; Chu, Liang-Yin

    2010-09-15

    Smart responsive microcapsules capable of recognizing heavy metal ions are successfully prepared with oil-in-water-in-oil double emulsions as templates for polymerization in this study. The microcapsules are featured with thin poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (P(NIPAM-co-BCAm)) membranes, and they can selectively recognize special heavy metal ions such as barium(II) or lead(II) ions very well due to the "host-guest" complexation between the BCAm receptors and barium(II) or lead(II) ions. The stable BCAm/Ba(2+) or BCAm/Pb(2+) complexes in the P(NIPAM-co-BCAm) membrane cause a positive shift of the volume phase transition temperature of the crosslinked P(NIPAM-co-BCAm) hydrogel to a higher temperature, and the repulsion among the charged BCAm/Ba(2+) or BCAm/Pb(2+) complexes and the osmotic pressure within the P(NIPAM-co-BCAm) membranes result in the swelling of microcapsules. Induced by recognizing barium(II) or lead(II) ions, the prepared microcapsules with P(NIPAM-co-BCAm) membranes exhibit isothermal and significant swelling not only in outer and inner diameters but also in the membrane thickness. The proposed microcapsules in this study are highly attractive for developing smart sensors and/or carriers for detection and/or elimination of heavy metal ions.

  13. Response of ozone to changes in hydrocarbon and nitrogen oxide concentrations in outdoor smog chambers filled with Los Angeles air

    NASA Astrophysics Data System (ADS)

    Kelly, Nelson A.; Gunst, Richard F.

    During the summer portion of the 1987 Southern California Air Quality Study (SCAQS), outdoor smog chamber experiments were performed on Los Angeles air to determine the response of maximum ozone levels, O 3(max), to changes in the initial concentrations of hydrocarbons, HC, and nitrogen oxides, NO x. These captive-air experiments were conducted in downtown Los Angeles and in the downwind suburb of Claremont. Typically, eight chambers were filled with LA air in the morning. In some chambers the initial HC and/or NO x concentrations were changed by 25% to 50% by adding various combinations of a mixture of HC, clean air, or NO x. The O 3 concentration in each chamber was monitored throughout the day to determine O 3(max). An empirical mathematical model for O 3(max) was developed from regression fits to the initial HC and NO x concentrations and to the average daily temperature at both sites. This is the first time that a mathematical expression for the O 3-precursor relationship and the positive effect of temperature on O 3(max) have been quantified using captive-air experiments. An ozone isopleth diagram prepared from the empirical model was qualitatively similar to those prepared from photochemical mechanisms. This constitutes the first solely empirical corroboration of the O 3 contour shape for Los Angeles. To comply with the Federal Ozone Standard in LA, O 3(max) must be reduced by approximately 50%. Several strategies for reducing O 3(max) by 50% were evaluated using the empirical model. For the average initial conditions that we measured in LA, the most efficient strategy is one that reduces HC by 55-75%, depending on the ambient HC/NO x ratio. Any accompanying reduction in NO x would be counter-productive to the benefits of HC reductions. In fact, reducing HC and NO x simultaneously requires larger percentage reductions for both than the reduction required when HC alone is reduced. The HC-reduction strategy is the most efficient on average, but no single

  14. A smog chamber study coupling a photoionization aerosol electron/ion spectrometer to VUV synchrotron radiation: organic and inorganic-organic mixed aerosol analysis

    NASA Astrophysics Data System (ADS)

    Baeza-Romero, María Teresa; Gaie-Levrel, Francois; Mahjoub, Ahmed; López-Arza, Vicente; Garcia, Gustavo A.; Nahon, Laurent

    2016-07-01

    A reaction chamber was coupled to a photoionization aerosol time-of-flight mass spectrometer based on an electron/ion coincidence scheme and applied for on-line analysis of organic and inorganic-organic mixed aerosols using synchrotron tunable vacuum ultraviolet (VUV) photons as the ionization source. In this proof of principle study, both aerosol and gas phase were detected simultaneously but could be differentiated. Present results and perspectives for improvement for this set-up are shown in the study of ozonolysis ([O3] = 0.13-3 ppm) of α-pinene (2-3 ppm), and the uptake of glyoxal upon ammonium sulphate. In this work the ozone concentration was monitored in real time, together with the particle size distributions and chemical composition, the latter taking advantage of the coincidence spectrometer and the tuneability of the synchrotron radiation as a soft VUV ionization source.

  15. Exposure chamber

    DOEpatents

    Moss, Owen R.

    1980-01-01

    A chamber for exposing animals, plants, or materials to air containing gases or aerosols is so constructed that catch pans for animal excrement, for example, serve to aid the uniform distribution of air throughout the chamber instead of constituting obstacles as has been the case in prior animal exposure chambers. The chamber comprises the usual imperforate top, bottom and side walls. Within the chamber, cages and their associated pans are arranged in two columns. The pans are spaced horizontally from the walls of the chamber in all directions. Corresponding pans of the two columns are also spaced horizontally from each other. Preferably the pans of one column are also spaced vertically from corresponding pans of the other column. Air is introduced into the top of the chamber and withdrawn from the bottom. The general flow of air is therefore vertical. The effect of the horizontal pans is based on the fact that a gas flowing past the edge of a flat plate that is perpendicular to the flow forms a wave on the upstream side of the plate. Air flows downwardly between the chamber walls and the outer edges of the pan. It also flows downwardly between the inner edges of the pans of the two columns. It has been found that when the air carries aerosol particles, these particles are substantially uniformly distributed throughout the chamber.

  16. Calcium ions facilitate body heat emission response to warming.

    PubMed

    Tkachenko, E Ya; Khramova, G M; Kozyreva, T V

    2015-01-01

    Involvement of various areas of the body surface in heat emission response to warming is characterized by a certain succession. The first response preceding the deep body temperature rise is dilation of ear skin vessels. Then, an increase in deep body temperature is counterbalanced by vascular reaction in the tail region, which plays the leading role in up-regulation of heat emission. Calcium ions accelerate the vascular response to warming in both regions, although they produce no effect on the maximum level of heat emission. Our findings confirm the involvement of Ca(2+)-dependent mechanisms in activation of the processes aimed at stabilization of body temperature in warm-blooded animals. The role of heat-sensitive TRPV1 ion channels determining modality of the temperature signal and direction of effector reactions is discussed.

  17. Role of calcium ions in phytochrome responses: an update

    NASA Technical Reports Server (NTRS)

    Roux, S. J.; Wayne, R. O.; Datta, N.

    1986-01-01

    Recent findings related to the role of calcium ions in phytochrome responses are reviewed and summarized. Hypotheses tested are the activation of calmodulin by light-regulated Ca2+ transport in cells and the photoinduction of calmodulin-activated enzyme activities. Discussion focuses on evidence that Ca2+ helps to regulate phytochrome responses, calcium requirements for photoinduced spore germination in the fern Onoclea, Ca2+ fluxes and phytochrome function in the alga Mougeotia, calmodulin antagonist blocking of red-light stimulated chloroplast rotation, the role of phosphorylation in calmodulin-regulated responses, and phytochrome regulation of nuclear protein phosphorylation.

  18. Role of calcium ions in phytochrome responses: an update

    NASA Technical Reports Server (NTRS)

    Roux, S. J.; Wayne, R. O.; Datta, N.

    1986-01-01

    Recent findings related to the role of calcium ions in phytochrome responses are reviewed and summarized. Hypotheses tested are the activation of calmodulin by light-regulated Ca2+ transport in cells and the photoinduction of calmodulin-activated enzyme activities. Discussion focuses on evidence that Ca2+ helps to regulate phytochrome responses, calcium requirements for photoinduced spore germination in the fern Onoclea, Ca2+ fluxes and phytochrome function in the alga Mougeotia, calmodulin antagonist blocking of red-light stimulated chloroplast rotation, the role of phosphorylation in calmodulin-regulated responses, and phytochrome regulation of nuclear protein phosphorylation.

  19. Physiological, Behavioral, and Histological Responses of Male C57BL/6N Mice to Different CO2 Chamber Replacement Rates

    PubMed Central

    Boivin, Gregory P; Bottomley, Michael A; Dudley, Emily S; Schiml, Patricia A; Wyatt, Christopher N; Grobe, Nadja

    2016-01-01

    Rodent euthanasia with CO2 by using gradual displacement of 10% to 30% of the chamber volume per minute is considered acceptable by the AVMA Panel on Euthanasia. However, whether a 50% to 100% chamber replacement rate (CRR) of CO2 is more painful or distressful than 10% to 30% CRR is unclear. Therefore, we examined physiological and behavioral parameters, corticosterone and ACTH levels, and lung histology of mice euthanized at CRR of 15%, 30%, 50%, or 100%. Adult male C57BL/6N mice were euthanized at different CO2 CRR as physiological parameters were recorded telemetrically. Video recordings were reviewed to determine when the mouse first became ataxic, when it was fully recumbent (characterized by the mouse's nose resting on the cage floor), and when breathing stopped. Overall, CO2 euthanasia increased cardiovascular parameters and activity. Specific significant differences that were associated with 50% to 100% compared with 15% to 30% CO2 CRR included an increase in systolic blood pressure per second from initiation of CO2 until ataxia, a decrease in total diastolic blood pressure until ataxia, and a decrease in total heart rate until ataxia, immobility, and death. All physiological responses occurred more rapidly with higher CRR. Activity levels, behavioral responses, plasma adrenocorticotropic hormone and corticosterone levels, and lung pathology were not different between groups. We found no physiological, behavioral, or histologic evidence that 15% or 30% CO2 CRR is less painful or distressful than is 50% or 100% CO2 CRR. We conclude that 50% to 100% CO2 CRR is acceptable for euthanizing adult male C57BL/6N mice. PMID:27423153

  20. Chamber dynamic research with pulsed power

    SciTech Connect

    PETERSON,ROBERT R.; OLSON,CRAIG L.; RENK,TIMOTHY J.; ROCHAU,GARY E.; SWEENEY,MARY ANN

    2000-05-15

    In Inertial Fusion Energy (IFE), Target Chamber Dynamics (TCD) is an integral part of the target chamber design and performance. TCD includes target output deposition of target x-rays, ions and neutrons in target chamber gases and structures, vaporization and melting of target chamber materials, radiation-hydrodynamics in target chamber vapors and gases, and chamber conditions at the time of target and beam injections. Pulsed power provides a unique environment for IFE-TCD validation experiments in two important ways: they do not require the very clean conditions which lasers need and they currently provide large x-ray and ion energies.

  1. Wire chamber

    DOEpatents

    Atac, Muzaffer

    1989-01-01

    A wire chamber or proportional counter device, such as Geiger-Mueller tube or drift chamber, improved with a gas mixture providing a stable drift velocity while eliminating wire aging caused by prior art gas mixtures. The new gas mixture is comprised of equal parts argon and ethane gas and having approximately 0.25% isopropyl alcohol vapor.

  2. Performance of Current-Mode Ion Chambers as Beam Monitors in a Pulsed Cold Neutron Beam for the NPDGamma experiment

    NASA Astrophysics Data System (ADS)

    Gillis, R. Chad

    2006-10-01

    The NPDGamma collaboration has built and commissioned an apparatus to measure the parity-violating gamma asymmetry A in the low energy np capture process n+p->d+ γ. The asymmetry in question is a 10-8 correlation between the spin of the incident (polarized) neutron and the outgoing 2.2 MeV gamma ray. A set of purpose-built, 3He-filled ionization chambers read out in current mode is used to monitor the incident neutron flux, the beam polarization, and the transmission of the liquid para-hydrogen target during the NPDGamma measurements. As will be described in the talk, these beam monitors are simple, reliable, low-noise detectors that have performed excellently for NPDGamma. We have verified that the beam monitor signals can be interpreted to reproduce the known time-of-flight dependence of beam flux from the LANSCE pulsed cold neutron source, and that the neutron beam polarization can be measured at the 2% level from direct measurements of the transmission of the beam through the beam polarizer.

  3. The response of scintillators to heavy ions: 1, Plastics

    SciTech Connect

    McMahan, M.A.

    1987-10-01

    The response of various scintillator detectors to ions of A = 1-84 and energies E/A = 5 to 30 MeV have been measured, and are found to be linear above an energy of 100 MeV. Results are presented for a typical organic plastic scintillator including parametrizations of the data as a function of Z, A, and energy. These results can be used by anyone using scintillators as heavy ion detectors, with one calibration point giving a normalization that allows use of the whole set of curves. The response functions are compared to previous parametrizations at lower energies and discussed in terms of the theory of delta-ray formation in the scintillator.

  4. IFE Chamber Technology - Status and Future Challenges

    SciTech Connect

    Meier, W.R.; Raffray, A.R.; Abdel-Khalik, S.I.; Kulcinski, G.L.; Latowski, J.F.; Najmabadi, F.; Olson, C.L.; Peterson, P.F.; Ying, A.; Yoda, M.

    2003-07-15

    Significant progress has been made on addressing critical issues for inertial fusion energy (IFE) chambers for heavy-ion, laser and Z-pinch drivers. A variety of chamber concepts are being investigated including drywall (currently favored for laser IFE), wetted-wall (applicable to both laser and ion drivers), and thick-liquid-wall (favored by heavy ion and z-pinch drivers). Recent progress and remaining challenges in developing IFE chambers are reviewed.

  5. IFE Chamber Technology - Status and Future Challenges

    SciTech Connect

    Meier, W R; Raffrary, A R; Abdel-Khalik, S; Kulcinski, G; Latkowski, J F; Najmabadi, F; Olson, C L; Peterson, P F; Ying, A; Yoda, M

    2002-11-15

    Significant progress has been made on addressing critical issues for inertial fusion energy (IFE) chambers for heavy-ion, laser and Z-pinch drivers. A variety of chamber concepts are being investigated including dry-wall (currently favored for laser IFE), wetted-wall (applicable to both laser and ion drivers), and thick-liquid-wall favored by heavy ion and z-pinch drivers. Recent progress and remaining challenges in developing IFE chambers are reviewed.

  6. Endothelial cell differentiation into capillary-like structures in response to tumour cell conditioned medium: a modified chemotaxis chamber assay.

    PubMed Central

    Garrido, T.; Riese, H. H.; Aracil, M.; Pérez-Aranda, A.

    1995-01-01

    We have developed a modified chemotaxis chamber assay in which bovine aortic endothelial (BAE) cells degrade Matrigel basement membrane and migrate and form capillary-like structures on type I collagen. This capillary formation occurs in the presence of conditioned media from highly metastatic tumour cell lines, such as B16F10 murine melanoma or MDA-MD-231 human breast adenocarcinoma, but not in the presence of conditioned medium (CM) from the less invasive B16F0 cell line. Replacement of tumour cell CM by 10 ng ml-1 basic fibroblast growth factor (bFGF) also results in capillary-like structure formation by BAE cells. An anti-bFGF antibody blocks this effect, showing that bFGF is one of the factors responsible for the angiogenic response induced by B16F10 CM in our assay. Addition of an anti-laminin antibody reduces significantly the formation of capillary-like structures, probably by blocking the attachment of BAE cells to laminin present in Matrigel. The anti-angiogenic compound suramin inhibits in a dose-dependent manner (complete inhibition with 100 microM suramin) the migration and differentiation of BAE cells on type I collagen in response to B16F10 CM. This assay represents a new model system to study tumour-induced angiogenesis in vitro. Images Figure 2 Figure 3 PMID:7536021

  7. Dosimetric Performance of Newly Developed Farmer-Type Ionization Chamber in Radiotherapy Practice.

    PubMed

    Saminathan, Sathiyan; Godson, Henry Finlay; Ponmalar, Retna; Manickam, Ravikumar; Mazarello, James; Fernandes, Rahul

    2016-12-01

    Dose measurement with ionization chamber is essential to deliver accurate dose to the tumor in radiotherapy. The cylindrical Farmer-type ionization chamber is recommended by various dosimetry protocols for dose measurement of radiotherapy beams. The air-equivalent graphite wall Farmer-type ionization chamber (FAR 65 GB) of active volume 0.65 cm(3) with aluminum as the central electrode material was fabricated. Various dosimetric parameters were studied for the newly developed ionization chamber in cobalt-60, 6 and 18 MV photon beams. The preirradiation and postirradiation leakage of the chamber was within 0.08%. The long-term stability and the stem effect of the chamber were within 0.07% and 0.3%, respectively. The sensitivity of the ionization chamber was found to be 22.15 nC/Gy. The chamber shows linear response with dose for cobalt-60, 6 and 18 MV photon beams. The ion recombination correction factor increases with increase in bias voltage. For all energies and field sizes, the polarity correction factor is almost closer to unity. The ion recombination and polarity correction measurements show that the polarizing potential and polarity recommended during the calibration of ionization chamber should be used for routine measurement to avoid the uncertainty. The chamber response is independent of dose rate and energy. The chamber is cost-effective and shows precise and reproducible response. The study carried out confirms that the newly fabricated ion chamber can be used in the measurement of absolute dose for high-energy photon beams. © The Author(s) 2015.

  8. IONIZATION CHAMBER

    DOEpatents

    Redman, W.C.; Shonka, F.R.

    1958-02-18

    This patent describes a novel ionization chamber which is well suited to measuring the radioactivity of the various portions of a wire as the wire is moved at a uniform speed, in order to produce the neutron flux traverse pattern of a reactor in which the wire was previously exposed to neutron radiation. The ionization chamber of the present invention is characterized by the construction wherein the wire is passed through a tubular, straight electrode and radiation shielding material is disposed along the wire except at an intermediate, narrow area where the second electrode of the chamber is located.

  9. Monte Carlo simulations and benchmark measurements on the response of TE(TE) and Mg(Ar) ionization chambers in photon, electron and neutron beams

    NASA Astrophysics Data System (ADS)

    Lin, Yi-Chun; Huang, Tseng-Te; Liu, Yuan-Hao; Chen, Wei-Lin; Chen, Yen-Fu; Wu, Shu-Wei; Nievaart, Sander; Jiang, Shiang-Huei

    2015-06-01

    The paired ionization chambers (ICs) technique is commonly employed to determine neutron and photon doses in radiology or radiotherapy neutron beams, where neutron dose shows very strong dependence on the accuracy of accompanying high energy photon dose. During the dose derivation, it is an important issue to evaluate the photon and electron response functions of two commercially available ionization chambers, denoted as TE(TE) and Mg(Ar), used in our reactor based epithermal neutron beam. Nowadays, most perturbation corrections for accurate dose determination and many treatment planning systems are based on the Monte Carlo technique. We used general purposed Monte Carlo codes, MCNP5, EGSnrc, FLUKA or GEANT4 for benchmark verifications among them and carefully measured values for a precise estimation of chamber current from absorbed dose rate of cavity gas. Also, energy dependent response functions of two chambers were calculated in a parallel beam with mono-energies from 20 keV to 20 MeV photons and electrons by using the optimal simple spherical and detailed IC models. The measurements were performed in the well-defined (a) four primary M-80, M-100, M120 and M150 X-ray calibration fields, (b) primary 60Co calibration beam, (c) 6 MV and 10 MV photon, (d) 6 MeV and 18 MeV electron LINACs in hospital and (e) BNCT clinical trials neutron beam. For the TE(TE) chamber, all codes were almost identical over the whole photon energy range. In the Mg(Ar) chamber, MCNP5 showed lower response than other codes for photon energy region below 0.1 MeV and presented similar response above 0.2 MeV (agreed within 5% in the simple spherical model). With the increase of electron energy, the response difference between MCNP5 and other codes became larger in both chambers. Compared with the measured currents, MCNP5 had the difference from the measurement data within 5% for the 60Co, 6 MV, 10 MV, 6 MeV and 18 MeV LINACs beams. But for the Mg(Ar) chamber, the derivations reached 7

  10. Inverse combustion force estimation based on response measurements outside the combustion chamber and signal processing

    NASA Astrophysics Data System (ADS)

    Hosseini Fouladi, Mohammad; Mohd. Nor, Mohd. Jailani; Kamal Ariffin, Ahmad; Abdullah, Shahrir

    2009-11-01

    Exposure to vibration has various physiological effects on vehicle passengers. Engine is one of the main sources of vehicle vibration. The major causes of engine vibration are combustion forces transmitted through the pistons and connection rods. Evaluation of sources is the first step to attenuate this vibration. Assessment of these sources is not an easy task because internal parts of machinery are not accessible. Often, instrumentation for such systems is costly, time consuming and some modifications would be necessary. Aim of the first part of this paper was to validate an inverse technique and carry out mobility analysis on a vehicle crankshaft to achieve matrix of Frequency Response Functions (FRFs). Outcomes were implemented to reconstruct the applied force for single and multiple-input systems. In the second part, the validated inverse technique and FRFs were used to estimate piston forces of an operating engine. Bearings of crankshaft were chosen as nearest accessible parts to piston connecting rods. Accelerometers were connected to the bearings for response measurement during an ideal engine operation. These responses together with FRFs, which were estimated in the previous part, were utilised in the inverse technique. Tikhonov regularization was used to solve the ill-conditioned inverse system. Two methods, namely L-curve criterion and Generalized Cross Validation (GCV), were employed to find the regularization parameter for the Tikhonov method. The inverse problem was solved and piston forces applied to crankpins were estimated. Results were validated by pressure measurement inside a cylinder and estimating the corresponding combustion force. This validation showed that inverse technique and measurement outcomes were roughly in agreement. In presence of various noise, L-curve criterion conduces to more robust results compared to the GCV method. But in the absence of high correlation between sources ( f>600 HzHz), the GCV technique leads to more accurate

  11. SU-E-T-172: Characterization of TLD-100 (LiF:Mg,Ti) Microcube Energy Response in a Cylindrical Chamber Phantom

    SciTech Connect

    Desai, V; Hammer, C; Kunugi, K; Culberson, W; DeWerd, L

    2015-06-15

    Purpose: To characterize the energy response of TLD-100 microcubes inside a Virtual Water chamber phantom. Methods: Four TLD microcubes were placed inside a water-proof Virtual Water (VW) chamber phantom and irradiated to a known dose on a Varian linac in a 1D water tank. These chamber phantoms were then replaced by TLD-100 chips inside a separate VW paddle and irradiated to the same dose. Each energy response reading was calculated as light output per unit dose in nC/cGy and normalized to a calibration set irradiated to the same dose in 60Co. The differences in response between the TLD chips and microcubes were then analyzed. Results: Across all energies, the average microcube response was less sensitive to energy than the average chip response with both falling consistently within 2.8% of previously established values in the literature Conclusion: TLD microcubes showed a lower average sensitivity to energy than their TLD chip counterparts. The use of TLD-100 microcubes inside the chamber phantom was validated against TLD-100 chips inside of VW paddles.

  12. [Dual chamber rate responsive pacing and chronotropic insufficiency. Comparison of double and respiratory sensors].

    PubMed

    Lascault, G; Pansard, Y; Scholl, J M; Abraham, P; Dupuis, J M; Victor, J; Copie, X; Alonso, C; Sarrazin, E

    2001-03-01

    Late responsive DDD pacemakers are the most technically advanced devices presently available. These pacemakers are particularly useful in patients with chronotropic insufficiency when the sinus node is incapable of accelerating during exercise. The latest pacemakers have two sensors to reproduce optimal physiological sinus acceleration. The aim of this study was to analyse the performances of a new rate responsive pacemaker with a double activity and respiratory sensor, the interaction of which is automatically controlled by a sophisticated algorithm, in 12 patients (8 men and 4 women) with a mean age of 75 +/- 7 years. Analysis was based on the performance of the sensors used singly or in association: during three exercise stress tests with measurement of the VO2 max; during everyday activities using the data archived by the pacemaker and the answers to a simplified questionnaire on quality of life. The results showed that during exercise stress testing with measurement of VO2 max, the best performances were obtained with the double sensor or the respiratory sensor compared with the activity sensor alone, suggesting that these two sensors are more effective in intense exercise. This tendency was also observed in the analysis of the memory bank of the pacemaker which showed that the total duration of the faster heart rates was greater with the two sensors. On the other hand, the quality of life was not significantly different, whichever sensor was studied. Longer scale trials are necessary to appreciate the real value of these new double sensor pacing devices and to identify the best indications for their usage.

  13. Osmotic response of oocytes using a microscope diffusion chamber: a preliminary study comparing murine and human ova.

    PubMed

    Bernard, A; McGrath, J J; Fuller, B J; Imoedemhe, D; Shaw, R W

    1988-12-01

    The hydraulic conductivity (Lp) of the plasma membrane determines how cells respond to the stresses of dehydration encountered during cryopreservation. We have used a microscope diffusion chamber which allows for direct real-time observation of the dynamic osmotic response of individual cells in microvolume suspension to compare the Lp of murine and human unfertilized ova. In this system, the response of an individual cell to the induced osmotic imbalance is documented via a series of photomicrographs or videotape; from these data the Lp can be computed. Donated human preovulatory oocytes were compared with macroscopically normal human ova, 43 hr after insemination, which had failed to fertilize (Ff) and with murine ova collected 13 hr post human chorionic gonadotropin injection. The permeability coefficients were 0.65 +/- 0.43, 0.84 +/- 0.39, and 0.36 +/- 0.07 micron3/micron2/atm/min. The results suggest that it may be possible to use Ff ova for experiments to design suitable cryopreservation procedures.

  14. Study of timing response and charge spectra of glass based Resistive Plate Chamber detectors for INO-ICAL experiment

    NASA Astrophysics Data System (ADS)

    Gaur, A.; Kumar, A.; Naimuddin, Md.

    2017-03-01

    Resistive Plate chambers (RPCs) are robust and affordable gaseous detectors that combine low cost with excellent timing, good spatial resolution and fast response to the incoming particles. The India Based Neutrino Observatory is an approved project aimed at building a magnetised Iron Calorimeter (ICAL) detector to study Neutrino physics and related issues. The ICAL experiment will utilize about 29000 RPC's as active detector elements, sandwiched between alternate plates of thick iron. The RPC detectors will be used to detect muons produced from the atmospheric neutrinos interaction with an iron target. The spatial information of the muons will be extracted from the two dimensional readout and the hit position in the respective layers. The up going and down going directionality will be obtained using the time stamp of hits in the active detectors. The charge induced by the particle and its behaviour with respect to the applied voltage play a significant role in designing the readout electronics for the detector. In this paper, we present the timing and charge measurement of single gap glass based RPC detectors. We will also report about studies on the dependence of the timing and charge response of these RPC detectors as a function of the gas composition.

  15. A photoperiod-responsive protein compendium and conceptual proteome roadmap outline in maize grown in growth chambers with controlled conditions

    PubMed Central

    Li, You-Zhi; Fan, Xian-Wei; Chen, Qiang; Zhong, Hao

    2017-01-01

    Maize (Zea mays L.) is one of the major staple food crops of the world. However, high photoperiod sensitivity, especially for tropical germplasms, impedes attempts to improve maize agronomical traits by integration of tropical and temperate maize germplasms. Physiological and phenotypic responses of maize to photoperiod have widely been investigated based on multi-site field observations; however, proteome-based responsive mechanisms under controlled photoperiod regimes, nutrient and moisture soils are not yet well understood. In the present study, we sequenced and analyzed six proteomes of tropically-adapted and photoperiod-sensitive M9 inbred line at the vegetative 3 stage and proteomes from tropically-adapted and photoperiod-sensitive Shuang M9 (SM9) inbred line at the vegetative-tasseling stage. All plants were grown in growth chambers with controlled soil and temperature and three photoperiod regimes, a short photoperiod (SP) of 10 h light/14 h dark, a control neutral photoperiod (NP) of 12 h light/12 h dark, and a long photoperiod (LP) of 16 h light/8 h dark for a daily cycle. We identified 4,395 proteins of which 401 and 425 differentially-expressed proteins (DPs) were found in abundance in M9 leaves and in SM9 leaves as per SP/LP vs. NP, respectively. Some DPs showed responses to both SP and LP while some only responded to either SP or LP, depending on M9 or SM9. Our study showed that the photoperiodic response pathway, circadian clock rhythm, and high light density/intensity crosstalk with each other, but apparently differ from dark signaling routes. Photoperiod response involves light-responsive or dark-responsive proteins or both. The DPs positioned on the signaling routes from photoperiod changes to RNA/DNA responses involve the mago nashi homolog and glycine-rich RNA-binding proteins. Moreover, the cell-to-cell movement of ZCN14 through plasmodesmata is likely blocked under a 16-h-light LP. Here, we propose a photoperiodic model based on our findings

  16. A photoperiod-responsive protein compendium and conceptual proteome roadmap outline in maize grown in growth chambers with controlled conditions.

