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Sample records for 3he ionization chambers

  1. Fast-Neutron Spectrometry Using a 3He Ionization Chamber and Digital Pulse Shape Analysis

    SciTech Connect

    D. L. Chichester; J. T. Johnson; E. H. Seabury

    2010-05-01

    Digital pulse shape analysis (dPSA) has been used with a Cuttler-Shalev type 3He proportional counter to measure the fast neutron spectra of bare 252Cf and 241AmBe neutron sources. Measurements have also been made to determine the attenuated fast neutron spectra of 252Cf shielded by several materials including water, graphite, liquid nitrogen, magnesium, and tungsten. Rise-time dPSA has been employed using the common rise-time approach for analyzing n +3He ? 1H + 3H ionization events and a new approach has been developed to improve the fidelity of these measurements. Simulations have been performed for the different experimental arrangements and are compared, demonstrating general agreement between the dPSA processed fast neutron spectra and predictions.

  2. Overview of the n3He Experiment and Target Chamber

    NASA Astrophysics Data System (ADS)

    McCrea, Mark; n3He Collaboration

    2017-01-01

    The n3He Experiment aims to measure the parity-violating asymmetry in the direction of proton emission relative to the initial neutron polarization direction in the reaction n-> +3 He -> T + p + 765 keV to a high precision. The size of the asymmetry is estimated to be in the range - 9 . 5 - 2 . 5 ×10-8 , and our goal statistical accuracy is 2 ×10-8 . The experiment ran at the Spallation Neutron Source with data taking completing at the end of 2015. The experiment used a Helium-3 ionization chamber as the combined target and detector. Data analysis is underway and is currently in an advanced stage

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Ionization-chamber smoke detector system

    DOEpatents

    Roe, Robert F.

    1976-10-19

    This invention relates to an improved smoke-detection system of the ionization-chamber type. In the preferred embodiment, the system utilizes a conventional detector head comprising a measuring ionization chamber, a reference ionization chamber, and a normally non-conductive gas triode for discharging when a threshold concentration of airborne particulates is present in the measuring chamber. The improved system is designed to reduce false alarms caused by fluctuations in ambient temperature. Means are provided for periodically firing the gas discharge triode and each time recording the triggering voltage required. A computer compares each triggering voltage with its predecessor. The computer is programmed to energize an alarm if the difference between the two compared voltages is a relatively large value indicative of particulates in the measuring chamber and to disregard smaller differences typically resulting from changes in ambient temperature.

  8. 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.

  9. 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.

  10. Current-voltage characteristic of parallel-plane ionization chamber with inhomogeneous ionization

    NASA Astrophysics Data System (ADS)

    Stoyanov, D. G.

    2007-08-01

    The balances of particles and charges in the volume of parallel-plane ionization chamber are considered. Differential equations describing the distribution of current densities in the chamber volume are obtained. As a result of the differential equations solution an analytical form of the current-voltage characteristic of parallel-plane ionization chamber with inhomogeneous ionization in the volume is obtained.

  11. A new ring-shaped graphite monitor ionization chamber

    NASA Astrophysics Data System (ADS)

    Yoshizumi, M. T.; Caldas, L. V. E.

    2010-07-01

    A ring-shaped monitor ionization chamber was developed at the Instituto de Pesquisas Energéticas e Nucleares. This ionization chamber presents an entrance window of aluminized polyester foil. The guard ring and collecting electrode are made of graphite coated Lucite plates. The main difference between this new ionization chamber and commercial monitor chambers is its ring-shaped design. The new monitor chamber has a central hole, allowing the passage of the direct radiation beam without attenuation; only the penumbra radiation is measured by the sensitive volume. This kind of ionization chamber design has already been tested, but using aluminium electrodes. By changing the electrode material from aluminium to a graphite coating, an improvement in the chamber response stability was expected. The pre-operational tests, as saturation curve, recombination loss and polarity effect showed satisfactory results. The repeatability and the long-term stability tests were also evaluated, showing good agreement with international recommendations.

  12. Ionization Chamber for Prompt Fission Neutron Investigations

    NASA Astrophysics Data System (ADS)

    Zeynalov, Sh.; Zeynalova, O.; Hambsch, F.-J.; Sedyshev, P.; Shvetsov, V.

    In this work we report recent achievements in design of twin back-to-back ionization chamber (TIC) for fission fragment (FF) mass and kinetic energy measurement. Correlated FF kinetic energies, their masses and the angle of FF in respect to the axes in 3D Cartesian coordinates can be determined from analysis of the heights and shapes of the pulses induced by the fission fragments on the anodes of TIC. Anodes of TIC were designed as consisting of isolated strips each having independent electronic circuitry and special multi-channel pulse processing apparatus. Mathematical formulae provided for FF angles measured in respect to the coordinate axes. It was shown how the point of fission fragments origin on the target plane may be determined using the same measured data. The last feature made the TIC a rather powerful tool for prompt fission neutron (PFN) emission investigation in event-by-event analysis of individual fission reactions from non- point fissile source. Position sensitive neutron induced fission detector for neutron-imaging applications with both thermal and low energy neutrons was found as another possible implementation of the designed TIC.

  13. 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.

  14. The Analysis of Ionization Chambers Used for Detecting Smoke Particles

    NASA Astrophysics Data System (ADS)

    Turlej, Z. (Bish).

    Ionization type cells using a radioactive source of primary ions have been used as fire detectors for many years. They have proven sufficiently sensitive to give an alarm when exposed to the relatively small concentration of smoke particles that occur during the early stages of combustion when control of a fire is still possible. In this work the charging of smoke particles in ionization chambers such as typically employed in ionization smoke detectors are investigated theoretically and experimentally. The ionization chambers investigated in this work have parallel plate and spherical electrode geometries. In the absence of smoke particles, the ionization chambers were operated at some ambient electrode current, which depends upon the ion generation rate, the electrode geometries, the potential difference between the electrodes, and the thermodynamic properties of the gas within the chamber volume. When smoke particles are introduced into the ionization chamber they act as an additional sink for the ions, so that the ion current is reduced. The smoke particles in the experiment performed in this work were transferred from the particle generator to the volume surrounding the ionization chamber and allowed to diffuse inside the ionization chamber. An Aitken nuclei counter was employed to measure the concentration of smoke particles inside the ionization chamber. The electric current flowing through the ionization chamber was recorded as a function of time and concentration of the smoke particles inside the chamber. The current loss due to the particles present inside the chamber was calculated and compared with the experimental results. It was found that at the certain level of ambient electrode current, the current loss due to the smoke particles assumes a maximum value. This optimum operating electrode current was predicted by the mathematical model employed in this work. In the light of this model experimental ionization chambers of both parallel and spherical

  15. Fundamental Studies of In Situ Plasma Chamber Cleaning Chemistries: C2F6/O2, C3F8/O2, and NF3/He.

    NASA Astrophysics Data System (ADS)

    Entley, William R.; Hennessy, William J.; Langan, John G.

    1999-10-01

    The plasma etching of SiO2 and Si3N4 in C2F6-O2 and C3F8-O2 mixtures has been studied as a function of feed gas composition (SiO2 substrates), pressure (Si3N4 substrates), and power (SiO2 substrates) in a modified commercial RIE chamber. The chamber has been modified to permit in situ electrical measurements, which allows us to correlate the substrate etch rates and power coupling efficiencies to the discharge impedance. In addition, gas-phase FTIR spectroscopy was used to quantify the PFC emissions for the various gas mixtures investigated. For a fixed rf power, pressure, and total gas flow rate, the maximum etch rate of SiO2 was found to occur within a relatively narrow range of oxygen concentrations, centered near a gas composition of 33 mol observed for a wider range of oxygen concentrations in C2F6 based plasmas. Although the destruction efficiency (the percentage of PFC destroyed in the plasma) of C2F6 and C3F8 in O2 based mixtures are comparable under similar operating conditions, significantly larger quantities of plasma generated CF4 are formed in C3F8-O2 gas mixtures. Comparisons are made to NF3/He discharges, which show higher etch rates and higher destruction efficiencies for appropriately chosen operating conditions.

  16. 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.

  17. 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)

  18. 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.

  19. Quantification of static magnetic field effects on radiotherapy ionization chambers.

    PubMed

    Agnew, J; O'Grady, F; Young, R; Duane, S; Budgell, G J

    2017-03-07

    Integrated magnetic resonance (MR) imaging and radiotherapy (RT) delivery machines are currently being developed, with some already in clinical use. It is anticipated that the strong magnetic field used in some MR-RT designs will have a significant impact on routine measurements of dose in the MR-linac performed using ionization chambers, which provide traceability back to a primary standard definition of dose. In particular, the presence of small air gaps around ionization chambers may introduce unacceptably high uncertainty into these measurements. In this study, we investigate and quantify the variation attributable to air gaps for several routinely-used cylindrical ionization chambers in a magnetic field, as well as the effect of the magnetic field alone on the response of the chambers. The measurements were performed in a Co-60 beam, while the ionization chambers were positioned in custom-made Perspex phantoms between the poles of an electromagnet, which was capable of generating magnetic fields of up to 2 T field strength, although measurements were focused around 1.5 T. When an asymmetric air gap was rotated at cardinal angles around the ionization chambers investigated here, variation of up to 8.5  ±  0.2 percentage points (PTW 31006 chamber) was observed in an applied magnetic field of 1.5 T. The minimum peak-to-peak variation was 1.1  ±  0.1% (Exradin A1SL). When the same experiment was performed with a well-defined air gap of known position using the PTW 30013 chamber, a variation of 3.8  ±  0.2% was observed. When water was added to the phantom cavity to eliminate all air gaps, the variation for the PTW 30013 was reduced to 0.2  ±  0.01%.

  20. Quantification of static magnetic field effects on radiotherapy ionization chambers

    NASA Astrophysics Data System (ADS)

    Agnew, J.; O’Grady, F.; Young, R.; Duane, S.; Budgell, G. J.

    2017-03-01

    Integrated magnetic resonance (MR) imaging and radiotherapy (RT) delivery machines are currently being developed, with some already in clinical use. It is anticipated that the strong magnetic field used in some MR-RT designs will have a significant impact on routine measurements of dose in the MR-linac performed using ionization chambers, which provide traceability back to a primary standard definition of dose. In particular, the presence of small air gaps around ionization chambers may introduce unacceptably high uncertainty into these measurements. In this study, we investigate and quantify the variation attributable to air gaps for several routinely-used cylindrical ionization chambers in a magnetic field, as well as the effect of the magnetic field alone on the response of the chambers. The measurements were performed in a Co-60 beam, while the ionization chambers were positioned in custom-made Perspex phantoms between the poles of an electromagnet, which was capable of generating magnetic fields of up to 2 T field strength, although measurements were focused around 1.5 T. When an asymmetric air gap was rotated at cardinal angles around the ionization chambers investigated here, variation of up to 8.5  ±  0.2 percentage points (PTW 31006 chamber) was observed in an applied magnetic field of 1.5 T. The minimum peak-to-peak variation was 1.1  ±  0.1% (Exradin A1SL). When the same experiment was performed with a well-defined air gap of known position using the PTW 30013 chamber, a variation of 3.8  ±  0.2% was observed. When water was added to the phantom cavity to eliminate all air gaps, the variation for the PTW 30013 was reduced to 0.2  ±  0.01%.

  1. CHAMBER - IONIZATION - EXPERIMENT - GEMINI-TITAN (GT)-6 EQUIPMENT - CAPE

    NASA Image and Video Library

    1965-12-10

    S65-61788 (For release: 11 Dec. 1965) --- Close-up view of equipment which will be used in the D-8 (Radiation in Spacecraft) experiment on the National Aeronautics and Space Administration's Gemini-6 spaceflight. This experiment is designed to make highly accurate measurements of the absorbed dose rate of radiation which penetrates the Gemini spacecraft, and determine the spatial distribution of dose levels inside the spacecraft particularly in the crew area. This is experimentation of the U.S. Air Force Weapons Laboratory, Kirtland AFB, N.M. LOWER LEFT: The second ionization chamber, this one is unshielded. This chamber can be removed from its bracket by the astronaut who will periodically take measurements at various locations in the spacecraft. Nearby is Passive Dosimeter Unit which is one of five small packets each containing a standard pocket ionization chamber, gamma electron sensitive film, glass needles and thermo luminescent dosimeters which are mounted at various locations in the cabin. UPPER LEFT: Photo illustrates how ionization chamber can be removed from bracket for measurements. LOWER RIGHT: Shield of bulb-shaped chamber will be removed (shown in photo) as the spacecraft passes through the South Atlantic anomaly, the area where the radiation belt dips closest to Earth's surface. UPPER RIGHT: Dome-shaped object is shield covering one of two Tissue Equivalent Ionization Chambers (sensors) which will read out continuously the instantaneous rate at which dose is delivered during the flight. This chamber is mounted permanently. The information will be recorded aboard the spacecraft, and will also be received directly by ground stations. This chamber is shielded to simulate the amount of radiation the crew members are receiving beneath their skin. Photo credit: NASA or National Aeronautics and Space Administration

  2. Characterization of a CT ionization chamber for radiation field mapping.

    PubMed

    Perini, Ana P; Neves, Lucio P; Vivolo, Vitor; Xavier, Marcos; Khoury, Helen J; Caldas, Linda V E

    2012-07-01

    A pencil-type ionization chamber, developed at Instituto de Pesquisas Energéticas e Nucleares (IPEN), was characterized with the objective to verify the possibility of its application in radiation field mapping procedures. The characterization tests were evaluated, and the results were satisfactory. The results obtained for the X radiation field mapping with the homemade chamber were compared with those of a PTW Farmer-type chamber (TN 30011-1). The maximum difference observed in this comparison was only 1.25%, showing good agreement. Copyright © 2011 Elsevier Ltd. All rights reserved.

  3. Segmented ionization chambers for beam monitoring in hadrontherapy

    NASA Astrophysics Data System (ADS)

    Braccini, Saverio; Cirio, Roberto; Donetti, Marco; Marchetto, Flavio; Pittà, Giuseppe; Lavagno, Marco; La Rosa, Vanessa

    2015-05-01

    Segmented ionization chambers represent a good solution to monitor the position, the intensity and the shape of ion beams in hadrontherapy. Pixel and strip chambers have been developed for both passive scattering and active scanning dose delivery systems. In particular, strip chambers are optimal for pencil beam scanning, allowing for spatial and time resolutions below 0.1 mm and 1 ms, respectively. The MATRIX pixel and the Strip Accurate Monitor for Beam Applications (SAMBA) detectors are described in this paper together with the results of several beam tests and industrial developments based on these prototypes.

  4. Search for muon catalyzed d 3He-fusion

    NASA Astrophysics Data System (ADS)

    Maev, E. M.; Balin, D. V.; Case, T.; Crowe, K. M.; Del Rosso, A.; Ganzha, V. A.; Hartmann, F. J.; Kozlov, S. M.; Lauss, B.; Maev, O. E.; Mühlbauer, M.; Mulhauser, F.; Petitjean, C.; Petrov, G. E.; Sadetsky, S. M.; Schapkin, G. N.; Schott, W.; Semenchuk, G. G.; Smirenin, Yu. V.; Soroka, M. A.; Vasiliev, A. A.; Vorobyov, A. A.; Voropaev, N. I.; Zmeskal, J.

    1999-06-01

    We report on the results of an experiment aimed at observing muon-catalyzed d 3He-fusion with a setup previously used for studies of the muon-catalyzed dd-fusion. The basic element of the setup is a high pressure ionization chamber operating as an active target. In this experiment the chamber was filled with an HD + 3He (5.6%) gas mixture at 13.2 bar pressure and 50 K temperature. These conditions were chosen as optimal for formation of the 3Heμd-molecules with a low level of background from the d-μ-d fusion. The chamber was exposed to the negative muon beam at PSI. During a 3-week data-taking period, 9.7 × 108 muon stops have been selected. The analysis of the data was able to determine a new upper limit for the d 3He-fusion rate in the 3Heμd-molecule (λf≤ 6× 104 s-1), which is more than three orders of magnitude lower than the previously existed limit.

  5. A multiple sampling ionization chamber for the External Target Facility

    NASA Astrophysics Data System (ADS)

    Zhang, X. H.; Tang, S. W.; Ma, P.; Lu, C. G.; Yang, H. R.; Wang, S. T.; Yu, Y. H.; Yue, K.; Fang, F.; Yan, D.; Zhou, Y.; Wang, Z. M.; Sun, Y.; Sun, Z. Y.; Duan, L. M.; Sun, B. H.

    2015-09-01

    A multiple sampling ionization chamber used as a particle identification device for high energy heavy ions has been developed for the External Target Facility. The performance of this detector was tested with a 239Pu α source and RI beams. A Z resolution (FWHM) of 0.4-0.6 was achieved for nuclear fragments of 18O at 400 AMeV.

  6. EML pulse ionization chamber systems for /sup 222/Rn measurements

    SciTech Connect

    Fisenne, I M; Keller, H W

    1985-03-01

    Radon measurements have been performed with pulse ionization chambers at the Environmental Measurements Laboratory (EML) for over 35 years. This report describes the evolution of radon measurement systems, with emphasis on the continuous quality control efforts at EML. 38 refs., 3 figs., 3 tabs.

  7. 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 %.

  8. Absolute neutron dosimetry: Effects of ionization chamber wall thickness

    SciTech Connect

    Ten Haken, R.K.; Awschalom, M.; Rosenberg, I.

    1985-01-01

    To assess the effect of ionization chamber wall thickness on absolute neutron absorbed dose determinations, measurements were made of the charge collected by an A-150 tissue-equivalent plastic ionization chamber irradiated by a p(66)Be(49) neutron therapy beam as a function of chamber wall thickness both in air and in four different media: tissue-equivalent solution, water, motor oil, and glycerin. Wall thicknesses ranged from 1 to 31 mm, where isolation of the chamber gas volume from protons originating outside the chamber wall was assured. The in-air measurements compare favorably with earlier buildup measurements performed with an A-150 extrapolation chamber in an A-150 phantom. The in-phantom results may be explained if the effect of charged particles reaching the gas volume from the medium and the wall as well as the differences in neutron attenuation by the wall and the medium displaced by the wall are taken into account. The errors in absolute absorbed dose determination caused by ignoring the above processes are assessed.

  9. Ionization chamber gradient effects in nonstandard beam configurations

    SciTech Connect

    Bouchard, Hugo; Seuntjens, Jan; Carrier, Jean-Francois; Kawrakow, Iwan

    2009-10-15

    Purpose: For the purpose of nonstandard beam reference dosimetry, the current concept of reporting absorbed dose at a point in water located at a representative position in the chamber volume is investigated in detail. As new nonstandard beam reference dosimetry protocols are under development, an evaluation of the role played by the definition of point of measurement could lead to conceptual improvements prior to establishing measurement procedures. Methods: The present study uses the current definition of reporting absorbed dose to calculate ionization chamber perturbation factors for two cylindrical chamber models (Exradin A12 and A14) using the Monte Carlo method. The EGSnrc based user-code EGS lowbar chamber is used to calculate chamber dose responses of 14 IMRT beams chosen to cause considerable dose gradients over the chamber volume as previously used by Bouchard and Seuntjens [''Ionization chamber-based reference dosimetry of intensity modulated radiation beams,'' Med. Phys. 31(9), 2454-5465 (2004)]. Results: The study shows conclusively the relative importance of each physical effect involved in the nonstandard beam correction factors of 14 IMRT beams. Of all correction factors involved in the dosimetry of the beams studied, the gradient perturbation correction factor has the highest magnitude, on average, 11% higher compared to reference conditions for the Exradin A12 chamber and about 5% higher for the Extradin A14 chamber. Other perturbation correction factors (i.e., P{sub wall}, P{sub stem}, and P{sub cel}) are, on average, less than 0.8% different from reference conditions for the chambers and beams studied. The current approach of reporting measured absorbed dose at a point in water coinciding with the location of the centroid of the chamber is the main factor responsible for large correction factors in nonstandard beam deliveries (e.g., intensity modulated radiation therapy) reported in literature. Conclusions: To reduce or eliminate the magnitude

  10. Examining the influence of humidity on reference ionization chamber performance.

    PubMed

    McEwen, Malcolm R; Taank, Jaswinder

    2017-02-01

    International dosimetry protocols require measurements made with a vented ionization chamber to be corrected for the influence of air density by using the standard temperature-pressure correction factor. The effect of humidity, on the other hand, is generally ignored with the provision that the relative humidity (RH) is within certain limits (typically 20% to 80%). However, there is little experimental data in the published literature as to the true effect of humidity on modern reference-class ionization chambers. This investigation used two different radiation beams - a Co-60 irradiator and an Sr-90 check source - to examine the effect of humidity on several Farmer-type ionization chambers. An environmental cabinet controlled the humidity. For the Co-60 beam, the irradiation was external, whereas for the Sr-90 measurements, the source itself was placed within the cabinet. Extensive measurements were carried out to ensure that the experimental setup provided reproducible readings. Four chamber types were investigated: IBA FC65-G, IBA FC65-P, PTW 30013 and Exradin A19. The different wall materials provided potentially different mechanical responses (i.e., in terms of expansion/contraction) to the water content in the air. The relative humidity was varied between 8% and 98% and measurements were made with both increasing and decreasing humidity to investigate any possible hysteresis effects. Measurements in Co-60 were consistent with the published data obtained with primary standard cavity chambers in ICRU Report 31 (i.e., a very small variation <0.1% for RH >10%). The measurements in the Sr-90 field showed no dependence with the relative humidity, within the measurement uncertainties (0.05%, k = 1). Very good repeatability of the ionization current was obtained over successive wet/dry cycles, no hysteresis was observed, and there was no dependence on chamber type. These results indicate that humidity has no significant effect on these particular types of ionization

  11. Ionization chamber for measurements of high-level tritium gas

    SciTech Connect

    Carstens, D.H.W.; David, W.R.

    1980-01-01

    The construction and calibration of a simple ionization-chamber apparatus for measurement of high level tritium gas is described. The apparatus uses an easily constructed but rugged chamber containing the unknown gas and an inexpensive digital multimeter for measuring the ion current. The equipment after calibration is suitable for measuring 0.01 to 100% tritium gas in hydrogen-helium mixes with an accuracy of a few percent. At both the high and low limits of measurements deviations from the predicted theoretical current are observed. These are briefly discussed.

  12. Neutron Dosimetry Using a Tissue-Equivalent Ionization Chamber.

    DTIC Science & Technology

    1980-05-01

    procedures are described, and correction factors discussed. /’ On a montg et v~rifiA un systtme de niesure d’oZz la dose ou le kerma tissulaire neutronique ...tube 3.8 cm in diameter. At the same time, it is advantageous to keep the active volume as large as possible in order to maximize sensitivity. The...CHAMBER The construction of the FWT TE Ionization chamber is Illustrated in figure 1. The active volume lies between the central electrode and the

  13. a Liquid Ionization Chamber as Monitor in Radiotherapy

    NASA Astrophysics Data System (ADS)

    Berghöfer, Th.; Engler, J.; Milke, J. M.; Hörandel, J. R.; Hartmann, G. H.

    2006-04-01

    First measurements with a prototype liquid ionization chamber are described to be applied as an online-monitor for intensity modulated radiotherapy. The detector consists of 480 individual electronic channels which allow parallel read-out of radiation induced currents at frequencies exceeding 10 Hz. Dose gradients in the direction of leaf movement of a multileaf collimator have been measured and a reconstruction method for individual leaf positions has been developed. The achieved reconstruction accuracy will be described.

  14. Properties of liquid ionization chambers at LDR brachytherapy dose rates.

    PubMed

    Johansson, B; Wickman, G; Holmström, T

    1995-04-01

    Properties such as sensitivity, general recombination and reproducibility of liquid-filled parallel-plate ionization chambers for dosimetry in low-dose-rate brachytherapy radiation fields have been evaluated. Two different dielectric liquids, isooctane (C8H(1)8) and tetramethylsilane (Si(CH3)4), have been used as sensitive media in chambers having a coin-shaped sensitive volume of 3 mm in diameter and 1 mm thickness. An electric field strength of 300 kV m-1 was found to be optimal with respect to sensitivity, leakage current and general recombination. At absorbed dose rates from 0.1-100 mGy min-1 the ionization charge measurements at an irradiation time of 1 min showed a reproducibility better than 1%, and a general recombination not exceeding 0.5%. The calibration--absorbed dose to water against ionization charge at a 60Co reference source--did not show any significant change over an observation time of one year for any of the chambers.

  15. Use of a liquid ionization chamber for stereotactic radiotherapy dosimetry

    NASA Astrophysics Data System (ADS)

    Wagner, A.; Crop, F.; Lacornerie, T.; Vandevelde, F.; Reynaert, N.

    2013-04-01

    Liquid ionization chambers (LICs) offer an interesting tool in the field of small beam dosimetry, allowing better spatial resolution and reduced perturbation effects. However, some aspects remain to be addressed, such as the higher recombination and the effects from the materials of the detector. Our aim was to investigate these issues and their impact. The first step was the evaluation of the recombination effects. Measurements were performed at different SSDs to vary the dose per pulse, and the collection efficiency was obtained. The BEAMnrc code was then used to model the Cyberknife head. Finally, the liquid ionization chamber itself was modelled using the EGSnrc-based code Cavity allowing the evaluation of the influence of the volume and the chamber materials. The liquid ionization charge collection efficiency is approximately 0.98 at 1.5 mGy pulse-1, the highest dose per pulse that we have measured. Its impact on the accuracy of output factors is less than half a per cent. The detector modelling showed a significant contribution from the graphite electrode, up to 6% for the 5 mm collimator. The dependence of the average electronic mass collision stopping power of iso-octane with beam collimation is negligible and thus has no influence on output factor measurements. Finally, the volume effect reaches 5% for the small 5 mm collimator and becomes much smaller (<0.5%) for diameters above 10 mm. LICs can effectively be used for small beam relative dosimetry as long as adequate correction factors are applied, especially for the electrode and volume effects.

  16. Comparison of ionization chamber efficiencies for activity measurements.

    PubMed

    Schrader, H; Svec, A

    2004-01-01

    The calibration of ionization chamber measuring systems in terms of activity is described. The energy-dependent efficiency curves of three chambers at the Bureau International des Poids et Mesures, the National Physical Laboratory and the Physikalisch-Technische Bundesanstalt are determined and compared using a fitting procedure for the experimental radionuclide efficiencies by the Microsoft (MS) EXCEL Solver program. An estimation of the uncertainty of the efficiency curves and the deviations of experimental and calculated radionuclide efficiencies are given. By this fitting method, discrepancies in the efficiency determination can be detected at a level of about one percent. Systematic deviations entering into the calculations either from emission probabilities per decay or from absolute activity standardization are discussed.

  17. Amplitude distribution of ionization jerks in ionization-chamber ASK-1 according long-term measurements

    NASA Astrophysics Data System (ADS)

    Timofeev, Vladislav

    2016-07-01

    As part of the Yakut complex systems by measuring the intensity of cosmic rays has a unique device spherical - ionization chamber ASK-1 with a lead screen thickness of 12 cm. The camera allows you to explore the physical characteristics of the so-called "ionization jerks " - sharp increases ionization current caused by the passage through the device much ionizing particles of cosmic origin. Due to a large increase in current nuclear cascade "showers", formed mainly by particles of cosmic rays in the camera screen. Over the entire period of observation (50 years old) camera ASK-1 was registered 59125 aftershocks. Their nature and properties still does not sufficiently studied, especially in medium and large amplitudes.

  18. Performance parameters of a liquid filled ionization chamber array.

    PubMed

    Poppe, B; Stelljes, T S; Looe, H K; Chofor, N; Harder, D; Willborn, K

    2013-08-01

    In this work, the properties of the two-dimensional liquid filled ionization chamber array Octavius 1000SRS (PTW-Freiburg, Germany) for use in clinical photon-beam dosimetry are investigated. Measurements were carried out at an Elekta Synergy and Siemens Primus accelerator. For measurements of stability, linearity, and saturation effects of the 1000SRS array a Semiflex 31013 ionization chamber (PTW-Freiburg, Germany) was used as a reference. The effective point of measurement was determined by TPR measurements of the array in comparison with a Roos chamber (type 31004, PTW-Freiburg, Germany). The response of the array with varying field size and depth of measurement was evaluated using a Semiflex 31010 ionization chamber as a reference. Output factor measurements were carried out with a Semiflex 31010 ionization chamber, a diode (type 60012, PTW-Freiburg, Germany), and the detector array under investigation. The dose response function for a single detector of the array was determined by measuring 1 cm wide slit-beam dose profiles and comparing them against diode-measured profiles. Theoretical aspects of the low pass properties and of the sampling frequency of the detector array were evaluated. Dose profiles measured with the array and the diode detector were compared, and an intensity modulated radiation therapy (IMRT) field was verified using the Gamma-Index method and the visualization of line dose profiles. The array showed a short and long term stability better than 0.1% and 0.2%, respectively. Fluctuations in linearity were found to be within ±0.2% for the vendor specified dose range. Saturation effects were found to be similar to those reported in other studies for liquid-filled ionization chambers. The detector's relative response varied with field size and depth of measurement, showing a small energy dependence accounting for maximum signal deviations of ±2.6% from the reference condition for the setup used. The σ-values of the Gaussian dose response

  19. Performance of electret ionization chambers in magnetic field.

    PubMed

    Kotrappa, P; Stieff, L R; Mengers, T F; Shull, R D

    2006-04-01

    Electret ionization chambers are widely used for measuring radon and radiation. The radiation measured includes alpha, beta, and gamma radiation. These detectors do not have any electronics and as such can be introduced into magnetic field regions. It is of interest to study the effect of magnetic fields on the performance of these detectors. Relative responses are measured with and without magnetic fields present. Quantitative responses are measured as the magnetic field is varied from 8 kA/m to 716 kA/m (100 to 9,000 gauss). No significant effect is observed for measuring alpha radiation and gamma radiation. However, a significant systematic effect is observed while measuring beta radiation from a 90Sr-Y source. Depending upon the field orientation, the relative response increased from 1.0 to 2.7 (vertical position) and decreased from 1.0 to 0.60 (horizontal position). This is explained as due to the setting up of a circular motion for the electrons by the magnetic field, which may increase or decrease the path length in air depending upon the experimental configuration. It is concluded that these ionization chambers can be used for measuring alpha (and hence radon) and gamma radiation in the range of magnetic fields studied. However, caution must be exercised if measuring beta radiation.

  20. Analytical form of current-voltage characteristic of parallel-plane, cylindrical and spherical ionization chambers with homogeneous ionization

    NASA Astrophysics Data System (ADS)

    Stoyanov, D. G.

    2007-11-01

    The elementary processes taking place in the formation of charged particles and their flow in parallel-plane, cylindrical and spherical geometry cases of ionization chamber are considered. On the basis of particles and charges balance a differential equation describing the distribution of current densities in the ionization chamber volume is obtained. As a result of the differential equation solution an analytical form of the current-voltage characteristic of an ionization chamber with homogeneous ionization is obtained. For the parallel-plane case comparision with experimental data is performed.

  1. Fast-neutron spectrometry using a ³He ionization chamber and digital pulse shape analysis.

    PubMed

    Chichester, D L; Johnson, J T; Seabury, E H

    2012-08-01

    Digital pulse shape analysis (dPSA) has been used with a Cuttler-Shalev type (3)He ionization chamber to measure the fast-neutron spectra of a deuterium-deuterium electronic neutron generator, a bare (252)Cf spontaneous fission neutron source, and of the transmitted fast neutron spectra of a (252)Cf source attenuated by water, graphite, liquid nitrogen, and magnesium. Rise-time dPSA has been employed using the common approach for analyzing n +(3)He→(1)H+(3)H ionization events and improved to account for wall-effect and pile-up events, increasing the fidelity of these measurements. Simulations have been performed of the different experimental arrangements and compared with the measurements, demonstrating general agreement between the dPSA-processed fast-neutron spectra and predictions. The fast-neutron resonance features of the attenuation cross sections of the attenuating materials are clearly visible within the resolution limits of the electronics used for the measurements, and the potential applications of high-resolution fast-neutron spectrometry for nuclear nonproliferation and safeguards measurements are discussed.

  2. An automated ionization chamber for secondary radioactivity standards.

    PubMed

    Fitzgerald, R

    2010-01-01

    I report on the operation and characterization of a new ionization chamber system, "AUTOIC", featuring a commercial digital electrometer and a commercial robotic sample changer. The relative accuracy of the electrometer was improved significantly beyond the manufacturer's specifications through an in-house calibration of the various ranges, applied via software. The measurement precision and repeatability of the system have been determined by measuring multiple samples of the same radionuclide over the span of two or three years. The linearity of the system was examined by following the decay of (99m)Tc, (99)Mo and (133)Xe sources for up to 19 half-lives and determining half-life values. All of these values agree with the accepted literature values, within their combined uncertainties. Published by Elsevier Ltd.

  3. A multiwire ionization chamber readout circuit using current mirrors

    NASA Astrophysics Data System (ADS)

    Rawnsley, W. R.; Smith, D.; Moskven, T.

    1997-01-01

    A circuit which utilizes current mirrors has been used to apply high voltage bias to the wires of a multiwire ionization chamber (MWIC) profile monitor while still allowing measurement of the beam-induced ion-electron currents collected on the wires. Bias voltages of up to 250 V have been used while wire currents over a range of 0.5 nA to 50 nA have been measured. The circuit is unipolar but can be designed for positive or negative bias. The mirrors also provide a current gain of 10, reducing the effects of transistor leakage and extending the useful range of the circuit to lower signal levels. A module containing 32 Wilson current mirrors has been constructed and is used with a MWIC monitor in TRIUMF's Parity experiment beamline.

  4. A well-type ionization chamber geometric correction factor

    NASA Astrophysics Data System (ADS)

    Meiler, R. J.; Sibata, C. H.; Ho, A. K.; de Souza, C.; Shin, K. H.

    1996-07-01

    To correct for the influence of source configuration on the measured activity of spherical and cylindrical brachytherapy sources, a geometric correction factor was calculated for the Standard Imaging HDR-1000 well-type ionization chamber. A Fortran program modelled each source as a lattice of point sources. Because of the cylindrical symmetry of the well chamber, it could be uniquely modelled by point detectors along the perimeter of the radial plane of the detection volume. Path lengths were calculated and attenuation factors were applied to each source - detector point combination individually. The total dose rate at each detection point was found through a Sievert summation of the point source contributions. For sources with identical activities, a correction factor of was calculated, equal to the ratio of the dose rate of the cylindrical source to that of the sphere. Experimental verification using a Nuclear Associates 67-809 series cylindrical source and an Amersham spherical source yielded a correction factor of .

  5. NIST Ionization Chamber "A" Sample-Height Corrections.

    PubMed

    Fitzgerald, Ryan

    2012-01-01

    For over 30 years scientists in the NIST radioactivity group have been using their pressurized ionization chamber "A" (PIC "A") to make measurements of radioactivity and radioactive half-lives. We now have evidence that some of those reported measurements were incorrect due to slippage of the source positioning ring over time. The temporal change in the holder caused an error in the source-height within the chamber, which was thought to be invariant. This unaccounted-for height change caused a change in the detector response and thus a relative error in measured activity on the order of 10(-5) to 10(-3) per year, depending on the radionuclide. The drifting detector response affected calibration factors and half-life determinations. After discovering the problem, we carried out historic research and new sensitivity tests. As a result, we have created a quantitative model of the effect and have used that model to estimate corrections to some of the past measurement results from PIC "A". In this paper we report the details and results of that model. Meanwhile, we have fixed the positioning ring and are recalibrating the detector using primary measurement methods and enhanced quality control measures.

  6. Polarity correction factor for flattening filter free photon beams in several cylindrical ionization chambers.

    PubMed

    Ogata, Toshiyuki; Uehara, Kazuyuki; Nakayama, Masao; Tsudou, Shinji; Masutani, Takashi; Okayama, Takanobu

    2016-07-01

    In this study, we aimed to compare the polarity correction factor in ionization chambers for flattening filter free (FFF) photon beams and flattening filter (FF) beams. Measurements were performed with both 6 and 10 MV FFF and FF beams. Five commercial ionization chambers were evaluated: PTW TN30013; IBA Dosimetry CC01, CC04, and CC13; and Exradin A12S. Except for the CC01 ionization chamber, the other four chambers showed less than a 0.3 % difference in the polarity effect between the FFF and the FF beams. The CC01 chamber showed a strong field-size-dependence, unlike the other chambers. The polarity effect for all chambers with FFF beams did not change with the dose rate. Except in the case of the CC01 chamber, the difference in the polarity effect between FFF and FF beams was not significant.

  7. Polarity effect in plane-parallel ionization chambers using air or a dielectric liquid as ionization medium

    SciTech Connect

    Wickman, G.; Holmstroem, T. )

    1992-05-01

    A plane-parallel ionization chamber having a sensitive volume of 2 mm{sup 3} and using the dielectric liquid tetramethylsilane as the sensitive medium instead of air is described. In the design of the chamber special attention was given to the factors that can cause unwanted currents in the cable, stem, or the chamber dielectric material. The chamber has been tested with respect to the polarity effect in regions of radiation fields where ordinary plane-parallel ionization chambers will often fail. These regions are the build-up region in photon fields, and the region close to the practical range for electrons where nonelectronic equilibrium is significant. Experimental results show that, despite the extremely small ionization volume in the liquid ionization chamber, the polarity effect never exceeds a few tenths of a percent in field positions where well-known commercially available chambers with much less spatial resolution designed for measurements in radiation therapy fields can show polarity effects of 5% to 30%. The origin of spurious currents and how they must be minimized in the design of either a liquid- or gas-filled ionization chamber is discussed.

  8. Evaluation of Gas-filled Ionization Chamber Method for Radon Measurement at Two Reference Facilities

    SciTech Connect

    Ishikawa, Tetsuo; Tokonami, Shinji; Kobayashi, Yosuke; Sorimachi, Atsuyuki; Yatabe, Yoshinori; Miyahara, Nobuyuki

    2008-08-07

    For quality assurance, gas-filled ionization chamber method was tested at two reference facilities for radon calibration: EML (USA) and PTB (Germany). Consequently, the radon concentrations estimated by the ionization chamber method were in good agreement with the reference radon concentrations provided by EML as well as PTB.

  9. Ionization chamber volume averaging effects in dynamic intensity modulated radiation therapy beams.

    PubMed

    Low, Daniel A; Parikh, Parag; Dempsey, James F; Wahab, Sasha; Huq, Saiful

    2003-07-01

    The commercial cylindrical ionization chamber ionization integration accuracy of dynamically moving fields was evaluated. The ionization chambers were exposed to long (14 cm), narrow (0.6, 1.0, 2.0, and 4.0 cm) 6 MV and 18 MV fields. Rather than rely on the linear accelerator to reproducibly scan across the chamber, the chambers were scanned beneath fixed portals. A water-equivalent phantom was constructed with cavities that matched the chambers and placed on a computer-controlled one-dimensional table. Computer-controlled electrometers were utilized in continuous charge integrate mode, with 10 samples of the charge, along with time stamps, acquired for each chamber location. A reference chamber was placed just beneath the linear accelerator jaws to adjust for variations in linear accelerator dose rate. The scan spatial resolution was selected to adequately sample regions of steep dose gradient and second spatial derivative (curvature). A fixed measurement in a 10 x 10 cm2 field was used to normalize the profiles to absolute chamber response. Three ionization chambers were tested, a microchamber (0.009 cm3), a Farmer chamber (0.6 cm3) and a waterproof scanning chamber (0.125 cm3). The larger chambers exhibited severe under-response at the small field's centers, but all of the chambers, independent of orientation, accurately integrated the ionization across the scanned portal. This indicates that the tested ionization chambers provide accurate integrated charges in regions of homogeneous dose regions. Partial integration (less than the field width plus the chamber length plus 2 cm), yielded integration errors of greater than 1% and 2% for 6 MV and 18 MV, respectively, with errors for the Farmer chamber of greater than 10% even for the 4 cm wide field.

  10. Investigation of electric field distribution on FAC-IR-300 ionization chamber

    NASA Astrophysics Data System (ADS)

    Mohammadi, S. M.; Tavakoli-Anbaran, H.; Zeinali, H. Z.

    2016-07-01

    One of the important parameters for establishing charge particle equilibrium (CPE) conditions of free-air ionization chamber is an electric field distribution. In this paper, electric field distribution inside the ionization chamber was investigated by finite element method. For this purpose, the effects of adding guard plate and guard strips on the electric field distribution in the ionization chamber were studied. it is necessary to apply a lead box around the ionization chamber body to avoid of scattered radiation effects on the ionization chamber operation, but the lead box changes the electric field distribution. In the following, the effect of lead box on the electric field distribution was studied. Finally, electric field distribution factor (kfield) was calculated by the simulation. The results of the simulation showed that presence of the guard plate and guard strips, and applying a suitable potential to lead box, a convergence of kfield to 1 was achieved.

  11. 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.

  12. Cross sections of electron capture and electron capture with ionization of argon atoms by fast 3He2+ ions at various impact parameters

    NASA Astrophysics Data System (ADS)

    Afrosimov, V. V.; Basalaev, A. A.; Panov, M. N.

    2017-01-01

    The absolute differential cross sections of scattering of fast particles formed in processes with capture of one or two electrons from Ar atoms have been measured for 6-keV He2+ ions in the interval of scattering angles within 0°-2.5°. The cross sections of electron capture and electron capture with ionization have been determined as functions of the impact parameter. The probabilities of these processes are compared to the distribution of electron density in various shells of target atoms. Applicability of the models of screened Coulomb interaction potentials to description of the scattering of recharged particles is assessed.

  13. Recombination factors for the cylindrical FC65-G ionization chamber in pulsed photon beams and the plane-parallel Roos ionization chamber in pulsed electron beams.

    PubMed

    Berg, Martin; Noerrevang, Ole

    2004-12-07

    The use of ionization chambers in linac radiotherapy dosimetry requires various corrections to the measured charges, one of these being the recombination correction. The recombination correction factor (k(s)) is generally estimated from the two-voltage analysis (TVA) for each beam quality. However, it is possible that the ionization chamber above some threshold polarizing voltage does not follow the accepted Boag theory very well. Secondly the TVA is time-consuming as the chamber needs to stabilize after each polarizing voltage change and since it must be performed for each beam quality. Another approach consists in using the fact that k(s) is predicted to depend linearly on dose per pulse by Boag theory: determining this relationship once and for all using a multi-voltage analysis (MVA), one also checks the range validity of the Boag theory for the chamber considered. This work presents a thorough analysis of k(s) dependence on dose per pulse of FC65-G (cylindrical) and Roos (plane-parallel) ionization chambers in pulsed photon and electron beams, respectively. Within the uncertainties, the recombination factors are found to be independent of beam quality, and no deviation from the Boag theory is observed within the tested range of polarizing voltages. Before adapting the equations given using the MVA other users should check that their ionization chambers show the same dose per pulse dependence using the TVA for a few beam qualities.

  14. Monte Carlo calculation of energy deposition in ionization chambers for tritium measurements

    NASA Astrophysics Data System (ADS)

    Zhilin, Chen; Shuming, Peng; Dan, Meng; Yuehong, He; Heyi, Wang

    2014-10-01

    Energy deposition in ionization chambers for tritium measurements has been theoretically studied using Monte Carlo code MCNP 5. The influence of many factors, including carrier gas, chamber size, wall materials and gas pressure, has been evaluated in the simulations. It is found that β rays emitted by tritium deposit much more energy into chambers flowing through with argon than with deuterium in them, as much as 2.7 times higher at pressure 100 Pa. As chamber size gets smaller, energy deposition decreases sharply. For an ionization chamber of 1 mL, β rays deposit less than 1% of their energy at pressure 100 Pa and only 84% even if gas pressure is as high as 100 kPa. It also indicates that gold plated ionization chamber results in the highest deposition ratio while aluminum one leads to the lowest. In addition, simulations were validated by comparison with experimental data. Results show that simulations agree well with experimental data.

  15. 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.

  16. [Absorbed dose measurement of photon beam with Farmer-type ionization chambers in Japanese dosimetry protocols].

    PubMed

    Fujisaki, Tatsuya; Hiraoka, Takeshi; Osawa, Atsushi; Nakajima, Masaru; Kuwabara, Akio; Yokoyama, Koichi; Saitoh, Hidetoshi; Tomaru, Teizo; Inada, Tetsuo

    2004-01-01

    The Japan Society of Medical Physics (JSMP) has published a new dosimetry protocol "JSMP-01" (standard dosimetry of absorbed dose in external beam radiotherapy) which conforms to the recommendations of the International Atomic Energy Agency (IAEA TRS-398) and the American Association of Physicists in Medicine (AAPM TG-51) protocols for the calibration of radiotherapy beams. Since the new protocol offers the physical data for the Famer-type ionization chambers of the various wall materials, the user can measure the absorbed dose at reference point (D(r)) using most of the commercially available Famer-type ionization chambers. In this paper, the six Famer-type ionization chambers of the various wall materials are examined for photon beam by two ways. To verify the JSMP-01 protocol as the first way, D(r) was cross-measured based on the JSMP-01 protocol using a Farmer-type ionization chamber of the acrylic wall material which is called "JARP-chamber" and the Farmer-type ionization chambers of the various wall materials, and compared. To compare the basic data in previous and new protocols as the second way, D(r) was measured based on the previous protocol (JSMP-86) and the JSMP-01 protocol using the Farmer-type ionization chambers of the various wall materials. Dose calculation was made using common exposure calibration factor for (60)Co gamma-rays (Nc) for each of the Farmer-type ionization chambers. Measurement was made with each ionization chamber for 6 and 10 MV photon beams in two facilities. D(r) were found to agree to that of JARP-chamber within about +/- 1% despite significant differences of ratio of calibration factor (k(D,X)) and beam quality conversion factor (k(Q)) for photon beams. The ratios JSMP-01/JSMP-86 of the reference dose were found to lie on between 0.999 and 1.004 for 6 MV and on between 0.999 and 1.005 for 10 MV depending upon the Farmer-type ionization chambers used. The largest discrepancies between the previous and new protocols arise from

  17. Experimental and Monte Carlo evaluation of an ionization chamber in a 60Co beam

    NASA Astrophysics Data System (ADS)

    Perini, A. P.; Neves, L. P.; Santos, W. S.; Caldas, L. V. E.

    2016-07-01

    Recently a special parallel-plate ionization chamber was developed and characterized at the Instituto de Pesquisas Energeticas e Nucleares. The operational tests presented results within the recommended limits. In order to determine the influence of some components of the ionization chamber on its response, Monte Carlo simulations were carried out. The experimental and simulation results pointed out that the dosimeter evaluated in the present work has favorable properties to be applied to 60Co dosimetry at calibration laboratories.

  18. Construction of an ionization chamber for the measurement of dose of low energy x-rays

    SciTech Connect

    Perez, Y. B. Alcantara; Jimenez, F. J. Ramirez

    2008-08-11

    We designed and constructed the prototype of an ionization chamber to measure the dose of an X-ray tube with Molybdenum anode. This X-ray tube is located in the Physics department at CINVESTAV and is used for medical physics purposes in the imaging area. The ionization chamber is designed to measure doses on biological samples exposed to X-rays and will be applied in radiation protection studies.

  19. On line high dose static position monitoring by ionization chamber detector for industrial gamma irradiators.

    PubMed

    Rodrigues, Ary A; Vieira, Jose M; Hamada, Margarida M

    2010-01-01

    A 1 cm(3) cylindrical ionization chamber was developed to measure high doses on line during the sample irradiation in static position, in a (60)Co industrial plant. The developed ionization chamber showed to be suitable for use as a dosimeter on line. A good linearity of the detector was found between the dose and the accumulated charge, independently of the different dose rates caused by absorbing materials.

  20. Pencil beam proton radiography using a multilayer ionization chamber

    NASA Astrophysics Data System (ADS)

    Farace, Paolo; Righetto, Roberto; Meijers, Arturs

    2016-06-01

    A pencil beam proton radiography (PR) method, using a commercial multilayer ionization chamber (MLIC) integrated with a treatment planning system (TPS) was developed. A Giraffe (IBA Dosimetry) MLIC (±0.5 mm accuracy) was used to obtain pencil beam PR by delivering spots uniformly positioned at a 5.0 mm distance in a 9  ×  9 square of spots. PRs of an electron-density (with tissue-equivalent inserts) phantom and a head phantom were acquired. The integral depth dose (IDD) curves of the delivered spots were computed by the TPS in a volume of water simulating the MLIC, and virtually added to the CT at the exit side of the phantoms. For each spot, measured and calculated IDD were overlapped in order to compute a map of range errors. On the head-phantom, the maximum dose from PR acquisition was estimated. Additionally, on the head phantom the impact on the range errors map was estimated in case of a 1 mm position misalignment. In the electron-density phantom, range errors were within 1 mm in the soft-tissue rods, but greater in the dense-rod. In the head-phantom the range errors were  -0.9  ±  2.7 mm on the whole map and within 1 mm in the brain area. On both phantoms greater errors were observed at inhomogeneity interfaces, due to sensitivity to small misalignment, and inaccurate TPS dose computation. The effect of the 1 mm misalignment was clearly visible on the range error map and produced an increased spread of range errors (-1.0  ±  3.8 mm on the whole map). The dose to the patient for such PR acquisitions would be acceptable as the maximum dose to the head phantom was  <2cGyE. By the described 2D method, allowing to discriminate misalignments, range verification can be performed in selected areas to implement an in vivo quality assurance program.

  1. Performances of a VLSI wide dynamic range current-to-frequency converter for strip ionization chambers

    NASA Astrophysics Data System (ADS)

    Bonazzola, G. C.; Cirio, R.; Donetti, M.; Marchetto, F.; Mazza, G.; Peroni, C.; Zampieri, A.

    1998-02-01

    In this paper we report on the design and test of a 14-channel VLSI chip to perform the current to frequency conversion for parallel plate strip ionization chambers. The chambers measure the intensity and the geometrical characteristics of a therapeutical beam.

  2. Quantitative ionization chamber alignment to a water surface: Performance of multiple chambers.

    PubMed

    Ververs, James D; McEwen, Malcolm R; Siebers, Jeffrey V

    2017-07-01

    The purpose of this study was to experimentally examine the reliability of the gradient chamber alignment point (gCAP) determination method for accurately identifying water surface location with a range of ionization chambers (ICs). Twelve cylindrical ICs were scanned from depth through a water surface into air using a customized high-accuracy scanning system which allows for accurate alignment of the IC with respect to the true water surface. Thirteen other cylindrical ICs and five parallel-plate ICs were scanned using a standard commercially available scanning system. The thirty different ICs used in this study represent 22 different IC models. Measurements were taken with different radiation field parameters such as incident photon beam energies and field sizes. The effects of scan direction and water surface tension were also investigated. The depth at which the gradient of the relative ionization was maximized and discontinuous, the gCAP, was found for each curve. Each measured gCAP depth was compared with the theoretically expected gCAP location, the depth at which the submerged IC outer radius (OR) coincides with the water surface. When scanning an IC from in water to air, the only parameter that affects the gCAP location is the IC OR. The gCAP location corresponds with the IC central axis positioned at a depth equal to the IC OR within the 0.1 mm measurement scan resolution for all eighteen ICs studied with the commercially available system. Using the customized scanning system, all but three ICs were identified exhibiting a gCAP within the scan resolution, with the other three within 0.25 mm of the expected location. This discrepancy was not observed in the same IC model when using the conventional scanning system. Altering the beam energy from 6 to 25 MV did not alter the gCAP location, nor did variations in the radiation field size or scan parameters. In-air IC response is proportional to the IC wall thickness. The water-to-air scanning method coupled

  3. Consistency in quality correction factors for ionization chamber dosimetry in scanned proton beam therapy.

    PubMed

    Sorriaux, Jefferson; Testa, Mauro; Paganetti, Harald; Bertrand, Damien; Lee, John Aldo; Palmans, Hugo; Vynckier, Stefaan; Sterpin, Edmond

    2017-09-01

    The IAEA TRS-398 code of practice details the reference conditions for reference dosimetry of proton beams using ionization chambers and the required beam quality correction factors (kQ ). Pencil beam scanning (PBS) systems cannot approximate reference conditions using a single spot. However, dose distributions requested in TRS-398 can be reproduced with PBS using a combination of spots. This study aims to demonstrate, using Monte Carlo (MC) simulations, that kQ factors computed/measured for broad beams can be used with scanned beams for similar reference dose distributions with no additional significant uncertainty. We consider the Alfonso formalism(13) usually employed for nonstandard photon beams. To approach reference conditions similar as IAEA TRS-398 and the associated dose distributions, PBS must combine many pencil beams with range or energy modulation and shaping techniques that differ from those used in passive systems (broad beams). In order to evaluate the impact of these differences on kQ factors, ionization chamber responses are computed with MC (Geant4 9.6) in three different proton beams, with their corresponding quality factors (Q), producing a 10 × 10 cm(2) field with a flat dose distribution for (a) a dedicated scanned pencil beam (Qpbs ), (b) a hypothetical proton source (Qhyp ), and (c) a double-scattering beam (Qds ). The tested ionization chamber cavities are a 2 × 2 × 0.2 mm³ air cavity, a Roos-type ionization chamber, and a Farmer-type ionization chamber. Ranges of Qpbs , Qhyp , and Qds are consistent within 0.4 mm. Flatnesses of dose distributions are better than 0.5%. Calculated kQpbs,Qhypfpbs,fref is 0.999 ± 0.002 for the air cavity and the Farmer-type ionization chamber and 1.001 ± 0.002 for the Roos-type ionization chamber. The quality correction factors kQpbs,Qdsfpbs,fref is 0.999 ± 0.002 for the Farmer-type and Roos-type ionization chambers and 1.001 ± 0.001 for the Roos-type ionization chamber. The Alfonso formalism was

  4. A new parallel-plate graphite ionization chamber as a 60Co gamma radiation reference instrument

    NASA Astrophysics Data System (ADS)

    Perini, Ana P.; Neves, Lucio P.; Fernández-Varea, José M.; Cassola, Vagner F.; Kramer, Richard; Khoury, Helen J.; Caldas, Linda V. E.

    2014-02-01

    The calibration procedure in radiotherapy treatments is very important and a sensitive task due to the high doses delivered to the patients. Generally, the air-kerma cavity standards for 60Co gamma rays are graphite cavity ionization chambers. In this work a new parallel-plate graphite ionization chamber was studied to analyze its potential use as a reference instrument. In order to evaluate its performance in 60Co beams, it was submitted to several characterization tests. Moreover, Monte Carlo simulations were undertaken using the EGSnrc code to study the influence of the chamber components on its response. The results obtained showed that this new ionization chamber presented a satisfactory performance in all evaluated tests.

  5. 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.

  6. The 3He Supply Problem

    SciTech Connect

    Kouzes, Richard T.

    2009-05-01

    One of the main uses for 3He is in gas proportional counters for neutron detection. Radiation portal monitors deployed for homeland security and non-proliferation use such detectors. Other uses of 3He are for research detectors, commercial instruments, well logging detectors, dilution refrigerators, for targets or cooling in nuclear research, and for basic research in condensed matter physics. The US supply of 3He comes almost entirely from the decay of tritium used in nuclear weapons by the US and Russia. A few other countries contribute a small amount to the world’s 3He supply. Due to the large increase in use of 3He for homeland security, the supply has dwindled, and can no longer meet the demand. This white paper reviews the problems of supply, utilization, and alternatives.

  7. Absolute dosimetry on a dynamically scanned sample for synchrotron radiotherapy using graphite calorimetry and ionization chambers

    NASA Astrophysics Data System (ADS)

    Lye, J. E.; Harty, P. D.; Butler, D. J.; Crosbie, J. C.; Livingstone, J.; Poole, C. M.; Ramanathan, G.; Wright, T.; Stevenson, A. W.

    2016-06-01

    The absolute dose delivered to a dynamically scanned sample in the Imaging and Medical Beamline (IMBL) on the Australian Synchrotron was measured with a graphite calorimeter anticipated to be established as a primary standard for synchrotron dosimetry. The calorimetry was compared to measurements using a free-air chamber (FAC), a PTW 31 014 Pinpoint ionization chamber, and a PTW 34 001 Roos ionization chamber. The IMBL beam height is limited to approximately 2 mm. To produce clinically useful beams of a few centimetres the beam must be scanned in the vertical direction. In practice it is the patient/detector that is scanned and the scanning velocity defines the dose that is delivered. The calorimeter, FAC, and Roos chamber measure the dose area product which is then converted to central axis dose with the scanned beam area derived from Monte Carlo (MC) simulations and film measurements. The Pinpoint chamber measures the central axis dose directly and does not require beam area measurements. The calorimeter and FAC measure dose from first principles. The calorimetry requires conversion of the measured absorbed dose to graphite to absorbed dose to water using MC calculations with the EGSnrc code. Air kerma measurements from the free air chamber were converted to absorbed dose to water using the AAPM TG-61 protocol. The two ionization chambers are secondary standards requiring calibration with kilovoltage x-ray tubes. The Roos and Pinpoint chambers were calibrated against the Australian primary standard for air kerma at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Agreement of order 2% or better was obtained between the calorimetry and ionization chambers. The FAC measured a dose 3-5% higher than the calorimetry, within the stated uncertainties.

  8. Absolute dosimetry on a dynamically scanned sample for synchrotron radiotherapy using graphite calorimetry and ionization chambers.

    PubMed

    Lye, J E; Harty, P D; Butler, D J; Crosbie, J C; Livingstone, J; Poole, C M; Ramanathan, G; Wright, T; Stevenson, A W

    2016-06-07

    The absolute dose delivered to a dynamically scanned sample in the Imaging and Medical Beamline (IMBL) on the Australian Synchrotron was measured with a graphite calorimeter anticipated to be established as a primary standard for synchrotron dosimetry. The calorimetry was compared to measurements using a free-air chamber (FAC), a PTW 31 014 Pinpoint ionization chamber, and a PTW 34 001 Roos ionization chamber. The IMBL beam height is limited to approximately 2 mm. To produce clinically useful beams of a few centimetres the beam must be scanned in the vertical direction. In practice it is the patient/detector that is scanned and the scanning velocity defines the dose that is delivered. The calorimeter, FAC, and Roos chamber measure the dose area product which is then converted to central axis dose with the scanned beam area derived from Monte Carlo (MC) simulations and film measurements. The Pinpoint chamber measures the central axis dose directly and does not require beam area measurements. The calorimeter and FAC measure dose from first principles. The calorimetry requires conversion of the measured absorbed dose to graphite to absorbed dose to water using MC calculations with the EGSnrc code. Air kerma measurements from the free air chamber were converted to absorbed dose to water using the AAPM TG-61 protocol. The two ionization chambers are secondary standards requiring calibration with kilovoltage x-ray tubes. The Roos and Pinpoint chambers were calibrated against the Australian primary standard for air kerma at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Agreement of order 2% or better was obtained between the calorimetry and ionization chambers. The FAC measured a dose 3-5% higher than the calorimetry, within the stated uncertainties.

  9. Theoretical study of energy deposition in ionization chambers for tritium measurements

    SciTech Connect

    Chen, Zhilin; Peng, Shuming; Meng, Dan; He, Yuehong; Wang, Heyi

    2013-10-15

    Energy deposition in ionization chambers has been theoretically studied for tritium measurements in gaseous form. A one-dimension model is introduced to establish the quantitative relationship between energy deposition rate and many factors, including carrier gas, gas pressure, wall material, chamber size, and gas temperature. Energy deposition rate has been calculated at pressure varying from 5 kPa to 500 kPa based on some approximations. It is found that energy deposition rate varies greatly for different parameters, especially at low gas pressure. For the same chamber, energy deposition rate in argon is much higher than in deuterium, as much as 70.7% higher at 5 kPa. Gold plated chamber gives highest energy deposition rate in the calculations while aluminum chamber results in the lowest. As chamber size gets smaller, β ray emitted by tritium will deposit less energy in the sensitive region of the chamber. For chambers flowing through with the same gas, energy deposition rate in a 10 L chamber is 23.9% higher than in a 0.05 L chamber at 5 kPa. Gas temperature also places slight influence on energy deposition rate, and 373 K will lead to 6.7% lower deposition rate than 233 K at 5 kPa. In addition, experiments have been performed to obtain energy deposition rate in a gold plated chamber, which show good accordance with theoretical calculations.