    PubMed

    Li, You-Zhi; Fan, Xian-Wei; Chen, Qiang; Zhong, Hao

    2017-01-01

    Maize (Zea mays L.) is one of the major staple food crops of the world. However, high photoperiod sensitivity, especially for tropical germplasms, impedes attempts to improve maize agronomical traits by integration of tropical and temperate maize germplasms. Physiological and phenotypic responses of maize to photoperiod have widely been investigated based on multi-site field observations; however, proteome-based responsive mechanisms under controlled photoperiod regimes, nutrient and moisture soils are not yet well understood. In the present study, we sequenced and analyzed six proteomes of tropically-adapted and photoperiod-sensitive M9 inbred line at the vegetative 3 stage and proteomes from tropically-adapted and photoperiod-sensitive Shuang M9 (SM9) inbred line at the vegetative-tasseling stage. All plants were grown in growth chambers with controlled soil and temperature and three photoperiod regimes, a short photoperiod (SP) of 10 h light/14 h dark, a control neutral photoperiod (NP) of 12 h light/12 h dark, and a long photoperiod (LP) of 16 h light/8 h dark for a daily cycle. We identified 4,395 proteins of which 401 and 425 differentially-expressed proteins (DPs) were found in abundance in M9 leaves and in SM9 leaves as per SP/LP vs. NP, respectively. Some DPs showed responses to both SP and LP while some only responded to either SP or LP, depending on M9 or SM9. Our study showed that the photoperiodic response pathway, circadian clock rhythm, and high light density/intensity crosstalk with each other, but apparently differ from dark signaling routes. Photoperiod response involves light-responsive or dark-responsive proteins or both. The DPs positioned on the signaling routes from photoperiod changes to RNA/DNA responses involve the mago nashi homolog and glycine-rich RNA-binding proteins. Moreover, the cell-to-cell movement of ZCN14 through plasmodesmata is likely blocked under a 16-h-light LP. Here, we propose a photoperiodic model based on our findings

  17. Multi-anode ionization chamber

    DOEpatents

    Bolotnikov, Aleksey E.; Smith, Graham; Mahler, George J.; Vanier, Peter E.

    2010-12-28

    The present invention includes a high-energy detector having a cathode chamber, a support member, and anode segments. The cathode chamber extends along a longitudinal axis. The support member is fixed within the cathode chamber and extends from the first end of the cathode chamber to the second end of the cathode chamber. The anode segments are supported by the support member and are spaced along the longitudinal surface of the support member. The anode segments are configured to generate at least a first electrical signal in response to electrons impinging thereon.

  18. A novel fast neutron dosemeter based on fission chambers. Part I: Principles of operation and theoretical response in neutron therapy radiation fields.

    PubMed

    Porter, D; Lawson, R C; Hannan, W J

    1975-05-01

    A novel method is proposed of accurately measuring fast neutron doses of interest in radiotherapy. The technique, which utilizes calculated neutron fluence-to-kerma conversion factors, is based upon the combination of measurements with calibrated neptunium-237 and uranium-238 pulse fission chambers to obtain a response which matches the variation of kerma with neutron energy. The theoretical performance of a practical instrument has been assessed for a variety of neutron spectra to evaluate the spectrum dependence of the dosemeter. The overall systematic uncertainty using this absolute method of determining the neutron dose under charged particle equilibrium conditions is comparable to that encountered with ionization chamber techniques.

  19. SU-E-T-448: On the Perturbation Factor P-cav of the Markus Parallel Plate Ion Chambers in Clinical Electron Beams, Monte Carlo Based Reintegration of An Historical Experiment

    SciTech Connect

    Voigts-Rhetz, P von; Zink, K

    2014-06-01

    Purpose: All present dosimetry protocols recommend well-guarded parallel-plate ion chambers for electron dosimetry. For the guard-less Markus chamber an energy dependent fluence perturbation correction pcav is given. This perturbation correction was experimentally determined by van der Plaetsen by comparison of the read-out of a Markus and a NACP chamber, which was assumed to be “perturbation-free”. Aim of the present study is a Monte Carlo based reiteration of this experiment. Methods: Detailed models of four parallel-plate chambers (Roos, Markus, NACP and Advanced Markus) were designed using the Monte Carlo code EGSnrc and placed in a water phantom. For all chambers the dose to the active volume filled with low density water was calculated for 13 clinical electron spectra (E{sub 0}=6-21 MeV) at the depth of maximum and at the reference depth under reference conditions. In all cases the chamber's reference point was positioned at the depth of measurement. Moreover, the dose to water DW was calculated in a small water voxel positioned at the same depth. Results: The calculated dose ratio D{sub NACP}/D{sub Markus}, which according to van der Plaetsen reflects the fluence perturbation correction of the Markus chamber, deviates less from unity than the values given by van der Plaetsen's but exhibits a similar energy dependence. The same holds for the dose ratios of the other well guarded chambers. But, in comparison to water, the Markus chamber reveals the smallest overall perturbation correction which is nearly energy independent at both investigated depths. Conclusion: The simulations principally confirm the energy dependence of the dose ratio D{sub NACP}/D{sub Markus} as published by van der Plaetsen. But, as shown by our simulations of the ratio D{sub W}/D{sub Markus}, the conclusion drawn in all dosimetry protocols is questionable: in contrast to all well-guarded chambers the guard-less Markus chamber reveals the smallest overall perturbation correction and

  20. Dosimetry for the MRI accelerator: the impact of a magnetic field on the response of a Farmer NE2571 ionization chamber.

    PubMed

    Meijsing, I; Raaymakers, B W; Raaijmakers, A J E; Kok, J G M; Hogeweg, L; Liu, B; Lagendijk, J J W

    2009-05-21

    The UMC Utrecht is constructing a 1.5 T MRI scanner integrated with a linear accelerator (Lagendijk et al 2008 Radiother. Oncol. 86 25-9). The goal of this device is to facilitate soft-tissue contrast based image-guided radiotherapy, in order to escalate the dose to the tumour while sparing surrounding normal tissues. Dosimetry for the MRI accelerator has to be performed in the presence of a magnetic field. This paper investigates the feasibility of using a Farmer NE2571 ionization chamber for absolute dosimetry. The impact of the mcagnetic field on the response of this ionization chamber has been measured and simulated using GEANT4 Monte Carlo simulations. Two orientations of the ionization chamber with respect to the incident beam and the magnetic field which are feasible in the MRI accelerator configuration are taken into account. Measurements are performed using a laboratory magnet ranging from 0 to 1.2 T. In the simulations a range from 0 to 2 T is used. For both orientations, the measurements and simulations agreed within the uncertainty of the measurements and simulations. In conclusion, the response of the ionization chamber as a function of the magnetic field is understood and can be simulated using GEANT4 Monte Carlo simulations.

  1. Consequences of air around an ionization chamber: Are existing solid phantoms suitable for reference dosimetry on an MR-linac?

    PubMed

    Hackett, S L; van Asselen, B; Wolthaus, J W H; Kok, J G M; Woodings, S J; Lagendijk, J J W; Raaymakers, B W

    2016-07-01

    A protocol for reference dosimetry for the MR-linac is under development. The 1.5 T magnetic field changes the mean path length of electrons in an air-filled ionization chamber but has little effect on the electron trajectories in a surrounding phantom. It is therefore necessary to correct the response of an ionization chamber for the influence of the magnetic field. Solid phantoms are used for dosimetry measurements on the MR-linac, but air is present between the chamber wall and phantom insert. This study aimed to determine if this air influences the ion chamber measurements on the MR-linac. The absolute response of the chamber and reproducibility of dosimetry measurements were assessed on an MR-linac in solid and water phantoms. The sensitivity of the chamber response to the distribution of air around the chamber was also investigated. Measurements were performed on an MR-linac and replicated on a conventional linac for five chambers. The response of three waterproof chambers was measured with air and with water between the chamber and the insert to measure the influence of the air volume on absolute chamber response. The distribution of air around the chamber was varied indirectly by rotating each chamber about the longitudinal chamber axis in a solid phantom and a water phantom (waterproof chambers only) and measuring the angular dependence of the chamber response, and varied directly by displacing the chamber in the phantom insert using a paper shim positioned at different orientations between the chamber casing and the insert. The responses of the three waterproof chambers measured on the MR-linac were 0.7%-1.2% higher with water than air in the chamber insert. The responses of the chambers on the conventional linac changed by less than 0.3% when air in the insert was replaced with water. The angular dependence of the chambers ranged from 0.6% to 1.9% in the solid phantom on the MR-linac but was less than 0.5% in water on the MR-linac and less than 0.3% in

  2. Cellular and tissue responses to heavy ions: basic considerations.

    PubMed

    Lett, J T; Cox, A B; Bergtold, D S

    1986-01-01

    Responses of the S/S variant of the L5178Y murine leukemic lymphoblast, the photoreceptor cell of the rabbit retina and the lenticular epithelium of the rabbit to heavy ions (20Ne, 28Si, 40Ar and 56Fe) are described and discussed primarily from the standpoint of the need for a comprehensive theory of cellular radiosensitivity from which a general theory of tissue radiosensitivity can be constructed. The radiation responses of the very radiosensitive, repair-deficient S/S variant during the G1- and early S phases of the cell cycle were found to be unlike those of normally radioresistant cells in culture: the relative biological effectiveness (RBE) did not increase with the linear energy transfer (LET infinity) of the incident radiation. Such behavior could be anticipated for a cell which is lacking the repair system that operates in other (normal) cells when they are exposed to ionizing radiations in the G1 phase of the cell cycle. The S/S variant does exhibit a peak of radioresistance to X-photons mid-G1 + 8 h into the cell cycle, however, and as the LET infinity was increased, the repair capacity responsible for that radioresistance was reduced progressively. Sensory cells (photoreceptors) in the retina of the New Zealand white (NZW) rabbit are very radioresistant to ionizing radiations, and several years elapsed after localized exposure (e.g., 5-10 Gy) to heavy ions (20Ne, 40Ar) before photoreceptor cells were lost from the retina. During the first few weeks after such irradiations, damage to DNA in the photoreceptor cells was repaired to a point where it could not be demonstrated by reorienting gradient sedimentation under alkaline conditions, a technique that can detect DNA damage produced by less than 0.1 Gy of X-photons. Restitution of DNA structure was not permanent, however, and months or years later, but before loss of photoreceptor cells from the retina could be detected, progressive deterioration of the DNA structure began. Age dependencies of late

  3. The response of visco-elastic crust and mantle to the inflation/deflation of magma chamber

    NASA Astrophysics Data System (ADS)

    Yamasaki, T.

    2015-12-01

    It is important to quantitatively evaluate how magmatic activities at depth are reflected in geodetically (GPS and/or InSAR) observed surface deformation in order to distinguish magma-induced crustal deformation. This study employs 3-D finite element model to examine response of the linear Maxwell visco-elastic crust and mantle to a development of sill. Models with instantaneous and/or time-dependent inflation/deflation of sill at various depths in the crust have predicted geodetically detectable surface deformation, providing important constraints on spatio-temporal-scale of magmatic activities. Instantaneous inflation of sill in the crust causes the surface uplift. The amplitude and wavelength of the uplift are amplified for shallower and deeper inflations, respectively. The inflation occurred over a greater horizontal extent intensify both the amplitude and wavelength. The inflation-induced surface uplift would however abate with time by visco-elastic relaxation. Any signature of sill would disappear in ~ 50 - 100 times Maxwell relaxation time of the crust unless the inflation occurred within the uppermost layer that effectively acts as elastic layer. Time-dependent inflation accompanies with visco-elastic relaxation, and the inflation having occurred over the time-scale of ~ 50 - 100 times crustal relaxation time would provide insignificant signature at the surface, which in turn tells us that crustal deformation would reflect the development of magma chamber only if it has occurred in that time-scale. This study also has found that an ascent of magma into shallower depth may be recognised by an observation such that a horizontal extent over which the surface uplift is progressively intensified focusses into a narrower region.

  4. SU-E-T-83: A Study On Evaluating the Directional Dependency of 2D Seven 29 Ion Chamber Array Clinically with Different IMRT Plans

    SciTech Connect

    Kumar, Syam; Aswathi, C.P.

    2015-06-15

    Purpose: To evaluate the directional dependency of 2D seven 29 ion chamber array clinically with different IMRT plans. Methods: 25 patients already treated with IMRT plans were selected for the study. Verification plans were created for each treatment plan in eclipse 10 treatment planning system using the AAA algorithm with the 2D array and the Octavius CT phantom. Verification plans were done 2 times for a single patient. First plan with real IMRT (plan-related approach) and second plan with zero degree gantry angle (field-related approach). Measurements were performed on a Varian Clinac-iX, linear accelerator equipped with a millennium 120 multileaf collimator. Fluence was measured for all the delivered plans and analyzed using the verisoft software. Comparison was done by selecting the fluence delivered in static gantry (zero degree gantry) versus IMRT with real gantry angles. Results: The gamma pass percentage is greater than 97 % for all IMRT delivered with zero gantry angle and between 95%–98% for real gantry angles. Dose difference between the TPS calculated and measured for IMRT delivered with zero gantry angle was found to be between (0.03 to 0.06Gy) and with real gantry angles between (0.02 to 0.05Gy). There is a significant difference between the gamma analysis between the zero degree and true angle with a significance of 0.002. Standard deviation of gamma pass percentage between the IMRT plans with zero gantry angle was 0.68 and for IMRT with true gantry angle was found to be 0.74. Conclusion: The gamma analysis for IMRT with zero degree gantry angles shows higher pass percentage than IMRT delivered with true gantry angles. Verification plans delivered with true gantry angles lower the verification accuracy when 2D array is used for measurement.

  5. Isotopic zonations in silicic magma chambers: conventional and ion-microprobe data from the late-Oligocene Questa caldera, northern New Mexico

    SciTech Connect

    Johnson, C.M.

    1985-01-01

    The >400km3 peralkaline high-SiO/sub 2/ rhyolite ash-flow tuff erupted form the Questa caldera is strongly zoned in trace elements and in initial 87Sr/86Sr, from 0.7082 at the top to 0.7123 at the base. This is accompanied by increasing abundance of zircons with inherited cores, as identified using the ANU SHRIMP ion-microprobe. Cores that are concordant at 1700, 100 and 1430 Ma occur within late-Oligocene zircons in the ash-flow tuff. Such inherited cores is best explained by a greater degree of assimilation of Precambrian roof rocks toward the top of the magma chamber prior to eruption. In contrast, element of Nd and delta 180 values are constant at -6 and +7, respectively. Mass-balance calculations using observed compositions of the Precambrian wall-rocks and the low Sr peralkaline magmas indicate that the amount of assimilation required is less than 15 percent. Peralkaline and metaluminous intrusions cogenetic with the ash flow tuff also have relatively constant element of Nd and delta 180 values of -6 and +7, but have initial 87Sr/86Sr between from 0.7077 to 0.7050. None of the intrusive bodies contain inherited zircons, in contrast with many other Tertiary granitic rocks in the western US. Comparison of isotopic zonations in magmas that are largely liquid with those in their solidified equivalents is important for distinguishing assimilation vs source effects, since the assimilation potential of volatile-rich, crystal-poor magmas is much different from that of the crystal-rich magmas that become plutons.

  6. Dosimetric verification of intensity modulated radiation therapy of 172 patients treated for various disease sites: comparison of EBT film dosimetry, ion chamber measurements, and independent MU calculations.

    PubMed

    Wilcox, Ellen E; Daskalov, George M; Pavlonnis, George; Shumway, Richard; Kaplan, Bruce; VanRooy, Eric

    2008-01-01

    Three independent dose verification methods for intensity modulated radiation therapy (IMRT) were evaluated. Planar IMRT dose distributions were delivered to EBT film and scanned with the Epson Expression 1680 flatbed scanner. The measured dose distributions were then compared to those calculated with a Pinnacle treatment planning system. The IMRT treatments consisted of 7 to 9 6-MV beams for different treatment sites. The films were analyzed using FilmQA (3cognition LLC, Great Neck, NY) software. Comparisons between measured and calculated dose distributions are reported as dose difference (DD) (pixels within +/- 5%), distance to agreement (DTA) (3 mm), as well as gamma values (gamma) (dose = +/- 3%, distance = 2 mm). Point dose measurements with an ion chamber at isocenter were compared to dose calculated at that point. An independent monitor units (MUs) calculation program was also used for verification. For the film dose distributions, DD values varied from 92% to 97%, with head-and-neck and lung treatments showing lower values. Gamma varied from 93% to 98%, and DTA was well above 99%. The isocenter dose measurements deviated from 0.008 to 0.028 from the calculated dose. The larger deviations were attributed to high-dose gradients at the isocenter. RadCalc MU calculations gave differences from 0.027 to 0.079. The larger differences observed were for beams crossing large areas of heterogeneous tissue and were attributed to the limitations of the simple path-length correction method employed in RadCalc. In conclusion, the 3 independent verification methods for each IMRT patient at our institution demonstrated very good agreement between measurements and calculations and gave us the confidence that our IMRT treatments are delivered accurately.

  7. Simulation of target response due to uranium ion beam impact

    NASA Astrophysics Data System (ADS)

    Richter, H.; Noah, E.; Aiginger, H.; Poljanc, K.

    2009-12-01

    Metal targets were irradiated at GSI with a highly focused uranium ion beam with a kinetic energy of 350MeV/u. Out of these targets two copper samples, that had been irradiated multiple times with a maximum intensity of 2.36 · 109 , were chosen for simulations. In order to characterize the behavior of the target under the load of the ion beam, FLUKA was used to generate the initial distribution of deposited energy which was in turn used as an input for ANSYS AUTODYN to calculate the dynamic response of the target. In the simulations of the first sample a good approximation of the so-called hydrodynamic tensile limit, the crucial parameter for target failure, was found to be -1.08 GPa. This acquired value was used for the simulation of the second sample which had been irradiated with two high-intensity shots. These simulations resulted in the full penetration of the sample which was in agreement with metallurgical examinations. This paper presents the performed simulations.

  8. Closure characteristic of thermally responsive ion track membranes

    NASA Astrophysics Data System (ADS)

    Reber, N.; Omichi, H.; Spohr, R.; Wolf, A.; Yoshida, M.

    1999-05-01

    The surface of ion track membranes with single or many pores of cylindrical geometry were covered with poly-N-isopropylacrylamide. Given by the properties of this hydrogel, the opening and closing of the modified pores can be controlled by temperature. Above 31°C, in the shrunken state of the hydrogel, ions and molecules can freely pass through the membrane whereas below 31°C, in the swollen state, the hydrogel clogs the pore. The closure characteristic of single responsive pores for polyethylene glycol (PEG) molecules of various sizes was studied by electrical conductivity measurements. As demonstrated for single pores, the passage of PEG molecules larger than 2 nm is prevented in the closed state. Complementary experiments were performed with membranes containing between 10 6 and 5 × 10 7 pores per cm 2. The flow for different molecules (methyleneblue, orange G and bovine albumin) was investigated by means of a dialysis cell. For different membranes with pores of an initial diameter of 0.6 and 3.5 μm, the flow through the membrane in the swollen state is completely blocked for the bovine albumin molecules. In the open state, both dye and albumin molecules could pass the 3.5 μm pores freely, whereas the flow ratio was considerably reduced for the 0.6 μm pores.

  9. SU-E-T-350: Effective Point of Measurement and Total Perturbation Correction P for Parallel-Plate Ion Chambers in High-Energy Photon Beams

    SciTech Connect

    Langner, N; Czarnecki, D; Voigts-Rhetz, P von; Zink, K

    2015-06-15

    Purpose: This paper aims to determine the effective point of measurement and the total perturbation correction p of parallel-plate chambers for clinical photon dosimetry. Methods: The effective point of measurement (EPOM) was calculated using the EGSnrc Monte Carlo code system with the EGSnrc user code egs- chamber. Depth dose curves of the ionization chambers were calculated in a water phantom for several high energy photon spectra (4, 6, 10, 15, 18 MV-X). Different normalization criterions (normalization to the maximum of the depth dose curve and normalization to the value in 10 cm depth) have been applied. The EPOM was determined by shifting the normalized depth dose curve of a small water voxel against the depth ionization curve until the disagreement (calculated by the root mean square deviation) reaches a minimum. In addition, the total perturbation correction p was calculated by the ratio of the dose to water and the product of the dose determined in the chamber and the water to air stopping power ratio. Results: The EPOM varied slightly depending on the chosen normalization criterion. For all chambers the necessary shift of the EPOM decreased linearly with increasing beam quality specifier TPR{sub 20/10}. For the Roos and NACP chamber, the results were positive suggesting that the chambers need to be shifted towards the focus. For the Markus chamber, the required shift was negative and for the Advanced Markus chamber partly negative and partly positive. The total perturbation correction p was almost independent of the depth. Only for regions below 1 cm the perturbation correction deviated significantly from unity. Conclusion: In the present study, the effective point of measurement and the total perturbation correction p was determined for four parallel-plate ionization chambers and five clinical relevant photon spectra. Applying the calculated EPOM, the residual perturbation correction p was mostly depth independent.

  10. Study of the single cluster response of a helium-isobutane drift chamber prototype using 8 keV X-rays

    NASA Astrophysics Data System (ADS)

    Cavoto, G.; Dabagov, S.; Hampai, D.; Piredda, G.; Renga, F.; Ripiccini, E.; Voena, C.; Zullo, A.

    2015-03-01

    The identification of single clusters in the electronic signals produced by ionizing particles within a drift chamber is expected to significantly improve the performances of this kind of detectors in terms of particle identification capabilities and space resolution. In order to develop refined cluster recognition algorithms, it is essential to measure the response of the chamber and its electronics to single ionization clusters. This can be done by irradiating the chamber with X-rays. We report here on the studies performed on a drift chamber prototype for the MEG-II experiment at the X-ray facility of the INFN Frascati's National Laboratories ``XLab Frascati''. The prototype is operated with a helium-isobutane mixture and instrumented with high bandwidth custom pre-amplifiers. The results of this study have been used to develop an innovative method for cluster recognition, based on the Wiener filter technique, which has been tested on data collected at the Frascati's Beam Test Facility. As a side measurement, we also performed a study of the gas gain in a configuration which is similar to that of the MEG-II experiment.

  11. Liquid Wall Chambers

    SciTech Connect

    Meier, W R

    2011-02-24

    The key feature of liquid wall chambers is the use of a renewable liquid layer to protect chamber structures from target emissions. Two primary options have been proposed and studied: wetted wall chambers and thick liquid wall (TLW) chambers. With wetted wall designs, a thin layer of liquid shields the structural first wall from short ranged target emissions (x-rays, ions and debris) but not neutrons. Various schemes have been proposed to establish and renew the liquid layer between shots including flow-guiding porous fabrics (e.g., Osiris, HIBALL), porous rigid structures (Prometheus) and thin film flows (KOYO). The thin liquid layer can be the tritium breeding material (e.g., flibe, PbLi, or Li) or another liquid metal such as Pb. TLWs use liquid jets injected by stationary or oscillating nozzles to form a neutronically thick layer (typically with an effective thickness of {approx}50 cm) of liquid between the target and first structural wall. In addition to absorbing short ranged emissions, the thick liquid layer degrades the neutron flux and energy reaching the first wall, typically by {approx}10 x x, so that steel walls can survive for the life of the plant ({approx}30-60 yrs). The thick liquid serves as the primary coolant and tritium breeding material (most recent designs use flibe, but the earliest concepts used Li). In essence, the TLW places the fusion blanket inside the first wall instead of behind the first wall.

  12. Calibration and performance of a secondary emission chamber as a beam intensity monitor

    SciTech Connect

    Sivertz, M.; Chiang, I-H,; Rusek, A.

    2011-03-28

    We report on a study of the behavior of a secondary emission chamber (SEC). We show the dependence of the SEC signal on the charge and velocity of the primary beam for beams of protons, and heavy ions including Helium, Neon, Chlorine and Iron. We fill the SEC with a selection of different gases including Hydrogen, Helium, Nitrogen, Argon, and air, studying the SEC response when it is acting as an ion chamber. We also investigate the behavior of the SEC at intermediate pressures between 10{sup -8} torr and atmospheric pressure. The SEC uses thin conducting foils as the source and collector of electrons in a vacuum chamber. When charged particles traverse the vacuum chamber, they pass through a series of thin conducting foils, alternating anode and cathode. Ionization produced in the cathode foils travels across the intervening gap due to an applied high voltage and is collected on the anode foils. Electron production is very inefficient because most of the ionization in the foils remains trapped within the foil due to the short range of most delta-rays and the work function of the foil. It is this inefficiency that allows the SEC to operate at high dose rates and short pulse duration where the standard ion chambers cannot function reliably. The SEC was placed in the NSRL ion beam to receive a variety of heavy ion beams under different beam conditions. We used these ion beams to study the response of the SEC to different species of heavy ion, comparing with proton beams. We studied the response to beam of different energies, and as a function of different counting rate. We compared the behaviour of the SEC when operating under positive and negative high voltage. The SEC can operate as an ion chamber if it is filled with gas. We measured the response of the SEC when filled with a variety of gases, from Hydrogen to Helium, Nitrogen, Argon and air. The performance of the SEC as an ion chamber is compared with the standard NSRL ion chamber, QC3. By evacuating the SEC and

  13. Migration to new ampoule types for the NPL secondary standard ionisation chambers.

    PubMed

    Baker, M; Fenwick, A; Ferreira, K; Keightley, J; Johansson, L; Collins, S

    2014-05-01

    As the pre-calibrated sample containers used for activity assay in the two NPL secondary standards ionisation chambers are being phased out, suitable replacements have been identified. Characterisation checks have been carried out on the new ISO ampoules and a long-term recalibration schedule has been devised. Around 40 calibration factors have been determined so far and comparison of ion chamber responses for the two ampoule types showed variations of up to 7% for low energy photon emitting radionuclides.

  14. Responses of soybeans and wheat to elevated CO2 in free-air and open top chamber systems

    USDA-ARS?s Scientific Manuscript database

    With increasing demand for agricultural products, more confidence is needed concerning impacts of rising atmospheric CO2 on crop yields. Despite debate about the merits of free-air CO2 enrichment (FACE) and open top chamber (OTC) systems, there has been only one reported experiment directly compari...

  15. Growth responses, biomass partitioning, and nitrogen isotopes of prairie legumes in response to elevated temperature and varying nitrogen source in a growth chamber experiment.

    PubMed

    Whittington, Heather R; Deede, Laura; Powers, Jennifer S

    2012-05-01

    Because legumes can add nitrogen (N) to ecosystems through symbiotic fixation, they play important roles in many plant communities, such as prairies and grasslands. However, very little research has examined the effect of projected climate change on legume growth and function. Our goal was to study the effects of temperature on growth, nodulation, and N chemistry of prairie legumes and determine whether these effects are mediated by source of N. We grew seedlings of Amorpha canescens, Dalea purpurea, Lespedeza capitata, and Lupinus perennis at 25/20°C (day/night) or 28/23°C with and without rhizobia and mineral N in controlled-environment growth chambers. Biomass, leaf area, nodule number and mass, and shoot N concentration and δ(15)N values were measured after 12 wk of growth. Both temperature and N-source affected responses in a species-specific manner. Lespedeza showed increased growth and higher shoot N content at 28°C. Lupinus showed decreases in nodulation and lower shoot N concentration at 28°C. The effect of temperature on shoot N concentration occurred only in individuals whose sole N source was N(2)-fixation, but there was no effect of temperature on δ(15)N values in these plants. Elevated temperature enhanced seedling growth of some species, while inhibiting nodulation in another. Temperature-induced shifts in legume composition or nitrogen dynamics may be another potential mechanism through which climate change affects unmanaged ecosystems.

  16. A new re-entrant ionization chamber for the calibration of iridium-192 high dose rate sources.

    PubMed

    Goetsch, S J; Attix, F H; DeWerd, L A; Thomadsen, B R

    1992-01-01

    A re-entrant (well-type) ionization chamber has been designed and fabricated at the University of Wisconsin for use with iridium-192 high dose-rate (HDR) remote after-loading brachytherapy devices. The chamber was designed to provide an ionization current of about 10(-8) ampere with a nominal 10 curie iridium-192 source. A narrow opening is provided into the sensitive volume of the chamber to insert a Nucletron MicroSelectron catheter, or catheters with similar diameters from other HDR manufacturers. The chamber exhibits a flat response (+/- 0.1%) for any source position within +/-4 mm of the chamber center. A 300 volt chamber bias yields a 99.96% ion collection efficiency. The chamber is capable of being calibrated directly with an iridium-192 source which has in turn been calibrated with thimble-type ion chambers. Reproducibility for readings in the current mode for 10 consecutive insertions of the MicroSelectron iridium-192 HDR source is within 0.02% or less. Two thimble chambers calibrated by the U.S. National Institute of Standards and Technology provide calibration traceability of iridium-192 HDR sources and re-entrant chambers to a primary national standards laboratory. Results of activity measurements of 6 commercial iridium-192 HDR sources are reported.

  17. Fast ionospheric response to enhanced activity in geospace: Ion feeding of the inner magnetotail

    SciTech Connect

    Daglis, I.A.; Axford, I.A.

    1996-03-01

    The authors look at the question of the ionosphere feeding ions into the magnetosphere/magnetotail, in response to magnetic storm activity, or coupling of the solar wind into the system. They are concerned with fast response, not the question of whether the ionosphere feeds ions in general. The dynamics which results in the inner magnetosphere in response to the input of cold ions from the ionosphere is of interest to the authors. They review recent and older data which has shed light on this question. They look at outflow data, and heating mechanisms for these cold ions, as well as the impact such ions may have on the dynamics of magnetic storms. They observe that fast feeding of ions out of the ionosphere may leave the inner magnetosphere heavily populated with heavy ions such as O{sup +}, which can have a definite impact on the dynamic development of the magnetosphere.