  10. Theoretical study of energy deposition in ionization chambers for tritium measurements

    NASA Astrophysics Data System (ADS)

    Chen, Zhilin; Peng, Shuming; Meng, Dan; He, Yuehong; Wang, Heyi

    2013-10-01

    Energy deposition in ionization chambers has been theoretically studied for tritium measurements in gaseous form. A one-dimension model is introduced to establish the quantitative relationship between energy deposition rate and many factors, including carrier gas, gas pressure, wall material, chamber size, and gas temperature. Energy deposition rate has been calculated at pressure varying from 5 kPa to 500 kPa based on some approximations. It is found that energy deposition rate varies greatly for different parameters, especially at low gas pressure. For the same chamber, energy deposition rate in argon is much higher than in deuterium, as much as 70.7% higher at 5 kPa. Gold plated chamber gives highest energy deposition rate in the calculations while aluminum chamber results in the lowest. As chamber size gets smaller, β ray emitted by tritium will deposit less energy in the sensitive region of the chamber. For chambers flowing through with the same gas, energy deposition rate in a 10 L chamber is 23.9% higher than in a 0.05 L chamber at 5 kPa. Gas temperature also places slight influence on energy deposition rate, and 373 K will lead to 6.7% lower deposition rate than 233 K at 5 kPa. In addition, experiments have been performed to obtain energy deposition rate in a gold plated chamber, which show good accordance with theoretical calculations.

  11. Current saturation in free-air ionization chambers with chopped synchrotron radiation

    PubMed Central

    Nariyama, Nobuteru

    2013-01-01

    Saturation curves for free-air ionization chambers with electrode gap widths of 4.2, 8.4 and 18 mm were obtained for 10 and 15 keV undulator synchrotron radiation thinned with a 230 Hz rotating-disk chopper. Ion recombination in free-air ionization chambers was found to be inversely proportional to the applied electric field, and an expression that satisfactorily reproduced the ion-recombination rate is determined. A comparison of the expressions for continuous and pulsed X-rays revealed that chopped high-intensity X-rays require a higher voltage to attain saturation when the product of the pulse width and electric field exceeds a value that depends on the X-ray energy. This behaviour was observed explicitly for 10 keV X-rays in measurements with the ionization chamber placed before and after the chopper. PMID:23955032

  12. Initial test results of an ionization chamber shower detector for a LHC luminosity monitor

    SciTech Connect

    Datte, P.; Beche, J.-F.; Haguenauer, M.; Manfredi, P.F.; Manghisoni, M.; Millaud, J.; Placidi, M.; Ratti, L.; Riot, V.; Schmickler, H.; Speziali, V.; Turner, W.

    2002-11-05

    A novel, segmented, multi-gap, pressurized gas ionization chamber is being developed for optimization of the luminosity of the LHC. The ionization chambers are to be installed in the front quadrupole and zero degree neutral particle absorbers in the high luminosity IRs and sample the energy deposited near the maxima of the hadronic/electromagnetic showers in these absorbers. The ionization chambers are instrumented with low noise, fast, pulse shaping electronics to be capable of resolving individual bunch crossings at 40 MHz. In this paper we report the initial results of our second test of this instrumentation in an SPS external proton beam. Single 300 GeV protons are used to simulate the hadronic/electromagnetic shower produced by the forward collision products from the interaction regions of the LHC. The capability of instrumentations to measure the luminosity of individual bunches in a 40 MHz bunch train is demonstrated.

  13. Development of a 3He-hydraulic actuator for spin pump in superfluid 3He-A1

    NASA Astrophysics Data System (ADS)

    Yamaguchi, A.; Wada, M.; Tanaka, H.; Motoyama, G.; Sumiyama, A.; Aoki, Y.; Okuda, Y.; Murakawa, S.; Karaki, Y.; Kubota, M.; Kojima, H.

    2012-12-01

    The superfluid 3He A1 phase contains a spin-polarized condensate. This property allows novel superfluid spin current experiments. In the mechano-spin effect of the A1 phase a mechanically applied pressure gradient and a superleak-spin filter enable to directly boost spin polarization of 3He in a small chamber. Using a flexible membrane as an electrostatically actuated pump, we carried out such experiments and observed 50% enhancement of spin density. Here we report on a new 3He-hydraulic actuator for achieving greater enhancement of spin density. The actuator consists of two liquid 3He chambers located at a 4.2 K plate and in the interior of the cell. The pressure in the 4.2 K chamber is heater-controlled and it transmits a force onto a membrane in the cell. The motion of the membrane induces spin-polarized current into an accumulation chamber.

  14. Dosimetric characterization of a large area pixel-segmented ionization chamber.

    PubMed

    Amerio, S; Boriano, A; Bourhaleb, F; Cirio, R; Donetti, M; Fidanzio, A; Garelli, E; Giordanengo, S; Madon, E; Marchetto, F; Nastasi, U; Peroni, C; Piermattei, A; Sanz Freire, C J; Sardo, A; Trevisiol, E

    2004-02-01

    A pixel-segmented ionization chamber has been designed and built by Torino University and INFN. The detector features a 24 x 24 cm2 active area divided in 1024 independent cylindrical ionization chambers and can be read out in 500 micros without introducing dead time; the digital charge quantum can be adjusted between 100 fC and 800 fC. The sensitive volume of each single ionization chamber is 0.07 cm3. The purpose of the detector is to ease the two-dimensional (2D) verifications of fields with complex shapes and large gradients. The detector was characterized in a PMMA phantom using 60Co and 6 MV x-ray photon beams. It has shown good signal linearity with respect to dose and dose rate to water. The average sensitivity of a single ionization chamber was 2.1 nC/Gy, constant within 0.5% over one month of daily measurements. Charge collection efficiency was 0.985 at the operating polarization voltage of 400 V and 3.5 Gy/min dose rate. Tissue maximum ratio and output factor have been compared with a Farmer ionization chamber and were found in good agreement. The dose profiles have been compared with the ones obtained with an ionization chamber in water phantom for the field sizes supplied by a 3D-Line dynamic multileaf collimator. These results show that this detector can be used for 2D dosimetry of x-ray photon beams, supplying a good spatial resolution and sensibly reducing the time spent in dosimetric verification of complex radiation fields.

  15. Nuclear signal simulation applied to gas ionizing chambers

    SciTech Connect

    Coulon, Romain; Dumazert, Jonathan

    2015-07-01

    Particle transport codes used in detector simulation allow the calculation of the energy deposited by charged particles produced following an interaction. The pulses temporal shaping is more and more used in nuclear measurement into pulse shape analysis techniques. A model is proposed in this paper to simulate the pulse temporal shaping and the associated noise level thanks to the output track file PTRAC provides by Monte-Carlo particle transport codes. The model has been dedicated to ion chambers and more especially for High Pressure Xenon chambers HPXe where the pulse shape analysis can resolve some issues regarding with this technology as the ballistic deficit phenomenon. The model is fully described and an example is presented as a validation of such full detector simulation. (authors)

  16. IEC-^3He Breeder for D-^3He Satellite Systems.

    NASA Astrophysics Data System (ADS)

    Chacon, L.; Miley, G. H.

    1996-11-01

    D-^3He fusion minimizes neutrons and maximizes charged fusion products, enabling increased energy recovery efficiency by direct conversion. However, scarce ^3He terrestrial resources have deterred R&D on this alternative. Here, we explore ^3He production through Inertial Electrostatic Confinement^1 (IEC) D-breeders, which supply ^3He to FRC D-^3He satellite reactors.^2 Favorable features for the IEC breeder include simplicity, low cost, easy extraction of fusion products, and compatibility with direct conversion. The breeder-satellite system energy balance is analyzed taking the net energy gain of the overall system, Q_N, as the figure of merit. Breeding is applicable for systems where the satellite Q-value, Q_S, > the breeder Q-value, Q_B. For improved performance, i.e., for high Q_N, QS >= QB >> 1 is needed; however, lower QB values (typical of the IEC) are permissible and still offer sufficient Q_N. An economic study determined breeding produces ^3He at a cost comparable to lunar ^3He, already shown to lead to competitive power.^3 The cost of electricity (COE) for the breeder-satellite complex was compared with the ARTEMIS COE,^4 using lunar ^3He fuel: assuming one satellite (1000 MWe)/breeder (170 MWe), the ratio of the breeding system COE to the lunar mining base COE is ~ 1.2. However, economic breeding is driven by large IEC breeder powers, i.e., increased ^3He breeding rates. Thus, the COE ratio approaches unity with two or three satellites/breeder, requiring increased breeder size and power (340 MWe for 2 satellites, 510 MWe for 3 satellites). Such systems potentially provide a ``bridge'' to a future lunar ^3He economy. 1. G.H. Miley et al., Dense Z-pinches, AIP Conf. 299, AIP Press, 675-689 (1994). 2. G.H. Miley, Nucl. Instrum. Methods, A271, 197-202 (1988). 3. L.J. Wittenberg et al., Fusion Technol., 10, 167-178 (1986). 4. H. Momota et al., Fusion Technol., 21, 2307-2323 (1992).

  17. High resolution gas ionization chamber in proportional mode for low energy applications

    NASA Astrophysics Data System (ADS)

    Müller, Arnold Milenko; Döbeli, Max; Synal, Hans-Arno

    2017-09-01

    The operation of the ETH gas ionization detector as a proportional chamber, where a secondary ionization avalanche is initiated between the Frisch grid and anode, was investigated for ions covering the mass range from H to 127I. By amplifying the detector electron signal through secondary ionization, the limitations due to the sensitivity of the detector electronics are minimized. It could be demonstrated that in the energy range of a few hundreds of keV and below a proportional chamber clearly outperforms a conventionally used gas ionization detector. Protons below 10 keV were measured with a resolution better than 1.4 keV and a good linearity of the particle energy and detector signal was found in the energy range between 50 and 1000 keV. At higher energies almost no difference in resolution for the two operation modes could be found.

  18. An improved leakage current compensation technique for a 4πγ ionization chamber system

    NASA Astrophysics Data System (ADS)

    Hino, Y.; Kawada, Y.; Nazaroh

    1996-02-01

    A current integration method using a small capacitor is most commonly employed for precise measurements of small currents from 4πγ ionization chambers for the secondary standardization of radionuclides. An improved technique has been developed for eliminating the possible effect due to the electrical leakage and/or current loss across the feedback capacitor used in the integration of the ionization current. This method is based upon charge integration from a fixed negative level of potential to nearly the same level of positive potential via the zero point. The validity of this method is demonstrated for some typical applications of 4πγ ionization chamber systems. This technique can contribute to the improvement of accuracy and to the extension of the intensity range of radioactive source in 4πγ ionization measurement.

  19. 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.

  20. Update of NIST half-life results corrected for ionization chamber source-holder instability.

    PubMed

    Unterweger, M P; Fitzgerald, R

    2014-05-01

    As reported at the ICRM 2011, it was discovered that the source holder used for calibrations in the NIST 4πγ ionization chamber (IC) was not stable. This has affected a large number of half-life measurement results previously reported and used in compilations of nuclear data. Corrections have been made on all of the half-life data based on the assumption that the changes to the ionization chamber response were gradual. The corrections are energy dependent and therefore radionuclide specific. This presentation will review our results and present the recommended changes in half-life values and/or uncertainties. © 2013 Published by Elsevier Ltd.

  1. Design of ionization chambers for use in teaching x-ray dosimetry

    NASA Astrophysics Data System (ADS)

    Ross, Joseph

    Ionization chambers are one of the most commonly used radiation detectors in radiation dosimetry. In this project, nine ionization chambers were constructed for use in teaching radiation dosimetry to students of health physics, medical physics, nuclear engineering, and related disciplines. The components of these detectors such as detector wall composition, type of electrode, type of leakage current guard ring, fill gas pressure, and interior conducting material differ in a systematic way to show that various parameters of ionization chamber design can affect the response of the detectors. Each of these variables was investigated using an 80 keV x-ray machine to determine detector response in terms of absorbed dose, HVL, polarity, and operating voltage. Of the components studied, wall thickness and composition was found to be the most sensitive variable. The pressure inside the chamber did have a significant effect on the amount of charge collected and the absorbed dose. The leakage current guard ring was not a critical component for this ionization chamber design.

  2. Pulse mode readout techniques for use with non-gridded industrial ionization chambers

    SciTech Connect

    Popov, Vladimir E.; Degtiarenko, Pavel V.

    2011-10-01

    Highly sensitive readout technique for precision long-term radiation measurements has been developed and tested in the Radiation Control Department at Jefferson Lab. The new electronics design is used to retrieve ionization data in a pulse mode. The dedicated data acquisition system works with M=Audio Audiophile 192 High-Definition 24-bit/192 kHz audio cards, taking data in continuous waveform recording mode. The on-line data processing algorithms extract signals of the ionization events from the data flow and measure the ionization value for each event. Two different ion chambers are evaluated. The first is a Reuter-Stokes Argon-filled (at 25 atm) High Pressure Ionization Chamber (HPIC), commonly used as a detector part in many GE Reuter-Stokes instruments of the RSS series. The second is a VacuTec Model 70181, 5 atm Xenon-filled ionization chamber. Results for both chambers indicate that the techniques allow using industrial ICs for high sensitivity and precision long-term radiation measurements, while at the same time providing information about spectral characteristics of the radiation fields.

  3. 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.

  4. Assessment of small volume ionization chambers as reference dosimeters in high-energy photon beams

    NASA Astrophysics Data System (ADS)

    Le Roy, M.; de Carlan, L.; Delaunay, F.; Donois, M.; Fournier, P.; Ostrowsky, A.; Vouillaume, A.; Bordy, J. M.

    2011-09-01

    LNE-LNHB is involved in a European project aiming at establishing absorbed dose-to-water standards for photon-radiation fields down to 2 × 2 cm2. This requires the calibration of reference ionization chambers of small volume. Twenty-four ionization chambers of eight different types with volume ranging from 0.007 to 0.057 cm3 were tested in a 60Co beam. For each chamber, two major characteristics were investigated: (1) the stability of the measured current as a function of the irradiation time under continuous irradiation. At LNE-LNHB, the variation of the current should be less than ±0.1% in comparison with its first value (over a 16 h irradiation time); (2) the variation of the ionization current with the applied polarizing voltage and polarity. Leakage currents were also measured. Results show that (1) every tested PTW (31015, 31016 and 31014) and Exradin A1SL chambers demonstrate a satisfying stability under irradiation. Other types of chambers have a stability complying with the stability criterion for some or none of them. (2) IBA CC01, IBA CC04 and Exradin A1SL show a proper response as a function of applied voltage for both polarities. PTW, Exradin A14SL and Exradin A16 do not. Only three types of chambers were deemed suitable as reference chambers according to LNE-LNHB requirements and specifications from McEwen (2010 Med. Phys. 37 2179-93): Exradin A1SL chambers (3/3), IBA CC04 (2/3) and IBA CC01 (1/3). The Exradin A1SL type with an applied polarizing voltage of 150 V was chosen as an LNE-LNHB reference chamber type in 2 × 2 cm2 radiation fields.

  5. Development of 10B-Based 3He Replacement Neutron Detectors

    NASA Astrophysics Data System (ADS)

    King, Michael J.; Gozani, Tsahi; Hilliard, Donald B.

    2011-12-01

    Radiation portal monitors (RPM) are currently deployed at United States border crossings to passively inspect vehicles and persons for any emission of neutrons and/or gamma rays, which may indicate the presence of unshielded nuclear materials. The RPM module contains an organic scintillator with 3He proportional counters to detect gamma rays and thermalized neutrons, respectively. The supply of 3He is rapidly dwindling, requiring alternative detectors to provide the same function and performance. Our alternative approach is one consisting of a thinly-coated 10B flat-panel ionization chamber neutron detector that can be deployed as a direct drop-in replacement for current RPM 3He detectors. The uniqueness of our approach in providing a large-area detector is in the simplicity of construction, scalability of the unit cell detector, ease of adaptability to a variety of applications and low cost. Currently, Rapiscan Laboratories and Helicon Thin Film Systems have designed and developed an operational 100 cm2 multi-layer prototype 10BB-based ionization chamber.

  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. Absorbed dose dependence of the correction factors for ionization chamber cable irradiation effects.

    PubMed

    Campos, L L; Caldas, L V

    1991-03-01

    A simple method was developed, for possible use by hospital physicists, to evaluate the irradiation effects on cables and connectors during large-radiation-field dosimetry with ionization chambers and to determine correction factors for the used system or geometry. This method was based on the absorbed dose dependence of the correction factor.

  8. Development of a pixel ionization chamber for beam monitor in proton therapy

    NASA Astrophysics Data System (ADS)

    La Rosa, A.; Garella, M. A.; Attili, A.; Bourhaleb, F.; Cirio, R.; Donetti, M.; Giordanengo, S.; Givehchi, N.; Marchetto, F.; Mazza, G.; Meyroneinc, S.; Pecka, A.; Peroni, C.; Pittà, G.

    2007-03-01

    We have developed a detector to be used as monitor for proton therapy beam lines. The detector is a 2-D parallel plate ionization chamber, with the anode segmented in 1024 square pixels arranged in a 32×32 matrix. The detector characterization is presented.

  9. a Solution for Dosimetry and Quality Assurance in Imrt and Hadrontherapy:. the Pixel Ionization Chamber

    NASA Astrophysics Data System (ADS)

    Amerio, S.; Coda, S.; Nastasi, U.; Belletti, S.; Ghedi, B.; Boriano, A.; Cirio, R.; Luparia, A.; Marchetto, F.; Peroni, C.; Sanz Freire, C. J.; Donetti, M.; Madon, E.; Trevisiol, E.; Urgesi, A.

    2002-11-01

    The new radiotherapy techniques require new detectors to monitor and measure the clinical field. The Intensity Modulated Radiation Therapy (IMRT) techniques like step and shoot, sliding window, dynamic wedge or scanning beam add the time variable to the treatment field. In this case the water phantom with a single ionization chamber moving inside the field needs very long measurement time. Linear arrays of ionization chambers or diodes measure the field only along a line. 2D detectors like radiographic or gafchromic film are not suitable to be used as on line detectors. We have developed, built and tested an ionization chamber segmented in pixels that measure the dose in a plane at several points. Every channel has a dedicated electronic chain that digitizes the collected charge and data from all the channels are sent to the computer that performs the data acquisition. One read out cycle is very fast allowing to measure in real time the fluency and the shape of the field. The chamber can be used in two different ways, as monitor chamber and as relative dosemeter. A description of the detector, the electronics, and test results with both photon and hadron beams will be reported.

  10. 3He on preplated graphite

    NASA Astrophysics Data System (ADS)

    Gordillo, M. C.; Boronat, J.

    2016-10-01

    By using the diffusion Monte Carlo method, we obtained the full phase diagram of 3He on top of graphite preplated with a solid layer of 4He. All the 4He atoms of the substrate were explicitly considered and allowed to move during the simulation. We found that the ground state is a liquid of density 0.007 ±0.001 Å-2, in good agreement with available experimental data. This is significantly different from the case of 3He on clean graphite, in which both theory and experiment agree on the existence of a gas-liquid transition at low densities. Upon an increase in 3He density, we predict a first-order phase transition between a dense liquid and a registered 7/12 phase, the 4/7 phase being found metastable in our calculations. At larger second-layer densities, a final transition is produced to an incommensurate triangular phase.

  11. 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.

  12. 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.

  13. Development for the study of a Cross Sectional Measurement of 3He-3He Solar Reaction

    NASA Astrophysics Data System (ADS)

    Kudomi, N.; Itahashi, T.; Kume, K.; Takahisa, K.; Yoshida, S.; Ejiri, H.; Toki, H.; Nagai, Y.; Komori, M.; Ohsumi, H.

    2003-04-01

    The design and construction of a low-energy, high current accelerator for the study of fusion reactions are reported. The accelerator can produce an intense beam of 3He1+ and 3He2+ ions of more than 1mA. It enables us to provide extremely fine cross-section measurements of the 3He(3He,2p)α at 40 to 50 keV. A detection efficiency for proposed detector assembly of ΔE-E counter telescope is simulated with GEANT program and it expects a detection efficiency about 10% for the two proton coincidence for 3He+3He→2p+α. Deuter contaminations in target chamber is estimated to be less than ppm by quadrupole mass spectrometer. To further develop the study of nuclear astrophysics, a plasma target as an experimental apparatus for electron screening effects is proposed. Some parts of such apparatus are assembled. A combination ECR plasma target with a high current ion generator is under construction. The facility will be installed in the underground laboratory, Oto Cosmo Observatory. The facility has just started to operate and, as explained here, it already has been used for the double beta decay measurement and dark matter search programs. The present status of the experimental apparatus and its development are described.

  14. Free-air ionization chamber, FAC-IR-300, designed for medium energy X-ray dosimetry

    NASA Astrophysics Data System (ADS)

    Mohammadi, S. M.; Tavakoli-Anbaran, H.; Zeinali, H. Z.

    2017-01-01

    The primary standard for X-ray photons is based on parallel-plate free-air ionization chamber (FAC). Therefore, the Atomic Energy Organization of Iran (AEOI) is tried to design and build the free-air ionization chamber, FAC-IR-300, for low and medium energy X-ray dosimetry. The main aim of the present work is to investigate specification of the FAC-IR-300 ionization chamber and design it. FAC-IR-300 dosimeter is composed of two parallel plates, a high voltage (HV) plate and a collector plate, along with a guard electrode that surrounds the collector plate. The guard plate and the collector were separated by an air gap. For obtaining uniformity in the electric field distribution, a group of guard strips was used around the ionization chamber. These characterizations involve determining the exact dimensions of the ionization chamber by using Monte Carlo simulation and introducing correction factors.

  15. 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.

  16. The central electrode correction factor for high-Z electrodes in small ionization chambers.

    PubMed

    Muir, B R; Rogers, D W O

    2011-02-01

    Recent Monte Carlo calculations of beam quality conversion factors for ion chambers that use high-Z electrodes [B. R. Muir and D. W. O. Rogers, Med. Phys. 37, 5939-5950 (2010)] have shown large deviations of kQ values from values calculated using the same techniques as the TG-51 and TRS-398 protocols. This report investigates the central electrode correction factor, Pcel, for these chambers. Ionization chambers are modeled and Pcel is calculated using the EGSnrc user code egs_chamber for three cases: in photon and electron beams under reference conditions; as a function of distance from an iridium-192 point source in a water phantom; and as a function of depth in a water phantom on which a 200 kVp x-ray source or 6 MV beam is incident. In photon beams, differences of up to 3% between Pcel calculations for a chamber with a high-Z electrode and those used by TG-51 for a 1 mm diameter aluminum electrode are observed. The central electrode correction factor for a given value of the beam quality specifier is different depending on the amount of filtration of the photon beam. However, in an unfiltered 6 MV beam, Pcel, varies by only 0.3% for a chamber with a high-Z electrode as the depth is varied from 1 to 20 cm in water. The difference between Pcel calculations for chambers with high-Z electrodes and TG-51 values for a chamber with an aluminum electrode is up to 0.45% in electron beams. The central electrode correction, which is roughly proportional to the chambers absorbed dose sensitivity, is found to be large and variable as a function of distance for chambers with high-Z and aluminum electrodes in low-energy photon fields. In this work, ionization chambers that employ high-Z electrodes have been shown to be problematic in various situations. For beam quality conversion factors, the ratio of Pcel in a beam quality Q to that in a Co-60 beam is required; for some chambers, kQ is significantly different from current dosimetry protocol values because of central

  17. Influence of ambient humidity on the current delivered by air-vented ionization chambers revisited

    NASA Astrophysics Data System (ADS)

    Poirier, Aurélie; Douysset, Guilhem

    2006-10-01

    The influence of ambient humidity on the current delivered by a vented ionization chamber has been re-investigated. A Nucletron 077.091 well-type chamber together with a 192Ir HDR brachytherapy source was enclosed in a climatic test chamber and the current was recorded for various humidity values. Great care has been taken for the design of the experimental setup in order to obtain reliable measurements of currents and humidity values inside the chamber active volume. A ±0.35% linear variation of the measured currents has been observed over a common range of humidities. This result is larger than the expected variation. No formal explanation of such a discrepancy has been found yet, however the present results could lead to a set of recommendations.

  18. SU-E-T-623: Polarity Effects for Small Volume Ionization Chambers in Cobalt-60 Beams

    SciTech Connect

    Xu, Y; Bhatnagar, J; Huq, M Saiful

    2015-06-15

    Purpose: To investigate the polarity effects for small volume ionization chambers in {sup 60}Co gamma-ray beams using the Leksell Gamma Knife Perfexion. Methods: Measurements were made for 7 small volume ionization chambers (a PTW 31016, an Exradin A14, 2 Capintec PR0-5P, and 3 Exradin A16) using a PTW UNIDOSwebline Universal Dosemeter and an ELEKTA solid water phantom with proper inserts. For each ion chamber, the temperature/pressure corrected electric charge readings were obtained for 16 voltage values (±50V, ±100V, ±200V, ±300V, ±400V, ±500V, ±600V, ±700V). For each voltage, a five-minute leakage charge reading and a series of 2-minute readings were continuously taken during irradiation until 5 stable signals (less than 0.05% variation) were obtained. The average of the 5 reading was then used for the calculation of the polarity corrections at the voltage and for generating the saturation curves. Results: The polarity effects are more pronounced at high or low voltages than at the medium voltages for all chambers studied. The voltage dependence of the 3 Exradin A16 chambers is similar in shape. The polarity corrections for the Exradin A16 chambers changes rapidly from about 1 at 500V to about 0.98 at 700V. The polarity corrections for the 7 ion chambers at 300V are in the range from 0.9925 (for the PTW31016) to 1.0035 (for an Exradin A16). Conclusion: The polarity corrections for certain micro-chambers are large even at normal operating voltage.

  19. Calculation of correction factors for ionization chamber measurements with small fields in low-density media

    NASA Astrophysics Data System (ADS)

    Pisaturo, O.; Pachoud, M.; Bochud, F. O.; Moeckli, R.

    2012-07-01

    The quantity of interest for high-energy photon beam therapy recommended by most dosimetric protocols is the absorbed dose to water. Thus, ionization chambers are calibrated in absorbed dose to water, which is the same quantity as what is calculated by most treatment planning systems (TPS). However, when measurements are performed in a low-density medium, the presence of the ionization chamber generates a perturbation at the level of the secondary particle range. Therefore, the measured quantity is close to the absorbed dose to a volume of water equivalent to the chamber volume. This quantity is not equivalent to the dose calculated by a TPS, which is the absorbed dose to an infinitesimally small volume of water. This phenomenon can lead to an overestimation of the absorbed dose measured with an ionization chamber of up to 40% in extreme cases. In this paper, we propose a method to calculate correction factors based on the Monte Carlo simulations. These correction factors are obtained by the ratio of the absorbed dose to water in a low-density medium □Dw,Q,V1low averaged over a scoring volume V1 for a geometry where V1 is filled with the low-density medium and the absorbed dose to water □Dw,QV2low averaged over a volume V2 for a geometry where V2 is filled with water. In the Monte Carlo simulations, □Dw,QV2low is obtained by replacing the volume of the ionization chamber by an equivalent volume of water, according to the definition of the absorbed dose to water. The method is validated in two different configurations which allowed us to study the behavior of this correction factor as a function of depth in phantom, photon beam energy, phantom density and field size.

  20. Towards reference dosimetry for the MR-linac: magnetic field correction of the ionization chamber reading

    NASA Astrophysics Data System (ADS)

    Smit, K.; van Asselen, B.; Kok, J. G. M.; Aalbers, A. H. L.; Lagendijk, J. J. W.; Raaymakers, B. W.

    2013-09-01

    In the UMC Utrecht a prototype MR-linac has been installed. The system consists of a 6 MV Elekta (Crawley, UK) linear accelerator and a 1.5 T Philips (Best, The Netherlands) Achieva MRI system. This paper investigates the feasibility to correct the ionization chamber reading for the magnetic field within the dosimetry calibration method described by Almond et al (1999 Med. Phys. 26 1847-70). Firstly, the feasibility of using an ionization chamber in an MR-linac was assessed by investigating possible influences of the magnetic field on NE2571 Farmer-type ionization chamber characteristics: linearity, repeatability, orientation in the magnetic field; and AAPM TG51 correction factor for voltage polarity and ion recombination. We found that these AAPM correction factors for the NE2571 chamber were not influenced by the magnetic field. Secondly, the influence of the permanent 1.5 T magnetic field on the NE2571 chamber reading was quantified. The reading is influenced by the magnetic field; therefore, a correction factor has been added. For the standardized setup used in this paper, the NE2571 chamber reading increases by 4.9% (± 0.2%) due to the transverse 1.5 T magnetic field. Dosimetry measurements in an MR-linac are feasible, if a setup-specific magnetic field correction factor (P1.5 T) for the charge reading is introduced. For the setup investigated in this paper, the P1.5 T has a value of 0.953.

  1. Towards reference dosimetry for the MR-linac: magnetic field correction of the ionization chamber reading.

    PubMed

    Smit, K; van Asselen, B; Kok, J G M; Aalbers, A H L; Lagendijk, J J W; Raaymakers, B W

    2013-09-07

    In the UMC Utrecht a prototype MR-linac has been installed. The system consists of a 6 MV Elekta (Crawley, UK) linear accelerator and a 1.5 T Philips (Best, The Netherlands) Achieva MRI system. This paper investigates the feasibility to correct the ionization chamber reading for the magnetic field within the dosimetry calibration method described by Almond et al (1999 Med. Phys. 26 1847-70). Firstly, the feasibility of using an ionization chamber in an MR-linac was assessed by investigating possible influences of the magnetic field on NE2571 Farmer-type ionization chamber characteristics: linearity, repeatability, orientation in the magnetic field; and AAPM TG51 correction factor for voltage polarity and ion recombination. We found that these AAPM correction factors for the NE2571 chamber were not influenced by the magnetic field. Secondly, the influence of the permanent 1.5 T magnetic field on the NE2571 chamber reading was quantified. The reading is influenced by the magnetic field; therefore, a correction factor has been added. For the standardized setup used in this paper, the NE2571 chamber reading increases by 4.9% (± 0.2%) due to the transverse 1.5 T magnetic field. Dosimetry measurements in an MR-linac are feasible, if a setup-specific magnetic field correction factor (P1.5 T) for the charge reading is introduced. For the setup investigated in this paper, the P1.5 T has a value of 0.953.

  2. 4He/ 3He thermochronometry

    NASA Astrophysics Data System (ADS)

    Shuster, David L.; Farley, Kenneth A.

    2004-01-01

    Using classical diffusion theory, we present a mathematical technique for the determination of 4He concentration profiles in minerals. This approach should prove useful for constraining the low-temperature cooling histories of individual samples and for correcting (U-Th)/He ages for partial diffusive loss. The calculation assumes that the mineral of interest contains an artificially produced and uniform distribution of 3He obtained by proton irradiation [Shuster et al., Earth Planet. Sci. Lett. 217 (2004) 19-32]. In minerals devoid of natural helium, this isotope allows measurement of He diffusion coefficients; in minerals with measurable radiogenic He, it permits determination of 4He profiles arising during ingrowth and diffusion in nature. The 4He profile can be extracted from stepwise degassing experiments in which the 4He/ 3He ratio is measured. The evolution of the 4He/ 3He ratio as a function of cumulative 3He released can be compared with forward models to constrain the shape of the profile. Alternatively, we present a linear inversion that can be used to directly solve for the unknown 4He distribution. The inversion incorporates a standard regularization technique to filter the influence of random measurement errors on the solution. Using either approach we show that stepwise degassing data can yield robust and high-resolution information on the 4He profile. Profiles of radiogenic He are a sensitive function of the time-Temperate ( t- T) path that a cooling sample experienced. Thus, by step heating a proton-irradiated sample it is possible to restrict the sample's acceptable t- T paths. The sensitivity of this approach was explored by forward-modeling 4He profiles resulting from a range of realistic t- T paths, using apatite as an example. Results indicate that 4He profiles provide rich information on t- T paths, especially when the profiles are coupled with (U-Th)/He cooling ages on the same sample. Samples that experienced only moderate diffusive loss

  3. Characterization of a 2D ionization chamber array for IMRT plan verification

    NASA Astrophysics Data System (ADS)

    Alashrah, S.; Kandaiya, S.; Yong, S. Y.; Cheng, S. K.

    2010-07-01

    A commercialized array of 2D pixel ionization chambers MatriXX from Scanditronix Wellhöfer was evaluated with the objective to implement for quality assurance in IMRT treatment plan verification. The device consists of 1020 chambers arranged in a 32×32 grid. The distance between the chamber centres is 7.6 mm and the volume of the chamber is 0.08 cm 3. The effective point measurement of the MatriXX was verified and it agreed with the MatriXX's manual specifications. The start-up behaviour, and the short- and long-term reproducibilities of the array detector were tested. Dose linearity and energy independence were also analyzed. The results showed that the dose was linear within the range 9-800 cGy and the response of the 2D array was independent of energy for 6 and 10 MV photon beams. The MatriXX was independent of dose rate ranging from 183 to 483 cGy/min. For field sizes 3×3 cm 2 and above the output factors of the 2D agreed within 1% with those obtained using the FC65-G ionization chamber. But at field size 2×2 cm 2 the percentage difference was 5%. However, there was a poor correlation with differences greater than 1 mm in the penumbra region. The preliminary investigations indicate that the detector is suitable for IMRT plan verifications but corrections have to be applied in regions of high dose gradient.

  4. Comparison of experimental and calculated calibration coefficients for a high sensitivity ionization chamber.

    PubMed

    Amiot, M N; Mesradi, M R; Chisté, V; Morin, M; Rigoulay, F

    2012-09-01

    The response of a Vacutec 70129 ionization chamber was calculated using the PENELOPE-2008 Monte Carlo code and compared to experimental data. The filling gas mixture composition and its pressure have been determined using IC simulated response adjustment to experimental results. The Monte Carlo simulation revealed a physical effect in the detector response to photons due to the presence of xenon in the chamber. A very good agreement is found between calculated and experimental calibration coefficients for 17 radionuclides. Copyright © 2012 Elsevier Ltd. All rights reserved.

  5. Particle and energy dependence of the statistical fluctuations of an ionization chamber current

    NASA Astrophysics Data System (ADS)

    Purghel, Lidia; Vaˆlcov, Nicolae

    For the purpose of getting more detailed information concerning the processes leading to statistical fluctuations of an ionization chamber current, measurements with various radioactive sources have been done. By using the experimental arrangement described elsewhere [A. Necula et al. Nucl. Instr. and Meth. A 332 (1993) 501] the mean value and the standard deviation of the ionization current for 3H (water vapours), 60Co (sealed source), 85Kr (gas), 204Tl (8 mm diameter disk) and 239Pu (10 mm diameter disk), beta, gamma and alpha sources have been measured. A statistical model explaining the experimental data is proposed.

  6. Threshold electrodisintegration of 3He

    NASA Astrophysics Data System (ADS)

    Hicks, R. S.; Hotta, A.; Churchwell, S.; Jiang, X.; Peterson, G. A.; Shaw, J.; Asavapibhop, B.; Berisso, M. C.; Bosted, P. E.; Burchesky, K.; Miskimen, R. A.; Rock, S. E.; Nakagawa, I.; Tamae, T.; Suda, T.; Golak, J.; Skibiński, R.; Witała, H.; Casagrande, F.; Turchinetz, W.; Cichocki, A.; Wang, K.; Glöckle, W.; Kamada, H.; Kobayashi, T.; Nogga, A.

    2003-06-01

    Cross sections were measured for the near-threshold electrodisintegration of 3He at momentum transfer values of q=2.4, 4.4, and 4.7 fm-1. From these and prior measurements the transverse and longitudinal response functions RT and RL were deduced. Comparisons are made against previously published and new nonrelativistic A=3 calculations using the best available nucleon-nucleon NN potentials. In general, for q<2 fm-1 these calculations accurately predict the threshold electrodisintegration of 3He. Agreement at increasing q demands consideration of two-body terms, but discrepancies still appear at the highest momentum transfers probed, perhaps due to the neglect of relativistic dynamics, or to the underestimation of high-momentum wave-function components.

  7. Neutron and gamma detector using an ionization chamber with an integrated body and moderator

    DOEpatents

    Ianakiev, Kiril D.; Swinhoe, Martyn T.; Lestone, John Paul

    2006-07-18

    A detector for detecting neutrons and gamma radiation includes a cathode that defines an interior surface and an interior volume. A conductive neutron-capturing layer is disposed on the interior surface of the cathode and a plastic housing surrounds the cathode. A plastic lid is attached to the housing and encloses the interior volume of the cathode forming an ionization chamber, into the center of which an anode extends from the plastic lid. A working gas is disposed within the ionization chamber and a high biasing voltage is connected to the cathode. Processing electronics are coupled to the anode and process current pulses which are converted into Gaussian pulses, which are either counted as neutrons or integrated as gammas, in response to whether pulse amplitude crosses a neutron threshold. The detector according to the invention may be readily fabricated into single or multilayer detector arrays.

  8. PTRAC File Utilization for Calculation of Free-Air Ionization Chamber Correction Factors by MCNPX

    NASA Astrophysics Data System (ADS)

    Šolc, Jaroslav; Sochor, Vladimír

    2014-06-01

    A free-air ionization chamber is used as a standard of photon air-kerma. Several correction factors are applied to the air-kerma value. Correction factors for electron loss (kloss) and for additional ionization current caused by photon scatter (ksc), photon fluorescence (kfl), photon transmission through diaphragm edge (kdtr), and photon scatter from the surface of the diaphragm aperture (kdsc) were determined by the MCNPX code utilizing information stored in Particle Track (PTRAC) output files. Individual steps of the procedure are described and the calculated values of the correction factors are presented. The values are in agreement with the correction factors published in a literature for similar free-air chambers.

  9. Hard disk drive based microsecond x-ray chopper for characterization of ionization chambers and photodiodes

    NASA Astrophysics Data System (ADS)

    Müller, O.; Lützenkirchen-Hecht, D.; Frahm, R.

    2015-03-01

    A fast X-ray chopper capable of producing ms long X-ray pulses with a typical rise time of few μs was realized. It is ideally suited to investigate the temporal response of X-ray detectors with response times of the order of μs to ms, in particular, any kind of ionization chambers and large area photo diodes. The drive mechanism consists of a brushless DC motor and driver electronics from a common hard disk drive, keeping the cost at an absolute minimum. Due to its simple construction and small dimensions, this chopper operates at home lab based X-ray tubes and synchrotron radiation sources as well. The dynamics of the most important detectors used in time resolved X-ray absorption spectroscopy, namely, ionization chambers and Passivated Implanted Planar Silicon photodiodes, were investigated in detail. The results emphasize the applicability of this X-ray chopper.

  10. Hard disk drive based microsecond x-ray chopper for characterization of ionization chambers and photodiodes

    SciTech Connect

    Müller, O. Lützenkirchen-Hecht, D.; Frahm, R.

    2015-03-15

    A fast X-ray chopper capable of producing ms long X-ray pulses with a typical rise time of few μs was realized. It is ideally suited to investigate the temporal response of X-ray detectors with response times of the order of μs to ms, in particular, any kind of ionization chambers and large area photo diodes. The drive mechanism consists of a brushless DC motor and driver electronics from a common hard disk drive, keeping the cost at an absolute minimum. Due to its simple construction and small dimensions, this chopper operates at home lab based X-ray tubes and synchrotron radiation sources as well. The dynamics of the most important detectors used in time resolved X-ray absorption spectroscopy, namely, ionization chambers and Passivated Implanted Planar Silicon photodiodes, were investigated in detail. The results emphasize the applicability of this X-ray chopper.

  11. Hard disk drive based microsecond X-ray chopper for characterization of ionization chambers and photodiodes.

    PubMed

    Müller, O; Lützenkirchen-Hecht, D; Frahm, R

    2015-03-01

    A fast X-ray chopper capable of producing ms long X-ray pulses with a typical rise time of few μs was realized. It is ideally suited to investigate the temporal response of X-ray detectors with response times of the order of μs to ms, in particular, any kind of ionization chambers and large area photo diodes. The drive mechanism consists of a brushless DC motor and driver electronics from a common hard disk drive, keeping the cost at an absolute minimum. Due to its simple construction and small dimensions, this chopper operates at home lab based X-ray tubes and synchrotron radiation sources as well. The dynamics of the most important detectors used in time resolved X-ray absorption spectroscopy, namely, ionization chambers and Passivated Implanted Planar Silicon photodiodes, were investigated in detail. The results emphasize the applicability of this X-ray chopper.

  12. Some specific features of ionization chamber calibrations in linac x-ray beams at the LNE-LNHB.

    PubMed

    Delaunay, F; Ostrowsky, A

    2007-05-07

    The purpose of this note is to give some details about the modus operandi employed today to calibrate ionization chambers in radiotherapy linac photon beams at the Laboratoire National Henri Becquerel (LNE-LNHB). Some specific features are described: first the equipment (including the external monitoring ionization chambers), second the calculations of the profile or radial non-uniformity correction factors (up to 0.5% effect for commonly used ionization chambers) and finally the calculations to get the calibration coefficients for customer beam qualities.

  13. 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

  14. Fast-neutron and photon doses determined with proportional counters and ionization chambers

    SciTech Connect

    DeLuca, P.M. Jr.; Higgins, P.D.; Schell, M.C.; Pearson, D.W.

    1981-01-01

    A /sup 60/Co teletherapy source has recently been coupled to an existing source of fast neutrons. These sources may be operated to provide precise and controlled mixtures of photons and neutrons. In this work we report the application of paired miniature proportional counters to n/..gamma.. dose separation. Graphite- and A150 plastic-walled proportional counters were employed. Results are compared to dose values deduced from a cnventional A150 plastic ionization chamber and a neutron insensitive GM counter.

  15. SU-E-T-525: Ionization Chamber Perturbation in Flattening Filter Free Beams

    SciTech Connect

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

    2015-06-15

    Purpose: Changing the characteristic of a photon beam by mechanically removing the flattening filter may impact the dose response of ionization chambers. Thus, perturbation factors of cylindrical ionization chambers in conventional and flattening filter free photon beams were calculated by Monte Carlo simulations. Methods: The EGSnrc/BEAMnrc code system was used for all Monte Carlo calculations. BEAMnrc models of nine different linear accelerators with and without flattening filter were used to create realistic photon sources. Monte Carlo based calculations to determine the fluence perturbations due to the presens of the chambers components, the different material of the sensitive volume (air instead of water) as well as the volume effect were performed by the user code egs-chamber. Results: Stem, central electrode, wall, density and volume perturbation factors for linear accelerators with and without flattening filter were calculated as a function of the beam quality specifier TPR{sub 20/10}. A bias between the perturbation factors as a function of TPR{sub 20/10} for flattening filter free beams and conventional linear accelerators could not be observed for the perturbations caused by the components of the ionization chamber and the sensitive volume. Conclusion: The results indicate that the well-known small bias between the beam quality correction factor as a function of TPR20/10 for the flattening filter free and conventional linear accelerators is not caused by the geometry of the detector but rather by the material of the sensitive volume. This suggest that the bias for flattening filter free photon fields is only caused by the different material of the sensitive volume (air instead of water)

  16. Dosimetric characteristics of the novel 2D ionization chamber array OCTAVIUS Detector 1500.

    PubMed

    Stelljes, T S; Harmeyer, A; Reuter, J; Looe, H K; Chofor, N; Harder, D; Poppe, B

    2015-04-01

    The dosimetric properties of the OCTAVIUS Detector 1500 (OD1500) ionization chamber array (PTW-Freiburg, Freiburg, Germany) have been investigated. A comparative study was carried out with the OCTAVIUS Detector 729 and OCTAVIUS Detector 1000 SRS arrays. The OD1500 array is an air vented ionization chamber array with 1405 detectors in a 27 × 27 cm(2) measurement area arranged in a checkerboard pattern with a chamber-to-chamber distance of 10 mm in each row. A sampling step width of 5 mm can be achieved by merging two measurements shifted by 5 mm, thus fulfilling the Nyquist theorem for intensity modulated dose distributions. The stability, linearity, and dose per pulse dependence were investigated using a Semiflex 31013 chamber (PTW-Freiburg, Freiburg, Germany) as a reference detector. The effective depth of measurement was determined by measuring TPR curves with the array and a Roos chamber type 31004 (PTW-Freiburg, Freiburg, Germany). Comparative output factor measurements were performed with the array, the Semiflex 31010 ionization chamber and the Diode 60012 (both PTW-Freiburg, Freiburg, Germany). The energy dependence of the OD1500 was measured by comparing the array's readings to those of a Semiflex 31010 ionization chamber for varying mean photon energies at the depth of measurement, applying to the Semiflex chamber readings the correction factor kNR for nonreference conditions. The Gaussian lateral dose response function of a single array detector was determined by searching the convolution kernel suitable to convert the slit beam profiles measured with a Diode 60012 into those measured with the array's central chamber. An intensity modulated dose distribution measured with the array was verified by comparing a OD1500 measurement to TPS calculations and film measurements. The stability and interchamber sensitivity variation of the OD1500 array were within ±0.2% and ±0.58%, respectively. Dose linearity was within 1% over the range from 5 to 1000 MU. The

  17. Dosimetric characteristics of the novel 2D ionization chamber array OCTAVIUS Detector 1500

    SciTech Connect

    Stelljes, T. S. Looe, H. K.; Chofor, N.; Poppe, B.; Harmeyer, A.; Reuter, J.; Harder, D.

    2015-04-15

    Purpose: The dosimetric properties of the OCTAVIUS Detector 1500 (OD1500) ionization chamber array (PTW-Freiburg, Freiburg, Germany) have been investigated. A comparative study was carried out with the OCTAVIUS Detector 729 and OCTAVIUS Detector 1000 SRS arrays. Methods: The OD1500 array is an air vented ionization chamber array with 1405 detectors in a 27 × 27 cm{sup 2} measurement area arranged in a checkerboard pattern with a chamber-to-chamber distance of 10 mm in each row. A sampling step width of 5 mm can be achieved by merging two measurements shifted by 5 mm, thus fulfilling the Nyquist theorem for intensity modulated dose distributions. The stability, linearity, and dose per pulse dependence were investigated using a Semiflex 31013 chamber (PTW-Freiburg, Freiburg, Germany) as a reference detector. The effective depth of measurement was determined by measuring TPR curves with the array and a Roos chamber type 31004 (PTW-Freiburg, Freiburg, Germany). Comparative output factor measurements were performed with the array, the Semiflex 31010 ionization chamber and the Diode 60012 (both PTW-Freiburg, Freiburg, Germany). The energy dependence of the OD1500 was measured by comparing the array’s readings to those of a Semiflex 31010 ionization chamber for varying mean photon energies at the depth of measurement, applying to the Semiflex chamber readings the correction factor k{sub NR} for nonreference conditions. The Gaussian lateral dose response function of a single array detector was determined by searching the convolution kernel suitable to convert the slit beam profiles measured with a Diode 60012 into those measured with the array’s central chamber. An intensity modulated dose distribution measured with the array was verified by comparing a OD1500 measurement to TPS calculations and film measurements. Results: The stability and interchamber sensitivity variation of the OD1500 array were within ±0.2% and ±0.58%, respectively. Dose linearity was within 1

  18. A position-sensitive twin ionization chamber for fission fragment and prompt neutron correlation experiments

    NASA Astrophysics Data System (ADS)

    Göök, A.; Geerts, W.; Hambsch, F.-J.; Oberstedt, S.; Vidali, M.; Zeynalov, Sh.

    2016-09-01

    A twin position-sensitive Frisch grid ionization chamber, intended as a fission fragment detector in experiments to study prompt fission neutron correlations with fission fragment properties, is presented. Fission fragment mass and energies are determined by means of the double kinetic energy technique, based on conservation of mass and linear momentum. The position sensitivity is achieved by replacing each anode plate in the standard twin ionization chamber by a wire plane and a strip anode, both readout by means of resistive charge division. This provides information about the fission axis orientation, which is necessary to reconstruct the neutron emission process in the fully accelerated fragment rest-frame. The energy resolution compared to the standard twin ionization chamber is found not to be affected by the modification. The angular resolution of the detector relative to an arbitrarily oriented axis is better than 7° FWHM. Results on prompt fission neutron angular distributions in 235U(n,f) obtained with the detector in combination with an array of neutron scintillation detectors is presented as a proof of principle.

  19. Differences between signal currents for both polarities of applied voltages on cavity ionization chambers

    NASA Astrophysics Data System (ADS)

    Takata, N.

    2001-06-01

    A difference between the surface potential of the charge collecting electrode and that of the guard electrode of an ionization chamber changes the charge collecting volume depending on the applied voltage. If the difference is large, the saturation curve of the signal current shows a maximum at a low applied voltage. Even when there is no electrical or mechanical defect, the signal current from a parallel plate ionization chamber irradiated with 60Co γ-rays increases or decreases with the applied voltage beyond the recombination region depending on the polarity of the applied voltage. The variation in the signal current is explained as a result of the change in the stopping power of air due to the acceleration or deceleration of secondary electrons. These electrons are emitted from the polarizing electrode towards the collector as a result of Compton scattering. In a range of low applied voltages, the signal current from a cylindrical ionization chamber is expected to be smaller for a negative applied voltage than for a positive applied voltage. This is because epithermal electrons are expected to have a higher probability of being lost by back diffusion than positive ions which are originally produced in a thermal equilibrium condition. An experimental result, however, showed no difference in the polarities of the applied voltage. The result may be explained as a consequence of the fact that epithemal electrons do not drift for long distances and maintain their energies.

  20. An evaluation of ionization chambers for the relative dosimetry of kilovoltage x-ray beams

    SciTech Connect

    Hill, Robin; Mo Zhao; Haque, Mamoon; Baldock, Clive

    2009-09-15

    In this work, the authors have evaluated ten different ionization chambers for the relative dosimetry of kilovoltage x-ray beams in the energy range of 50-280 kVp. Percentage depth doses in water and relative detector response (in Solid Water and in air) were measured for each of the x-ray beams studied using a number of chambers. Measured depth dose data were compared with Monte Carlo calculated depth doses using the EGSnrc Monte Carlo package and the BEAMnrc user code. The accuracy of the phase space files generated by BEAMnrc was verified by calculating the half-value layer and comparing with the measured half-value layer of each x-ray beam. The results indicate that the Advanced Markus, Markus, NACP, and Roos parallel plate ionization chambers were suitable for the measurement of depth dose data in this beam quality range with an uncertainty of less than 3%, including in the regions close to the water surface. While the relative detector response of the Farmer and scanning thimble chambers exhibited a better energy response, they were not suitable for depth dose measurements in the first 5 mm below the water surface with differences of up to 12% in the surface dose measurement for the 50 kVp x-ray beam. These differences were due to dose artifacts generated by the chamber size and the dose gradient. However, at depths greater than 5 mm, the Farmer and thimble scanning chambers gave uncertainties of less than 3% for the depth dose measurements for all beam energies. The PTW PinPoint 31006 chamber was found to give varying dose differences of up to 8% depending on the x-ray beam energy; this was attributed to the steel central electrode. The authors recommend that one of the parallel plate ionization chambers investigated be used to determine depth dose data for kilovoltage x-ray beams in the energy range studied and give correct dose information close to the surface and at depth in the water phantom.

  1. 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.

  2. 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.

  3. Application of the two-dose-rate method for general recombination correction for liquid ionization chambers in continuous beams

    NASA Astrophysics Data System (ADS)

    Andersson, Jonas; Tölli, Heikki

    2011-01-01

    A method to correct for the general recombination losses for liquid ionization chambers in continuous beams has been developed. The proposed method has been derived from Greening's theory for continuous beams and is based on measuring the signal from a liquid ionization chamber and an air filled monitor ionization chamber at two different dose rates. The method has been tested with two plane parallel liquid ionization chambers in a continuous radiation x-ray beam with a tube voltage of 120 kV and with dose rates between 2 and 13 Gy min-1. The liquids used as sensitive media in the chambers were isooctane (C8H18) and tetramethylsilane (Si(CH3)4). The general recombination effect was studied using chamber polarizing voltages of 100, 300, 500, 700 and 900 V for both liquids. The relative standard deviation of the results for the collection efficiency with respect to general recombination was found to be a maximum of 0.7% for isooctane and 2.4% for tetramethylsilane. The results are in excellent agreement with Greening's theory for collection efficiencies over 90%. The measured and corrected signals from the liquid ionization chambers used in this work are in very good agreement with the air filled monitor chamber with respect to signal to dose linearity.

  4. Application of the two-dose-rate method for general recombination correction for liquid ionization chambers in continuous beams.

    PubMed

    Andersson, Jonas; Tölli, Heikki

    2011-01-21

    A method to correct for the general recombination losses for liquid ionization chambers in continuous beams has been developed. The proposed method has been derived from Greening's theory for continuous beams and is based on measuring the signal from a liquid ionization chamber and an air filled monitor ionization chamber at two different dose rates. The method has been tested with two plane parallel liquid ionization chambers in a continuous radiation x-ray beam with a tube voltage of 120 kV and with dose rates between 2 and 13 Gy min(-1). The liquids used as sensitive media in the chambers were isooctane (C(8)H(18)) and tetramethylsilane (Si(CH(3))(4)). The general recombination effect was studied using chamber polarizing voltages of 100, 300, 500, 700 and 900 V for both liquids. The relative standard deviation of the results for the collection efficiency with respect to general recombination was found to be a maximum of 0.7% for isooctane and 2.4% for tetramethylsilane. The results are in excellent agreement with Greening's theory for collection efficiencies over 90%. The measured and corrected signals from the liquid ionization chambers used in this work are in very good agreement with the air filled monitor chamber with respect to signal to dose linearity.

  5. Calibration of the KRISS reference ionization chamber for certification of ²²²Rn gaseous sources.

    PubMed

    Lee, J M; Lee, K B; Lee, S H; Oh, P J; Park, T S; Kim, B C; Lee, M S

    2013-11-01

    A primary measurement system for gaseous (222)Rn based on the defined solid angle counting method has recently been constructed at KRISS and the reference ionization chamber used to measure the activities of gamma-emitting single radionuclides was adopted as a secondary standard for gaseous (222)Rn. A 20 mL flame-sealed glass ampoule source from the primary measurement system was used to calibrate the ionization chamber for (222)Rn. The (222)Rn efficiency of the ionization chamber was compared with that calculated by using a photon energy-dependent efficiency curve and that measured by using a standard (226)Ra solution. From the comparisons we draw the conclusion that the reference ionization chamber for gamma-emitting radionuclides can be a suitable secondary measurement system for gaseous (222)Rn sources.

  6. 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

    Air-communicating well ionization chambers are commonly used to assess air kerma strength of sources used in brachytherapy. The signal produced is supposed to be proportional to the air density within the chamber and, therefore, a density-independent air kerma strength is obtained when the measurement is corrected to standard atmospheric conditions using the usual temperature and pressure correction factor. Nevertheless, when assessing low energy sources, the ionization chambers may not fulfill that condition and a residual density dependence still remains after correction. In this work, the authors examined the behavior of the PTW 34051 SourceCheck ionization chamber when measuring the air kerma strength of (125)I seeds. Four different SourceCheck chambers were analyzed. With each one of them, two series of measurements of the air kerma strength for (125)I selectSeed(TM) brachytherapy sources were performed inside a pressure chamber and varying the pressure in a range from 747 to 1040 hPa (560 to 780 mm Hg). The temperature and relative humidity were kept basically constant. An analogous experiment was performed by taking measurements at different altitudes above sea level. Contrary to other well-known ionization chambers, like the HDR1000 PLUS, in which the temperature-pressure correction factor overcorrects the measurements, in the SourceCheck ionization chamber they are undercorrected. At a typical atmospheric situation of 933 hPa (700 mm Hg) and 20 °C, this undercorrection turns out to be 1.5%. Corrected measurements show a residual linear dependence on the density and, as a consequence, an additional density dependent correction must be applied. The slope of this residual linear density dependence is different for each SourceCheck chamber investigated. The results obtained by taking measurements at different altitudes are compatible with those obtained with the pressure chamber. Variations of the altitude and changes in the weather conditions may produce

  7. The calibration and use of plane-parallel ionization chambers for dosimetry of electron beams.

    PubMed

    Almond, P R; Xu, Z; Li, H; Park, H C

    1995-08-01

    The AAPM TG 39 protocol has proposed three different methods of calibrating plane-parallel ionization chambers, i.e., in-phantom irradiation with a high-energy electron beam and in-phantom and in-air 60Co irradiation. To verify the consistency of the three methods, we have measured Ngaspp values using each of these techniques for the five most commonly used plane-parallel chambers considered by the protocol. Our results demonstrate that the measured Ngaspp values for the three different methods for any of the chambers agree to within +/- 0.6%. Once Ngaspp was measured, the determination of absorbed dose for electron beams with different energies for an AECL Therac 20 and Philips SL25 was carried out according to the AAPM TG 39 protocol. The results show that the determination of the absorbed dose outputs for any of the five chambers agree to within +/- 0.7% for electron-beam energies of 4-20 MeV if all five chambers had Ngaspp values determined by the electron-beam method. The uncertainties are well within the expected error for these approaches.

  8. An online proton beam monitor for cancer therapy based on ionization chambers with micro pattern readout

    NASA Astrophysics Data System (ADS)

    Basile, E.; Carloni, A.; Castelluccio, D. M.; Cisbani, E.; Colilli, S.; De Angelis, G.; Fratoni, R.; Frullani, S.; Giuliani, F.; Gricia, M.; Lucentini, M.; Santavenere, F.; Vacca, G.

    2012-03-01

    A unique compact LINAC accelerator for proton therapy is under development in Italy within the TOP-IMPLART project. The proton beam will reach the kinetic energy of 230 MeV, it will have a widely variable current intensity (0.1-10 μA, with average up to 3.5 nA) associated with a high pulse repetition frequency (1-3.5 μs long pulses at 10-100 Hz). The TOP-IMPLART system will provide a fully active 3+1D dose delivery, that is longitudinal (energy modulation), transverse active spot scanning, and current intensity modulation. These accelerator features will permit a highly conformational dose distribution, which therefore requires an effective, online, beam monitor system with wide dynamic range, good sensitivity, adequate spatial resolution and rapid response. In order to fulfill these requisites a new device is under development for the monitoring of the beam intensity profile, its centroid and direction; it is based on transmission, segmented, ionization chambers with typical active area of 100 × 100 mm2. Micro pattern x/y pad like design has been used for the readout plane in order to maximize the field uniformity, reduce the chamber thickness and obtain both beam coordinates on a single chamber. The chamber prototype operates in ionization region to minimize saturation and discharge effects. Simulations (based on FLUKA) have been carried on to study the perturbation of the chamber on the beam parameters and the effects on the delivered dose (on a water phantom). The charge collected in each channel is integrated by dedicated auto-ranging readout electronics: an original scheme has been developed in order to have an input dynamic range greater than 104 with sensitivity better than 3%. This is achieved by a dynamical adjustment of the integrating capacitance to the signal intensity.

  9. 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.

  10. Precise measurement of the cross section of 3He ( 3He ,2p) 4He by using 3He doubly charged beam

    NASA Astrophysics Data System (ADS)

    Kudomi, Nobuyuki; Komori, Masataka; Takahisa, Keiji; Yoshida, Sei; Kume, Kyo; Ohsumi, Hideaki; Itahashi, Takahisa

    2004-01-01

    The fusion cross section of 3He ( 3He ,2p) 4He at a center of mass energy of 30 50 keV has been measured by using a helium-3 doubly ionized beam at a low-energy high current accelerator facility OCEAN. Free from molecular interference in the beam, the measurement determines the astrophysical S factor with better statistical and systematic errors than previous data. By using singly and doubly charged helium-3 ions, the facility envisages to provide the data from high-energy to Gamow energy regions.

  11. Apparatus for deformation tests of solids in liquid 3He

    NASA Astrophysics Data System (ADS)

    Hashimoto, T.; Katakura, S.; Edagawa, K.; Takeuchi, S.; Suzuki, T.

    2000-07-01

    An apparatus for deformation of solids in liquid 3He is constructed. Either tensile deformation or compression of a specimen can be performed by exchanging the assemblies in the 3He pot which has a capacity of about 30 cm3. The pulling rod for transmitting load from the tensile testing machine to the specimen runs inside the outlet tube of 3He, being isolated from 4He bath and almost free from mechanical friction. To measure the change in flow stress with the supernormal transition of superconducting metals, a superconducting magnet is mounted outside of the vacuum chamber which separates the 3He pot and the 4He bath. Under an applied load for plastic deformation the system is stably operative down to 0.6 K, while the lowest temperature achieved is 0.5 K. Some results on Ta and NaCl are presented.

  12. Development of a thermodynamic model for a cold cycle 3He-4He dilution refrigerator

    NASA Astrophysics Data System (ADS)

    Mueller, B. W.; Miller, F. K.

    2016-10-01

    A thermodynamic model of a 3He-4He cold cycle dilution refrigerator with no actively-driven mechanical components is developed and investigated. The refrigerator employs a reversible superfluid magnetic pump, passive check valves, a phase separation chamber, and a series of recuperative heat exchangers to continuously circulate 3He-4He and maintain a 3He concentration gradient across the mixing chamber. The model predicts cooling power and mixing chamber temperature for a range of design and operating parameters, allowing an evaluation of feasibility for potential 3He-4He cold cycle dilution refrigerator prototype designs. Model simulations for a prototype refrigerator design are presented.

  13. Use of relativistic rise in ionization chambers for measurement of high energy heavy nuclei

    NASA Technical Reports Server (NTRS)

    Barthelmy, S. D.; Israel, M. H.; Klarmann, J.; Vogel, J. S.

    1983-01-01

    A balloon-borne instrument has been constructed to measure the energy spectra of cosmic-ray heavy nuclei in the range of about 0.3 to about 100 GeV/amu. It makes use of the relativistic rise portion of the Bethe-Bloch curve in ionization chambers for energy determination in the 10- to 100-GeV/amu interval. The instrument consists of six layers of dual-gap ionization chambers for energy determination above 10 GeV/amu. Charge is determined with a NE114 scintillator and a Pilot 425 plastic Cerenkov counter. A CO2 gas Cerenkov detector (1 atm; threshold of 30 GeV/amu) calibrates the ion chambers in the relativistic rise region. The main emphasis of the instrument is the determination of the change of the ratio of Iron (26) to the Iron secondaries (21-25) in the energy range of 10 to 100 GeV/amu. Preliminary data from a balloon flight in the fall of 1982 from Palestine, TX is presented.

  14. Measurement of photon flux with a miniature gas ionization chamber in a Material Testing Reactor

    NASA Astrophysics Data System (ADS)

    Fourmentel, D.; Filliatre, P.; Villard, J. F.; Lyoussi, A.; Reynard-Carette, C.; Carcreff, H.

    2013-10-01

    Nuclear heating measurements in Material Testing Reactors (MTR) are crucial for the design of the experimental devices and the prediction of the temperature of the hosted samples. Nuclear heating in MTR materials (except fuel) is mainly due to the energy deposition by the photon flux. Therefore, the photon flux is a key input parameter for the computer codes which simulate nuclear heating and temperature reached by samples/devices under irradiation. In the Jules Horowitz MTR under construction at the CEA Cadarache, the maximal expected nuclear heating levels will be about 15 to 18 W g-1 and it will be necessary to assess this parameter with the best accuracy. An experiment was performed at the OSIRIS reactor to combine neutron flux, photon flux and nuclear heating measurements to improve the knowledge of the nuclear heating in MTR. There are few appropriate sensors for selective measurement of the photon flux in MTR even if studies and developments are ongoing. An experiment, called CARMEN-1, was conducted at the OSIRIS MTR and we used in particular a gas ionization chamber based on miniature fission chamber design to measure the photon flux. In this paper, we detail Monte-Carlo simulations to analyze the photon fluxes with ionization chamber measurements and we compare the photon flux calculations to the nuclear heating measurements. These results show a good accordance between photon flux measurements and nuclear heating measurement and allow improving the knowledge of these parameters.

  15. Use of relativistic rise in ionization chambers for measurement of high energy heavy nuclei

    NASA Technical Reports Server (NTRS)

    Barthelmy, S. D.; Israel, M. H.; Klarmann, J.; Vogel, J. S.

    1983-01-01

    A balloon-borne instrument has been constructed to measure the energy spectra of cosmic-ray heavy nuclei in the range of about 0.3 to about 100 GeV/amu. It makes use of the relativistic rise portion of the Bethe-Bloch curve in ionization chambers for energy determination in the 10- to 100-GeV/amu interval. The instrument consists of six layers of dual-gap ionization chambers for energy determination above 10 GeV/amu. Charge is determined with a NE114 scintillator and a Pilot 425 plastic Cerenkov counter. A CO2 gas Cerenkov detector (1 atm; threshold of 30 GeV/amu) calibrates the ion chambers in the relativistic rise region. The main emphasis of the instrument is the determination of the change of the ratio of Iron (26) to the Iron secondaries (21-25) in the energy range of 10 to 100 GeV/amu. Preliminary data from a balloon flight in the fall of 1982 from Palestine, TX is presented.

  16. Ambiguities in the grid-inefficiency correction for Frisch-Grid Ionization Chambers

    NASA Astrophysics Data System (ADS)

    Al-Adili, A.; Hambsch, F.-J.; Bencardino, R.; Oberstedt, S.; Pomp, S.

    2012-05-01

    Ionization chambers with Frisch grids have been very successfully applied to neutron-induced fission-fragment studies during the past 20 years. They are radiation resistant and can be easily adapted to the experimental conditions. The use of Frisch grids has the advantage to remove the angular dependency from the charge induced on the anode plate. However, due to the Grid Inefficiency (GI) in shielding the charges, the anode signal remains slightly angular dependent. The correction for the GI is, however, essential to determine the correct energy of the ionizing particles. GI corrections can amount to a few percent of the anode signal. Presently, two contradicting correction methods are considered in literature. The first method adding the angular-dependent part of the signal to the signal pulse height; the second method subtracting the former from the latter. Both additive and subtractive approaches were investigated in an experiment where a Twin Frisch-Grid Ionization Chamber (TFGIC) was employed to detect the spontaneous fission fragments (FF) emitted by a 252Cf source. Two parallel-wire grids with different wire spacing (1 and 2 mm, respectively), were used individually, in the same chamber side. All the other experimental conditions were unchanged. The 2 mm grid featured more than double the GI of the 1 mm grid. The induced charge on the anode in both measurements was compared, before and after GI correction. Before GI correction, the 2 mm grid resulted in a lower pulse-height distribution than the 1 mm grid. After applying both GI corrections to both measurements only the additive approach led to consistent grid independent pulse-height distributions. The application of the subtractive correction on the contrary led to inconsistent, grid-dependent results. It is also shown that the impact of either of the correction methods is small on the FF mass distributions of 235U(nth, f).

  17. Monte Carlo calculations of correction factors for plane-parallel ionization chambers in clinical electron dosimetry

    SciTech Connect

    Araki, Fujio

    2008-09-15

    Recent standard dosimetry protocols recommend that plane-parallel ionization chambers be used in the measurements of depth-dose distributions or the calibration of low-energy electron beams with beam quality R{sub 50}<4 g/cm{sup 2}. In electron dosimetry protocols with the plane-parallel chambers, the wall correction factor, P{sub wall}, in water is assumed to be unity and the replacement correction factor, P{sub repl}, is taken to be unity for well-guarded plane-parallel chambers, at all measurement depths. This study calculated P{sub wall} and P{sub repl} for NACP-02, Markus, and Roos plane-parallel chambers in clinical electron dosimetry using the EGSnrc Monte Carlo code system. The P{sub wall} values for the plane-parallel chambers increased rapidly as a function of depth in water, especially at lower energy. The value around R{sub 50} for NACP-02 was about 10% greater than unity at 4 MeV. The effect was smaller for higher electron energies. Similarly, P{sub repl} values with depth increased drastically at the region with the steep dose gradient for lower energy. For Markus P{sub repl} departed more than 10% from unity close to R{sub 50} due to the narrow guard ring width. P{sub repl} for NACP-02 and Roos was close to unity in the plateau region of depth-dose curves that includes a reference depth, d{sub ref}. It was also found that the ratio of the dose to water and the dose to the sensitive volume in the air cavity for the plane-parallel chambers, D{sub w}/[D{sub air}]{sub pp}, at d{sub ref} differs significantly from that assumed by electron dosimetry protocols.

  18. Feasibility of calibrating elongated brachytherapy sources using a well-type ionization chamber

    SciTech Connect

    Meigooni, Ali S.; Awan, Shahid B.; Dou, Kai

    2006-11-15

    Recently, elongated brachytherapy sources (active length >1 cm) have become commercially available for interstitial prostate implants. These sources were introduced to improve the quality of brachytherapy procedures by eliminating the migration and seed bunching associated with loose seed-type implants. However, the inability to calibrate elongated brachytherapy sources with the Wide-Angle Free-Air Chamber (WAFAC) used by the National Institute of Standards and Technology (NIST) hinders the experimental determination of dosimetric parameters of these source types. In order to resolve this shortcoming, an interim solution has been introduced for calibration of elongated brachytherapy sources using a commercially available well-type ionization chamber. The feasibility of this procedure was examined by calibrating RadioCoil{sup Tm} {sup 103}Pd sources with active lengths ranging from 1 to 7 cm.

  19. Argon/propane ionization-chamber dosimetry for mixed x-ray/neutron fields.

    PubMed

    Schulz, R J

    1978-01-01

    The photoneutrons produced by high-energy x-ray machines can diffuse through the mazes usually employed at the treatment-room entrance and readily penetrate the lead-lined doors used for x-ray shielding. The measurement of these neutrons in the presence of x-rays and the determination of dose equivalent poses a problem for which there is currently no standard method of solution. In order to separate x-ray dose from neutron dose, the author employed an ionization chamber alternately filled with argon or propane. The response characteristics of this chamber to x-ray and neutrons are described. Quality factors were determined from a calculated neutron spectrum. As a result of these measurements, a 10-in. polyethylene door was added to the entranceway of a 25-MV linear accelerator.

  20. Multi-Sampling Ionization Chamber (MUSIC) for measurements of fusion reactions with radioactive beams

    NASA Astrophysics Data System (ADS)

    Carnelli, P. F. F.; Almaraz-Calderon, S.; Rehm, K. E.; Albers, M.; Alcorta, M.; Bertone, P. F.; Digiovine, B.; Esbensen, H.; Fernández Niello, J.; Henderson, D.; Jiang, C. L.; Lai, J.; Marley, S. T.; Nusair, O.; Palchan-Hazan, T.; Pardo, R. C.; Paul, M.; Ugalde, C.

    2015-11-01

    A detection technique for high-efficiency measurements of fusion reactions with low-intensity radioactive beams was developed. The technique is based on a Multi-Sampling Ionization Chamber (MUSIC) operating as an active target and detection system, where the ionization gas acts as both target and counting gas. In this way, we can sample an excitation function in an energy range determined by the gas pressure, without changing the beam energy. The detector provides internal normalization to the incident beam and drastically reduces the measuring time. In a first experiment we tested the performance of the technique by measuring the 10,13,15C+12C fusion reactions at energies around the Coulomb barrier.

  1. Application of patent BR102013018500-0 in well type ionization chambers

    NASA Astrophysics Data System (ADS)

    Sousa, C. H. S.; Peixoto, J. G. P.

    2016-07-01

    The definition of the radioactive sample position in a well type ionization chamber is the largest source of uncertainty in the measurement of quantity activity. The determination of this parameter in two activimeters helped to improve their accuracies, from 2.62 and 2.59% to 3.87 and 1.74%, with and without the use of the positioning device, concluding, that with their use has reached an uncertainty of U =2276 and 0.2677% (k = 2) 95.45%.

  2. Calibration and efficiency curve of SANAEM ionization chamber for activity measurements.

    PubMed

    Yeltepe, Emin; Kossert, Karsten; Dirican, Abdullah; Nähle, Ole; Niedergesäß, Christiane; Kemal Şahin, Namik

    2016-03-01

    A commercially available Fidelis ionization chamber was calibrated and assessed in PTB with activity standard solutions. The long-term stability and linearity of the system was checked. Energy-dependent efficiency curves for photons and beta particles were determined, using an iterative method in Excel™, to enable calibration factors to be calculated for radionuclides which were not used in the calibration. Relative deviations between experimental and calculated radionuclide efficiencies are of the order of 1% for most photon emitters and below 5% for pure beta emitters. The system will enable TAEK-SANAEM to provide traceable activity measurements. Copyright © 2015 Elsevier Ltd. All rights reserved.

  3. 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

  4. 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

  5. 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.

  6. High-rate axial-field ionization chamber for particle identification of Radioactive beams

    NASA Astrophysics Data System (ADS)

    Desouza, Romualdo; Vadas, Justin; Singh, Varinderjit; Visser, G.; Alexander, A.; Hudan, S.; Huston, J.; Wiggins, B.; Chbihi, A.; Famiano, M.; Bischak, M.

    2017-01-01

    The design, construction and performance characteristics of a simple axial-field ionization chamber suitable for identifying ions in a radioactive beam are presented. The detector is optimized for use with low-energy radioactive beams (<) 5 MeV/A. A fast charge sensitive amplifier (CSA) integrated into the detector design is also described. Coupling this fast CSA to the axial field ionization chamber produces an output pulse with a rise-time of 60 to 70 ns and a fall time of 100 ns, making the detector capable of sustaining a relatively high rate while providing a time resolution of 6 to 8 ns. Tests with an α source establish the detector energy resolution as 8 % for an energy deposit of 3.5 MeV. Beam tests indicate that the detector is an effective tool for the characterization of low-energy radioactive beams at beam intensities up to 3 x 105 ions/s. Supported by the U.S. DOE under Award # DE-FG02-88ER-40404 and the NSF under Grant No. 1342962.

  7. Strip Ionization Chamber as Beam Monitor in the Proton Therapy Eye Treatment

    NASA Astrophysics Data System (ADS)

    Marchetto, F.; Cirio, R.; Garella, M. A.; Giordanengo, S.; Boriano, A.; Givehchi, N.; La Rosa, A.; Peroni, C.; Donetti, M.; Bourhaleb, F.; Pitta', G.; Cirrone, G. A. P.; Cuttone, G.; Raffaele, L.; Sabini, M. G.; Valastro, L.

    2006-04-01

    Since spring 2002, ocular pathologies have been treated in Catania at the Centro di AdroTerapia e Applicazioni Nucleari Avanzate (CATANA) within a collaboration between INFN Laboratori Nazionali del Sud (LNS), Physics Department, Ophthalmology Institute, Radiology Institute of the Catania University and CSFNSM Catania. A beam line from a 62 MeV Superconducting Cyclotron is used to treat shallow tumors. The beam is conformed to the tumor shape with a passive delivery system. A detector system has been developed in collaboration with INFN-Torino to be used as real time beam monitor. The detector, placed upstream of the patient collimator, consists of two parallel plate ionization chambers with the anode segmented in strips. Each anode is made of 0.5 mm-wide 256 strips corresponding to (12.8 × 12.8) cm2 sensitive area. With the two strip ionization chambers one can measure the relevant beam parameters during treatment to probe both asymmetry and flatness. In the test carried out at CATANA the detector has been used under different and extreme beam conditions. Preliminary results are given for profiles and skewness, together with a comparison with reference detectors.

  8. An ionization chamber and a Si-detector for lead-210 chronology

    NASA Astrophysics Data System (ADS)

    Farid, M.; El-Daoushy, A. F.; El-Daoushy, M. F. A. F.

    1981-09-01

    Radon emanation and isotopic dilution techniques were used for the determination of 226Ra and "total" 210Pb in sediment samples. The "unsupported" 210Pb were then used to construct lake-sediment chronologies. Polonium was extracted at 550-600°C, transferred to chloride, then plated by self-deposition on silver disks. Memory effects due to adsorption of polonium on glass were carefully studied. Si-detectors were used for α-activity measurements. Background studies indicated instabilities in a Si-detector when left without bias for longer periods. The radium was extracted with the help of a barium carrier, which not only made the extraction quantitative but also eliminated the adsorption of radium on the glasses used. The 222Rn was measured in an ionization chamber. The gas counter with its modified filling system allowed both low level measurements of sediment samples and counter calibration with comparably active 226Ra standards. The increasing background of the ionization chamber was explained by the adsorption of 222Rn on the surfaces of the counter. The background was reduced by the removal of the adsorbed atoms. Normalization for discrimination shifts, due to electronegative impurities, is required in case the counting gas is impure.

  9. High-rate axial-field ionization chamber for particle identification of radioactive beams

    NASA Astrophysics Data System (ADS)

    Vadas, J.; Singh, Varinderjit; Visser, G.; Alexander, A.; Hudan, S.; Huston, J.; Wiggins, B. B.; Chbihi, A.; Famiano, M.; Bischak, M. M.; deSouza, R. T.

    2016-11-01

    The design, construction and performance characteristics of a simple axial-field ionization chamber suitable for identifying ions in a radioactive beam are presented. Optimized for use with low-energy radioactive beams (< 5 MeV / A) the detector presents only three 0.5 μm/cm2 foils to the beam in addition to the detector gas. A fast charge sensitive amplifier (CSA) integrated into the detector design is also described. Coupling this fast CSA to the axial field ionization chamber produces an output pulse with a risetime of 60-70 ns and a fall time of 100 ns, making the detector capable of sustaining a relatively high rate and providing a time resolution of 6-8 ns. Tests with an α source establish the detector energy resolution as ∼ 8 % for an energy deposit of ∼3.5 MeV. The energy resolution with beams of 2.5 and 4.0 MeV/A 39K ions and the dependence of the energy resolution on beam intensity is measured. At an instantaneous rate of 3×105 ions/s the energy resolution has degraded to 14% with a pileup of 12%. The good energy resolution of this detector at rates up to 3×105 ions/s makes it an effective tool in the characterization of low-energy radioactive beams.

  10. Technical Note: Experimental determination of the effective point of measurement of two cylindrical ionization chambers in a clinical proton beam

    SciTech Connect

    Sugama, Yuya; Nishio, Teiji; Onishi, Hiroshi

    2015-07-15

    Purpose: IAEA TRS-398 notes that cylindrical ionization chambers are preferred for reference proton dosimetry. If a cylindrical ionization chamber is used in a phantom to measure the dose as a function of depth, the effective point of measurement (EPOM) must be taken into account. IAEA TRS-398 recommends a displacement of 0.75 times the inner cavity radius (0.75R) for heavy ion beams. Theoretical models by Palmans and by Bhullar and Watchman confirmed this value. However, the experimental results vary from author to author. The purpose of this study is to accurately measure the displacement and explain the past experimental discrepancies. Methods: In this work, we measured the EPOM of cylindrical ionization chambers with high accuracy by comparing the Bragg-peak position obtained with cylindrical ionization chambers (PTW 30013, PTW 31016) to that obtained using a plane-parallel ionization chamber (PTW 34045). Results: The EPOMs of PTW 30013 and 31016 were shifted by 0.92 ± 0.07 R with R = 3.05 mm and 0.90 ± 0.14 R with R = 1.45 mm, respectively, from the reference point toward the source. Conclusions: The EPOMs obtained were greater than the value of 0.75R proposed by the IAEA TRS-398 and the analytical results.

  11. 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.

  12. 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.

  13. Matrix:. AN Innovative Pixel Ionization Chamber for On-Line Beam Monitoring in Hadrontherapy

    NASA Astrophysics Data System (ADS)

    Braccini, S.; Pitta', G.; Donetti, M.; Cirio, R.; La Rosa, A.; Garella, M. A.; Giordanengo, S.; Marchetto, F.; Peroni, C.

    2006-04-01

    The control of intensity, position and shape of clinical beams are key issues in the treatment of tumours using hadron beams, especially in the case of active dose distribution systems. For this purpose an innovative pixel ionization chamber, named MATRIX, has been designed, constructed and tested. The chamber is conceived to be located very near the patient to precisely monitor the beam parameters used to verify the treatment planning specifications. MATRIX operates in air and is characterized by a 21 × 21 cm2 sensitive area subdivided in 1024 pixels of 6.5 × 6.5 mm2. To minimize the amount of material crossed by the beam, the anode is made of a 50 μm kapton foil, with a deposit of 17 μm copper on each side. A very sensitive electronics is used for the readout, based on a dedicated chip. In this paper the construction of the chamber and the very positive results of the first beam tests are described.

  14. 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

  15. Determination of small-field correction factors for cylindrical ionization chambers using a semiempirical method

    NASA Astrophysics Data System (ADS)

    Park, Kwangwoo; Bak, Jino; Park, Sungho; Choi, Wonhoon; Park, Suk Won

    2016-02-01

    A semiempirical method based on the averaging effect of the sensitive volumes of different air-filled ionization chambers (ICs) was employed to approximate the correction factors for beam quality produced from the difference in the sizes of the reference field and small fields. We measured the output factors using several cylindrical ICs and calculated the correction factors using a mathematical method similar to deconvolution; in the method, we modeled the variable and inhomogeneous energy fluence function within the chamber cavity. The parameters of the modeled function and the correction factors were determined by solving a developed system of equations as well as on the basis of the measurement data and the geometry of the chambers. Further, Monte Carlo (MC) computations were performed using the Monaco® treatment planning system to validate the proposed method. The determined correction factors (k{{Q\\text{msr}},Q}{{f\\text{smf}}, {{f}\\text{ref}}} ) were comparable to the values derived from the MC computations performed using Monaco®. For example, for a 6 MV photon beam and a field size of 1  ×  1 cm2, k{{Q\\text{msr}},Q}{{f\\text{smf}}, {{f}\\text{ref}}} was calculated to be 1.125 for a PTW 31010 chamber and 1.022 for a PTW 31016 chamber. On the other hand, the k{{Q\\text{msr}},Q}{{f\\text{smf}}, {{f}\\text{ref}}} values determined from the MC computations were 1.121 and 1.031, respectively; the difference between the proposed method and the MC computation is less than 2%. In addition, we determined the k{{Q\\text{msr}},Q}{{f\\text{smf}}, {{f}\\text{ref}}} values for PTW 30013, PTW 31010, PTW 31016, IBA FC23-C, and IBA CC13 chambers as well. We devised a method for determining k{{Q\\text{msr}},Q}{{f\\text{smf}}, {{f}\\text{ref}}} from both the measurement of the output factors and model-based mathematical computation. The proposed method can be useful in case the MC simulation would not be applicable for the clinical settings.

  16. 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

  17. Performance of a multi-axis ionization chamber array in a 1.5 T magnetic field.

    PubMed

    Smit, K; Kok, J G M; Lagendijk, J J W; Raaymakers, B W

    2014-04-07

    At the UMC Utrecht a prototype MR-linac has been installed. The system consists of an 8 MV Elekta linear accelerator and a 1.5 T Philips MRI system. This paper investigates the performance of the IC PROFILER™, a multi-axis ionization chamber array, in a 1.5 T magnetic field. The influence of the magnetic field on the IC PROFILER™ reproducibility, dose response linearity, pulse rate frequency dependence, power to electronics, panel orientation and ionization chamber shape were investigated. The linearity, reproducibility, pulse rate frequency dependence, panel orientation and ionization chamber shape are unaffected by the magnetic field. When the measurements results are normalized to the centre reference chamber, the measurements can commence unaltered. Orientation of the ionization chambers in the magnetic field is of importance, therefore caution must be taken when comparing or normalizing results from several different axes. IC PROFILER™ dose profiles were compared with film dose profiles obtained simultaneously in the MR-linac. Deviation between the film and the IC PROFILER™ data was caused by the noise in the film, indicating correct performance of the IC PROFILER™ in the transverse 1.5 T magnetic field.

  18. [Theoretical investigation of the saturation correction for ionization chambers irradiated with pulsed beams of arbitrary pulse length].

    PubMed

    Karsch, Leonhard; Pawelke, Jörg

    2014-09-01

    In ionization chambers, not all released charge is collected due to the recombination of charge carriers. This effect is taken into account by the saturation correction factor kS. A physical description of the correction factor has been established for pulsed radiation. However, it is only accurate when the pulse length is short compared with the collection time of the ionization chamber. In this paper we develop a description of the saturation correction for radiation pulses of arbitrary length. For this, a system of partial differential equations is solved iteratively. The numerical solutions are verified experimentally for a Roos ionization chamber (PTW TM34001) exposed to a pulsed electron beam. The results of this iterative procedure describe the experimental data well. The calculations are also possible for beam structures which are experimentally hard to get and thereby contribute to a better understanding and correct description of the saturation correction at arbitrary pulse length. Among other things the pulse length dependent distributions of the charge carriers in the ionization chamber is calculated, inclusive of the transition to the conditions prevailing in the case of continuous irradiation. Furthermore is shown that the formula for kS established by Hochhäuser and Balk is applicable even at arbitrary pulse length, if pulse duration dependent effective values are used for the parameters a and p. These effective values have been determined for the Roos chamber at pulse lengths up to 300 μs.

  19. Performance of a multi-axis ionization chamber array in a 1.5 T magnetic field

    NASA Astrophysics Data System (ADS)

    Smit, K.; Kok, J. G. M.; Lagendijk, J. J. W.; Raaymakers, B. W.

    2014-04-01

    At the UMC Utrecht a prototype MR-linac has been installed. The system consists of an 8 MV Elekta linear accelerator and a 1.5 T Philips MRI system. This paper investigates the performance of the IC PROFILER™, a multi-axis ionization chamber array, in a 1.5 T magnetic field. The influence of the magnetic field on the IC PROFILER™ reproducibility, dose response linearity, pulse rate frequency dependence, power to electronics, panel orientation and ionization chamber shape were investigated. The linearity, reproducibility, pulse rate frequency dependence, panel orientation and ionization chamber shape are unaffected by the magnetic field. When the measurements results are normalized to the centre reference chamber, the measurements can commence unaltered. Orientation of the ionization chambers in the magnetic field is of importance, therefore caution must be taken when comparing or normalizing results from several different axes. IC PROFILER™ dose profiles were compared with film dose profiles obtained simultaneously in the MR-linac. Deviation between the film and the IC PROFILER™ data was caused by the noise in the film, indicating correct performance of the IC PROFILER™ in the transverse 1.5 T magnetic field.

  20. Monte Carlo Simulation in the Optimization of a Free-Air Ionization Chamber for Dosimetric Control in Medical Digital Radiography

    SciTech Connect

    Leyva, A.; Pinera, I.; Abreu, Y.; Cruz, C. M.; Montano, L. M.

    2008-08-11

    During the earliest tests of a free-air ionization chamber a poor response to the X-rays emitted by several sources was observed. Then, the Monte Carlo simulation of X-rays transport in matter was employed in order to evaluate chamber behavior as X-rays detector. The photons energy deposition dependence with depth and its integral value in all active volume were calculated. The obtained results reveal that the designed device geometry is feasible to be optimized.

  1. Comparison of pencil-type ionization chamber calibration results and methods between dosimetry laboratories.

    PubMed

    Hourdakis, Costas J; Büermann, Ludwig; Ciraj-Bjelac, Olivera; Csete, Istvan; Delis, Harry; Gomola, Igor; Persson, Linda; Novak, Leos; Petkov, Ivailo; Toroi, Paula

    2016-01-01

    A comparison of calibration results and procedures in terms of air kerma length product, PKL, and air kerma, K, was conducted between eight dosimetry laboratories. A pencil-type ionization chamber (IC), generally used for computed tomography dose measurements, was calibrated according to three calibration methods, while its residual signal and other characteristics (sensitivity profile, active length) were assessed. The results showed that the "partial irradiation method" is the preferred method for the pencil-type IC calibration in terms of PKL and it could be applied by the calibration laboratories successfully. Most of the participating laboratories achieved high level of agreement (>99%) for both dosimetry quantities (PKL and K). Estimated relative standard uncertainties of comparison results vary among laboratories from 0.34% to 2.32% depending on the quantity, beam quality and calibration method applied. Detailed analysis of the assigned uncertainties have been presented and discussed.

  2. Unexpected bias in NIST 4πγ ionization chamber measurements.

    PubMed

    Unterweger, M P; Fitzgerald, R

    2012-09-01

    In January of 2010, it was discovered that the source holder used for calibrations in the NIST 4πγ ionization chamber (IC) has not been stable. The positioning ring that determines the height of the sample in the reentrant tube of the IC has slowly shifted during 35 years of use. This has led to a slow change in the calibration factors for the various radionuclides measured by this instrument. The changes are dependent on γ-ray energy and the time the IC was calibrated for a given radionuclide. A review of the historic data with regard to when the calibrations were done has enabled us to approximate the magnitude of the changes with time. This requires a number of assumptions, and corresponding uncertainty components, including whether the changes in height were gradual or in steps as will be shown in drawings of sample holder. For calibrations the changes in calibration factors have been most significant for low energy gamma emitters such as (133)Xe, (241)Am, (125)I and (85)Kr. The corrections to previous calibrations can be approximated and the results corrected with an increase in the overall uncertainty. At present we are recalibrating the IC based on new primary measurements of the radionuclides measured on the IC. Likewise we have been calibrating a new automated ionization-chamber system. A bigger problem is the significant number of half-life results NIST has published over the last 35 years that are based on IC measurements. The effect on half-life is largest for long-lived radionuclei, especially low-energy γ-ray emitters. This presentation will review our results and recommend changes in values and/or uncertainties. Any recommendation for withdrawal of any results will also be undertaken. Published by Elsevier Ltd.

  3. 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

    Purpose: Air-communicating well ionization chambers are commonly used to assess air kerma strength of sources used in brachytherapy. The signal produced is supposed to be proportional to the air density within the chamber and, therefore, a density-independent air kerma strength is obtained when the measurement is corrected to standard atmospheric conditions using the usual temperature and pressure correction factor. Nevertheless, when assessing low energy sources, the ionization chambers may not fulfill that condition and a residual density dependence still remains after correction. In this work, the authors examined the behavior of the PTW 34051 SourceCheck ionization chamber when measuring the air kerma strength of {sup 125}I seeds.Methods: Four different SourceCheck chambers were analyzed. With each one of them, two series of measurements of the air kerma strength for {sup 125}I selectSeed{sup TM} brachytherapy sources were performed inside a pressure chamber and varying the pressure in a range from 747 to 1040 hPa (560 to 780 mm Hg). The temperature and relative humidity were kept basically constant. An analogous experiment was performed by taking measurements at different altitudes above sea level.Results: Contrary to other well-known ionization chambers, like the HDR1000 PLUS, in which the temperature-pressure correction factor overcorrects the measurements, in the SourceCheck ionization chamber they are undercorrected. At a typical atmospheric situation of 933 hPa (700 mm Hg) and 20 °C, this undercorrection turns out to be 1.5%. Corrected measurements show a residual linear dependence on the density and, as a consequence, an additional density dependent correction must be applied. The slope of this residual linear density dependence is different for each SourceCheck chamber investigated. The results obtained by taking measurements at different altitudes are compatible with those obtained with the pressure chamber.Conclusions: Variations of the altitude and

  4. Monte Carlo aided design of an improved well-type ionization chamber for low energy brachytherapy sources

    SciTech Connect

    Bohm, Tim D.; Micka, John A.; De Werd, Larry A.

    2007-04-15

    The determination of the air kerma strength of a brachytherapy seed is necessary for effective treatment planning. Well-type ionization chambers are used on site at therapy clinics to determine the air kerma strength of seeds. In this work, an improved well-type ionization chamber for low energy, low dose rate brachytherapy sources is designed using Monte Carlo transport calculations to aid in the design process. The design improvements are the elimination of the air density induced over-response effect seen in other air-communicating chambers for low energy photon sources, and a larger signal strength (response or current) for {sup 103}Pd and {sup 125}I based seeds. A prototype well chamber based on the Monte Carlo aided design but using graphite coated acrylic walls rather than the design basis air equivalent plastic (C-552) walls was constructed and experimentally evaluated. The prototype chamber produced an 85% stronger signal when measuring a commonly used {sup 103}Pd seed and a 26% stronger signal when measuring a commonly used {sup 125}I seed when compared to another commonly used well chamber. The normalized P{sub TP} corrected chamber response is, at most, 1.3% and 2.4% over unity for air densities/pressures corresponding to an elevation of 3048 m (10 000 feet) above sea level for the commonly used {sup 103}Pd and {sup 125}I based seeds respectively. Comparing calculated and measured chamber responses for common {sup 103}Pd and {sup 125}I based brachytherapy seeds show agreement within 0.6% and 0.2%, respectively. We conclude that Monte Carlo transport calculations accurately model the response of this new well chamber and in general can be used to predict the response of well chambers. The prototype chamber built in this work responds as predicted by the Monte Carlo calculations.

  5. Decoupling of Confined Normal 3He

    NASA Astrophysics Data System (ADS)

    Dimov, S. G.; Bennett, R. G.; Ilic, B.; Verbridge, S. S.; Levitin, L. V.; Fefferman, A. D.; Casey, A.; Saunders, J.; Parpia, J. M.

    2010-01-01

    Anodic bonding was used to fabricate a 10 mm diameter × 640 nm tall annular geometry suitable for torsion pendulum studies of confined 3He. For pure 3He at saturated vapor pressure the inertia of the confined fluid was seen to be only partially coupled to the pendulum at 160 mK. Below 100 mK the liquid’s inertial contribution was negligible, indicating a complete decoupling of the 3He from the pendulum.

  6. The properties of the ultramicrocylindrical ionization chamber for small field used in stereotactic radiosurgery.

    PubMed

    Vahc, Y W; Chung, W K; Park, K R; Lee, J Y; Lee, Y H; Kwon, O; Kim, S

    2001-03-01

    Accurate dosimetry of small-field photon beams tends to be difficult to perform due to the presence of lateral electronic disequilibrium and steep dose gradients. In stereotactic radiosurgery (SRS), small fields of 6-30 mm in diameter are used. Generally thermoluminescence dosimetry chips, Farmer, Thimble ion chamber, and film dosimetry are not adequate to measure dose in SRS beams. These techniques generally do not provide the required precision due to their energy dependence and/or poor resolution. It is necessary to construct a small, accurate detector with high spatial resolution for the small fields used in SRS. The ultramicrocylindrical ionization chamber (UCIC) with a gold wall of 2.2 mm in diameter and 4.0 mm in length has dual sensitive volumes of air (8.0 mm3) and borosilicate (2.6 mm3) cavity. Reproducibility, linearity, and radiation damage with respect to absorbed dose, beam profile of small beam, and independence of dose rate of the UCIC are tested by the dose measurements in high energy photon (5, 15 MV) and electron (9 MeV) beams. The UCIC with a unique supporting system in the polystyrene phantom is demonstrated to be a suitable detector for the dose measurements in a small beam size.

  7. The magic cube and the pixel ionization chamber: detectors for monitor and dosimetry of radiotherapy beams

    NASA Astrophysics Data System (ADS)

    Amerio, S.; Boriano, A.; Bourhaleb, F.; Cirio, R.; Donetti, M.; Garelli, E.; Giordanengo, S.; Madon, E.; Marchetto, F.; Nastasi, U.; Peroni, C.; Sanz Freire, C. J.; Sardo, A.; Trevisiol, E.

    2003-09-01

    Tumor therapy takes advantage of the energy deposition of radiation to concentrate high doses in the target while sparing healthy tissue. Elective pathologies for highly conformal radiotherapies such as photon Intensity Modulated Radiotherapy (IMRT) and radiotherapy with hadrons are head and neck, eye, prostate and in general all tumors that are either deep or located close to critical organs. In the world there are several centers that are using such techniques and a common problem that is being experienced is the verification of treatment plans and monitoring of the beam. We have designed and built two detectors that allow 2D and 3D measurements of dose and fluence of such beams. The detectors allow measurements on big surfaces, up to 25∗25 cm2. The active media are parallel plate, strip and pixel segmented ionization chambers with front-end Very Large Scale Integration (VLSI) readout and PC based data acquistion. The description of dosimeter, chamber and electronics will be given with results from beam tests and therapy plan verification.

  8. Scintillation properties of N2 and CF4 and performances of a scintillating ionization chamber

    NASA Astrophysics Data System (ADS)

    Lehaut, G.; Salvador, S.; Fontbonne, J.-M.; Lecolley, F.-R.; Perronnel, J.; Vandamme, Ch.

    2015-10-01

    In this work, we studied the emission yields, decay times and coincidence resolving times (CRT) of two gases, nitrogen (N2) and tetrafluoromethane (CF4), used for particle detection in the context of fission products measurement. The set-up was made of an ionization chamber and two photomultiplier tubes (PMTs) placed front-to-front on each side of the active zone of the chamber. Using the photomultiplier tubes, the number of photoelectrons (phe) converted at the photocathodes from the scintillation processes in each gas was quantified and the scintillation time spectra were recorded. A scintillation emission yield of 24 phe MeV-1 with a decay time of τd = 2.5 ns in N2, and 225 phe MeV-1 with τd = 6.2 ns for CF4, has been measured. With our set-up, the coincidence resolving time (σ values) between the two PMTs have been measured using alpha particles at 1.4 ns and 0.34 ns for N2 and CF4, respectively.

  9. 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.

  10. A two-dose-rate method for general recombination correction for liquid ionization chambers in pulsed beams

    NASA Astrophysics Data System (ADS)

    Tölli, Heikki; Sjögren, Rickard; Wendelsten, Mikael

    2010-08-01

    The correction for general recombination losses in liquid ionization chambers (LICs) is more complex than that in air-filled ionization chambers. The reason for this is that the saturation charge in LICs, i.e. the charge that escapes initial recombination, depends on the applied voltage. This paper presents a method, based on measurements at two different dose rates in a pulsed beam, for general recombination correction in LICs. The Boag theory for pulsed beams is used and the collection efficiency is determined by numerical methods which are equivalent to the two-voltage method used in dosimetry with air-filled ionization chambers. The method has been tested in experiments in water in a 20 MeV electron beam using two LICs filled with isooctane and tetramethylsilane. The dose per pulse in the electron beam was varied between 0.1 mGy/pulse and 8 mGy/pulse. The relative standard deviations of the collection efficiencies determined with the two-dose-rate method ranged between 0.1% and 1.5%. The dose-rate variations of the general recombination corrected charge measured with the LICs are in excellent agreement with the corresponding values obtained with an air-filled plane parallel ionization chamber.

  11. Source geometry factors for HDR ¹⁹²Ir brachytherapy secondary standard well-type ionization chamber calibrations.

    PubMed

    Shipley, D R; Sander, T; Nutbrown, R F

    2015-03-21

    Well-type ionization chambers are used for measuring the source strength of radioactive brachytherapy sources before clinical use. Initially, the well chambers are calibrated against a suitable national standard. For high dose rate (HDR) (192)Ir, this calibration is usually a two-step process. Firstly, the calibration source is traceably calibrated against an air kerma primary standard in terms of either reference air kerma rate or air kerma strength. The calibrated (192)Ir source is then used to calibrate the secondary standard well-type ionization chamber. Calibration laboratories are usually only equipped with one type of HDR (192)Ir source. If the clinical source type is different from that used for the calibration of the well chamber at the standards laboratory, a source geometry factor, k(sg), is required to correct the calibration coefficient for any change of the well chamber response due to geometric differences between the sources. In this work we present source geometry factors for six different HDR (192)Ir brachytherapy sources which have been determined using Monte Carlo techniques for a specific ionization chamber, the Standard Imaging HDR 1000 Plus well chamber with a type 70010 HDR iridium source holder. The calculated correction factors were normalized to the old and new type of calibration source used at the National Physical Laboratory. With the old Nucletron microSelectron-v1 (classic) HDR (192)Ir calibration source, ksg was found to be in the range 0.983 to 0.999 and with the new Isodose Control HDR (192)Ir Flexisource k(sg) was found to be in the range 0.987 to 1.004 with a relative uncertainty of 0.4% (k = 2). Source geometry factors for different combinations of calibration sources, clinical sources, well chambers and associated source holders, can be calculated with the formalism discussed in this paper.

  12. 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.

  13. Correction factors for the INER-improved free-air ionization chambers calculated with the Monte Carlo method.

    PubMed

    Lin, Uei-Tyng; Chu, Chien-Hau

    2006-05-01

    Monte Carlo method was used to simulate the correction factors for electron loss and scattered photons for two improved cylindrical free-air ionization chambers (FACs) constructed at the Institute of Nuclear Energy Research (INER, Taiwan). The method is based on weighting correction factors for mono-energetic photons with X-ray spectra. The newly obtained correction factors for the medium-energy free-air chamber were compared with the current values, which were based on a least-squares fit to experimental data published in the NBS Handbook 64 [Wyckoff, H.O., Attix, F.H., 1969. Design of free-air ionization chambers. National Bureau Standards Handbook, No. 64. US Government Printing Office, Washington, DC, pp. 1-16; Chen, W.L., Su, S.H., Su, L.L., Hwang, W.S., 1999. Improved free-air ionization chamber for the measurement of X-rays. Metrologia 36, 19-24]. The comparison results showed the agreement between the Monte Carlo method and experimental data is within 0.22%. In addition, mono-energetic correction factors for the low-energy free-air chamber were calculated. Average correction factors were then derived for measured and theoretical X-ray spectra at 30-50 kVp. Although the measured and calculated spectra differ slightly, the resulting differences in the derived correction factors are less than 0.02%.

  14. DNP for polarizing liquid {sup 3}He

    SciTech Connect

    Uemtasu, H.; Iwata, T.; Kato, S.; Michigami, T.; Ohizumi, S.; Shishido, T.; Tanaka, A.; Toyama, K.; Tajima, Y.; Yoshida, H. Y.; Kuriyama, N.

    2008-02-06

    Using DNP with zeolite powders and TEMPO, we have developed a method to enhance polarization of liquid {sup 3}He. At magnetic field of 2.5 T and a temperature of around 1.5 K, we have obatined polarization enhancement of liquid {sup 3}He, 2.34 and -1.59 for positive and negative enhancements, respectively.

  15. 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

  16. Investigation of electron-loss and photon scattering correction factors for FAC-IR-300 ionization chamber

    NASA Astrophysics Data System (ADS)

    Mohammadi, S. M.; Tavakoli-Anbaran, H.; Zeinali, H. Z.

    2017-02-01

    The parallel-plate free-air ionization chamber termed FAC-IR-300 was designed at the Atomic Energy Organization of Iran, AEOI. This chamber is used for low and medium X-ray dosimetry on the primary standard level. In order to evaluate the air-kerma, some correction factors such as electron-loss correction factor (ke) and photon scattering correction factor (ksc) are needed. ke factor corrects the charge loss from the collecting volume and ksc factor corrects the scattering of photons into collecting volume. In this work ke and ksc were estimated by Monte Carlo simulation. These correction factors are calculated for mono-energy photon. As a result of the simulation data, the ke and ksc values for FAC-IR-300 ionization chamber are 1.0704 and 0.9982, respectively.

  17. Vortices in rotating superfluid 3He

    PubMed Central

    Lounasmaa, Olli V.; Thuneberg, Erkki

    1999-01-01

    In this review we first present an introduction to 3He and to the ROTA collaboration under which most of the knowledge on vortices in superfluid 3He has been obtained. In the physics part, we start from the exceptional properties of helium at millikelvin temperatures. The dilemma of rotating superfluids is presented. In 4He and in 3He-B the problem is solved by nucleating an array of singular vortex lines. Their experimental detection in 3He by NMR is described next. The vortex cores in 3He-B have two different structures, both of which have spontaneously broken symmetry. A spin-mass vortex has been identified as well. This object is characterized by a flow of spins around the vortex line, in addition to the usual mass current. A great variety of vortices exist in the A phase of 3He; they are either singular or continuous, and their structure can be a line or a sheet or fill the whole liquid. Altogether seven different types of vortices have been detected in 3He by NMR. We also describe briefly other experimental methods that have been used by ROTA scientists in studying vortices in 3He and some important results thus obtained. Finally, we discuss the possible applications of experiments and theory of 3He to particle physics and cosmology. In particular, we report on experiments where superfluid 3He-B was heated locally by absorption of single neutrons. The resulting events can be used to test theoretical models of the Big Bang at the beginning of our universe. PMID:10393895

  18. Vortices in rotating superfluid 3He.

    PubMed

    Lounasmaa, O V; Thuneberg, E

    1999-07-06

    In this review we first present an introduction to 3He and to the ROTA collaboration under which most of the knowledge on vortices in superfluid 3He has been obtained. In the physics part, we start from the exceptional properties of helium at millikelvin temperatures. The dilemma of rotating superfluids is presented. In 4He and in 3He-B the problem is solved by nucleating an array of singular vortex lines. Their experimental detection in 3He by NMR is described next. The vortex cores in 3He-B have two different structures, both of which have spontaneously broken symmetry. A spin-mass vortex has been identified as well. This object is characterized by a flow of spins around the vortex line, in addition to the usual mass current. A great variety of vortices exist in the A phase of 3He; they are either singular or continuous, and their structure can be a line or a sheet or fill the whole liquid. Altogether seven different types of vortices have been detected in 3He by NMR. We also describe briefly other experimental methods that have been used by ROTA scientists in studying vortices in 3He and some important results thus obtained. Finally, we discuss the possible applications of experiments and theory of 3He to particle physics and cosmology. In particular, we report on experiments where superfluid 3He-B was heated locally by absorption of single neutrons. The resulting events can be used to test theoretical models of the Big Bang at the beginning of our universe.

  19. Assessment of ionization chamber correction factors in photon beams using a time saving strategy with PENELOPE code.

    PubMed

    Reis, C Q M; Nicolucci, P

    2016-02-01

    The purpose of this study was to investigate Monte Carlo-based perturbation and beam quality correction factors for ionization chambers in photon beams using a saving time strategy with PENELOPE code. Simulations for calculating absorbed doses to water using full spectra of photon beams impinging the whole water phantom and those using a phase-space file previously stored around the point of interest were performed and compared. The widely used NE2571 ionization chamber was modeled with PENELOPE using data from the literature in order to calculate absorbed doses to the air cavity of the chamber. Absorbed doses to water at reference depth were also calculated for providing the perturbation and beam quality correction factors for that chamber in high energy photon beams. Results obtained in this study show that simulations with phase-space files appropriately stored can be up to ten times shorter than using a full spectrum of photon beams in the input-file. Values of kQ and its components for the NE2571 ionization chamber showed good agreement with published values in the literature and are provided with typical statistical uncertainties of 0.2%. Comparisons to kQ values published in current dosimetry protocols such as the AAPM TG-51 and IAEA TRS-398 showed maximum percentage differences of 0.1% and 0.6% respectively. The proposed strategy presented a significant efficiency gain and can be applied for a variety of ionization chambers and clinical photon beams. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  20. Determinations of the correction factors for small fields in cylindrical ionization chambers based on measurement and numerical calculation

    NASA Astrophysics Data System (ADS)

    Park, Kwangwoo; Choi, Wonhoon; Park, Sungho; Choi, Jin Hwa; Park, Suk Won; Bak, Jino

    2015-07-01

    We investigated the volume averaging effect for air-filled cylindrical ionization chambers to determine the correction factors in a small photon field for a given chamber. We measured output factors with several cylindrical ionization chambers, and by using a mathematical method similar to deconvolution, we modeled the non-constant and inhomogeneous exposure function in the cavity of the chamber. The parameters in the exposure function and the correction factors were determined by solving a system of equations that we had developed by using the measured data and the geometry of the given chamber. The correction factors (CFs) were very similar to those obtained from Monte Carlo (MC) simulations. For example, the CFs in this study were found to be 1.116 for PTW31010 and 1.0225 for PTW31016 while the CFs obtained from MC simulations were reported as being approximately between 1.17 and 1.20 for PTW31010 and between 1.02 and 1.06 for PTW31016 in a 6-MV photon beam of 1 × 1 cm2. Furthermore, the method of deconvolution combined with the MC result for the chamber's response function showed a similar CF for PTW 30013, which was reported as 2.29 and 1.54 for a 1 × 1 cm2 and a 1.5 × 1.5 cm2 field size, respectively. The CFs from our method were similar, 2.42 and 1.54. In addition, we report CFs for PTW30013, PTW31010, PTW31016, IBA FC23-C, and IBA CC13. As a consequence, we suggest the use of our method to measure the correct output factor by using the fact that an inhomogeneous exposure causes a volume averaging effect in the cavity of air-filled cylindrical ionization chamber. The result obtained by using our method is very similar to that obtained from MC simulations. The method we developed can easily be applied in clinics.

  1. Time-resolved dosimetry using a pinpoint ionization chamber as quality assurance for IMRT and VMAT

    SciTech Connect

    Louwe, Robert J. W. Satherley, Thomas; Day, Rebecca A.; Greig, Lynne; Wendling, Markus; Monshouwer, René

    2015-04-15

    Purpose: To develop a method to verify the dose delivery in relation to the individual control points of intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) using an ionization chamber. In addition to more effective problem solving during patient-specific quality assurance (QA), the aim is to eventually map out the limitations in the treatment chain and enable a targeted improvement of the treatment technique in an efficient way. Methods: Pretreatment verification was carried out for 255 treatment plans that included a broad range of treatment indications in two departments using the equipment of different vendors. In-house developed software was used to enable calculation of the dose delivery for the individual beamlets in the treatment planning system (TPS), for data acquisition, and for analysis of the data. The observed deviations were related to various delivery and measurement parameters such as gantry angle, field size, and the position of the detector with respect to the field edge to distinguish between error sources. Results: The average deviation of the integral fraction dose during pretreatment verification of the planning target volume dose was −2.1% ± 2.2% (1 SD), −1.7% ± 1.7% (1 SD), and 0.0% ± 1.3% (1 SD) for IMRT at the Radboud University Medical Center (RUMC), VMAT (RUMC), and VMAT at the Wellington Blood and Cancer Centre, respectively. Verification of the dose to organs at risk gave very similar results but was generally subject to a larger measurement uncertainty due to the position of the detector at a high dose gradient. The observed deviations could be related to limitations of the TPS beam models, attenuation of the treatment couch, as well as measurement errors. The apparent systematic error of about −2% in the average deviation of the integral fraction dose in the RUMC results could be explained by the limitations of the TPS beam model in the calculation of the beam penumbra. Conclusions: This

  2. The control system of the multi-strip ionization chamber for the HIMM

    NASA Astrophysics Data System (ADS)

    Li, Min; Yuan, Y. J.; Mao, R. S.; Xu, Z. G.; Li, Peng; Zhao, T. C.; Zhao, Z. L.; Zhang, Nong

    2015-03-01

    Heavy Ion Medical Machine (HIMM) is a carbon ion cancer treatment facility which is being built by the Institute of Modern Physics (IMP) in China. In this facility, transverse profile and intensity of the beam at the treatment terminals will be measured by the multi-strip ionization chamber. In order to fulfill the requirement of the beam position feedback to accomplish the beam automatic commissioning, less than 1 ms reaction time of the Data Acquisition (DAQ) of this detector must be achieved. Therefore, the control system and software framework for DAQ have been redesigned and developed with National Instruments Compact Reconfigurable Input/Output (CompactRIO) instead of PXI 6133. The software is Labview-based and developed following the producer-consumer pattern with message mechanism and queue technology. The newly designed control system has been tested with carbon beam at the Heavy Ion Research Facility at Lanzhou-Cooler Storage Ring (HIRFL-CSR) and it has provided one single beam profile measurement in less than 1 ms with 1 mm beam position resolution. The fast reaction time and high precision data processing during the beam test have verified the usability and maintainability of the software framework. Furthermore, such software architecture is easy-fitting to applications with different detectors such as wire scanner detector.

  3. Preliminary results with a strip ionization chamber used as beam monitor for hadrontherapy treatments

    NASA Astrophysics Data System (ADS)

    Boriano, A.; Bourhaleb, F.; Cirio, R.; Cirrone, G. A. P.; Cuttone, G.; Donetti, M.; Garelli, E.; Giordanengo, S.; Luparia, A.; Marchette, F.; Peroni, C.; Raffaele, L.; Sabini, M. G.; Valastro, L.

    2006-01-01

    Preliminary results are presented from a test of a parallel plate ionization chamber with the anode segmented in strips (MOPI) to be used as a beam monitor for therapeutical treatments on the 62 MeV proton beam line of the INFN-LNS Superconducting Cyclotron. Ocular pathologies have been treated at the Catana facility since March 2002. The detector, placed downstream of the patient collimator, will allow the measurement of the relevant beam diagnostic parameters during treatment such as integrated beam fluence, for dose determination; the beam baricentre, width and asymmetry will be obtained from the fluence profile sampled with a resolution of about 100 Urn at a rate up to 1 kHz with no dead time. In this test, carried out at LNS, the detector has been exposed to different beam shapes and the integrated fluence derived by the measured beam profiles has been compared with that obtained with other dosimeters normally used for treatment. The skewness of the beam profile has been measured and shown to be suitable to on-line check variations of the beam shape.

  4. Optimization of signal extraction and front-end design in a fast,multigap ionization chamber

    SciTech Connect

    Datte, P.S.; Manfredi, P.F.; Millaud, J.E.; Placidi, M.; Ratti,L.; Speziali, V.; Traversi, G.; Turner, W.C.

    2001-11-05

    This paper discusses the criteria that have been adopted tooptimize the signal processing in a shower detector to be employed as LHCbeam luminosity monitor. The original aspect ofthis instrument is itsablility to operate on a bunch-by-bunch basis. This means that it mustperform accurate charge measurements at a repetition rate of 40 MHz. Thedetector must withstand an integrated dose of 100 Grad, that is, two tothree orders of magnitude beyond those expected in the experiments. Tomeet the above requirements, an ionization chamber consisting of severalgaps of thickness 0.5 mm, filled with a gas that is expected to beradiation resistant, has been designed. Crucial in the development of thesystem is the signal processing, as the electronic noise may set thedominant limitation to the accuracy of the measurement. This is relatedto two aspects. One is the short time available for the chargemeasurement. The second one is the presence of a few meter cable betweenthe detector and the preamplifier, as this must be located out of theregion of highest radiation field. Therefore the optimization of thesignal-to-noise ratio requires that the best configuration of the chambergaps be determined under the constraint of the presence of a cable ofnon-negligible length between detector and preamplifier. The remoteplacement of the amplifying electronics will require that the front-endelectronics be radiation hard although to a lesser extent than thedetector.

  5. Technical note: a method for improving the calibration reproducibility of an ionization chamber detector array.

    PubMed

    Goodall, Simon; Morgan, Steve

    2014-09-01

    This paper describes an extension to a wide field calibration method implemented on a commercial detector array in order to improve the reproducibility of the calibration procedure. Following the standard array calibration procedure, two additional 10×10 cm exposures were acquired for each array axis with the detector array shifted by ±10 cm in the transverse or axial axes, or by ±10√2 cm in the positive or negative diagonal axes. These exposures were compared with a final baseline 10×10 cm exposure captured with the detector repositioned at the isocenter. The measurements were used to calculate a linear off-axis correction gradient which was then applied to the stored calibration factors. The mean coefficient of variation between five repeat calibrations was reduced from 4.17% to 0.48% and the maximum percentage error in individual calibration factors was reduced from 6.46% to 0.77%. The reproducibility of the calibration factors of an ionization chamber array was increased by capturing a baseline exposure and two further off-axis readings per calibration axis.

  6. Detecting MLC errors in stereotactic radiotherapy plans with a liquid filled ionization chamber array.

    PubMed

    O'Connor, Patrick; Seshadri, Venkatakrisnan; Charles, Paul

    2016-03-01

    Quality assurance of stereotactic radiotherapy demands the use of equipment with the highest resolution and sensitivity available. This study examines the sensitivity of a commercially available liquid-filled ionization chamber array--the Octavius 1000 SRS (PTW, Frieburg, Germany) for detecting small (sub-millimetre) multi-leaf collimator (MLC) alignment errors in static square fields (side length 16-40 mm). Furthermore, the effectiveness of detecting small MLC errors in clinical stereotactic radiotherapy patient plans using the device was also evaluated. The commonly used gamma pass rate metric (of the measurements compared with treatment planning system generated results) was used. The gamma pass rates were then evaluated as a function of MLC position error (MLC error size 0.1-2.5 mm). The detector array exhibited a drop in pass rate between plans without error and those which had MLC errors induced. For example a drop in pass rate of 4.5% (gamma criteria 3%, 1 mm) was observed when a 0.8 mm error was introduced into a 16 mm square field. Furthermore the drop in pass rate increased as the MLC position error increased. This study showed that the Octavius 1000 SRS array could be a useful tool for applications requiring the detection of small geometric delivery uncertainties.

  7. Liquid ionization chamber initial recombination dependence on LET for electrons and photons.

    PubMed

    Johansson, Erik; Andersson, Jonas; Johansson, Lennart; Tölli, Heikki

    2013-06-21

    The possibility of indirect measurements of linear energy transfer (LET) with a liquid ionization chamber (LIC) has been investigated by studying initial recombination losses at different applied voltages. A linear fit is made to the voltage-signal curve and the intersection point of the fit and the voltage-axis is shown to correlate with LET. The LIC applied voltages were 100-700 V, which corresponds to electric field strengths between 0.3 and 2.0 MV m(-1). Several different photon and electron beams have been studied, and by using MCNPX™ the respective LET spectra have been determined. The beam qualities in this study were found to have a fluence averaged LET between 0.17 and 1.67 keV µm(-1) and a corresponding dose averaged LET between 0.97 and 4.62 keV µm(-1). For the experimental data in this study the linear fit method yields consistent results with respect to Monte Carlo simulated LET values. A calibration curve for LET determination is provided for the LIC used in the present work.

  8. D-IMRT verification with a 2D pixel ionization chamber: dosimetric and clinical results in head and neck cancer.

    PubMed

    Stasi, M; Giordanengo, S; Cirio, R; Boriano, A; Bourhaleb, F; Cornelius, I; Donetti, M; Garelli, E; Gomola, I; Marchetto, F; Porzio, M; Sanz Freire, C J; Sardo, A; Peroni, C

    2005-10-07

    Dynamic intensity-modulated radiotherapy (D-IMRT) using the sliding-window technique is currently applied for selected treatments of head and neck cancer at Institute for Cancer Research and Treatment of Candiolo (Turin, Italy). In the present work, a PiXel-segmented ionization Chamber (PXC) has been used for the verification of 19 fields used for four different head and neck cancers. The device consists of a 32x32 matrix of 1024 parallel-plate ionization chambers arranged in a square of 24x24 cm2 area. Each chamber has 0.4 cm diameter and 0.55 cm height; a distance of 0.75 cm separates the centre of adjacent chambers. The sensitive volume of each single ionization chamber is 0.07 cm3. Each of the 1024 independent ionization chambers is read out with a custom microelectronics chip.The output factors in water obtained with the PXC at a depth of 10 cm were compared to other detectors and the maximum difference was 1.9% for field sizes down to 3x3 cm2. Beam profiles for different field dimensions were measured with the PXC and two other types of ionization chambers; the maximum distance to agreement (DTA) in the 20-80% penumbra region of a 3x3 cm2 field was 0.09 cm. The leaf speed of the multileaf collimator was varied between 0.07 and 2 cm s-1 and the detector response was constant to better than 0.6%. The behaviour of the PXC was measured while varying the dose rate between 0.21 and 1.21 Gy min-1; the mean difference was 0.50% and the maximum difference was 0.96%. Using fields obtained with an enhanced dynamic wedge and a staircase-like (step) IMRT field, the PXC has been tested for simple 1D modulated beams; comparison with film gave a maximum DTA of 0.12 cm. The PXC was then used to check four different IMRT plans for head and neck cancer treatment: cervical chordoma, parotid, ethmoid and skull base. In the comparison of the PXC versus film and PXC versus treatment planning system, the number of pixels with gamma parameter

  9. D-IMRT verification with a 2D pixel ionization chamber: dosimetric and clinical results in head and neck cancer

    NASA Astrophysics Data System (ADS)

    Stasi, M.; Giordanengo, S.; Cirio, R.; Boriano, A.; Bourhaleb, F.; Cornelius, I.; Donetti, M.; Garelli, E.; Gomola, I.; Marchetto, F.; Porzio, M.; Sanz Freire, C. J.; Sardo, A.; Peroni, C.

    2005-10-01

    Dynamic intensity-modulated radiotherapy (D-IMRT) using the sliding-window technique is currently applied for selected treatments of head and neck cancer at Institute for Cancer Research and Treatment of Candiolo (Turin, Italy). In the present work, a PiXel-segmented ionization Chamber (PXC) has been used for the verification of 19 fields used for four different head and neck cancers. The device consists of a 32 × 32 matrix of 1024 parallel-plate ionization chambers arranged in a square of 24 × 24 cm2 area. Each chamber has 0.4 cm diameter and 0.55 cm height; a distance of 0.75 cm separates the centre of adjacent chambers. The sensitive volume of each single ionization chamber is 0.07 cm3. Each of the 1024 independent ionization chambers is read out with a custom microelectronics chip. The output factors in water obtained with the PXC at a depth of 10 cm were compared to other detectors and the maximum difference was 1.9% for field sizes down to 3 × 3 cm2. Beam profiles for different field dimensions were measured with the PXC and two other types of ionization chambers; the maximum distance to agreement (DTA) in the 20-80% penumbra region of a 3 × 3 cm2 field was 0.09 cm. The leaf speed of the multileaf collimator was varied between 0.07 and 2 cm s-1 and the detector response was constant to better than 0.6%. The behaviour of the PXC was measured while varying the dose rate between 0.21 and 1.21 Gy min-1; the mean difference was 0.50% and the maximum difference was 0.96%. Using fields obtained with an enhanced dynamic wedge and a staircase-like (step) IMRT field, the PXC has been tested for simple 1D modulated beams; comparison with film gave a maximum DTA of 0.12 cm. The PXC was then used to check four different IMRT plans for head and neck cancer treatment: cervical chordoma, parotid, ethmoid and skull base. In the comparison of the PXC versus film and PXC versus treatment planning system, the number of pixels with γ parameter <=1 was 97.7% and 97

  10. Investigation of the initial and volume recombination losses in gamma versatile cylindrical ionization chamber VGIC developed for gamma ray dosimetry

    SciTech Connect

    Fares, M.; Mameri, S.; Abdlani, I.; Negara, K.