  18. Loss of Ca2+-mediated ion transport during colitis correlates with reduced ion transport responses to a Ca2+-activated K+ channel opener

    PubMed Central

    Hirota, Christina L; McKay, Derek M

    2009-01-01

    Background and purpose: Epithelial surface hydration is critical for proper gut function. However, colonic tissues from individuals with inflammatory bowel disease or animals with colitis are hyporesponsive to Cl− secretagogues. The Cl− secretory responses to the muscarinic receptor agonist bethanechol are virtually absent in colons of mice with dextran sodium sulphate (DSS)-induced colitis. Our aim was to define the mechanism underlying this cholinergic hyporesponsiveness. Experimental approach: Colitis was induced by 4% DSS water, given orally. Epithelial ion transport was measured in Ussing chambers. Colonic crypts were isolated and processed for mRNA expression via RT-PCR and protein expression via immunoblotting and immunolocalization. Key results: Expression of muscarinic M3 receptors in colonic epithelium was not decreased during colitis. Short-circuit current (ISC) responses to other Ca2+-dependent secretagogues (histamine, thapsigargin, cyclopiazonic acid and calcium ionophore) were either absent or severely attenuated in colonic tissue from DSS-treated mice. mRNA levels of several ion transport molecules (a Ca2+-regulated Cl− channel, the intermediate-conductance Ca2+-activated K+ channel, the cystic fibrosis transmembrane conductance regulator, the Na+/K+-ATPase pump or the Na+/K+/2Cl− co-transporter) were not reduced in colonic crypts from DSS-treated mice. However, protein expression of Na+/K+-ATPase α1 subunits was decreased twofold during colitis. Activation of Ca2+-activated K+ channels increased ISC significantly less in DSS colons compared with control, as did the protein kinase C activator, phorbol 12-myristate 13-acetate. Conclusions and implications: Decreased Na+/K+-ATPase expression probably contributes to overall epithelial hyporesponsiveness during colitis, while dysfunctional K+ channels may account, at least partially, for lack of epithelial secretory responses to Ca2+-mediated secretagogues. PMID:19298254

  19. Implementation of Gas Sampling Chamber and Measuring Hardware for Capnograph System Considering Thermal Noise Effect and Time Response Characteristics

    DTIC Science & Technology

    2007-11-02

    chamber, thermal background effect I. INTRODUCTION As a measuring method for a capnograph system that determines indirectly the level of pCO2 in a...The chopping frequency of an IR lamp corresponds to the sampling frequency for the continuous measurement of the CO2 gas concentration without aliasing...order MFB(multiple feedback) lowpass filter. Finally, the use of 240×64 graphic LCD makes it easy to continuously observe and measure the CO2 gas

  20. Ionization chamber dosimeter

    DOEpatents

    Renner, Tim R.; Nyman, Mark A.; Stradtner, Ronald

    1991-01-01

    A method for fabricating an ion chamber dosimeter collecting array of the type utilizing plural discrete elements formed on a uniform collecting surface which includes forming a thin insulating layer over an aperture in a frame having surfaces, forming a predetermined pattern of through holes in the layer, plating both surfaces of the layer and simultaneously tilting and rotating the frame for uniform plate-through of the holes between surfaces. Aligned masking and patterned etching of the surfaces provides interconnects between the through holes and copper leads provided to external circuitry.

  1. Chamber Clearing First Principles Modeling

    SciTech Connect

    Loosmore, G

    2009-06-09

    LIFE fusion is designed to generate 37.5 MJ of energy per shot, at 13.3 Hz, for a total average fusion power of 500 MW. The energy from each shot is partitioned among neutrons ({approx}78%), x-rays ({approx}12%), and ions ({approx}10%). First wall heating is dominated by x-rays and debris because the neutron mean free path is much longer than the wall thickness. Ion implantation in the first wall also causes damage such as blistering if not prevented. To moderate the peak-pulse heating, the LIFE fusion chamber is filled with a gas (such as xenon) to reduce the peak-pulse heat load. The debris ions and majority of the x-rays stop in the gas, which re-radiates this energy over a longer timescale (allowing time for heat conduction to cool the first wall sufficiently to avoid damage). After a shot, because of the x-ray and ion deposition, the chamber fill gas is hot and turbulent and contains debris ions. The debris needs to be removed. The ions increase the gas density, may cluster or form aerosols, and can interfere with the propagation of the laser beams to the target for the next shot. Moreover, the tritium and high-Z hohlraum debris needs to be recovered for reuse. Additionally, the cryogenic target needs to survive transport through the gas mixture to the chamber center. Hence, it will be necessary to clear the chamber of the hot contaminated gas mixture and refill it with a cool, clean gas between shots. The refilling process may create density gradients that could interfere with beam propagation, so the fluid dynamics must be studied carefully. This paper describes an analytic modeling effort to study the clearing and refilling process for the LIFE fusion chamber. The models used here are derived from first principles and balances of mass and energy, with the intent of providing a first estimate of clearing rates, clearing times, fractional removal of ions, equilibrated chamber temperatures, and equilibrated ion concentrations for the chamber. These can be used

  2. WE-EF-207-11: Energy and Depth Response of Thermoluminescent Dosimeters and Ionization Chambers in Water for Kilovoltage X-Ray Beams

    SciTech Connect

    Lawless, M; Palmer, B; DeWerd, L

    2015-06-15

    Purpose: To assess the effects of changes in beam quality on detector response in the kilovoltage energy range by modulating the x-ray tube voltage and the measurement depth in water. Methods: Measurements were performed with TLD-100 and TLD-100H thermoluminescent dosimeters and an A12 farmer-type ionization chamber. To assess the energy response of the detectors, irradiations were performed at a depth of 3 cm in a custom-built thin-window water phantom using the moderately filtered x-ray beams at the UWADCL (20 kVp-250 kVp) and a Co-60 beam.The x-ray beams and detectors were modeled using the EGSnrc Monte Carlo code. The model was validated by simulating dose to the collecting volume of an A12 farmer chamber and comparing it with measured A12 signal as a function of depth. Dose was tallied to each detector and to water for comparison with measurements. Simulations were used to calculate the predicted energy response, which was compared to the measured response of each detector. Dose to each detector and dose to water as a function of depth were also simulated. Results: Detector output per dose to water was found to deviate by up to 15%, 20% and 30% as a function of energy relative to Co-60 for the A12, TLD-100H and TLD-100, respectively. The EGSnrc simulations produced results similar to the measurements for ionization chambers, but discrepancies of up to 30% were observed for TLD-100H. Simulated detector response as a function of depth was found to vary by up to 3%. Conclusion: These results suggest that changes in beam quality in kilovoltage x-ray beams can have a significant impact on detector response. In-water detector response was found to differ from the previously investigated in-air response. Deviations in detector response as a function of depth were less significant, but could potentially cause dosimetric errors if ignored.

  3. ION SOURCE FOR A CALUTRON

    DOEpatents

    Lofgren, E.J.

    1959-04-14

    This patcnt relates to calutron devices and deals particularly with the mechanism used to produce the beam of ions wherein a charge material which is a vapor at room temperature is used. A charge container located outside the tank is connected through several conduits to various points along the arc chamber of the ion source. In addition, the rate of flow of the vapor to the arc chamber is controlled by a throttle valve in each conduit. By this arrangement the arc can be regulated accurately and without appreciable time lag, inasmuch as the rate of vapor flow is immediately responsive to the manipulation of the throttle valves.

  4. Ion Trapping with Fast-Response Ion-Selective Microelectrodes Enhances Detection of Extracellular Ion Channel Gradients

    PubMed Central

    Messerli, Mark A.; Collis, Leon P.; Smith, Peter J.S.

    2009-01-01

    Previously, functional mapping of channels has been achieved by measuring the passage of net charge and of specific ions with electrophysiological and intracellular fluorescence imaging techniques. However, functional mapping of ion channels using extracellular ion-selective microelectrodes has distinct advantages over the former methods. We have developed this method through measurement of extracellular K+ gradients caused by efflux through Ca2+-activated K+ channels expressed in Chinese hamster ovary cells. We report that electrodes constructed with short columns of a mechanically stable K+-selective liquid membrane respond quickly and measure changes in local [K+] consistent with a diffusion model. When used in close proximity to the plasma membrane (<4 μm), the ISMs pose a barrier to simple diffusion, creating an ion trap. The ion trap amplifies the local change in [K+] without dramatically changing the rise or fall time of the [K+] profile. Measurement of extracellular K+ gradients from activated rSlo channels shows that rapid events, 10–55 ms, can be characterized. This method provides a noninvasive means for functional mapping of channel location and density as well as for characterizing the properties of ion channels in the plasma membrane. PMID:19217875

  5. Effect of nebulizer/spray chamber interfaces on simultaneous, axial view inductively coupled plasma optical emission spectrometry for the direct determination of As and Se species separated by ion exchange high-performance liquid chromatography

    NASA Astrophysics Data System (ADS)

    Gettar, Raquel T.; Smichowski, Patricia; Garavaglia, Ricardo N.; Farías, Silvia; Batistoni, Daniel A.

    2005-06-01

    Different nebulizer/expansion chamber combinations were evaluated to assess their performance for sample introduction in the direct coupling with an axial view inductively coupled plasma multielement spectrometer for on-line determination of As and Se species previously separated by ion exchange-high performance liquid chromatography. The column effluents were injected into the plasma without prior derivatization. The instrument operation software was adapted for data acquisition and processing to allow multi-wavelength recording of the transient chromatographic peaks. After optimization of the chromatographic operating conditions, separation of mixtures of inorganic As and Se species, and of inorganic and two organic As species (monomethylarsonic and dimethylarsinic acids), was achieved with excellent resolution. Species discrimination from mixtures of As and Se oxyanions was further improved by the simultaneous element detection at specific analytical wavelengths. Three nebulizers and three spray chambers, employed in seven combinations, were tested as interfaces. Concentric nebulizers associated to a glass cyclonic chamber appear most suitable regarding sensitivity and signal to noise ratio. Measured element detection limits (3 σ) were around 10 ng ml - 1 for all the species considered, making the method a viable alternative to similar procedures that employ volatile hydride generation previous to sample injection into the plasma. Analytical recoveries both for inorganic and organic species ranged between 92 and 107%. The method was demonstrated to be apt for the analysis of surface waters potentially subjected to natural contamination with arsenic.

  6. Transferring calibration coefficients from ionisation chambers used for diagnostic radiology to transmission chambers.

    PubMed

    Yoshizumi, Maíra T; Caldas, Linda V E

    2012-07-01

    In this work, the response of a double volume transmission ionisation chamber, developed at the Instituto de Pesquisas Energéticas e Nucleares, was compared to that of a commercial transmission chamber. Both ionisation chambers were tested in different X-ray beam qualities using secondary standard ionisation chambers as reference dosimeters. These standard ionisation chambers were a parallel-plate and a cylindrical ionisation chambers, used for diagnostic radiology and mammography beam qualities, respectively. The response of both transmission chambers was compared to that of the secondary standard chambers to obtain coefficients of equivalence. These coefficients allow the transmission chambers to be used as reference equipment. Copyright © 2011 Elsevier Ltd. All rights reserved.

  7. Neutron detection via bubble chambers.

    PubMed

    Jordan, D V; Ely, J H; Peurrung, A J; Bond, L J; Collar, J I; Flake, M; Knopf, M A; Pitts, W K; Shaver, M; Sonnenschein, A; Smart, J E; Todd, L C

    2005-01-01

    Research investigating the application of pressure-cycled bubble chambers to fast neutron detection is described. Experiments with a Halon-filled chamber showed clear sensitivity to an AmBe neutron source and insensitivity to a (137)Cs gamma source. Bubble formation was documented using high-speed photography, and a ceramic piezo-electric transducer element registered the acoustic signature of bubble formation. In a second set of experiments, the bubble nucleation response of a Freon-134a chamber to an AmBe neutron source was documented with high-speed photography.

  8. Ionospheric Plasma Outflow in Response to Transverse Ion Heating: Self-Consistent Macroscopic Treatment

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra

    1995-01-01

    During the grant period starting July 1, 1994, our major effort has been on the following two problems: (1) Temporal behavior of heavy Oxygen ion outflow in response to a transverse heating event; and (2) Continued effort on ion heating by lower hybrid waves. We briefly describe here the research performed under these topics.

  9. Identification of a calcineurin-independent pathway required for sodium ion stress response in Saccharomyces cerevisiae.

    PubMed Central

    Ganster, R W; McCartney, R R; Schmidt, M C

    1998-01-01

    The calcium-dependent protein phosphatase calcineurin plays an essential role in ion homeostasis in yeast. In this study, we identify a parallel ion stress response pathway that is independent of the calcineurin signaling pathway. Cells with null alleles in both STD1 and its homologue, MTH1, manifest numerous phenotypes observed in calcineurin mutants, including sodium, lithium, manganese, and hydroxyl ion sensitivity, as well as alpha factor toxicity. Furthermore, increased gene dosage of STD1 suppresses the ion stress phenotypes in calcineurin mutants and confers halotolerance in wild-type cells. However, Std1p functions in a calcineurin-independent ion stress response pathway, since a std1 mth1 mutant is FK506 sensitive under conditions of ion stress. Mutations in other genes known to regulate gene expression in response to changes in glucose concentration, including SNF3, RGT2, and SNF5, also affect cell growth under ion stress conditions. Gene expression studies indicate that the regulation of HAL1 and PMR2 expression is affected by STD1 gene dosage. Taken together, our data demonstrate that response to ion stress requires the participation of both calcineurin-dependent and -independent pathways. PMID:9725828

  10. Growth and ion accumulation responses of four grass species to salinity

    USDA-ARS?s Scientific Manuscript database

    In plants, tolerance to saline environments can be achieved either through ion inclusion or ion exclusion. This greenhouse study measured shoot sodium (Na+), potassium (K+), and calcium (Ca2+) responses in four perennial grass species (tall wheatgrass, Nuttall's alkaligrass, creeping foxtail, and s...

  11. Non-Targeted Effects and the Dose Response for Heavy Ion Tumorigenesis

    NASA Technical Reports Server (NTRS)

    Chappell, Lori J.; Cucinotta, Francis A.

    2010-01-01

    There is no human epidemiology data available to estimate the heavy ion cancer risks experienced by astronauts in space. Studies of tumor induction in mice are a necessary step to estimate risks to astronauts. Previous experimental data can be better utilized to model dose response for heavy ion tumorigenesis and plan future low dose studies.

  12. Evaluation of physiological and biochemical responses of two rice (Oryza sativa L.) cultivars to ambient air pollution using open top chambers at a rural site in India.

    PubMed

    Rai, Richa; Agrawal, Madhoolika

    2008-12-15

    Air pollutant concentrations are rising in India, causing potential threats to crop production. As air pollutants are known to interfere with physiological processes, this study was conducted to assess the relative responses of physiological and biochemical characteristics of two cultivars of rice (Oryza sativa L. cv. Saurabh 950 and NDR 97) leading to variable yield responses. Twelve hour monitoring of ambient concentrations of SO2, NO2 and O3 in filtered chambers (FCs), non-filtered chambers (NFCs) and open plots (OPs) showed that O3 was the main pollutant at the experimental site. Ozone concentrations often exceeded 40 ppb during anthesis but not during the vegetative growth period. Photosynthetic rate (Ps), stomatal conductance (g(s)) and Fv/Fm ratio, superoxide dismutase (SOD) and peroxidase (POD) activities and photosynthetic pigments, ascorbic acid, total phenolics and protein contents were assessed at different developmental stages and yield of grains were quantified. Lipid peroxidation, SOD and POD activities, ascorbic acid and total phenolics were higher, whereas Ps, g(s), Fv/Fm ratio and contents of protein and photosynthetic pigment were lower in plants of NFCs as compared to FCs. Yield decreased significantly in both cultivars grown in NFCs. NDR 97 showed less reductions in physiological characteristics, photosynthetic pigments and protein, but a greater increase in the antioxidative defense system as compared to Saurabh 950. Yield reduction was higher in NDR 97 than in Saurabh 950. This suggested that NDR 97 utilized more photosynthate in maintaining the metabolic machinery against O3 stress leading to lower translocation of photosynthate to reproductive parts. The study concluded that under natural field conditions, physiological and biochemical responses of plants varied with pollutant concentrations leading to different translocation strategies in plants, modifying their yield responses. NDR 97, a fast growing and high yielding cultivar was more

  13. Leakage of K+ ions from Staphylococcus aureus in response to tea tree oil.

    PubMed

    Hada, Toshiko; Inoue, Yoshihiro; Shiraishi, Akiko; Hamashima, Hajime

    2003-06-01

    The leakage of K(+) ions from Staphylococcus aureus in response to tea tree oil (TTO) was investigated with an ion-selective electrode. The amount of leaked K(+) ions and the rate of leakage of K(+) ions induced by TTO were dependent on the concentration of TTO. Measurements of initial rates required less time than measurements of total amounts and provided an index of the interaction between TTO and the cell membrane. Thus, the initial rate of leakage might be a more useful measure of the antibacterial activity of TTO than the total amount.

  14. Modeling and validation of single-chamber microbial fuel cell cathode biofilm growth and response to oxidant gas composition

    DOE PAGES

    Ou, Shiqi; Zhao, Yi; Aaron, Douglas S.; ...

    2016-08-15

    This work describes experiments and computational simulations to analyze single-chamber, air-cathode microbial fuel cell (MFC) performance and cathodic limitations in terms of current generation, power output, mass transport, biomass competition, and biofilm growth. Steady-state and transient cathode models were developed and experimentally validated. Two cathode gas mixtures were used to explore oxygen transport in the cathode: the MFCs exposed to a helium-oxygen mixture (heliox) produced higher current and power output than the group of MFCs exposed to air or a nitrogen-oxygen mixture (nitrox), indicating a dependence on gas-phase transport in the cathode. Multi-substance transport, biological reactions, and electrochemical reactions inmore » a multi-layer and multi-biomass cathode biofilm were also simulated in a transient model. The transient model described biofilm growth over 15 days while providing insight into mass transport and cathodic dissolved species concentration profiles during biofilm growth. Lastly, simulation results predict that the dissolved oxygen content and diffusion in the cathode are key parameters affecting the power output of the air-cathode MFC system, with greater oxygen content in the cathode resulting in increased power output and fully-matured biomass.« less

  15. Modeling and validation of single-chamber microbial fuel cell cathode biofilm growth and response to oxidant gas composition

    NASA Astrophysics Data System (ADS)

    Ou, Shiqi; Zhao, Yi; Aaron, Douglas S.; Regan, John M.; Mench, Matthew M.

    2016-10-01

    This work describes experiments and computational simulations to analyze single-chamber, air-cathode microbial fuel cell (MFC) performance and cathodic limitations in terms of current generation, power output, mass transport, biomass competition, and biofilm growth. Steady-state and transient cathode models were developed and experimentally validated. Two cathode gas mixtures were used to explore oxygen transport in the cathode: the MFCs exposed to a helium-oxygen mixture (heliox) produced higher current and power output than the group of MFCs exposed to air or a nitrogen-oxygen mixture (nitrox), indicating a dependence on gas-phase transport in the cathode. Multi-substance transport, biological reactions, and electrochemical reactions in a multi-layer and multi-biomass cathode biofilm were also simulated in a transient model. The transient model described biofilm growth over 15 days while providing insight into mass transport and cathodic dissolved species concentration profiles during biofilm growth. Simulation results predict that the dissolved oxygen content and diffusion in the cathode are key parameters affecting the power output of the air-cathode MFC system, with greater oxygen content in the cathode resulting in increased power output and fully-matured biomass.

  16. Modeling and validation of single-chamber microbial fuel cell cathode biofilm growth and response to oxidant gas composition

    SciTech Connect

    Ou, Shiqi; Zhao, Yi; Aaron, Douglas S.; Regan, John M.; Mench, Matthew M.

    2016-08-15

    This work describes experiments and computational simulations to analyze single-chamber, air-cathode microbial fuel cell (MFC) performance and cathodic limitations in terms of current generation, power output, mass transport, biomass competition, and biofilm growth. Steady-state and transient cathode models were developed and experimentally validated. Two cathode gas mixtures were used to explore oxygen transport in the cathode: the MFCs exposed to a helium-oxygen mixture (heliox) produced higher current and power output than the group of MFCs exposed to air or a nitrogen-oxygen mixture (nitrox), indicating a dependence on gas-phase transport in the cathode. Multi-substance transport, biological reactions, and electrochemical reactions in a multi-layer and multi-biomass cathode biofilm were also simulated in a transient model. The transient model described biofilm growth over 15 days while providing insight into mass transport and cathodic dissolved species concentration profiles during biofilm growth. Lastly, simulation results predict that the dissolved oxygen content and diffusion in the cathode are key parameters affecting the power output of the air-cathode MFC system, with greater oxygen content in the cathode resulting in increased power output and fully-matured biomass.

  17. Hormone-responsive cells derived from human dental papilla: characterization in vitro and in vivo in diffusion chambers.

    PubMed

    Shteyer, A; Gazit, D; Binderman, I; Bab, I A

    1987-01-01

    Cells of the dental papilla are capable of odontoblastic, fibroblastic, and endothelial differentiation and formation of dentin and the dental pulp. In the present study dental papilla cells, obtained from human tooth buds (HDP cells), were cultured in vitro through 3 to 7 passages. After exposure to prostaglandin E2 there was a marked decrease in intracellular cyclic AMP (cAMP) levels as compared to hormone-free controls. Parathyroid hormone and calcitonin had stimulatory effects with 1 and 2 log increases in cAMP, respectively. The HDP cells showed moderate activity of alkaline phosphatase, 1 log higher than that of hamster kidney fibroblasts (BHK 13) and 1 log lower than that of osteoblastic osteosarcoma cells (ROS 17/2). When cultured for 4 or 8 wk in diffusion chambers (DC) implanted in athymic mice, many of the HDP cells underwent odontoblastic morphodifferentiation with very long, single processes extending into the matrix. This matrix contained banded and unbanded collagen fibers. Neither light nor electron microscopy of the DC content revealed mineral deposits. These results suggest that HDP cells have an intrinsic potential for partial odontoblastic differentiation; inductive signals like those originating from odontogenic epithelium are probably essential for the completion of hard tissue formation.

  18. Modeling and validation of single-chamber microbial fuel cell cathode biofilm growth and response to oxidant gas composition

    SciTech Connect

    Ou, Shiqi; Zhao, Yi; Aaron, Douglas S.; Regan, John M.; Mench, Matthew M.

    2016-08-15

    This work describes experiments and computational simulations to analyze single-chamber, air-cathode microbial fuel cell (MFC) performance and cathodic limitations in terms of current generation, power output, mass transport, biomass competition, and biofilm growth. Steady-state and transient cathode models were developed and experimentally validated. Two cathode gas mixtures were used to explore oxygen transport in the cathode: the MFCs exposed to a helium-oxygen mixture (heliox) produced higher current and power output than the group of MFCs exposed to air or a nitrogen-oxygen mixture (nitrox), indicating a dependence on gas-phase transport in the cathode. Multi-substance transport, biological reactions, and electrochemical reactions in a multi-layer and multi-biomass cathode biofilm were also simulated in a transient model. The transient model described biofilm growth over 15 days while providing insight into mass transport and cathodic dissolved species concentration profiles during biofilm growth. Lastly, simulation results predict that the dissolved oxygen content and diffusion in the cathode are key parameters affecting the power output of the air-cathode MFC system, with greater oxygen content in the cathode resulting in increased power output and fully-matured biomass.

  19. ION SOURCE

    DOEpatents

    Bell, W.A. Jr.; Love, L.O.; Prater, W.K.

    1958-01-28

    An ion source is presented capable of producing ions of elements which vaporize only at exceedingly high temperatures, i.e.,--1500 degrees to 3000 deg C. The ion source utilizes beams of electrons focused into a first chamber housing the material to be ionized to heat the material and thereby cause it to vaporize. An adjacent second chamber receives the vaporized material through an interconnecting passage, and ionization of the vaporized material occurs in this chamber. The ionization action is produced by an arc discharge sustained between a second clectron emitting filament and the walls of the chamber which are at different potentials. The resultant ionized material egresses from a passageway in the second chamber. Using this device, materials which in the past could not be processed in mass spectometers may be satisfactorily ionized for such applications.

  20. Portable Hyperbaric Chamber

    NASA Technical Reports Server (NTRS)

    Schneider, William C. (Inventor); Locke, James P. (Inventor); DeLaFuente, Horacio (Inventor)

    2001-01-01

    A portable, collapsible hyperbaric chamber was developed. A toroidal inflatable skeleton provides initial structural support for the chamber, allowing the attendant and/or patient to enter the chamber. Oval hatches mate against bulkhead rings, and the hyperbaric chamber is pressurized. The hatches seal against an o-ring, and the internal pressure of the chamber provides the required pressure against the hatch to maintain an airtight seal. In the preferred embodiment, the hyperbaric chamber has an airlock to allow the attendant to enter and exit the patient chamber during treatment. Visual communication is provided through portholes in the patient and/or airlock chamber. Life monitoring and support systems are in communication with the interior of the hyperbaric chamber and/or airlock chamber through conduits and/or sealed feed-through connectors into the hyperbaric chamber.

  1. Portable Hyperbaric Chamber

    NASA Technical Reports Server (NTRS)

    Schneider, William C. (Inventor); Locke, James P. (Inventor); DeLaFuente, Horacio (Inventor)

    2001-01-01

    A portable, collapsible hyperbaric chamber was developed. A toroidal inflatable skeleton provides initial structural support for the chamber, allowing the attendant and/or patient to enter the chamber. Oval hatches mate against bulkhead rings, and the hyperbaric chamber is pressurized. The hatches seal against an o-ring, and the internal pressure of the chamber provides the required pressure against the hatch to maintain an airtight seal. In the preferred embodiment, the hyperbaric chamber has an airlock to allow the attendant to enter and exit the patient chamber during treatment. Visual communication is provided through portholes in the patient and/or airlock chamber. Life monitoring and support systems are in communication with the interior of the hyperbaric chamber and/or airlock chamber through conduits and/or sealed feed-through connectors into the hyperbaric chamber.

  2. Diogene pictorial drift chamber

    SciTech Connect

    Gosset, J.

    1984-01-01

    A pictorial drift chamber, called DIOGENE, has been installed at Saturne in order to study central collisions of high energy heavy ions. It has been adapted from the JADE internal detector, with two major differences to be taken into account. First, the center-of-mass of these collisions is not identical to the laboratory reference frame. Second, the energy loss and the momentum ranges of the particles to be detected are different from the ones in JADE. It was also tried to keep the cost as small as possible, hence the choice of minimum size and minimum number of sensitive wires. Moreover the wire planes are shifted from the beam axis: this trick helps very much to quickly reject the bad tracks caused by the ambiguity of measuring drift distances (positive or negative) through times (always positive).

  3. Relative abundances of elements (20 or = Z or = 28) at energies up to 70 GeV/amu using relativistic rise in ion chambers

    NASA Technical Reports Server (NTRS)

    Barthelmy, S. D.; Israel, M. H.; Klarmann, J.

    1985-01-01

    The results of a new balloon borne cosmic ray detector flown from Palestine, TX in Sept., 1982 are discussed. The exposure of 62 square meter-ster-hr is sufficient to prove the concept of using gas ionization chambers as energy measuring devices in the relativistic rise region. The abundances, relative Fe-26, of the pure secondaries Cr-22 and Ti-24, the pure primary Ni26, and the mixed primary and secondary Ca-20 between 6 and 70GeV/amu were measured.

  4. Interaction of (12)C ions with the mouse retinal response to light.

    PubMed

    Carozzo, Simone; Ball, Sherry L; Narici, Livio; Schardt, Dieter; Sannita, Walter G

    2015-06-26

    Astronauts in orbit reported phosphenes varying in shape and orientation across the visual field; incidence was correlated with the radiation flux. Patients with skull tumors treated by (12)C ions and volunteers whose posterior portion of the eye was exposed to highly ionizing particles in early studies reported comparable percepts. An origin in radiation activating the visual system is suggested. Bursts (∼ 4 ms) of (12)C ions evoked electrophysiological mass responses comparable to those to light in the retina of anesthetized wild-type mice at threshold flux intensities consistent with the incidence observed in humans. The retinal response amplitude increased in mice with ion intensity to a maximum at ∼ 2000 ions/burst, to decline at higher intensities; the inverted-U relationship suggests complex effects on retinal structures. Here, we show that bursts of (12)C ions presented simultaneously to white light stimuli reduced the presynaptic mass response to light in the mouse retina, while increasing the postsynaptic retinal and cortical responses amplitude and the phase-locking to stimulus of cortical low frequency and gamma (∼ 25-45 Hz) responses. These findings suggest (12)C ions to interfere with, rather than mimicking the light action on photoreceptors; a parallel action on other retinal structures/mechanisms resulting in cortical activation is conceivable. Electrophysiological visual testing appears applicable to monitor the radiation effects and in designing countermeasures to prevent functional visual impairment during operations in space. Copyright © 2015. Published by Elsevier Ireland Ltd.