    2015-07-01

    A versatile Gamma ionization chambers are used for flow control in systems with gamma nuclear reactors and reprocessing plants in and monitoring atmosphere around these facilities, this in order to protect staff. In the Laboratory Detection and Measures (LDM) Division for Study and Development of Nuclear Instrumentation (DSDNI) of CRNB, we designed, developed and characterized a versatile gamma ionization chamber (VGIC) to study experimentally its characteristics according to the geometry of the electrodes, the volume and pressure of the filler gas for the design of a gamma sealed chamber. The tests were conducted under the IEC (International Electro-technical Commission). In this paper, we present the results obtained in the various nuclear tests for characterization and calibration that we have made on the ionization chamber gamma VGIC prototype developed at our Department. To do this, three irradiators were operated at the Laboratory Calibration (SSDL) of the Department of Medical Physics Nuclear Research Center of Algiers (CRNA). Irradiator intensive gamma ({sup 60}Co: 1.25 MeV), one medium intensity gamma ({sup 137}Cs: 0.662 MeV) and 3rd low intensity ({sup 60}Co). Saturation curves and linearity were identified and the operating range and the sensitivity of the chamber have been deducted. The (I,V) characteristics of the chamber filled, with argon gas at 3 bar (0.3 M pa) pressure, for gamma ray irradiator sources were studied. To do so, the chamber was irradiated with gamma rays using different numbers of gamma sources (i.e. Up to 5). The plateau region is reached above 200 V and the detector operating voltage is found to be 600 V. It is observed that in the plateau region the slope is constant with an increase in the exposure rate. The (1/I, 1/V) and (I, l/V{sup 2}) characteristic curves reveal the presence of the initial and volume recombination losses. The volume recombination losses are found to be smaller than the initial recombination losses. Finally

  11. Effect of the calibration in water and the build-up cap on the Mg(Ar) ionization chamber measurements.

    PubMed

    Koivunoro, H; Hyvönen, H; Uusi-Simola, J; Jokelainen, I; Kosunen, A; Kortesniemi, M; Seppälä, T; Auterinen, I; Savolainen, S

    2011-12-01

    Magnesium-walled argon gas flow ionization chamber (Mg(Ar)) is used for photon dose measurements in the epithermal neutron beam of FiR 1 reactor in Finland. In this study, the photon dose measurements were re-evaluated against calculations applying a new chamber calibration factor defined in water instead of in air. Also, effect of the build-up cap on the measurements was investigated. The new calibration factor provides improved agreement between measured and calculated photon dose. Use of the build-up cap does not affect the measured signal in water in neutron beam. Copyright © 2011 Elsevier Ltd. All rights reserved.

  12. First result of the cross sectional measurement of 3He-3He solar reaction in OCEAN

    NASA Astrophysics Data System (ADS)

    Itahashi, T.; Kudomi, N.; Kume, K.; Takahisa, K.; Yoshida, S.; Ejiri, H.; Toki, H.; Nagai, Y.; Komori, M.; Ohsumi, H.

    2001-04-01

    The first result in OCEAN measurement of the fusion reactions 3He(3He,2p)α at the energy of 40 to 50 keV by means of a low-energy, high current accelerator are reported. The accelerator in this facility can produce an intense beam of 3He1+ and 3He2+ ions of more than 1mA. A detection efficiency for proposed detector assembly of ΔE-E counter telescope is simulated with GEANT program and it expects a detection efficiency about 10% for the two proton coincidence for 3He+3He-->2p+α reaction. The accuracy of Monte Carlo program was checked by D(3He,p)α reaction by replacing the target gas to deuterium. .

  13. A patient-specific quality assurance study on absolute dose verification using ionization chambers of different volumes in RapidArc treatments.

    PubMed

    Syam Kumar, S A; Sukumar, Prabakar; Sriram, Padmanaban; Rajasekaran, Dhanabalan; Aketi, Srinu; Vivekanandan, Nagarajan

    2012-01-01

    The recalculation of 1 fraction from a patient treatment plan on a phantom and subsequent measurements have become the norms for measurement-based verification, which combines the quality assurance recommendations that deal with the treatment planning system and the beam delivery system. This type of evaluation has prompted attention to measurement equipment and techniques. Ionization chambers are considered the gold standard because of their precision, availability, and relative ease of use. This study evaluates and compares 5 different ionization chambers: phantom combinations for verification in routine patient-specific quality assurance of RapidArc treatments. Fifteen different RapidArc plans conforming to the clinical standards were selected for the study. Verification plans were then created for each treatment plan with different chamber-phantom combinations scanned by computed tomography. This includes Medtec intensity modulated radiation therapy (IMRT) phantom with micro-ionization chamber (0.007 cm(3)) and pinpoint chamber (0.015 cm(3)), PTW-Octavius phantom with semiflex chamber (0.125 cm(3)) and 2D array (0.125 cm(3)), and indigenously made Circular wax phantom with 0.6 cm(3) chamber. The measured isocenter absolute dose was compared with the treatment planning system (TPS) plan. The micro-ionization chamber shows more deviations when compared with semiflex and 0.6 cm(3) with a maximum variation of -4.76%, -1.49%, and 2.23% for micro-ionization, semiflex, and farmer chambers, respectively. The positive variations indicate that the chamber with larger volume overestimates. Farmer chamber shows higher deviation when compared with 0.125 cm(3). In general the deviation was found to be <1% with the semiflex and farmer chambers. A maximum variation of 2% was observed for the 0.007 cm(3) ionization chamber, except in a few cases. Pinpoint chamber underestimates the calculated isocenter dose by a maximum of 4.8%. Absolute dose measurements using the semiflex

  14. Determination of the thermal neutron flux in a fast neutron beam by use of a boron-coated ionization chamber.

    PubMed

    Lüdemann, L; Matzen, T; Matzke, M; Schmidt, R; Scobel, W

    1995-11-01

    The thermal neutron distribution in slow and fast neutron beams is usually determined using the foil activation method. In this work a small magnesium walled ionization chamber, in which the inner surface of the wall has been coated with 10B to increase the sensitivity for thermal neutrons, is used to estimate the thermal neutron component of the beam. After calibration and determination of the directional response in a thermal neutron beam a comparison with foil activation at different depths in water was performed to investigate the reliability of the ionization measurements. The chamber was used in a computer controlled water phantom to measure the depth and lateral distribution of the thermal neutron dose. With this arrangement two-dimensional scans of the thermal neutrons could be performed quickly and with high accuracy.

  15. Wall correction factors for calibration of plane-parallel ionization chambers with high-energy photon beams.

    PubMed

    Araki, F; Ikeda, R; Shirakawa, Y; Shimonobou, T; Moribe, N; Takada, T; Takahashi, M; Oura, H; Matoba, M

    2000-09-01

    Most dosimetry protocols recommend that calibration of plane-parallel ionization chambers be performed in an electron beam of sufficiently high energy by comparison with cylindrical chambers. For various plane-parallel chambers, the 1997 IAEA TRS-381 protocol includes an overall perturbation factor pQ for electron beams, a wall correction factor p(wall) for a 60Co beam and the product of two wall corrections k(att)k(m) for 60Co in-air calibration. The recommended values of p(wall) for plane-parallel chambers, however, are limited to certain phantom materials and a 60Co beam, and are not given for other phantom materials and x-ray beams. In this work, the p(wall) values of the commercially available NACP, PTW/Markus and PTW/Roos plane-parallel chambers in a solid water phantom have been determined with 60Co and 4 and 10 MV photon beams. The k(att)k(m) values for the NACP and PTW/Markus chambers have also been obtained. The wall correction factors p(wall) and k(att)k(m) have been determined by intercomparison with a calibrated Farmer chamber. The average value of p(wall) for these plane-parallel chambers was 1.005 +/- 0.1% (1 SD) for 60Co beams and 1.007 +/- 0.2% (1 SD) for both 4 MV and 10 MV photons. The k(att)k(m) values for the NACP and PTW/Markus chambers were about 1.5% lower than other published data.

  16. Experimental derivation of wall correction factors for ionization chambers used in high dose rate 192Ir source calibration.

    PubMed

    Maréchal, M H; de Almeida, C E; Ferreira, I H; Sibata, C H

    2002-01-01

    At present there are no specific primary standards for 192Ir high dose rate sources used in brachytherapy. Traceability to primary standards is guaranteed through the method recommended by the AAPM that derives the air kerma calibration factor for the 192Ir gamma rays as the average of the air kerma calibration factors for x-rays and 137Cs gamma-rays or the Maréchal et al. method that uses the energy-weighted air kerma calibration factors for 250 kV x rays and 60Co gamma rays as the air kerma calibration factor for the 192Ir gamma rays. In order to use these methods, it is necessary to use the same buildup cap for all energies and the appropriate wall correction factor for each chamber. This work describes experimental work used to derive the A(W) for four different ionization chambers and different buildup cap materials for the three energies involved in the Maréchal et al. method. The A(W) for the two most common ionization chambers used in hospitals, the Farmer NE 2571 and PTW N30001 is 0.995 and 0.997, respectively, for 250 kV x rays, 0.982 and 0.985 for 192Ir gamma rays, and 0.979 and 0.991 for 60Co gamma rays, all for a PMMA build-up cap of 0.550 gm cm(-2). A comparison between the experimental values and Monte Carlo calculations shows an agreement better than 0.9%. Availability of the A(W) correction factors for all commercial chambers allows users of the in-air calibration jig, provided by the manufacturer, to alternatively use the Maréchal et al. method. Calibration laboratories may also used this method for calibration of a well-type ionization chamber with a comparable accuracy to the AAPM method.

  17. Cosmogenic 3He in detrital gold

    NASA Astrophysics Data System (ADS)

    Stuart, Finlay; Yakubovich, Olga; Caracedo, Ana; Nesterenok, Alexander

    2017-04-01

    Since the measurement of cosmogenic He in an alluvial diamond by McConville and Reynolds (1996) the application of cosmogenic noble gases to individual detrital grains to quantify surface processes has not been vigorously pursued. The likely low rate of diffusion of cosmogenic He in native metals, and their resistance to weathering and disintegration during erosion and transport, makes them a potential record of long-term Earth surface processes. In an effort to assess the extent that detrital refractory metals record the exposure history during transport and storage we have undertaken a reconnaissance study of the He isotope composition in 18 grains (2-200 mg) of native gold, copper, silver, and PtPd, Pt3Fe and OsIr alloys from alluvial placer deposits from around the world. 4He is dominantly the result of U and Th decay within the grains, or decay of 190Pt in the Pt-rich alloys. 3He is measurable in 13 grains, concentrations range up to 2.7E+6 atoms/g. 3He/4He are always in excess of the crustal radiogenic ratio, up to 306 Ra. Although nucleogenic 3He produced by (n,α) reactions on 6Li, and 3He from trapped hydrothermal fluids, are present, the majority of the 3He is cosmogenic in origin. Using newly calculated cosmogenic 3He production rates in heavy metals, and a determination of the effect of implantation based on the stopping distances of spallogenic 3He and 3H, the grains have 3Hecos concentrations that are equivalent to 0.35 to 1.5 Ma exposure at Earth's surface. In a study of detrital gold grains from several sites in Scotland we have found that 10 % have 3He concentrations that are significantly in excess of that generated since the Last Glacial Maximum. These studies demonstrate that, with refinement, cosmogenic 3He in refractory detrital minerals can be used to quantify sediment transport and storage on the 1-10 Ma timescale. P. McConville & J.H. Reynolds (1989). Geochim. Cosmochim. Acta, 53, 2365-75.

  18. Zircon 4He/3He thermochronometry

    NASA Astrophysics Data System (ADS)

    Tripathy-Lang, Alka; Fox, Matthew; Shuster, David L.

    2015-10-01

    Multiple thermochronometric methods are often required to constrain time-continuous rock exhumation for studying tectonic processes or development of km-scale topography at Earth's surface. Here, we explore 4He/3He thermochronometry of zircon as a method for constraining continuous time-temperature (t-T) paths of individual samples through a temperature range that is complementary to methods such as 40Ar/39Ar thermochronometry of K-feldspar and 4He/3He thermochronometry of apatite. For different cooling rates and diffusion domain size, the temperature sensitivity of zircon 4He/3He thermochronometry ranges from slightly less than 100 °C to slightly greater than 250 °C; a typical sample provides continuous thermal constraints over ∼100 °C within that range. Outside these temperatures, 4He in zircon will either be quantitatively retained or completely lost by volume diffusion. As proof-of-concept, we present stepwise release 4He/3He spectra and associated U and Th concentration maps measured by laser ablation ICP-MS analysis of individual crystal aliquots of Fish Canyon Tuff (FCT) zircon and of a more complex setting in the Sierra Nevada batholith that experienced reheating from a proximal basaltic intrusion, the Little Devil's Postpile (LDP). The FCT zircon 4He/3He release spectra are consistent with a 4He spatial distribution dominated by alpha-ejection from crystal surfaces. The spatial distributions of U and Th measured in the same crystals do not substantially influence 4He/3He release spectra that are predicted for the known thermal history, even when incorporating spatially variable diffusivity due to accumulation of radiation damage. Conversely, the LDP 4He/3He release spectra are strongly influenced by the observed parent nuclide zonation. A three-dimensional (3D) numerical model of 4He production and diffusion, which incorporates crystal geometry, U and Th zonation, and spatially variable He diffusion kinetics, substantially improves the fit between

  19. The stability of liquid-filled matrix ionization chamber electronic portal imaging devices for dosimetry purposes.

    PubMed

    Louwe, R J W; Tielenburg, R; van Ingen, K M; Mijnheer, B J; van Herk, M B

    2004-04-01

    This study was performed to determine the stability of liquid-filled matrix ionization chamber (LiFi-type) electronic portal imaging devices (EPID) for dosimetric purposes. The short- and long-term stability of the response was investigated, as well as the importance of factors influencing the response (e.g., temperature fluctuations, radiation damage, and the performance of the electronic hardware). It was shown that testing the performance of the electronic hardware as well as the short-term stability of the imagers may reveal the cause of a poor long-term stability of the imager response. In addition, the short-term stability was measured to verify the validity of the fitted dose-response curve immediately after beam startup. The long-term stability of these imagers could be considerably improved by correcting for room temperature fluctuations and gradual changes in response due to radiation damage. As a result, the reproducibility was better than 1% (1 SD) over a period of two years. The results of this study were used to formulate recommendations for a quality control program for portal dosimetry. The effect of such a program was assessed by comparing the results of portal dosimetry and in vivo dosimetry using diodes during the treatment of 31 prostate patients. The improvement of the results for portal dosimetry was consistent with the deviations observed with the reproducibility tests in that particular period. After a correction for the variation in response of the imager, the average difference between the measured and prescribed dose during the treatment of prostate patients was -0.7%+/-1.5% (1 SD), and -0.6%+/-1.1% (1 SD) for EPID and diode in vivo dosimetry, respectively. It can be concluded that a high stability of the response can be achieved for this type of EPID by applying a rigorous quality control program.

  20. Photoproduction of eta-mesic 3He.

    PubMed

    Pfeiffer, M; Ahrens, J; Annand, J R M; Beck, R; Caselotti, G; Cherepnya, S; Föhl, K; Fog, L S; Hornidge, D; Janssen, S; Kashevarov, V; Kondratiev, R; Kotulla, M; Krusche, B; McGeorge, J C; MacGregor, I J D; Mengel, K; Messchendorp, J G; Metag, V; Novotny, R; Rost, M; Sack, S; Sanderson, R; Schadmand, S; Thomas, A; Watts, D P

    2004-06-25

    The photoproduction of eta-mesic 3He has been investigated using the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI. The total inclusive cross section for the reaction gamma3He-->etaX has been measured for photon energies from threshold to 820 MeV. The total and angular differential coherent eta cross sections have been extracted up to energies of 745 MeV. A resonancelike structure just above the eta production threshold with an isotropic angular distribution suggests the existence of a resonant quasibound state. This is supported by studies of a competing decay channel of such a quasibound eta-mesic nucleus into pi(0)pX. A binding energy of (-4.4+/-4.2) MeV and a width of (25.6+/-6.1) MeV is deduced for the quasibound eta-mesic state in 3He.

  1. Nuclear electric dipole moment of 3He

    SciTech Connect

    Stetcu, Ionel; Friar, J L; Hayes, A C; Liu, C P; Navratil, P

    2008-01-01

    In the no-core shell model (NCSM) framework, we calculate the {sup 3}He electric dipole moment (EDM) generated by parity- and time-reversal violation in the nucleon-nucleon interaction. While the results are somehow sensitive to the interaction model chosen for the strong two- and three-body interactions, we demonstrate the pion-exchange dominance to the EDM of {sup 3}He, if the coupling constants for {pi}, {rho} and {omega}-exchanges are of comparable magnitude, as expected. Finally, our results suggest that a measurement of {sup 3}He EDM would be complementary to the currently planned neutron and deuteron experiments, and would constitute a powerful constraint to the models of the pion P- and T-violating interactions.

  2. Coherent Photoproduction of pi^+ from 3/^He

    SciTech Connect

    Rakhsha Nasseripour, Barry Berman

    2011-03-01

    We have measured the differential cross section for the $\\gamma$$^3$He$\\rightarrow \\pi^+ t$ reaction. This reaction was studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. Real photons produced with the Hall-B bremsstrahlung tagging system in the energy range from 0.50 to 1.55 GeV were incident on a cryogenic liquid $^3$He target. The differential cross sections for the $\\gamma$$^3$He$\\rightarrow \\pi^+ t$ reaction were measured as a function of photon-beam energy and pion-scattering angle. Theoretical predictions to date cannot explain the large cross sections except at backward angles, showing that additional components must be added to the model.

  3. The effect of air cavity size in cylindrical ionization chambers on the measurements in high-energy radiotherapy photon beams—an experimental study

    NASA Astrophysics Data System (ADS)

    Swanpalmer, John; Johansson, Karl-Axel

    2012-07-01

    The present investigation is a continuation of a previous study on the effect of the diameter of the air cavity in cylindrical ionization chambers on perturbation correction factors. Measurements were made using high-energy radiotherapy photon beams (4, 6 and 15 MV) in a water phantom. Two different pairs of cylindrical ionization chambers were used. The chambers in each pair had identical materials and construction but different air cavity diameters. The same methods were employed as in our previous investigation. The diameter of the air cavity in cylindrical ionization chambers influences the mass ionization (the measured ionization expressed per unit mass of air in the chamber air cavity) at the depth where the maximum ionization is observed and a normalization at this depth is therefore not correct. The corrections obtained at depths of 50 and 100 mm in the phantom showed that the air cavity diameter in cylindrical ionization chambers has a greater effect on the perturbation effects than the photon beam quality. The corrections found at depths of 50 and 100 mm are smaller than those currently used in dosimetry protocols.

  4. Use of a novel two-dimensional ionization chamber array for pencil beam scanning proton therapy beam quality assurance.

    PubMed

    Lin, Liyong; Kang, Minglei; Solberg, Timothy D; Mertens, Thierry; Baeumer, Christian; Ainsley, Christopher G; McDonough, James E

    2015-05-08

    The need to accurately and efficiently verify both output and dose profiles creates significant challenges in quality assurance of pencil beam scanning (PBS) proton delivery. A system for PBS QA has been developed that combines a new two-dimensional ionization chamber array in a waterproof housing that is scanned in a water phantom. The MatriXX PT has the same detector array arrangement as the standard MatriXX(Evolution) but utilizes a smaller 2 mm plate spacing instead of 5mm. Because the bias voltage of the MatriXX PT and Evolution cannot be changed, PPC40 and FC65-G ionization chambers were used to assess recombination effects. The PPC40 is a parallel plate chamber with an electrode spacing of 2mm, while the FC65-G is a Farmer chamber FC65-G with an electrode spacing of 2.8 mm. Three bias voltages (500, 200, and 100 V) were used for both detectors to determine which radiation type (continuous, pulse or pulse-scanned beam) could closely estimate Pion from the ratios of charges collected. In comparison with the MatriXX(Evolution), a significant improvement in measurement of absolute dose with the MatriXX PT was observed. While dose uncertainty of the MatriXX(Evolution) can be up to 4%, it is < 1% for the MatriXX PT. Therefore the MatriXX(Evolution) should not be used for QA of PBS for conditions in which ion recombination is not negligible. Farmer chambers should be used with caution for measuring the absolute dose of PBS beams, as the uncertainty of Pion can be > 1%; chambers with an electrode spacing of 2 mm or smaller are recommended.

  5. Use of a novel two-dimensional ionization chamber array for pencil beam scanning proton therapy beam quality assurance.

    PubMed

    Lin, Liyong; Kang, Minglei; Solberg, Timothy D; Mertens, Thierry; Baumer, Christian; Ainsley, Christopher G; McDonough, James E

    2015-05-01

    The need to accurately and efficiently verify both output and dose profiles creates significant challenges in quality assurance of pencil beam scanning (PBS) proton delivery. A system for PBS QA has been developed that combines a new two-dimensional ionization chamber array in a waterproof housing that is scanned in a water phantom. The MatriXX PT has the same detector array arrangement as the standard MatriXXEvolution but utilizes a smaller 2 mm plate spacing instead of 5 mm. Because the bias voltage of the MatriXX PT and Evolution cannot be changed, PPC40 and FC65-G ionization chambers were used to assess recombination effects. The PPC40 is a parallel plate chamber with an electrode spacing of 2 mm, while the FC65-G is a Farmer chamber FC65-G with an electrode spacing of 2.8 mm. Three bias voltages (500, 200, and 100 V) were used for both detectors to determine which radiation type (continuous, pulse or pulse-scanned beam) could closely estimate Pion from the ratios of charges collected. In comparison with the MatriXXEvolution, a significant improvement in measurement of absolute dose with the MatriXX PT was observed. While dose uncertainty of the MatriXXEvolution can be up to 4%, it is <1% for the MatriXX PT. Therefore the MatriXXEvolution should not be used for QA of PBS for conditions in which ion recombination is not negligible. Farmer chambers should be used with caution for measuring the absolute dose of PBS beams, as the uncertainty of Pion can be <1%; chambers with an electrode spacing of 2 mm or smaller are recommended. PACS number: 87.53.Qc.

  6. Superfluid 3He in ``nematically ordered'' aerogel

    NASA Astrophysics Data System (ADS)

    Dmitriev, Vladimir

    2014-03-01

    Liquid 3He immersed in aerogel allows investigation of the influence of impurities on unconventional superfluidity. In most of such experiments silica aerogels are used. These aerogels consist of thin strands which form a ``wisp.'' Although it is established that superfluid phases of 3He in silica aerogels (A-like and B-like) have the same order parameters as A and B phases of bulk 3He, many new phenomena were observed. In particular, it was found that global anisotropy of aerogel (e.g. caused by squeezing or stretching) can orient the order parameter. Depending on prehistory and on the type of the anisotropy the A-like phase may be homogeneous or in a state with random orbital part of the order parameter. Theory predicts that a large stretching anisotropy may even influence the order parameter structure: polar phase (or A phase with polar distortion), which are not realized in bulk 3He, may become more favorable than pure A phase. Large stretching anisotropy is hardly achievable in silica aerogel. Therefore in experiments described in the talk we used a new type of aerogel, consisting of Al2O3 . H2O strands which are parallel to each other, i.e. this aerogel may be considered as infinitely stretched. We found that the superfluid phase diagram of 3He in such ``nematically ordered'' aerogel is different from the case of 3He in silica aerogel and that both observed A and B phases have large polar distortion. This distortion is larger at low pressures and grows on warming. There are indications that a pure polar phase appears near the superfluid transition temperature. Recent results will be also presented.

  7. The multiuniverse transition in superfluid 3He.

    PubMed

    Bunkov, Yury

    2013-10-09

    The symmetry-breaking phase transitions of the universe and of superfluid (3)He may lead to the formation of different states with different order parameters. In both cases the energy potential below the transition temperature has a complicated multidimensional profile with many local minima and saddle points, which correspond to different states. Consequently, not only topological defects, but also islands of different metastable states can be created. Using (3)He we can analyse the properties and experimental consequences of such transitions and, in particular, the first-order phase transition between the two low symmetry states.

  8. The multiuniverse transition in superfluid 3He

    NASA Astrophysics Data System (ADS)

    Bunkov, Yury

    2013-10-01

    The symmetry-breaking phase transitions of the universe and of superfluid 3He may lead to the formation of different states with different order parameters. In both cases the energy potential below the transition temperature has a complicated multidimensional profile with many local minima and saddle points, which correspond to different states. Consequently, not only topological defects, but also islands of different metastable states can be created. Using 3He we can analyse the properties and experimental consequences of such transitions and, in particular, the first-order phase transition between the two low symmetry states.

  9. Beam quality conversion factors for parallel-plate ionization chambers in MV photon beams

    SciTech Connect

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

    2012-03-15

    Purpose: To investigate the behavior of plane-parallel ion chambers in high-energy photon beams through measurements and Monte Carlo simulations. Methods: Ten plane-parallel ion chamber types were obtained from the major ion chamber manufacturers. Absorbed dose-to-water calibration coefficients are measured for these chambers and k{sub Q} factors are determined. In the process, the behaviors of the chambers are characterized through measurements of leakage currents, chamber settling in cobalt-60, polarity and ion recombination behavior, and long-term stability. Monte Carlo calculations of the absorbed dose to the air in the ion chamber and absorbed dose to water are obtained to calculate k{sub Q} factors. Systematic uncertainties in Monte Carlo calculated k{sub Q} factors are investigated by varying material properties and chamber dimensions. Results: Chamber behavior was variable in MV photon beams, especially with regard to chamber leakage and ion recombination. The plane-parallel chambers did not perform as well as cylindrical chambers. Significant differences up to 1.5% were observed in calibration coefficients after a period of eight months although k{sub Q} factors were consistent on average within 0.17%. Chamber-to-chamber variations in k{sub Q} factors for chambers of the same type were at the 0.2% level. Systematic uncertainties in Monte Carlo calculated k{sub Q} factors ranged between 0.34% and 0.50% depending on the chamber type. Average percent differences between measured and calculated k{sub Q} factors were - 0.02%, 0.18%, and - 0.16% for 6, 10, and 25 MV beams, respectively. Conclusions: Excellent agreement is observed on average at the 0.2% level between measured and Monte Carlo calculated k{sub Q} factors. Measurements indicate that the behavior of these chambers is not adequate for their use for reference dosimetry of high-energy photon beams without a more extensive QA program than currently used for cylindrical reference-class ion chambers.

  10. Beam quality conversion factors for parallel-plate ionization chambers in MV photon beams.

    PubMed

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

    2012-03-01

    To investigate the behavior of plane-parallel ion chambers in high-energy photon beams through measurements and Monte Carlo simulations. Ten plane-parallel ion chamber types were obtained from the major ion chamber manufacturers. Absorbed dose-to-water calibration coefficients are measured for these chambers and k(Q) factors are determined. In the process, the behaviors of the chambers are characterized through measurements of leakage currents, chamber settling in cobalt-60, polarity and ion recombination behavior, and long-term stability. Monte Carlo calculations of the absorbed dose to the air in the ion chamber and absorbed dose to water are obtained to calculate k(Q) factors. Systematic uncertainties in Monte Carlo calculated k(Q) factors are investigated by varying material properties and chamber dimensions. Chamber behavior was variable in MV photon beams, especially with regard to chamber leakage and ion recombination. The plane-parallel chambers did not perform as well as cylindrical chambers. Significant differences up to 1.5% were observed in calibration coefficients after a period of eight months although k(Q) factors were consistent on average within 0.17%. Chamber-to-chamber variations in k(Q) factors for chambers of the same type were at the 0.2% level. Systematic uncertainties in Monte Carlo calculated k(Q) factors ranged between 0.34% and 0.50% depending on the chamber type. Average percent differences between measured and calculated k(Q) factors were - 0.02%, 0.18%, and - 0.16% for 6, 10, and 25 MV beams, respectively. Excellent agreement is observed on average at the 0.2% level between measured and Monte Carlo calculated k(Q) factors. Measurements indicate that the behavior of these chambers is not adequate for their use for reference dosimetry of high-energy photon beams without a more extensive QA program than currently used for cylindrical reference-class ion chambers.

  11. DETECTORS AND EXPERIMENTAL METHODS: Design and construction of the first prototype ionization chamber for CSNS and PA beam loss monitor (BLM) system

    NASA Astrophysics Data System (ADS)

    Xu, Mei-Hang; Tian, Jian-Min; Chen, Chang; Chen, Yuan-Bo; Xu, Tao-Guang; Lu, Shuang-Tong

    2009-02-01

    Design and construction of the first prototype ionization chamber for CSNS and Proton Accelerator (PA) beam loss monitor (BLM) system is reported. The low leakage current (<0.1 pA), good plateau (approx800 V) and linearity range up to 200 Roentgen/h are obtained in the first prototype. All of these give us good experience for further improving the ionization chamber construction.

  12. Experimental determination of the effective point of measurement of cylindrical ionization chambers for high-energy photon and electron beams.

    PubMed

    Huang, Yanxiao; Willomitzer, Christian; Zakaria, Golam Abu; Hartmann, Guenther H

    2010-01-01

    Measurements of depth-dose curves in water phantom using a cylindrical ionization chamber require that its effective point of measurement is located at the measuring depth. Recommendations for the position of the effective point of measurement with respect to the central axis valid for high-energy electron and photon beams are given in dosimetry protocols. According to these protocols, the use of a constant shift P(eff) is currently recommended. However, this is still based on a very limited set of experimental results. It is therefore expected that an improved knowledge of the exact position of the effective point of measurement will further improve the accuracy of dosimetry. Recent publications have revealed that the position of the effective point of measurement is indeed varying with beam energy, field size and also with chamber geometry. The aim of this study is to investigate whether the shift of P(eff) can be taken to be constant and independent from the beam energy. An experimental determination of the effective point of measurement is presented based on a comparison between cylindrical chambers and a plane-parallel chamber using conventional dosimetry equipment. For electron beams, the determination is based on the comparison of halfvalue depth R(50) between the cylindrical chamber of interest and a well guarded plane-parallel Roos chamber. For photon beams, the depth of dose maximum, d(max), the depth of 80% dose, d(80), and the dose parameter PDD(10) were used. It was again found that the effective point of measurement for both, electron and photon beams Dosimetry, depends on the beam energy. The deviation from a constant value remains very small for photons, whereas significant deviations were found for electrons. It is therefore concluded that use of a single upstream shift value from the centre of the cylindrical chamber as recommended in current dosimetry protocols is adequate for photons, however inadequate for accurate electron beam dosimetry.

  13. SU-E-T-415: An Ionization Chamber Array with High Spatial Resolution for External Beam Radiotherapy

    SciTech Connect

    Togno, M; Wilkens, J; Menichelli, D

    2014-06-01

    Purpose: To characterize an ionization chamber array technology with high spatial resolution and high charge collection efficiency for external beam radiotherapy. Methods: The prototype under test is a linear array of air vented ionization chambers developed by IBA Dosimetry, consisting of 80 pixels with 3.5mm spatial resolution and 4mm{sup 3} sensitive volume. The detector was characterized in a plastic phantom with {sup 60} Co radiation and MV X-rays from an ELEKTA Agility LINAC (with flattened and unflattened beam qualities). Bias voltage was varied in order to evaluate charge collection efficiency. A commercial array of ionization chambers (MatriXX Evolution, IBA Dosimetry) and an amorphous silicon flat panel in direct conversion configuration were used as references. Results: Repeatability (0.4%) and stability under continuous gamma irradiation (0.3%) are very good, in spite of low active volume and sensitivity (∼200pC/Gy). Charge collection efficiency is higher than 99% already at 150V with ∼2mGy dose per pulse, leading to a ±1.1% sensitivity change with dose per pulse in the range 0.09-2mGy (covering all flattened and unflattened applications). Measured dose profiles are in agreement with MatriXX for fields larger than 2×2cm{sup 2}, in which case the linear array offers a much better characterization of the penumbra region. Down to 1×1cm{sup 2}, measured profiles are in very good agreement with the flat panel. Conclusion: The array represents a valuable tool for the characterization of treatment fields in which high spatial resolution is required, together with the dosimetric performance of air vented ionization chambers. Such a technology would be particularly valuable in association with advanced treatment modalities such as rotational radiotherapy, stereotactic treatments (even with unflattened beam qualities) and proton therapy, due to the insensitivity of the chambers on dose per pulse. In the future, a two dimensional prototype based on this

  14. Gaseous [sup 3]He-[sup 3]He magnetic dipolar spin relaxation

    SciTech Connect

    Newbury, N.R.; Barton, A.S.; Cates, G.D.; Happer, W.; Middleton, H. )

    1993-12-01

    We derive the nuclear-spin relaxation rate of gaseous [sup 3]He due to the magnetic-dipole interaction between the [sup 3]He nuclear spins. This dipolar relaxation rate is numerically evaluated for temperatures from 0.1 K to 550 K. At room temperature, the relaxation time for a [sup 3]He density of 10 amagats is 74.4 h. We have made a series of high-density (4--12 amagat) [sup 3]He samples for which nulcear relaxation is limited by the magnetic-dipole interaction. Both our theoretical and experimental results are particularly important for the growing use of [sup 3]He, polarized through spin exchange with optically pumped Rb vapor.

  15. Neutron Polarizers Based on Polarized 3He

    SciTech Connect

    William M. Snow

    2005-05-01

    The goal of this work, which is a collaborative effort between Indiana University, NIST, and Hamilton College, is to extend the technique of polarized neutron scattering into new domains by the development and application of polarized 3He-based neutron spin filters. After the IPNS experiment which measured Zeeman sp[litting in surface scattered neutrons using a polarized 3He cell as a polarization analyzer transporterd by car from Bloomington to Chicago, the Indiana work focused on technical developments to improve the 3He polarization of the Indiana compression system. The compression system was rebuilt with a new valve system which allows gas trapped in the dead volume of the compressors at the end of the piston stroke to be exhausted and conducted back to the optical pumping cell where it can be repolarized. We also incorporated a new intermediate storage volume made at NIST from 1720 glass which will reduce polarization losses between the compressors. Furthermore, we improved the stability of the 1083 nm laser by cooling the LMA rod. We achieved 60% 3he polarization in the optical pumping cell and 87% preservation of the polarization during compression. In parallel we built a magnetically-shielded transport solenoid for use on neutron scattering instruments such as POSY which achieves a fractional field uniformity of better than 10-3 per cm. The field was mapped using an automated 3D field mapping system for in-situ measurement of magnetic field gradients Diluted magnetic semiconductors offer many exciting opportunities for investigation of spintronic effects in solids and are certain to be one of the most active areas of condensed matter physics over then next several years. These materials can act as efficient spin injectors for devices that make use of spin-dependent transport phenomena. We just (late July 2002) finished a neutron reflectivity experiment at NIST on a GaMnAs trilayer film. This material is a ferromagnetic semiconductor which is of interest

  16. Measurements of neutron energy using a recoil-proton telescope and a high-pressure ionization chamber.

    PubMed

    Folkard, M; Makrigiorgos, G; Roper, M J; Waker, A J; Michael, B D

    1989-04-01

    Two very different techniques for measuring the energy of neutrons in the energy range 0.1-10 MeV are presented and compared. A recoil-proton spectrometer is used to determine the energy spectra of neutrons produced by the d(4)-Be and p(4)-Be reactions down to the low-energy threshold of 0.7 MeV. The same radiation fields are also measured with a recently developed method using a high-pressure ionization chamber that can be used to determine the mean energy of the neutrons in a mixed neutron-gamma radiation field provided the gamma-ray absorbed dose fraction is determined independently. An intercomparison of the two methods shows that the high-pressure ionization chamber compares well and supplements the established recoil-proton spectrometer technique. The almost isotropic response of the chamber has enabled measurements to be made of the variation of mean neutron energy with depth in water for the two radiation fields.

  17. Translational applications of hyperpolarized 3He and 129Xe.

    PubMed

    Walkup, Laura L; Woods, Jason C

    2014-12-01

    Clinical magnetic resonance imaging of the lung is technologically challenging, yet over the past two decades hyperpolarized noble gas ((3)He and (129)Xe) imaging has demonstrated the ability to measure multiple pulmonary functional biomarkers. There is a growing need for non-ionizing, non-invasive imaging techniques due to increased concern about cancer risk from ionizing radiation, but the translation of hyperpolarized gas imaging to the pulmonary clinic has been stunted by limited access to the technology. New developments may open doors to greater access and more translation to clinical studies. Here we briefly review a few translational applications of hyperpolarized gas MRI in the contexts of ventilation, diffusion, and dissolved-phase imaging, as well as comparing and contrasting (3)He and (129)Xe gases for these applications. Simple static ventilation MRI reveals regions of the lung not participating in normal ventilation, and these defects have been observed in many pulmonary diseases. Biomarkers related to airspace size and connectivity can be quantified by apparent diffusion coefficient measurements of hyperpolarized gas, and have been shown to be more sensitive to small changes in lung morphology than standard clinical pulmonary functional tests and have been validated by quantitative histology. Parameters related to gas uptake and exchange and lung tissue density can be determined using (129)Xe dissolved-phase MRI. In most cases functional biomarkers can be determined via MRI of either gas, but for some applications one gas may be preferred, such as (3)He for long-range diffusion measurements and (129)Xe for dissolved-phase imaging. Greater access to hyperpolarized gas imaging coupled with newly developing therapeutics makes pulmonary medicine poised for a potential revolution, further adding to the prospects of personalized medicine already evidenced by advancements in molecular biology. Hyperpolarized gas researchers have the opportunity to

  18. (3) He Spin Filter for Neutrons.

    PubMed

    Batz, M; Baeßler, S; Heil, W; Otten, E W; Rudersdorf, D; Schmiedeskamp, J; Sobolev, Y; Wolf, M

    2005-01-01

    The strongly spin-dependent absorption of neutrons in nuclear spin-polarized (3)He opens up the possibility of polarizing neutrons from reactors and spallation sources over the full kinematical range of cold, thermal and hot neutrons. This paper gives a report on the neutron spin filter (NSF) development program at Mainz. The polarization technique is based on direct optical pumping of metastable (3)He atoms combined with a polarization preserving mechanical compression of the gas up to a pressure of several bar, necessary to run a NSF. The concept of a remote type of operation using detachable NSF cells is presented which requires long nuclear spin relaxation times of order 100 hours. A short survey of their use under experimental conditions, e.g. large solid-angle polarization analysis, is given. In neutron particle physics NSFs are used in precision measurements to test fundamental symmetry concepts.

  19. An experimental study of recombination and polarity effect in a set of customized plane parallel ionization chambers.

    PubMed

    Kron, T; McNiven, A; Witruk, B; Kenny, M; Battista, J

    2006-12-01

    Plane parallel ionization chambers are an important tool for dosimetry and absolute calibration of electron beams used for radiotherapy. Most dosimetric protocols require corrections for recombination and polarity effects, which are to be determined experimentally as they depend on chamber design and radiation quality. Both effects were investigated in electron beams from a linear accelerator (Varian 21CD) for a set of four tissue equivalent plane parallel ionization chambers customized for the present research by Standard Imaging (Madison WI). All four chambers share the same design and air cavity dimensions, differing only in the diameter of their collecting electrode and the corresponding width of the guard ring. The diameters of the collecting electrodes were 2 mm, 4 mm, 10 mm and 20 mm. Measurements were taken using electron beams of nominal energy 6 to 20 MeV in a 10 cm x 10 cm field size with a SSD of 100 cm at various depths in a Solid Water slab phantom. No significant variation of recombination effect was found with radiation quality, depth of measurement or chamber design. However, the polarity effect exceeded 5% for the chambers with small collecting electrode for an effective electron energy below 4 MeV at the point of measurement. The magnitude of the effect increased with decreasing electron energy in the phantom. The polarity correction factor calculated following AAPM protocol TG51 ranged from approximately 1.00 for the 20.0 mm chamber to less than 0.95 for the 2 mm chamber at 4.1 cm depth in a electron beam of nominally 12 MeV. By inverting the chamber it could be shown that the polarity effect did not depend on the polarity of the electrode first traversed by the electron beam. Similarly, the introduction of an air gap between the overlying phantom layer and the chambers demonstrated that the angular distribution of the electrons at the point of measurement had a lesser effect on the polarity correction than the electron energy itself. The

  20. 3He: cosmological and atomic physics experiments.

    PubMed

    Bunkov, Yuriy M

    2008-08-28

    Because the superfluid 3He order parameter exhibits many similarities with that of our Universe, the superfluid condensate may be considered as a quantum vacuum that carries various types of quasiparticles and topological defects. The condensate thus provides a test system for the experimental investigation of many general physics problems in cosmology, atomic or nuclear physics that are otherwise difficult or even impossible to investigate experimentally.

  1. Study of the influence of phantom material and size on the calibration of ionization chambers in terms of absorbed dose to water.

    PubMed

    Arib, Mehenna; Medjadj, Toufik; Boudouma, Youcef

    2006-08-24

    In the International Atomic Energy Agency's (IAEA) code of practice (TRS 398) and the American Association of Physicists in Medicine's dosimetry protocol (TG-51), full-scatter water phantoms are recommended for the determination of the absorbed dose for both photon and electron beams and, consequently, for the calibration of the user's ionization chambers. This procedure is applied in the Secondary Standard Dosimetry Laboratory, where the calibration is performed on a 60Co gamma beam, in comparison with reference chambers whose absorbed dose-to-water calibration coefficients, ND,w, are known. In this work, we present the results of the calibration of 10 Farmer-like ionization chambers calibrated in three water phantoms (sizes 20 x 20 x 15 cm3, 30 x 30 x 30 cm3, and 35 x 35 x 37 cm3) and two plastic phantoms (size 20 x 20 x 20 cm3) polymethyl methacrlyate (PMMA) and polystyrene). Calibrations are performed by the substitution method using an ionization chamber whose ND,w has been supplied by the IAEA's reference laboratory. It is shown that the results, expressed as the percentage ratio of the calibration coefficient in a given phantom to that of the standard IAEA phantom, is less than 0.35% for all investigated chambers, and that the standard deviation of the mean of the ND,w calibration coefficients determined in all five phantoms is less than 0.06%, except for one nylon-walled ionization chamber, where the observed 0.34% value could be explained by the hygroscopic properties of nylon. Furthermore, a chamber-to-chamber dependence of the calibration coefficient has been shown to vary by up to 2.8%. These results emphasize that the phantom dimensions and its material are not sensitive criteria for the calibration of cylindrical ionization chambers in terms of absorbed dose to water. The results also show that generic calibration coefficients could not be considered for a given type of chamber.

  2. Patient specific quality assurance of RapidArc pre treatment plans using semiflex 0.125 cc ionization chamber

    NASA Astrophysics Data System (ADS)

    Kumar, S. A. Syam; Vivekanandan, Nagarajan

    2017-01-01

    Patient specific pre-treatment quality assurance for RapidArc plans were analyzed for hundred patients for different sites. Verification plan was created for each treatment plan in Eclipse 8.6 treatment planning system with the semiflex ionization chamber and the octavius phantom. Absolute point dose were measured for head and neck, thorax and abdomen cases using semiflex (0.125 cc) ionization chamber. Positive absolute mean dose variation of 0.56% was observed with thorax cases with a standard deviation (SD) of ±1.13 between the plans with a range of -1.78% to 2.70%. Negative percentage dose errors were found with head and neck and abdomen cases, with a mean variation of -0.43% (SD±1.50), (range -3.25% to 2.85%) and -0.35% (SD±1.48), (range -3.10% to 2.65%) for head and neck and abdomen cases respectively. Evaluation has been done using PTW verisoft software by keeping the passing criteria as 3 mm DTA, 3% DD, for 95% of the evaluated dose points. The maximum percentage value failed in gamma analysis was found to be 4.95, 4.75, and 4.88 for head and neck, thorax, and abdomen cases respectively. In all the cases analyzed the percentage dose points failed the gamma criteria is less than 5%. On the basis of the studies performed it can be concluded that the semiflex ionization chamber having a volume of 0.125 cc can be used efficiently for measuring the pre-treatment quality assurance of RapidArc plans for all the sites.

  3. [The development of the ionization chamber and the researching of its characteristics for automatic exposure controlling in the X-ray diagnosis machine].

    PubMed

    Weng, P; Liu, S; Wang, H; Cao, Y; Wang, X; Li, Y

    1999-01-01

    An ionization chamber for automatic exposure controlling used in X ray diagnosis machine was developped, and its characteristics were measured and researched. The electrodes of measuring field were made of carbon, such couldn't leave it's imaging on the film. In order to increase the ionization efficiency and decrease the thickness and electric capacity between electrodes, the chamber was constructed in multilayers. The chamber we developed can be fixed in different x ray machines convenientlly, there is a fine linearity between it's signal output and the exposures, the beam quality response is uniform and output-timing response is also good.

  4. A method for measuring the electron drift velocity in working gas using a Frisch-grid ionization chamber

    NASA Astrophysics Data System (ADS)

    Bai, Huaiyong; Wang, Zhimin; Zhang, Luyu; Chen, Jinxiang; Zhang, Guohui

    2016-12-01

    A method for measuring the electron drift velocity in working gas is proposed. Based on the cathode and the anode signal waveforms of the Frisch-grid ionization chamber, the electron drift velocity is extracted. With this method, the electron drift velocities in Ar + 10% CH4, Ar + 3.5% CO2 and Kr + 2.7% CO2 gases have been measured and the results are compared with the existing measurements and the simulating results. Using this method, the electron drift velocity can be monitored throughout the experiment of charged particle without bothering the measurement of other parameters, such as the energy and orientation.

  5. Correction factors for ionization chamber dosimetry in CyberKnife: Machine-specific, plan-class, and clinical fields

    SciTech Connect

    Gago-Arias, Araceli; Antolin, Elena; Fayos-Ferrer, Francisco; Simon, Rocio; Gonzalez-Castano, Diego M.; Palmans, Hugo; Sharpe, Peter; Gomez, Faustino; Pardo-Montero, Juan

    2013-01-15

    Purpose: The aim of this work is the application of the formalism for ionization chamber reference dosimetry of small and nonstandard fields [R. Alfonso, P. Andreo, R. Capote, M. S. Huq, W. Kilby, P. Kjaell, T. R. Mackie, H. Palmans, K. Rosser, J. Seuntjens, W. Ullrich, and S. Vatnitsky, 'A new formalism for reference dosimetry of small and nonstandard fields,' Med. Phys. 35, 5179-5186 (2008)] to the CyberKnife robotic radiosurgery system. Correction factors for intermediate calibration fields, a machine-specific reference field (msr) and two plan-class specific reference fields (pcsr), have been studied. Furthermore, the applicability of the new formalism to clinical dosimetry has been analyzed through the investigation of two clinical treatments. Methods: PTW31014 and Scanditronix-Wellhofer CC13 ionization chamber measurements were performed for the fields under investigation. Absorbed dose to water was determined using alanine reference dosimetry, and experimental correction factors were calculated from alanine to ionization chamber readings ratios. In addition, correction factors were calculated for the intermediate calibration fields and one of the clinical treatment fields using the Monte Carlo method and these were compared with the experimental values. Results: Overall correction factors deviating from unity by approximately 2% were obtained from both measurements and simulations, with values below and above unity for the studied intermediate calibration fields and clinical fields for the ionization chambers under consideration. Monte Carlo simulations yielded correction factors comparable with those obtained from measurements for the machine-specific reference field, although differences from 1% to 3.3% were observed between measured and calculated correction factors for the composite intermediate calibration fields. Dose distribution inhomogeneities are thought to be responsible for such discrepancies. Conclusions: The differences found between overall

  6. Dosimetric Verification and Validation of Conformal and IMRT Treatments Fields with an Ionization Chamber 2D-Array

    SciTech Connect

    Evangelina, Figueroa M.; Gabriel, Resendiz G.; Miguel, Perez P.

    2008-08-11

    A three-dimensional treatment planning system requires comparisons of calculated and measured dose distributions. It is necessary to confirm by means of patient specific QA that the dose distributions are correctly calculated, and that the patient data is correctly transferred to and delivered by the treatment machine. We used an analysis software for bi-dimensional dosimetric verification of conformal treatment and IMRT fields using as objective criterion the gamma index. An ionization chamber bi-dimensional array was used for absolute dose measurement in the complete field area.

  7. Particle identification in a LKr ionization chamber by multiple induced current measurements using the shape analysis of the signal

    NASA Astrophysics Data System (ADS)

    Diaferia, R.; Lanni, F.; Maggi, B.; Palombo, F.; Sala, A.; Cantoni, P.; Frabetti, P. L.; Stagni, L.

    1996-01-01

    Charged particle (π/K) separation in the momentum range 0.5-0.7 GeV/c using a new method of shape analysis of the signal from a liquid krypton ionization chamber has been studied experimentally. The detector has been exposed to pions and protons at the T11 test beam at CERN PS. The shape of preamplifier output signal has been recorded by a waveform digitizer and differentiated to obtain multiple measurements of induced current inside a 2 cm gap. Results on particle separation are presented and compared with a Monte Carlo simulation.

  8. Particle identification in a LKr ionization chamber by multiple induced current measurements using the shape analysis of the signal

    NASA Astrophysics Data System (ADS)

    Cantoni, P.; Frabetti, P. L.; Stagni, L.; Diaferia, R.; Lanni, F.; Maggi, B.; Palombo, F.; Sala, A.; Manfredi, P. F.; Re, V.; Speziali, V.

    1995-02-01

    Charged particle ( {π}/{K}) separation in the momentum range 0.5-0.7 GeV/ c using a new method of shape analysis of the signal from a liquid krypton ionization chamber has been studied experimentally. The detector has been exposed to the T11 test beam at CERN PS. The shape of the preamplifier output signal has been recorded by a waveform digitizer and differentiated to obtain multiple measurements of induced current inside a 2 cm gap. Results on particle separation are presented.

  9. Discovery of multiple, ionization-created CS{sub 2} anions and a new mode of operation for drift chambers

    SciTech Connect

    Snowden-Ifft, Daniel P.

    2014-01-15

    This paper focuses on the surprising discovery of multiple species of ionization-created CS{sub 2} anions in gas mixtures containing electronegative CS{sub 2} and O{sub 2}, identified by their slightly different drift velocities. Data are presented to understand the formation mechanism and identity of these new anions. Regardless of the micro-physics, however, this discovery offers a new, trigger-less mode of operation for the drift chambers. A demonstration of trigger-less operation is presented.

  10. 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.

  11. 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.

  12. The calibration of parallel-plate electron ionization chambers at NPL for use with the IPEM 2003 code of practice: summary data.

    PubMed

    Bass, Graham; Thomas, Russell; Pearce, Julia

    2009-04-21

    The most recent electron dosimetry code of practice for radiotherapy written by the Institute of Physics and Engineering in Medicine was published in 2003 and is based on the NPL electron absorbed dose to water calibration service. NPL has calibrated many Scanditronix type NACP-02 and PTW Roos type 34001 parallel plate ionization chambers in terms of absorbed dose to water, for use with the code of practice. The results of the calibrations of these chamber types summarized here include the absorbed dose to water sensitivity, where the mean calibration factor standard deviations are 5.8% for NACP-02 chambers and 1.1% for PTW Roos chambers. The correction for the polarity effect is shown to be small (less than 0.2% for all beam qualities) but with a discernible beam quality dependence. The correction for recombination is shown to be consistent and reproducible, and an analysis of these results suggests that the plate separation of the NACP-02 chambers is more variable from chamber to chamber than with the PTW Roos chambers. The calibration of these chambers is shown to be repeatable within +/-0.2% over 2-3 years. It is also shown that check source measurements can be repeated within +/-0.3% over several years. The results justify the use of NACP-02 and PTW 34001 chambers as secondary standards, but also indicate that the PTW 34001 chambers show less variation from chamber to chamber.

  13. NOTE: The calibration of parallel-plate electron ionization chambers at NPL for use with the IPEM 2003 code of practice: summary data

    NASA Astrophysics Data System (ADS)

    Bass, Graham; Thomas, Russell; Pearce, Julia

    2009-04-01

    The most recent electron dosimetry code of practice for radiotherapy written by the Institute of Physics and Engineering in Medicine was published in 2003 and is based on the NPL electron absorbed dose to water calibration service. NPL has calibrated many Scanditronix type NACP-02 and PTW Roos type 34001 parallel plate ionization chambers in terms of absorbed dose to water, for use with the code of practice. The results of the calibrations of these chamber types summarized here include the absorbed dose to water sensitivity, where the mean calibration factor standard deviations are 5.8% for NACP-02 chambers and 1.1% for PTW Roos chambers. The correction for the polarity effect is shown to be small (less than 0.2% for all beam qualities) but with a discernible beam quality dependence. The correction for recombination is shown to be consistent and reproducible, and an analysis of these results suggests that the plate separation of the NACP-02 chambers is more variable from chamber to chamber than with the PTW Roos chambers. The calibration of these chambers is shown to be repeatable within ±0.2% over 2-3 years. It is also shown that check source measurements can be repeated within ±0.3% over several years. The results justify the use of NACP-02 and PTW 34001 chambers as secondary standards, but also indicate that the PTW 34001 chambers show less variation from chamber to chamber.

  14. Coupling between Solid 3He on Aerogel and Superfluid 3He in the Low Temperature Limit

    SciTech Connect

    Bradley, D. I.; Fisher, S. N.; Guenault, A. M.; Haley, R. P.; Pickett, G. R.; Tsepelin, V.; Whitehead, R. C. V.; Skyba, P.

    2006-09-07

    We have cooled liquid 3He contained in a 98% open aerogel sample surrounded by bulk superfluid 3He-B at zero pressure to below 120 {mu}K. The aerogel sample is placed in a quasiparticle blackbody radiator cooled by a Lancaster-style nuclear cooling stage to {approx}200 {mu}K. We monitor the temperature of the 3He inside the blackbody radiator using a vibrating wire resonator. We find that reducing the magnetic field on the aerogel sample causes substantial cooling of all the superfluid inside the blackbody radiator. We believe this is due to the demagnetization of the solid 3He layers on the aerogel strands. This system has potential for achieving extremely low temperatures in the confined fluid.

  15. Intense polarized /sup 3/He ion source

    SciTech Connect

    Slobodrian, R.J.; Bertrand, R.; Grioux, J.; Labrie, R.; Lapainte, R.; Meunier, J.F.; Pigeon, G.; Pouliot, L.; Rioux, C.; Roy, R.

    1985-10-01

    This source is based on the atomic polarization of the 2/sup 3/S/sub 1/ metastable state of the neutral atom. A version suitable for operation on the high voltage terminal of a CN Van de Graaff has been constructed, bench tested and installed in the terminal of a 7.5 MV machine. The polarization of the atomic beam is higher than 90%. It is now fully operational and a current of /sup 3/He/sup +/ of 300 nA has been measured after acceleration.

  16. 3He Diffusion MRI of the Lung

    PubMed Central

    Conradi, Mark S.; Yablonskiy, Dmitriy A.; Woods, Jason C.; Gierada, David S.; Jacob, Richard E.; Chang, Yulin V.; Choong, Cliff K.; Sukstanskii, Alex L.; Tanoli, Tariq; Lefrak, Stephen S.; Cooper, Joel D.

    2007-01-01

    Rationale and Objectives MR imaging of the restricted diffusion of laser-polarized 3He gas provides unique insights into the changes in lung microstructure in emphysema. Results We discuss measurements of ventilation (spin density), mean diffusivity, and the anisotropy of diffusion, which yields the mean acinar airway radius. In addition, the use of spatially modulated longitudinal magnetization allows diffusion to be measured over longer distances and times, with sensitivity to collateral ventilation paths. Early results are also presented for spin density and diffusivity maps made with a perfluorinated inert gas, C3F8. Methods Techniques for purging and imaging excised lungs are discussed. PMID:16253852

  17. Neutron scattering from solid 3He

    NASA Astrophysics Data System (ADS)

    Schanen, R.; Sherline, T. E.; Toader, A. M.; Boyko, V.; Mat'as, S.; Meschke, M.; Schöttl, S.; Adams, E. D.; Cowan, B.; Godfrin, H.; Goff, J. P.; Roger, M.; Saunders, J.; Siemensmeyer, K.; Takano, Y.

    2003-05-01

    Multiple spin exchange leads, according to present understanding, to a variety of magnetically ordered states in solid 3He, depending on pressure and applied magnetic field. We report the status of experiments to directly determine these structures by neutron scattering. The large neutron absorption cross section, and associated sample heating, impose severe experimental demands on the design of the sample cell. We report on our proposed solution, including details of the sintered heat exchanger necessary to cool the sample, as well as the PrNi 5 nuclear demagnetization stage. The use of NMR in parallel experiments to characterise growth of the solid sample within the sinter is also discussed.

  18. 3He-melting-curve thermometry

    NASA Astrophysics Data System (ADS)

    Greywall, Dennis S.; Busch, Paul A.

    1982-03-01

    Precise measurements of the P-T relation along the melting curve of3He have been made for 8≲ T≲330 mK. The results are in excellent agreement with other precise data for temperatures near the extremes of this range. A best-fit relation is provided which describes the melting curve to within ±1 mbar between the superfluid A transition and the pressure minimum. Detailed descriptions of the melting curve and magnetic thermometers used for the calibration are also given.

  19. General collection efficiency for liquid isooctane and tetramethylsilane used as sensitive media in a parallel-plate ionization chamber.

    PubMed

    Johansson, B; Wickman, G

    1997-01-01

    The general collection efficiency has been measured in liquid isooctane (C8H18) and tetramethylsilane (Si(CH3)4) used as the sensitive media in a parallel-plate ionization chamber, with an electrode distance of 1 mm, intended for photon and electron dosimetry applications. The liquid ionization chamber was irradiated at different dose rates by 140 keV photons from the decay of radioactive 99mTc. The measurements were made at potential differences of 50, 100, 200 and 500 V. Measurements were performed for each liquid and electric field strength, with the decay rate of 99mTc used as the dose-rate reference. The maximum dose rate was about 150 mGy min-1 in each experiment. When the measured general collection efficiency values are compared with the theoretical predictions for collection efficiency in gases, it is found that the latter also describe the general collection efficiency in the two liquids within 1% of the saturation current for collection efficiencies down to 60% when using experimentally determined recombination rate constants and on mobilities characteristic of each of the liquids.

  20. 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.

  1. Experimental investigation of the effect of air cavity size in cylindrical ionization chambers on the measurements in 60Co radiotherapy beams

    NASA Astrophysics Data System (ADS)

    Swanpalmer, John; Johansson, Karl-Axel

    2011-11-01

    In the late 1970s, Johansson et al (1978 Int. Symp. National and International Standardization of Radiation Dosimetry (Atlanta 1977) vol 2 (Vienna: IAEA) pp 243-70) reported experimentally determined displacement correction factors (pdis) for cylindrical ionization chamber dosimetry in 60Co and high-energy photon beams. These pdis factors have been implemented and are currently in use in a number of dosimetry protocols. However, the accuracy of these factors has recently been questioned by Wang and Rogers (2009a Phys. Med. Biol. 54 1609-20), who performed Monte Carlo simulations of the experiments performed by Johansson et al. They reported that the inaccuracy of the pdis factors originated from the normalization procedure used by Johansson et al. In their experiments, Johansson et al normalized the measured depth-ionization curves at the depth of maximum ionization for each of the different ionization chambers. In this study, we experimentally investigated the effect of air cavity size of cylindrical ionization chambers in a PMMA phantom and 60Co γ-beam. Two different pairs of air-filled cylindrical ionization chambers were used. The chambers in each pair had identical construction and materials but different air cavity volume (diameter). A 20 MeV electron beam was utilized to determine the ratio of the mass of air in the cavity of the two chambers in each pair. This ratio of the mass of air in each pair was then used to compare the ratios of the ionizations obtained at different depths in the PMMA phantom and 60Co γ-beam using the two pairs of chambers. The diameter of the air cavity of cylindrical ionization chambers influences both the depth at which the maximum ionization is observed and the ionization per unit mass of air at this depth. The correction determined at depths of 50 mm and 100 mm is smaller than the correction currently used in many dosimetry protocols. The results presented here agree with the findings of Wang and Rogers' Monte Carlo

  2. Investigation and performance tests of a new parallel plate ionization chamber with double sensitive volume for measuring diagnostic X-rays

    NASA Astrophysics Data System (ADS)

    Sharifi, B.; Zamani Zeinali, H.; Soltani, J.; Negarestani, A.; Shahvar, A.

    2015-01-01

    Medical diagnostic equipment, like diagnostic radiology and mammography require a dosimeter with high accuracy for dosimetry of the diagnostic X-ray beam. Ionization chambers are suitable instruments for dosimetry of diagnostic-range X-ray beams because of their appropriate response and high reliability. This work introduces the design and fabrication of a new parallel plate ionization chamber with a PMMA body, graphite-coated PMMA windows (0.5 mm thick) and a graphite-foil central electrode (0.1 mm thick, 0.7 g/cm3 dense). This design improves upon the response characteristics of existing designs through the specific choice of materials as well as the appropriate size and arrangement of the ionization chamber components. The results of performance tests conducted at the Secondary Standard Dosimetry laboratory in Karaj-Iran demonstrated the short and long-term stability, the low leakage current, the low directional dependence, and the high ion collection efficiency of the design. Furthermore, the FLUKA Monte Carlo simulations confirmed the low effect of central electrode on this new ionization chamber response. The response characteristics of the parallel plate ionization chamber presented in this work makes the instrument suitable for use as a standard dosimeter in laboratories.

  3. Use of a two-dimensional ionization chamber array for proton therapy beam quality assurance.

    PubMed

    Arjomandy, Bijan; Sahoo, Narayan; Ding, Xiaoning; Gillin, Michael

    2008-09-01

    Two-dimensional ion chamber arrays are primarily used for conventional and intensity modulated radiotherapy quality assurance. There is no commercial device of such type available on the market that is offered for proton therapy quality assurance. We have investigated suitability of the MatriXX, a commercial two-dimensional ion chamber array detector for proton therapy QA. This device is designed to be used for photon and electron therapy QA. The device is equipped with 32 x 32 parallel plate ion chambers, each with 4.5 mm diam and 7.62 mm center-to-center separation. A 250 MeV proton beam was used to calibrate the dose measured by this device. The water equivalent thickness of the buildup material was determined to be 3.9 mm using a 160 MeV proton beam. Proton beams of different energies were used to measure the reproducibility of dose output and to evaluate the consistency in the beam flatness and symmetry measured by MatriXX. The output measurement results were compared with the clinical commissioning beam data that were obtained using a 0.6 cc Farmer chamber. The agreement was consistently found to be within 1%. The profiles were compared with film dosimetry and also with ion chamber data in water with an excellent agreement. The device is found to be well suited for quality assurance of proton therapy beams. It provides fast two-dimensional dose distribution information in real time with the accuracy comparable to that of ion chamber measurements and film dosimetry.

  4. Spin Pumping in Superfluid ^3He in High Magnetic Field

    NASA Astrophysics Data System (ADS)

    Kojima, H.; Suzuki, K.; Aoki, Y.; Yamaguchi, A.; Ishimoto, H.

    2008-03-01

    The spin flow dynamics in superfluid ^3He A1 phase in magnetic field has been studied up to 13 tesla. The apparatus consists of a large reservoir of of A1 phase in which a small enclosed chamber with a built-in differential pressure sensor is immersed. The chamber is connected to the reservoir via a superleak channel. The chamber is fabricated from Macor parts such that the residual heat leak is much reduced from those in our experiments. Our focus is on the measurement of relaxation of the induced pressure subsequent to either magnetically induced spin-polarized superflow or by electrostatic spin pumping. In general, both methods of measurement show that the relaxation time (τ) of the induced pressure tends to vanish smoothly as the transition temperature Tc2 is approached. However, the observed dependence of τ on magnetic field is different. The measured τ by the field gradient method continues to increase up to 8 tesla. On the other hand, τ measured by the spin pumping method tends to saturate to a constant between 5 and 13 tesla. The discrepancy is unexpected and not yet understood.

  5. Correction of measured Gamma-Knife output factors for angular dependence of diode detectors and PinPoint ionization chamber.

    PubMed

    Hršak, Hrvoje; Majer, Marija; Grego, Timor; Bibić, Juraj; Heinrich, Zdravko

    2014-12-01

    Dosimetry for Gamma-Knife requires detectors with high spatial resolution and minimal angular dependence of response. Angular dependence and end effect time for p-type silicon detectors (PTW Diode P and Diode E) and PTW PinPoint ionization chamber were measured with Gamma-Knife beams. Weighted angular dependence correction factors were calculated for each detector. The Gamma-Knife output factors were corrected for angular dependence and end effect time. For Gamma-Knife beams angle range of 84°-54°. Diode P shows considerable angular dependence of 9% and 8% for the 18 mm and 14, 8, 4 mm collimator, respectively. For Diode E this dependence is about 4% for all collimators. PinPoint ionization chamber shows angular dependence of less than 3% for 18, 14 and 8 mm helmet and 10% for 4 mm collimator due to volumetric averaging effect in a small photon beam. Corrected output factors for 14 mm helmet are in very good agreement (within ±0.3%) with published data and values recommended by vendor (Elekta AB, Stockholm, Sweden). For the 8 mm collimator diodes are still in good agreement with recommended values (within ±0.6%), while PinPoint gives 3% less value. For the 4 mm helmet Diodes P and E show over-response of 2.8% and 1.8%, respectively. For PinPoint chamber output factor of 4 mm collimator is 25% lower than Elekta value which is generally not consequence of angular dependence, but of volumetric averaging effect and lack of lateral electronic equilibrium. Diodes P and E represent good choice for Gamma-Knife dosimetry. Copyright © 2014 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  6. Effect of recombination in a high quantum efficiency prototype ionization-chamber-based electronic portal imaging device.

    PubMed

    Gopal, A; Samant, S S

    2007-08-01

    The quantum efficiency (QE) of an imaging detector can be increased by utilizing a thick, high-density detection medium to increase the number of quantum interactions. However, image quality is more accurately described by the detection quantum efficiency (DQE). If a significant fraction of the increase in the number of detected quanta from a thick, dense detector were to result in useful imaging signal, this represents a favorable case where enhanced QE leads to increased DQE. However, for ionization-type detectors, one factor that limits DQE is the recombination between ion pairs that acts as a secondary quantum sink due to which enhancement in QE may not result in higher DQE depending on the extent of the signal loss from recombination. Therefore, an analysis of signal loss mechanisms or quantum sinks in an imaging system is essential for validating the overall benefit of high QE detectors. In this paper, a study of ion recombination as a secondary quantum sink is presented for a high QE prototype ion-chamber-based electronic portal imaging device (EPID): the kinestatic charge detector (KCD). The KCD utilizes a high pressure noble gas (krypton or xenon at 100 atm) and an arbitrarily large detector thickness (of the order of centimeters), resulting in a high QE imager. Compared with commercial amorphous silicon flat panel imagers that provide DQE(0) approximately 0.01, the KCD has much higher DQE. Studies indicated that DQE(0) = 0.20 for 6.1 cm thick, 100 atm (rho = 3.4 g/cm3) xenon chamber, and DQE(0)=0.34 for a 9.1 cm thick chamber. A series of experiments was devised and conducted to determine the signal loss due to recombination for a KCD chamber. The measurements indicated a fractional recombination loss of about 14% for a krypton chamber and about 18% for a xenon chamber under standard operating conditions (100 atm chamber pressure and 1275 V/cm electric field intensity). A theoretical treatment of the effect of recombination on imaging signal

  7. 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.

  8. 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.

  9. Monte Carlo study of the depth-dependent fluence perturbation in parallel-plate ionization chambers in electron beams.

    PubMed

    Zink, K; Czarnecki, D; Looe, H K; von Voigts-Rhetz, P; Harder, D

    2014-11-01

    The electron fluence inside a parallel-plate ionization chamber positioned in a water phantom and exposed to a clinical electron beam deviates from the unperturbed fluence in water in absence of the chamber. One reason for the fluence perturbation is the well-known "inscattering effect," whose physical cause is the lack of electron scattering in the gas-filled cavity. Correction factors determined to correct for this effect have long been recommended. However, more recent Monte Carlo calculations have led to some doubt about the range of validity of these corrections. Therefore, the aim of the present study is to reanalyze the development of the fluence perturbation with depth and to review the function of the guard rings. Spatially resolved Monte Carlo simulations of the dose profiles within gas-filled cavities with various radii in clinical electron beams have been performed in order to determine the radial variation of the fluence perturbation in a coin-shaped cavity, to study the influences of the radius of the collecting electrode and of the width of the guard ring upon the indicated value of the ionization chamber formed by the cavity, and to investigate the development of the perturbation as a function of the depth in an electron-irradiated phantom. The simulations were performed for a primary electron energy of 6 MeV. The Monte Carlo simulations clearly demonstrated a surprisingly large in- and outward electron transport across the lateral cavity boundary. This results in a strong influence of the depth-dependent development of the electron field in the surrounding medium upon the chamber reading. In the buildup region of the depth-dose curve, the in-out balance of the electron fluence is positive and shows the well-known dose oscillation near the cavity/water boundary. At the depth of the dose maximum the in-out balance is equilibrated, and in the falling part of the depth-dose curve it is negative, as shown here the first time. The influences of both the

  10. Monte Carlo study of the depth-dependent fluence perturbation in parallel-plate ionization chambers in electron beams

    SciTech Connect

    Zink, K.; Czarnecki, D.; Voigts-Rhetz, P. von; Looe, H. K.; Harder, D.

    2014-11-01

    Purpose: The electron fluence inside a parallel-plate ionization chamber positioned in a water phantom and exposed to a clinical electron beam deviates from the unperturbed fluence in water in absence of the chamber. One reason for the fluence perturbation is the well-known “inscattering effect,” whose physical cause is the lack of electron scattering in the gas-filled cavity. Correction factors determined to correct for this effect have long been recommended. However, more recent Monte Carlo calculations have led to some doubt about the range of validity of these corrections. Therefore, the aim of the present study is to reanalyze the development of the fluence perturbation with depth and to review the function of the guard rings. Methods: Spatially resolved Monte Carlo simulations of the dose profiles within gas-filled cavities with various radii in clinical electron beams have been performed in order to determine the radial variation of the fluence perturbation in a coin-shaped cavity, to study the influences of the radius of the collecting electrode and of the width of the guard ring upon the indicated value of the ionization chamber formed by the cavity, and to investigate the development of the perturbation as a function of the depth in an electron-irradiated phantom. The simulations were performed for a primary electron energy of 6 MeV. Results: The Monte Carlo simulations clearly demonstrated a surprisingly large in- and outward electron transport across the lateral cavity boundary. This results in a strong influence of the depth-dependent development of the electron field in the surrounding medium upon the chamber reading. In the buildup region of the depth-dose curve, the in–out balance of the electron fluence is positive and shows the well-known dose oscillation near the cavity/water boundary. At the depth of the dose maximum the in–out balance is equilibrated, and in the falling part of the depth-dose curve it is negative, as shown here the

  11. {sup 3}He melting pressure thermometry

    SciTech Connect

    Ni, W.; Xia, J.S.; Adams, E.D.

    1995-10-01

    High-precision measurements of the {sup 3}He melting pressure versus temperature have been made from 500 {mu}K to 25 mK using a {sup 60}Co nuclear orientation primary thermometer and a Pt NMR susceptibility secondary thermometer. Temperatures for the fixed points on the melting curve are: the superfluid A transition T{sub A}=2.505 mK, the A-B transition T{sub AB}=1.948 mK, and the solid ordering temperature T{sub N}=0.934 mK. These fixed points and a functional form for P(T) constitute a convenient temperature scale, based on a primary thermometer, usable to well below 1 mK.

  12. A novel convolution-based approach to address ionization chamber volume averaging effect in model-based treatment planning systems

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    The ionization chamber volume averaging effect is a well-known issue without an elegant solution. The purpose of this study is to propose a novel convolution-based approach to address the volume averaging effect in model-based treatment planning systems (TPSs). Ionization chamber-measured beam profiles can be regarded as the convolution between the detector response function and the implicit real profiles. Existing approaches address the issue by trying to remove the volume averaging effect from the measurement. In contrast, our proposed method imports the measured profiles directly into the TPS and addresses the problem by reoptimizing pertinent parameters of the TPS beam model. In the iterative beam modeling process, the TPS-calculated beam profiles are convolved with the same detector response function. Beam model parameters responsible for the penumbra are optimized to drive the convolved profiles to match the measured profiles. Since the convolved and the measured profiles are subject to identical volume averaging effect, the calculated profiles match the real profiles when the optimization converges. The method was applied to reoptimize a CC13 beam model commissioned with profiles measured with a standard ionization chamber (Scanditronix Wellhofer, Bartlett, TN). The reoptimized beam model was validated by comparing the TPS-calculated profiles with diode-measured profiles. Its performance in intensity-modulated radiation therapy (IMRT) quality assurance (QA) for ten head-and-neck patients was compared with the CC13 beam model and a clinical beam model (manually optimized, clinically proven) using standard Gamma comparisons. The beam profiles calculated with the reoptimized beam model showed excellent agreement with diode measurement at all measured geometries. Performance of the reoptimized beam model was comparable with that of the clinical beam model in IMRT QA. The average passing rates using the reoptimized beam model increased substantially from 92.1% to

  13. A novel convolution-based approach to address ionization chamber volume averaging effect in model-based treatment planning systems.

    PubMed

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

    2015-08-21

    The ionization chamber volume averaging effect is a well-known issue without an elegant solution. The purpose of this study is to propose a novel convolution-based approach to address the volume averaging effect in model-based treatment planning systems (TPSs). Ionization chamber-measured beam profiles can be regarded as the convolution between the detector response function and the implicit real profiles. Existing approaches address the issue by trying to remove the volume averaging effect from the measurement. In contrast, our proposed method imports the measured profiles directly into the TPS and addresses the problem by reoptimizing pertinent parameters of the TPS beam model. In the iterative beam modeling process, the TPS-calculated beam profiles are convolved with the same detector response function. Beam model parameters responsible for the penumbra are optimized to drive the convolved profiles to match the measured profiles. Since the convolved and the measured profiles are subject to identical volume averaging effect, the calculated profiles match the real profiles when the optimization converges. The method was applied to reoptimize a CC13 beam model commissioned with profiles measured with a standard ionization chamber (Scanditronix Wellhofer, Bartlett, TN). The reoptimized beam model was validated by comparing the TPS-calculated profiles with diode-measured profiles. Its performance in intensity-modulated radiation therapy (IMRT) quality assurance (QA) for ten head-and-neck patients was compared with the CC13 beam model and a clinical beam model (manually optimized, clinically proven) using standard Gamma comparisons. The beam profiles calculated with the reoptimized beam model showed excellent agreement with diode measurement at all measured geometries. Performance of the reoptimized beam model was comparable with that of the clinical beam model in IMRT QA. The average passing rates using the reoptimized beam model increased substantially from 92.1% to

  14. Cross section of 3He( 3He,2p) 4He measured near the Gamow peak

    NASA Astrophysics Data System (ADS)

    Itahashi, T.; Kudomi, N.; Yoshida, S.; Kume, K.; Komori, M.; Ohsumi, H.

    2003-06-01

    We measured the cross section of 3He( 3He,2p) 4He in the energy region of 30-50 keV center of mass energy by using the OCEAN facility. The resulting astrophysical S-factors are in agreement with the existing data and their total errors are as good as those of the previous experiment. For further study we tried the measurements at lower energies than E cm = 30 keV. It will require running times of one month with more improvements such as background reduction and steady operation of the detection system.

  15. A radiation quality correction factor k for well-type ionization chambers for the measurement of the reference air kerma rate of (60)Co HDR brachytherapy sources.

    PubMed

    Schüller, Andreas; Meier, Markus; Selbach, Hans-Joachim; Ankerhold, Ulrike

    2015-07-01

    The aim of this study was to investigate whether a chamber-type-specific radiation quality correction factor kQ can be determined in order to measure the reference air kerma rate of (60)Co high-dose-rate (HDR) brachytherapy sources with acceptable uncertainty by means of a well-type ionization chamber calibrated for (192)Ir HDR sources. The calibration coefficients of 35 well-type ionization chambers of two different chamber types for radiation fields of (60)Co and (192)Ir HDR brachytherapy sources were determined experimentally. A radiation quality correction factor kQ was determined as the ratio of the calibration coefficients for (60)Co and (192)Ir. The dependence on chamber-to-chamber variations, source-to-source variations, and source strength was investigated. For the PTW Tx33004 (Nucletron source dosimetry system (SDS)) well-type chamber, the type-specific radiation quality correction factor kQ is 1.19. Note that this value is valid for chambers with the serial number, SN ≥ 315 (Nucletron SDS SN ≥ 548) onward only. For the Standard Imaging HDR 1000 Plus well-type chambers, the type-specific correction factor kQ is 1.05. Both kQ values are independent of the source strengths in the complete clinically relevant range. The relative expanded uncertainty (k = 2) of kQ is UkQ = 2.1% for both chamber types. The calibration coefficient of a well-type chamber for radiation fields of (60)Co HDR brachytherapy sources can be calculated from a given calibration coefficient for (192)Ir radiation by using a chamber-type-specific radiation quality correction factor kQ. However, the uncertainty of a (60)Co calibration coefficient calculated via kQ is at least twice as large as that for a direct calibration with a (60)Co source.

  16. Two-dimensional and quasi-three-dimensional dosimetry of hadron and photon beams with the Magic Cube and the Pixel Ionization Chamber.

    PubMed

    Cirio, R; Garelli, E; Schulte, R; Amerio, S; Boriano, A; Bourhaleb, F; Coutrakon, G; Donetti, M; Giordanengo, S; Koss, P; Madon, E; Marchetto, F; Nastasi, U; Peroni, C; Santuari, D; Sardo, A; Scielzo, G; Stasi, M; Trevisiol, E

    2004-08-21

    Two detectors for fast two-dimensional (2D) and quasi-three-dimensional (quasi-3D) verification of the dose delivered by radiotherapy beams have been developed at University and Istituto Nazionale di Fisica Nucleare (INFN) of Torino. The Magic Cube is a stack of strip-segmented ionization chambers interleaved with water-equivalent slabs. The parallel plate ionization chambers have a sensitive area of 24 x 24 cm2, and consist of 0.375 cm wide and 24 cm long strips. There are a total of 64 strips per chamber. The Magic Cube has been tested with the clinical proton beam at Loma Linda University Medical Centre (LLUMC), and was shown to be capable of fast and precise quasi-3D dose verification. The Pixel Ionization Chamber (PXC) is a detector with pixel anode segmentation. It is a 32 x 32 matrix of 1024 cylindrical ionization cells arranged in a square 24 x 24 cm2 area. Each cell has 0.4 cm diameter and 0.55 cm height, at a pitch of 0.75 cm separates the centre of adjacent cells. The sensitive volume of each single ionization cell is 0.07 cm3. The detectors are read out using custom designed front-end microelectronics and a personal computer-based data acquisition system. The PXC has been used to verify dynamic intensity-modulated radiotherapy for head-and-neck and breast cancers.

  17. Two-dimensional and quasi-three-dimensional dosimetry of hadron and photon beams with the Magic Cube and the Pixel Ionization Chamber

    NASA Astrophysics Data System (ADS)

    Cirio, R.; Garelli, E.; Schulte, R.; Amerio, S.; Boriano, A.; Bourhaleb, F.; Coutrakon, G.; Donetti, M.; Giordanengo, S.; Koss, P.; Madon, E.; Marchetto, F.; Nastasi, U.; Peroni, C.; Santuari, D.; Sardo, A.; Scielzo, G.; Stasi, M.; Trevisiol, E.

    2004-08-01

    Two detectors for fast two-dimensional (2D) and quasi-three-dimensional (quasi-3D) verification of the dose delivered by radiotherapy beams have been developed at University and Istituto Nazionale di Fisica Nucleare (INFN) of Torino. The Magic Cube is a stack of strip-segmented ionization chambers interleaved with water-equivalent slabs. The parallel plate ionization chambers have a sensitive area of 24 × 24 cm2, and consist of 0.375 cm wide and 24 cm long strips. There are a total of 64 strips per chamber. The Magic Cube has been tested with the clinical proton beam at Loma Linda University Medical Centre (LLUMC), and was shown to be capable of fast and precise quasi-3D dose verification. The Pixel Ionization Chamber (PXC) is a detector with pixel anode segmentation. It is a 32 × 32 matrix of 1024 cylindrical ionization cells arranged in a square 24 × 24 cm2 area. Each cell has 0.4 cm diameter and 0.55 cm height, at a pitch of 0.75 cm separates the centre of adjacent cells. The sensitive volume of each single ionization cell is 0.07 cm3. The detectors are read out using custom designed front-end microelectronics and a personal computer-based data acquisition system. The PXC has been used to verify dynamic intensity-modulated radiotherapy for head-and-neck and breast cancers.

  18. A pixel ionization chamber used as beam monitor at the Institut Curie—Centre de Protontherapie de Orsay (CPO)

    NASA Astrophysics Data System (ADS)

    La Rosa, A.; Garella, M. A.; Bourhaleb, F.; Cirio, R.; Donetti, M.; Giordanengo, S.; Givehchi, N.; Marchetto, F.; Martin, F.; Meyroneinc, S.; Peroni, C.; Pittà, G.

    2006-09-01

    The Dipartimento di Fisica Sperimentale and the Istituto Nazionale di Fisica Nucleare (INFN), Torino, in collaboration with the Institut Curie—Centre de Protontherapie de Orsay (CPO), have developed and built a pixel parallel plate ionization chamber to be used as monitor for the proton therapy beam line at the Institut Curie—CPO (Orsay, France). The sensitive area of the detector is (160×160) mm 2, with the anode segmented in 1024 square pixels arranged in a 32×32 matrix; the area of each pixel is (5×5) mm 2. The detector has been placed on the beam line just upstream of the last collimator to monitor the beam shape and to measure the stability and reproducibility of the delivery system. In this paper, we present a detailed description of the detector and the results of a set of preliminary tests.

  19. Computation of the electron beam quality [Formula: see text] factors for the NE2571, NE2571A and NE2581A thimble ionization chambers using PENELOPE.

    PubMed

    Erazo, F; Brualla, L; Lallena, A M

    2017-06-01

    The quality correction factor [Formula: see text] for electron beams was calculated for three thimble ionization chambers, namely, NE2571, NE2571A and NE2581A. The Monte Carlo code PENELOPE was used to estimate the overall correction factor fc,Q of these chambers for electron beams with nominal energies ranging between 6 and 22MeV, corresponding to a Varian Clinac 2100 C/D. A (60)Co beam was used as reference quality Q0. Also eight monoenergetic electron beams reproducing the quality index R50 of the Clinac beams were considered. The [Formula: see text] factors were calculated as the ratio between fc,Q and [Formula: see text] . Those obtained for the NE2571 ionization chamber show a nice agreement with those calculated by Muir and Rogers with EGSnrc. As it occurred to other ionization chambers analyzed in previous works, the [Formula: see text] factors found for the monoenergetic beams are larger (smaller) than those corresponding to the Clinac beams at low (high) R50 values, the differences being slightly above 0.5%. Finally, the [Formula: see text] factors obtained in the case of the NE2571A chamber are systematically ∼0.5% below those of its predecessor chamber, the NE2571. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  20. Simulation of the Mg(Ar) ionization chamber currents by different Monte Carlo codes in benchmark gamma fields

    NASA Astrophysics Data System (ADS)

    Lin, Yi-Chun; Liu, Yuan-Hao; Nievaart, Sander; Chen, Yen-Fu; Wu, Shu-Wei; Chou, Wen-Tsae; Jiang, Shiang-Huei

    2011-10-01

    High energy photon (over 10 MeV) and neutron beams adopted in radiobiology and radiotherapy always produce mixed neutron/gamma-ray fields. The Mg(Ar) ionization chambers are commonly applied to determine the gamma-ray dose because of its neutron insensitive characteristic. Nowadays, many perturbation corrections for accurate dose estimation and lots of treatment planning systems are based on Monte Carlo technique. The Monte Carlo codes EGSnrc, FLUKA, GEANT4, MCNP5, and MCNPX were used to evaluate energy dependent response functions of the Exradin M2 Mg(Ar) ionization chamber to a parallel photon beam with mono-energies from 20 keV to 20 MeV. For the sake of validation, measurements were carefully performed in well-defined (a) primary M-100 X-ray calibration field, (b) primary 60Co calibration beam, (c) 6-MV, and (d) 10-MV therapeutic beams in hospital. At energy region below 100 keV, MCNP5 and MCNPX both had lower responses than other codes. For energies above 1 MeV, the MCNP ITS-mode greatly resembled other three codes and the differences were within 5%. Comparing to the measured currents, MCNP5 and MCNPX using ITS-mode had perfect agreement with the 60Co, and 10-MV beams. But at X-ray energy region, the derivations reached 17%. This work shows us a better insight into the performance of different Monte Carlo codes in photon-electron transport calculation. Regarding the application of the mixed field dosimetry like BNCT, MCNP with ITS-mode is recognized as the most suitable tool by this work.

  1. Characterization and performances of a monitoring ionization chamber dedicated to IBA-universal irradiation head for Pencil Beam Scanning

    NASA Astrophysics Data System (ADS)

    Courtois, C.; Boissonnat, G.; Brusasco, C.; Colin, J.; Cussol, D.; Fontbonne, J. M.; Marchand, B.; Mertens, T.; de Neuter, S.; Peronnel, J.

    2014-02-01

    Every radiotherapy center has to be equipped with real-time beam monitoring devices. In 2008, we developed an ionization chamber in collaboration with the IBA (Ion Beam Applications) company. This monitoring device called IC2/3 was developed to be used in IBA universal irradiation head for Pencil Beam Scanning (PBS). Here we present the characterization of the IC2/3 monitor in the energy and flux ranges used in protontherapy. The equipment has been tested with an IBA cyclotron able to deliver proton beams from 70 to 230 MeV. This beam monitoring device has been validated and is now installed at the Westdeutsches Protonentherapiezentrum Essen protontherapy center (WPE, Germany). The results obtained in both terms of spatial resolution and dose measurements are at least equal to the initial specifications needed for PBS purposes. The detector measures the dose with a relative uncertainty lower than 1% in the range from 0.5 Gy/min to 8 Gy/min while the spatial resolution is better than 250 μm. The technology has been patented and five IC2/3 chambers were delivered to IBA. Nowadays, IBA produces the IC2/3 beam monitoring device as a part of its Proteus 235 product.

  2. 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.

  3. Elastic Compton Scattering from 3He

    NASA Astrophysics Data System (ADS)

    Margaryan, Arman; Griesshammer, Harald W.; Phillips, Daniel R.; Strandberg, Bruno; McGovern, Judith A.; Shukla, Deepshikha

    2017-01-01

    We study elastic Compton scattering on 3He using chiral effective field theory (χEFT) at photon energies from 60 MeV to approximately 120 MeV. Experiments to measure this process have been proposed for both MAMI at Mainz and the HI γS facility at TUNL. I will present the revised results of a full calculation at third order in the expansion (O (Q3)). The amplitude involves a sum of both one- and two-nucleon Compton-scattering mechanisms. We have recently computed the fourth-order two-nucleon diagrams. The numerical impact they have on the cross-section results will be discussed. I will also present results in which amplitudes used so far are augmented by the leading effects from Δ (1232) degrees of freedom, a step which has already been performed for the proton and deuteron processes. Both cross sections and doubly-polarized asymmetries will be presented, and the sensitivity of these observables to the values of neutron scalar and spin polarizabilities will be assessed. This material is based upon work supported in part by DOE and George Washington University.

  4. Electron beam quality kQ,Q0 factors for various ionization chambers: a Monte Carlo investigation with penelope

    NASA Astrophysics Data System (ADS)

    Erazo, F.; Brualla, L.; Lallena, A. M.

    2014-11-01

    In this work we calculate the beam quality correction factor {{k}\\text{Q,{{\\text{Q}}0}}} for various plane-parallel ionization chambers. A set of Monte Carlo calculations using the code penelope/penEasy have been carried out to calculate the overall correction factor fc,Q for eight electron beams corresponding to a Varian Clinac 2100 C/D, with nominal energies ranging between 6 MeV and 22 MeV, for a 60Co beam, that has been used as the reference quality Q0 and also for eight monoenergetic electron beams reproducing the quality index R50 of the Clinac beams. Two field sizes, 10 × 10 cm2 and 20 × 20 cm2 have been considered. The {{k}\\text{Q,{{\\text{Q}}0}}} factors have been calculated as the ratio between fc,Q and {{f}\\text{c,{{\\text{Q}}0}}} . Values for the Exradin A10, A11, A11TW, P11, P11TW, T11 and T11TW ionization chambers, manufactured by Standard Imaging, as well as for the NACP-02 have been obtained. The results found with the Clinac beams for the two field sizes analyzed show differences below 0.6%, even in the case of the higher energy electron beams. The {{k}\\text{Q,{{\\text{Q}}0}}} values obtained with the Clinac beams are 1% larger than those found with the monoenergetic beams for the higher energies, above 12 MeV. This difference can be ascribed to secondary photons produced in the linac head and the air path towards the phantom. Contrary to what was quoted in a previous work (Sempau et al 2004 Phys. Med. Biol. 49 4427-44), the beam quality correction factors obtained with the complete Clinac geometries and with the monoenergetic beams differ significantly for energies above 12 MeV. Material differences existing between chambers that have the same geometry produce non-negligible modifications in the value of these correction factors.

  5. Radiation dosimetry in magnetic fields with Farmer-type ionization chambers: determination of magnetic field correction factors for different magnetic field strengths and field orientations

    NASA Astrophysics Data System (ADS)

    Spindeldreier, C. K.; Schrenk, O.; Bakenecker, A.; Kawrakow, I.; Burigo, L.; Karger, C. P.; Greilich, S.; Pfaffenberger, A.

    2017-08-01

    The aim of this work was to determine magnetic field correction factors that are needed for dosimetry in hybrid devices for MR-guided radiotherapy for Farmer-type ionization chambers for different magnetic field strengths and field orientations. The response of six custom-built Farmer-type chambers irradiated at a 6 MV linac was measured in a water tank positioned in a magnet with magnetic field strengths between 0.0 T and 1.1 T. Chamber axis, beam and magnetic field were perpendicular to each other and both magnetic field directions were investigated. EGSnrc Monte Carlo simulations were compared to the measurements and simulations with different field orientations were performed. For all geometries, magnetic field correction factors, kBQ , and perturbation factors were calculated. A maximum increase of 8.8% in chamber response was measured for the magnetic field perpendicular to chamber and beam axis. The measured chamber response could be reproduced by adjusting the dead volume layer near the chamber stem in the Monte Carlo simulations. For the magnetic field parallel to the chamber axis or parallel to the beam, the simulated response increased by 1.1% at maximum for field strengths up to 1.1 T. A complex dependence of the response was found on chamber radius, magnetic field strength and orientation of beam, chamber axis and magnetic field direction. Especially for magnetic fields perpendicular to beam and chamber axis, the exact sensitive volume has to be considered in the simulations. To minimize magnetic field correction factors and the influence of dead volumes on the response of Farmer chambers, a measurement set-up with the magnetic field parallel to the chamber axis or parallel to the beam is recommended for dosimetry.

  6. 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.

  7. Dose measurement using Al2O3 dosimeter in comparison to LiF:Mg,Ti dosimeter and ionization chamber at low and high energy x-ray

    NASA Astrophysics Data System (ADS)

    Yusof, Mohd Fahmi Mohd; Yahya, Muhammad Hadzmi; Rosnan, Muhammad Syazwan; Abdullah, Reduan; Kadir, Ahmad Bazlie Abdul

    2017-01-01

    The dose measurement using Al2O3 OSL dosimeter (OSLD) was carried out at low and high energy x-ray. The dose at low energy x-ray was measured at 40, 71 and 125 kVp x-ray energies. The dose ar high energy x-ray was measured at 6 and 10 MV x-ray energies measured at the depth of maximum dose (Zmax). The results were compared to that in ionization chamber and LiF: Mg,Ti thermoluminescent dosimeters (TLD100). The results showed that the dose of OSLD were less in agreement to ionization chamber compared to that in TLD100. The dose of OSLD however was in good agreement to that in ionization chamber at high energy x-ray. The dose measured using OSLD were found to be more consistence at high energy x-ray shown by the standard deviation of the readings. The measurement of x2 showed that the readings of OSLD were close to that in ionization chamber with values of 2.21 and 4.63 for 6 and 10 MV respectively. The results indicated that OSLD is more suitable for dose measurement at high energy x-ray.

  8. sup 3 He- sup 3 He dating: A case for mixing of young and old groundwaters

    SciTech Connect

    Kamensky, I.L.; Tolstikhin, I.N. ); Tokarev, I.V. )

    1991-10-01

    {sup 3}He/{sup 4}He and {sup 20}Ne/{sup 4}He ratios were measured in shallow underground waters (opened by water-supplying wells) of the Large Vud-Javr intramountain artesian basin in the Khibiny alkaline massif, the Kola Peninsula. The ratios vary from 1.321 {times} 10{sup {minus}6} to 2.065 {times} 10{sup {minus}6} and from 1.412 to 2.941, respectively, and a well-defined correlation is observed between them. Both these ratios in aquifers are known to be time-dependent, the former increases with time due to accumulation of {sup 3}He, produced in waters by {sup 3}H {beta}-decay; the latter decreases due to migration of helium from water-bearing rocks into the waters. The correlation is interpreted as a result of the mixing of two different types of waters. The approximation line enables the authors to estimate the isotopic ratios for the endmembers participating in the mixing and the mean residence time ({tau}) of tritigenic helium-3 in the water: (1) {sup 3}He/{sup 4}He = 3.655 {times} 10{sup {minus}6}, {sup 20}Ne/{sup 4}He = 4.03, and taking into consideration {sup 3}H concentrations in the well waters, {sup 3}H = 31.1 TU (practically the same for all samples), {tau} = 15.8 {plus minus} 1.5 years for the young water; (2) {sup 3}He/{sup 4}He = 0.20 {times} 10{sup {minus}6}, {sup 20}Ne/{sup 4}He = 0.18 and T = 0.11 Ma for the old one, the contribution of the old water being less than 10%. In one well a considerable contribution of modern-day meteoric water, about 16%, is observed.

  9. Laser Induced Fluorescence Spectroscopy of Neutral and Ionized Polycyclic Aromatic Hydrocarbons in the Cosmic Simulation Chamber

    NASA Technical Reports Server (NTRS)

    Bejaoui, Salma; Salama, Farid; Contreras, Cesar; Sciamma O'Brien, Ella; Foing, Bernard; Pascale, Ehrenfreund

    2015-01-01

    Polycyclic aromatic hydrocarbon (PAH) molecules are considered the best carriers to account for the ubiquitous infrared emission bands. PAHs have also been proposed as candidates to explain the diffuse interstellar bands (DIBs), a series of absorption features seen on the interstellar extinction curve and are plausible carriers for the extended red emission (ERE), a photoluminescent process associated with a wide variety of interstellar environments. Extensive efforts have been devoted over the past two decades to characterize the physical and chemical properties of PAH molecules and ions in space. Absorption spectra of PAH molecules and ions trapped in solid matrices have been compared to the DIBs. Absorption spectra of several cold, isolated gas-phase PAHs have also been measured under experimental conditions that mimic the interstellar conditions. The purpose of this study is to provide a new dimension to the existing spectroscopic database of neutral and single ionized PAHs that is largely based on absorption spectra by adding emission spectroscopy data. The measurements are based on the laser induced fluorescence (LIF) technique and are performed with the Pulsed Discharge Nozzle (PDN) of the COSmIC laboratory facility at NASA Ames laboratory. The PDN generates a plasma in a free supersonic jet expansion to simulate the physical and the chemical conditions in interstellar environments. We focus, here, on the fluorescence spectra of large neutral PAHs and their cations where there is a lack of fluorescence spectroscopy data. The astronomical implications of the data (e.g., ERE) are examined.

  10. Determination of the recombination correction factor kS for some specific plane-parallel and cylindrical ionization chambers in pulsed photon and electron beams.

    PubMed

    Bruggmoser, G; Saum, R; Schmachtenberg, A; Schmid, F; Schüle, E

    2007-01-21

    It has been shown from an evaluation of the inverse reading of the dosemeter (1/M) against the inverse of the polarizing voltage (1/V), obtained with a number of commercially available ionization chambers, using dose per pulse values between 0.16 and 5 mGy, that a linear relationship between the recombination correction factor kS and dose per pulse (DPP) can be found. At dose per pulse values above 1 mGy the method of a general equation with coefficients dependent on the chamber type gives more accurate results than the Boag method. This method was already proposed by Burns and McEwen (1998, Phys. Med. Biol. 43 2033) and avoids comprehensive and time-consuming measurements of Jaffé plots which are a prerequisite for the application of the multi-voltage analysis (MVA) or the two-voltage analysis (TVA). We evaluated and verified the response of ionization chambers on the recombination effect in pulsed accelerator beams for both photons and electrons. Our main conclusions are: (1) The correction factor k(S) depends only on the DPP and the chamber type. There is no influence of radiation type and energy. (2) For all the chambers investigated there is a linear relationship between kS and DPP up to 5 mGy/pulse, and for two chambers we could show linearity up to 40 mGy/pulse. (3) A general formalism, such as that of Boag, characterizes chambers exclusively by the distance of the electrodes and gives a trend for the correction factor, and therefore (4) a general formalism has to reflect the influence of the chamber construction on the recombination by the introduction of chamber-type dependent coefficients.

  11. 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.

  12. 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.

  13. Laser Induced Fluorescence Spectroscopy of Neutral and Ionized Polycyclic Aromatic Hydrocarbons in a Cosmic Simulation Chamber

    NASA Astrophysics Data System (ADS)

    Bejaoui, Salma; Salama, Farid

    2015-08-01

    Polycyclic aromatic hydrocarbon (PAH) molecules are considered the best carriers to account for the ubiquitous infrared emission bands. PAHs have also been proposed as candidates to explain the diffuse interstellar bands (DIBs), a series of absorption features seen on the interstellar extinction curve and are plausible carriers for the extended red emission (ERE), a photoluminescent process associated with a wide variety of interstellar environments. Extensive efforts have been devoted over the past two decades to characterize the physical and chemical properties of PAH molecules and ions in space. Absorption spectra of PAH molecules and ions trapped in solid matrices have been compared to the DIBs [1, 2]. Absorption spectra of several cold, isolated gas-phase PAHs have also been measured under experimental conditions that mimic the interstellar conditions [see 3 for a review]. The purpose of this study is to provide a new dimension to the existing spectroscopic database of neutral and single ionized PAHs that is largely based on absorption spectra by adding emission spectroscopy data. The measurements are based on the laser-induced fluorescence (LIF) technique [4] and are performed with the Pulsed Discharge Nozzle (PDN) of the COSmIC laboratory facility at NASA Ames laboratory. The PDN generates plasma in a free supersonic jet expansion to simulate the physical and the chemical conditions in interstellar environments. We focus, here, on the fluorescence spectra of large neutral PAHs and their cations where there is a lack of fluorescence spectroscopy data. The astronomical implications of the data (e.g., ERE) are examinedReferences[1] F. Salama, E. Bakes, L.J. Allamandola, A.G.G.M. Tielens, Astrophys. J., 458 (1996) p.621[2] F. Salama, The ISO Revolution, EDP Sciences, Les Ulis, France (1999) p.65[3] Salama F., In Organic Matter in Space, IAU Symposium 251, Kwok & Sandford Eds.Cambridge University Press,4, S251,(2008), p. 357 (2008) and references therein.[4

  14. The effect of influence quantities and detector orientation on small-field patient-specific IMRT QA: comparison of measurements with various ionization chambers.

    PubMed

    Godson, Henry Finlay; Manickam, Ravikumar; Saminathan, Sathiyan; Ganesh, Kadirampatti Mani; Ponmalar, Retna

    2017-06-01

    Intensity-modulated radiation therapy (IMRT) requires a patient-specific quality assurance (QA) program to validate the treatment plan and a high level of dosimetric accuracy in the treatment delivery. Dosimetric verification generally consists of both absolute- and relative-dose measurements in a phantom using ionization chambers. Measurements were carried out with three different ionization chambers (Scanditronix FC 65G, Exradin A18, and PTW PinPoint 31014) to assess the effects of influence quantities such as the stability, pre- and post-irradiation leakage, stem effect, polarity, and ion recombination on the IMRT point-dose verification with two different orientations. The Exradin A18 and PTW PinPoint ion chambers demonstrated noticeable leakage to magnitudes of 0.6 and 1.2%, whereas negligible leakage was observed with FC 65G ion chamber. Maximum deviations of 0.5 and 0.6% were noticed for the smallest field owing to the ion recombination effect with the PTW PinPoint ion chamber in the parallel and perpendicular orientations, respectively. The calculated total uncertainties of all influence quantities for the FC 65G, A18, and PTW PinPoint ion chambers were 0.5, 0.7, and 1.3%, respectively. The uncertainties determined for each chamber were incorporated into the point-dose measurements of 30 head and neck patient-specific QA plans, and the variation was found to be within ±3%. The magnitude of the leakage in a small-volume ion chamber indicated the significance of incorporating the correction factors in the absolute-dose measurement. A paired t test analysis indicated that the influence quantities significantly affect the point-dose measurements in the patient-specific IMRT QA.

  15. Studies of 3He+3He, T+3He, and p +D nuclear reactions relevant to stellar or Big-Bang Nucleosynthesis using ICF plasmas at OMEGA

    NASA Astrophysics Data System (ADS)

    Zylstra, Alex; Gatu Johnson, Maria; Frenje, Johan; Li, Chikang; Seguin, Fredrick; Sio, Hong; Rosenberg, Michael; Rinderknecht, Hans; Petrasso, Richard; Herrmann, Hans; Kim, Yong Ho; Hale, Gerry; McNabb, Dennis; Sayre, Dan; Pino, Jesse; Brune, Carl; Bacher, Andy; Forrest, Chad; Glebov, Vladimir; Stoeckl, Christian; Janezic, Roger; Sangster, Craig

    2014-10-01

    The 3He+3He, T+3He, and p +D reactions directly relevant to Stellar or Big-Bang Nucleosynthesis (BBN) have been studied at the OMEGA laser facility using high-temperature low-density `exploding pusher' implosions. The advantage of using these plasmas is that they better mimic astrophysical systems than cold-target accelerator experiments. Measured proton spectra from the 3He3He reaction are used to constrain nuclear R-matrix modeling. The resulting T+3He γ-ray data rule out an anomalously-high 6Li production during BBN as an explanation to the high observed values in primordial material. The proton spectrum from the T+3He reaction is also being used to constrain the R-matrix model. Recent experiments have probed the p +D reaction for the first time in a plasma; this reaction is relevant to energy production in protostars, brown dwarfs and at higher CM energies to BBN. This work was partially supported by the US DOE, NLUF, LLE, and GA.

  16. A two-dimensional liquid-filled ionization chamber array prototype for small-field verification: characterization and first clinical tests

    NASA Astrophysics Data System (ADS)

    Brualla-González, Luis; Gómez, Faustino; Vicedo, Aurora; González-Castaño, Diego M.; Gago-Arias, Araceli; Pazos, Antonio; Zapata, Martín; Roselló, Joan V.; Pardo-Montero, Juan

    2012-08-01

    In this work we present the design, characterization and first clinical tests of an in-house developed two-dimensional liquid-filled ionization chamber prototype for the verification of small radiotherapy fields and treatments containing such small fields as in radiosurgery, which consists of 2 mm × 2 mm pixels arranged on a 16×8 rectangular grid. The ionization medium is isooctane. The characterization of the device included the study of depth, field-size and dose-rate dependences, which are sufficiently moderate for a good operation at therapy radiation levels. However, the detector presents an important anisotropic response, up to ≃ 12% for front versus near-lateral incidence, which can impact the verification of full treatments with different incidences. In such a case, an anisotropy correction factor can be applied. Output factors of small square fields measured with the device show a small systematic over-response, less than 1%, when compared to unshielded diode measurements. An IMRT radiosurgery treatment has been acquired with the liquid-filled ionization chamber device and compared with film dosimetry by using the gamma method, showing good agreement: over 99% passing rates for 1.2% and 1.2 mm for an incidence-per-incidence analysis; 100% passing rates for tolerances 1.8% and 1.8 mm when the whole treatment is analysed and the anisotropy correction factor is applied. The point dose verification for each incidence of the treatment performed with the liquid-filled ionization chamber agrees within 1% with a CC01 ionization chamber. This prototype has shown the utility of this kind of technology for the verification of small fields/treatments. Currently, a larger device covering a 5 cm × 5 cm area is under development.

  17. On the interpretation of current-voltage curves in ionization chambers using the exact solution of the Thomson problem

    NASA Astrophysics Data System (ADS)

    Ridenti, M. A.; Pascholati, P. R.; Gonçalves, J. A. C.; Bueno, C. C.

    2015-09-01

    The I - ΔV characteristic curve of a well type ionization chamber irradiated with 192Ir sources (0.75 Ci-120 Ci) was fitted using the exact solution of the Thomson problem. The recombination coefficient and saturation current were estimated using this new approach. The saturation current was compared with the results of the conventional method based on Boag-Wilson formula. It was verified that differences larger than 1% between both methods only occurred at activities higher than 55 Ci. We concluded that this new approach is recommended for a more accurate estimate of the saturation current when it is not possible to measure currents satisfying the condition I /Isat > 0.95. From the calibration curve the average value of pairs of carriers created per unit volume was estimated to be equal to η = 8.1 ×10-3cm-3s-1 Bq-1 and from that value it was estimated that ~ 17 pairs were created on average per second for each decay of the source.

  18. Performance Limits of Pulse Tube Cryocoolers Using 3HE

    NASA Astrophysics Data System (ADS)

    Kittel, P.

    2008-03-01

    The enthalpy, entropy, and exergy flows resulting from the real gas effects of 3He in ideal pulse tube cryocoolers are described. The discussion follows a previous description of the real gas effects of 4He in ideal pulse tube cryocoolers and makes use of a recently developed model of the thermophysical properties of 3He. This model is used to describe how the thermodynamic flows are affected by real gas phenomena of 3He and compares these effects to similar effects for 4He. The analysis was done over the pressure range 0.3-2 MPa and temperatures down to 1 K. At 2 MPa there is almost no difference in the cooling power between 3He and 4He. At lower pressures, using 3He is advantageous. There is a 1-2 K reduction in the 3He cooling power vs. temperature curves compared to those for 4He in the 0.3-1 MPa range.

  19. Recycling of 3He from lung magnetic resonance imaging.

    PubMed

    Salhi, Z; Grossmann, T; Gueldner, M; Heil, W; Karpuk, S; Otten, E W; Rudersdorf, D; Surkau, R; Wolf, U

    2012-06-01

    We have developed the means to recycle (3) He exhaled by patients after imaging the lungs using magnetic resonance of hyperpolarized (3) He. The exhaled gas is collected in a helium leak proof bag and further compressed into a steel bottle. The collected gas contains about 1-2% of (3) He, depending on the amount administered and the number of breaths collected to wash out the (3) He gas from the lungs. (3) He is separated from the exhaled air using zeolite molecular sieve adsorbent at 77 K followed by a cold head at 8 K. Residual gaseous impurities are finally absorbed by a commercial nonevaporative getter. The recycled (3) He gas features high purity, which is required for repolarization by metastability exchange optical pumping. At present, we achieve a collection efficiency of 80-84% for exhaled gas from healthy volunteers and cryogenic separation efficiency of 95%.

  20. /sup 3/He functions in tokamak-pumped laser systems

    SciTech Connect

    Jassby, D.L.

    1986-10-01

    /sup 3/He placed in an annular cell around a tokamak fusion generator can convert moderated fusion neutrons to energetic ions by the /sup 3/He(n,p)T reaction, and thereby excite gaseous lasants mixed with the /sup 3/He while simultaneously breeding tritium. The total /sup 3/He inventory is about 4 kg for large tokamak devices. Special configurations of toroidal-field magnets, neutron moderators and beryllium reflectors are required to permit nearly uniform neutron current into the laser cell with minimal attenuation. The annular laser radiation can be combined into a single output beam at the top of the tokamak.

  1. Commissioning of a PTW 34070 large-area plane-parallel ionization chamber for small field megavoltage photon dosimetry.

    PubMed

    Kupfer, Tom; Lehmann, Joerg; Butler, Duncan J; Ramanathan, Ganesan; Bailey, Tracy E; Franich, Rick D

    2017-10-04

    This study investigates a large-area plane-parallel ionization chamber (LAC) for measurements of dose-area product in water (DAPw ) in megavoltage (MV) photon fields. Uniformity of electrode separation of the LAC (PTW34070 Bragg Peak Chamber, sensitive volume diameter: 8.16 cm) was measured using high-resolution microCT. Signal dependence on angle α of beam incidence for square 6 MV fields of side length s = 20 cm and 1 cm was measured in air. Polarity and recombination effects were characterized in 6, 10, and 18 MV photons fields. To assess the lateral setup tolerance, scanned LAC profiles of a 1 × 1 cm(2) field were acquired. A 6 MV calibration coefficient, ND,w,LAC , was determined in a field collimated by a 5 cm diameter stereotactic cone with known DAPw . Additional calibrations in 10 × 10 cm(2) fields at 6, 10, and 18 MV were performed. Electrode separation is uniform and agrees with specifications. Volume-averaging leads to a signal increase proportional to ~1/cos(α) in small fields. Correction factors for polarity and recombination range between 0.9986 to 0.9996 and 1.0007 to 1.0024, respectively. Off-axis displacement by up to 0.5 cm did not change the measured signal in a 1 × 1 cm(2) field. ND,w,LAC was 163.7 mGy cm(-2) nC(-1) and differs by +3.0% from the coefficient derived in the 10 × 10 cm(2) 6 MV field. Response in 10 and 18 MV fields increased by 1.0% and 2.7% compared to 6 MV. The LAC requires only small correction factors for DAPw measurements and shows little energy dependence. Lateral setup errors of 0.5 cm are tolerated in 1 × 1 cm(2) fields, but beam incidence must be kept as close to normal as possible. Calibration in 10 × 10 fields is not recommended because of the LAC's over-response. The accuracy of relative point-dose measurements in the field's periphery is an important limiting factor for the accuracy of DAPw measurements. © 2017 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on

  2. Large area neutron detector based on Li6 ionization chamber with integrated body-moderator of high density polyethylene

    SciTech Connect

    Ianakiev, Kiril D.; Swinhoe, Martyn T.; Chung, Kiwhan; Makela, Mark F.

    2009-06-30

    A detector was developed and funded by DHS to be a lower cost alternative to 3He detectors. A 6Li foil-lined ionization chamber was prepared with fill gas at one atmosphere and pulse mode operation. The high-density polyethylene (HOPE) body serves also as a neutron moderator. All electrodes, including high voltage bias supply, are hermetically sealed within the plastic slabs.

  3. Comparison of depth-dose distributions of proton therapeutic beams calculated by means of logical detectors and ionization chamber modeled in Monte Carlo codes

    NASA Astrophysics Data System (ADS)

    Pietrzak, Robert; Konefał, Adam; Sokół, Maria; Orlef, Andrzej

    2016-08-01

    The success of proton therapy depends strongly on the precision of treatment planning. Dose distribution in biological tissue may be obtained from Monte Carlo simulations using various scientific codes making it possible to perform very accurate calculations. However, there are many factors affecting the accuracy of modeling. One of them is a structure of objects called bins registering a dose. In this work the influence of bin structure on the dose distributions was examined. The MCNPX code calculations of Bragg curve for the 60 MeV proton beam were done in two ways: using simple logical detectors being the volumes determined in water, and using a precise model of ionization chamber used in clinical dosimetry. The results of the simulations were verified experimentally in the water phantom with Marcus ionization chamber. The average local dose difference between the measured relative doses in the water phantom and those calculated by means of the logical detectors was 1.4% at first 25 mm, whereas in the full depth range this difference was 1.6% for the maximum uncertainty in the calculations less than 2.4% and for the maximum measuring error of 1%. In case of the relative doses calculated with the use of the ionization chamber model this average difference was somewhat greater, being 2.3% at depths up to 25 mm and 2.4% in the full range of depths for the maximum uncertainty in the calculations of 3%. In the dose calculations the ionization chamber model does not offer any additional advantages over the logical detectors. The results provided by both models are similar and in good agreement with the measurements, however, the logical detector approach is a more time-effective method.

  4. SU-E-T-561: Development of Depth Dose Measurement Technique Using the Multilayer Ionization Chamber for Spot Scanning Method

    SciTech Connect

    Takayanagi, T; Fujitaka, S; Umezawa, M; Ito, Y; Nakashima, C; Matsuda, K

    2014-06-01

    Purpose: To develop a measurement technique which suppresses the difference between profiles obtained with a multilayer ionization chamber (MLIC) and with a water phantom. Methods: The developed technique multiplies the raw MLIC data by a correction factor that depends on the initial beam range and water equivalent depth. The correction factor is derived based on a Bragg curve calculation formula considering range straggling and fluence loss caused by nuclear reactions. Furthermore, the correction factor is adjusted based on several integrated depth doses measured with a water phantom and the MLIC. The measured depth dose profiles along the central axis of the proton field with a nominal field size of 10 by 10 cm were compared between the MLIC using the new technique and the water phantom. The spread out Bragg peak was 20 cm for fields with a range of 30.6 cm and 6.9 cm. Raw MLIC data were obtained with each energy layer, and integrated after multiplying by the correction factor. The measurements were performed by a spot scanning nozzle at Nagoya Proton Therapy Center, Japan. Results: The profile measured with the MLIC using the new technique is consistent with that of the water phantom. Moreover, 97% of the points passed the 1% dose /1mm distance agreement criterion of the gamma index. Conclusion: We have demonstrated that the new technique suppresses the difference between profiles obtained with the MLIC and with the water phantom. It was concluded that this technique is useful for depth dose measurement in proton spot scanning method.

  5. Measurement of absorbed dose-to-water for an HDR {sup 192}Ir source with ionization chambers in a sandwich setup

    SciTech Connect

    Araki, Fujio; Kouno, Tomohiro; Ohno, Takeshi; Kakei, Kiyotaka; Yoshiyama, Fumiaki; Kawamura, Shinji

    2013-09-15

    Purpose: In this study, a dedicated device for ion chamber measurements of absorbed dose-to-water for a Nucletron microSelectron-v2 HDR {sup 192}Ir brachytherapy source is presented. The device uses two ionization chambers in a so-called sandwich assembly. Using this setup and by taking the average reading of the two chambers, any dose error due to difficulties in absolute positioning (centering) of the source in between the chambers is cancelled to first order. The method's accuracy was examined by comparing measurements with absorbed dose-to-water determination based on the AAPM TG-43 protocol.Methods: The optimal source-to-chamber distance (SCD) for {sup 192}Ir dosimetry was determined from ion chamber measurements in a water phantom. The {sup 192}Ir source was sandwiched between two Exradin A1SL chambers (0.057 cm{sup 3}) at the optimal SCD separation. The measured ionization was converted to the absorbed dose-to-water using a {sup 60}Co calibration factor and a Monte Carlo-calculated beam quality conversion factor, k{sub Q}, for {sup 60}Co to {sup 192}Ir. An uncertainty estimate of the proposed method was determined based on reproducibility of measurements at different institutions for the same type of source.Results: The optimal distance for the A1SL chamber measurements was determined to be 5 cm from the {sup 192}Ir source center, considering the depth dependency of k{sub Q} for {sup 60}Co to {sup 192}Ir and the chamber positioning. The absorbed dose to water measured at (5 cm, 90°) on the transverse axis was 1.3% lower than TG-43 values and its reproducibility and overall uncertainty were 0.8% and 1.7%, respectively. The measurement doses at anisotropic points agreed within 1.5% with TG-43 values.Conclusions: The ion chamber measurement of absorbed dose-to-water with a sandwich method for the {sup 192}Ir source provides a more accurate, direct, and reference dose compared to the dose-to-water determination based on air-kerma strength in the TG-43 protocol

  6. Early Days of Superfluid ^3He: An Experimenter's View

    NASA Astrophysics Data System (ADS)

    Lee, David

    2010-03-01

    The formulation of the BCS theory led theorists to investigate possible non-S-wave pairing in liquid ^3He. Unfortunately as time went on, estimates for the pairing temperature became unattainably low. Nevertheless, the push to lower temperatures by experimentalists continued and was facilitated by the invention of the dilution refrigerator. Nuclear adiabatic demagnetization could then be used to cool liquid ^3He to ˜1 mK as demonstrated by Goodkind. An alternate approach, suggested by Pomeranchuk, involved adiabatic compression of liquid ^3He into the solid phase. Efforts to develop this technique at the Kapitza Institute, La Jolla and Cornell achieved success in demonstrating cooling of mixtures of liquid and solid ^3He to ˜ 1 mK following dilution refrigerator pre-cooling. Although there was great pessimism regarding the possible observation of pairing in liquid ^3He, the unsettled problem of magnetic ordering in solid ^3He beckoned. Ultimately two phase transition along the melting curve were observed by Osheroff et al at Cornell. Although first associated with solid ^3He, extensive NMR studies showed them to be two new phases of liquid ^3He. A brief history of experiments at various laboratories following the discovery is given, along with early interpretations given by Anderson and Morel and Balian and Werthamer. The key role of Leggett's spin dynamics is also discussed.

  7. Dynamics of magnetic solitons in /sup 3/He-B

    SciTech Connect

    Rozhkov, S.S.

    1981-01-05

    The production and propagation of n-texture solitons in the B phase of /sup 3/He in a magnetic field is analyzed. It is conceivable that n solitons were observed in /sup 3/He-B by Webb, Sager, and Wheatley/sup 3/ in their experiments after the magnetic field was turned off.

  8. 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

  9. 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

  10. SU-D-213-04: Accounting for Volume Averaging and Material Composition Effects in An Ionization Chamber Array for Patient Specific QA

    SciTech Connect

    Fugal, M; McDonald, D; Jacqmin, D; Koch, N; Ellis, A; Peng, J; Ashenafi, M; Vanek, K

    2015-06-15

    Purpose: This study explores novel methods to address two significant challenges affecting measurement of patient-specific quality assurance (QA) with IBA’s Matrixx Evolution™ ionization chamber array. First, dose calculation algorithms often struggle to accurately determine dose to the chamber array due to CT artifact and algorithm limitations. Second, finite chamber size and volume averaging effects cause additional deviation from the calculated dose. Methods: QA measurements were taken with the Matrixx positioned on the treatment table in a solid-water Multi-Cube™ phantom. To reduce the effect of CT artifact, the Matrixx CT image set was masked with appropriate materials and densities. Individual ionization chambers were masked as air, while the high-z electronic backplane and remaining solid-water material were masked as aluminum and water, respectively. Dose calculation was done using Varian’s Acuros XB™ (V11) algorithm, which is capable of predicting dose more accurately in non-biologic materials due to its consideration of each material’s atomic properties. Finally, the exported TPS dose was processed using an in-house algorithm (MATLAB) to assign the volume averaged TPS dose to each element of a corresponding 2-D matrix. This matrix was used for comparison with the measured dose. Square fields at regularly-spaced gantry angles, as well as selected patient plans were analyzed. Results: Analyzed plans showed improved agreement, with the average gamma passing rate increasing from 94 to 98%. Correction factors necessary for chamber angular dependence were reduced by 67% compared to factors measured previously, indicating that previously measured factors corrected for dose calculation errors in addition to true chamber angular dependence. Conclusion: By comparing volume averaged dose, calculated with a capable dose engine, on a phantom masked with correct materials and densities, QA results obtained with the Matrixx Evolution™ can be significantly

  11. The Map of 3He Abundance for the Moon Nearside

    NASA Astrophysics Data System (ADS)

    Kaydash, V. G.; Shkuratov, Yu. G.; Starukhina, L. V.

    1999-09-01

    In [1] strong correlation between 3He content in the lunar soils and the product of the soil maturity Is/FeO upon the content of TiO2 has been presented. Using this correlation we mapped the abundance of 3He for the nearside of the Moon. For this purpose the maps [2] of the maturity degree Is/FeO and abundance of titanium in the regolith of visible hemisphere were taken. The greatest 3He abundance is predicted for the west part of mare Serenitatis (16-20 ppb) associated with ilmenite basalts areas. The lowest 3He (1-5 ppb) is characteristic of the north and south highlands. As 3He is implanted by solar wind, the variation of its average normal flux with latitude and longitude of a lunar site could affect the 3He abundance. If so, 3He content near the poles should be less than that in equatorial zones. However, 3He content is controlled by degassing rates, which is proved by great difference between the abundance ratios of the gases in solar wind and in lunar soils [3]. Moreover, lower temperature in polar regions prevent degassing so effectively that even higher 3He content can be predicted there. As a first approximation we did not take the latitude and longitude dependence of 3He abundance into account. Refs.: [1] Taylor L.A. Engr., constr., & Oper. In Space IV, Proc. of Space'94, 678. [2] Shkuratov Yu.G. et al. 1999. Icarus, 137, 222-234. [3] Haskin L., Warren P. Lunar chemistry. Lunar sourcebook. /Eds. Heiken G. H. et al.. N. Y., 1991. 357-474.