  5. Charge exchange molecular ion source

    DOEpatents

    Vella, Michael C.

    2003-06-03

    Ions, particularly molecular ions with multiple dopant nucleons per ion, are produced by charge exchange. An ion source contains a minimum of two regions separated by a physical barrier and utilizes charge exchange to enhance production of a desired ion species. The essential elements are a plasma chamber for production of ions of a first species, a physical separator, and a charge transfer chamber where ions of the first species from the plasma chamber undergo charge exchange or transfer with the reactant atom or molecules to produce ions of a second species. Molecular ions may be produced which are useful for ion implantation.

  6. Improved Bakeout Chambers Within Vacuum Chambers

    NASA Technical Reports Server (NTRS)

    Johnson, Kenneth R.; Taylor, Daniel M.; Lane, Robert W.; Cortez, Maximo G.; Anderson, Mark R.

    1995-01-01

    Improved bakeout chamber incorporates hardware features that, in conjunction with improved bakeout procedure, reduce spurious contamination and increase accuracy of contamination measurements. When operated according to revised bakeout procedure, they yield measurements of contamination on vacuum-bake test articles more accurate than available previously, and potential for post-bake recontamination of vacuum-baked articles reduced. These chambers improved versions of one described in "Bakeout Chamber Within Vacuum Chamber" (NPO-18959). By enclosing test article in enclave and keeping walls of enclave hotter than test article during bakeout, one prevents condensation of contaminants on inner walls of enclave.

  7. Soil and ecosystem respiration responses to grazing, watering and experimental warming chamber treatments across topographical gradients in northern Mongolia.

    PubMed

    Sharkhuu, Anarmaa; Plante, Alain F; Enkhmandal, Orsoo; Gonneau, Cédric; Casper, Brenda B; Boldgiv, Bazartseren; Petraitis, Peter S

    2016-05-01

    Globally, soil respiration is one of the largest fluxes of carbon to the atmosphere and is known to be sensitive to climate change, representing a potential positive feedback. We conducted a number of field experiments to study independent and combined impacts of topography, watering, grazing and climate manipulations on bare soil and vegetated soil (i.e., ecosystem) respiration in northern Mongolia, an area known to be highly vulnerable to climate change and overgrazing. Our results indicated that soil moisture is the most important driving factor for carbon fluxes in this semi-arid ecosystem, based on smaller carbon fluxes under drier conditions. Warmer conditions did not result in increased respiration. Although the system has local topographical gradients in terms of nutrient, moisture availability and plant species, soil respiration responses to OTC treatments were similar on the upper and lower slopes, implying that local heterogeneity may not be important for scaling up the results. In contrast, ecosystem respiration responses to OTCs differed between the upper and the lower slopes, implying that the response of vegetation to climate change may override microbial responses. Our results also showed that light grazing may actually enhance soil respiration while decreasing ecosystem respiration, and grazing impact may not depend on climate change. Overall, our results indicate that soil and ecosystem respiration in this semi-arid steppe are more sensitive to precipitation fluctuation and grazing pressure than to temperature change.

  8. Soil and ecosystem respiration responses to grazing, watering and experimental warming chamber treatments across topographical gradients in northern Mongolia

    PubMed Central

    Sharkhuu, Anarmaa; Plante, Alain F.; Enkhmandal, Orsoo; Gonneau, Cédric; Casper, Brenda B.; Boldgiv, Bazartseren; Petraitis, Peter S.

    2017-01-01

    Globally, soil respiration is one of the largest fluxes of carbon to the atmosphere and is known to be sensitive to climate change, representing a potential positive feedback. We conducted a number of field experiments to study independent and combined impacts of topography, watering, grazing and climate manipulations on bare soil and vegetated soil (i.e., ecosystem) respiration in northern Mongolia, an area known to be highly vulnerable to climate change and overgrazing. Our results indicated that soil moisture is the most important driving factor for carbon fluxes in this semi-arid ecosystem, based on smaller carbon fluxes under drier conditions. Warmer conditions did not result in increased respiration. Although the system has local topographical gradients in terms of nutrient, moisture availability and plant species, soil respiration responses to OTC treatments were similar on the upper and lower slopes, implying that local heterogeneity may not be important for scaling up the results. In contrast, ecosystem respiration responses to OTCs differed between the upper and the lower slopes, implying that the response of vegetation to climate change may override microbial responses. Our results also showed that light grazing may actually enhance soil respiration while decreasing ecosystem respiration, and grazing impact may not depend on climate change. Overall, our results indicate that soil and ecosystem respiration in this semi-arid steppe are more sensitive to precipitation fluctuation and grazing pressure than to temperature change. PMID:28239190

  9. Protein-responsive assemblies from catechol-metal ion supramolecular coordination.

    PubMed

    Yuan, C; Chen, J; Yu, S; Chang, Y; Mao, J; Xu, Y; Luo, W; Zeng, B; Dai, L

    2015-03-21

    Supramolecular self-assembly driven by catechol-metal ion coordination has gained great success in the fabrication of functional materials including adhesives, capsules, coatings and hydrogels. However, this route has encountered a great challenge in the construction of nanoarchitectures in the absence of removable templates, because of the uncontrollable crosslinking of catechol-metal ion coordination. Herein, we show that a supramolecular approach, combining both catechol-metal ion coordination and polymer self-assembly together, can organize polymers into hybrid nanoassemblies ranging from solid particles, homogeneous vesicles to Janus vesicles. Without the introduction of a specific binding ligand or complicated molecular design, these assemblies can totally disassemble in response to proteins. UV/vis absorption, fluorescence quenching and recovery investigations have confirmed that proteins can seize metal ions from the hybrid nanoassemblies, thus causing the degradation of catechol-metal ion coordination networks.

  10. Interferometric pump-probe characterization of the nonlocal response of optically transparent ion implanted polymers

    NASA Astrophysics Data System (ADS)

    Stefanov, Ivan L.; Hadjichristov, Georgi B.

    2012-03-01

    Optical interferometric technique is applied to characterize the nonlocal response of optically transparent ion implanted polymers. The thermal nonlinearity of the ion-modified material in the near-surface region is induced by continuous wave (cw) laser irradiation at a relatively low intensity. The interferometry approach is demonstrated for a subsurface layer of a thickness of about 100 nm formed in bulk polymethylmethacrylate (PMMA) by implantation with silicon ions at an energy of 50 keV and fluence in the range 1014-1017 cm-2. The laser-induced thermooptic effect in this layer is finely probed by interferometric imaging. The interference phase distribution in the plane of the ion implanted layer is indicative for the thermal nonlinearity of the near-surface region of ion implanted optically transparent polymeric materials.

  11. Effect of Home Cage Bedding in the Induction Chamber on Serum Cortisol and Corticosterone Levels in Response to Isoflurane-induced Anesthesia in C57BL/6J Mice.

    PubMed

    Reiter, Cara P; Christy, Amanda C; Olsen, Cara H; Bentzel, David E

    2017-03-01

    Mice are routinely anesthetized with isoflurane in an induction chamber. The AVMA Guidelines for the Euthanasia of Animals states that distress should be minimized during euthanasia but does not address this point in regard to induction of anesthesia. Here we evaluated the potential for familiar surroundings to reduce the adrenocortical response of mice during anesthesia induction with isoflurane. However, adding bedding from the animals' home cage to the induction chamber failed to significantly reduce serum cortisol or corticosterone levels in male and female C57BL/6J mice. These results indicate that familiar surroundings do not appear sufficient to reduce the adrenocortical response of mice during anesthesia induction with isoflurane.

  12. Caging metal ions with visible light-responsive nanopolymersomes.

    PubMed

    Griepenburg, Julianne C; Sood, Nimil; Vargo, Kevin B; Williams, Dewight; Rawson, Jeff; Therien, Michael J; Hammer, Daniel A; Dmochowski, Ivan J

    2015-01-20

    Polymersomes are bilayer vesicles that self-assemble from amphiphilic diblock copolymers, and provide an attractive system for the delivery of biological and nonbiological molecules due to their environmental compatibility, mechanical stability, synthetic tunability, large aqueous core, and hyperthick hydrophobic membrane. Herein, we report a nanoscale photoresponsive polymersome system featuring a meso-to-meso ethyne-bridged bis[(porphinato)zinc] (PZn2) fluorophore hydrophobic membrane solute and dextran in the aqueous core. Upon 488 nm irradiation in solution or in microinjected zebrafish embryos, the polymersomes underwent deformation, as monitored by a characteristic red-shifted PZn2 emission spectrum and confirmed by cryo-TEM. The versatility of this system was demonstrated through the encapsulation and photorelease of a fluorophore (FITC), as well as two different metal ions, Zn(2+) and Ca(2+).

  13. Thickness dependence of surface plasmon resonance sensor response for metal ion detection

    NASA Astrophysics Data System (ADS)

    Jung, Seung-A.; Lee, Taek-Sung; Kim, Won Mok; Lee, Kyeong-Seok; Jeong, Doo Seok; Lee, Wook Seong; Kim, Inho

    2013-08-01

    Surface plasmon resonance (SPR) sensor is one of the most viable technologies for portable and highly sensitive sensing in clinical and environmental applications. A lot of research on SPR sensors based on plasticized polyvinyl chloride (PVC) sensing layers for detection of various metal ions has been well reported, but a study on their correlation between sensing layer thickness and sensor response has been rarely done. The purpose of this study is to investigate thickness dependence of sensing layers on the response time and the sensitivity of SPR sensors based on plasticized PVC. Calcium ionophore was incorporated in the sensing layers for calcium ion detection. Our experimental results showed that thicker sensing layers exhibited higher sensitivity and wider detection range but longer response time. We discussed metal ion diffusion in plasticized sensing layers by correlating numerical calculations with experimental ones in order to understand temporal response of our SPR sensor. The response time also relied on the flow rate of calcium ion solutions, indicating that metal ion diffusion in bulk media is one of the limiting factors.

  14. Control Effect of a Large Geological Discontinuity on the Seismic Response and Stability of Underground Rock Caverns: A Case Study of the Baihetan #1 Surge Chamber

    NASA Astrophysics Data System (ADS)

    Cui, Zhen; Sheng, Qian; Leng, Xianlun

    2016-06-01

    In this paper, the seismic stability of the #1 surge chamber of the Baihetan hydropower plant, which is influenced by a large dominating geological discontinuity [the interlayer shear weakness zone (ISWZ) C2)], is studied. An advanced, nonlinear, continuously yielding (CY) model was adopted to describe the complex mechanical properties of ISWZ C2. This model considers a power function type, normal stress dependent behavior and the progressive damage that occurred during shear tests. The applicability of the CY model is proved via a comparison with field test results and the theoretical solution. Verification work was conducted in 3DEC code to show that the 3DEC software is suitable for implementing this model. Three ground motion waveforms were utilized to conduct a seismic analysis of the #1 surge chamber after a special response spectrum matching process. The seismic analysis confirmed the control effect of ISWZ C2 on the seismic stability of the cavern. The majority of the cavern's seismic displacement consists of elastic body movement, while the plastic deformation is relatively limited. Further, most of the deformations were caused by the contact deformation of C2. For the contact deformation of C2, the magnitude of permanent shear deformation is larger than that of the normal deformation. The magnitude of permanent shear deformation is more notable along the strike direction of C2, and the permanent normal displacement n of C2 mainly occurs along the dip direction of C2. Finally, the seismic stability of the cavern is assessed via the overload method. The seismic safety factor of the cavern is approximately 2-3.

  15. A numerical model of initial recombination for high-LET irradiation: Application to liquid-filled ionization chambers

    NASA Astrophysics Data System (ADS)

    Aguiar, P.; Pardo-Montero, J.

    2016-02-01

    In this paper we present a numerical model of initial recombination in media irradiated with high linear energy transfer (LET) ions, which relies on an amorphous track model of ionization of high LET particles, and diffusion, drift and recombination of ionized charge carriers. The model has fundamental applications for the study of recombination in non-polar liquids, as well as practical ones, like in modelling hadrontherapy dosimetry with ionization chambers. We have used it to study the response of liquid-filled ionization chambers to hadrontherapy beams: dependence of initial recombination on ion species, energy and applied external electric field.

  16. Calibration of BAS-TR image plate response to high energy (3-300 MeV) carbon ions

    NASA Astrophysics Data System (ADS)

    Doria, D.; Kar, S.; Ahmed, H.; Alejo, A.; Fernandez, J.; Cerchez, M.; Gray, R. J.; Hanton, F.; MacLellan, D. A.; McKenna, P.; Najmudin, Z.; Neely, D.; Romagnani, L.; Ruiz, J. A.; Sarri, G.; Scullion, C.; Streeter, M.; Swantusch, M.; Willi, O.; Zepf, M.; Borghesi, M.

    2015-12-01

    The paper presents the calibration of Fuji BAS-TR image plate (IP) response to high energy carbon ions of different charge states by employing an intense laser-driven ion source, which allowed access to carbon energies up to 270 MeV. The calibration method consists of employing a Thomson parabola spectrometer to separate and spectrally resolve different ion species, and a slotted CR-39 solid state detector overlayed onto an image plate for an absolute calibration of the IP signal. An empirical response function was obtained which can be reasonably extrapolated to higher ion energies. The experimental data also show that the IP response is independent of ion charge states.

  17. Multispecimen dual-beam irradiation damage chamber

    SciTech Connect

    Packan, N.H.; Buhl, R.A.

    1980-06-01

    An irradiation damage chamber that can be used to rapidly simulate fast neutron damage in fission or fusion materials has been designed and constructed. The chamber operates in conjunction with dual Van de Graaff accelerators at ORNL to simulate a wide range of irradiation conditions, including pulsed irradiation. Up to six experiments, each with up to nine 3-mm disk specimens, can be loaded into the ultrahigh vacuum chamber. Specimen holders are heated with individual electron guns, and the temperature of each specimen can be monitored during bombardment by an infrared pyrometer. Three different dose levels may be obtained during any single bombardment, and the heavy-ion flux on each of the nine specimens can be measured independently with only a brief interruption of the beam. The chamber has been in service for nearly three years, during which time approximately 250 bombardments have been successfully carried out. An appendix contains detailed procedures for operating the chamber.

  18. Effects of CO2 enrichment and drought pretreatment on metabolite responses to water stress and subsequent rehydration using potato tubers from plants grown in sunlit chambers.

    PubMed

    Yang, Jinyoung; Fleisher, David H; Sicher, Richard C; Kim, Joonyup; Baligar, Virupax C; Reddy, Vangimalla R

    2015-09-15

    Experiments were performed using naturally sunlit Soil-Plant-Atmosphere Research chambers that provided ambient or twice ambient CO2. Potato plants were grown in pots that were water sufficient (W), water insufficient for 12-18 days during both vegetative and tuber development stages (VR), or water insufficient solely during tuber development (R). In the ambient CO2 treatment, a total of 17 and 20 out of 31 tuber metabolites differed when comparing the W to the R and VR treatments, respectively. Hexoses, raffinose, mannitol, branched chain amino acids, phenylalanine and proline increased, although most organic acids remained unchanged or decreased in response to drought. Osmolytes, including glucose, branched chain amino acids and proline, remained elevated following 2 weeks of rehydration in both the ambient and elevated CO2 treatments, whereas fructose, raffinose, mannitol and some organic acids reverted to control levels. Failure of desiccated plant tissues to mobilize specific osmolytes after rehydration was unexpected and was likely because tubers function as terminal sinks. Tuber metabolite responses to single or double drought treatments were similar under the same CO2 levels but important differences were noted when CO2 level was varied. We also found that metabolite changes to water insufficiency and/or CO2 enrichment were very distinct between sink and source tissues, and total metabolite changes to stress were generally greater in leaflets than tubers. Published by Elsevier GmbH.

  19. Sensitive detection of copper ions via ion-responsive fluorescence quenching of engineered porous silicon nanoparticles

    PubMed Central

    Hwang, Jangsun; Hwang, Mintai P.; Choi, Moonhyun; Seo, Youngmin; Jo, Yeonho; Son, Jaewoo; Hong, Jinkee; Choi, Jonghoon

    2016-01-01

    Heavy metal pollution has been a problem since the advent of modern transportation, which despite efforts to curb emissions, continues to play a critical role in environmental pollution. Copper ions (Cu2+), in particular, are one of the more prevalent metals that have widespread detrimental ramifications. From this perspective, a simple and inexpensive method of detecting Cu2+ at the micromolar level would be highly desirable. In this study, we use porous silicon nanoparticles (NPs), obtained via anodic etching of Si wafers, as a basis for undecylenic acid (UDA)- or acrylic acid (AA)-mediated hydrosilylation. The resulting alkyl-terminated porous silicon nanoparticles (APS NPs) have enhanced fluorescence stability and intensity, and importantly, exhibit [Cu2+]-dependent quenching of fluorescence. After determining various aqueous sensing conditions for Cu2+, we demonstrate the use of APS NPs in two separate applications – a standard well-based paper kit and a portable layer-by-layer stick kit. Collectively, we demonstrate the potential of APS NPs in sensors for the effective detection of Cu2+. PMID:27752120

  20. Sensitive detection of copper ions via ion-responsive fluorescence quenching of engineered porous silicon nanoparticles

    NASA Astrophysics Data System (ADS)

    Hwang, Jangsun; Hwang, Mintai P.; Choi, Moonhyun; Seo, Youngmin; Jo, Yeonho; Son, Jaewoo; Hong, Jinkee; Choi, Jonghoon

    2016-10-01

    Heavy metal pollution has been a problem since the advent of modern transportation, which despite efforts to curb emissions, continues to play a critical role in environmental pollution. Copper ions (Cu2+), in particular, are one of the more prevalent metals that have widespread detrimental ramifications. From this perspective, a simple and inexpensive method of detecting Cu2+ at the micromolar level would be highly desirable. In this study, we use porous silicon nanoparticles (NPs), obtained via anodic etching of Si wafers, as a basis for undecylenic acid (UDA)- or acrylic acid (AA)-mediated hydrosilylation. The resulting alkyl-terminated porous silicon nanoparticles (APS NPs) have enhanced fluorescence stability and intensity, and importantly, exhibit [Cu2+]-dependent quenching of fluorescence. After determining various aqueous sensing conditions for Cu2+, we demonstrate the use of APS NPs in two separate applications – a standard well-based paper kit and a portable layer-by-layer stick kit. Collectively, we demonstrate the potential of APS NPs in sensors for the effective detection of Cu2+.

  1. CONTINUOUS ROTATION SCATTERING CHAMBER

    DOEpatents

    Verba, J.W.; Hawrylak, R.A.

    1963-08-01

    An evacuated scattering chamber for use in observing nuclear reaction products produced therein over a wide range of scattering angles from an incoming horizontal beam that bombards a target in the chamber is described. A helically moving member that couples the chamber to a detector permits a rapid and broad change of observation angles without breaching the vacuum in the chamber. Also, small inlet and outlet openings are provided whose size remains substantially constant. (auth)

  2. Intrinsic slow charge response in the perovskite solar cells: Electron and ion transport

    SciTech Connect

    Shi, Jiangjian; Xu, Xin; Zhang, Huiyin; Luo, Yanhong; Li, Dongmei; Meng, Qingbo

    2015-10-19

    The intrinsic charge response and hysteresis characteristic in the perovskite solar cell has been investigated by an electrically modulated transient photocurrent technology. An ultraslow charge response process in the timescale of seconds is observed, which can be well explained by the ion migration in the perovskite CH{sub 3}NH{sub 3}PbI{sub 3} film driven by multiple electric fields derived from the heterojunction depletion charge, the external modulation, and the accumulated ion charge. Furthermore, theoretical calculation of charge transport reveals that the hysteresis behavior is also significantly influenced by the interfacial charge extraction velocity and the carrier transport properties inside the cell.

  3. Two chamber reaction furnace

    DOEpatents

    Blaugher, R.D.

    1998-05-05

    A vertical two chamber reaction furnace is described. The furnace comprises a lower chamber having an independently operable first heating means for heating the lower chamber and a gas inlet means for admitting a gas to create an ambient atmosphere, and an upper chamber disposed above the lower chamber and having an independently operable second heating means for heating the upper chamber. Disposed between the lower chamber and the upper chamber is a vapor permeable diffusion partition. The upper chamber has a conveyor means for conveying a reactant there through. Of particular importance is the thallinating of long-length thallium-barium-calcium-copper oxide (TBCCO) or barium-calcium-copper oxide (BCCO) precursor tapes or wires conveyed through the upper chamber to thereby effectuate the deposition of vaporized thallium (being so vaporized as the first reactant in the lower chamber at a temperature between about 700 C and 800 C) on TBCCO or BCCO tape or wire (the second reactant) at its simultaneous annealing temperature in the upper chamber of about 800 to 950 C to thereby replace thallium oxide lost from TBCCO tape or wire because of the high annealing temperature or to deposit thallium on BCCO tape or wire. Continuously moving the tape or wire provides a single-step process that effectuates production of long-length TBCCO superconducting product. 2 figs.

  4. Two chamber reaction furnace

    DOEpatents

    Blaugher, Richard D.

    1998-05-05

    A vertical two chamber reaction furnace. The furnace comprises a lower chamber having an independently operable first heating means for heating the lower chamber and a gas inlet means for admitting a gas to create an ambient atmosphere, and an upper chamber disposed above the lower chamber and having an independently operable second heating means for heating the upper chamber. Disposed between the lower chamber and the upper chamber is a vapor permeable diffusion partition. The upper chamber has a conveyor means for conveying a reactant there through. Of particular importance is the thallinating of long-length thallium-barium-calcium-copper oxide (TBCCO) or barium-calcium-copper oxide (BCCO) precursor tapes or wires conveyed through the upper chamber to thereby effectuate the deposition of vaporized thallium (being so vaporized as the first reactant in the lower chamber at a temperature between about 700.degree. and 800.degree. C.) on TBCCO or BCCO tape or wire (the second reactant) at its simultaneous annealing temperature in the upper chamber of about 800.degree. to 950.degree. C. to thereby replace thallium oxide lost from TBCCO tape or wire because of the high annealing temperature or to deposit thallium on BCCO tape or wire. Continuously moving the tape or wire provides a single-step process that effectuates production of long-length TBCCO superconducting product.

  5. RADIATION MONITOR CONTAINING TWO CONCENTRIC IONIZATION CHAMBERS AND MEANS FOR INSULATING THE SEPARATE CHAMBERS

    DOEpatents

    Braestrup, C.B.; Mooney, R.T.

    1964-01-21

    This invention relates to a portable radiation monitor containing two concentric ionization chambers which permit the use of standard charging and reading devices. It is particularly adapted as a personnel x-ray dosimeter and to this end comprises a small thin walled, cylindrical conductor forming an inner energy dependent chamber, a small thin walled, cylindrical conductor forming an outer energy independent chamber, and polymeric insulation means which insulates said chambers from each other and holds the chambers together with exposed connections in a simple, trouble-free, and compact assembly substantially without variation in directional response. (AEC)

  6. Utilizing Chamber Data for Developing and Validating Climate Change Models

    NASA Technical Reports Server (NTRS)

    Monje, Oscar

    2012-01-01

    Controlled environment chambers (e.g. growth chambers, SPAR chambers, or open-top chambers) are useful for measuring plant ecosystem responses to climatic variables and CO2 that affect plant water relations. However, data from chambers was found to overestimate responses of C fluxes to CO2 enrichment. Chamber data may be confounded by numerous artifacts (e.g. sidelighting, edge effects, increased temperature and VPD, etc) and this limits what can be measured accurately. Chambers can be used to measure canopy level energy balance under controlled conditions and plant transpiration responses to CO2 concentration can be elucidated. However, these measurements cannot be used directly in model development or validation. The response of stomatal conductance to CO2 will be the same as in the field, but the measured response must be recalculated in such a manner to account for differences in aerodynamic conductance, temperature and VPD between the chamber and the field.

  7. Species- and chamber-specific responses of 12 kDa FK506-binding protein to temperature in fish heart.

    PubMed

    Korajoki, Hanna; Vornanen, Matti

    2014-04-01

    The sarcoplasmic reticulum (SR) Ca(2+) release channel or ryanodine receptor (RyR) of the vertebrate heart is regulated by the FK506-binding proteins, FKBP12 and FKBP12.6. This study examines whether temperature-related changes in the SR function of fish hearts are associated with changes in FKBP12 expression. For this purpose, a polyclonal antibody against trout FKBP12 was used to compare FKPB12 expression in cold-acclimated (4 °C, CA) and warm-acclimated (18 °C, WA) rainbow trout (Oncorhynchus mykiss), burbot (Lota lota) and crucian carp (Carassius carassius) hearts. FKBP12 expression was modulated in a species- and tissue-specific manner. Temperature acclimation affected FKBP12 expression only in atrial tissue. Changes in the ventricular FKBP12 expression were not detected in any of the fish species. In the atria of rainbow trout and crucian carp, temperature acclimation produced opposite thermal responses: FKBP12 increased in the trout atrium and decreased in the crucian carp atrium under cold acclimation. In the burbot heart, chronic temperature changes did not affect cardiac FKBP12 levels. Expression of FKBP12 mRNA in rainbow trout and crucian carp hearts suggests that the transcript levels are higher in the ventricle than in the atrium and are elevated by cold acclimation in trout, but not in crucian carp. Since FKBP12 is known to increase the Ca(2+) sensitivity of cardiac RyRs and thereby the opening frequency of the Ca(2+) release channels, temperature-related changes in FKBP12 expression may modify the SR function in excitation-contraction coupling. The cold-induced increase in FKBP12 in the trout atrium and decrease in the crucian carp atrium are consistent with the previously noted increase and decrease, respectively, of SR Ca(2+) stores in cardiac contraction in these species.

  8. Construction of a fast ionization chamber for high-rate particle identification

    NASA Astrophysics Data System (ADS)

    Chae, K. Y.; Ahn, S.; Bardayan, D. W.; Chipps, K. A.; Manning, B.; Pain, S. D.; Peters, W. A.; Schmitt, K. T.; Smith, M. S.; Strauss, S. Y.

    2014-07-01

    A new gas-filled ionization chamber for high count rate particle identification has been constructed and commissioned at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL). To enhance the response time of the ionization chamber, a design utilizing a tilted entrance window and tilted electrodes was adopted, which is modified from an original design by Kimura et al. [1]. A maximum counting rate of 700 , 000 particles per second has been achieved. The detector has been used for several radioactive beam measurements performed at the HRIBF.

  9. The responses of Petunia to simulated pollutants in chamber conditions and its uses as bioindicator of pollution

    NASA Astrophysics Data System (ADS)

    Oguntimehin, I. I.; Kondo, H.; Sakugawa, H. H.

    2010-12-01

    Plants damage that results from air pollution are often confused with plant diseases, nutritional deficiency or natural senescence. Bio-indicating plants are used to obtain the direct identification of air pollutants on plants and determine the geographical distribution of pollutants. The responses of two varieties of Petunia (purple and white) to ten treatments including fumigated ozone (‘O’AOT40 28.2 ppm h), 10 µM fluoranthene ‘F’ and H2SO4 (‘A’ pH 3) mist, MQ water sprayed on plants as control ‘C’ with other mixtures were investigated in 30 d under controlled conditions. Also, a 1:1 mixture of Na2S2O3 and 1mM NaOOCCC6H5 form part of the treatments and was used as scavenging solution ‘S’ against Reactive Oxygen Species (ROS). Eco-physiological traits are leaf chlorophyll, carotenoids contents and chlorophyll fluorescence. Metal analysis was by ICP-AES, Histochemical analysis using 3’3-diaminobenzidine (DAB)-HCl, combined with Evans blue staining procedure for hydrogen peroxide deposition and dead cell portion of leaves. Plants health determined as SPAD chlorophyll values at 7, 14, 21 and 28 d of treatments (DOT) were significantly reduced after 28 DOT for the petunia . Chlorophyll depreciation ‘CD’ was > 40% in purple petunia for the ‘O’ containing treatments, < 25% for other treatments and ≈ 10% for ‘C’ whereas it ranged from 25-28% in ‘O’ containing treatments, < 20% for other treatments and 10% for ‘C’. A derivative to assess plant health status by the variation of the ratio (total chlorophyll content: carotenoids) against CD was obtained. Higher R2 value for this derivative in the white petunia suggested that though the leaf of purple petunia indicated higher sensitivity to ozone than the white, white petunia is a better bio-indicator of the stresses examined from the present study. Also, the leaf chlorophyll fluorescence showed higher significant values in the ‘O’ containing and the other treatments in the

  10. Studying Phototropism Using a Small Growth Chamber.

    ERIC Educational Resources Information Center

    Fisher, Maryanna, F.; Llewellyn, Gerald C.

    1978-01-01

    Describes a simple and inexpensive way to construct two small growth chambers for studying phototropism in the science classroom. One chamber is designed to illustrate how plants grow around obstacles to reach light and the other to illustrate directional light responses. (HM)

  11. ION SOURCE

    DOEpatents

    Leland, W.T.

    1960-01-01

    The ion source described essentially eliminater the problem of deposits of nonconducting materials forming on parts of the ion source by certain corrosive gases. This problem is met by removing both filament and trap from the ion chamber, spacing them apart and outside the chamber end walls, placing a focusing cylinder about the filament tip to form a thin collimated electron stream, aligning the cylinder, slits in the walls, and trap so that the electron stream does not bombard any part in the source, and heating the trap, which is bombarded by electrons, to a temperature hotter than that in the ion chamber, so that the tendency to build up a deposit caused by electron bombardment is offset by the extra heating supplied only to the trap.

  12. SU-D-19A-01: Can Farmer-Type Ionization Chambers Be Used to Improve the Accuracy of Low-Energy Electron Beam Reference Dosimetry?

    SciTech Connect

    Muir, B R; McEwen, M R

    2014-06-01

    Purpose: To investigate the use of cylindrical Farmer-type ionization chambers to improve the accuracy of low-energy electron beam calibration. Historically, these chamber types have not been used in beams with incident energies less than 10 MeV (R{sub 5} {sub 0} < 4.3 cm) because early investigations suggested large (up to 5 %) fluence perturbation factors in these beams, implying that a significant component of uncertainty would be introduced if used for calibration. More recently, the assumptions used to determine perturbation corrections for cylindrical chambers have been questioned. Methods: Measurements are made with cylindrical chambers in Elekta Precise 4, 8 and 18 MeV electron beams. Several chamber types are investigated that employ graphite walls and aluminum electrodes with very similar specifications (NE2571, NE2505/3, FC65-G). Depth-ionization scans are measured in water in the 8 and 18 MeV beams. To reduce uncertainty from chamber positioning, measurements in the 4 MeV beam are made at the reference depth in Virtual Water™. The variability of perturbation factors is quantified by comparing normalized response of various chambers. Results: Normalized ion chamber response varies by less than 0.7 % for similar chambers at average electron energies corresponding to that at the reference depth from 4 or 6 MeV beams. Similarly, normalized measurements made with similar chambers at the reference depth in the 4 MeV beam vary by less than 0.4 %. Absorbed dose calibration coefficients derived from these results are stable within 0.1 % on average over a period of 6 years. Conclusion: These results indicate that the uncertainty associated with differences in fluence perturbations for cylindrical chambers with similar specifications is only 0.2 %. The excellent long-term stability of these chambers in both photon and electron beams suggests that these chambers might offer the best performance for all reference dosimetry applications.

  13. Neutron Detection via Bubble Chambers

    SciTech Connect

    Jordan, David V.; Ely, James H.; Peurrung, Anthony J.; Bond, Leonard J.; Collar, J. I.; Flake, Matthew; Knopf, Michael A.; Pitts, W. K.; Shaver, Mark W.; Sonnenschein, Andrew; Smart, John E.; Todd, Lindsay C.

    2005-10-06

    The results of a Pacific Northwest National Laboratory (PNNL) exploratory research project investigating the feasibility of fast neutron detection using a suitably prepared and operated, pressure-cycled bubble chamber are described. The research was conducted along two parallel paths. Experiments with a slow pressure-release Halon chamber at the Enrico Fermi Institute at the University of Chicago showed clear bubble nucleation sensitivity to an AmBe neutron source and insensitivity to the 662 keV gammas from a 137Cs source. Bubble formation was documented via high-speed (1000 frames/sec) photography, and the acoustic signature of bubble formation was detected using a piezo-electric transducer element mounted on the base of the chamber. The chamber’s neutron sensitivity as a function of working fluid temperature was mapped out. The second research path consisted of the design, fabrication, and testing of a fast pressure-release Freon-134a chamber at PNNL. The project concluded with successful demonstrations of the PNNL chamber’s AmBe neutron source sensitivity and 137Cs gamma insensitivity. The source response tests of the PNNL chamber were documented with high-speed photography.

  14. ION-1 technical manual

    SciTech Connect

    Halbig, J.K.; Caine, J.C.

    1985-07-01

    The portable gamma-ray and neutron detector electronics (ION-1) gives a digital readout of the current-mode response produced by gamma rays in an ion chamber and of amplification and scaling of pulses received from a neutron detector. The primary application is the measurement of gamma-ray and neutron activity of irradiated reactor fuels stored at a reactor or at a storage pond away from a reactor. ION-1 is the first such instrument to use a design that allows communication of procedures, response, and results between instrument and inspector. It prompts the inspector through procedures, carries out programmed measurement steps, calculates results and error estimates, and performs internal diagnostic checks. This Technical Manual describes adjustment procedures and limited technical information that enable the inspector to troubleshoot at the board level. 5 figs., 10 tabs.

  15. RESPONSE OF THE GREEK EARLY WARNING SYSTEM REUTER-STOKES IONIZATION CHAMBERS TO TERRESTRIAL AND COSMIC RADIATION EVALUATED IN COMPARISON WITH SPECTROSCOPIC DATA AND TIME SERIES ANALYSIS.

    PubMed

    Leontaris, F; Clouvas, A; Xanthos, S; Maltezos, A; Potiriadis, C; Kiriakopoulos, E; Guilhot, J

    2017-08-10

    The Telemetric Early Warning System Network of the Greek Atomic Energy Commission consists mainly of a network of 24 Reuter-Stokes high-pressure ionization chambers (HPIC) for gamma dose rate measurements and covers all Greece. In the present work, the response of the Reuter-Stokes HPIC to terrestrial and cosmic radiation was evaluated in comparison with spectroscopic data obtained by in situ gamma spectrometry measurements with portable hyper pure Germanium detectors (HPGe), near the Reuter-Stokes detectors and time series analysis. For the HPIC detectors, a conversion factor for the measured absorbed dose rate in air (in nGy h-1) to the total ambient dose equivalent rate Ḣ*(10), due to terrestrial and cosmic component, was deduced by the field measurements. Time series analysis of the mean monthly dose rate (measured by the Reuter-Stokes detector in Thessaloniki, northern Greece, from 2001 to 2016) was performed with advanced statistical methods (Fast Fourier Analysis and Zhao Atlas Marks Transform). Fourier analysis reveals several periodicities (periodogram). The periodogram of the absorbed dose rate in air values was compared with the periodogram of the values measured for the same period (2001-16) and in the same location with a NaI (Tl) detector which in principle is not sensitive to cosmic radiation. The obtained results are presented and discussed. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  16. Dual chamber rate responsive pacing system driven by contractility: final assessment after 1-year follow-up. The European PEA Clinical Investigation Group.

    PubMed

    Clémenty, J

    1998-11-01

    The aim of this study was to assess the long-term performance of a new dual chamber rate responsive pacing system based on the dynamic measurement of the peak endocardial acceleration (PEA) index of cardiac contractility. Seventy patients who participated in the Multicenter European Clinical Evaluation were studied 1 year after implantation by continuously recording the PEA and the heart rate (HR) during exercise stress testing and during 24 hours of usual activities. A complete examination of standard parameters was also performed to assess the pacing/sensing lead characteristics. Statistical comparisons were performed with the data recorded with the same protocol at 1 month after implant for each patient. A linear correlation coefficient was calculated between PEA and sinus rate when the patient showed predominant atrial tracked rhythm. There were no significant differences between PEA values measured at 1 month and 1 year (PEA = 0.41 +/- 0.26 g vs 0.45 +/- 0.29 g at rest and PEA = 1.63 +/- 0.77 g vs 1.72 +/- 0.83 g during peak exercise). The correlation coefficient remained stable (0.67 +/- 0.15 vs 0.65 +/- 0.14 during daily life and 0.74 +/- 0.14 vs 0.77 +/- 0.11 during exercise). The PEA signal detected by the sensor was reliable and stable. No long-term complications or adverse effects were observed, and the lead performance was comparable to that of a standard lead.

  17. Stream mesocosm response sensitivities to simulated ion stress in produced waters from resource extraction activities

    EPA Science Inventory

    To increase the ecological relevance of laboratory exposures intent on determining species sensitivity to ion stress from resource extraction activities we have conducted several stream mesocosm dosing studies that pair single-species and community-level responses in-situ and all...

  18. Stream mesocosm response sensitivities to simulated ion stress in produced waters from resource extraction activities

    EPA Science Inventory

    To increase the ecological relevance of laboratory exposures intent on determining species sensitivity to ion stress from resource extraction activities we have conducted several stream mesocosm dosing studies that pair single-species and community-level responses in-situ and all...

  19. Mesocosm Community Response Sensitivities to Specific Conductivity Comprised of Different Major Ions

    EPA Science Inventory

    Traditional toxicity test assays have been used to evaluate the relative sensitivity to different major ion mixtures as a proxy for understanding what the response of aquatic species growing in their natural environment would be during exposure to specific conductivity stress ema...

  20. Mesocosm Community Response Sensitivities to Specific Conductivity Comprised of Different Major Ions

    EPA Science Inventory

    Traditional toxicity test assays have been used to evaluate the relative sensitivity to different major ion mixtures as a proxy for understanding what the response of aquatic species growing in their natural environment would be during exposure to specific conductivity stress ema...

  1. Comparison of chamber 6.6-h exposures to 0.04-0.08 PPM ozone via square-wave and triangular profiles on pulmonary responses.

    PubMed

    Adams, William C

    2006-02-01

    It has become increasingly well realized that laboratory simulations of air pollution risk assessment need to employ O(3) concentration profiles that more accurately mimic those encountered during summer daylight ambient air pollution episodes. The present study was designed to compare the pulmonary function and symptoms of breathing discomfort responses to a 6.6-h square-wave 0.08-ppm O(3) chamber exposure to those observed in a triangular O(3) exposure profile (mean of 0.08 ppm), as well as to both a 0.06-ppm square-wave and triangular mean 0.06-ppm exposure, and to those observed during a triangular mean 0.04-ppm exposure and to a filtered air (FA) square-wave exposure. Thirty young adults (15 of each gender) served as subjects, each completing all exposures. While the 6.6-h postexposure responses to the acute triangular exposure to a mean O(3) concentration of 0.08 ppm did not differ significantly from those observed in the square-wave exposure, forced expiratory volume in 1 s (FEV)(1.0) and total symptoms severity (TSS) were significantly different from preexposure at 4.6 h (when O(3) concentration was 0.15 ppm) in the triangular exposure, but not until 6.6 h in the square-wave exposure. Thus, significant pulmonary function and symptoms responses were observed over a longer period in the triangular exposure protocol at a mean O(3) concentration of 0.08 ppm. These results support previous evidence that O(3) concentration has a greater singular effect in the total inhaled O(3) dose than do V(E) and exposure duration. Subtracting pulmonary function effects consequent to O(3) exposure to existent 8-h average background levels (e.g., approximately 0.04 ppm, rather than those observed in FA exposures) from those observed at higher concentrations (e.g., approximately 0.08 ppm) represents a means of focusing the regulatory effort on effects that can be controlled. The greatest pulmonary function and symptoms responses observed for a 0.04-ppm triangular exposure were

  2. Response to rhinovirus infection by human airway epithelial cells and peripheral blood mononuclear cells in an in vitro two-chamber tissue culture system.

    PubMed

    Rajan, Devi; Gaston, Kelsey A; McCracken, Courtney E; Erdman, Dean D; Anderson, Larry J

    2013-01-01

    Human rhinovirus (HRV) infections are associated with the common cold, occasionally with more serious lower respiratory tract illnesses, and frequently with asthma exacerbations. The clinical features of HRV infection and its association with asthma exacerbation suggest that some HRV disease results from virus-induced host immune responses to infection. To study the HRV-infection-induced host responses and the contribution of these responses to disease, we have developed an in vitro model of HRV infection of human airway epithelial cells (Calu-3 cells) and subsequent exposure of human peripheral blood mononuclear cells (PBMCs) to these infected cells in a two-chamber trans-well tissue culture system. Using this model, we studied HRV 14 (species B) and HRV 16 (species A) induced cytokine and chemokine responses with PBMCs from four healthy adults. Infection of Calu-3 cells with either virus induced HRV-associated increases in FGF-Basic, IL-15, IL-6, IL-28A, ENA-78 and IP-10. The addition of PBMCs to HRV 14-infected cells gave significant increases in MIP-1β, IL-28A, MCP-2, and IFN-α as compared with mock-infected cells. Interestingly, ENA-78 levels were reduced in HRV 14 infected cells that were exposed to PBMCs. Addition of PBMCs to HRV 16-infected cells did not induce MIP-1β, IL-28A and IFN-α efficiently nor did it decrease ENA-78 levels. Our results demonstrate a clear difference between HRV 14 and HRV 16 and the source of PBMCs, in up or down regulation of several cytokines including those that are linked to airway inflammation. Such differences might be one of the reasons for variation in disease associated with different HRV species including variation in their link to asthma exacerbations as suggested by other studies. Further study of immune responses associated with different HRVs and PBMCs from different patient groups, and the mechanisms leading to these differences, should help characterize pathogenesis of HRV disease and generate novel approaches to

  3. Detection of Large Ions in Time-of-Flight Mass Spectrometry: Effects of Ion Mass and Acceleration Voltage on Microchannel Plate Detector Response

    NASA Astrophysics Data System (ADS)

    Liu, Ranran; Li, Qiyao; Smith, Lloyd M.

    2014-08-01

    In time-of-flight mass spectrometry (TOF-MS), ion detection is typically accomplished by the generation and amplification of secondary electrons produced by ions colliding with a microchannel plate (MCP) detector. Here, the response of an MCP detector as a function of ion mass and acceleration voltage is characterized, for singly charged peptide/protein ions ranging from 1 to 290 kDa in mass, and for acceleration voltages from 5 to 25 kV. A nondestructive inductive charge detector (ICD) employed in parallel with MCP detection provides a reliable reference signal to allow accurate calibration of the MCP response. MCP detection efficiencies were very close to unity for smaller ions at high acceleration voltages (e.g., angiotensin, 1046.5 Da, at 25 kV acceleration voltage), but decreased to ~11% for the largest ions examined (immunoglobulin G (IgG) dimer, 290 kDa) even at the highest acceleration voltage employed (25 kV). The secondary electron yield γ (average number of electrons produced per ion collision) is found to be proportional to mv3.1 (m: ion mass, v: ion velocity) over the entire mass range examined, and inversely proportional to the square root of m in TOF-MS analysis. The results indicate that although MCP detectors indeed offer superlative performance in the detection of smaller peptide/protein species, their performance does fall off substantially for larger proteins, particularly under conditions of low acceleration voltage.

  4. Detection of large ions in time-of-flight mass spectrometry: effects of ion mass and acceleration voltage on microchannel plate detector response.

    PubMed

    Liu, Ranran; Li, Qiyao; Smith, Lloyd M

    2014-08-01

    In time-of-flight mass spectrometry (TOF-MS), ion detection is typically accomplished by the generation and amplification of secondary electrons produced by ions colliding with a microchannel plate (MCP) detector. Here, the response of an MCP detector as a function of ion mass and acceleration voltage is characterized, for singly charged peptide/protein ions ranging from 1 to 290 kDa in mass, and for acceleration voltages from 5 to 25 kV. A nondestructive inductive charge detector (ICD) employed in parallel with MCP detection provides a reliable reference signal to allow accurate calibration of the MCP response. MCP detection efficiencies were very close to unity for smaller ions at high acceleration voltages (e.g., angiotensin, 1046.5 Da, at 25 kV acceleration voltage), but decreased to ~11% for the largest ions examined (immunoglobulin G (IgG) dimer, 290 kDa) even at the highest acceleration voltage employed (25 kV). The secondary electron yield γ (average number of electrons produced per ion collision) is found to be proportional to mv(3.1) (m: ion mass, v: ion velocity) over the entire mass range examined, and inversely proportional to the square root of m in TOF-MS analysis. The results indicate that although MCP detectors indeed offer superlative performance in the detection of smaller peptide/protein species, their performance does fall off substantially for larger proteins, particularly under conditions of low acceleration voltage.

  5. Dual mode ion mobility spectrometer and method for ion mobility spectrometry

    DOEpatents

    Scott, Jill R [Idaho Falls, ID; Dahl, David A [Idaho Falls, ID; Miller, Carla J [Idaho Falls, ID; Tremblay, Paul L [Idaho Falls, ID; McJunkin, Timothy R [Idaho Falls, ID

    2007-08-21

    Ion mobility spectrometer apparatus may include an ion interface that is operable to hold positive and negative ions and to simultaneously release positive and negative ions through respective positive and negative ion ports. A first drift chamber is operatively associated with the positive ion port of the ion interface and encloses an electric field therein. A first ion detector operatively associated with the first drift chamber detects positive ions from the first drift chamber. A second drift chamber is operatively associated with the negative ion port of the ion interface and encloses an electric field therein. A second ion detector operatively associated with the second drift chamber detects negative ions from said second drift chamber.

  6. The effect of a compression paddle on energy response, calibration and measurement with mammographic dosimeters using ionization chambers and solid-state detectors.

    PubMed

    Hourdakis, C J; Boziari, A; Koumbouli, E

    2009-02-21

    A compression paddle is always used in mammography x-ray examinations, in order to improve image quality and reduce patient doses. Although clinical dose measurements should be performed with the paddle to interfere with the x-ray beam, calibration of mammography dosimeters is performed free in air without the presence of the paddle. The paddle hardens the x-ray beam, which has an impact on a dosimeter performance, particularly on high-energy-dependent detectors. Due to the paddle, clinical mammography x-ray systems may exhibit beams with HVL values exceeding those of the IEC 61267 RQR-M series qualities at which dosimeters are usually calibrated. In this study, the influence of the paddle in mammography dosimetry is examined, in Mo/Mo anode/filter x-ray qualities. PMMA slabs of 1, 2 and 3 mm thickness and Al foils of 0.05, 0.10 and 0.15 mm thicknesses were used to simulate the paddles, producing beams with HVL values from 0.28 up to 0.43 mmAl. In these qualities, four solid-state (ST) detectors and three ionizations chambers (IC) were calibrated in terms of Kair and N(K) and k(Q) were deduced. The results showed that all IC and two modern-type ST dosimeters have a flat energy response in the above HVL range (less than 3%), so their calibration factor at RQR-M2 quality could be safely used for clinical measurements. Two other ST dosimeters exhibit up to 20% energy response, so differences up to 15% in dose measurement may be observed if the effect of paddle on their performance is ignored. Finally, the need of additional mammographic calibration qualities to the existing IEC 61267 RQR-M series is examined and discussed.

  7. Woodstove for heated air forced into a secondary combustion chamber and method of operating same

    SciTech Connect

    Hall, R.E.; Spolek, G.A.; Wasser, J.H.; Butts, N.L.

    1991-04-16

    This patent describes a woodstove comprising a primary combustion chamber for receiving a load of wood fuel, a secondary combustion chamber in fluid flow relation with the primary chamber, fan means for forcing air from outside the woodstove into the secondary chamber, the air from outside the woodstove forced into the secondary chamber being heated prior to entering the secondary chamber, and means for controlling the fan means in response to the temperature of gases in the secondary chamber.

  8. Mechanical response to swift ion irradiation-induced nano-tracks in silica

    NASA Astrophysics Data System (ADS)

    Páramo, Ángel R.; Sordo, F.; Garoz, D.; Peña-Rodríguez, O.; Prada, A.; Olivares, J.; Crespillo, M. L.; Perlado, J. M.; Rivera, A.

    2015-06-01

    Ion irradiation on dielectric materials produces several processes, such ionization and defect formation followed by a decay governed by thermal processes such as heat diffusion and atomic rearrangement. Finally in the irradiated region the mechanical properties are altered, strain and stress fields appear, a densification takes places and other properties such as the refractive index are affected. In order to simulate the mechanical response of silica to swift ion irradiation we use a methodology based on molecular dynamics (MD) and finite element methods (FEM). We use information from MD to obtain the local densification generated by an incoming swift ion. Finally we calculate the densification in the ion track using FEM. This method provides information on the strain and stress field along the material as a function of ion irradiation fluence. For this work an experimental campaign using Br ions from 5 to 50 MeV has been done at CMAM accelerator (Madrid). We measured the refractive index and we observe that for high fluences the refractive index decreases. The effect of the strain field on the density could explain the decrease in the refractive index. We check this hypothesis using our methodology coupling MD and FEM.

  9. Subcellular Spatial Correlation of Particle Traversal and Biological Response in Clinical Ion Beams

    SciTech Connect

    Niklas, Martin; Abdollahi, Amir; Akselrod, Mark S.; Debus, Jürgen; Jäkel, Oliver; and others

    2013-12-01

    Purpose: To report on the spatial correlation of physical track information (fluorescent nuclear track detectors, FNTDs) and cellular DNA damage response by using a novel hybrid detector (Cell-Fit-HD). Methods and Materials: The FNTDs were coated with a monolayer of human non-small cell lung carcinoma (A549) cells and irradiated with carbon ions (270.55 MeV u{sup −1}, rising flank of the Bragg peak). Phosphorylated histone variant H2AX accumulating at the irradiation-induced double-strand break site was labeled (RIF). The position and direction of ion tracks in the FNTD were registered with the location of the RIF sequence as an ion track surrogate in the cell layer. Results: All RIF sequences could be related to their corresponding ion tracks, with mean deviations of 1.09 μm and −1.72 μm in position and of 2.38° in slope. The mean perpendicular between ion track and RIF sequence was 1.58 μm. The mean spacing of neighboring RIFs exhibited a regular rather than random spacing. Conclusions: Cell-Fit-HD allows for unambiguous spatial correlation studies of cell damage with respect to the intracellular ion traversal under therapeutic beam conditions.

  10. Quantised transistor response to ion channels revealed by nonstationary noise analysis

    NASA Astrophysics Data System (ADS)

    Becker-Freyseng, C.; Fromherz, P.

    2011-11-01

    We report on the quantised response of a field-effect transistor to molecular ion channels in a biomembrane. HEK293-type cells overexpressing the Shaker B potassium channel were cultured on a silicon chip. An enhanced noise of the transistor is observed when the ion channels are activated. The analysis of the fluctuations in terms of binomial statistics identifies voltage quanta of about 1 μV on the gate. They are attributed to the channel currents that affect the gate voltage according to the Green's function of the cell-chip junction.

  11. SU-E-T-156: Can Sr-90 Check Sources Replace Co-60 Measurements for Monitoring of Reference Chamber Stability?

    SciTech Connect

    McEwen, M; Niven, D; Miksys, N

    2015-06-15

    Purpose: To determine the ultimate precision of a system for monitoring reference-class ion chamber stability using a commercial Sr-90 check source. Methods: A detailed investigation of a commercial Sr-90 check source (PTW48002) was carried out using a series of Farmer-type ionization chambers. Investigations included: positioning repeatability (angular variation as chamber is rotated in source, variation in ionization current with vertical alignment); chamber settling; short and long term repeatability Results: i) Measurement precision – the ionization current was typically 10 pA, and therefore a high-precision electrometer is required to prevent electrometer noise/resolution/leakage biaising the results. ii) Chamber settling - the chamber response stabilizes after approximately 10 minutes, which is longer than reported for linac beams and is likely due to the low doserate of the source.iii) The measured response depended at the 1 % level on the orientation of the chamber with respect to the source. However, consistent positioning resulted in repeatability at the 0.05 % level. Care was also required to ensure that the chamber was consistently positioned vertically with respect to the source. The sensitivity to vertical position was found to be > 1 % per mm.iv)With a uniform procedure the long-term (> 6 month) repeatability was found to be better than 0.1 % for multiple chamber types and potentially a precision of 0.05 % is achievable. Conclusion: A Sr-90 check source is easy to use and is a viable alternative to Co-60 for monitoring reference chamber stability.

  12. Altered ion transport and responsiveness to methacholine and hyperosmolarity in air interface-cultured guinea-pig tracheal epithelium.

    PubMed

    Fedan, Jeffrey S; Wu, David X-Y; Van Scott, Michael R

    2007-01-01

    Challenge of guinea-pig tracheal epithelium with hyperosmolar solution alters ion transport and evokes the release of epithelium-derived relaxing factor (EpDRF). Cultured tracheal epithelial cells (CE) offer the potential to examine biochemical pathways related to EpDRF release, but whether the bioelectric properties and responses of fresh, adherent epithelial cells (FE) are modeled by CE has not been established. Tracheal epithelial cells grown in air-interface culture and fresh tracheal segments were mounted in Ussing chambers to determine short circuit current (I(sc)) and transepithelial resistance (R(t)) and to compare responses to transport inhibitors, methacholine and hyperosmolarity. Significant differences in basal I(sc) and R(t) between FE and CE were observed (I(sc), 41.3+/-3.5 and 8.5+/-0.8 microA/cm(2), P<0.05; R(t), 106+/-7 and 422+/-4 Omega cm(2), P<0.05; respectively); basal spontaneous potential difference values were not different (4.2+/-0.3 and 3.4+/-0.3 mV, respectively). Amiloride (mucosal, 3 x 10(-5) M), bumetanide (basolateral, 10(-5) M) and ouabain (basolateral, 10(-5) M) reduced I(sc) equally in FE and CE. In contrast, NPPB (10(-5) M) in the presence of amiloride had a differential effect, decreasing I(sc) by 11% in FE and 71% in CE (P<0.05). Iberiotoxin (basolateral, 10(-7) M) was without effect in either preparation. In FE, serosal methacholine (3x10(-5) M) elicited an NPPB-insensitive monotonic increase in I(sc), but in CE caused a large, transient, NPPB-inhibitable increase which was followed by an NPPB-resistant plateau. Addition of apical D-mannitol (0.3-267 mosM) to increase osmolarity decreased I(sc) in FE, whereas in CE d-mannitol initially increased (0.3-84.3 mosM) and then decreased (84.3-267 mosM) I(sc). Cell culture causes substantial changes in the bioelectric and pharmacological properties of respiratory epithelium. Caution should be exercised when using CE as a substitute for FE in studies of ion transport- and cell volume

  13. Ion producing mechanism

    DOEpatents

    Oppenheimer, F. F.

    1959-04-14

    This patent pertains to calutrons and more particularly to means for introducing gas at selected points in the arc chamber of a calutron source to remedy unsteadiness in the arc. The disclosed ion source has a baffle at the gas entrance in the arc chamber for directing part of the gas flow toward the anode end of the chamber. The resulting arc is much steadier, resulting in an ion beam of increased current.

  14. ION PRODUCING MECHANISM

    DOEpatents

    Oppenheimer, F.F.

    1959-04-14

    This patent pertains to calutrons and more particularly to means for introducing gas at selected points in the arc chamber of a calutron source to remedy unsteadiness in the arc, The disclosed ion source has a baffle at the gas entrance in the arc chamber for directing part of the gas fiow toward the anodc end of the chamber. The resulting arc is much steadier, resulting in an ion beam of increased current.

  15. Ion electric propulsion unit

    DOEpatents

    Light, Max E; Colestock, Patrick L

    2014-01-28

    An electron cyclotron resonance (ECR) thruster is disclosed having a plasma chamber which is electrically biased with a positive voltage. The chamber bias serves to efficiently accelerate and expel the positive ions from the chamber. Electrons follow the exiting ions, serving to provide an electrically neutral exhaust plume. In a further embodiment, a downstream shaping magnetic field serves to further accelerate and/or shape the exhaust plume.

  16. [Open-top Chamber for in situ Research on Response of Mercury Enrichment in Rice to the Rising Gaseous Elemental Mercury in the Atmosphere].

    PubMed

    Chen, Jian; Wang, Zhang-wei; Zhang, Xiao-shan; Qin, Pu-feng; Lu, Hai-jun

    2015-08-01

    In situ research was conducted on the response of mercury enrichment in rice organs to elevated gaseous elemental mercury (GEM) with open-top chambers (OTCs) fumigation experiment and soil Hg enriched experiment. The results showed that Hg concentrations in roots were generally correlated with soil Hg concentrations (R = 0.9988, P < 0.05) but insignificantly correlated with air Hg concentrations (P > 0.05), indicating that Hg in rice roots was mainly from soil. Hg concentrations in stems increased linearly (R(B) = 0.9646, R(U) = 0.9831, P < 0.05) with elevated GEM, and Hg concentrations in upper stems were usually higher than those in bottom stems in OTCs experiment. Hg concentrations in bottom stems were generally correlated with soil Hg concentrations (R = 0.9901, P < 0.05) and second-order polynomial (R = 0.9989, P < 0.05) was fitted for Hg concentrations in upper stems to soil Hg concentrations, and Hg concentrations in bottom stems were usually higher than those in upper stems in soil Hg enriched experiment, indicating the combining impact of Hg from air and soil on the accumulation of mercury in stems. Hg concentrations in foliage were significantly correlated (P < 0.05) with air Hg and linearly correlated with soil Hg (R = 0.9983, P = 0.0585), implying that mercury in foliage was mainly from air and some of Hg in root from soil was transferred to foliage through stem. Based on the function in these filed experiments, it was estimated that at least 60%-94% and 56%-77% of mercury in foliage and upper-stem of rice was from the atmosphere respectively, and yet only 8%-56% of mercury in bottom-stem was attributed to air. Therefore, mercury in rice aboveground biomass was mainly from the atmosphere, and these results will provide theoretical basis for the regional atmospheric mercury budgets and the model of mercury cycling.