  12. SU-E-T-174: Synopsis of the Experimental and Monte Carlo Calculated Values of the Radial EPOM Shift of Cylindrical Ionization Chambers for Photon-Beam Dosimetry.

    PubMed

    Harder, D; Looe, H; Poppe, B

    2012-06-01

    According to the concept of the effective point of measurement (EPOM), the values of depth z serving as the variable of photon-beam depth dose distributions in water measured with cylindrical ionization chambers are commonly corrected according to the formula zeff=zR+▵z, were zeff is the depth of the EPOM, zR the depth of the reference point of the chamber, i.e. of its symmetry axis, and Az the EPOM shift. Agreed-upon values of the EPOM shift are for instance ▵z=-0.6r (IAEA TRS 398, 2000) and ▵z=-0.5r (DIN6800-2,2008) with r=radius of the air-filled volume. The EPOM concept holds in the falling as well as in the rising curve branch. The Az versus r relationship is currently reviewed. Measurements of the EPOM shift of cylindrical ionization chambers for 6/15 MV photons had been based upon a comparison with depth dependent dose distributions in water measured with the Roos chamber (PTW Freiburg). Its EPOM position (1.5 mm below the front face) had been determined by comparison with radiochrome films. (Looe et al, Phys.Med.Biol. 2011;56:4267-4290). Available are also the experimental EPOM shift values by Huang et al, Physica Medica 2010;26:126-131 and the classical value of Johansson et al, IAEA -SM-222/35,243-270(1978). Accurate Monte Carlo values had been supplied by Tessier and Kawrakow, Med.Phys. 2010;37:96-107. As shown by the graphical display of Az versus r, the relationship is nonlinear, shaped as a hockey stick, with values around -0.2 mm for the "pinpoint" chambers and with values near -1.4 mm for the often-used chambers with radii near 3 mm. For r ranging from 1 to 4 mm, the relationship can be approximated by ▵z = -(2.25 mm)×[1-exp(-0.0122 r̂4)] with r in mm. Time has come for a nonlinear updating of the EPOM shift versus radius relationship of cylindrical ionization chambers applied in photon-beam dosimetry. © 2012 American Association of Physicists in Medicine.

  13. Solar Source Regions of Energetic 3He Emission

    NASA Astrophysics Data System (ADS)

    Mason, G. M.; Nitta, N. V.; Cohen, C. M.; Wiedenbeck, M. E.

    2012-12-01

    One of the surprising observations from the ACE mission has been the detection of energetic 3He emission occurring over multi-day periods. Previously observations of solar energetic 3He had detected short-lived "impulsive" energetic particle events which were associated with type III bursts and energetic electrons. The ACE observations were able to detect 3He at very low levels (<1% of 4He compared to ~10% in most earlier work) and this showed that the impulsive events often occurred during seemingly continuous multi-day periods of 3He emission. During solar active periods, 3He was present at 1 AU the majority of the time, giving evidence for either semi-continuous processes or else unresolved multiple small injections. The obvious injections during such periods were strongly associated with jet activity By adding STEREO and SDO observations we are seeking to extend the observational picture for these events. First, by following single 3He emitting regions from STEREO-B to ACE to STEREO-A we seek to examine for how long the 3He emission can continue, since any single spacecraft can be magnetically connected to a single region for only a few days and ACE often sees emission periods of that length. Second, by using SDO-AIA we seek to probe further the properties of the emitting regions to see if the previously reported association with jets is seen in events which we can now observe with greater resolution, sensitivity, and cadence than previously possible.

  14. ^3He neutron spin filters for polarized neutron scattering.

    NASA Astrophysics Data System (ADS)

    Chen, Wangchun; Borchers, Julie; Chen, Ying; O'Donovan, Kevin; Erwin, Ross; Lynn, Jeffrey; Majkrzak, Charles; McKenney, Sarah; Gentile, Thomas

    2006-03-01

    Polarized neutron scattering (PNS) is a powerful tool that probes the magnetic structures in a wide variety of magnetic materials. Polarized ^3He gas, produced by optical pumping, can be used to polarize or analyze neutron beams because of the strong spin dependence of the neutron absorption cross section for ^3He. Polarized ^3He neutron spin filters (NSF) have been of great interest in PNS community due to recent significant improvement of their performance. Here I will discuss successful applications using ^3He NSFs in polarized neutron reflectometry (PNR) and triple-axis spectrometry (TAS). In PNR, a ^3He NSF in conjunction with a position-sensitive detector allows for efficient polarization analysis of off-specular scattering over a broad range of reciprocal space. In TAS, a ^3He NSF in combination with a double focusing pyrolytic graphite monochromator provides greater versatility and higher intensity compared to a Heusler polarizer. Finally I will present the results from patterned magnetically-coupled thin films in PNR and our first ``proof-of-principle'' experiment in TAS, both of which were performed using ^3He NSF(s) at the NIST Center for Neutron Research.

  15. 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

  16. Neutron Detection Alternatives to 3He for National Security Applications

    SciTech Connect

    Kouzes, Richard T.; Ely, James H.; Erikson, Luke E.; Kernan, Warnick J.; Lintereur, Azaree T.; Siciliano, Edward R.; Stephens, Daniel L.; Stromswold, David C.; Van Ginhoven, Renee M.; Woodring, Mitchell L.

    2010-11-21

    One of the main uses for 3He is in gas proportional counters for neutron detection. Large radiation detection systems deployed for homeland security and proliferation detection applications use such systems. Due to the large increase in use of 3He for homeland security and basic research, the supply has dwindled, and can no longer meet the demand. This has led to the search for an alternative technology to replace the use of 3He-based neutron detectors. In this paper, we review the testing of currently commercially available alternative technologies for neutron detection in large systems used in various national security applications.

  17. Recent Advances of Polarized 3He Target at Jefferson Lab

    SciTech Connect

    Yi Qiang

    2011-10-01

    Polarized {sup 3}He target has been widely used in nuclear and particle experiments to study the neutron structure in the spin degree of freedom, as most of the {sup 3}He spin is carried by the unpaired neutron. Spin-Exchange Optical Pumping (SEOP) process is used in Jefferson Lab Hall A to polarize its {sup 3}He target. Through developments in recent years, both the performance and corresponding polarimetry of such a target were greatly improved. Several experiments recently carried out in Hall A benefited remarkably from this target for the record highest figure of merit.

  18. Experiments on polarization-dependent transport in 3He systems

    NASA Astrophysics Data System (ADS)

    Candela, D.; McAllaster, D. R.; Wei, L.-J.; Kalechofsy, N.

    1994-03-01

    Spin and momentum transport experiments are described for very dilute 3He- 4He mixtures and pure 3He brute-force polarized by a static field. Spin diffusion and rotation were observed in very dilute mixtures using a spin-wave resonance technique, and the viscosity increase due to polarization was observed using a vibrating wire. The mixture results are all well fit by the recent kinetic-equation calculations of Mullin and Jeon. Spin echoes were used to study transverse spin diffusion in pure 3He, providing the first clear evidence for polarization-induced relaxation-time anisotropy in a degenerate Fermi liquid.

  19. Long-term stability of liquid ionization chambers with regard to their qualification as local reference dosimeters for low dose-rate absorbed dose measurements in water.

    PubMed

    Bahar-Gogani, J; Grindborg, J E; Johansson, B E; Wickman, G

    2001-03-01

    The long-term sensitivity and calibration stability of liquid ionization chambers (LICs) has been studied at a local and a secondary standards dosimetry laboratory over a period of 3 years. The chambers were transported several times by mail between the two laboratories for measurements. The LICs used in this work are designed for absorbed dose measurements in the dose rate region of 0.1-100 mGy min(-1) and have a liquid layer thickness of 1 mm and a sensitive volume of 16.2 mm3. The liquids used as sensitive media in the chambers are mixtures of isooctane (C8H18) and tetramethylsilane (Si(CH3)4) in different proportions (about 2 to 1). Operating at a polarizing voltage of 300 V the leakage current of the chambers was stable and never exceeded 3% of the observable current at a dose rate of about 1 mGy min(-1). The volume sensitivity of the chambers was measured to be of the order of 10(-9) C Gy(-1) mm3. No systematic changes in the absorbed dose to water calibration was observed for any of the chambers during the test period (sigma < 0.2%). Variations in chamber dose response with small changes in the polarizing voltage as well as sensitivity changes with accumulated absorbed dose were also investigated. Measurements showed that the LIC response varies by 0.15% per 1% change in applied voltage around 300 V. No significant change could be observed in the LIC sensitivity after a single absorbed dose of 15 kGy. The results indicate that the LIC can be made to serve as a calibration transfer instrument and a reference detector for absorbed dose to water determinations providing good precision and long-term reproducibility.

  20. SU-E-T-645: Qualification of a 2D Ionization Chamber Array for Beam Steering and Profile Measurement

    SciTech Connect

    Gao, S; Balter, P; Rose, M; Simon, W

    2015-06-15

    Purpose: Establish a procedure for beam steering and profile measurement using a 2D ionization chamber array and show equivalence to a water scanning system. Methods: Multiple photon beams (30×30cm{sup 2} field) and electron beams (25×25cm{sup 2} cone) were steered in the radial and transverse directions using Sun Nuclear’s IC PROFILER (ICP). Solid water was added during steering to ensure measurements were beyond the buildup region. With steering complete, servos were zeroed and enabled. Photon profiles were collected in a 30×30cm{sup 2} field at dmax and 2.9 cm depth for flattened and FFF beams respectively. Electron profiles were collected with a 25×25cm{sup 2} cone and effective depth (solid water + 0.9 cm intrinsic buildup) as follows: 0.9 cm (6e), 1.9 cm (9e), 2.9 cm (12e, 16e, 20e). Profiles of the same energy, field size and depth were measured in water with Sun Nuclear’s 3D SCANNER (3DS). Profiles were re-measured using the ICP after the in-water scans. Profiles measured using the ICP and 3DS were compared by (a) examining the differences in Varian’s “Point Difference Symmetry” metric, (b) visual inspection of the overlaid profile shapes and (c) calculation of point-by-point differences. Results: Comparing ICP measurements before and after water scanning showed very good agreement indicating good stability of the linac and measurement system. Comparing ICP Measurements to water phantom measurements using Varian’s symmetry metric showed agreement within 0.5% for all beams. The average magnitude of the agreement was within 0.2%. Comparing ICP Measurements to water phantom measurements using point-by-point difference showed agreement within 0.5% inside of 80% area of the field width. Conclusion: Profile agreement to within 0.5% was observed between ICP and 3DS after steering multiple energies with the ICP. This indicates that the ICP may be used for steering electron beams, and both flattened and FFF photon beams. Song Gao: Sun Nuclear

  1. 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

  2. SU-E-T-134: Patient Specific Quality Assurance of RapidArc Pre Treatment Plans Using Semiflex 0.125 Cc Ionization Chamber.

    PubMed

    Kumar, Sa Syam; Prabakar, S; Sriram, P; Vivekanandan, N

    2012-06-01

    To evaluate the Patient specific pre-treatment quality assurance for hundred RapidArc plans using semiflex (0.125cc) ionization chambers. Absolute point dose were measured for head and neck, thorax and abdomen cases using semiflex (0.125 cc) ionization chamber. Verification plan was created for each treatment plan in eclipse 8.6 treatment planning system with the semiflex ionization chamber and the octavius phantom. Measurements were performed on a Varian Clinac2100C/D linear accelerator equipped with a millennium 120 leaf collimator. All the results were compared with the fluence measurements using 2D Seven29 ion chamber array combined with octavius phantom. Positive absolute mean dose variation of 0.56 % was observed with thorax cases with a standard deviation (SD) of ± 1.13 between the plans with a range of -1.78% to 2.70%. Negative percentage dose errors were found with head and neck and abdomen cases, with a mean variation of -0.43 % (SD ± 1.50), (range -3.25 % to 2.85 %) and -0.35 % (SD ± 1.48), (range -3.10 % to 2.65 %) for head and neck and abdomen cases respectively. Relative dose measurements with 2D array agreed well with the TPS calculate for all the cases. The maximum percentage value failed in gamma analysis was found to be 4.95, 4.75, and 4.88 for head and neck, thorax, and abdomen cases respectively. In all the cases analysed the percentage dose points failed the gamma criteria was less than 5%. On the basis of the studies performed it can be concluded that the semiflex ionization chamber having a volume of 0.125cc can be used efficiently for measuring the pre-treatment quality assurance of RapidArc plans for all the sites. The results provide an overall accuracy when compared to fluence measurement done using 2D array seven29. © 2012 American Association of Physicists in Medicine.

  3. Chiral symmetry breaking in superfluid 3He-A.

    PubMed

    Ikegami, H; Tsutsumi, Y; Kono, K

    2013-07-05

    Spontaneous symmetry breaking is an important concept in many branches of physics. In helium-3 ((3)He), the breaking of symmetry leads to the orbital chirality in the superfluid phase known as (3)He-A. Chirality is a fundamental property of (3)He-A, but its direct detection has been challenging. We report direct detection of chirality by transport measurements of electrons trapped below a free surface of (3)He-A. In particular, we observed the so-called intrinsic Magnus force experienced by a moving electron; the direction of the force directly reflected the chirality. We further showed that, at the superfluid transition, the system selected either right- or left-handed chirality. The observation of such selection directly demonstrates chiral symmetry breaking.

  4. Absolute dose measurements by means of a small cylindrical ionization chamber for very high dose per pulse high energy electron beams

    SciTech Connect

    Karaj, E.; Righi, S.; Di Martino, F.

    2007-03-15

    Very high dose per pulse (3-13 cGy/pulse) high energy electron beams are currently produced by special linear accelerators (linac) dedicated to Intra Operative Radiation Therapy (IORT). The electron beams produced by such linacs are collimated by special Perspex applicators of various size and cylindrically shaped. The biggest problems from the dosimetric point of view are caused by the high dose-per-pulse values and the use of inclined applicators. In this work measurements of absolute dose for the inclined applicators were done by using a small cylindrical ionization chamber, type CC01 (Wellhofer), a parallel plane ionization chamber type Markus (PTW 23343) and radiochromic films type EBT. We show a method which allows calculating the quality correction factors for CC01 chamber with an uncertainty of 1% and the absolute dose value for the inclined applicators using CC01 with an uncertainty of 3.1% for electron beams of energy of 6 and 7 MeV produced by the linac dedicated to IORT Novac7.

  5. [Experimental investigation of the collection efficiency of a PTW Roos ionization chamber irradiated with pulsed beams at high pulse dose with different pulse lengths].

    PubMed

    Karsch, Leonhard; Richter, Christian; Pawelke, Jörg

    2011-01-01

    In gas-filled ionization chambers as radiation detectors, the collection of the charge carriers is affected by the recombination effect. In dosimetry this effect must be accounted for by the saturation correction factor k(S). The physical description of the correction factor by Boag, Hochhäuser and Balk for pulsed radiation is well established. However, this description is only accurate when the pulse length is short compared to the collection time of the ionization chamber. In this work experimental investigations of the saturation correction factor have been made for pulses of 4 μ s up to pulse doses of about 230 mGy, and the theory of Boag, Hochhäuser and Balk was again confirmed. For longer pulses, however, the correction factor decreases and at a pulse duration of about 200μs reaches 75% of the value valid for short pulses. This reduced influence of the ion recombination is interpreted by the reaction kinetics of ion recombination as a second-order reaction. This effect is negligible for PTW Roos chambers at clinical linear accelerators with 4 μ s pulse duration for pulse doses up to 120 mGy.

  6. ^3He + ^3He measurement at E_cm = 45keV ~25keV

    NASA Astrophysics Data System (ADS)

    Itahashi, Takahisa; Komori, M.; Kudomi, N.; Yoshida, S.; Takahisa, K.

    2001-10-01

    A high brightness ion source and a precise low energy beam accelerator are indispensable tools in the study of fusion reactions in nuclear astrophysics. Of the reactions that follows the basic fusion in the sun, we have focused on the measurement of the ^3He+^3He reaction at the effective energy E_cm=17-27 keV. Currently the LUNA group has presented data down to 20.7 keV. The present paper describes the construction of a compact ion accelerator facility and results in the energy region of 25keV to 45keV. The experimental apparatus, OCEAN consists of (1) a powerful ion source that provides an intense current of ^3He^1+ or ^3He^2+ more than 1 mA at 30-50 keV (2) a low-energy beam transport with good transmission (30% for ^3He^1+ and 3% for ^3He^2+), (3) a windowless gas target and a circulation/purification system (4) a reliable calorimeter(accuracy 2%). (5) detectors, and (6) a data acquisition system. In the analysis, effective region for true reaction on E-ΔE plot was estimated as the followings. 1)The ^3He+^3He reaction was generated by simulation. 2)The Background contribution from ^3He+D reaction was generated by simulation, and those of cosmic rays, electrical noise and so on, were obtained by the background run. 3)ΔE and E distribution was divided into 16000 partitions, and signal to noise ratio were evaluated. From this procedure, S-factors were obtained as about 5 ~6 MeV \\cdotb.

  7. Development of a Polarized 3He Ion Source for RHIC

    SciTech Connect

    Milner, Richard G.

    2013-01-15

    The goal of the project was to design and construct a source of polarized 3He atoms for injection into EBIS. This is the initial step in producing polarized 3He beams in RHIC in collaboration with physicists from Columbia University and Brookhaven National Laboratory. These beams can be used to probe the spin structure of the neutron in the existing RHIC complex as well as to measure precisely the Bjorken Sum Rule at a future eRHIC electron-ion collider.

  8. Phase Shifts of p-3He Scattering at Low Energies

    NASA Astrophysics Data System (ADS)

    Yoshino, Y.; Limkaisang, V.; Nagata, J.; Yoshino, H.; Matsuda, M.

    2000-01-01

    A method employing single-energy phase-shift analysis of p-3He scattering is developed by using the S matrix in the Matsuda-Watari representation. This method can be applied for analyses in the low-energy region and also in the inelastic region. Phase-shift solutions of p-3He scattering are given at TL = 4.0, 5.5, 6.8, 8.5, 9.5 and 19.48 MeV.

  9. The SLAC E-154 {sup 3}He polarimeter

    SciTech Connect

    Romalis, M. V.; Bogorad, P. L.; Cates, G. D.; Kumar, K. S.; Chupp, T. E.; Coulter, K. P.; Smith, T. B.; Welsh, R.; Hughes, E. W.; Johnson, J. R.; Thompson, A. K.

    1998-01-20

    We describe the NMR and Rb Zeeman frequency shift polarimeters used for determining the {sup 3}He polarization in a recent precision measurement of the neutron spin structure function g{sub 1} at SLAC (E-154). We performed a detailed study of the systematic errors associated with the calibration of the NMR polarimeter. A new technique was used for determining the {sup 3}He polarization from the frequency shift of the Rb Zeeman resonance.

  10. Pickup coil optimization for polarized 3He system

    NASA Astrophysics Data System (ADS)

    Tu, X. Q.; Zheng, H.; Sun, G. A.; Gong, J.; Ren, Y.; Liu, L. J.; Gao, P. L.; Wang, W. Z.; Yan, H.

    2017-07-01

    Not only can polarized 3He gas work as neutron spin filters (NSF) but also search for spin-dependent new interactions beyond the standard model. For both cases, the relative polarization of the spin polarized noble gas needs to be measured precisely. Various NMR techniques are applied practically to monitor the 3He cell's polarization. In this work, we tried to optimize the pickup coil for the spin exchange optical pump (SEOP) based 3He system. By optimizing the signal-to-noise ratio (SNR), we found that the coil should be wound by thin wire for a higher number of turns. The optimized sizes of the pickup coils depend on the detailed configurations. For a spherical 3He cell with radius a, we found the optimized coil radius is √{5}(a+d), where d is the coil to cell surface distance. For a cylindrical 3He cell with height h, for the configurations where the coils were placed either along or perpendicular to the longitudinal axis of the target cell, we derived the optimized sizes for the specific configurations. We believe these results are practically useful for designing pickup coils of polarized 3He systems.

  11. Hyperpolarized 3He diffusion MRI and histology in pulmonary emphysema.

    PubMed

    Woods, Jason C; Choong, Cliff K; Yablonskiy, Dmitriy A; Bentley, John; Wong, Jonathan; Pierce, John A; Cooper, Joel D; Macklem, Peter T; Conradi, Mark S; Hogg, James C

    2006-12-01

    Diffusion MRI of hyperpolarized (3)He shows that the apparent diffusion coefficient (ADC) of (3)He gas is highly restricted in the normal lung and becomes nearly unrestricted in severe emphysema. The nature of this restricted diffusion provides information about lung structure; however, no direct comparison with histology in human lungs has been reported. The purpose of this study is to provide information about (3)He gas diffusivity in explanted human lungs, and describe the relationship between (3)He diffusivity and the surface area to lung volume ratio (SA/V) and mean linear intercept (L(m)) measurements--the gold standard for diagnosis of emphysema. Explanted lungs from patients who were undergoing lung transplantation for advanced COPD, and donor lungs that were not used for transplantation were imaged via (3)He diffusion MRI. Histological measurements were made on the same specimens after they were frozen in the position of study. There is an inverse correlation between diffusivity and SA/V (and a positive correlation between diffusivity and L(m)). An important result is that restricted (3)He diffusivity separated normal from emphysematous lung tissue more clearly than the morphometric analyses. This effect may be due to the smaller histologic sampling size compared to the MRI voxel sizes.

  12. MIMAC-He3: MICRO-TPC MATRIX OF CHAMBERS OF 3He

    NASA Astrophysics Data System (ADS)

    Santos, D.; Guillaudin, O.; Lamy, Th.; Mayet, F.; Moulin, E.

    2007-08-01

    The project of a micro-TPC matrix of chambers of 3He for direct detection of non-baryonic dark matter is outlined. The privileged properties of 3He are highlighted. The double detection (ionization - projection of tracks) will assure the electron-recoil discrimination. The complementarity of MIMAC-He3 for supersymmetric dark matter search with respect to other experiments is illustrated. The modular character of the detector allows to have different gases to get A-dependence. The pressure degreee of freedom gives the possibility to work at high and low pressure. The low pressure regime gives the possibility to get the directionality of the tracks. The first measurements of ionization at very few keVs for 3He in 4He gas are described.

  13. Photoneutron production of a Siemens Primus linear accelerator studied by Monte Carlo methods and a paired magnesium and boron coated magnesium ionization chamber system.

    PubMed

    Becker, J; Brunckhorst, E; Schmidt, R

    2007-11-07

    When radiotherapy with photon energies greater than 10 MV is performed neutrons contaminate the photon beam. In this paper the neutron contamination of the 15 MV photon mode of the Siemens Primus accelerator was studied. The Monte Carlo code MCNPX was used for the description of the treatment head and treatment room. The Monte Carlo results were verified by studying the photon depth dose curve and beam profiles in a water phantom. After these verifications the locations of neutron production were studied and the neutron source spectrum and strength were calculated. The neutron response of the paired Mg/Ar and MgB/Ar ionization chamber system was calculated and experimentally verified for two experimental set-ups. The paired chamber system allowed us to measure neutrons inside the field borders and allowed rapid and point wise measurement in contrast to other methods of neutron detection.

  14. CORRECTION FACTORS FOR ATTENUATION AND SCATTERING OF THE WALL OF A CYLINDRICAL IONIZATION CHAMBER IN THE 6-7 MeV HIGH-ENERGY PHOTON REFERENCE FIELD.

    PubMed

    Kowatari, M; Zutz, H; Hupe, O

    2017-06-07

    In high-energy photon reference fields the value of the air kerma rate is determined by using ionization chambers (ICs). From the charge collected inside the IC the dose can be calculated using a set of calibration and correction factors according to ISO 4037-2. A crucial parameter is the correction for the attenuation and scattering of the primary radiation due to the chamber wall. This parameter can be determined using Monte Carlo calculations. The evaluation of the factor was performed for a commercially available IC of the type Victoreen 550-3 under different build-up conditions. The results were verified by measurements in the R-F high-energy photon fields according to ISO 4037-1 at the Physikalisch-Technische Bundesanstalt (PTB) and the Japan Atomic Energy Agency (JAEA). © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  15. (18)F primary standard at ENEA-INMRI by three absolute techniques and calibration of a well-type IG11 ionization chamber.

    PubMed

    Capogni, Marco; Carconi, Pierluigi; De Felice, Pierino; Fazio, Aldo

    2016-03-01

    A new (18)F primary standardization carried out at ENEA-INMRI by three different absolute techniques, i.e. 4πγNaI(Tl)γ high-efficiency counting, TDCR and 4πβ(LS)-γ[NaI(Tl)] coincidence counting method, allowed the calibration of a fixed well-reentrant IG11 ionization chamber (IC), with an uncertainty lower than 1%, and to check the calibration factor of a portable well-type IC NPL-CRC model, previously calibrated. By the new standard the ENEA-INMRI was linked to the BIPM International Reference System (SIR) through the BIPM SIR Transfer Instrument (SIRTI).

  16. Instantaneous and continuous measurement of /sup 14/C-labeled substrate oxidation to /sup 14/CO2 by minute tissue specimens: an ionization chamber method

    SciTech Connect

    Davidson, W.D.; Klein, K.L.; Kurokawa, K.; Soll, A.H.

    1981-06-01

    The vibrating reed electrometer and ionization chamber have been adapted for the instantaneous and continuous measurement of /sup 14/C-labeled substrate oxidation to /sup 14/CO2 by minute quantities of isolated tissues. This modified technique, utilizing a ''closed'' circulation incubation system, is 10-50 times as sensitive as the previously described ''open'' circulation techniques. Substrate oxidation curves are described for human erythrocytes and polymorphonuclear leucocytes, canine parietal cells and isolated segments of the rat nephron. This apparatus should prove to be a useful tool for metabolic studies of small quantities of isolated tissue.

  17. The effective point of measurement of ionization chambers and the build-up anomaly in MV x-ray beams.

    PubMed

    McEwen, M R; Kawrakow, I; Ross, C K

    2008-03-01

    A precision experimental investigation of the effective point of measurement (EPOM) of ion chambers in megavoltage beams has been carried out. A one-dimensional scanning phantom system was developed with an overall accuracy in the positioning of a chamber of better than 0.15 mm. Depth-dose data were acquired for a 25 MV beam from an Elekta Precise linac (field sizes of 10 x 10 cm and 25 x 25 cm) for measurement depths in the range 0.6-6 cm. The results confirmed the Monte Carlo calculations of an earlier theoretical investigation by Kawrakow [Med. Phys. 33, 1829-1839 (2006)] that the standard shift for cylindrical chambers, recommended in dosimetry protocols of -0.6r (where r is the internal radius of the cavity), is incorrect. A wide range of ion chambers were investigated and it was found that errors of up to 1.4 mm could occur for certain chamber designs (although typical errors for common chambers were around 0.5 mm). A comparison between measurements and Monte Carlo simulations showed that once the correct EPOM is used, the details of the linac geometry are correct, and the parameters of the electron beam striking the bremsstrahlung target have been adequately determined, the EGSnrc Monte Carlo package is capable of reproducing the experimental data to 0.2 mm or better. The investigation also confirmed that for the highest accuracy depth-dose curves in megavoltage photon beams one should use a well-guarded parallel-plate ion chamber. Three chamber designs were tested here and found to be satisfactory-the Scanditronix-Wellhöfer NACP-02, PTW Roos and Exradin All.

  18. Solar source regions of 3HE-rich particle events

    NASA Technical Reports Server (NTRS)

    Kahler, S. W.; Lin, R. P.; Reames, D. V.; Stone, R. G.; Liggett, M.

    1985-01-01

    Hydrogen alpha X-ray, and metric and kilometric radio data to examine the solar sources of energetic 3He-rich particle events observed near earth in association with impulsive 2 to 100 keV electron events were applied. Each 3He/electron event is associated with a kilometric type 3 burst belonging to a family of such bursts characterized by similar interplanetary propagation paths from the same solar active region. The 3He/electron events correlate very well with the interplanetary low frequency radio brightnesses of these events, but progressively worse with signatures from regions closer to the Sun. When H alpha brightnings can be associated with 3He/electron events, they have onsets coinciding to within 1 min of that of the associated metric type 3 burst but are often too small to be reported. The data are consistent with the earlier idea that many type 3 bursts, the 3He/electron events, are due to particle acceleration in the corona, well above the associated H alpha and X-ray flares.

  19. Experimental Search for μd 3He Fusion

    NASA Astrophysics Data System (ADS)

    Knowles, P. E.; Boreiko, V. M.; Bystritsky, V. M.; Filipowicz, M.; Huot, O.; Mulhauser, F.; Pavlov, V. N.; Penkov, F. M.; Petitjean, C.; Popov, N. P.; Sandukovsky, V. G.; Schaller, L. A.; Schneuwly, H.; Stolupin, V. A.; Woźniak, J.

    2001-12-01

    The vast majority of muon catalyzed fusion research has been concerned with muonic molecules of hydrogen isotopes only, since the dynamics of higher-Z muonic atoms in general preclude the formation of molecular systems. In the specific case of hydrogen helium mixtures, bound muonic molecular states can exist, and thus it is possible to search for the reaction μd 3He xrightarrow{{tilde λ f}} μ+α(3.66 MeV)+p(14.64 MeV). Until recently, the theoretical predictions for the nuclear fusion rate in the μd 3He molecule, {tilde λ } f , ranged over one order of magnitude, from 105 to 106 per second. An experimental upper limit has been measured for {tilde λ } f in HD + 3He giving a value (<6×104 s-1 [1]). We report on the analysis of an experiment in D2 + 3He which has shown a signal coming either from the muon catalyzed reaction, or from the fusion in flight of 3He's formed from dμd fusion.

  20. Optical Pumping / Spin Exchange ^3He Neutron Spin Filter Development

    NASA Astrophysics Data System (ADS)

    Hwang, Shenq-Rong; Coulter, Kevin P.; Chupp, Timothy E.; Welsh, Robert C.

    1998-04-01

    We have instrumented a thermal neutron beam line at the 2MW Ford reactor at the University of Michigan to develop a ^3He neutron spin filter test stand. Due to a large, spin depedent neutron cross section at low energies, polarized ^3He can be used as a neutron spin filter. Our ^3He spin filter is a 10 amagat-cm ^3He cell polarized via optical pumping/spin exchange with Rb. The filter is made of Corning 7056 glass filled with Rb , several atmosphere of ^3He and a few hundred torr nitrogen as buffer gas. We apply two 15W diode array lasers to optically pump Rb. In this presentation we will discuss some progress of this development, including a rotating oven design and a stepping motor driven neutron chopper. Preliminary results of the 10 amagat-cm filter will be presented and compared with theoretical calculations. A study of systematic errors from the data acquisition system and the neutron chopper will also be discussed.

  1. Polarized (3) He Spin Filters for Slow Neutron Physics.

    PubMed

    Gentile, T R; Chen, W C; Jones, G L; Babcock, E; Walker, T G

    2005-01-01

    Polarized (3)He spin filters are needed for a variety of experiments with slow neutrons. Their demonstrated utility for highly accurate determination of neutron polarization are critical to the next generation of betadecay correlation coefficient measurements. In addition, they are broadband devices that can polarize large area and high divergence neutron beams with little gamma-ray background, and allow for an additional spin-flip for systematic tests. These attributes are relevant to all neutron sources, but are particularly well-matched to time of flight analysis at spallation sources. There are several issues in the practical use of (3)He spin filters for slow neutron physics. Besides the essential goal of maximizing the (3)He polarization, we also seek to decrease the constraints on cell lifetimes and magnetic field homogeneity. In addition, cells with highly uniform gas thickness are required to produce the spatially uniform neutron polarization needed for beta-decay correlation coefficient experiments. We are currently employing spin-exchange (SE) and metastability-exchange (ME) optical pumping to polarize (3)He, but will focus on SE. We will discuss the recent demonstration of 75 % (3)He polarization, temperature-dependent relaxation mechanism of unknown origin, cell development, spectrally narrowed lasers, and hybrid spin-exchange optical pumping.

  2. Polarized 3He Spin Filters for Slow Neutron Physics

    PubMed Central

    Gentile, T. R.; Chen, W. C.; Jones, G. L.; Babcock, E.; Walker, T. G.

    2005-01-01

    Polarized 3He spin filters are needed for a variety of experiments with slow neutrons. Their demonstrated utility for highly accurate determination of neutron polarization are critical to the next generation of betadecay correlation coefficient measurements. In addition, they are broadband devices that can polarize large area and high divergence neutron beams with little gamma-ray background, and allow for an additional spin-flip for systematic tests. These attributes are relevant to all neutron sources, but are particularly well-matched to time of flight analysis at spallation sources. There are several issues in the practical use of 3He spin filters for slow neutron physics. Besides the essential goal of maximizing the 3He polarization, we also seek to decrease the constraints on cell lifetimes and magnetic field homogeneity. In addition, cells with highly uniform gas thickness are required to produce the spatially uniform neutron polarization needed for beta-decay correlation coefficient experiments. We are currently employing spin-exchange (SE) and metastability-exchange (ME) optical pumping to polarize 3He, but will focus on SE. We will discuss the recent demonstration of 75 % 3He polarization, temperature-dependent relaxation mechanism of unknown origin, cell development, spectrally narrowed lasers, and hybrid spin-exchange optical pumping. PMID:27308140

  3. 3He Neutron Detector Pressure Effect and Comparison to Models

    SciTech Connect

    Kouzes, Richard T.; Ely, James H.; Lintereur, Azaree T.; Siciliano, Edward R.; Stromswold, David C.; Woodring, Mitchell L.

    2010-01-14

    Reported here are the results of measurements performed to determine the efficiency of 3He filled proportional counters as a function of gas pressure in the SAIC system. Motivation for these measurements was largely to validate the current model of the SAIC system. Those predictions indicated that the neutron detection efficiency plotted as a function of pressure has a simple, logarithmic shape. As for absolute performance, the model results indicated the 3He pressure in the current SAIC system could not be reduced appreciably while meeting the current required level of detection sensitivity. Thus, saving 3He by reducing its pressure was predicted not to be a viable option in the current SAIC system.

  4. Ultrasensitive 3He magnetometer for measurements of high magnetic fields

    NASA Astrophysics Data System (ADS)

    Nikiel, Anna; Blümler, Peter; Heil, Werner; Hehn, Manfred; Karpuk, Sergej; Maul, Andreas; Otten, Ernst; Schreiber, Laura M.; Terekhov, Maxim

    2014-11-01

    We describe a 3He magnetometer capable to measure high magnetic fields ( B> 0.1 T) with a relative accuracy of better than 10-12. Our approach is based on the measurement of the free induction decay of gaseous, nuclear spin polarized 3He following a resonant radio frequency pulse excitation. The measurement sensitivity can be attributed to the long coherent spin precession time T2 ∗ being of order minutes which is achieved for spherical sample cells in the regime of "motional narrowing" where the disturbing influence of field inhomogeneities is strongly suppressed. The 3He gas is spin polarized in situ using a new, non-standard variant of the metastability exchange optical pumping. We show that miniaturization helps to increase T2 ∗ further and that the measurement sensitivity is not significantly affected by temporal field fluctuations of order 10-4.

  5. Neutron (3He) Spin Structure Functions at Low Q^2

    SciTech Connect

    Vincent Sulkosky

    2009-07-01

    Experiment E97-110 was performed at the Thomas Jefferson National Accelerator Facility to provide a precise measurement of the $^{3}$He spin structure functions at low $Q^{2}$ from 0.02 to 0.3~[GeV$/c$]$^{2}$. A longitudinally-polarized electron beam was scattered from a longitudinally or transversely polarized $^{3}$He target. From these data, we have extracted moments of the neutron and $^{3}$He spin structure functions at very low momentum transfers. These data allow us to make a benchmark check of Chiral Perturbation Theory calculations in a region where they are expected to be valid. In these proceedings, the experimental details are discussed and preliminary results on the first moments of the $g_1\\left(x,Q^{2}\\right)$ and $g_2\\left(x,Q^{2}\\right)$ structure functions are presented.

  6. Nonlinear acoustic effects in superfluid 3He-B

    NASA Astrophysics Data System (ADS)

    McKenzie, Ross H.; Sauls, J. A.

    1992-05-01

    We consider the nonlinear interaction of zero sound with the collective modes of the order-parameter in superfluid 3He-B. The approximate particle-hole symmetry of the 3He-Fermi liquid determines selection rules for the linear and nonlinear coupling of zero sound to the collective modes. Starting from the quasiclassical theory of superfluid 3He, we have shown that the coupling strenghts have a simple representation in terms of Feynman diagrams. We predict measurable two-photon absorption and nonlinear-Raman scattering by the J = 2 + (real squashing) modes at low pressures. Recent observations of two-phonon absorption by a group in Helsinki are compared to the theoretical predictions. Two-phonon absorption can be used to determine the dispersion of the J = 2 + modes.

  7. Nonlinear acoustics in superfluid 3He-B

    NASA Astrophysics Data System (ADS)

    McKenzie, Ross H.; Sauls, J. A.

    1989-10-01

    The nonlinear interaction of zero sound with the order parameter collective modes in superfluid 3He-B is considered within perturbation theory in the amplitude of the sound field. Selection rules for nonlinear excitation of the order parameter modes are determined by the approximate particle-hole symmetry of the 3He Fermi liquid. A diagrammatic algorithm, based on the quasiclassical theory of superfluid 3He, is used to calculate nonlinear coupling constants. These nonlinearities are sufficiently large that it should be possible to observe two phonon absorption and stimulated Raman scattering of zero sound by the real squashing (J=2+) mode. Finally, we discuss the possibility of using these nonlinearities to produce zero sound with `squeezed' noise.

  8. Quark-Hadron Duality in Neutron (3He) Spin Structure

    SciTech Connect

    Solvignon, Patricia; Liyanage, Nilanga; Chen, Jian-Ping; Choi, Seonho; Aniol, Konrad; Averett, Todd; Boeglin, Werner; Camsonne, Alexandre; Cates, Gordon; Chang, C.; Chang, C.C.; Chang, C.; Chang, C.C.; Chudakov, Eugene; Craver, Brandon; Cusanno, Francesco; Deur, Alexandre; Dutta, Dipangkar; Ent, Rolf; Feuerbach, Robert; Frullani, Salvatore; Gao, Haiyan; Garibaldi, Franco; Gilman, Ronald; Glashausser, Charles; Gorbenko, Viktor; Hansen, Jens-Ole; Higinbotham, Douglas; Ibrahim, Hassan; Jiang, Xiaodong; Jones, Mark; Kelleher, Aidan; Kelly, J.; Keppel, Cynthia; Kim, Wooyoung; Korsch, Wolfgang; Kramer, Kevin; Kumbartzki, Gerfried; LeRose, John; Lindgren, Richard; Ma, Bin; Margaziotis, Demetrius; Markowitz, Pete; McCormick, Kathy; Meziani, Zein-Eddine; Michaels, Robert; Moffit, Bryan; Monaghan, Peter; Munoz-Camacho, Carlos; Paschke, Kent; Reitz, Bodo; Saha, Arunava; Sheyor, Ran; Singh, Jaideep; Slifer, Karl; Sulkosky, Vince; Sulkosky, Vincent; Sulkosky, Vince; Sulkosky, Vincent; Tobias, William; Urciuoli, Guido; Wang, Kebin; Wijesooriya, Krishni; Wojtsekhowski, Bogdan; Woo, Seungtae; Yang, Jae-Choon; Zheng, Xiaochao; Zhu, Lingyan

    2008-10-01

    We present experimental results of the first high-precision test of quark-hadron duality in the spin-structure function g_1 of the neutron and $^3$He using a polarized 3He target in the four-momentum-transfer-squared range from 0.7 to 4.0 (GeV/c)^2. Global duality is observed for the spin-structure function g_1 down to at least Q^2 = 1.8 (GeV/c)^2 in both targets. We have also formed the photon-nucleon asymmetry A_1 in the resonance region for 3He and found no strong Q^2-dependence above 2.2 (GeV/c)^2.

  9. Feasibility of neutron diffraction on solid 3He

    NASA Astrophysics Data System (ADS)

    Siemensmeyer, K.; Schuberth, E. A.; Adams, E. D.; Takano, Y.; Guckelsberger, K.

    2000-07-01

    We have investigated the feasibility of neutron diffraction from solid 3He. The experiment will be performed at the HMI, first aiming for the properties of the antiferromagnetic ordering in the BCC phase and the ferromagnetic order in the HCP phase. Signal and beam heating considerations are essential to account for the enormous neutron absorption cross section of 3He. The study shows that neutron diffraction and transmission experiments are possible, relying on the experience gained from the neutron diffraction experiments on Cu and Ag at nanokelvin temperatures. A pressure cell has been developed which complies with the conflicting demands arising from the neutron and ultralow temperature aspects of the experiment. This work is a first step in an extensive effort to characterize 3He by neutron diffraction.

  10. Strong-Coupling and the Stripe Phase of ^3He

    NASA Astrophysics Data System (ADS)

    Wiman, Joshua J.; Sauls, J. A.

    2016-09-01

    Thin films of superfluid 3He were predicted, based on weak-coupling BCS theory, to have a stable phase which spontaneously breaks translational symmetry in the plane of the film. This crystalline superfluid, or "stripe" phase, develops as a one-dimensional periodic array of domain walls separating degenerate B phase domains. We report calculations of the phases and phase diagram for superfluid 3He in thin films using a strong-coupling Ginzburg-Landau theory that accurately reproduces the bulk 3He superfluid phase diagram. We find that the stability of the Stripe phase is diminished relative to the A phase, but the Stripe phase is stable in a large range of temperatures, pressures, confinement, and surface conditions.

  11. 3He melting-curve thermometry at millikelvin temperatures

    NASA Astrophysics Data System (ADS)

    Greywall, Dennis S.

    1985-03-01

    A pressure-versus-temperature calibration of the 3He melting curve is given for 13He [i.e., Tc(P)] as a basis for intercomparison, the melting-curve scale is found to be proportional to the magnetic temperature scales of Paulson et al. and Haavasoja et al. Included is a description of the PrNi5 nuclear demagnetization refrigerator which was used to cool the 3He samples to less than 0.3 mK.

  12. Quark-hadron duality in neutron (3He) spin structure.

    PubMed

    Solvignon, P; Liyanage, N; Chen, J-P; Choi, Seonho; Aniol, K; Averett, T; Boeglin, W; Camsonne, A; Cates, G D; Chang, C C; Chudakov, E; Craver, B; Cusanno, F; Deur, A; Dutta, D; Ent, R; Feuerbach, R; Frullani, S; Gao, H; Garibaldi, F; Gilman, R; Glashausser, C; Gorbenko, V; Hansen, O; Higinbotham, D W; Ibrahim, H; Jiang, X; Jones, M; Kelleher, A; Kelly, J; Keppel, C; Kim, W; Korsch, W; Kramer, K; Kumbartzki, G; Lerose, J J; Lindgren, R; Ma, B; Margaziotis, D J; Markowitz, P; McCormick, K; Meziani, Z-E; Michaels, R; Moffit, B; Monaghan, P; Munoz Camacho, C; Paschke, K; Reitz, B; Saha, A; Sheyor, R; Singh, J; Slifer, K; Sulkosky, V; Tobias, A; Urciuoli, G M; Wang, K; Wijesooriya, K; Wojtsekhowski, B; Woo, S; Yang, J-C; Zheng, X; Zhu, L

    2008-10-31

    We present experimental results of the first high-precision test of quark-hadron duality in the spin-structure function g_{1} of the neutron and 3He using a polarized 3He target in the four-momentum-transfer-squared range from 0.7 to 4.0 (GeV/c);{2}. Global duality is observed for the spin-structure function g_{1} down to at least Q;{2}=1.8 (GeV/c);{2} in both targets. We have also formed the photon-nucleon asymmetry A1 in the resonance region for 3He and found no strong Q2 dependence above 2.2 (GeV/c);{2}.

  13. 3He spin exchange cells for magnetic resonance imaging

    NASA Astrophysics Data System (ADS)

    Jacob, R. E.; Morgan, S. W.; Saam, B.

    2002-08-01

    We present a protocol for the consistent fabrication of glass cells to provide hyperpolarized (HP) 3He for pulmonary magnetic resonance imaging. The method for producing HP 3He is spin-exchange optical pumping. The valved cells must hold of order 1 atm[middle dot]L of gas at up to 15 atm pressure. Because characteristic spin-exchange times are several hours, the longitudinal nuclear relaxation time T1 for 3He must be several tens of hours and robust with respect to repeated refilling and repolarization. Collisions with the cell wall are a significant and often dominant cause of relaxation. Consistent control of wall relaxation through cell fabrication procedures has historically proven difficult. With the help of the discovery of an important mechanism for wall relaxation that involves magnetic surface sites in the glass, and with the further confirmation of the importance of Rb metal to long wall-relaxation times, we have developed a successful protocol for fabrication of 3He spin exchange cells from inexpensive and easily worked borosilicate (Pyrex) glass. The cells are prepared under vacuum using a high-vacuum oil-free turbomolecular pumping station, and they are sealed off under vacuum after [greater-than-or-equal, slanted]100 mg of distilled Rb metal is driven in. Filling of cells with the requisite 3He-N2 mixture is done on an entirely separate gas-handling system. Our cells can be refilled and the gas repolarized indefinitely with no significant change in their wall properties. Relaxation data are presented for about 30 cells; the majority of these reach a "40/40" benchmark: T1>40 h, and 3He polarizations reach or exceed 40%. Typical polarization times range from 12 to 20 h; 20% polarization can be achieved in 3-5 h.

  14. SU-E-T-17: Comparison of MCNP5 Calculations in the Buildup Region with Plane Parallel Ionization Chamber Measurements for 6 and 18 MV Photon Beams.

    PubMed

    Abbas, H; Satti, J; MacDonald, C

    2012-06-01

    Cylindrical ion chambers are known to overestimate the dose in the buildup region, where gradients are high. The potential for MCNP5 to produce accurate calculations in this region, even when benchmarked with a large volume chamber, was tested. MCNP5 was used to model 6 and 18 MV photon beams for a Varian accelerator using vendor geometry with the collimator corrections of Chibani and Ma. Modeling was benchmarked by adjusting electron beam energy and diameter to match calculations with ionization chamber (with 0.125 cm(3) sensitive volume) measurements of percent depth doses (PDDs) beyond dmax and cross dose profiles for 5×5, 10×10 and 30×30 cm(2) field sizes. For comparison in the buildup region, the MCNP5 voxel was reduced to 1 mm, with extrapolation to find surface dose. In this region a plane parallel chamber (with 0.055 cm(3) sensitive volume) was used to measure PDDs at 0, 2 and 4 mm depths for the three field sizes, using the Khan over-response correction. Calculations and cylindrical chamber measurements for PDDs beyond dmax agree within 2% for all field sizes and energies. Dose profiles at dmax (1.5 cm and 3.3 cm for 6 and 18 MV) and at 10 cm agree within 2% in the flat region and within 10% in the penumbra. In the buildup region, the MCNP5 calculations agree with plane parallel PDD measurements within 3% at 2 and 4 mm depths. The extrapolation of the MCNP5 PDD overestimates the surface dose for the 18 MV beam for the 30×30 cm(2) field, and is within 4.2% for the smaller fields and for all field sizes at 6 MV. Improved extrapolation techniques may yield better surface dose agreement. Accurate dose in the buildup region can be calculated by MCNP5. © 2012 American Association of Physicists in Medicine.

  15. Conception and realization of a parallel-plate free-air ionization chamber for the absolute dosimetry of an ultrasoft X-ray beam

    SciTech Connect

    Groetz, J.-E. Mavon, C.; Fromm, M.; Ounoughi, N.; Belafrites, A.

    2014-08-15

    We report the design of a millimeter-sized parallel plate free-air ionization chamber (IC) aimed at determining the absolute air kerma rate of an ultra-soft X-ray beam (E = 1.5 keV). The size of the IC was determined so that the measurement volume satisfies the condition of charged-particle equilibrium. The correction factors necessary to properly measure the absolute kerma using the IC have been established. Particular attention was given to the determination of the effective mean energy for the 1.5 keV photons using the PENELOPE code. Other correction factors were determined by means of computer simulation (COMSOL™and FLUKA). Measurements of air kerma rates under specific operating parameters of the lab-bench X-ray source have been performed at various distances from that source and compared to Monte Carlo calculations. We show that the developed ionization chamber makes it possible to determine accurate photon fluence rates in routine work and will constitute substantial time-savings for future radiobiological experiments based on the use of ultra-soft X-rays.

  16. Conception and realization of a parallel-plate free-air ionization chamber for the absolute dosimetry of an ultrasoft X-ray beam

    NASA Astrophysics Data System (ADS)

    Groetz, J.-E.; Ounoughi, N.; Mavon, C.; Belafrites, A.; Fromm, M.

    2014-08-01

    We report the design of a millimeter-sized parallel plate free-air ionization chamber (IC) aimed at determining the absolute air kerma rate of an ultra-soft X-ray beam (E = 1.5 keV). The size of the IC was determined so that the measurement volume satisfies the condition of charged-particle equilibrium. The correction factors necessary to properly measure the absolute kerma using the IC have been established. Particular attention was given to the determination of the effective mean energy for the 1.5 keV photons using the PENELOPE code. Other correction factors were determined by means of computer simulation (COMSOL™and FLUKA). Measurements of air kerma rates under specific operating parameters of the lab-bench X-ray source have been performed at various distances from that source and compared to Monte Carlo calculations. We show that the developed ionization chamber makes it possible to determine accurate photon fluence rates in routine work and will constitute substantial time-savings for future radiobiological experiments based on the use of ultra-soft X-rays.

  17. T2-Shortening of 3He Gas by Magnetic Microspheres

    SciTech Connect

    Minard, Kevin R; Timchalk, Chuck; Corley, Rick A

    2005-03-01

    In the interconnected pores of a material like the lung the transverse relaxation time (T2) for 3He gas is shortened by the deposition of magnetic microspheres and rapid molecular diffusion through induced field distortions. Here, this unique relaxation process is described theoretically and predicted T2-shortening is validated using pressurized 3He gas in a foam model of lung tissue. Results demonstrate that – 1) significant T2-shortening is induced by microsphere deposition, 2) shortened T2’s are accurately predicted, and 3) measured relaxation times are exploitable for quantifying the local volume fraction of magnetic microspheres deposited in gas-filled spaces.

  18. Neutron-scattering experiment on solid 3He

    NASA Astrophysics Data System (ADS)

    Mat'aš, S.; Bat'ko, I.; Boyko, V.; Schöttl, S.; Siemensmeyer, K.; Raasch, S.; Radulov, I.; Adams, E. D.; Scherline, T. E.

    The central aim of our work is the characterisation of magnetic and crystallographic properties of solid 3He on a microscopic scale. This can only be achieved using neutron-diffraction techniques. The potential of neutron methods in magnetism and their application to nuclear magnetism is well known. They were very successful in the recent investigation of spontaneous nuclear order in copper and silver. The high neutron absorption cross section makes the application of neutron diffraction in solid 3He very difficult - but a careful feasibility study of diffraction experiments shows that new results of fundamental importance in the field of magnetism may be gained.

  19. Anisotropic Phases of Superfluid 3He in Compressed Aerogel

    NASA Astrophysics Data System (ADS)

    Li, J. I. A.; Zimmerman, A. M.; Pollanen, J.; Collett, C. A.; Halperin, W. P.

    2015-03-01

    It has been shown that the relative stabilities of various superfluid states of 3He can be influenced by anisotropy in a silica aerogel framework. We prepared a suite of aerogel samples compressed up to 30% for which we performed pulsed NMR on 3He imbibed within the aerogel. We identified A and B phases and determined their magnetic field-temperature phase diagrams as a function of strain. From these results, we infer that the B phase is distorted by negative strain forming an anisotropic superfluid state more stable than the A phase.

  20. A Study of 3He detectors for Active Interrogation

    SciTech Connect

    E.H. Seabury; D.L. Chichester

    2009-10-01

    3He proportional counters have long been used as neutron detectors for both passive and active detection of Special Nuclear Material (SNM). The optimal configuration of these detectors as far as gas pressure, amount of moderating material, and size are concerned is highly dependent on what neutron signatures are being used to detect and identify SNM. We present here a parametric study of the neutron capture response of 3He detectors, based on Monte Carlo simulations using the MCNPX radiation transport code. The neutron capture response of the detectors has been modeled as a function of time after an incident neutron pulse.

  1. Removing gaseous contaminants in {sup 3}He by cryogenic stripping

    SciTech Connect

    Benapfl, M.; Biltoft, P.; Coombs, A.

    1995-08-17

    The Tritium Operations Group at LLNL, Tritium Facility has recently developed a {sup 3}He recovery system to remove argon, xenon, neon, hydrogen, and all other contaminants from the {sup 3}He stream in an Accelerator Production of Tritium (APT) experimental apparatus. In this paper the authors will describe in detail the background information, technical requirements, the design approach, and the results of their experimental tests. The authors believe this gas purification system may have other applications as it provides at a reasonable cost an efficient method for purification of gaseous helium.

  2. High energy photon reference for radiation protection: technical design of the LINAC beam and ionization chambers; and calculation of monoenergetic conversion coefficients

    NASA Astrophysics Data System (ADS)

    Dusciac, D.; Bordy, J.-M.; Daures, J.; Blideanu, V.

    2016-09-01

    In this work, we present the results of the first part of a research project aimed at offering a complete response to dosimeters providers and nuclear physicists' demands for high-energy (6 - 9 MeV) photon beams for radiation protection purposes. Classical facilities allowing the production of high-energy photonic radiation (proton accelerators, nuclear reactors) are very rare and need large investment for development and use. A novel solution is proposed, consisting in the use of a medical linear accelerator, allowing a significant decrease of all costs.Using Monte Carlo simulations (MCNP5 and PENELOPE codes), a specifically designed electron-photon conversion target allowing for obtaining a high energy photon beam (with an average energy weighted by fluence of about 6 MeV) has been built for radiation protection purposes. Due to the specific design of the target, this "realistic" radiation protection high-energy photon beam presents a uniform distribution of air kerma rate at a distance of 1 m, over a 30 × 30 cm2 surface. Two graphite cavity ionizing chambers for ionometric measurements have been built. For one of these chambers, the charge collection volume has been measured allowing for its use as a primary standard. The second ionizing chamber is used as a transfer standard; as such it has been calibrated in a 60Co beam, and in the high energy photon beam for radiation protection.The measurements with these ionizing chambers allowed for an evaluation of the air kerma rate in the LINAC based high-energy photon beam for radiation protection: the values cover a range between 36 mGy/h and 210 mGy/h, compatible with radiation protection purposes.Finally, using Monte Carlo simulations, conversion coefficients from air kerma to dose equivalent quantities have been calculated in the range between 10 keV and 22.4 MeV, for the spectral distribution of the fluence corresponding to the beam produced by the linear accelerator of the LNE-LNHB.

  3. Experimental determination of the effective point of measurement and the displacement correction factor for cylindrical ionization chambers in a 6 MV photon beam

    NASA Astrophysics Data System (ADS)

    Legrand, C.; Hartmann, G. H.; Karger, C. P.

    2012-11-01

    The displacement effect of cylindrical ionization chambers is taken into account either by an effective point of measurement (EPOM) or, alternatively, by using a displacement correction factor. The dependence of these effects on water was examined as a function of the cavity radius for 60Co gamma radiation in a previous paper. This paper describes results for high-energy photon beams using the same measurement technique. Additionally, the displacement correction factor was directly measured. Absorbed doses measured under reference conditions following the international protocol IAEA TRS-398 and the German protocol DIN 6800-2 agreed well between the chambers with different cavity radii within a standard uncertainty of 0.2%. However, there was a constant difference of 0.2% between both protocols. Similar to our observations made in 60Co, absorbed doses measured with the different chambers at depths beyond the maximum showed deviations of up to 0.6% and 0.5% for IAEA TRS-398 and DIN 6800-2, respectively, and deviations of more than 1% were found for both protocols in the build-up and maximum region. We therefore propose modified formulas for the determination of the EPOM and the displacement correction factor.

  4. Experimental determination of the effective point of measurement and the displacement correction factor for cylindrical ionization chambers in a 6 MV photon beam.

    PubMed

    Legrand, C; Hartmann, G H; Karger, C P

    2012-11-07

    The displacement effect of cylindrical ionization chambers is taken into account either by an effective point of measurement (EPOM) or, alternatively, by using a displacement correction factor. The dependence of these effects on water was examined as a function of the cavity radius for (60)Co gamma radiation in a previous paper. This paper describes results for high-energy photon beams using the same measurement technique. Additionally, the displacement correction factor was directly measured. Absorbed doses measured under reference conditions following the international protocol IAEA TRS-398 and the German protocol DIN 6800-2 agreed well between the chambers with different cavity radii within a standard uncertainty of 0.2%. However, there was a constant difference of 0.2% between both protocols. Similar to our observations made in (60)Co, absorbed doses measured with the different chambers at depths beyond the maximum showed deviations of up to 0.6% and 0.5% for IAEA TRS-398 and DIN 6800-2, respectively, and deviations of more than 1% were found for both protocols in the build-up and maximum region. We therefore propose modified formulas for the determination of the EPOM and the displacement correction factor.

  5. Comparison of various stopping gases for 3He-based position sensitive neutron detectors

    NASA Astrophysics Data System (ADS)

    Doumas, A.; Smith, G. C.

    2012-05-01

    A range of solid state, scintillator and gas based detectors are being developed for use at the next generation of high flux neutron facilities. Since gas detectors are expected to continue to play a key role in future specific thermal neutron experiments, a comparison of the performance characteristics of prospective stopping gases is beneficial. Gas detectors typically utilize the reaction 3He(n,p)t to detect thermal neutrons; the 3He gas is used in a mixture containing a particular stopping gas in order to maintain relatively short ranges for the proton and triton pair emitted from the n-3He reaction. Common stopping gases include hydrocarbons (e.g. propane), carbon tetrafluoride, and noble gases such as argon and xenon. For this study, we utilized the Monte Carlo simulation code "Stopping and Range of Ions in Matter" to analyze the expected behavior of argon, xenon, carbon dioxide, difluoroethane and octafluoropropane as stopping gases for thermal neutron detectors. We also compare these findings to our previously analyzed performance of propane, butane and carbon tetrafluoride. A discussion of these gases includes their behavior in terms of proton and triton range, ionization distribution and straggle.

  6. Minimal mass size of a stable {sup 3}He cluster

    SciTech Connect

    Guardiola, R.; Navarro, J.

    2005-03-01

    The minimal number of {sup 3}He atoms required to form a bound cluster has been estimated by means of a diffusion Monte Carlo procedure within the fixed-node approximation. Several importance sampling wave functions have been employed in order to consider different shell-model configurations. The resulting upper bound for the minimal number is 32 atoms.

  7. Internal Magnus effects in superfluid sup 3 He- A

    SciTech Connect

    Salmelin, R.H.; Salomaa, M.M. ); Mineev, V.P.

    1989-08-21

    Orbital angular momentum of the coherently aligned Cooper pairs in superfluid {sup 3}He-{ital A} is encountered by an object immersed in the condensate. We evaluate the associated quasiparticle-scattering asymmetry experienced by a negative ion; this leads to a measureable, purely quantum-mechanical reactive force deflecting the ion's trajectory. Possible hydrodynamic Magnus effects are also discussed.

  8. {sup 3}He neutral current detectors at SNO

    SciTech Connect

    Elliott, S.R.; Browne, M.C.; Doe, P.J.

    1998-09-01

    The flux of solar neutrinos measured via charged and neutral current interactions can provide a model independent test of neutrino oscillations. Since the Sudbury Neutrino Observatory uses heavy water as a target, it has a large sensitivity to both interactions. A technique for observing the neutral current breakup of the deuteron using {sup 3}He proportional counters is described.

  9. The Momentum Distribution of Liquid 3He, Revisited

    NASA Astrophysics Data System (ADS)

    Sokol, Paul; Bryan, Matthew; Prisk, Timothy

    Liquid 3He is a system of fundamental importance to condensed matter physics because it is a prototypical example of a strongly interacting fermion system whose interactions are well known. Quantum Monte Carlo calculations predict that the atomic momentum distribution of liquid 3He contains a Fermi surface discontinuity and an average atomic kinetic energy in the range 12-13 K at saturated vapor pressure. A number of high-resolution neutron Compton scattering studies of liquid 33He have been described in the literature, with experimenters observing no Fermi surface discontinuity and obtaining kinetic energies in the range of 8-10 K. In this presentation, we reconsider measurements of the momentum distribution of liquid 3He taken at 500 mK under 0, 10, 15 bar of pressure [R.M. Dimeo et al Physica B 241-243, 952 (1998)]. We demonstrate that there is complete agreement between the experimental data and quantum Monte Carlo calculations when instrumental resolution and final state effect corrections are taken into account. We also consider the prospects for a direct observation of the Fermi surface discontinuity in liquid 3He using neutron Compton scattering. This research was supported by NSF Award DGE-1069091.