  17. Response of potato to discontinuous exposures of atmospheric ethylene: results of a long-term experiment in open-top chambers and crop growth modelling

    NASA Astrophysics Data System (ADS)

    Dueck, Th. A.; Van Dijk, C. J.; Grashoff, C.; Groenwold, J.; Schapendonk, A. H. C. M.; Tonneijck, A. E. G.

    A field experiment in open-top chambers (OTCs) was performed to quantitatively assess the growth and yield response of potato to discontinuous exposures to atmospheric ethylene (200, 400 and 800 ppb, applied twice weekly and 200 and 400 ppb applied 4 times weekly, each for 3 h/event). To evaluate the effect of ethylene on potato tuber yield, a module was developed for an existing crop growth simulation model by incorporating the effects of ethylene on epinasty and photosynthesis. Explorations with the model showed that in a worst case scenario, ethylene-induced epinasty had only a marginal effect on tuber yield. Short-term exposures to ethylene under laboratory conditions inhibited photosynthesis, but it recovered within 48 h. When exposed to ethylene for longer than 12 h, irreversible damage of the photosynthesis apparatus occurred. Exposure to ethylene in the OTCs resulted in epinasty and reduced flowering. The number of flowers on potato decreased with increasing concentrations of ethylene, irrespective of the exposure frequency. Calculations showed that the number of flowers was significantly reduced at ca. 170 ppb ethylene, averaged over the hours of exposure. Ethylene concentrations up to 800 ppb, administered 4 times weekly for 3 h during the growing season, did not affect vegetative growth and yield in fumigated potatoes. Under these experimental conditions, the modified simulation model incorporating the effects of ethylene on epinasty and photosynthesis forecasts a 5% effect on tuber yield at concentrations of 1600 ppb. All results indicate that ethylene concentrations higher than 800 ppb are required to adversely affect tuber yield of potato.

  18. Morphological and biochemical responses of Oryza sativa L. (cultivar MR219) to ion beam irradiation*

    PubMed Central

    Ling, Anna Pick Kiong; Ung, Ying Chian; Hussein, Sobri; Harun, Abdul Rahim; Tanaka, Atsushi; Yoshihiro, Hase

    2013-01-01

    Objective: Heavy ion beam, which has emerged as a new mutagen in the mutation breeding of crops and ornamental plants, is expected to result in the induction of novel mutations. This study investigates the morphological and biochemical responses of Oryza sativa toward different doses of carbon ion beam irradiation. Methods: In this study, the dry seeds of O. sativa were irradiated at 0, 20, 40, 60, 80, 100, and 120 Gy, followed by in-vitro germination under controlled conditions. Morphological and biochemical studies were conducted to investigate the morphological and physiological responses of O. sativa towards ion beam irradiation. Results: The study demonstrated that low doses (10 Gy) of ion beam have a stimulating effect on the height, root length, and fresh weight of the plantlets but not on the number of leaves. Meanwhile, doses higher than 10 Gy caused reductions in all the morphological parameters studied as compared to the control samples. The highest total soluble protein content [(2.11±0.47) mg/g FW] was observed in plantlets irradiated at 20 Gy. All irradiated plantlets were found to have 0.85% to 58.32% higher specific activity of peroxidase as compared to the control samples. The present study also revealed that low doses of ion beam (10 and 20 Gy) had negligible effect on the total chlorophyll content of O. sativa plantlets while 40 Gy had a stimulating effect on the chlorophyll content. Plantlets irradiated between 40 to 120 Gy were shown to be 0.38% to 9.98% higher in total soluble nitrogen content which, however, was not significantly different from the control samples. Conclusions: Carbon ion beam irradiation administered at low to moderate doses of 10 to 40 Gy may induce O. sativa mutants with superior characteristics. PMID:24302713

  19. Fibroblast Response to Lanthanoid Metal Ion Stimulation: Potential Contribution to Fibrotic Tissue Injury

    PubMed Central

    Jenkins, William; Perone, Patricia; Walker, Kyle; Bhagavathula, Narasimharao; Aslam, Muhammad Nadeem; DaSilva, Marissa; Dame, Michael K.; Varani, James

    2011-01-01

    The purpose of this study was to compare each of the 14 naturally occurring lanthanoid metal ions for ability to stimulate pro-fibrotic responses in human dermal fibroblasts. When fibroblasts were exposed to individual lanthanoids over the concentration range of 1–100 μM, increased proliferation was observed with each of the agents as compared with control cells that were already proliferating rapidly in a growth factor-enriched culture medium. Dose-response differences were observed among the individual metal ions. Matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of metalloproteinase-1 levels were also increased in response to lanthanoid exposure but type I procollagen production was not. A dose–response relationship between induction of proliferation and increased MMP-1 was observed. Non-lanthanoid transition metal ions (aluminum, copper, cobalt, iron, magnesium, manganese, nickel, and zinc) were examined in the same assays; there was little stimulation with any of these metals. When epidermal keratinocytes were examined in place of dermal fibroblasts, there was no growth stimulation with any of the lanthanoids. Several of the lanthanoid metals inhibited keratinocyte proliferation at higher concentrations (50–100 μM). PMID:21484406

  20. Inorganic backbone ionomers: Design and dielectric response of single-ion conducting polymers

    NASA Astrophysics Data System (ADS)

    Bartels, Joshua

    analysis of the static dielectric constant and show excellent agreement with x-ray scattering and DFT calculations, each ionomer strongly favoring the formation of quadrupoles. Finally a polysiloxane ionomer was considered and was mixed with three anion and/or cation solvating additives, tetraglyme, tetraethylene glycol, and branched poly(ethylenimine). The EP model of the dielectric response gives the conducting ion concentration and the mobility of conducting ions and shows an increase in conducting ion concentration with both anion solvating and cation solvating additives. The static dielectric constant indicates an increased preference for ion pairs when anion receptors are present. Most interestingly, the additive that best decreased the glass transition temperature and increased the static dielectric constant did not result in the best dc conductivity. The best dc conductivity resulted from tetraglyme because it solvated cations without interacting with the polymer. High ion conductivities have not been observed in polymer systems that decouple charge transport from polymer motion, and therefore low Tg ionomers are the natural path forward for commercially viable ionomers. Inorganic backbone polymers impart a low Tg without bringing any strong disadvantage to ionomers. These materials are very important for developing superior ion conductors and should be pursued in future ionomer research.

  1. Large-format, high-speed, X-ray pnCCDs combined with electron and ion imaging spectrometers in a multipurpose chamber for experiments at 4th generation light sources

    NASA Astrophysics Data System (ADS)

    Strüder, Lothar; Epp, Sascha; Rolles, Daniel; Hartmann, Robert; Holl, Peter; Lutz, Gerhard; Soltau, Heike; Eckart, Rouven; Reich, Christian; Heinzinger, Klaus; Thamm, Christian; Rudenko, Artem; Krasniqi, Faton; Kühnel, Kai-Uwe; Bauer, Christian; Schröter, Claus-Dieter; Moshammer, Robert; Techert, Simone; Miessner, Danilo; Porro, Matteo; Hälker, Olaf; Meidinger, Norbert; Kimmel, Nils; Andritschke, Robert; Schopper, Florian; Weidenspointner, Georg; Ziegler, Alexander; Pietschner, Daniel; Herrmann, Sven; Pietsch, Ullrich; Walenta, Albert; Leitenberger, Wolfram; Bostedt, Christoph; Möller, Thomas; Rupp, Daniela; Adolph, Marcus; Graafsma, Heinz; Hirsemann, Helmut; Gärtner, Klaus; Richter, Rainer; Foucar, Lutz; Shoeman, Robert L.; Schlichting, Ilme; Ullrich, Joachim

    2010-03-01

    Fourth generation accelerator-based light sources, such as VUV and X-ray Free Electron Lasers (FEL), deliver ultra-brilliant (˜10 12-10 13 photons per bunch) coherent radiation in femtosecond (˜10-100 fs) pulses and, thus, require novel focal plane instrumentation in order to fully exploit their unique capabilities. As an additional challenge for detection devices, existing (FLASH, Hamburg) and future FELs (LCLS, Menlo Park; SCSS, Hyogo and the European XFEL, Hamburg) cover a broad range of photon energies from the EUV to the X-ray regime with significantly different bandwidths and pulse structures reaching up to MHz micro-bunch repetition rates. Moreover, hundreds up to trillions of fragment particles, ions, electrons or scattered photons can emerge when a single light flash impinges on matter with intensities up to 10 22 W/cm 2. In order to meet these challenges, the Max Planck Advanced Study Group (ASG) within the Center for Free Electron Laser Science (CFEL) has designed the CFEL-ASG MultiPurpose (CAMP) chamber. It is equipped with specially developed photon and charged particle detection devices dedicated to cover large solid-angles. A variety of different targets are supported, such as atomic, (aligned) molecular and cluster jets, particle injectors for bio-samples or fixed target arrangements. CAMP houses 4π solid-angle ion and electron momentum imaging spectrometers ("reaction microscope", REMI, or "velocity map imaging", VMI) in a unique combination with novel, large-area, broadband (50 eV-25 keV), high-dynamic-range, single-photon-counting and imaging X-ray detectors based on the pnCCDs. This instrumentation allows a new class of coherent diffraction experiments in which both electron and ion emission from the target may be simultaneously monitored. This permits the investigation of dynamic processes in this new regime of ultra-intense, high-energy radiation—matter interaction. After an introduction into the salient features of the CAMP chamber and

  2. Accuracy of the electron transport in mcnp5 and its suitability for ionization chamber response simulations: A comparison with the egsnrc and penelope codes

    SciTech Connect

    Koivunoro, Hanna; Siiskonen, Teemu; Kotiluoto, Petri; Auterinen, Iiro; Hippelaeinen, Eero; Savolainen, Sauli

    2012-03-15

    Purpose: In this work, accuracy of the mcnp5 code in the electron transport calculations and its suitability for ionization chamber (IC) response simulations in photon beams are studied in comparison to egsnrc and penelope codes. Methods: The electron transport is studied by comparing the depth dose distributions in a water phantom subdivided into thin layers using incident energies (0.05, 0.1, 1, and 10 MeV) for the broad parallel electron beams. The IC response simulations are studied in water phantom in three dosimetric gas materials (air, argon, and methane based tissue equivalent gas) for photon beams ({sup 60}Co source, 6 MV linear medical accelerator, and mono-energetic 2 MeV photon source). Two optional electron transport models of mcnp5 are evaluated: the ITS-based electron energy indexing (mcnp5{sub ITS}) and the new detailed electron energy-loss straggling logic (mcnp5{sub new}). The electron substep length (ESTEP parameter) dependency in mcnp5 is investigated as well. Results: For the electron beam studies, large discrepancies (>3%) are observed between the mcnp5 dose distributions and the reference codes at 1 MeV and lower energies. The discrepancy is especially notable for 0.1 and 0.05 MeV electron beams. The boundary crossing artifacts, which are well known for the mcnp5{sub ITS}, are observed for the mcnp5{sub new} only at 0.1 and 0.05 MeV beam energies. If the excessive boundary crossing is eliminated by using single scoring cells, the mcnp5{sub ITS} provides dose distributions that agree better with the reference codes than mcnp5{sub new}. The mcnp5 dose estimates for the gas cavity agree within 1% with the reference codes, if the mcnp5{sub ITS} is applied or electron substep length is set adequately for the gas in the cavity using the mcnp5{sub new}. The mcnp5{sub new} results are found highly dependent on the chosen electron substep length and might lead up to 15% underestimation of the absorbed dose. Conclusions: Since the mcnp5 electron

  3. Growth, Yield, and Nutritional Responses of Chamber-Grown Sweet Potato to Elevated Carbon Dioxide Levels Expected Across the Next 200 Years

    NASA Astrophysics Data System (ADS)

    Czeck, B. C.; Jahren, H.; Deenik, J. L.; Crow, S. E.; Schubert, B.; Stewart, M.

    2012-12-01

    Understanding the effects of increasing atmospheric carbon dioxide (CO2) concentrations on crops will be critical to assuring that sufficient food is available to the world's growing population. Previous work has shown that slightly elevated CO2 levels (CO2 = 550-700 ppm) increase the economic yield of most crops by ~33%, on average. The majority of these studies have focused on rice, wheat, and soybean; however, climate change is expected to have greatest impact on regions of the world that rely heavily on root crops, such as sweet potato (Ipomoea batatas). Sweet potato is cultivated in more than 100 developing countries; it is ranked seventh in world crop statistics and can produce more edible energy per hectare and per day than wheat, rice or cassava. In order to quantify the effect that rising CO2 levels will have on sweet potato, we grew a total of 64 sweet potato plants to maturity in large controlled growth chambers at ambient, 760, 1,140, and 1,520-ppm CO2 levels. At planting, initial measurements (of mass, length, and number of nodes) for each plant were recorded. Throughout the duration of the experiment (90 days) measurements (of stem length, and number of leaves) were recorded every 7 to 14 days. To ensure optimum growing conditions moisture content was monitored using soil tensiometers; temperature, relative humidity and CO2 concentrations were recorded every ten minutes. Half the plants were supplemented with an inorganic fertilizer and the other half with an organic fertilizer to test the effect of nutrient availability on biomass production under elevated CO2 levels. After 3 months of growth, we measured fresh and dry biomass of all above- and below-ground tissues. Results showed a substantial increase in both above- and below-ground biomass at elevated levels of CO2. For the organic treatment, a 43% increase in aboveground dry biomass at the highest CO2 concentration (1520ppm) was found; the inorganic treatment showed a 31% increase. The

  4. The effects of depth-dependent crustal viscosity variation on visco-elastic response to inflation/deflation of magma chamber

    NASA Astrophysics Data System (ADS)

    Yamasaki, Tadashi

    2016-04-01

    Development of the satellite observations (GPS and/or InSAR) has allowed us to precisely measure surface deformation. However any geodetic observation by itself does not tell us a mechanism of the deformation. All we can do the most is to compare such an observation to some quantitative predictions, only from which we can deduce a possible deformation mechanism. We therefore need to understand characteristic deformation pattern for a given source mechanism. This study particularly pays attention to magmatic activity in depth as the source, aiming to distinguish magma-induced crustal deformation by better knowing how the activity can be reflected in geodetically observable surface deformation. A parallelized 3-D finite element code, OREGANO_VE [e.g., Yamasaki and Houseman, 2015, J. Geodyn., 88, 80-89], is used to solve the linear Maxwell visco-elastic response to an applied internal inflation/deflation of magma chamber. The rectangular finite element model is composed with a visco-elastic layer overlaid by an elastic layer with thickness of H, and the visco-elastic layer extends over the rest of crust and the uppermost mantle. The visco-elastic crust has a depth-dependent viscosity (DDV) as an exponential function of depth due to temperature-dependent viscosity: hc = h0 exp[c(1 - z/L0)], where h0 is the viscosity at the bottom of the crust, c is a constant; c > 0 for DDV model and c = 0 for uniform viscosity (UNV) model, z is the depth, and L0 is a reference length-scale. The visco-elastic mantle has a spatially uniform viscosity hm. The inflation and/or deflation of sill-like magma chamber is implemented by using the split node method developed by Melosh and Raefsky [1981, Bull. Seism. Soc. Am., 71, 1391-1400]. UNV model with c = 0 employed in this study shows that the inflation-induced surface uplift would abate with time by visco-elastic relaxation. The post-inflation subsidence would erase the uplift in ~ 50 - 100 times Maxwell relaxation time of the crust

  5. A soundproof pressure chamber.

    PubMed

    Kitahara, M; Kodama, A; Ozawa, H; Inoue, S

    1994-01-01

    For neurotological research we designed a soundproof pressure chamber in which pressure can be adjusted +/- 1000 mmH2O at the rate of less than 100 mmH2O per second. Noise in the chamber can be maintained under 30-35 dB while pressure is kept at a given level.

  6. Static diffusion cloud chambers

    NASA Technical Reports Server (NTRS)

    Ayers, G.

    1981-01-01

    The chamber geometry and optical arrangement are described. The supersaturation range is given and consists of readings taken at five fixed points: 0.25%, 0.5%, 0.75%, 1.0%, and 1.25%. The detection system is described including light source, cameras, and photocell detectors. The temperature control and the calibration of the chamber are discussed.

  7. High resolution drift chambers

    SciTech Connect

    Va'vra, J.

    1985-07-01

    High precision drift chambers capable of achieving less than or equal to 50 ..mu..m resolutions are discussed. In particular, we compare so called cool and hot gases, various charge collection geometries, several timing techniques and we also discuss some systematic problems. We also present what we would consider an ''ultimate'' design of the vertex chamber. 50 refs., 36 figs., 6 tabs.

  8. The Mobile Chamber

    NASA Technical Reports Server (NTRS)

    Scharfstein, Gregory; Cox, Russell

    2012-01-01

    A document discusses a simulation chamber that represents a shift from the thermal-vacuum chamber stereotype. This innovation, currently in development, combines the capabilities of space simulation chambers, the user-friendliness of modern-day electronics, and the modularity of plug-and-play computing. The Mobile Chamber is a customized test chamber that can be deployed with great ease, and is capable of bringing payloads at temperatures down to 20 K, in high vacuum, and with the desired metrology instruments integrated to the systems control. Flexure plans to lease Mobile Chambers, making them affordable for smaller budgets and available to a larger customer base. A key feature of this design will be an Apple iPad-like user interface that allows someone with minimal training to control the environment inside the chamber, and to simulate the required extreme environments. The feedback of thermal, pressure, and other measurements is delivered in a 3D CAD model of the chamber's payload and support hardware. This GUI will provide the user with a better understanding of the payload than any existing thermal-vacuum system.

  9. Media Ion Composition Controls Regulatory and Virulence Response of Salmonella in Spaceflight

    PubMed Central

    Wilson, James W.; Ott, C. Mark; Quick, Laura; Davis, Richard; zu Bentrup, Kerstin Höner; Crabbé, Aurélie; Richter, Emily; Sarker, Shameema; Barrila, Jennifer; Porwollik, Steffen; Cheng, Pui; McClelland, Michael; Tsaprailis, George; Radabaugh, Timothy; Hunt, Andrea; Shah, Miti; Nelman-Gonzalez, Mayra; Hing, Steve; Parra, Macarena; Dumars, Paula; Norwood, Kelly; Bober, Ramona; Devich, Jennifer; Ruggles, Ashleigh; CdeBaca, Autumn; Narayan, Satro; Benjamin, Joseph; Goulart, Carla; Rupert, Mark; Catella, Luke; Schurr, Michael J.; Buchanan, Kent; Morici, Lisa; McCracken, James; Porter, Marc D.; Pierson, Duane L.; Smith, Scott M.; Mergeay, Max; Leys, Natalie; Stefanyshyn-Piper, Heidemarie M.; Gorie, Dominic; Nickerson, Cheryl A.

    2008-01-01

    The spaceflight environment is relevant to conditions encountered by pathogens during the course of infection and induces novel changes in microbial pathogenesis not observed using conventional methods. It is unclear how microbial cells sense spaceflight-associated changes to their growth environment and orchestrate corresponding changes in molecular and physiological phenotypes relevant to the infection process. Here we report that spaceflight-induced increases in Salmonella virulence are regulated by media ion composition, and that phosphate ion is sufficient to alter related pathogenesis responses in a spaceflight analogue model. Using whole genome microarray and proteomic analyses from two independent Space Shuttle missions, we identified evolutionarily conserved molecular pathways in Salmonella that respond to spaceflight under all media compositions tested. Identification of conserved regulatory paradigms opens new avenues to control microbial responses during the infection process and holds promise to provide an improved understanding of human health and disease on Earth. PMID:19079590

  10. High accuracy position response calibration method for a micro-channel plate ion detector

    NASA Astrophysics Data System (ADS)

    Hong, R.; Leredde, A.; Bagdasarova, Y.; Fléchard, X.; García, A.; Müller, P.; Knecht, A.; Liénard, E.; Kossin, M.; Sternberg, M. G.; Swanson, H. E.; Zumwalt, D. W.

    2016-11-01

    We have developed a position response calibration method for a micro-channel plate (MCP) detector with a delay-line anode position readout scheme. Using an in situ calibration mask, an accuracy of 8 μm and a resolution of 85 μm (FWHM) have been achieved for MeV-scale α particles and ions with energies of ∼10 keV. At this level of accuracy, the difference between the MCP position responses to high-energy α particles and low-energy ions is significant. The improved performance of the MCP detector can find applications in many fields of AMO and nuclear physics. In our case, it helps reducing systematic uncertainties in a high-precision nuclear β-decay experiment.

  11. Note: Small anaerobic chamber for optical spectroscopy

    SciTech Connect

    Chauvet, Adrien A. P. Chergui, Majed; Agarwal, Rachna; Cramer, William A.

    2015-10-15

    The study of oxygen-sensitive biological samples requires an effective control of the atmosphere in which they are housed. In this aim however, no commercial anaerobic chamber is adequate to solely enclose the sample and small enough to fit in a compact spectroscopic system with which analysis can be performed. Furthermore, spectroscopic analysis requires the probe beam to pass through the whole chamber, introducing a requirement for adequate windows. In response to these challenges, we present a 1 l anaerobic chamber that is suitable for broad-band spectroscopic analysis. This chamber has the advantage of (1) providing access, via a septum, to the sample and (2) allows the sample position to be adjusted while keeping the chamber fixed and hermetic during the experiment.

  12. Aging in large CDF tracking chambers

    SciTech Connect

    M. Binkley et al.

    2001-03-19

    The experience of the Collider Detector at Fermilab (CDF) with aging in the large axial drift chamber responsible for tracking in the central region is presented. Premature aging in the Run 1 chamber was observed after only 0.02 C/cm. After cleaning much of the gas system and making modifications to reduce aerosols from the alcohol bubbler, the observed aging rate fell dramatically in test chambers. Considerable effort has been made to better understand the factors that affect aging since the replacement chamber for Run 2 will accumulate about 1.0 C/cm. Current test chambers using the full CDF gas system show aging rates of less than 5%/C/cm.

  13. Note: Small anaerobic chamber for optical spectroscopy.

    PubMed

    Chauvet, Adrien A P; Agarwal, Rachna; Cramer, William A; Chergui, Majed

    2015-10-01

    The study of oxygen-sensitive biological samples requires an effective control of the atmosphere in which they are housed. In this aim however, no commercial anaerobic chamber is adequate to solely enclose the sample and small enough to fit in a compact spectroscopic system with which analysis can be performed. Furthermore, spectroscopic analysis requires the probe beam to pass through the whole chamber, introducing a requirement for adequate windows. In response to these challenges, we present a 1 l anaerobic chamber that is suitable for broad-band spectroscopic analysis. This chamber has the advantage of (1) providing access, via a septum, to the sample and (2) allows the sample position to be adjusted while keeping the chamber fixed and hermetic during the experiment.

  14. The response of the pyrochlore structure-type to ion-beam irradiation

    NASA Astrophysics Data System (ADS)

    Lian, Jie

    Pyrochlore with the general formula of A3+2B4+2O7 (Fd3m; Z = 8) has been proposed as the candidate waste form for the immobilization of actinides, particularly plutonium from dismantled nuclear weapons. Because actinides decay by alpha-decay events, radiation effects on the waste form are a concern. The effects of radiation on different pyrochlore compositions, A2B2O7 (A = La ˜ Lu, and Y; B = Ti, Sn, and Zr), have been investigated by 50 KeV He+, 600 KeV Ar+, 1.0 MeV Kr+, and 1.5 MeV Xe+ ion irradiations. Titanate pyrochlores are generally sensitive to ion beam damage and can be amorphized at a low damage level (˜0.2 dpa). The critical amorphization temperature, Tc, increases from ˜480 to ˜1120 K with increasing A-site cation size. A dramatically increasing radiation "resistance" to ion beam induced-amorphization has been observed with increasing Zr-content in the Gd2Ti2-xZrxO7 system. The pure end-member, Gd2Zr2O7, cannot be amorphized, even at doses as high as ˜100 dpa. Although zirconate pyrochlores are generally considered to be radiation "resistant", ion beam-induced amorphization occurs for La2Zr2O7 at a dose of ˜5.5 dpa at room temperature. Stannate pyrochlores A2Sn 2O7 (A = La, Nd, Gd) are readily amorphized by ion beam damage at a relatively low dose (˜1 dpa) at room temperature; while no evidence of amorphization has been observed in A2Sn2O7 (A = Er, Y, Lu) irradiated with 1 MeV Kr+ ions at a dose of ˜6 dpa at 25 K. The factors that influence the response of different pyrochlore compositions to ion irradiation-induced amorphization are discussed in terms of cation radius ratio, defect formation energies, and the tendency of the pyrochlore structure-type to undergo an order-disorder transition to the defect-fluorite structure. The "resistance" of the pyrochlore structure to ion beam-induced amorphization is not only affected by the relative sizes of the A- and B-site cations, but also the cation electronic configurations. Pyrochlore compositions

  15. Effects of separator breakdown on abuse response of 18650 Li-ion cells

    NASA Astrophysics Data System (ADS)

    Roth, E. P.; Doughty, D. H.; Pile, D. L.

    The thermal abuse tolerance of Li-ion cells depends not only on the stability of the active materials in the anode and cathode but also on the stability of the separator which prevents direct interaction between these electrodes. Separator response has been measured as a function of temperature and high voltage both for isolated materials and in full 18650 cells. Separators with different compositions and properties were measured to determine the effect of separator melt integrity on cell response under abusive conditions. These studies were performed as part of the U.S. Department of Energy (DOE) Advanced Technology Development (ATD) Program.

  16. [Study of the response characteristics of PVC membrane ion-associate type electrodes for organic base cations].

    PubMed

    Kang, X J; Wang, C Y

    1990-01-01

    A new type of ISEs which only uses alkaloid precipitants in place of ion pairs as active materials in polyvinyl chloride was recommended. The characteristics of the electrodes sensing over ten kinds of organic bases have been studied in comparison with those based on ion pairs. It can be concluded that the response characteristics of ion-associate type ISEs depend on the strength of the association between ion-exchange site and principal ions. Visual turbidimetry was used to select active materials for ISEs in advance. Among six alkaloid precipitants (silicotungstic acid, tetraphenyl borate, dipicrylamine, picric acid, picrolonic acid and Reineckate), silicotungstic acid is the most active material for ion-associate type organic base cation ISEs. With it, the sensor has wider Nernst linearity and lower detection limit than some ion pair based ones in literature.

  17. Radiation damage to tetramethylsilane and tetramethylgermanium ionization chambers

    SciTech Connect

    Hoshi, Y.; Higuchi, M.; Oyama, K. . Dept. of Applied Physics)

    1994-08-01

    Two detector media suitable for a warm liquid, ionization chamber filled with tetramethylsilane (TMS) and tetramethylgermanium (TMG) were exposed to [gamma] radiation form a [sup 60]Co source up to dose 579 Gray and 902 Gray, respectively. The electron lifetimes and the free ion yields were measured as a function of accumulated radiation dose. A similar behavior of the electron lifetimes and the free ion yields with increasing radiation does was observed between the TMS and TMG ionization chambers.

  18. Continuously perfused, non-cross-contaminating microfluidic chamber array for studying cellular responses to orthogonal combinations of matrix and soluble signals.

    PubMed

    Park, Edward S; Brown, Ashley C; DiFeo, Michael A; Barker, Thomas H; Lu, Hang

    2010-03-07

    We present a microfluidic cell culture array with unique versatility and parallelization for experimental trials requiring perfusion cultures. Specifically, we realize a rectangular chamber array in a PDMS device with three attributes: (i) continuous perfusion; (ii) flow paths that forbid cross-chamber contamination; and (iii) chamber shielding from direct perfusion to minimize shear-induced cell behaviour. These attributes are made possible by a bridge-and-underpass architecture, where flow streams travel vertically to pass over (or under) channels and on-chip valves. The array is also designed for considerable versatility, providing subarray, row, column, or single chamber addressing. It allows for incubation with adsorbed molecules, perfusion of differing media, seeding or extraction of cells, and assay staining. We use the device to characterize different phenotypes of alveolar epithelial type II (ATII) cells, particularly the extent of epithelial-to-mesenchymal transition (EMT), a highly suspected pathway in tissue regeneration and fibrosis. Cells are cultured on combinations of matrix proteins (fibronectin or laminin by row) and soluble signals (with or without transforming growth factor-beta1 by column) with two repeats per chip. Fluorescent assays are performed in the array to assess viability, cytoskeletal organization, and cell-cell junction formation. Assay and morphological data are used to tease-out effects of cues driving each phenotype, confirming this as an effective and versatile combinatorial screening platform.

  19. Effects of CO2 enrichment and drought pretreatment on metabolite responses to water stress and subsequent rehydration using potato tubers from plants grown in sunlit SPAR chambers

    USDA-ARS?s Scientific Manuscript database

    Experiments were performed using naturally sunlit Soil–Plant–Atmosphere-Research chambers that provided ambient or elevated CO2. Potato plants were grown in pots that were water sufficient (W), water insufficient for 12 to 18 days during both vegetative and tuber development stages (VR), or water i...