  10. Progress in Polarized 3He Ion Source at RCNP

    SciTech Connect

    Tanaka, M.; Takahashi, Y.; Shimoda, T.; Yasui, S.; Yosoi, M.; Takahisa, K.; Shimakura, N.; Plis, Yu. A.; Donets, E. D.

    2007-06-13

    A long history on the polarized 3He ion source developed at RCNP is presented. We started with an 'OPPIS' (Optical Pumping Polarized Ion Source) and later found the fundamental difficulties in the OPPIS. To overcome them an 'EPPIS' (Electron Pumping Polarized Ion Source) was proposed and its validity was experimentally proven. However, a serious technical disadvantage was also found in the EPPIS. To avoid this disadvantage we proposed a new concept, 'SEPIS' (Spin Exchange Polarized Ion Source), which uses an enhanced spin-exchange cross section theoretically expected at low 3He+ incident energies in the 3He+ + Rb system. Next, we describe the present status of the SEPIS development: construction of a bench test device allowing the measurements of not only the spin-exchange cross sections {sigma}se but also the electron capture cross sections {sigma}ec for the 3He+ + Rb system. The latest experimental data on {sigma}ec are presented and compared with other previous experimental data and the theoretical calculations.Finally, a design study of the SEPIS for practical use in nuclear (cyclotron) and particle physics (synchrotron) is shortly mentioned.

  11. Stability and Spectra of Small 3He-4He Clusters

    NASA Astrophysics Data System (ADS)

    Navarro, J.; Fantoni, S.; Guardiola, R.; Zuker, A.

    Diffusion Monte Carlo calculations have been systematically performed to analyze the stability of small mixed 3He-4He clusters, as well as their excitation spectra. The picture that emerges is that of systems with strong shell effects whose binding and excitation energies are essentially determined by the monopole properties of an effective Hamiltonian.

  12. Symmetry protected topological superfluid (3)He-B.

    PubMed

    Mizushima, Takeshi; Tsutsumi, Yasumasa; Sato, Masatoshi; Machida, Kazushige

    2015-03-25

    Owing to the richness of symmetry and well-established knowledge of bulk superfluidity, the superfluid (3)He has offered a prototypical system to study intertwining of topology and symmetry. This article reviews recent progress in understanding the topological superfluidity of (3)He in a multifaceted manner, including symmetry considerations, the Jackiw-Rebbi's index theorem, and the quasiclassical theory. Special focus is placed on the symmetry protected topological superfuidity of the (3)He-B confined in a slab geometry. The (3)He-B under a magnetic field is separated to two different sub-phases: the symmetry protected topological phase and non-topological phase. The former phase is characterized by the existence of symmetry protected Majorana fermions. The topological phase transition between them is triggered by the spontaneous breaking of a hidden discrete symmetry. The critical field is quantitatively determined from the microscopic calculation that takes account of magnetic dipole interaction of the (3)He nucleus. It is also demonstrated that odd-frequency even-parity Cooper pair amplitudes are emergent in low-lying quasiparticles. The key ingredients, symmetry protected Majorana fermions and odd-frequency pairing, bring an important consequence that the coupling of the surface states to an applied field is prohibited by the hidden discrete symmetry, while the topological phase transition with the spontaneous symmetry breaking is accompanied by anomalous enhancement and anisotropic quantum criticality of surface spin susceptibility. We also illustrate common topological features between topological crystalline superconductors and symmetry protected topological superfluids, taking UPt3 and Rashba superconductors as examples.

  13. Direct measurement of absorbed dose to water in HDR {sup 192}Ir brachytherapy: Water calorimetry, ionization chamber, Gafchromic film, and TG-43

    SciTech Connect

    Sarfehnia, Arman; Kawrakow, Iwan; Seuntjens, Jan

    2010-04-15

    Purpose: Gafchromic film and ionometric calibration procedures for HDR {sup 192}Ir brachytherapy sources in terms of dose rate to water are presented and the experimental results are compared to the TG-43 protocol as well as with the absolute dose measurement results from a water calorimetry-based primary standard. Methods: EBT-1 Gafchromic films, an A1SL Exradin miniature Shonka thimble type chamber, and an SI HDR 1000 Plus well-type chamber (Standard Imaging, Inc., Middleton, WI) with an ADCL traceable S{sub k} calibration coefficient (following the AAPM TG-43 protocol) were used. The Farmer chamber and Gafchromic film measurements were performed directly in water. All results were compared to direct and absolute absorbed dose to water measurements from a 4 deg. C stagnant water calorimeter. Results: Based on water calorimetry, the authors measured the dose rate to water to be 361{+-}7 {mu}Gy/(h U) at a 55 mm source-to-detector separation. The dose rate normalized to air-kerma strength for all the techniques agree with the water calorimetry results to within 0.83%. The overall 1-sigma uncertainty on water calorimetry, ionization chamber, Gafchromic film, and TG-43 dose rate measurement amounts to 1.90%, 1.44%, 1.78%, and 2.50%, respectively. Conclusions: This work allows us to build a more realistic uncertainty estimate for absorbed dose to water determination using the TG-43 protocol. Furthermore, it provides the framework necessary for a shift from indirect HDR {sup 192}Ir brachytherapy dosimetry to a more accurate, direct, and absolute measurement of absorbed dose to water.

  14. Correction factors for the NMi free-air ionization chamber for medium-energy x-rays calculated with the Monte Carlo method.

    PubMed

    Grimbergen, T W; van Dijk, E; de Vries, W

    1998-11-01

    A new method is described for the determination of x-ray quality dependent correction factors for free-air ionization chambers. The method is based on weighting correction factors for mono-energetic photons, which are calculated using the Monte Carlo method, with measured air kerma spectra. With this method, correction factors for electron loss, scatter inside the chamber and transmission through the diaphragm and front wall have been calculated for the NMi free-air chamber for medium-energy x-rays for a wide range of x-ray qualities in use at NMi. The newly obtained correction factors were compared with the values in use at present, which are based on interpolation of experimental data for a specific set of x-ray qualities. For x-ray qualities which are similar to this specific set, the agreement between the correction factors determined with the new method and those based on the experimental data is better than 0.1%, except for heavily filtered x-rays generated at 250 kV. For x-ray qualities dissimilar to the specific set, differences up to 0.4% exist, which can be explained by uncertainties in the interpolation procedure of the experimental data. Since the new method does not depend on experimental data for a specific set of x-ray qualities, the new method allows for a more flexible use of the free-air chamber as a primary standard for air kerma for any x-ray quality in the medium-energy x-ray range.

  15. SU-E-T-414: Experimental Correction of High-Z Electrode Effect in Mini-Ionization Chambers for Small Beam Dosimetry

    SciTech Connect

    Larraga-Gutierrez, J

    2015-06-15

    Purpose: To correct for the over-response of mini-ionization chambers with high-Z central electrodes. The hypothesis is that by applying a negative/reverse voltage, it is possible to suppress the signal generated in the high-Z central electrode by low-energy photons. Methods: The mini-ionization chambers used in the experiments were a PTW-31014, PTW-31006 and IBA-CC01. The PTW-31014 has an aluminum central electrode while the PTW-31006 and IBA-CC01 have a steel one. Total scatter factors (Scp) were measured for a 6 MV photon beam down to a square field size of 0.5 cm. The measurements were performed in water at 10 cm depth with SAD of 100 cm. The Scp were measured with the dosimeters with +400V bias voltage. In the case of the PTW-31006 and IBA-CC01, the measurements were repeated with −400V bias voltage. Also, the field factors in water were calculated with Monte Carlo simulations for comparison. Results: The measured Scp at +400V with the PTW-31006 and IBA-CC01 detectors were in agreement within 0.2% down to a field size of 1.5 cm. Both dosimeters shown a systematic difference about 2.5% with the Scp measured with the PTW-31014 and the Monte Carlo calculated field factors. The measured Scp at −400V with the PTW-31006 and IBA-CC01 detectors were in close agreement with the PTW-31014 measured Scp and the field factors within 0.3 and 1.0%, respectively. In the case of the IBA-CC01 it was found a good agreement (1%) down to field size of 1.0 cm. All the dosimeters shown differences up to 17% between the measured Scp and the field factor for the 0.5 cm field size. Conclusion: By applying a negative/reverse voltage to the mini-ionization chambers with high-Z central electrode it was possible to correct for their over-response to low energy photons.

  16. A D-3He IEC power unit for space applications

    NASA Astrophysics Data System (ADS)

    Miley, G. H.

    1999-01-01

    There is an urgent need for small power units for on-board and landing site power for space travel. The conceptual design of a 1-MWe Inertial Electrostatic Confinement (IEC) fusion unit burning D-3He fuel is considered here for such applications. The IEC is attractive for space power-its non-Maxwellian beam-beam character is well-suited for D-3He operation, small size units with a high specific power density are conceivable. Small scale IEC experiments have produced encouraging results and are used here as the basis for extrapolation to the space power unit. However, critical scale-up experiments are essential to verify the feasibility of the concept.

  17. Evidence for Split NMR Lines in Ferromagnetic 3He Films

    NASA Astrophysics Data System (ADS)

    Guo, Lei; Zhang, Jinshan; Du, Yuliang; Gould, C. M.; Bozler, H. M.

    2006-09-01

    In earlier experiments on ferromagnetic 3He films, we observed a complex lineshape due in part to the dipolar field generated by polarization of the 3He nuclei. Much of the complex lineshape can be explained by the known distribution of the Grafoil platelets. However, there remained some evidence for a split NMR line at some temperatures. In our new experiments on ZYX grade exfoliated graphite where the size of individual platelets is much larger and the angular distribution is three times smaller, this splitting has become more evident over a wider range of temperatures. Now it is clear that the complex lineshape includes two peaks along with remaining orientation effects. We also find that roughly 2% of our signal comes from randomly oriented platelets. We present the details of our model for analyzing these lineshapes and the experimental results for the line splitting at several coverages in the ferromagnetic range. We discuss the possible sources of this line splitting.

  18. Data acquisition system for the n3He experiment

    NASA Astrophysics Data System (ADS)

    Kabir, Latiful

    2014-03-01

    The n3He experiment at the Spallation Neutron Source will measure the parity violating spin asymmetry of the recoil proton in the reaction n+3He -->p +T +765 KeV. This is sensitive to ΔI = 0 and 1 components of the Hadronic Weak Interaction (HWI), and is expected to be extremely small (of the order 10-7) . Protons from the reaction are recorded in current mode in order to achieve a statistical sensitivity of 10-8 in a reasonable amount of time. In addition instrumental asymmetries must be suppressed by an additional order of magnitude. The asymmetry is measured as a function of time-of-flight of the neutron to study the energy dependence of any systematic effects. We will present details and preliminary tests of the 144 channel data acquisition system designed to meet these requirements.

  19. Acceleration of 3HE and heavy ions at interplanetary shocks

    NASA Astrophysics Data System (ADS)

    Desai, M. I.; Mason, G. M.; Dwyer, J. R.; Mazur, J. E.; Smith, C. W.; Koug, R. M.

    2001-08-01

    We have surveyed the 0.5-2.0 MeV nucleon-1 ion composition of 56 interplanetary shocks (IP) observed with the Ultra-Low-Energy Isotope Spectrometer (ULEIS) on board the Advanced Composition Explorer (ACE) from 1997 October 1 through 2000 November 30. Our results show the first ever measurement (25 cases) of 3 He ions being accelerated at IP shocks. The 3 He/4 He ratio at the 25 shocks exhibited a wide range of values between 0.00140.24; the ratios were enhanced between factors of ~3-600 over the solar wind value. During the survey period, the occurrence probability of 3 He-rich shocks increased with rising solar activity as measured in terms of the daily occurrence rates of sunspots and X-ray flares. The 3 He enhancements at IP shocks cannot be attributed to rigidity dependent acceleration of solar wind ions and are better explained if the shocks accelerate ions from multiple sources, one being remnant impulsive solar flare material enriched in 3 He ions. Our results also indicate that the contribution of impulsive flares to the seed population for IP shocks varies from event to event, and that the interplanetary medium is being replenished with impulsive material more frequently during periods of increased solar activity. 1. Introduction Enhancements in the intensities of energetic ions associated with transient interplanetary (IP) shocks have been observed routinely at 1 AU since the 1960's (e.g., Reames 1999). It is presently believed that the majority of such IP shocks are driven by fast coronal mass ejections or CMEs as they propagate through interplanetary space (e.g., Gosling 1993), and that the associated ion intensity enhancements are due to diffusive shock acceleration of solar wind ions (Lee 1983; Jones and Ellison 1991; Reames 1999). However, the putative solar wind origin of the IP-shock accelerated ions is based on composition measurements associated with a very limited number of individual IP shocks (Klecker et al. 1981; Hovestadt et al. 1982; Tan et

  20. Proton polarization from π+ absorption in 3He

    NASA Astrophysics Data System (ADS)

    Maytal-Beck, S.; Aclander, J.; Altman, A.; Ashery, D.; Hahn, H.; Moinester, M. A.; Rahav, A.; Feltham, A.; Jones, G.; Pavan, M.; Sevior, M.; Hutcheon, D.; Ottewell, D.; Smith, G. R.; Niskanen, J. A.

    1992-05-01

    We present the first polarization measurements for pion absorption on a nucleus heavier than the deuteron. The polarization of protons resulting from π+ absorption in the 3He was measured at bombarding energies of 120 and 250 MeV. Protons from absorption in a quasideuteron were selected by applying kinematical constraints. A significant discrepancy was observed between the experimental results and theoretical predictions. At 120 MeV the measured polarizations for 3He are consistent with those of the deuteron. At 250 MeV the angular distribution of the polarization is significantly different than for the deuteron, showing sensitivity to the nuclear density, and thus may be sensitive to short range correlations between nucleons.

  1. Thermal Conductivity of Spin-Polarized Liquid {sup 3}He

    SciTech Connect

    Sawkey, D.; Puech, L.; Wolf, P.E.

    2006-06-02

    We present the first measurements of the thermal conductivity of spin-polarized normal liquid {sup 3}He. Using the rapid melting technique to produce nuclear polarizations up to 0.7, and a vibrating wire both as a heater and a thermometer, we show that, unlike the viscosity, the conductivity increases much less than predicted for s-wave scattering. We suggest that this might be due to a small probability for head-on collisions between quasiparticles.

  2. NOVEL CONCEPTS FOR ISOTOPIC SEPARATION OF 3HE/4HE

    SciTech Connect

    Roy, L.; Nigg, H.; Watson, H.

    2012-09-04

    The research outlined below established theoretical proof-of-concept using ab initio calculations that {sup 3}He can be separated from {sup 4}He by taking advantage of weak van der Waals interactions with other higher molecular weight rare gases such as xenon. To the best of our knowledge, this is the only suggested method that exploits the physical differences of the isotopes using a chemical interaction.

  3. Hard Two-body Photodisintegration of ^3He

    SciTech Connect

    Pomerantz, Ishay Ari; Ilieva, Yordanka Yordanova; Gilman, Ronald; Higinbotham, Douglas W.; Piasetzky, Eliazer Israel; Strauch, Steffen

    2013-06-01

    We have measured cross sections for the {gamma}+{sup 3}He->p+d reaction at photon energies of 0.4 - 1.4 GeV and a center-of-mass angle of 90 deg. We observe dimensional scaling above 0.7 GeV at this center-of-mass angle. This is the first observation of dimensional scaling in the photodisintegration of a nucleus heavier than the deuteron.

  4. Hard two-body photodisintegration of 3He.

    PubMed

    Pomerantz, I; Ilieva, Y; Gilman, R; Higinbotham, D W; Piasetzky, E; Strauch, S; Adhikari, K P; Aghasyan, M; Allada, K; Amaryan, M J; Anefalos Pereira, S; Anghinolfi, M; Baghdasaryan, H; Ball, J; Baltzell, N A; Battaglieri, M; Batourine, V; Beck, A; Beck, S; Bedlinskiy, I; Berman, B L; Biselli, A S; Boeglin, W; Bono, J; Bookwalter, C; Boiarinov, S; Briscoe, W J; Brooks, W K; Bubis, N; Burkert, V; Camsonne, A; Canan, M; Carman, D S; Celentano, A; Chandavar, S; Charles, G; Chirapatpimol, K; Cisbani, E; Cole, P L; Contalbrigo, M; Crede, V; Cusanno, F; D'Angelo, A; Daniel, A; Dashyan, N; de Jager, C W; De Vita, R; De Sanctis, E; Deur, A; Djalali, C; Dodge, G E; Doughty, D; Dupre, R; Dutta, C; Egiyan, H; El Alaoui, A; El Fassi, L; Eugenio, P; Fedotov, G; Fegan, S; Fleming, J A; Fradi, A; Garibaldi, F; Geagla, O; Gevorgyan, N; Giovanetti, K L; Girod, F X; Glister, J; Goetz, J T; Gohn, W; Golovatch, E; Gothe, R W; Griffioen, K A; Guegan, B; Guidal, M; Guo, L; Hafidi, K; Hakobyan, H; Harrison, N; Heddle, D; Hicks, K; Ho, D; Holtrop, M; Hyde, C E; Ireland, D G; Ishkhanov, B S; Isupov, E L; Jiang, X; Jo, H S; Joo, K; Katramatou, A T; Keller, D; Khandaker, M; Khetarpal, P; Khrosinkova, E; Kim, A; Kim, W; Klein, F J; Koirala, S; Kubarovsky, A; Kubarovsky, V; Kuleshov, S V; Kvaltine, N D; Lee, B; LeRose, J J; Lewis, S; Lindgren, R; Livingston, K; Lu, H Y; MacGregor, I J D; Mao, Y; Martinez, D; Mayer, M; McCullough, E; McKinnon, B; Meekins, D; Meyer, C A; Michaels, R; Mineeva, T; Mirazita, M; Moffit, B; Mokeev, V; Montgomery, R A; Moutarde, H; Munevar, E; Munoz Camacho, C; Nadel-Turonski, P; Nasseripour, R; Nepali, C S; Niccolai, S; Niculescu, G; Niculescu, I; Osipenko, M; Ostrovidov, A I; Pappalardo, L L; Paremuzyan, R; Park, K; Park, S; Petratos, G G; Phelps, E; Pisano, S; Pogorelko, O; Pozdniakov, S; Procureur, S; Protopopescu, D; Puckett, A J R; Qian, X; Qiang, Y; Ricco, G; Rimal, D; Ripani, M; Ritchie, B G; Rodriguez, I; Ron, G; Rosner, G; Rossi, P; Sabatié, F; Saha, A; Saini, M S; Sarty, A J; Sawatzky, B; Saylor, N A; Schott, D; Schulte, E; Schumacher, R A; Seder, E; Seraydaryan, H; Shneor, R; Smith, G D; Sokhan, D; Sparveris, N; Stepanyan, S S; Stepanyan, S; Stoler, P; Subedi, R; Sulkosky, V; Taiuti, M; Tang, W; Taylor, C E; Tkachenko, S; Ungaro, M; Vernarsky, B; Vineyard, M F; Voskanyan, H; Voutier, E; Walford, N K; Wang, Y; Watts, D P; Weinstein, L B; Weygand, D P; Wojtsekhowski, B; Wood, M H; Yan, X; Yao, H; Zachariou, N; Zhan, X; Zhang, J; Zhao, Z W; Zheng, X; Zonta, I

    2013-06-14

    We have measured cross sections for the γ(3)He → pd reaction at photon energies of 0.4-1.4 GeV and a center-of-mass angle of 90°. We observe dimensional scaling above 0.7 GeV at this center-of-mass angle. This is the first observation of dimensional scaling in the photodisintegration of a nucleus heavier than the deuteron.

  5. Internal Magnus effects in superfluid 3He-A

    NASA Astrophysics Data System (ADS)

    Salmelin, R. H.; Salomaa, M. M.; Mineev, V. P.

    The orbital angular momentum of the coherently aligned Cooper pairs in superfluid (3)He-A is transmitted to an object immersed in the condensate. The authors evaluate the quasiparticle-scattering asymmetry experienced by a negative ion; this leads to a measurable, purely quantum-mechanical Magnus force deflecting the ion's trajectory. Close to T(sub c), possible hydrodynamic Magnus effects are smaller by the factor delta sub A/(k sub B)(T sub c).

  6. Perturbed gap functions in superfluid /sup 3/He

    SciTech Connect

    McInerney, M.F.

    1980-12-01

    New forms of the Balian-Werthamer (BW) and of the Anderson-Brinkman--Morel (ABM) gap solutions for superfluid /sup 3/He are found in the presence of perturbations. Using the perturbed form of the BW solution, a discrepancy is found between the static and dynamic magnetic susceptibilities, which is shown to be in reasonable agreement with the experimental measurements of Sager and Webb. A self-consistent diagrammatic Green's function approach is used.

  7. Comparison of dosimeter response: ionization chamber, TLD, and Gafchromic EBT2 film in 3D-CRT, IMRT, and SBRT techniques for lung cancer

    NASA Astrophysics Data System (ADS)

    Fitriandini, A.; Wibowo, W. E.; Pawiro, S. A.

    2016-03-01

    This research was conducted by measuring point dose in the target area (lungs), heart, and spine using four dosimeters (PTW N30013, Exradin A16, TLD, and the Gafchromic EBT2 film). The measurement was performed in CIRS 002LFC thorax phantom. The main objective of this study was to compare the dosimetry of those different systems. Dose measurements performed only in a single fraction of irradiation. The measurements result shown that TLD has the least accuracy and precision. As the effect of volume averaging, ionization chamber reaches the discrepancy value up to -13.30% in the target area. EBT2 film has discrepancy value of <1% in the 3D-CRT and IMRT techniques. This dosimeter is proposed to be an appropriate alternative dosimeter to be used at point dose verification.

  8. Resonant quasiparticle-ion scattering in anisotropic superfluid 3He

    NASA Astrophysics Data System (ADS)

    Salmelin, R. H.; Salomaa, M. M.

    1990-03-01

    Low-energy excitations in quantum fluids are most directly encountered by ions. In the superfluid phases of 3He the relevant elementary excitations are Bogoliubov quasiparticles, which undergo repeated scattering off an ion in the presence of a divergent density of states. We present a quantum-mechanical calculation of the resonant 3He quasiparticle-scattering-limited mobility for negative ions in the anisotropic bulk 3A (A phase) and 3P (polar phase) that is exact when the quasiparticles scatter elastically. We develop a numerical scheme to solve the singular equations for quasiparticle-ion scattering in the A and P phases. Both of these superfluid phases feature a uniaxially symmetric order parameter but distinct topology for the magnitude of the energy gap on the Fermi sphere, i.e., points versus lines of nodes. In particular, the perpetual orbital circulation of Cooper pairs in 3A results in a novel, purely quantum-mechanical intrinsic Magnus effect, which is absent in the polar phase, where Cooper pairs possess no spontaneous orbital angular momentum. This is of interest also for transport properties of heavy-fermion superconductors. We discuss the 3He quasiparticle-ion cross sections, which allow one to account for the mobility data with essentially no free parameters. The calculated mobility thus facilitates an introduction of ``ion spectroscopy'' to extract useful information on fundamental properties of the superfluid state, such as the temperature dependence of the energy gap in 3A.

  9. Incorporating metal into polarized 3He target cells

    NASA Astrophysics Data System (ADS)

    Katugampola, Sumudu K.; Matyas, Daniel J.; Wang, Yunxiao; Tobias, William A.; Nelyubin, Vladimir; Cates, Gordon D.

    2017-01-01

    An upcoming measurement at Jefferson Laboratory (JLab) of the electric form factor of the neutron will utilize a polarized 3He target at high luminosity. While polarized 3He targets at JLab have previously been made entirely of glass, we describe progress toward incorporating metal windows for the electron beam. Under the conditions of our targets, very few studies have been done on the spin-relaxation of nuclear-polarized 3He on metal surfaces. We have found good performance by using Oxygen Free High Conductivity (OFHC) copper substrates electroplated with gold. The glass-to-metal transitions within our test cells were based on Housekeeper seals. We have further established that Uranium glass (Canary glass) has excellent spin-relaxation properties, and can serve as a transition glass from Pyrex to Aluminosilicate glass (GE180). Another finding was that spin-relaxation properties were sensitive to the manner in which cells were annealed, an important issue because of constraints when annealing cells containing both metal and glass.

  10. Probing the Faraday Effect of Polarized ^3He

    NASA Astrophysics Data System (ADS)

    Phelps, Gretchen; Abney, Josh; Korsch, Wolfgang

    2013-04-01

    The Faraday Effect refers to the phenomenon in which the polarization of light transmitted through a magnetized medium is rotated. The relation φ=VlB describes the magnitude of the rotation, where V is the material dependent Verdet constant and l is the length of the medium in an applied magnetic field B. Polarized ^3He, generated in a glass cell constructed of GE-180, gives rise to a Faraday rotation via nuclear spin optical rotation (NSOR), a measure of which establishes a new technique in ^3He polarization monitoring. Our set-up incorporates a triple-modulation technique with present sensitivities at the μrad level. This is accomplished through the combination of a photo-elastic modulator, an optical chopper, and a sinusoidally driven magnetic field. Several calibration samples were used to test the triple-modulation method. Good agreement between our results and the commonly accepted values for the Verdet constant was achieved. Technical challenges and progress towards the determination of V^3He will be presented.

  11. Chiral Phases of Superfluid 3He in an Anisotropic Medium

    NASA Astrophysics Data System (ADS)

    Sauls, James

    2013-03-01

    I report theoretical results for the phases of superfluid 3He infused into homogeneous uniaxial aerogel. Ginzburg-Landau (GL) theory for a class of equal-spin-pairing (ESP) states in a medium with uniaxial anisotropy is developed and used to analyze recent experiments on uniaxially strained aerogels. For 3He in an axially ``stretched'' aerogel GL theory predicts a transition from normal liquid into a chiral ABM phase in which the chirality axis is aligned along the strain axis. This state is protected from random fluctuations in the anisotropy direction, has a positive NMR shift, a sharp NMR resonance line and is in quantitative agreement with NMR in the high-temperature ESP-1 phase of superfluid 3He in axially stretched aerogel. A second transition into a bi-axial phase is predicted to onset at a slightly lower temperature. This phase is an ESP state, breaks time-reversal symmetry, and is defined by an order parameter that spontaneously breaks axial rotation symmetry. The bi-axial phase has a continuous degeneracy associated with broken axial symmetry. Theoretical predictions for the NMR frequency shifts provide an identification of the ESP-2 phase as the bi-axial state, partially disordered by random anisotropy (Larkin-Imry-Ma effect). Supported by National Science Foundation Grant DMR-1106315.

  12. Uranium Neutron Coincidence Collar Model Utilizing 3He

    SciTech Connect

    Siciliano, Edward R.; Rogers, Jeremy L.; Schweppe, John E.; Lintereur, Azaree T.; Kouzes, Richard T.

    2012-07-30

    The Department of Energy Office of Nuclear Safeguards (NA-241) is supporting the project 'Coincidence Counting With Boron-Based Alternative Neutron Detection Technology' at Pacific Northwest National Laboratory (PNNL) for development of an alternative neutron coincidence counter. The goal of this project is to design, build and demonstrate a boron-lined proportional tube based alternative system in a configuration typically used for 3He-based coincidence counter applications. The specific application selected for boron-lined tube replacement in this project was one of the Uranium Neutron Coincidence Collar (UNCL) designs. This report, providing results for model development of a UNCL, is a deliverable under Task 2 of the project. The current UNCL instruments utilize 3He tubes. As the first step in developing and optimizing a boron-lined proportional counter based version of the UNCL, models of eight different 3He-based UNCL detectors currently in use were developed and evaluated. A comparison was made between the simulated results and measured efficiencies for those systems with values reported in the literature. The reported experimental measurements for efficiencies and die-away times agree to within 10%.

  13. High Efficiency Spin Flipper for the n3He Experiment

    NASA Astrophysics Data System (ADS)

    Hayes, Christopher; n3He Collaboration

    2015-10-01

    The n3He experiment, constructed on the Fundamental Neutron Physics Beamline (FnPB) at the Spallation Neutron Source, is designed to measure the parity violating (PV) proton asymmetry Ap in the capture reaction n +3 He -->3 H + p + 765 keV The asymmetry has an estimated value Ap ~ - 1 ×10-7 and is directly related to the weak isospin conserved couplings hρ0 and ωρ0 which are of fundamental interest in the verification of the meson exchange model of low energy NN intereactions. Data production for the n3He experiment began in February 2015 and is scheduled to continue thru December 2015 - reaching a statistical sensitivity δAp ~10-8 or better. I will discuss the spin flipper which is designed using the theory of double cosine-theta coils, and capable of flipping neutron spins with an efficiency approaching its maximum value ɛsf = 1 . I will also discuss the theory of Spin Magnetic Resonance (SMR) and how it is employed by the spin flipper to flip 60 Hz pulses of cold neutrons over a range of wavelengths.

  14. Development and clinical evaluation of an ionization chamber array with 3.5 mm pixel pitch for quality assurance in advanced radiotherapy techniques

    SciTech Connect

    Togno, M.; Wilkens, J. J.; Menichelli, D.; Oechsner, M.; Perez-Andujar, A.; Morin, O.

    2016-05-15

    Purpose: To characterize a new air vented ionization chamber technology, suitable to build detector arrays with small pixel pitch and independence of sensitivity on dose per pulse. Methods: The prototype under test is a linear array of air vented ionization chambers, consisting of 80 pixels with 3.5 mm pixel pitch distance and a sensitive volume of about 4 mm{sup 3}. The detector has been characterized with {sup 60}Co radiation and MV x rays from different linear accelerators (with flattened and unflattened beam qualities). Sensitivity dependence on dose per pulse has been evaluated under MV x rays by changing both the source to detector distance and the beam quality. Bias voltage has been varied in order to evaluate the charge collection efficiency in the most critical conditions. Relative dose profiles have been measured for both flattened and unflattened distributions with different field sizes. The reference detectors were a commercial array of ionization chambers and an amorphous silicon flat panel in direct conversion configuration. Profiles of dose distribution have been measured also with intensity modulated radiation therapy (IMRT), stereotactic radiosurgery (SRS), and volumetric modulated arc therapy (VMAT) patient plans. Comparison has been done with a commercial diode array and with Gafchromic EBT3 films. Results: Repeatability and stability under continuous gamma irradiation are within 0.3%, in spite of low active volume and sensitivity (∼200 pC/Gy). Deviation from linearity is in the range [0.3%, −0.9%] for a dose of at least 20 cGy, while a worsening of linearity is observed below 10 cGy. Charge collection efficiency with 2.67 mGy/pulse is higher than 99%, leading to a ±0.9% sensitivity change in the range 0.09–2.67 mGy/pulse (covering all flattened and unflattened beam qualities). Tissue to phantom ratios show an agreement within 0.6% with the reference detector up to 34 cm depth. For field sizes in the range 2 × 2 to 15 × 15 cm{sup 2}, the

  15. Development and clinical evaluation of an ionization chamber array with 3.5 mm pixel pitch for quality assurance in advanced radiotherapy techniques.

    PubMed

    Togno, M; Wilkens, J J; Menichelli, D; Oechsner, M; Perez-Andujar, A; Morin, O

    2016-05-01

    To characterize a new air vented ionization chamber technology, suitable to build detector arrays with small pixel pitch and independence of sensitivity on dose per pulse. The prototype under test is a linear array of air vented ionization chambers, consisting of 80 pixels with 3.5 mm pixel pitch distance and a sensitive volume of about 4 mm(3). The detector has been characterized with (60)Co radiation and MV x rays from different linear accelerators (with flattened and unflattened beam qualities). Sensitivity dependence on dose per pulse has been evaluated under MV x rays by changing both the source to detector distance and the beam quality. Bias voltage has been varied in order to evaluate the charge collection efficiency in the most critical conditions. Relative dose profiles have been measured for both flattened and unflattened distributions with different field sizes. The reference detectors were a commercial array of ionization chambers and an amorphous silicon flat panel in direct conversion configuration. Profiles of dose distribution have been measured also with intensity modulated radiation therapy (IMRT), stereotactic radiosurgery (SRS), and volumetric modulated arc therapy (VMAT) patient plans. Comparison has been done with a commercial diode array and with Gafchromic EBT3 films. Repeatability and stability under continuous gamma irradiation are within 0.3%, in spite of low active volume and sensitivity (∼200 pC/Gy). Deviation from linearity is in the range [0.3%, -0.9%] for a dose of at least 20 cGy, while a worsening of linearity is observed below 10 cGy. Charge collection efficiency with 2.67 mGy/pulse is higher than 99%, leading to a ±0.9% sensitivity change in the range 0.09-2.67 mGy/pulse (covering all flattened and unflattened beam qualities). Tissue to phantom ratios show an agreement within 0.6% with the reference detector up to 34 cm depth. For field sizes in the range 2 × 2 to 15 × 15 cm(2), the output factors are in agreement with a

  16. Direct reference air-kerma rate calibration of 192Ir for a thimble-type ionization chamber in a cylindrical solid phantom

    NASA Astrophysics Data System (ADS)

    Kaulich, Theodor W.; Quast, Ulrich; Bamberg, Michael; Selbach, Hans-Joachim

    2012-10-01

    International and national reports strongly recommend experimental verification of the calibration of new HDR 192Ir sources prior to their clinical application for afterloading brachytherapy. To guarantee traceability, calibrated transfer standards are used, e.g. the recommended well-type ionization chambers (WIC) or certain detector-phantom arrangements (DPA) consisting of a thimble-type ionization chamber with a solid phantom. In Germany, direct calibrations for 192Ir were only provided for WICs. In June 2010, the PTB directly calibrated a DPA-transfer standard in the quantity reference air-kerma rate (RAKR) for 192Ir photons for the University Hospital Tübingen. This direct calibration provides the advantage that the comprehensive RAKR 192Ir calibration coefficient already takes all influence quantities into account—their correction factors are thus unified—except for the air-density correction kρ. The DPA-transfer standard described above and a WIC used as a reference were compared for acceptance tests of three GammaMedplus HDR 192Ir afterloading sources. The measurement uncertainty of the WIC and of the DPA-transfer standard were ±2.6%(k = 2) and ±2.8%(k = 2) respectively. A strong correlation was found between these measurement results with a coefficient of determination of r2 = 0.9998. Determining the RAKR of an HDR 192Ir afterloading source is as simple with the DPA as it is with WIC. The direct 192Ir calibrated DPA-transfer standard can therefore be used alternatively in future with the same measurement uncertainty if no WIC is available.

  17. 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.

  18. Characterization of radiation beams used to determinate the correction factor for a CyberKnife® unit reference field using ionization chambers

    SciTech Connect

    Aragón-Martínez, Nestor Massillon-JL, Guerda; Gómez-Muñoz, Arnulfo

    2014-11-07

    This paper aimed to characterize a 6 MV x-ray beam from a Varian® iX linear accelerator in order to obtain the correction factors needed by the IAEA/AAPM new formalism{sup 1}. The experiments were performed in a liquid water phantom under different irradiation conditions: a) Calibration of the reference field of 10 cm × 10 cm at 90 cm SSD and 10 cm depth was carried out according to the TRS-398 protocol using three ionization chambers (IC) calibrated in different reference laboratory and b) Measurement of the absorbed dose rate at 70 cm SSD and 10 cm depth in a 10 cm × 10 cm and 5.4 cm × 5.4 cm fields was obtained in order to simulate the CyberKnife® conditions where maximum distance between the source and the detector is equal to 80 cm and the maximum field size is 6 cm diameter. Depending where the IC was calibrated, differences between 0.16% and 2.24% in the absorbed dose rate measured in the 10 cm × 10 cm field at 90 cm SSD were observed, while for the measurements at 70 cm SSD, differences between 1.27% and 3.88% were obtained. For the 5.4 cm × 5.4 cm field, the absorbed dose measured with the three ICs varies between 1.37% and 3.52%. The increase in the difference on the absorbed dose when decreasing the SSD could possibly be associated to scattering radiation generated from the collimators and/or the energy dependence of the ionization chambers to low-energy radiation. The results presented in this work suggest the importance of simulating the CyberKnife® conditions using other linear accelerator for obtaining the correction factors as proposed by the IAEA/AAPM new formalism in order to measure the absorbed dose with acceptable accuracy.

  19. Characterization of radiation beams used to determinate the correction factor for a CyberKnife® unit reference field using ionization chambers

    NASA Astrophysics Data System (ADS)

    Aragón-Martínez, Nestor; Gómez-Muñoz, Arnulfo; Massillon-JL, Guerda

    2014-11-01

    This paper aimed to characterize a 6 MV x-ray beam from a Varian® iX linear accelerator in order to obtain the correction factors needed by the IAEA/AAPM new formalism1. The experiments were performed in a liquid water phantom under different irradiation conditions: a) Calibration of the reference field of 10 cm × 10 cm at 90 cm SSD and 10 cm depth was carried out according to the TRS-398 protocol using three ionization chambers (IC) calibrated in different reference laboratory and b) Measurement of the absorbed dose rate at 70 cm SSD and 10 cm depth in a 10 cm × 10 cm and 5.4 cm × 5.4 cm fields was obtained in order to simulate the CyberKnife® conditions where maximum distance between the source and the detector is equal to 80 cm and the maximum field size is 6 cm diameter. Depending where the IC was calibrated, differences between 0.16% and 2.24% in the absorbed dose rate measured in the 10 cm × 10 cm field at 90 cm SSD were observed, while for the measurements at 70 cm SSD, differences between 1.27% and 3.88% were obtained. For the 5.4 cm × 5.4 cm field, the absorbed dose measured with the three ICs varies between 1.37% and 3.52%. The increase in the difference on the absorbed dose when decreasing the SSD could possibly be associated to scattering radiation generated from the collimators and/or the energy dependence of the ionization chambers to low-energy radiation. The results presented in this work suggest the importance of simulating the CyberKnife® conditions using other linear accelerator for obtaining the correction factors as proposed by the IAEA/AAPM new formalism in order to measure the absorbed dose with acceptable accuracy.

  20. Reference dosimetry at the Australian Synchrotron's imaging and medical beamline using free-air ionization chamber measurements and theoretical predictions of air kerma rate and half value layer

    SciTech Connect

    Crosbie, Jeffrey C.; Rogers, Peter A. W.; Stevenson, Andrew W.; Hall, Christopher J.; Lye, Jessica E.; Nordstroem, Terese; Midgley, Stewart M.; Lewis, Robert A.

    2013-06-15

    Purpose: Novel, preclinical radiotherapy modalities are being developed at synchrotrons around the world, most notably stereotactic synchrotron radiation therapy and microbeam radiotherapy at the European Synchrotron Radiation Facility in Grenoble, France. The imaging and medical beamline (IMBL) at the Australian Synchrotron has recently become available for preclinical radiotherapy and imaging research with clinical trials, a distinct possibility in the coming years. The aim of this present study was to accurately characterize the synchrotron-generated x-ray beam for the purposes of air kerma-based absolute dosimetry. Methods: The authors used a theoretical model of the energy spectrum from the wiggler source and validated this model by comparing the transmission through copper absorbers (0.1-3.0 mm) against real measurements conducted at the beamline. The authors used a low energy free air ionization chamber (LEFAC) from the Australian Radiation Protection and Nuclear Safety Agency and a commercially available free air chamber (ADC-105) for the measurements. The dimensions of these two chambers are different from one another requiring careful consideration of correction factors. Results: Measured and calculated half value layer (HVL) and air kerma rates differed by less than 3% for the LEFAC when the ion chamber readings were corrected for electron energy loss and ion recombination. The agreement between measured and predicted air kerma rates was less satisfactory for the ADC-105 chamber, however. The LEFAC and ADC measurements produced a first half value layer of 0.405 {+-} 0.015 and 0.412 {+-} 0.016 mm Cu, respectively, compared to the theoretical prediction of 0.427 {+-} 0.012 mm Cu. The theoretical model based upon a spectrum calculator derived a mean beam energy of 61.4 keV with a first half value layer of approximately 30 mm in water. Conclusions: The authors showed in this study their ability to verify the predicted air kerma rate and x-ray attenuation

  1. Reference dosimetry at the Australian Synchrotron's imaging and medical beamline using free-air ionization chamber measurements and theoretical predictions of air kerma rate and half value layer.

    PubMed

    Crosbie, Jeffrey C; Rogers, Peter A W; Stevenson, Andrew W; Hall, Christopher J; Lye, Jessica E; Nordström, Terese; Midgley, Stewart M; Lewis, Robert A

    2013-06-01

    Novel, preclinical radiotherapy modalities are being developed at synchrotrons around the world, most notably stereotactic synchrotron radiation therapy and microbeam radiotherapy at the European Synchrotron Radiation Facility in Grenoble, France. The imaging and medical beamline (IMBL) at the Australian Synchrotron has recently become available for preclinical radiotherapy and imaging research with clinical trials, a distinct possibility in the coming years. The aim of this present study was to accurately characterize the synchrotron-generated x-ray beam for the purposes of air kerma-based absolute dosimetry. The authors used a theoretical model of the energy spectrum from the wiggler source and validated this model by comparing the transmission through copper absorbers (0.1-3.0 mm) against real measurements conducted at the beamline. The authors used a low energy free air ionization chamber (LEFAC) from the Australian Radiation Protection and Nuclear Safety Agency and a commercially available free air chamber (ADC-105) for the measurements. The dimensions of these two chambers are different from one another requiring careful consideration of correction factors. Measured and calculated half value layer (HVL) and air kerma rates differed by less than 3% for the LEFAC when the ion chamber readings were corrected for electron energy loss and ion recombination. The agreement between measured and predicted air kerma rates was less satisfactory for the ADC-105 chamber, however. The LEFAC and ADC measurements produced a first half value layer of 0.405 ± 0.015 and 0.412 ± 0.016 mm Cu, respectively, compared to the theoretical prediction of 0.427 ± 0.012 mm Cu. The theoretical model based upon a spectrum calculator derived a mean beam energy of 61.4 keV with a first half value layer of approximately 30 mm in water. The authors showed in this study their ability to verify the predicted air kerma rate and x-ray attenuation curve on the IMBL using a simple experimental

  2. Field correction factors for a PTW-31016 Pinpoint ionization chamber for both flattened and unflattened beams. Study of the main sources of uncertainties.

    PubMed

    Puxeu-Vaqué, Josep; Duch, Maria A; Nailon, William H; Cruz Lizuain, M; Ginjaume, Mercè

    2017-05-01

    The primary aim of this study was to determine correction factors, kQclin,Qmsrfclin,fmsr for a PTW-31016 ionization chamber on field sizes from 0.5 cm × 0.5 cm to 2 cm × 2 cm for both flattened (FF) and flattened filter-free (FFF) beams produced in a TrueBeam clinical accelerator. The secondary objective was the determination of field output factors, ΩQclin,Qmsrfclin,fmsr over this range of field sizes using both Monte Carlo (MC) simulation and measurements. kQclin,Qmsrfclin,fmsr for the PTW-31016 chamber were calculated by MC simulation for field sizes of 0.5 cm × 0.5 cm, 1 cm × 1 cm, and 2 cm × 2 cm. MC simulations were performed with the PENELOPE code system for the 10 MV FFF Particle Space File from a TrueBeam linear accelerator (LINAC) provided by the manufacturer (Varian Medical Systems, Inc. Palo Alto, CA, USA). Simulations were repeated taking into account chamber manufacturing tolerances and accelerator jaw positioning in order to assess the uncertainty of the calculated correction factors. Output ratios were measured on square fields ranging from 0.5 cm × 0.5 cm to 10 cm × 10 cm for 6 MV and 10 MV FF and FFF beams produced by a TrueBeam using a PTW-31016 ionization chamber; a Sun Nuclear Edge detector (SunNuclear Corp., Melbourne, FL, USA) and TLD-700R (Harshaw, Thermo Scientific, Waltham, MA, USA). The validity of the proposed correction factors was verified using the calculated correction factors for the determination of ΩQclin,Qmsrfclin,fmsr using a PTW-31016 at the four TrueBeam energies and comparing the results with both TLD-700R measurements and MC simulations. Finally, the proposed correction factors were used to assess the correction factors of the SunNuclear Edge detector. The present work provides a set of MC calculated correction factors for a PTW-31016 chamber used on a TrueBeam FF and FFF mode. For the 0.5 cm × 0.5 cm square field size, kQclin,Qmsrfclin,fmsr is equal to 1.17 with a combined uncertainty of 2% (k = 1). A detailed

  3. Measurements of miniature ionization chamber currents in the JSI TRIGA Mark II reactor demonstrate the importance of the delayed contribution to the photon field in nuclear reactors

    NASA Astrophysics Data System (ADS)

    Radulović, Vladimir; Fourmentel, Damien; Barbot, Loïc; Villard, Jean-François; Kaiba, Tanja; Gašper, Žerovnik; Snoj, Luka

    2015-12-01

    The characterization of experimental locations of a research nuclear reactor implies the determination of neutron and photon flux levels within, with the best achievable accuracy. In nuclear reactors, photon fluxes are commonly calculated by Monte Carlo simulations but rarely measured on-line. In this context, experiments were conducted with a miniature gas ionization chamber (MIC) based on miniature fission chamber mechanical parts, recently developed by the CEA (French Atomic Energy and Alternative Energies Commission) irradiated in the core of the Jožef Stefan Institute TRIGA Mark II reactor in Ljubljana, Slovenia. The aim of the study was to compare the measured MIC currents with calculated currents based on simulations with the MCNP6 code. A discrepancy of around 50% was observed between the measured and the calculated currents; in the latter taking into consideration only the prompt photon field. Further experimental measurements of MIC currents following reactor SCRAMs (reactor shutdown with rapid insertions of control rods) provide evidence that over 30% of the total measured signal is due to the delayed photon field, originating from fission and activation products, which are untreated in the calculations. In the comparison between the measured and calculated values, these findings imply an overall discrepancy of less than 20% of the total signal which is still unexplained.

  4. Derivation of a formula describing the saturation correction of plane-parallel ionization chambers in pulsed fields with arbitrary repetition rate.

    PubMed

    Karsch, Leonhard

    2016-04-21

    Gas-filled ionization chambers are widely used radiation detectors in radiotherapy. A quantitative description and correction of the recombination effects exists for two cases, for continuous radiation exposure and for pulsed radiation fields with short single pulses. This work gives a derivation of a formula for pulsed beams with arbitrary pulse rate for which the prerequisites of the two existing descriptions are not fulfilled. Furthermore, an extension of the validity of the two known cases is investigated. The temporal evolution of idealized charge density distributions within a plane parallel chamber volume is described for pulsed beams of vanishing pulse duration and arbitrary pulse repetition rate. First, the radiation induced release, movement and collection of the charge carriers without recombination are considered. Then, charge recombination is calculated basing on these simplified charge distributions and the time dependent spatial overlap of positive and negative charge carrier distributions. Finally, a formula for the calculation of the saturation correction factor is derived by calculation and simplification of the first two terms of a Taylor expansion for small recombination. The new formula of saturation correction contains the two existing cases, descriptions for exposure by single pulses and continuous irradiation, as limiting cases. Furthermore, it is possible to determine the pulse rate range for which each of the three descriptions is applicable by comparing the dependencies of the new formula with the two existing cases. As long as the time between two pulses is lower than one third of the collection time of the chamber, the formalism for a continuous exposure can be used. The known description for single pulse irradiation is only valid if the repetition rate is less than 1.2 times the inverse collection time. For all other repetition rates in between the new formula should be used. The experimental determination by Jaffe diagrams can be

  5. TU-F-CAMPUS-T-01: Calculation of KQ for a Variety of Commercially Available Ionization Chambers in the Presence of An External Magnetic Field for MR-Linac Dosimetry

    SciTech Connect

    O’Brien, D J; Mathis, M V P; Ibbott, G; Sawakuchi, G O; Roberts, D A

    2015-06-15

    Purpose: The strong magnetic fields associated with MRI have a significant impact on the dosimetry of radiotherapy beams as well as on the response of the detectors used to measure it. In order to calibrate the dose delivered by these beams, it is necessary to correct for these effects when performing measurements with ionization chambers. Methods: Detailed models of 16 commercially-available ionization chambers were implemented in Geant4. To validate these models, calculations of the beam quality correction factor kQ (defined by TG-51) were performed using the spectrum from a 6 MV Elekta SL25. kQ values were then recalculated for each detector with a 1.5 T external magnetic field applied uniformly across the geometry. Chamber, beam and B-field were all orthogonal. Results: The comparison between the kQ calculations and TG-51 showed agreement within 1.4%. The B-field calculations indicate that the change in kQ values due to the B-field is strongly affected by the volume and material of the ionization chamber. All large volume (>0.5 cm {sup 3}) ionization chambers had lower kQ values when used in a B-field. The kQ values for small volume chambers were very sensitive to the chambers’ collecting volume and could be higher or lower when used in a B-field. Conclusions: Of the chambers tested, the PTW 30011 demonstrated the smallest correction of just 1.2%. The next step is to calculate kQ using the energy spectrum from an actual MR-linac. Further validation of these results against measurements will be paramount before they can be used. Funding provided by Elekta Limited. The MR-linac spectrum will be provided by Elekta Limited based on a machine they have designed.

  6. 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.

  7. Assaying multiple 125I seeds with the well-ionization chamber SourceCheck4π 33005 and a new insert

    PubMed Central

    Ballester, Facundo; Perez-Calatayud, Jose; Vijande, Javier

    2015-01-01

    Purpose To provide a practical solution that can be adopted in clinical routine to fulfill the AAPM-ESTRO recommendations regarding quality assurance of seeds used in prostate permanent brachytherapy. The aim is to design a new insert for the well-ionization chamber SourceCheck4π 33005 (PTW, Germany) that allows evaluating the mean air-kerma strength of up to ten 125I seeds with one single measurement instead of measuring each seed individually. Material and methods The material required is: a) the SourceCheck4π 33005 well-ionization chamber provided with a PTW insert to measure the air-kerma strength S K of one single seed at a time; b) a newly designed insert that accommodates ten seeds in one column, which allows measuring the mean S K of the ten seeds in one single measurement; and c) a container with ten seeds from the same batch and class of the seeds used for the patient implant, and a set of nine non-radioactive seeds. The new insert is characterized by determining its calibration coefficient, used to convert the reading of the well-chamber when ten seeds are measured to their mean S K. The proposed method is validated by comparing the mean S K of the ten seeds obtained from the new insert with the individual measurement of S K of each seed, evaluated with the PTW insert. Results The ratio between the calibration coefficient of the new insert and the calibration coefficient of the PTW insert for the SourceCheck4π 33005 is 1.135 ± 0.007 (k = 1). The mean S K of a set of ten seeds evaluated with this new system is in agreement with the mean value obtained from measuring independently the S K of each seed. Conclusions The new insert and procedure allow evaluating the mean S K of ten seeds prior to the implant in a single measurement. The method is faster and more efficient from radiation protection point of view than measuring the individual S K of each seed. PMID:26816507

  8. Monte Carlo study of conversion factors for ionization chamber dosimetry in solid slab phantoms for MV photon beams

    NASA Astrophysics Data System (ADS)

    Park, Dong-wook; Lee, Jai-ki

    2016-08-01

    For high energy photon beams, solid phantom to water dose conversion factors were calculated by using a Monte Carlo method, and the result were compared with measurements and published data. Based on the absorbed dose to water dosimetry protocol, the conversion factor was theoretically divided into stopping powers ratios, perturbation factors and ratios of absorbed dose to water and that to solid phantom. Data for a Farmer-type chamber and a solid phantom based on polystyrene which is one of the most common material were applied to calculate the conversion factors for 6 MV and 15 MV photon beams. All measurements were conducted after 10 Gy pre-irradiation and thermal equilibrium had been established with solid slabs in a treatment room. The calculated and the measured conversion factors were in good agreement and could be used to confirm the feasibility of the solid phantom as a substitute for water for high energy photon beam.

  9. Poster — Thur Eve — 21: Off-axis dose perturbation effects in water in a 5 × 5 cm{sup 2} 18 MV photon beam for the PTW microLion and Exradin A1SL ionization chambers

    SciTech Connect

    O'Grady, K; Davis, S D; Papaconstadopoulos, P; Seuntjens, J

    2014-08-15

    A PTW microLion liquid ionization chamber and an Exradin A1SL air-filled ionization chamber have been modeled using the egs-chamber user code of the EGSnrc system to determine their perturbation effects in water in a 5 × 5 cm{sup 2} 18 MV photon beam. A model of the Varian CL21EX linear accelerator was constructed using the BEAMnrc Monte Carlo code, and was validated by comparing measured PDDs and profiles from the microLion and A1SL chambers to calculated results that included chamber models. Measured PDDs for a 5 × 5 cm{sup 2} field for the microLion chamber agreed with calculations to within 1.5% beyond a depth of 0.5 cm, and the A1SL PDDs agreed within 1.0% beyond 1.0 cm. Measured and calculated profiles at 10 cm depth agreed within 1.0% for both chambers inside the field, and within 4.0% near the field edge. Local percent differences increased up to 15% at 4 cm outside the field. The ratio of dose to water in the absence of the chamber relative to dose in the chamber's active volume as a function of off-axis distance was calculated using the egs-chamber correlated sampling technique. The dose ratio was nearly constant inside the field and consistent with the stopping power ratios of water to detector material, but varied up to 3.3% near the field edge and 5.2% at 4 cm outside the field. Once these perturbation effects are fully characterized for more field sizes and detectors, they could be applied to clinical water tank measurements for improved dosimetric accuracy.

  10. Nuclear Ordered Phases of Solid 3He in Silver Sinters

    NASA Astrophysics Data System (ADS)

    Schuberth, Erwin A.; Kath, Matthias; Bago, Simone

    2006-09-01

    To determine the exact spin structure of the nuclear magnetic ordered phases of solid 3He, the U2D2 low field and the high field phases above 0.4 T, a European Research and Training Network for neutron scattering from the ordered solid was established which consisted of a collaboration with the Hahn Meitner Institute, Berlin, and other European and US groups. For this experiment it is crucial to grow a single crystal within the sinter needed for cooling the solid to temperatures of the order of 500 μK and to keep it cold long enough to measure a magnetic neutron diffraction. The sinter is also necessary to absorb the major part (> 90%) of the heat generated by the neutron capture and decay reaction of the 3He nucleus. In this work we studied the growth of crystals in Ag sinters of different pore sizes and with different growth speeds to find an optimal way to obtain single crystalline samples, or at least samples with only a few grains. We used SQUID magnetometry and NMR to measure the magnetization in the ordered phases. They were indicated by the known drop of the intensity, both in the NMR signal and in the dc magnetization, for the U2D2 phase, and by an increase of about 30% for the high field phase. The best results for cooling were obtained with sinters made from 700 Å "Japanese powder" with a packing fraction of 50% which were annealed at 130 °C after sintering and then had a calculated particle size of about 4200 Å. In the dc magnetization we found a paramagnetic surface contribution from a few monolayers of 3He down to 500 μK in addition to the bulk magnetization.

  11. Fermion Monte Carlo Calculations on Liquid-3He

    SciTech Connect

    Kalos, M H; Colletti, L; Pederiva, F

    2004-03-16

    Methods and results for calculations of the ground state energy of the bulk system of {sup 3}He atoms are discussed. Results are encouraging: they believe that they demonstrate that their methods offer a solution of the ''fermion sign problem'' and the possibility of direct computation of many-fermion systems with no uncontrolled approximations. Nevertheless, the method is still rather inefficient compared with variational or fixed-node approximate methods. There appears to be a significant populations size effect. The situation is improved by the inclusion of ''Second Stage Importance Sampling'' and of ''Acceptance/Rejection'' adapted to their needs.

  12. Hard Photodisintegration of Proton Pairs in {sup 3}He

    SciTech Connect

    Piasetzky, Eli; Pomerantz, Ishay; Higinbotham, D.; Strauch, S.; Gilman, R.

    2008-10-13

    Hard deuteron photodisintegration has been investigated for 20 years, as its cross section follows the constituent counting rule and it provides insight into the interplay between hadronic and quark-gluon degrees of freedom in high-momentum transfer exclusive reactions. We have now measured for the first time hard pp-pair disintegration in the reaction {gamma}{sup 3}He{yields}pp+n, using kinematics corresponding to a spectator neutron. Cross sections were measured for 90 deg. c.m. at 8 beam energies, from 0.8 to 4.7 GeV. Preliminary results will be presented and compared to the hard deuteron photodisintegration data.

  13. High-pressure /sup 3/He gas scintillation neutron spectrometer

    SciTech Connect

    Derzon, M.S.; Slaughter, D.R.; Prussin, S.G.

    1985-10-01

    A high-pressure, /sup 3/He-Xe gas scintillation spectrometer has been developed for neutron spectroscopy on D-D fusion plasmas. The spectrometer exhibits an energy resolution of (121 +- 20 keV) keV (FWHM) at 2.5 MeV and an efficiency of (1.9 +- 0.4) x 10/sup -3/ (n/cm/sup 2/)/sup -1/. The contribution to the resolution (FWHM) from counting statistics is only (22 +- 3 keV) and the remainder is due predominantly to the variation of light collection efficiency with location of neutron events within the active volume of the detector.

  14. High-momentum response of liquid 3He.

    PubMed

    Mazzanti, F; Polls, A; Boronat, J; Casulleras, J

    2004-02-27

    A final-state-effects formalism suitable to analyze the high-momentum response of Fermi liquids is presented and used to study the dynamic structure function of liquid 3He. The theory, developed as a natural extension of the Gersch-Rodriguez formalism, incorporates the Fermi statistics explicitly through a new additive term which depends on the semidiagonal two-body density matrix. The use of a realistic momentum distribution, calculated using the diffusion Monte Carlo method, and the inclusion of this additive correction allows for good agreement with available deep-inelastic neutron scattering data.

  15. Effective theory of superfluid 3He-A

    NASA Astrophysics Data System (ADS)

    Schakel, Adriaan M. J.; Batenburg, Peter

    1989-10-01

    From the symmetry content of the system an effective theory of superfluid 3He-A is derived. Two physically non-trivial implications of the theory are a relation between the chemical potential and the vorticity, and the observation that the superfluid cannot be accelerated if the vorticity is uniform. The theory also yields resolutions to two longstanding paradoxes, namely the mass current paradox and the angular momentum paradox. The resolution of the former turns out to provide a physical illustration of the Callan-Harvey effect, whereas the latter is resolved by utilizing Berry's geometrical phase.

  16. 3He Spin-Dependent Cross Sections and Sum Rules

    SciTech Connect

    Slifer, Karl; Amaryan, Moscov; Amaryan, Moskov; Auerbach, Leonard; Averett, Todd; Berthot, J.; Bertin, Pierre; Bertozzi, William; Black, Tim; Brash, Edward; Brown, D.; Burtin, Etienne; Calarco, John; Cates, Gordon; Chai, Zhengwei; Chen, Jian-Ping; Choi, Seonho; Chudakov, Eugene; Ciofi, Claudio; Cisbani, Evaristo; De Jager, Cornelis; Deur, Alexandre; DiSalvo, R.; Dieterich, Sonja; Djawotho, Pibero; Finn, John; Fissum, Kevin; Fonvieille, Helene; Frullani, Salvatore; Gao, Haiyan; Gao, Juncai; Garibaldi, Franco; Gasparian, Ashot; Gilad, Shalev; Gilman, Ronald; Glamazdin, Oleksandr; Glashausser, Charles; Glockle, W.; Golak, J.; Goldberg, Emma; Gomez, Javier; Gorbenko, Viktor; Hansen, Jens-Ole; Hersman, F.; Holmes, Richard; Huber, Garth; Hughes, Emlyn; Humensky, Thomas; Incerti, Sebastien; Iodice, Mauro; Jensen, S.; Jiang, Xiaodong; Jones, C.; Jones, G.; Jones, Mark; Jutier, Christophe; Kamada, H.; Ketikyan, Armen; Kominis, Ioannis; Korsch, Wolfgang; Kramer, Kevin; Kumar, Krishna; Kumbartzki, Gerfried; Kuss, Michael; Lakuriqi, Enkeleida; Laveissiere, Geraud; LeRose, John; Liang, Meihua; Liyanage, Nilanga; Lolos, George; Malov, Sergey; Marroncle, Jacques; McCormick, Kathy; McKeown, Robert; Meziani, Zein-Eddine; Michaels, Robert; Mitchell, Joseph; Nogga, Andreas; Pace, Emanuele; Papandreou, Zisis; Pavlin, Tina; Petratos, Gerassimos; Pripstein, David; Prout, David; Ransome, Ronald; Roblin, Yves; Rowntree, David; Rvachev, Marat; Sabatie, Franck; Saha, Arunava; Salme, Giovanni; SCOPETTA, S.; Skibinski, R.; Souder, Paul; Saito, Teijiro; Strauch, Steffen; Suleiman, Riad; Takahashi, Kazunori; Todor, Luminita; Tsubota, Hiroaki; Ueno, Hiroaki; Urciuoli, Guido; van der Meer, Rob; Vernin, Pascal; Voskanyan, Hakob; Witala, Henryk; Wojtsekhowski, Bogdan; Xiong, Feng; Xu, Wang; Yang, Jae-Choon; Zhang, Bin; Zolnierczuk, Piotr

    2008-07-01

    We present a measurement of the spin-dependent cross sections for the \\vec{^3He}(\\vec{e},e')X} reaction in the quasielastic and resonance regions at four-momentum transfer 0.1 < Q^2< 0.9 GeV^2. The spin-structure functions have been extracted and used to evaluate the nuclear Burkhardt--Cottingham and extended GDH sum rules for the first time. Impulse approximation and exact three-body Faddeev calculations are also compared to the data in the quasielastic region.