  20. 45. AUXILIARY CHAMBER BETWEEN CHAMBER AND CONCRETE ENCLOSURE (LOCATION DDD), ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    45. AUXILIARY CHAMBER BETWEEN CHAMBER AND CONCRETE ENCLOSURE (LOCATION DDD), VIEW LOOKING EAST. LEAD ENCLOSED PIPING IS DRAIN FROM BOILER CHAMBER No. 1 - Shippingport Atomic Power Station, On Ohio River, 25 miles Northwest of Pittsburgh, Shippingport, Beaver County, PA

  1. Ion transport mechanisms responsible for K+ secretion and the transepithelial voltage across marginal cells of stria vascularis in vitro.

    PubMed

    Wangemann, P; Liu, J; Marcus, D C

    1995-04-01

    It has long been accepted that marginal cells of stria vascularis are involved in the generation of the endocochlear potential and the secretion of K+. The present study was designed to provide evidence for this hypothesis and for a cell model proposed to explain K+ secretion and the generation of the endocochlear potential. Stria vascularis from the cochlea of the gerbil was isolated and mounted into a micro-Ussing chamber such that the apical and basolateral membrane of marginal cells could be perfused independently. In this preparation, the transepithelial voltage (Vt) and resistance (Rt) were measured across marginal cells and the resulting equivalent short circuit current (Isc) was calculated (Isc = Vt/Rt). Further, K+ secretion (JK+,probe) was measured with a K(+)-selective vibrating probe in the vicinity of the apical membrane. In the absence of extrinsic chemical driving forces, when both sides of the marginal cell epithelium were bathed with a perilymph-like solution, Vt was 8 mV (apical side positive), Rt was 10 ohm-cm2 and Isc was 850 microA/cm2 (N = 27). JK+,probe was outwardly directed from the apical membrane and reversibly inhibited by basolateral bumetanide, a blocker of the Na+/Cl-/K+ cotransporter. On the basolateral but not apical side, oubain and bumetanide each caused a decline of Vt and an increase of Rt suggesting the presence of the Na,K-ATPase and the Na+/Cl-/K+ cotransporter in the basolateral membrane. The responses to [Cl-] steps demonstrated a significant Cl- conductance in the basolateral membrane and a small Cl- conductance in the paracellular pathway or the apical membrane. The responses to [Na+] steps demonstrated no significant Na+ conductance in the basolateral membrane and a small Na+ or nonselective cation conductance in the apical membrane or paracellular pathway. The responses to [K+] steps demonstrated a large K+ conductance in the apical membrane. Apical application of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS

  2. Detection of large ions in time-of-flight mass spectrometry: effects of ion mass and acceleration voltage on microchannel plate detector response

    PubMed Central

    Liu, Ranran; Li, Qiyao; Smith, Lloyd M.

    2014-01-01

    In time-of-flight mass spectrometry (TOF-MS), ion detection is typically accomplished by the generation and amplification of secondary electrons produced by ions colliding with a microchannel plate (MCP) detector. Here, the response of an MCP detector as a function of ion mass and acceleration voltage is characterized, for peptide/protein ions ranging from 1 kDa to 290 kDa in mass, and for acceleration voltages from 5 kV to 25 kV. A non-destructive inductive charge detector (ICD) employed in parallel with MCP detection provides a reliable reference signal to allow accurate calibration of the MCP response. MCP detection efficiencies were very close to unity for smaller ions at high acceleration voltages (e.g. angiotensin, 1,046.5 Da, at 25 kV acceleration voltage), but decreased to ~11% for the largest ions examined (Immunoglobulin G (IgG) dimer, 290 kDa) even at the highest acceleration voltage employed (25 kV). The secondary electron yield γ (average number of electrons produced per ion collision) is found to be proportional to mv3.1 (m: ion mass, v: ion velocity) over the entire mass range examined, and inversely proportional to the square root of m in TOF-MS analysis. The results indicate that although MCP detectors indeed offer superlative performance in the detection of smaller peptide/protein species, their performance does fall off substantially for larger proteins, particularly under conditions of low acceleration voltage. PMID:24789774

  3. Commissioning of a well type chamber for HDR and LDR brachytherapy applications: a review of methodology and outcomes.

    PubMed

    Mukwada, Godfrey; Neveri, Gabor; Alkhatib, Zaid; Waterhouse, David K; Ebert, Martin

    2016-03-01

    For safe and accurate dose delivery in brachytherapy, associated equipment is subject to commissioning and ongoing quality assurance (QA). Many centres depend on the use of a well-type chamber ('well chamber') for performing brachytherapy dosimetry. Documentation of well chamber commissioning is scarce despite the important role the chamber plays in the whole brachytherapy QA process. An extensive and structured commissioning of the HDR 1000 plus well chamber (Standard Imaging Inc, Middleton WI) for HDR and LDR dosimetry was undertaken at Sir Charles Gairdner Hospital. The methodology and outcomes of this commissioning is documented and presented as a guideline to others involved in brachytherapy. The commissioning tests described include mechanical integrity, leakage current, directional dependence, response, length of uniform response, the influence of insert holders, ion collection efficiency, polarity effect, accuracy of measured air kerma strength (S(K)) or reference air kerma rate (K(R)) and baseline setting (for ongoing constancy checks). For the HDR 1000 plus well chamber, some of the insert holders modify the response curve. The measured sweet length was 2.5 cm which is within 0.5% of that specified by the manufacturer. Correction for polarity was negligible (0.9999) and ion recombination was small (0.9994). Directional dependence was small (less than 0.2%) and leakage current was negligible. The measured K(R) for (192)Ir agreed within 0.11% compared with a second well chamber of similar model and was within 0.5% of that determined via a free-in-air measurement method. Routine constancy checks over a year agreed with the baseline within 0.4%.

  4. Physical response of gold nanoparticles to single self-ion bombardment

    DOE PAGES

    Bufford, Daniel C.; Hattar, Khalid

    2014-09-23

    The reliability of nanomaterials depends on maintaining their specific sizes and structures. However, the stability of many nanomaterials in radiation environments remains uncertain due to the lack of a fully developed fundamental understanding of the radiation response on the nanoscale. To provide an insight into the dynamic aspects of single ion effects in nanomaterials, gold nanoparticles (NPs) with nominal diameters of 5, 20, and 60 nm were subjected to self-ion irradiation at energies of 46 keV, 2.8 MeV, and 10 MeV in situ inside of a transmission electron microscope. Ion interactions created a variety of far-from-equilibrium structures including small (~1more » nm) sputtered nanoclusters from the parent NPs of all sizes. Single ions created surface bumps and elongated nanofilaments in the 60 nm NPs. As a result, similar shape changes were observed in the 20 nm nanoparticles, while the 5 nm nanoparticles were transiently melted or explosively broken apart.« less

  5. Physical response of gold nanoparticles to single self-ion bombardment

    SciTech Connect

    Bufford, Daniel C.; Hattar, Khalid

    2014-09-23

    The reliability of nanomaterials depends on maintaining their specific sizes and structures. However, the stability of many nanomaterials in radiation environments remains uncertain due to the lack of a fully developed fundamental understanding of the radiation response on the nanoscale. To provide an insight into the dynamic aspects of single ion effects in nanomaterials, gold nanoparticles (NPs) with nominal diameters of 5, 20, and 60 nm were subjected to self-ion irradiation at energies of 46 keV, 2.8 MeV, and 10 MeV in situ inside of a transmission electron microscope. Ion interactions created a variety of far-from-equilibrium structures including small (~1 nm) sputtered nanoclusters from the parent NPs of all sizes. Single ions created surface bumps and elongated nanofilaments in the 60 nm NPs. As a result, similar shape changes were observed in the 20 nm nanoparticles, while the 5 nm nanoparticles were transiently melted or explosively broken apart.

  6. Altered ion-responsive gene expression in Mmp20 null mice.

    PubMed

    Tye, C E; Sharma, R; Smith, C E; Bartlett, J D

    2010-12-01

    During enamel maturation, hydroxyapatite crystallites expand in volume, releasing protons that acidify the developing enamel. This acidity is neutralized by the buffering activity of carbonic anhydrases and ion transporters. Less hydroxyapatite forms in matrix metalloproteinase-20 null (Mmp20(-/-)) mouse incisors, because enamel thickness is reduced by approximately 50%. We therefore asked if ion regulation was altered in Mmp20(-/-) mouse enamel. Staining of wild-type and Mmp20(-/-) incisors with pH indicators demonstrated that wild-type mice had pronounced changes in enamel pH as development progressed. These pH changes were greatly attenuated in Mmp20(-/-) mice. Expression of 4 ion-regulatory genes (Atp2b4, Slc4a2, Car6, Cftr) was significantly decreased in enamel organs from Mmp20(-/-) mice. Notably, expression of secreted carbonic anhydrase (Car6) was reduced to almost undetectable levels in the null enamel organ. In contrast, Odam and Klk4 expression was unaffected. We concluded that a feedback mechanism regulates ion-responsive gene expression during enamel development.

  7. The Light Response of the XENON100 Time Projection Chamber and the Measurements of the Optical Parameters with the Xenon Scintillation Light

    NASA Astrophysics Data System (ADS)

    Choi, Bin

    The XENON program is a phased project using liquid xenon as a sensitive detector medium in search for weakly interacting massive particles (WIMPs). These particles are the leading candidates to explain the non-baryonic, cold dark matter in our Universe. XENON100, the successor experiment of XENON10, has increased the target liquid xenon mass to 61 kg with a 100 times reduction in background rate enabling a large increase in sensitivity to WIMP-nucleon interaction cross-section. To-date, the most stringent limit on this cross-section over a wide range of WIMP masses have been obtained with XENON100. XENON100 is a detector responding to the scintillation of xenon and the work of this thesis will mainly focus on the light response of the detector. Chapter 1 describes the evidences for dark matter and some of the detection methods, roughly divided by the indirect and the direct detection. In the section 1.2.2 for direct detection, a treatment of interaction rate of WIMPs is introduced. Chapter 2 is a description of the XENON100 detector, some of the main characteristics of liquid xenon, followed by the detector design. In Chapter 3, the light response of the XENON100 time projection chamber (TPC) is explained, including the Monte Carlo simulation work that was carried out prior to the main data taking. The Monte Carlo provided the basic idea of understanding the detector in the early stage of design and calibration, but the actual corrections of the light signals were determined later with the real data. Several optical parameters are critical in explaining the light response, such as the quantum efficiency (QE) of the photomultipliers (PMTs) used in the detector and the reflectivity of the teflon (Polytetrafluoroethylene, PTFE) material that surrounds the liquid xenon target volume and defines the TPC. Since the few existing measurements of reflectivity of PTFE in liquid xenon were performed in different conditions and thus could not be applied, the XENON

  8. Ion beam generating apparatus

    DOEpatents

    Brown, Ian G.; Galvin, James

    1987-01-01

    An ion generating apparatus utilizing a vacuum chamber, a cathode and an anode in the chamber. A source of electrical power produces an arc or discharge between the cathode and anode. The arc is sufficient to vaporize a portion of the cathode to form a plasma. The plasma is directed to an extractor which separates the electrons from the plasma, and accelerates the ions to produce an ion beam.

  9. The Japanese Radon and Thoron Reference Chambers

    SciTech Connect

    Tokonami, Shinji; Ishikawa, Tetsuo; Sorimachi, Atsuyuki; Takahashi, Hiroyuki; Miyahara, Nobuyuki

    2008-08-07

    Passive detectors used for large-scale and long-term surveys are generally calibrated in a well-controlled environment such as a radon chamber. It has been also pointed out that some of them are sensitive to thoron. Thus it is necessary to check the thoron contribution to the detector response with the proposed or similar test before practical use. The NIRS accommodates radon/aerosol and thoron chambers for quality assurance and quality control of radon measurements. Thus both chambers work so well that they can supply us with the calibration technique and consequently, a good level of knowledge of the radon and thoron issue.

  10. Biphasic responses of human vascular smooth muscle cells to magnesium ion

    PubMed Central

    Ma, Jun; Zhao, Nan; Zhu, Donghui

    2016-01-01

    Magnesium-based alloys are promising in biodegradable cardiovascular stent applications. The degradation products of magnesium stents may have significant impacts on the surrounding vascular cells. However, knowledge on the interactions between magnesium ion and vascular cells at the molecular and cellular levels is still largely missing. Vascular smooth muscle cell (SMC) plays an important role in the pathogenesis of restenosis and wound healing after stent implantation. This study evaluated the short-term effects of extracellular magnesium ion (Mg2+) on the cellular behaviors of SMCs. Cellular responses to Mg2+ were biphasic and in a concentration-dependent manner. Low concentrations (10 mM) of Mg2+ increased cell viability, cell proliferation rate, cell adhesion, cell spreading, cell migration rate, and actin expression. In contrast, higher concentrations (40–60 mM) of Mg2+ had deleterious effects on cells. Gene expression analysis revealed that Mg2+ altered the expressions of genes mostly related to cell adhesion, cell injury, angiogenesis, inflammation, coagulation, and cell growth. Finding from this study provides some valuable information on SMC responses toward magnesium ions at the cellular and molecular levels, and guidance for future controlled release of magnesium from the stent material. PMID:26402437

  11. Biphasic responses of human vascular smooth muscle cells to magnesium ion.

    PubMed

    Ma, Jun; Zhao, Nan; Zhu, Donghui

    2016-02-01

    Magnesium-based alloys are promising in biodegradable cardiovascular stent applications. The degradation products of magnesium stents may have significant impacts on the surrounding vascular cells. However, knowledge on the interactions between magnesium ion and vascular cells at the molecular and cellular levels is still largely missing. Vascular smooth muscle cell (SMC) plays an important role in the pathogenesis of restenosis and wound healing after stent implantation. This study evaluated the short-term effects of extracellular magnesium ion (Mg(2+)) on the cellular behaviors of SMCs. Cellular responses to Mg(2+) were biphasic and in a concentration-dependent manner. Low concentrations (10 mM) of Mg(2+) increased cell viability, cell proliferation rate, cell adhesion, cell spreading, cell migration rate, and actin expression. In contrast, higher concentrations (40-60 mM) of Mg(2+) had deleterious effects on cells. Gene expression analysis revealed that Mg(2+) altered the expressions of genes mostly related to cell adhesion, cell injury, angiogenesis, inflammation, coagulation, and cell growth. Finding from this study provides some valuable information on SMC responses toward magnesium ions at the cellular and molecular levels, and guidance for future controlled release of magnesium from the stent material. © 2015 Wiley Periodicals, Inc.

  12. CHARACTERIZATION OF PIPES USING ELECTRET ION CHAMBERS

    SciTech Connect

    M.A. Ebadian, Ph.D.

    1999-01-01

    The decontamination and characterization of large-bore pipe is difficult because of the various geometries and diameters of pipe and its different material types. A robust decontamination system must be capable of adapting to different pipe diameters (p-eject scope is 6 inches to 24 inches), cleaning surfaces with various surface conditions and material types (i.e., painted, rusted, carbon steel, or stainless steel) and be cost-effective to operate and maintain. The characterization system must be capable of handling the different pipe parameters and detecting contamination on the inside and outside surfaces. It must also operate in a cost-effective manner. Current technology options do not provide a robust system to meet these objectives. The purpose of this project is to verify the need for this technology through determining quantities of pipe available for decontamination (completed FY97), perform a technology screening process to select technologies for decontamination (completed FY97) and characterization (completed FY98), perform treatability studies to collect required performance data (completed FY97), and design and fabricate a prototype system to decontaminate and characterize the internal and external surfaces of large-bore pipe. A field-mobile system capable of performing decontamination and characterization operations will be the main deliverable for this project. A summary of activities completed during FY97 is provided to understand the project development and implementation process.

  13. The response of tissue-equivalent proportional counters to heavy ions

    NASA Technical Reports Server (NTRS)

    Nikjoo, Hooshang; Khvostunov, Igor K.; Cucinotta, Francis A.

    2002-01-01

    The paper presents a theoretical model for the response of a tissue-equivalent proportional counter (TEPC) irradiated with charged particles. Heavy ions and iron ions in particular constitute a significant part of radiation in space. TEPCs are used for all space shuttle and International Space Station (ISS) missions to estimate the dose and radiation quality (in terms of lineal energy) inside spacecraft. The response of the tissue-equivalent proportional counters shows distortions at the wall/cavity interface. In this paper, we present microdosimetric investigation using Monte Carlo track structure calculations to simulate the response of a TEPC to charged particles of various LET (1 MeV protons, 2.4 MeV alpha particles, 46 MeV/nucleon 20Ne, 55 MeV/nucleon 20Ne, 45 MeV/nucleon 40Ar, and 1.05 GeV/nucleon 56Fe). Data are presented for energy lost and energy absorbed in the counter cavity and wall. The model calculations are in good agreement with the results of Rademacher et al. (Radiat. Res. 149, 387-389, 1998), including the study of the interface between the wall and the sensitive region of the counter. It is shown that the anomalous response observed at large event sizes in the experiment is due to an enhanced entry of secondary electrons from the wall into the gas cavity.

  14. Acoustic-Levitation Chamber

    NASA Technical Reports Server (NTRS)

    Barmatz, M. B.; Granett, D.; Lee, M. C.

    1984-01-01

    Uncontaminated environments for highly-pure material processing provided within completely sealed levitation chamber that suspends particles by acoustic excitation. Technique ideally suited for material processing in low gravity environment of space.

  15. The Mars Chamber

    NASA Image and Video Library

    The Mars chamber is a box about the size of a refrigerator that re-creates the temperatures, pressures, and atmosphere of the Martian surface, essentially creating a Mars environment on Earth! Scie...

  16. Deciphering the acute cellular phosphoproteome response to irradiation with X-rays, protons and carbon ions.

    PubMed

    Winter, Martin; Dokic, Ivana; Schlegel, Julian; Warnken, Uwe; Debus, Jürgen; Abdollahi, Amir; Schnölzer, Martina

    2017-03-16

    Radiotherapy is a cornerstone of cancer therapy. The recently established particle therapy with raster-scanning protons and carbon ions landmarks a new era in the field of high-precision cancer medicine. However, molecular mechanisms governing radiation induced intracellular signaling remain elusive. Here, we present the first comprehensive proteomic and phosphoproteomic study applying stable isotope labeling by amino acids in cell culture (SILAC) in combination with high-resolution mass spectrometry to decipher cellular response to irradiation with X-rays, protons and carbon ions. At protein expression level limited alterations were observed 2h post irradiation of human lung adenocarcinoma cells. In contrast, 181 phosphorylation sites were found to be differentially regulated out of which 151 sites were not hitherto attributed to radiation response as revealed by crosscheck with the PhosphoSitePlus database. Radiation-induced phosphorylation of the p(S/T)Q motif was the prevailing regulation pattern affecting proteins involved in DNA damage response signaling. Since radiation doses were selected to produce same level of cell kill and DNA double-strand breakage for each radiation quality, DNA damage responsive phosphorylation sites were regulated to same extent. However, differential phosphorylation between radiation qualities was observed for 55 phosphorylation sites indicating the existence of distinct signaling circuitries induced by X-ray versus particle (proton/carbon) irradiation beyond the canonical DNA damage response. This unexpected finding was confirmed in targeted spike-in experiments using synthetic isotope labeled phosphopeptides. Herewith, we successfully validated uniform DNA damage response signaling coexisting with altered signaling involved in apoptosis and metabolic processes induced by X-ray and particle based treatments. In summary, the comprehensive insight into the radiation-induced phosphoproteome landscape is instructive for the design of

  17. Abrupt onset of tongue deformation and phase space response of ions in magnetically-confined plasmas

    NASA Astrophysics Data System (ADS)

    Ida, K.; Kobayashi, T.; Itoh, K.; Yoshinuma, M.; Tokuzawa, T.; Akiyama, T.; Moon, C.; Tsuchiya, H.; Inagaki, S.; Itoh, S.-I.

    2016-10-01

    An abrupt onset of the new tongue-shaped deformation of magnetic surface in magnetized plasmas, which was conjectured in since the 1960s but has not been observed, is experimentally identified just before an abrupt onset of a large-scale collapse event. Two novel properties of the event are identified. First, the transition of symmetry of perturbation (rather than a growth of linearly unstable MHD modes) was found to be a key for the onset of abrupt collapse, i.e., the transition of symmetry gives a new route to the collapse from stable state. Second, as a phase-space response of ions, the distortion from Maxwell-Boltzmann distribution of epithermal ions was observed for the first time.

  18. Abrupt onset of tongue deformation and phase space response of ions in magnetically-confined plasmas

    PubMed Central

    Ida, K.; Kobayashi, T.; Itoh, K.; Yoshinuma, M.; Tokuzawa, T.; Akiyama, T.; Moon, C.; Tsuchiya, H.; Inagaki, S.; Itoh, S.-I.

    2016-01-01

    An abrupt onset of the new tongue-shaped deformation of magnetic surface in magnetized plasmas, which was conjectured in since the 1960s but has not been observed, is experimentally identified just before an abrupt onset of a large-scale collapse event. Two novel properties of the event are identified. First, the transition of symmetry of perturbation (rather than a growth of linearly unstable MHD modes) was found to be a key for the onset of abrupt collapse, i.e., the transition of symmetry gives a new route to the collapse from stable state. Second, as a phase-space response of ions, the distortion from Maxwell-Boltzmann distribution of epithermal ions was observed for the first time. PMID:27796370

  19. Sleeve reaction chamber system

    SciTech Connect

    Northrup, M Allen; Beeman, Barton V; Benett, William J; Hadley, Dean R; Landre, Phoebe; Lehew, Stacy L; Krulevitch, Peter A

    2009-08-25

    A chemical reaction chamber system that combines devices such as doped polysilicon for heating, bulk silicon for convective cooling, and thermoelectric (TE) coolers to augment the heating and cooling rates of the reaction chamber or chambers. In addition the system includes non-silicon-based reaction chambers such as any high thermal conductivity material used in combination with a thermoelectric cooling mechanism (i.e., Peltier device). The heat contained in the thermally conductive part of the system can be used/reused to heat the device, thereby conserving energy and expediting the heating/cooling rates. The system combines a micromachined silicon reaction chamber, for example, with an additional module/device for augmented heating/cooling using the Peltier effect. This additional module is particularly useful in extreme environments (very hot or extremely cold) where augmented heating/cooling would be useful to speed up the thermal cycling rates. The chemical reaction chamber system has various applications for synthesis or processing of organic, inorganic, or biochemical reactions, including the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction.

  20. Response of the rhizosphere prokaryotic community of barley (Hordeum vulgare L.) to elevated atmospheric CO2 concentration in open-top chambers.

    PubMed

    Szoboszlay, Márton; Näther, Astrid; Mitterbauer, Esther; Bender, Jürgen; Weigel, Hans-Joachim; Tebbe, Christoph C

    2017-08-01

    The effect of elevated atmospheric CO2 concentration [CO2 ] on the diversity and composition of the prokaryotic community inhabiting the rhizosphere of winter barley (Hordeum vulgare L.) was investigated in a field experiment, using open-top chambers. Rhizosphere samples were collected at anthesis (flowering stage) from six chambers with ambient [CO2 ] (approximately 400 ppm) and six chambers with elevated [CO2 ] (700 ppm). The V4 region of the 16S rRNA gene was PCR-amplified from the extracted DNA and sequenced on an Illumina MiSeq instrument. Above-ground plant biomass was not affected by elevated [CO2 ] at anthesis, but plants exposed to elevated [CO2 ] had significantly higher grain yield. The composition of the rhizosphere prokaryotic communities was very similar under ambient and elevated [CO2 ]. The dominant taxa were Bacteroidetes, Actinobacteria, Alpha-, Gamma-, and Betaproteobacteria. Elevated [CO2 ] resulted in lower prokaryotic diversity in the rhizosphere, but did not cause a significant difference in community structure. © 2017 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.

  1. Discharge Chamber Primary Electron Modeling Activities in Three-Dimensions

    NASA Technical Reports Server (NTRS)

    Steuber, Thomas J.

    2004-01-01

    Designing discharge chambers for ion thrusters involves many geometric configuration decisions. Various decisions will impact discharge chamber performance with respect to propellant utilization efficiency, ion production costs, and grid lifetime. These hardware design decisions can benefit from the assistance of computational modeling. Computational modeling for discharge chambers has been limited to two-dimensional codes that leveraged symmetry for interpretation into three-dimensional analysis. This paper presents model development activities towards a three-dimensional discharge chamber simulation to aid discharge chamber design decisions. Specifically, of the many geometric configuration decisions toward attainment of a worthy discharge chamber, this paper focuses on addressing magnetic circuit considerations with a three-dimensional discharge chamber simulation as a tool. With this tool, candidate discharge chamber magnetic circuit designs can be analyzed computationally to gain insight into factors that may influence discharge chamber performance such as: primary electron loss width in magnetic cusps, cathode tip position with respect to the low magnetic field volume, definition of a low magnetic field region, and maintenance of a low magnetic field region across the grid span. Corroborating experimental data will be obtained from mockup hardware tests. Initially, simulated candidate magnetic circuit designs will resemble previous successful thruster designs. To provide opportunity to improve beyond previous performance benchmarks, off-design modifications will be simulated and experimentally tested.

  2. Studies on the application of temperature-responsive ion exchange polymers with whey proteins.

    PubMed

    Maharjan, Pankaj; Campi, Eva M; De Silva, Kirthi; Woonton, Brad W; Jackson, W Roy; Hearn, Milton T W

    2016-03-18

    Several new types of temperature-responsive ion exchange resins of different polymer composition have been prepared by grafting the products from the co-polymerisation of N-phenylacrylamide, N-iso-propylacrylamide and acrylic acid derivatives onto cross-linked agarose. Analysis of the binding isotherms for these different resins obtained under batch adsorption conditions indicated that the resin based on N-iso-propylacrylamide containing 5% (w/w) N-phenylacrylamide and 5% (w/w) acrylic acid resulted in the highest adsorption capacity, Bmax, for the whey protein, bovine lactoferrin, e.g. 14 mg bovine lactoferrin/mL resin at 4 °C and 62 mg bovine lactoferrin/mL resin at 40 °C, respectively. Under dynamic loading conditions at 40 °C, 94% of the loaded bovine lactoferrin on a normalised mg protein per mL resin basis was adsorbed by this new temperature-responsive ion-exchanger, and 76% was eluted by a single cycle temperature shift to 4 °C without varying the composition of the 10mM sodium dihydrogen phosphate buffer, pH 6.5, or the flow rate. The binding characteristics of these different ion exchange resins with bovine lactoferrin were also compared to results obtained using other resins based on N-isopropylacrylamide but contained N-tert-butylacrylamide rather than N-phenylacrylamide, where the corresponding dynamic capture and release properties for bovine lactoferrin required different temperature conditions of 20 °C and 50 °C, respectively for optimal desorption/adsorption. The cationic protein, bovine lactoperoxidase, was also adsorbed and desorbed with these temperature-responsive resins under similar conditions of changing temperature, whereas the anionic protein, bovine β-lactoglobulin, was not adsorbed under this regime of temperature conditions but instead eluted in the flow-through.

  3. The LIFE Dynamic Chamber System

    NASA Astrophysics Data System (ADS)

    Rhodes, Mark; Kane, Jave; Latkowski, Jeffery; Cook, Andrew; Divol, Laurent; Loosmore, Gwendolen; Scott, Howard; Scullard, Christian; Tabak, Max; Wilks, Scott; Moses, Gregory; Heltemes, Thad; Sacks, Ryan; Pantano, Carlos; Kramer, Richard

    2011-10-01

    Dry-wall IFE designs such as LIFE utilize Xe fill gas to protect the target chamber first wall from x-ray heating and ionic debris. A key question is how cool, settled and clean the Xe must be to permit beam propagation and target transport, and how to reach this state at a 10+ Hz shot repetition rate. Xe is at low density in the target chamber, and purified Xe is reinjected at higher density and lower temperature into the larger outer chamber. Maintenance of this density difference due to blast waves generated by implosion of the target capsules is being assessed with HYDRA and 3D VTF, and possible validation experiments are being investigated. Detailed gas response near the wall is being studied using 3D Miranda. A laboratory-scale theta pinch experiment will study cooling and beam propagation in Xe. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  4. Thin-film silica sol-gels doped with ion responsive fluorescent lipid bilayers

    SciTech Connect

    Sasaki, D.Y.; Shea, L.E.; Sinclair, M.B.

    1999-01-12

    A metal ion sensitive, fluorescent lipid-b i layer material (5oA PSIDA/DSPC) was successfully immobilized in a silica matrix using a tetramethoxysilane (TMOS) sol-gel procedure. The sol-gel immobilization method was quantitative in the entrapment of seif-assembled Iipid-bilayers and yielded thin films for facile configuration to optical fiber piatforms. The silica matrix was compatible with the solvent sensitive lipid bilayers and provided physical stabilization as well as biological protection. Immobilization in the silica sol-gel produced an added benefit of improving the bilayer's metal ion sensitivity by up to two orders of magnitude. This enhanced performance was attributed to a preconcentrator effect from the anionic surface of the silica matrix. Thin gels (193 micron thickness) were coupled to a bifurcated fiber optic bundle to produce a metal ion sensor probe. Response times of 10 - 15 minutes to 0.1 M CUCIZ were realized with complete regeneration of the sensor using an ethylenediarninetetraacetic acid (EDTA) solution.

  5. Thin-film silica sol-gels doped with ion-responsive fluorescent lipid bilayers

    NASA Astrophysics Data System (ADS)

    Sasaki, Darryl Y.; Shea, Lauren E.; Sinclair, Michael B.

    1999-05-01

    A metal ion sensitive, fluorescent lipid-bilayer material (5% PSIDA/DSPC) was successfully immobilized in a silica matrix using a tetramethoxysilane (TMOS) sol-gel procedure. The sol- gel immobilization method was quantitative in the entrapment of self-assembled lipid-bilayers and yielded thin films for facile configuration to optical fiber platforms. The silica matrix was compatible with the solvent sensitive lipid bilayers and provided physical stabilization as well as biological protection. Immobilization in the silica sol-gel produced an added benefit of improving the bilayer's metal ion sensitivity by up to two orders of magnitude. This enhanced performance was attributed to a preconcentrator effect from the anionic surface of the silica matrix. Thin gels (193 micron thickness) were coupled to a bifurcated fiber optic bundle to produce a metal ion sensor probe. Response times of 10 - 15 minutes to 0.1 M CuCl2 were realized with complete regeneration of the sensor using an ethylenediaminetetraacetic acid (EDTA) solution.

  6. Synergistic effect of nanotopography and bioactive ions on peri-implant bone response

    PubMed Central

    Su, Yingmin; Komasa, Satoshi; Li, Peiqi; Nishizaki, Mariko; Chen, Luyuan; Terada, Chisato; Yoshimine, Shigeki; Nishizaki, Hiroshi; Okazaki, Joji

    2017-01-01

    Both bioactive ion chemistry and nanoscale surface modifications are beneficial for enhanced osseointegration of endosseous implants. In this study, a facile synthesis approach to the incorporation of bioactive Ca2+ ions into the interlayers of nanoporous structures (Ca-nano) formed on a Ti6Al4V alloy surface was developed by sequential chemical and heat treatments. Samples with a machined surface and an Na+ ion-incorporated nanoporous surface (Na-nano) fabricated by concentrated alkali and heat treatment were used in parallel for comparison. The bone response was investigated by microcomputed tomography assessment, sequential fluorescent labeling analysis, and histological and histomorphometric evaluation after 8 weeks of implantation in rat femurs. No significant differences were found in the nanotopography, surface roughness, or crystalline properties of the Ca-nano and Na-nano surfaces. Bone–implant contact was better in the Ca-nano and Na-nano implants than in the machined implant. The Ca-nano implant was superior to the Na-nano implant in terms of enhancing the volume of new bone formation. The bone formation activity consistently increased for the Ca-nano implant but ceased for the Na-nano implant in the late healing stage. These results suggest that Ca-nano implants have promising potential for application in dentistry and orthopedics. PMID:28184162

  7. Sputtering erosion in ion and plasma thrusters

    NASA Technical Reports Server (NTRS)

    Ray, Pradosh K.

    1995-01-01

    An experimental set-up to measure low-energy (below 1 keV) sputtering of materials is described. The materials to be bombarded represent ion thruster components as well as insulators used in the stationary plasma thruster. The sputtering takes place in a 9 inch diameter spherical vacuum chamber. Ions of argon, krypton and xenon are used to bombard the target materials. The sputtered neutral atoms are detected by a secondary neutral mass spectrometer (SNMS). Samples of copper, nickel, aluminum, silver and molybdenum are being sputtered initially to calibrate the spectrometer. The base pressure of the chamber is approximately 2 x 10(exp -9) Torr. the primary ion beam is generated by an ion gun which is capable of delivering ion currents in the range of 20 to 500 nA. The ion beam can be focused to a size approximately 1 mm in diameter. The mass spectrometer is positioned 10 mm from the target and at 90 deg angle to the primary ion beam direction. The ion beam impinges on the target at 45 deg. For sputtering of insulators, charge neutralization is performed by flooding the sample with electrons generated from an electron gun. Preliminary sputtering results, methods of calculating the instrument response function of the spectrometer and the relative sensitivity factors of the sputtered elements will be discussed.

  8. Sputtering erosion in ion and plasma thrusters

    NASA Technical Reports Server (NTRS)

    Ray, Pradosh K.

    1995-01-01

    An experimental set-up to measure low-energy (below 1 keV) sputtering of materials is described. The materials to be bombarded represent ion thruster components as well as insulators used in the stationary plasma thruster. The sputtering takes place in a 9 inch diameter spherical vacuum chamber. Ions of argon, krypton and xenon are used to bombard the target materials. The sputtered neutral atoms are detected by a secondary neutral mass spectrometer (SNMS). Samples of copper, nickel, aluminum, silver and molybdenum are being sputtered initially to calibrate the spectrometer. The base pressure of the chamber is approximately 2 x 10(exp -9) Torr. the primary ion beam is generated by an ion gun which is capable of delivering ion currents in the range of 20 to 500 nA. The ion beam can be focused to a size approximately 1 mm in diameter. The mass spectrometer is positioned 10 mm from the target and at 90 deg angle to the primary ion beam direction. The ion beam impinges on the target at 45 deg. For sputtering of insulators, charge neutralization is performed by flooding the sample with electrons generated from an electron gun. Preliminary sputtering results, methods of calculating the instrument response function of the spectrometer and the relative sensitivity factors of the sputtered elements will be discussed.

  9. Chamber B Thermal/Vacuum Chamber: User Test Planning Guide

    NASA Technical Reports Server (NTRS)

    Montz, Mike E.

    2012-01-01

    Test process, milestones and inputs are unknowns to first-time users of Chamber B. The User Test Planning Guide aids in establishing expectations for both NASA and non-NASA facility customers. The potential audience for this guide includes both internal and commercial spaceflight hardware/software developers. It is intended to assist their test engineering personnel in test planning and execution. Material covered includes a roadmap of the test process, roles and responsibilities of facility and user, major milestones, facility capabilities, and inputs required by the facility. Samples of deliverables, test article interfaces, and inputs necessary to define test scope, cost, and schedule are included as an appendix to the guide.

  10. Infrared responsivity enhancement for silicon detectors by non-mask reactive ion etching

    NASA Astrophysics Data System (ADS)

    Liao, Naiman; Kou, Linlai; Luo, Chunlin; Li, Renhao

    2016-10-01

    Near Infrared responsivity of silicon-based detectors is low for weak light absorption in the wavelengths exceeding 1000nm. For 1064nm wavelength applications, it is necessary to use thick Si wafers to manufacturing devices for higher NIR responsivity performance. However, this leads to high applied voltage, long response time, imposing limitations on device characteristics and applications. Black silicon (BS) appears very high absorptance of light from the near-ultraviolet (250nm) to the near-infrared (2500nm) wavelength region. And the black silicon detectors are many times more responsivity than conventional silicon detectors in the near infrared. In this article, BS is prepared using non-mask reactive ion etching technique and PIN BS detectors are fabricated. It is indicated that there is a disordered layer that is 2.0μm -3.5μm thick and made up of pillars with 90nm-400nm in diameter and 200nm-600nm in spacing interval. The reflectance of BS is less than 7% in the wavelength from 400nm to 1100nm, and rises from 1040nm. The absorptance of BS sample prepared by non-mask reactive ion etching remains more than 93% from 400nm to 1040nm, and the absorptance of 60% is observed at the wavelengths longer than 1500nm. High temperature annealing does not deteriorate its light absorption performance. The front-illuminated and back-illuminated BS PIN detectors are structured. At the wavelength of 1064nm, the responsivities of front-illuminated and back-illuminated BS PIN detectors are improved from 0.30A/W to 0.43A/W and 0.58A/W respectively.

  11. The NF-kB pathway: LET dependence of the biological response to heavy ion beams

    NASA Astrophysics Data System (ADS)

    Hellweg, Christine; Baumstark-Khan, Christa; Arenz, Andrea; Reitz, Guenther; Schmitz, Claudia; Spitta, Luis F.; Ruscher, Roland; Lau, Patrick; Meier, Matthias M.; Testard, Isabelle

    Radiation is an acknowledged primary concern for manned spaceflight and is a potentially limiting factor for long term orbital and interplanetary missions. A solar flare can threaten the astronauts' life, and long-term exposure to galactic cosmic rays may shorten the healthy life-span after return to Earth due to cancer induction. Understanding of the cellular and molecular processes underlying these phenomena may allow better risk estimation and development of appropriate countermeasures. A central factor in the cellular stress response is the transcription factor nuclear factor κB (NF-κB). As an antiapoptotic factor, if activated in human cells by ion beam exposure, it could influence the cancer risk of astronauts exposed to cosmic radiation and improve cellular survival after exposure to high radiation doses. In previous studies using a screening assay for the detection of NF-κB-dependent gene induction (HEK-pNF-κB-d2EGFP/Neo cells), the activation of this transcription factor by heavy ions was shown (Radiat. Res. 164: 527-530, 2005). In this work, the dependency of NF-κB activation on LET was examined. Accelerated argon ions (36 Ar, 95 MeV/u, LET 232 keV/` ım) activate the NF-κB pathway already at low particle densities (1-2 particle hits per nucleus), which result in as less as 5-50 induced double strand breaks per cell. Accelerated carbon ions (13 C, 75 MeV/u, LET 30 keV/µm) induce NF-κB-dependent gene expression at higher particle densities (50-500 particle hits per nucleus), but to a lower extent than the argon ions. Intermediate NF-κB activation is initiated by exposure of human cells with carbon ions with an LET of 70 keV/µm. Sparsely ionizing radiation such as X-rays activates the NF-κB pathway at high doses (> 4 Gy), neutrons at doses > 3 Gy. These results suggest a LET dependency of NF-κB activation: high LET radiation activates NF-κB - dependent on initial nuclear DNA damage followed by cytoplasmic signalling events - more efficiently

  12. Examination of the Ion Beam Response of III-V Semiconductor Substrates

    NASA Astrophysics Data System (ADS)

    Grossklaus, Kevin A.

    This work examines the response of the III-V materials to ion beam irradiation in a series of four experimental studies and describes the observed results in terms of the fundamental materials processes and properties that control ion-induced change in those compounds. Two studies investigate the use of Ga+ focused ion beam (FIB) irradiation of III-V substrate materials to create nanostructures. In the first, the creation of FIB induced group III nanodots on GaAs, InP, InAs, and AlAs is studied. The analysis of those results in terms of basic material properties and a simple nanodot growth model represents the first unified investigation of the fundamental processes that drive the nanodot forming behavior of the III-V compounds. The second nanostructure formation study reports the discovery and characterization of unique spike-like InAs nanostructures, termed "nanospikes," which may be useful for nanoscale electronic or thermoelectric applications. A novel method for controlling nanospike formation using InAs/InP heterostructures and film pre-patterning is developed, and the electrical properties of these ion erosion created nanostructures are characterized by in-situ TEM nanoprobe testing in a first-of-its-kind examination. The two remaining studies examine methods for using ion beam modification of III-V substrates to accommodate lattice-mismatched film growth with improved film properties. The first examines the effects of film growth on a wide range of different FIB created 3-D substrate patterns, and finds that 3-D surface features and patterns significantly alter film morphology and that growth on or near FIB irradiated regions does not improve film threading defect density. The second substrate modification study examines broad beam ion pre-implantation of GaAs wafers before InGaAs film growth, and is the first reported study of III-V substrate pre-implantation. Ar + pre-implantation was found to enhance the formation of threading defects in InGaAs films and

  13. Segmented ion thruster

    NASA Technical Reports Server (NTRS)

    Brophy, John R. (Inventor)

    1993-01-01

    Apparatus and methods for large-area, high-power ion engines comprise dividing a single engine into a combination of smaller discharge chambers (or segments) configured to operate as a single large-area engine. This segmented ion thruster (SIT) approach enables the development of 100-kW class argon ion engines for operation at a specific impulse of 10,000 s. A combination of six 30-cm diameter ion chambers operating as a single engine can process over 100 kW. Such a segmented ion engine can be operated from a single power processor unit.

  14. Selective ion source

    DOEpatents

    Leung, Ka-Ngo

    1996-01-01

    A ion source is described wherein selected ions maybe extracted to the exclusion of unwanted ion species of higher ionization potential. Also described is a method of producing selected ions from a compound, such as P.sup.+ from PH.sub.3. The invention comprises a plasma chamber, an electron source, a means for introducing a gas to be ionized by electrons from the electron source, means for limiting electron energy from the electron source to a value between the ionization energy of the selected ion species and the greater ionization energy of an unwanted ion specie, and means for extracting the target ion specie from the plasma chamber. In one embodiment, the electrons are generated in a plasma cathode chamber immediately adjacent to the plasma chamber. A small extractor draws the electrons from the plasma cathode chamber into the relatively positive plasma chamber. The energy of the electrons extracted in this manner is easily controlled. The invention is particularly useful for doping silicon with P.sup.+, AS.sup.+, and B.sup.+ without the problematic presence of hydrogen, helium, water, or carbon oxide ions. Doped silicon is important for manufacture of semiconductors and semiconductor devices.

  15. Selective ion source

    DOEpatents

    Leung, K.N.

    1996-05-14

    A ion source is described wherein selected ions maybe extracted to the exclusion of unwanted ion species of higher ionization potential. Also described is a method of producing selected ions from a compound, such as P{sup +} from PH{sub 3}. The invention comprises a plasma chamber, an electron source, a means for introducing a gas to be ionized by electrons from the electron source, means for limiting electron energy from the electron source to a value between the ionization energy of the selected ion species and the greater ionization energy of an unwanted ion specie, and means for extracting the target ion specie from the plasma chamber. In one embodiment, the electrons are generated in a plasma cathode chamber immediately adjacent to the plasma chamber. A small extractor draws the electrons from the plasma cathode chamber into the relatively positive plasma chamber. The energy of the electrons extracted in this manner is easily controlled. The invention is particularly useful for doping silicon with P{sup +}, As{sup +}, and B{sup +} without the problematic presence of hydrogen, helium, water, or carbon oxide ions. Doped silicon is important for manufacture of semiconductors and semiconductor devices. 6 figs.

  16. Thrust chamber life prediction

    NASA Technical Reports Server (NTRS)

    Kasper, H. J.

    1985-01-01

    The reusable life of the Space Shuttle main engine (SSME) is influenced by the cyclic life of the regeneratively liquid cooled main combustion chamber (MCC). During an operational duty cycle the MCC liner is subjected to a large transient thermal gradient that imparts a high thermal cyclic strain to the liner hot gas wall. Life predictions of such chambers have usually been based on low cycle fatigue (LCF) evaluations. Hot-fire testing, however, has shown significant mid-channel wall deformation and thinning during accrued cyclic testing. This phenomenon is termed cyclic creep and appears to be significantly accelerated at elevated temperatures. An analytical method that models the cyclic creep phenomenon and its application to thrust chamber life prediction is presented. The chamber finite element geometry is updated periodically to account for accrued wall thinning and distortion. Failure is based on the tensile instability failure criterion. Cyclic life results for several chamber life enhancing coolant channel designs are compared to the typically used LCF analysis that neglects cyclic creep. The results show that the usable cyclic creep life is approximately 30 to 50% of the commonly used LCF life.

  17. Improved Rhenium Thrust Chambers

    NASA Technical Reports Server (NTRS)

    O'Dell, John Scott

    2015-01-01

    Radiation-cooled bipropellant thrust chambers are being considered for ascent/ descent engines and reaction control systems on various NASA missions and spacecraft, such as the Mars Sample Return and Orion Multi-Purpose Crew Vehicle (MPCV). Currently, iridium (Ir)-lined rhenium (Re) combustion chambers are the state of the art for in-space engines. NASA's Advanced Materials Bipropellant Rocket (AMBR) engine, a 150-lbf Ir-Re chamber produced by Plasma Processes and Aerojet Rocketdyne, recently set a hydrazine specific impulse record of 333.5 seconds. To withstand the high loads during terrestrial launch, Re chambers with improved mechanical properties are needed. Recent electrochemical forming (EL-Form"TM") results have shown considerable promise for improving Re's mechanical properties by producing a multilayered deposit composed of a tailored microstructure (i.e., Engineered Re). The Engineered Re processing techniques were optimized, and detailed characterization and mechanical properties tests were performed. The most promising techniques were selected and used to produce an Engineered Re AMBR-sized combustion chamber for testing at Aerojet Rocketdyne.

  18. Target Chamber Manipulator

    NASA Astrophysics Data System (ADS)

    Tantillo, Anthony; Watson, Matthew

    2015-11-01

    A system has been developed to allow remote actuation of sensors in a high vacuum target chamber used with a particle accelerator. Typically, sensors of various types are placed into the target chamber at specific radial and angular positions relative to the beam line and target. The chamber is then evacuated and the experiments are performed for those sensor positions. Then, the chamber is opened, the sensors are repositioned to new angles or radii, and the process is repeated, with a separate pump-down cycle for each set of sensor positions. The new sensor positioning system allows scientists to pre-set the radii of up to a dozen sensors, and then remotely actuate their angular positions without breaking the vacuum of the target chamber. This reduces the time required to reposition sensors from 6 hours to 1 minute. The sensors are placed into one of two tracks that are separately actuated using vacuum-grade stepping motors. The positions of the sensors are verified using absolute optical rotary encoders, and the positions are accurate to 0.5 degrees. The positions of the sensors are electronically recorded and time-stamped after every change. User control is through a GUI using LabVIEW.

  19. Exchangeable Ions Are Responsible for the In Vitro Antibacterial Properties of Natural Clay Mixtures

    PubMed Central

    Otto, Caitlin C.; Haydel, Shelley E.

    2013-01-01

    We have identified a natural clay mixture that exhibits in vitro antibacterial activity against a broad spectrum of bacterial pathogens. We collected four samples from the same source and demonstrated through antibacterial susceptibility testing that these clay mixtures have markedly different antibacterial activity against Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA). Here, we used X-ray diffraction (XRD) and inductively coupled plasma – optical emission spectroscopy (ICP-OES) and – mass spectrometry (ICP-MS) to characterize the mineralogical and chemical features of the four clay mixture samples. XRD analyses of the clay mixtures revealed minor mineralogical differences between the four samples. However, ICP analyses demonstrated that the concentrations of many elements, Fe, Co, Cu, Ni, and Zn, in particular, vary greatly across the four clay mixture leachates. Supplementation of a non-antibacterial leachate containing lower concentrations of Fe, Co, Ni, Cu, and Zn to final ion concentrations and a pH equivalent to that of the antibacterial leachate generated antibacterial activity against E. coli and MRSA, confirming the role of these ions in the antibacterial clay mixture leachates. Speciation modeling revealed increased concentrations of soluble Cu2+ and Fe2+ in the antibacterial leachates, compared to the non-antibacterial leachates, suggesting these ionic species specifically are modulating the antibacterial activity of the leachates. Finally, linear regression analyses comparing the log10 reduction in bacterial viability to the concentration of individual ion species revealed positive correlations with Zn2+ and Cu2+ and antibacterial activity, a negative correlation with Fe3+, and no correlation with pH. Together, these analyses further indicate that the ion concentration of specific species (Fe2+, Cu2+, and Zn2+) are responsible for antibacterial activity and that killing activity is not solely attributed to pH. PMID:23691149

  20. Ectoenzyme activity in coastal marine waters: response to temperature and metal ion availability

    NASA Astrophysics Data System (ADS)

    Wiedenbeck, J. K.; Neino, V.; Allison, S. D.; Martiny, A.

    2009-12-01

    Ectoenzymes in the ocean are vital for the breakdown of complex organic substrates and for the uptake of nutrients by marine organisms. The activity levels of these enzymes affect the turnover rate of nutrient pools within the ocean, and thus have a significant impact on global biogeochemical nutrient cycles. This study measured the activity of extracellular enzymes from seawater samples under different environmental conditions. Samples were collected daily from coastal waters in the subtropical North Pacific (Lat.: 33°). Ambient seawater temperatures were between 18° and 20° C for the duration of the study. The activity response of four enzymes (alkaline phosphatase, β-glucosidase, β-N-acetyl glucosaminidase, and leucine aminopeptidase) was measured over a range of temperatures (4° to 40° C). The optimal temperatures of all four enzymes were above the ambient seawater temperature of the samples: optimal temperatures of β-glucosidase, β-N-acetyl glucosaminidase, and leucine aminopeptidase in the seawater samples were between 28° and 34° C, while alkaline phosphatase activity increased with the temperature over the range tested. Enzymatic activity of alkaline phosphatase was further investigated under several metal ion conditions. Activity was highest in the presence of Co2+ ions, while the availability of other ions (Ca2+ and Mg2+/Zn2+) had a lesser effect. The influence of Co2+ on alkaline phosphatase activity indicates the presence of a Co2+-dependent alkaline phosphatase in coastal marine waters. These results suggest that variations in environmental conditions (such as temperature and ion concentration) have discernable effects on enzyme activity, and thus affect turnover rates of nutrient pools in the ocean.

  1. Mechanosensitive ion channel Piezo2 is important for enterochromaffin cell response to mechanical forces.

    PubMed

    Wang, Fan; Knutson, Kaitlyn; Alcaino, Constanza; Linden, David R; Gibbons, Simon J; Kashyap, Purna; Grover, Madhusudan; Oeckler, Richard; Gottlieb, Philip A; Li, Hui Joyce; Leiter, Andrew B; Farrugia, Gianrico; Beyder, Arthur

    2017-01-01

    The gastrointestinal epithelial enterochromaffin (EC) cell synthesizes the vast majority of the body's serotonin. As a specialized mechanosensor, the EC cell releases this serotonin in response to mechanical forces. However, the molecular mechanism of EC cell mechanotransduction is unknown. In the present study, we show, for the first time, that the mechanosensitive ion channel Piezo2 is specifically expressed by the human and mouse EC cells. Activation of Piezo2 by mechanical forces results in a characteristic ionic current, the release of serotonin and stimulation of gastrointestinal secretion. Piezo2 inhibition by drugs or molecular knockdown decreases mechanosensitive currents, serotonin release and downstream physiological effects. The results of the present study suggest that the mechanosensitive ion channel Piezo2 is specifically expressed by the EC cells of the human and mouse small bowel and that it is important for EC cell mechanotransduction. The enterochromaffin (EC) cell in the gastrointestinal (GI) epithelium is the source of nearly all systemic serotonin (5-hydroxytryptamine; 5-HT), which is an important neurotransmitter and endocrine, autocrine and paracrine hormone. The EC cell is a specialized mechanosensor, and it is well known that it releases 5-HT in response to mechanical forces. However, the EC cell mechanotransduction mechanism is unknown. The present study aimed to determine whether Piezo2 is involved in EC cell mechanosensation. Piezo2 mRNA was expressed in human jejunum and mouse mucosa from all segments of the small bowel. Piezo2 immunoreactivity localized specifically within EC cells of human and mouse small bowel epithelium. The EC cell model released 5-HT in response to stretch, and had Piezo2 mRNA and protein, as well as a mechanically-sensitive inward non-selective cation current characteristic of Piezo2. Both inward currents and 5-HT release were inhibited by Piezo2 small interfering RNA and antagonists (Gd(3+) and D-GsMTx4

  2. Automated Electrostatics Environmental Chamber

    NASA Technical Reports Server (NTRS)

    Calle, Carlos; Lewis, Dean C.; Buchanan, Randy K.; Buchanan, Aubri

    2005-01-01

    The Mars Electrostatics Chamber (MEC) is an environmental chamber designed primarily to create atmospheric conditions like those at the surface of Mars to support experiments on electrostatic effects in the Martian environment. The chamber is equipped with a vacuum system, a cryogenic cooling system, an atmospheric-gas replenishing and analysis system, and a computerized control system that can be programmed by the user and that provides both automation and options for manual control. The control system can be set to maintain steady Mars-like conditions or to impose temperature and pressure variations of a Mars diurnal cycle at any given season and latitude. In addition, the MEC can be used in other areas of research because it can create steady or varying atmospheric conditions anywhere within the wide temperature, pressure, and composition ranges between the extremes of Mars-like and Earth-like conditions.

  3. Antipollution combustion chamber

    SciTech Connect

    Caruel, J.E.; Gastebois, P.M.

    1981-01-27

    The invention concerns a combustion chamber for turbojet engines. The combustion chamber is of the annular type and consists of two coaxial flame tubes opening into a common dilution and mixing zone. The inner tube is designed for low operating ratings of the engine, the outer tube for high ratings. Air is injected as far upstream as possible into the dilution zone, to enhance the homogenization of the gaseous flow issuing from the two tubes prior to their passage into the turbine and to assure the optimum radial distribution of temperatures. The combustion chamber according to the invention finds application in a particularly advantageous manner in turbojet engines used in aircraft propulsion because of the reduced emission of pollutants it affords.

  4. Chamber, Target and Final Focus Integrated Design

    SciTech Connect

    Moir, R.W.

    2000-03-03

    Liquid wall protection, which challenges chamber clearing, has such advantages it's Heavy Ion Fusion's (HIF) main line chamber design. Thin liquid protection from x rays is necessary to avoid erosion of structural surfaces and thick liquid makes structures behind 0.5 m of Flibe (7 mean free paths for 14 MeV neutrons), last the life of the plant. Liquid wall protection holds the promise of greatly increased economic competitiveness. Driver designers require {approx}200 beams to illuminate recent target designs from two sides. The illumination must be compatible with liquid wall protection. The ''best'' values for driver energy, gain, yield and pulse rate comes out of well-known trade-off studies. The chamber design is based on several key assumptions, which are to be proven before HIF can be shown to be feasible. The chamber R&D needed to reduce the unknowns and risks depend on resolving a few technical issues such as jet surface smoothness and rapid chamber clearing.

  5. Filament wound rocket motor chambers

    NASA Technical Reports Server (NTRS)

    1976-01-01

    The design, analysis, fabrication and testing of a Kevlar-49/HBRF-55A filament wound chamber is reported. The chamber was fabricated and successfully tested to 80% of the design burst pressure. Results of the data reduction and analysis from the hydrotest indicate that the chamber design and fabrication techniques used for the chamber were adequate and the chamber should perform adequately in a static test.

  6. Automated soil gas monitoring chamber

    DOEpatents

    Edwards, Nelson T.; Riggs, Jeffery S.

    2003-07-29

    A chamber for trapping soil gases as they evolve from the soil without disturbance to the soil and to the natural microclimate within the chamber has been invented. The chamber opens between measurements and therefore does not alter the metabolic processes that influence soil gas efflux rates. A multiple chamber system provides for repetitive multi-point sampling, undisturbed metabolic soil processes between sampling, and an essentially airtight sampling chamber operating at ambient pressure.

  7. Electrostatic Levitator Vacuum Chamber

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Optical ports ring the Electrostatic Levitator (ESL) vacuum chamber to admit light from the heating laser (beam passes through the window at left), positioning lasers (one port is at center), and lamps to allow diagnostic instruments to view the sample. The ESL uses static electricity to suspend an object (about 2-3 mm in diameter) inside a vacuum chamber while a laser heats the sample until it melts. This lets scientists record a wide range of physical properties without the sample contacting the container or any instruments, conditions that would alter the readings. The Electrostatic Levitator is one of several tools used in NASA's microgravity materials science program.

  8. Non-Targeted Effects and the Dose Response for Heavy Ion Tumorigenesis

    NASA Technical Reports Server (NTRS)

    Chappelli, Lori J.; Cucinotta, Francis A.

    2010-01-01

    BACKGROUND: There is no human epidemiology data available to estimate the heavy ion cancer risks experienced by astronauts in space. Studies of tumor induction in mice are a necessary step to estimate risks to astronauts. Previous experimental data can be better utilized to model dose response for heavy ion tumorigenesis and plan future low dose studies. DOSE RESPONSE MODELS: The Harderian Gland data of Alpen et al.[1-3] was re-analyzed [4] using non-linear least square regression. The data set measured the induction of Harderian gland tumors in mice by high-energy protons, helium, neon, iron, niobium and lanthanum with LET s ranging from 0.4 to 950 keV/micron. We were able to strengthen the individual ion models by combining data for all ions into a model that relates both radiation dose and LET for the ion to tumor prevalence. We compared models based on Targeted Effects (TE) to one motivated by Non-targeted Effects (NTE) that included a bystander term that increased tumor induction at low doses non-linearly. When comparing fitted models to the experimental data, we considered the adjusted R2, the Akaike Information Criteria (AIC), and the Bayesian Information Criteria (BIC) to test for Goodness of fit.In the adjusted R2test, the model with the highest R2values provides a better fit to the available data. In the AIC and BIC tests, the model with the smaller values of the summary value provides the better fit. The non-linear NTE models fit the combined data better than the TE models that are linear at low doses. We evaluated the differences in the relative biological effectiveness (RBE) and found the NTE model provides a higher RBE at low dose compared to the TE model. POWER ANALYSIS: The final NTE model estimates were used to simulate example data to consider the design of new experiments to detect NTE at low dose for validation. Power and sample sizes were calculated for a variety of radiation qualities including some not considered in the Harderian Gland data

  9. Understanding Molecular Ion-Neutral Atom Collisions for the Production of Ultracold Molecular Ions

    DTIC Science & Technology

    2016-06-06

    chamber