  17. Hard Photo-disintegration of proton pairs in 3He

    SciTech Connect

    Piasetzky, Eliazer; Pomerantz, Ishay; Higinbotham, Douglas; Strauch, Steffen; Gilman, Ronald

    2008-11-01

    Hard deuteron photodisintegration has been investigated for 20 years, as its cross section follows the constituent counting rule and it provides insight into the interplay between hadronic and quark-gluon degrees of freedom in high-momentum transfer exclusive reactions. We have now measured for the first time hard pp-pair disintegration in the reaction gamma 3He-->pp+n, using kinematics corresponding to a spectator neutron. Cross sections were measured for 90 deg. c.m. at 8 beam energies, from 0.8 to 4.7 GeV. Preliminary results will be presented and compared to the hard deuteron photodisintegration data.

  18. 3He spin-dependent cross sections and sum rules.

    PubMed

    Slifer, K; Amarian, M; Auerbach, L; Averett, T; Berthot, J; Bertin, P; Bertozzi, B; Black, T; Brash, E; Brown, D; Burtin, E; Calarco, J; Cates, G; Chai, Z; Chen, J-P; Choi, Seonho; Chudakov, E; Ciofi Degli Atti, C; Cisbani, E; de Jager, C W; Deur, A; DiSalvo, R; Dieterich, S; Djawotho, P; Finn, M; Fissum, K; Fonvieille, H; Frullani, S; Gao, H; Gao, J; Garibaldi, F; Gasparian, A; Gilad, S; Gilman, R; Glamazdin, A; Glashausser, C; Glöckle, W; Golak, J; Goldberg, E; Gomez, J; Gorbenko, V; Hansen, J-O; Hersman, B; Holmes, R; Huber, G M; Hughes, E; Humensky, B; Incerti, S; Iodice, M; Jensen, S; Jiang, X; Jones, C; Jones, G; Jones, M; Jutier, C; Kamada, H; Ketikyan, A; Kominis, I; Korsch, W; Kramer, K; Kumar, K; Kumbartzki, G; Kuss, M; Lakuriqi, E; Laveissiere, G; Lerose, J J; Liang, M; Liyanage, N; Lolos, G; Malov, S; Marroncle, J; McCormick, K; McKeown, R D; Meziani, Z-E; Michaels, R; Mitchell, J; Nogga, A; Pace, E; Papandreou, Z; Pavlin, T; Petratos, G G; Pripstein, D; Prout, D; Ransome, R; Roblin, Y; Rowntree, D; Rvachev, M; Sabatié, F; Saha, A; Salmè, G; Scopetta, S; Skibiński, R; Souder, P; Saito, T; Strauch, S; Suleiman, R; Takahashi, K; Teijiro, S; Todor, L; Tsubota, H; Ueno, H; Urciuoli, G; Van der Meer, R; Vernin, P; Voskanian, H; Witała, H; Wojtsekhowski, B; Xiong, F; Xu, W; Yang, J-C; Zhang, B; Zolnierczuk, P

    2008-07-11

    We present a measurement of the spin-dependent cross sections for the 3He over -->(e over -->,e')X reaction in the quasielastic and resonance regions at a four-momentum transfer 0.1< or =Q2< or =0.9 GeV2. The spin-structure functions have been extracted and used to evaluate the nuclear Burkhardt-Cottingham and extended Gerasimov-Drell-Hearn sum rules for the first time. The data are also compared to an impulse approximation calculation and an exact three-body Faddeev calculation in the quasielastic region.

  19. Textural domain walls in superfluid 3He-B

    NASA Astrophysics Data System (ADS)

    Mizushima, Takeshi

    Owing to the richness of symmetry, the superfluid 3He serves as a rich repository of topological quantum phenomena. This includes the emergence of surface Majorana fermions and their quantum mass acquisition at the topological critical point. Furthermore, the marriage of the prototype topological superfluid with nanofabrication techniques brings about a rich variety of spontaneous symmetry breaking, such as the formation of the stripe order and nontrivial domain walls. In this work, we examine the possible formation of textural domain walls in the superfluid 3He-B confined to a thin slab with a sub-micron thickness. When an applied magnetic field is much higher than the dipolar field, two nearly degenerate ground states appear, which are characterized by the Ising order associated with the spontaneous breaking of a magnetic order-two symmetry, lcirc;z = + 1 and - 1 . We here discuss the structure of the textural domain wall formed by the spatial modulation of the Ising order, such as low-lying quasiparticle excitations and spontaneous spin current. We also report bosonic modes bound to the textural domain wall.

  20. Duoplasmatron source modifications for {sup 3}He{sup +} Operation

    SciTech Connect

    Schmidt, C.W.; Popovic, M.

    1997-11-01

    A duoplasmatron ion source is used to produce 25 mA of {sup 3}He+ with a pulse width of {approximately}80 ms at 360 Hz for acceleration to 10.5 MeV. At this energy, {sup 3}He striking water or carbon targets can produce short lived isotopes of {sup 11}C, {sup 13}N, {sup 15}O and {sup 18}F for medical positron emission tomography (PET). A duoplasmatron ion source was chosen originally since it is capable of a sufficient singly-charged helium beam with an acceptable gas consumption. Stable long-term operation of the source required a change in the filament material to molybdenum, and a careful understanding of the oxide filament conditioning, operation and geometry. Other improvements, particularly in the electronics, were helpful to increasing the reliability. The source has operated for many months at {approximately}2.5% duty factor without significant problems and with good stability. We report here the effort that was done to make this source understandable and reliable.

  1. The 3H-3He Charge Radii Difference

    SciTech Connect

    Myers, Luke S.; Arrington, John R.; Higinbotham, Douglas W.

    2016-03-01

    The upcoming E12-14-009 [1] experiment at Jefferson Lab will determine the ratio of the electric form factors for the A=3 mirror nuclei 3He and 3H. The measurement will use a 1.1 GeV electron beam, a special collimator plate to allow for simultaneous optics measurements, and the low-activity tritium target being prepared for Jefferson Lab. By observing the dependence of the form factor ratio as a function of Q2 over 0.05–0.09 GeV2, the dependence of the radii extraction on the shape of the form factors is minimized. As a result, we anticipate the uncertainty of the extracted charge radii difference to be 0.03 fm, a reduction of 70% from the current measurement. Using precise measurements of the 3He charge radius from isotopic shift or μHe measurements [2–4], we can deduce the absolute 3H charge radius. The results will provide a direct comparison to recent calculations of the charge radii.

  2. Hard Photodisintegration of a Proton Pair in 3He

    SciTech Connect

    Brodsky, S.

    2003-09-30

    Hard photodisintegration of the deuteron has been extensively studied in order to understand the dynamics of the transition from hadronic to quark-gluon descriptions of the strong interaction. In this work, we discuss the extension of this program to hard photodisintegration of a pp pair in the {sup 3}He nucleus. Experimental confirmation of new features predicted here for the suggested reaction would advance our understanding of hard nuclear reactions. A main prediction, in contrast with low-energy observations, is that the pp breakup cross section is not much smaller than the one for pn break up.In some models, the energy-dependent oscillations observed for pp scattering are predicted to appear in the {gamma}{sup 3}He to pp + n reaction. Such an observation would open up a completely new field in studies of color coherence phenomena in hard nuclear reactions. We also demonstrate that, in addition to the energy dependence, the measurement of the light-cone momentum distribution of the recoil neutron provides an independent test of the underlying dynamics of hard disintegration.

  3. 3He film flow on a round rim beaker

    NASA Astrophysics Data System (ADS)

    Steel, S. C.; Harrison, J. P.; Zawadzki, P.; Sachrajda, A.

    1994-06-01

    The superfluid properties of thin (100 150 nm) of3He were investigated by measuring the rate at which a beaker of liquid3He emptied itself through the adsorbed film, with the film thickness δ decreasing as the level dropped. A beaker rim with a semicircular cross-section was used to provide a well defined geometry and to avoid the effects of small scratches that may have affected earlier experiments. The film thicknesses were determined by Atkins' oscillaton measurements of4He films on the same surface. The superfluid transition temperature in the film T {/c F } was suppressed below the bulk value T {/c B }, and was close to being described by 2δ/ξ( T {/c F }) = π, as expected for A-phase. The critical current density was more than an order of magnitude smaller than expected for pair-breaking. When a4He monolayer was adsorbed on the substrate, there was no suppresson of T {/c F }.

  4. Effective theory of 3H and 3He

    NASA Astrophysics Data System (ADS)

    König, Sebastian; Grießhammer, Harald W.; Hammer, H.-W.; van Kolck, U.

    2016-06-01

    We present a new perturbative expansion for pionless effective field theory with Coulomb interactions in which at leading order (LO) the spin-singlet nucleon-nucleon channels are taken in the unitarity limit. Presenting results up to next-to-leading order for the Phillips line and the neutron-deuteron doublet-channel phase shift, we find that a perturbative expansion in the inverse {}1{S}0 scattering lengths converges rapidly. Using a new systematic treatment of the proton-proton sector that isolates the divergence due to one-photon exchange, we renormalize the corresponding contribution to the {}3{{H}} -{}3{He} binding energy splitting and demonstrate that the Coulomb force in pionless EFT is a completely perturbative effect in the trinucleon bound-state regime. In our new expansion, the LO is exactly isospin-symmetric. At next-to-leading order, we include isospin breaking via the Coulomb force and two-body scattering lengths, and find for the energy splitting {({E}B{(}3{He})-{E}B{(}3{{H}}))}{NLO}\\quad =(-0.86+/- 0.17)\\quad {MeV}.

  5. Effect of Aerogel Anisotropy in Superfluid 3He-A

    NASA Astrophysics Data System (ADS)

    Zimmerman, A. M.; Li, J. I. A.; Pollanen, J.; Collett, C. A.; Gannon, W. J.; Halperin, W. P.

    2014-03-01

    Two theories have been advanced to describe the effects of anisotropic impurity introduced by stretched silica aerogel on the orientation of the orbital angular momentum l& circ; in superfluid 3He-A. These theories disagree on whether the anisotropy will orient l& circ; perpendicular[2] or parallel[3] to the strain axis. In order to examine this question we have produced and characterized a homogeneous aerogel sample with uniaxial anisotropy introduced during growth, corresponding to stretching of the aerogel. These samples have been shown to stabilize two new chiral states;[4] the higher temperature state being the subject of the present study. Using pulsed NMR we have performed experiments on 3He-A imbibed in this sample in two orientations: strain parallel and perpendicular to the applied magnetic field. From the NMR frequency shifts as a function of tip angle and temperature, we find that the angular momentum l& circ; is oriented along the strain axis, providing evidence for the theory advanced by Sauls. This work was supported by the National Science Foundation, DMR-1103625.

  6. Pion absorption on 3He at low energies

    NASA Astrophysics Data System (ADS)

    Hahn, H.; Altman, A.; Ashery, D.; Gefen, G.; Gill, D. R.; Johnson, R. R.; Levy-Nathansohn, R.; Moinester, M. A.; Sevior, M.; Trelle, R. P.

    1996-03-01

    The reactions 3He(π+,pp)p and 3He(π-,pn)n were studied at 37.0 MeV by coincidence detection of two nucleons. The differential cross sections were separated to two-nucleon (σ2N), three-nucleon (σ3N), and final-state interaction (σFSI) components. For π+, the σ2N angular distribution is symmetric about 90°, and the total cross section is 1.5 times the cross section measured for d(π+,pp). For π-, the angular distribution is asymmetric (backward peaked). The asymmetry increases with decreasing energy, indicating increasing pion s-wave contribution at lower energies. The fraction of the cross section induced by s-wave pions as calculated by a partial wave amplitude analysis is 13%. The measured total cross sections are σ2N(π-)=0.85+/-0.08 mb and σ2N(π+)=7.9+/-0.5 mb; σ3N(π-)=1.6+/-0.7 mb and σ3N(π+)=1.3+/-0.3 mb. A new evaluation of σ3N at Tπ=62.5 and 82.8 MeV is given, using data from an earlier experiment. The cross sections leading to the two-nucleon final-state interaction at Tπ=37.0 MeV are also estimated.

  7. 3He melting curve below 15 mK

    NASA Astrophysics Data System (ADS)

    Fukuyama, Hiroshi; Ishimoto, Hidehiko; Tazaki, Tetsurou; Ogawa, Shinji

    1987-12-01

    We have performed new measurements of the P-T relation along the 3He melting curve for temperatures between 0.4 and 15 mK in zero magnetic field. The temperature was determined by a Pt-wire nuclear-magnetic-resonance thermometer calibrated against the National Bureau of Standards scale (1983) above 15 mK. Three distinct points on the melting curve (the two superfluid transitions and the nuclear-spin ordering in the solid phase) were observed at temperatures lower than currently accepted values by about 10%. Our results are in good agreement with the P-T relation recently proposed by Greywall using a La-cerium magnesium nitrate thermometer, but differ seriously from the thermodynamic measurements by Halperin et al. From the measured melting curve, we could determine the ground-state energy of a nuclear spin in solid 3He to be -1.24 mK at the melting density. This value can be quantitatively explained by the current four-spin exchange theory.

  8. Interaction of Hydrogen Atoms with Helium Films: Sticking Probabilities for H on 3He and 4He, and the Binding Energy of H on 3He

    NASA Astrophysics Data System (ADS)

    Jochemsen, R.; Morrow, M.; Berlinsky, A. J.; Hardy, W. N.

    1981-09-01

    Magnetic resonance at 1420 MHz in zero magnetic field and for 0.063He, the rate constant for recombination and the frequency shift for H on 3He, and the sticking probability for H on 3He and 4He. The binding energy for H on liquid 3He is found to be 0.42+/-0.05 K, and the sticking probabilities are 0.035 for H on 4He and 0.016 for H on 3He.

  9. SU-E-T-105: The LET Dependence of Liquid Ionization Chambers (LICs) in High-LET Beams.

    PubMed

    Tegami, S; Gomez, F; Gónzales-Castaño, D; Jaekel, O; Pardo-Montero, J; Holzscheiter, M

    2012-06-01

    LICs are novel detectors for radiotherapy: the higher density of the medium allows to build them with a smaller sensitive volume, making them appealing in particle therapy. With RBE varying along the depth dose curve (DDC) and with the rising interest in dose/LET-painting, verifying the LET is becoming more important. Nevertheless, while the LET distributions for different ionizing particles have been calculated, they have never been directly measured in realistic therapeutic beams. Our interest in LICs is based on the characterization of the beam quality in terms of LET. It has been shown in earlier works that the extrapolation of the linear portion of the voltage curve yields an intercept with the x-axis that depends on LET. The quantitative establishment of this method, however, depends on how accurately recombination effects are taken into account. Due to the higher density of charge carriers produced in the liquid, LICs have high recombination effects: general recombination effects, involving pairs belonging to different tracks (dose rate dependent), and initial recombination between ion-electron pairs belonging to the same incident particle event (LET dependent). To perform this study we propose a two-dimensional array of LICs, composed by a 16×8 matrix of 2×2 mm(2) pixels, which gives a fine spatial resolution on the plane. Voltage curves have been measured for proton, carbon and oxygen beams available at the HIT facility in Heidelberg for different energies and dose rates. After correcting the curves for general recombination losses using the Three Voltage Method, we have indications of dose rate independence, indicating successful correction. Further investigations are foreseen to quantify the LET dependence along the DDC, where different LET values are expected. A comparison with simulated dose averaged LET values will give quantitative information about 2D LET distributions for different beam species. © 2012 American Association of Physicists in

  10. 3He specific heat and thermometry at millikelvin temperatures

    NASA Astrophysics Data System (ADS)

    Greywall, Dennis S.

    1986-06-01

    High-precision specific-heat measurements were made on pure liquid 3He in both the normal and superfluid phases for temperatures between 0.6 and 5 mK and for pressures between 0 and 34 bars. The data were obtained using a magnetic susceptibility thermometer which was calibrated against the National Bureau of Standards scale near 15 mK and at lower temperatures principally by the condition that the zero-pressure normal-phase specific heat be linear in temperature. The 3He phase diagram based on this scale is presented. In particular we find that TA=2.49 mK which differs quite substantially from the currently accepted value of about 2.7 mK. Multiplying the Pt NMR temperatures determined by Haavasoja and co-workers by a factor of 0.89 or subtracting 0.13 mK from the magnetic temperatures of Paulson et al. brings both of these scales into excellent agreement with the new scale. The 3He quasiparticle effective mass, m*3(P), extracted from the normal-phase data agrees well with our previously reported results based on higher-temperature specific-heat data. The values of m*3(P) from Haavasoja and co-workers are ~20% smaller. However, if their specific-heat data are reanalyzed using the new temperature scale, the two sets of m*3(P) values are brought into good agreement. We thus claim that the large discrepancies between previous specific-heat measurements are due almost entirely to differences in temperature scales. The new normal-phase specific-heat data at low pressures show no evidence of the anomalous behavior observed by Haavasoja and co-workers. Consequently, the size of the specific-heat jump at Tc could be determined with little ambiguity over the entire pressure range. ΔC/C> is only a few percent larger than the weak-coupling value at P=0 and increases linearly with sample density. At high density the temperature dependence of the specific heat below Tc shows small deviations from theory.

  11. Chiral phases of superfluid 3He in an anisotropic medium

    NASA Astrophysics Data System (ADS)

    Sauls, J. A.

    2013-12-01

    Recent advances in the fabrication and characterization of anisotropic silica aerogels with exceptional homogeneity provide new insight into the nature of unconventional pairing in disordered anisotropic media. I report theoretical analysis and predictions for the equilibrium phases of superfluid 3He infused into a low-density, homogeneous uniaxial aerogel. Ginzburg-Landau (GL) theory for a class of equal-spin-pairing (ESP) states in a medium with uniaxial anisotropy is developed and used to analyze recent experiments on uniaxially strained aerogels. For 3He in an axially “stretched” aerogel, GL theory predicts a transition from normal liquid into a chiral Anderson-Morel phase at Tc1 in which the chirality axis l̂ is aligned along the strain axis. This orbitally aligned state is protected from random fluctuations in the anisotropy direction, has a positive nuclear magnetic resonance (NMR) frequency shift, a sharp NMR resonance line, and is identified with the high-temperature ESP-1 phase of superfluid 3He in axially stretched aerogel. A second transition into a biaxial phase is predicted to onset at a slightly lower temperature Tc2

  12. Perspectives of hyperpolarized noble gas MRI beyond 3He

    PubMed Central

    Lilburn, David M.L.; Pavlovskaya, Galina E.; Meersmann, Thomas

    2013-01-01

    Nuclear Magnetic Resonance (NMR) studies with hyperpolarized (hp) noble gases are at an exciting interface between physics, chemistry, materials science and biomedical sciences. This paper intends to provide a brief overview and outlook of magnetic resonance imaging (MRI) with hp noble gases other than hp 3He. A particular focus are the many intriguing experiments with 129Xe, some of which have already matured to useful MRI protocols, while others display high potential for future MRI applications. Quite naturally for MRI applications the major usage so far has been for biomedical research but perspectives for engineering and materials science studies are also provided. In addition, the prospects for surface sensitive contrast with hp 83Kr MRI is discussed. PMID:23290627

  13. Alpha Backgrounds in the SNO ^3He Proportional Counter Array

    NASA Astrophysics Data System (ADS)

    Stonehill, Laura

    2006-04-01

    The Sudbury Neutrino Observatory (SNO) has recently deployed an array of proportional counters known as Neutral Current Detectors (NCDs) to detect thermalized neutrons via the ^3He(n,p)^3H reaction. The primary physics background to the neutron-capture signal is alpha particle emission from uranium- and thorium-chain decays in the NCD walls. The expected capture rate of neutrons from the neutral-current neutrino reaction on deuterium is three per day and the intrinsic alpha background rate is approximately 250 alphas per day. Fewer than 10% of these alphas fall into the energy range where neutron-capture signals occur, and a substantial number of these can be eliminated by pulse-shape analysis. This talk will focus on measurements of the alpha backgrounds in the NCDs and the extent to which these alphas contaminate the neutron-capture signal region.

  14. {sup 3}He target for Hall C at CEBAF

    SciTech Connect

    Zeidman, B.; Zeuli, A.

    1995-08-01

    A major fraction of the physics program for Hall C involves scattering from cryogenic targets of the lightest nuclei, i.e. H, D, and {sup 3,4}He. Argonne is constructing the He target that will consist of a 4cm cylinder, operating at a pressure of 10 atmospheres and a temperature of {approximately}5.2 degrees Kelvin. CEBAF is currently constructing a cryo-target system for liquid H and D cells and the cooled, pressurized helium targets. The He target system includes cell loop, the He supply systems, and the additional equipment needed to ensure minimum loss of {sup 3}He in the event of target rupture. Some of the major components have been completed, while the balance of the system will be ready for installation this fiscal year.

  15. Electrodisintegration of 3He below and above deuteron breakup threshold

    SciTech Connect

    Marcucci, L. E.; Viviani, M.; Schiavilla, R.; Kievsky, A.; Rosati, S.

    2005-02-01

    Recent advances in the study of electrodisintegration of 3He are presented and discussed. The pair-correlated hyperspherical harmonics method is used to calculate the initial and final state wave functions, with a realistic Hamiltonian consisting of the Argonne v18 two-nucleon and Urbana IX three-nucleon interactions. The model for the nuclear current and charge operators retains one- and many-body contributions. Particular attention is made in the construction of the two-body current operators arising from the momentum-dependent part of the two-nucleon interaction. Three-body current operators are also included so that the full current operator is strictly conserved. The present model for the nuclear current operator is tested comparing theoretical predictions and experimental data of pd radiative capture cross section and spin observables.

  16. Perspectives of hyperpolarized noble gas MRI beyond 3He.

    PubMed

    Lilburn, David M L; Pavlovskaya, Galina E; Meersmann, Thomas

    2013-04-01

    Nuclear Magnetic Resonance (NMR) studies with hyperpolarized (hp) noble gases are at an exciting interface between physics, chemistry, materials science and biomedical sciences. This paper intends to provide a brief overview and outlook of magnetic resonance imaging (MRI) with hp noble gases other than hp (3)He. A particular focus are the many intriguing experiments with (129)Xe, some of which have already matured to useful MRI protocols, while others display high potential for future MRI applications. Quite naturally for MRI applications the major usage so far has been for biomedical research but perspectives for engineering and materials science studies are also provided. In addition, the prospects for surface sensitive contrast with hp (83)Kr MRI is discussed. Copyright © 2012 Elsevier Inc. All rights reserved.

  17. Realization of administration unit for 3He with gas recycling

    NASA Astrophysics Data System (ADS)

    Güldner, M.; Becker, S.; Friesenecker, A.; Gast, K. K.; Heil, W.; Karpuk, S.; Otten, E. W.; Rivoire, J.; Salhi, Z.; Scholz, A.; Schreiber, L. M.; Terekhov, M.; Weiss, P.; Wolf, U.; Zentel, J.

    2011-06-01

    Hyperpolarized (HP) noble gases (3He,129Xe) are used for MR-imaging of the lung. In the majority of case the HP gas is filled in Tedlarbags and directly inhaled by the patients. Starting from an earlier pilot device, an administration unit was built respectively to the Medical Devices Law to administer patients HP noble gas boli in defined quantities and at a predefined time during inspiration with high reproducibility and reliability without reducing MR-quality. The patient's airflows are monitored and recorded. It is possible to use gas admixtures, measure the polarization on-line and collect the exhaled gas for later recycling. The first images with healthy volunteers were taken with this setup in a clinical study. Current results will be presented.

  18. Neutral beam injection in a D 3He FRC reactor

    NASA Astrophysics Data System (ADS)

    Ferrari, Hugo; Farengo, Ricardo

    2007-06-01

    The use of neutral beam injection (NBI) to sustain a fraction of the plasma current in a field reversed configuration (FRC) reactor operating with the D-3He reaction is studied. A Monte Carlo code already used to study NBI in medium size FRCs is employed (Lifschitz A F, Farengo R and Arista N R 2002 Nucl. Fusion 42 863, Lifschitz A F, Farengo R and Arista N R 2002 Plasma Phys. Control. Fusion 44 1979, Lifschitz A F, Farengo R and Hoffman A L 2004 Nucl. Fusion 44 1015) and the plasma parameters are similar to those proposed in the ARTEMIS (Momota H, Ishida A, Kohzaki Y, Miley G, Ohi S, Ohnishi M, Sato K, Steinhauer L, Tomita Y and Tuszewki M 1992 Fusion Technol. 21 2307) conceptual reactor design. A simple analysis shows that the driven current cannot reach the values quoted in the ARTEMIS project and a procedure to search for plasma parameters that result in higher efficiencies is presented.

  19. Perspectives of hyperpolarized noble gas MRI beyond 3He

    NASA Astrophysics Data System (ADS)

    Lilburn, David M. L.; Pavlovskaya, Galina E.; Meersmann, Thomas

    2013-04-01

    Nuclear Magnetic Resonance (NMR) studies with hyperpolarized (hp) noble gases are at an exciting interface between physics, chemistry, materials science and biomedical sciences. This paper intends to provide a brief overview and outlook of magnetic resonance imaging (MRI) with hp noble gases other than hp 3He. A particular focus are the many intriguing experiments with 129Xe, some of which have already matured to useful MRI protocols, while others display high potential for future MRI applications. Quite naturally for MRI applications the major usage so far has been for biomedical research but perspectives for engineering and materials science studies are also provided. In addition, the prospects for surface sensitive contrast with hp 83Kr MRI is discussed.

  20. Direct energy conversion system for D(3)-He fusion

    NASA Astrophysics Data System (ADS)

    Tomita, Y.; Shu, L. Y.; Momota, H.

    1993-11-01

    A novel and highly efficient direct energy conversion system is proposed for utilizing D(3)-He fueled fusion. In order to convert kinetic energy of ions, we applied a pair of direct energy conversion systems each of which has a cusp-type DEC and a traveling wave DEC (TWDEC). In a cusp-type DEC, electrons are separated from the escaping ions at the first line-cusp and the energy of thermal ion components is converted at the second cusp DEC. The fusion protons go through the cusp-type DEC and arrive at the TWDEC, which principle is similar to 'LINAC'. The energy of fusion protons is recovered to electricity with an efficiency of more than 70%. These DEC's bring about the high efficient fusion plant.

  1. 4He Versus 3He Josephson Effect: Vibration Decoherence

    SciTech Connect

    Pereverzev, Sergey V.

    2006-09-07

    Several on-going experiments searching for the Josephson effect in 4He close to the {lambda}-transition employ experimental cells with a weak link in the form of an array of submicron holes, with the size of the array and the cell dimensions very close to those used for 3He-B. In the same environment, the 4He experiment is more prone to decoherence by mechanical vibrations. The problem is due to the shift of the maximum of the vibration response of the experiment to low frequencies (0.1 Hz or less) and to the increase of the power spectrum density of the seismic velocities with decreasing frequency in this frequency range. To avoid decoherence, one needs to lower the cut-off frequency of the vibration isolation or to use an array with a larger open area. The latter option is briefly discussed.

  2. APT {sup 3}He target/blanket. Topical report

    SciTech Connect

    1995-03-01

    The {sup 3}He target/blanket (T/B) preconceptual design for the 3/8-Goal facility is based on a 1000-MeV, 200-mA accelerator to produce a high-intensity proton beam that is expanded and then strikes one of two T/B modules. Each module consists of a centralized neutron source made of tungsten and lead, a proton beam backstop region made of zirconium and lead, and a moderator made of D{sub 2}O. Helium-3 gas is circulated through the neutron source region and the blanket to create tritium through neutron capture. The gas is continually processed to extract the tritium with an online separation process.

  3. 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.

  4. A radiation quality correction factor k{sub Q} for well-type ionization chambers for the measurement of the reference air kerma rate of {sup 60}Co HDR brachytherapy sources

    SciTech Connect

    Schüller, Andreas Meier, Markus; Selbach, Hans-Joachim; Ankerhold, Ulrike

    2015-07-15

    Purpose: The aim of this study was to investigate whether a chamber-type-specific radiation quality correction factor k{sub Q} can be determined in order to measure the reference air kerma rate of {sup 60}Co high-dose-rate (HDR) brachytherapy sources with acceptable uncertainty by means of a well-type ionization chamber calibrated for {sup 192}Ir HDR sources. Methods: The calibration coefficients of 35 well-type ionization chambers of two different chamber types for radiation fields of {sup 60}Co and {sup 192}Ir HDR brachytherapy sources were determined experimentally. A radiation quality correction factor k{sub Q} was determined as the ratio of the calibration coefficients for {sup 60}Co and {sup 192}Ir. The dependence on chamber-to-chamber variations, source-to-source variations, and source strength was investigated. Results: For the PTW Tx33004 (Nucletron source dosimetry system (SDS)) well-type chamber, the type-specific radiation quality correction factor k{sub Q} is 1.19. Note that this value is valid for chambers with the serial number, SN ≥ 315 (Nucletron SDS SN ≥ 548) onward only. For the Standard Imaging HDR 1000 Plus well-type chambers, the type-specific correction factor k{sub Q} is 1.05. Both k{sub Q} values are independent of the source strengths in the complete clinically relevant range. The relative expanded uncertainty (k = 2) of k{sub Q} is U{sub k{sub Q}} = 2.1% for both chamber types. Conclusions: The calibration coefficient of a well-type chamber for radiation fields of {sup 60}Co HDR brachytherapy sources can be calculated from a given calibration coefficient for {sup 192}Ir radiation by using a chamber-type-specific radiation quality correction factor k{sub Q}. However, the uncertainty of a {sup 60}Co calibration coefficient calculated via k{sub Q} is at least twice as large as that for a direct calibration with a {sup 60}Co source.

  5. Neutron multiplicity ,easurements With 3He alternative: Straw neutron detectors

    DOE PAGES

    Mukhopadhyay, Sanjoy; Wolff, Ronald S.; Meade, John A.; ...

    2015-01-27

    Counting neutrons emitted by special nuclear material (SNM) and differentiating them from the background neutrons of various origins is the most effective passive means of detecting SNM. Unfortunately, neutron detection, counting, and partitioning in a maritime environment are complex due to the presence of high-multiplicity spallation neutrons (commonly known as “ship effect”) and to the complicated nature of the neutron scattering in that environment. In this study, a prototype neutron detector was built using 10B as the converter in a special form factor called “straws” that would address the above problems by looking into the details of multiplicity distributions ofmore » neutrons originating from a fissioning source. This paper describes the straw neutron multiplicity counter (NMC) and assesses the performance with those of a commercially available fission meter. The prototype straw neutron detector provides a large-area, efficient, lightweight, more granular (than fission meter) neutron-responsive detection surface (to facilitate imaging) to enhance the ease of application of fission meters. Presented here are the results of preliminary investigations, modeling, and engineering considerations leading to the construction of this prototype. This design is capable of multiplicity and Feynman variance measurements. This prototype may lead to a near-term solution to the crisis that has arisen from the global scarcity of 3He by offering a viable alternative to fission meters. This paper describes the work performed during a 2-year site-directed research and development (SDRD) project that incorporated straw detectors for neutron multiplicity counting. The NMC is a two-panel detector system. We used 10B (in the form of enriched boron carbide: 10B4C) for neutron detection instead of 3He. In the first year, the project worked with a panel of straw neutron detectors, investigated its characteristics, and developed a data acquisition (DAQ) system to collect

  6. Are high 3He/4He ratios in oceanic basalts an indicator of deep-mantle plume components?

    USGS Publications Warehouse

    Meibom, A.; Anderson, D.L.; Sleep, Norman H.; Frei, R.; Chamberlain, C.P.; Hren, M.T.; Wooden, J.L.

    2003-01-01

    The existence of a primordial, undegassed lower mantle reservoir characterized by high concentration of 3He and high 3He/4He ratios is a cornerstone assumption in modern geochemistry. It has become standard practice to interpret high 3He/4He ratios in oceanic basalts as a signature of deep-rooted plumes. The unfiltered He isotope data set for oceanic spreading centers displays a wide, nearly Gaussian, distribution qualitatively similar to the Os isotope (187Os/188 Os) distribution of mantle-derived Os-rich alloys. We propose that both distributions are produced by shallow mantle processes involving mixing between different proportions of recycled, variably aged radiogenic and unradiogenic domains under varying degrees of partial melting. In the case of the Re-Os isotopic system, radiogenic mid-ocean ridge basalt (MORB)-rich and unradiogenic (depleted mantle residue) endmembers are constantly produced during partial melting events. In the case of the (U+Th)-He isotope system, effective capture of He-rich bubbles during growth of phenocryst olivine in crystallizing magma chambers provides one mechanism for 'freezing in' unradiogenic (i.e. high 3He/4He) He isotope ratios, while the higher than chondritic (U+Th)/He elemental ratio in the evolving and partially degassed MORB melt provides the radiogenic (i.e. low 3He/4He) endmember. If this scenario is correct, the use of He isotopic signatures as a fingerprint of plume components in oceanic basalts is not justified. Published by Elsevier Science B.V.

  7. Optical interferometry in superfluid {sup 3}He-B

    SciTech Connect

    Alles, H.; Ruutu, J.P.; Babkin, A.V.; Hakonen, P.J.; Sonin, E.B.

    1996-03-01

    The authors report interferometric measurements in 0.1...1 mm thick films of superfluid {sup 3}He-B. The menisci of three different rotational states of the superfluid were observed and analyzed theoretically using two-fluid hydrodynamics: These are (i) the equilibrium vortex state in which the superfluid and the normal components corotate (solid body rotation), (ii) the vortex-free state (the Landau state), in which only the normal component rotates, and (iii) the quasistationary vortex state in which only the superfluid fraction rotates (pure superfluid rotation). The Landua state manifested itself by a reduced parabolic meniscus at rotation speeds below the critical angular velocity {Omega}{sub c}{approx_lt} 0.2 rad/s for vortex formation. Transition from the Landua state to the equilibrium vortex state yielded a sudden deepening of the meniscus when {Omega}{sub c} was exceeded. After a rapid halt of the cryostat, the authors observed a novel meniscus which was produced by the superfluid rotation while the normal component was at rest. The enhanced depth of this meniscus is governed by the reactive mutual friction parameter B{prime}. By employing laser light, both for imaging and for thermomechanical excitation, the authors measured the response of a thin superfluid layer to a heat pulse and analyzed it within the theory of two fluid hydrodynamics. The data were employed, using the dispersion relation for thin film oscillations, to deduce the second viscosity coefficient {zeta}{sub 3} close to T{sub c}.

  8. Andreev reflection in rotating superfluid {sup 3}He-B

    SciTech Connect

    Eltsov, V. B.; Hosio, J. J.; Krusius, M. Mäkinen, J. T.

    2014-12-15

    Andreev reflection of quasiparticle excitations from quantized line vortices is reviewed in the isotropic B phase of superfluid {sup 3}He in the temperature regime of ballistic quasiparticle transport at T ≤ 0.20T{sub c}. The reflection from an array of rectilinear vortices in solid-body rotation is measured with a quasiparticle beam illuminating the array mainly in the orientation along the rotation axis. The result is in agreement with the calculated Andreev reflection. The Andreev signal is also used to analyze the spin-down of the superfluid component after a sudden impulsive stop of rotation from an equilibrium vortex state. In a measuring setup where the rotating cylinder has a rough bottom surface, annihilation of the vortices proceeds via a leading rapid turbulent burst followed by a trailing slow laminar decay, from which the mutual friction dissipation can be determined. In contrast to the currently accepted theory, it is found to have a finite value in the zero-temperature limit: α(T→0) = (5 ± 0.5) × 10{sup −4}.

  9. Hard photodisintegration of 3He into a p d pair

    NASA Astrophysics Data System (ADS)

    Maheswari, Dhiraj; Sargsian, Misak M.

    2017-02-01

    The recent measurements of high energy photodisintegration of a 3He nucleus to a p d pair at 90∘ center of mass demonstrated an energy scaling consistent with the quark counting rule with an unprecedentedly large exponent of s-17. To understand the underlying mechanism of this process, we extended the theoretical formalism of the hard rescattering mechanism (HRM) to calculate the γ 3He→p d reaction. In HRM the incoming high energy photon strikes a quark from one of the nucleons in the target which subsequently undergoes hard rescattering with the quarks from the other nucleons, generating a hard two-body system in the final state of the reaction. Within the HRM we derived the parameter-free expression for the differential cross section of the reaction, which is expressed through the 3He→p d transition spectral function, the cross section of hard p d →p d scattering, and the effective charge of the quarks being interchanged during the hard rescattering process. The numerical estimates of all these factors resulted in the magnitude of the cross section, which is surprisingly in good agreement with the data.

  10. Proton-{sup 3}He elastic scattering at low energies

    SciTech Connect

    Fisher, B. M.; Brune, C. R.; Karwowski, H. J.; Leonard, D. S.; Ludwig, E. J.; Black, T. C.; Viviani, M.; Kievsky, A.; Rosati, S.

    2006-09-15

    We present new accurate measurements of the differential cross section {sigma}({theta}) and the proton analyzing power A{sub y} for proton-{sup 3}He elastic scattering at various energies. A supersonic gas-jet target has been employed to obtain these low-energy cross-section measurements. The {sigma}({theta}) distributions have been measured at E{sub p}=0.99, 1.59, 2.24, 3.11, and 4.02 MeV. Full angular distributions of A{sub y} have been measured at E{sub p}=1.60, 2.25, 3.13, and 4.05 MeV. This set of high-precision data is compared to four-body variational calculations employing realistic nucleon-nucleon (NN) and three-nucleon (3N) interactions. For the unpolarized cross section, the agreement between the theoretical calculation and data is good when a 3N potential is used. The comparison between the calculated and measured proton analyzing powers reveals discrepancies of approximately 50% at the maximum of each distribution. This is analogous to the existing 'A{sub y} puzzle' known for the past 20 years in nucleon-deuteron elastic scattering.

  11. Transfer Excitation Processes Observed in N3+-He and O3+-He Collisions at Elab = 33 eV

    NASA Astrophysics Data System (ADS)

    Itoh, Yoh

    2016-09-01

    We measured the relative state-selective differential cross sections (DCSs) for one-electron capture reactions using a crossed-beam apparatus. The scattering angle θlab studied in the laboratory frame ranged from -3.0 to 22° and the laboratory collision energy Elab was 33 eV. Only the transfer excitation processes, i.e., the electron capture reactions with the simultaneous excitation of the projectile, were observed. The DCSs were determined for the following reactions: N3+ (1s2 2s2 1S) + He (1s2 1S) → N2+ (1s2 2s2p2 2D) + He+ (1s 2S) + 10.3 eV, O3+ (1s2 2s2 2p 2P) + He (1s2 1S) → O2+ (1s2 2s 2p3 3P) + He+ (1s 2S) + 12.7 eV, and O3+ (1s2 2s2 2p 2P) + He (1s2 1S) → O2+ (1s2 2s 2p3 3D) + He+ (1s 2S) + 15.5 eV. In the N3+-He system, the DCSs for the reaction are zero at the center-of-mass angle θcm = 0 and show a peak at a certain angle and a shoulder at a larger angle. In the O3+-He system, the DCSs are again zero at θcm = 0. The capture process to the O2+ (1s2 2s 2p3 3P) state is mainly observed at smaller scattering angles, and the reaction to the O2+ (1s2 2s 2p3 3D) state becomes dominant with increasing scattering angle. A classical trajectory analysis within the two-state approximation based on the ab initio potentials for (NHe)3+ revealed that the transfer excitation of a two-electron process takes place through a single crossing of the relevant potentials.

  12. Comment on "Deep mixing of 3He: reconciling Big Bang and stellar nucleosynthesis".

    PubMed

    Balser, Dana S; Rood, Robert T; Bania, T M

    2007-08-31

    Eggleton et al. (Reports, 8 December 2006, p. 1580) reported on a deep-mixing mechanism in low-mass stars caused by a Rayleigh-Taylor instability that destroys all of the helium isotope 3He produced during the star's lifetime. Observations of 3He in planetary nebulae, however, indicate that some stars produce prodigious amounts of 3He. This is inconsistent with the claim that all low-mass stars should destroy 3He.

  13. Characterization of 2 MeV, 4 MeV, 6 MeV and 18 MeV buildup caps for use with a 0.6 cubic centimeter thimble ionization chamber

    SciTech Connect

    Salyer, R.L.; VanDenburg, J.W.; Prinja, A.K.; Kirby, T.; Busch, R.; Hong-Nian Jow

    1996-07-01

    The purpose of this research is to characterize existing 2 MeV, 4 MeV and 6 MeV buildup caps, and to determine if a buildup cap can be made for the 0.6 cm{sup 3} thimble ionization chamber that will accurately measure exposures in a high-energy photon radiation field. Two different radiation transport codes were used to computationally characterize existing 2 MeV, 4 MeV, and 6 MeV buildup caps for a 0.6 cm{sup 3} active volume thimble ionization chamber: ITS, The Integrated TIGER Series of Coupled Electron-Photon Monte Carlo Transport Codes; and CEPXS/ONEDANT, A One-Dimensional Coupled Electron-Photon Discrete Ordinates Code Package. These codes were also used to determine the design characteristics of a buildup cap for use in the 18 MeV photon beam produced by the 14 TW pulsed power HERMES-III electron accelerator. The maximum range of the secondary electron, the depth at which maximum dose occurs, and the point where dose and collision kerma are equal have been determined to establish the validity of electronic equilibrium. The ionization chamber with the appropriate buildup cap was then subjected to a 4 MeV and a 6 MeV bremmstrahlung radiation spectrum to determine the detector response.

  14. 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.

  15. Advances in the determination of absorbed dose to water in clinical high-energy photon and electron beams using ionization chambers.

    PubMed

    Huq, M Saiful; Andreo, Pedro

    2004-02-21

    During the last two decades, absorbed dose to water in clinical photon and electron beams was determined using dosimetry protocols and codes of practice based on radiation metrology standards of air kerma. It is now recommended that clinical reference dosimetry be based on standards of absorbed dose to water. Newer protocols for the dosimetry of radiotherapy beams, based on the use of an ionization chamber calibrated in terms of absorbed dose to water, N(D,w), in a standards laboratory's reference quality beam, have been published by several national or regional scientific societies and international organizations. Since the publication of these protocols multiple theoretical and experimental dosimetry comparisons between the various N(D,w) based recommendations, and between the N(D,w) and the former air kerma (NK) based protocols, have been published. This paper provides a comprehensive review of the dosimetry protocols based on these standards and of the intercomparisons of the different protocols published in the literature, discussing the reasons for the observed discrepancies between them. A summary of the various types of standards of absorbed dose to water, together with an analysis of the uncertainties along the various steps of the dosimetry chain for the two types of formalism, is also included. It is emphasized that the NK-N(D,air) and N(D,w) formalisms have very similar uncertainty when the same criteria are used for both procedures. Arguments are provided in support of the recommendation for a change in reference dosimetry based on standards of absorbed dose to water.

  16. Chemistry of α-pinene and naphthalene oxidation products generated in a Potential Aerosol Mass (PAM) chamber as measured by acetate chemical ionization mass spectrometry

    DOE PAGES

    Chhabra, P. S.; Lambe, A. T.; Canagaratna, M. R.; ...

    2014-07-01

    Recent developments in high resolution, time-of-flight chemical ionization mass spectrometry (HR-ToF-CIMS) have made possible the direct detection of atmospheric organic compounds in real-time with high sensitivity and with little or no fragmentation, including low volatility, highly oxygenated organic vapors that are precursors to secondary organic aerosol formation. Here, for the first time, we examine gas-phase O3 and OH oxidation products of α-pinene and naphthalene formed in the PAM flow reactor with an HR-ToF-CIMS using acetate reagent ion chemistry. Integrated OH exposures ranged from 1.2 × 1011 to 9.7 × 1011 molec cm−3 s, corresponding to approximately 1.0 to 7.5 daysmore » of equivalent atmospheric oxidation. Measured gas-phase organic acids are similar to those previously observed in environmental chamber studies. For both precursors, we find that acetate-CIMS spectra capture both functionalization (oxygen addition) and fragmentation (carbon loss) as a function of OH exposure. The level of fragmentation is observed to increase with increased oxidation. We present a method that estimates vapor pressures of organic molecules using the measured O/C ratio, H/C ratio, and carbon number for each compound detected by the CIMS. The predicted condensed-phase SOA average acid yields and O/C and H/C ratios agree within uncertainties with previous AMS measurements and ambient CIMS results. While acetate reagent ion chemistry is used to selectively measure organic acids, in principle this method can be applied to additional reagent ion chemistries depending on the application.« less

  17. NOTE: Hybrid plan verification for intensity-modulated radiation therapy (IMRT) using the 2D ionization chamber array I'mRT MatriXX—a feasibility study

    NASA Astrophysics Data System (ADS)

    Dobler, Barbara; Streck, Natalia; Klein, Elisabeth; Loeschel, Rainer; Haertl, Petra; Koelbl, Oliver

    2010-01-01

    The 2D ionization chamber array I'mRT MatriXX (IBA, Schwarzenbruck, Germany) has been developed for absolute 2D dosimetry and verification of intensity-modulated radiation therapy (IMRT) for perpendicular beam incidence. The aim of this study is to evaluate the applicability of I'mRT MatriXX for oblique beam incidence and hybrid plan verification of IMRT with original gantry angles. For the assessment of angular dependence, open fields with gantry angles in steps of 10° were calculated on a CT scan of I'mRT MatriXX. For hybrid plan verification, 17 clinical IMRT plans and one rotational plan were used. Calculations were performed with pencil beam (PB), collapsed cone (CC) and Monte Carlo (MC) methods, which had been previously validated. Measurements were conducted on an Elekta SynergyS linear accelerator. To assess the potential and limitations of the system, gamma evaluation was performed with different dose tolerances and distances to agreement. Hybrid plan verification passed the gamma test with 4% dose tolerance and 3 mm distance to agreement in all cases, in 82-88% of the cases for tolerances of 3%/3 mm, and in 59-76% of the cases if 3%/2 mm were used. Separate evaluation of the low dose and high dose regions showed that I'mRT MatriXX can be used for hybrid plan verification of IMRT plans within 3% dose tolerance and 3 mm distance to agreement with a relaxed dose tolerance of 4% in the low dose region outside the multileaf collimator (MLC).

  18. 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.

  19. Velocity of second sound in /sup 3/He-/sup 4/He mixtures: a revision

    SciTech Connect

    Bowley, R.M.

    1988-05-01

    Greywall has recently proposed a new temperature scale for the /sup 3/He melting curve thermometer. A reanalysis of the velocity of second sound in /sup 3/He-/sup 4/He mixtures using the data of Greywall and Paalanen with this new temperature scale shows that the interaction between /sup 3/He quasiparticles is now independent of concentration.

  20. Temporal Variability in the Accretion Rate of Interplanetary Dust Using (3)He as a Tracer

    NASA Technical Reports Server (NTRS)

    Farley, K. A.

    2005-01-01

    The research supported by this grant falls under three topics: 1) Weekly Interplanetary Dust Sampling via (3)He; 2) Extraterrestrial (3)He at Major Impact Boundaries; 3) Completing a Moderately-High Resolution Record of Extraterrestrial (3)He Flux: A Major Asteroidal Break up Event at 8.2 Ma.

  1. Efficient (3)He/(4)He separation in a nanoporous graphenylene membrane.

    PubMed

    Qu, Yuanyuan; Li, Feng; Zhao, Mingwen

    2017-08-16

    Helium-3 is a precious noble gas, which is essential in many advanced technologies such as cryogenics, isotope labeling and nuclear weapons. The current imbalance of (3)He demand and supply shortage leads to the search for an efficient membrane with high performance for (3)He separation. In this study, based on first-principles calculations, we demonstrated that highly efficient (3)He harvesting can be achieved in a nanoporous graphenylene membrane with industrially-acceptable selectivity and permeance. The quantum tunneling effect leads to (3)He harvesting with high efficiency via kinetic sieving. Both the quantum tunneling effect and zero-point energy (ZPE) determine the (3)He/(4)He separation via thermally-driven equilibrium sieving, where the ZPE effect dominates efficient (3)He/(4)He separation between two reservoirs. The quantum effects revealed in this work suggest that the nanoporous graphenylene membrane is promising for efficient (3)He harvesting that can be exploited for industrial applications.

  2. Monte Carlo calculations of the ionization chamber wall correction factors for 192Ir and 60Co gamma rays and 250 kV x-rays for use in calibration of 192Ir HDR brachytherapy sources.

    PubMed

    Ferreira, I H; de Almeida, C E; Marre, D; Marechal, M H; Bridier, A; Chavaudra, J

    1999-08-01

    As in the method for the calibration of 192Ir high-dose-rate (HDR) brachytherapy sources, the ionization chamber wall correction factor A(w), is needed for 192Ir and 60Co gamma rays and 250 kV x-rays. This factor takes into account the variation in chamber response due to the attenuation of the photon beam in the chamber wall and build-up cap and the contribution of scattered photons. Monte Carlo calculations were performed using the EGS4 code system with the PRESTA algorithm, to calculate the A(w) factor for 51 commercial ionization chambers and build-up caps exposed to the typical energy spectrum of 192Ir and 60Co gamma rays and 250 kV x-rays. The calculated A(w) correction factors for 192Ir and 60Co sources and 250 kV x-rays agree very well to within 0.1% with published experimental data (the statistical uncertainty is less than 0.1% of the calculated correction factor value). For the 192Ir sources, A(w) varies from 0.973 to 0.993 and for the 250 kV x-rays the minimum value of A(w) for all chambers studied is 0.983. The calculated A(w) correction factors can be used to calculate the air kerma calibration factor of HDR brachytherapy sources, when interpolative methods are considered, contributing to the reduction in the overall uncertainties in the calibration procedure.

  3. SU-E-T-35: An Investigation of the Accuracy of Cervical IMRT Dose Distribution Using 2D/3D Ionization Chamber Arrays System and Monte Carlo Simulation

    SciTech Connect

    Zhang, Y; Yang, J; Liu, H; Liu, D

    2014-06-01

    Purpose: The purpose of this work is to compare the verification results of three solutions (2D/3D ionization chamber arrays measurement and Monte Carlo simulation), the results will help make a clinical decision as how to do our cervical IMRT verification. Methods: Seven cervical cases were planned with Pinnacle 8.0m to meet the clinical acceptance criteria. The plans were recalculated in the Matrixx and Delta4 phantom with the accurate plans parameters. The plans were also recalculated by Monte Carlo using leaf sequences and MUs for individual plans of every patient, Matrixx and Delta4 phantom. All plans of Matrixx and Delta4 phantom were delivered and measured. The dose distribution of iso slice, dose profiles, gamma maps of every beam were used to evaluate the agreement. Dose-volume histograms were also compared. Results: The dose distribution of iso slice and dose profiles from Pinnacle calculation were in agreement with the Monte Carlo simulation, Matrixx and Delta4 measurement. A 95.2%/91.3% gamma pass ratio was obtained between the Matrixx/Delta4 measurement and Pinnacle distributions within 3mm/3% gamma criteria. A 96.4%/95.6% gamma pass ratio was obtained between the Matrixx/Delta4 measurement and Monte Carlo simulation within 2mm/2% gamma criteria, almost 100% gamma pass ratio within 3mm/3% gamma criteria. The DVH plot have slightly differences between Pinnacle and Delta4 measurement as well as Pinnacle and Monte Carlo simulation, but have excellent agreement between Delta4 measurement and Monte Carlo simulation. Conclusion: It was shown that Matrixx/Delta4 and Monte Carlo simulation can be used very efficiently to verify cervical IMRT delivery. In terms of Gamma value the pass ratio of Matrixx was little higher, however, Delta4 showed more problem fields. The primary advantage of Delta4 is the fact it can measure true 3D dosimetry while Monte Carlo can simulate in patients CT images but not in phantom.

  4. 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

  5. Technical Note: A direct ray-tracing method to compute integral depth dose in pencil beam proton radiography with a multilayer ionization chamber.

    PubMed

    Farace, Paolo; Righetto, Roberto; Deffet, Sylvain; Meijers, Arturs; Vander Stappen, Francois

    2016-12-01

    To introduce a fast ray-tracing algorithm in pencil proton radiography (PR) with a multilayer ionization chamber (MLIC) for in vivo range error mapping. Pencil beam PR was obtained by delivering spots uniformly positioned in a square (45 × 45 mm(2) field-of-view) of 9 × 9 spots capable of crossing the phantoms (210 MeV). The exit beam was collected by a MLIC to sample the integral depth dose (IDDMLIC). PRs of an electron-density and of a head phantom were acquired by moving the couch to obtain multiple 45 × 45 mm(2) frames. To map the corresponding range errors, the two-dimensional set of IDDMLIC was compared with (i) the integral depth dose computed by the treatment planning system (TPS) by both analytic (IDDTPS) and Monte Carlo (IDDMC) algorithms in a volume of water simulating the MLIC at the CT, and (ii) the integral depth dose directly computed by a simple ray-tracing algorithm (IDDdirect) through the same CT data. The exact spatial position of the spot pattern was numerically adjusted testing different in-plane positions and selecting the one that minimized the range differences between IDDdirect and IDDMLIC. Range error mapping was feasible by both the TPS and the ray-tracing methods, but very sensitive to even small misalignments. In homogeneous regions, the range errors computed by the direct ray-tracing algorithm matched the results obtained by both the analytic and the Monte Carlo algorithms. In both phantoms, lateral heterogeneities were better modeled by the ray-tracing and the Monte Carlo algorithms than by the analytic TPS computation. Accordingly, when the pencil beam crossed lateral heterogeneities, the range errors mapped by the direct algorithm matched better the Monte Carlo maps than those obtained by the analytic algorithm. Finally, the simplicity of the ray-tracing algorithm allowed to implement a prototype procedure for automated spatial alignment. The ray-tracing algorithm can reliably replace the TPS method in MLIC PR for in vivo range

  6. Development of D+3He Fusion Electric Thrusters and Power Supplies for Space

    NASA Astrophysics Data System (ADS)

    Morse, Thomas M.

    1994-07-01

    Development of D+3He Fusion Electric Thrusters (FET) and Power Supplies (FPS) should occur at a lunar base because of the following: availability of helium-3, a vacuum better than on Earth, low K in shade reachable by radiant cooling, supply of ``high temp'' superconducting ceramic-metals, and a low G environment. The early FET will be much smaller than an Apollo engine, with specific impulse of 10,000-100,000-s. Solar power and low G will aid early development. To counter the effect of low G on humans, centrifuges will be employed for sleeping and resting. Work will be done by telerobotic view control. The FPS will be of comparable size, and will generate power mainly by having replaceable rectennas, resonant to the fusion synchrotron radiation. FPSs are used for house keeping power and initiating superconduction. Spaceships will carry up to ten FETs and two FPSs. In addition to fusion fuel, the FET will inject H or Li low mass propellant into the fusion chamber. Developing an FET would be difficult on Earth. FET spaceships will park between missions in L1, and an FET Bus will fetch humans/supplies from Moon and Earth. Someday FETs, with rocket assist, will lift spaceships from Earth, and make space travel to planets far cheaper, faster, and safer, than at present. Too long a delay due to the space station, or the huge cost of getting into space by current means, will damage the morale of the space program.

  7. Ionization detection system for aerosols

    DOEpatents

    Jacobs, Martin E.

    1977-01-01

    This invention relates to an improved smoke-detection system of the ionization-chamber type. In the preferred embodiment, the system utilizes a conventional detector head comprising a measuring ionization chamber, a reference ionization chamber, and a normally non-conductive gas triode for discharging when a threshold concentration of airborne particulates is present in the measuring chamber. The improved system utilizes a measuring ionization chamber which is modified to minimize false alarms and reductions in sensitivity resulting from changes in ambient temperature. In the preferred form of the modification, an annular radiation shield is mounted about the usual radiation source provided to effect ionization in the measuring chamber. The shield is supported by a bimetallic strip which flexes in response to changes in ambient temperature, moving the shield relative to the source so as to vary the radiative area of the source in a manner offsetting temperature-induced variations in the sensitivity of the chamber.

  8. SU-E-T-552: Monte Carlo Calculation of Correction Factors for a Free-Air Ionization Chamber in Support of a National Air-Kerma Standard for Electronic Brachytherapy

    SciTech Connect

    Mille, M; Bergstrom, P

    2015-06-15

    Purpose: To use Monte Carlo radiation transport methods to calculate correction factors for a free-air ionization chamber in support of a national air-kerma standard for low-energy, miniature x-ray sources used for electronic brachytherapy (eBx). Methods: The NIST is establishing a calibration service for well-type ionization chambers used to characterize the strength of eBx sources prior to clinical use. The calibration approach involves establishing the well-chamber’s response to an eBx source whose air-kerma rate at a 50 cm distance is determined through a primary measurement performed using the Lamperti free-air ionization chamber. However, the free-air chamber measurements of charge or current can only be related to the reference air-kerma standard after applying several corrections, some of which are best determined via Monte Carlo simulation. To this end, a detailed geometric model of the Lamperti chamber was developed in the EGSnrc code based on the engineering drawings of the instrument. The egs-fac user code in EGSnrc was then used to calculate energy-dependent correction factors which account for missing or undesired ionization arising from effects such as: (1) attenuation and scatter of the x-rays in air; (2) primary electrons escaping the charge collection region; (3) lack of charged particle equilibrium; (4) atomic fluorescence and bremsstrahlung radiation. Results: Energy-dependent correction factors were calculated assuming a monoenergetic point source with the photon energy ranging from 2 keV to 60 keV in 2 keV increments. Sufficient photon histories were simulated so that the Monte Carlo statistical uncertainty of the correction factors was less than 0.01%. The correction factors for a specific eBx source will be determined by integrating these tabulated results over its measured x-ray spectrum. Conclusion: The correction factors calculated in this work are important for establishing a national standard for eBx which will help ensure that dose

  9. VizieR Online Data Catalog: Cross sections produced by 3He reactions (Murphy+,

    NASA Astrophysics Data System (ADS)

    Murphy, R. J.; Kozlovsky, B.; Share, G. H.

    2017-05-01

    The 3He abundance in impulsive solar energetic particle (SEP) is enhanced up to several orders of magnitude compared to its photospheric value of [3He]/[4He] = 1-3 x 10-4. Interplanetary magnetic field and timing observations suggest that these events are related to solar flares. Observations of 3He in flare-accelerated ions would clarify the relationship between these two phenomena. Energetic 3He interactions in the solar atmosphere produce gamma-ray nuclear-deexcitation lines, both lines that are also produced by protons and α particles and lines that are essentially unique to 3He. Gamma-ray spectroscopy can, therefore, reveal enhanced levels of accelerated 3He. In this paper, we identify all significant deexcitation lines produced by 3He interactions in the solar atmosphere. We evaluate their production cross sections and incorporate them into our nuclear deexcitation-line code. We find that enhanced 3He can affect the entire gamma-ray spectrum. We identify gamma-ray line features for which the yield ratios depend dramatically on the 3He abundance. We determine the accelerated 3He/α ratio by comparing these ratios with flux ratios measured previously from the gamma-ray spectrum obtained by summing the 19 strongest flares observed with the Solar Maximum Mission Gamma-Ray Spectrometer. All six flux ratios investigated show enhanced 3He, confirming earlier suggestions. The 3He/α weighted mean of these new measurements ranges from 0.05 to 0.3 (depending on the assumed accelerated α/proton ratio) and has a <1 x 10-3 probability of being consistent with the photospheric value. With the improved code, we can now exploit the full potential of gamma-ray spectroscopy to establish the relationship between flare-accelerated ions and 3He-rich SEPs. (3 data files).

  10. A possible in situ 3H and 3He source in Earth's interior: an alternative explanation of origin of 3He in deep Earth.

    PubMed

    Jiang, Songsheng; Liu, Jing; He, Ming

    2010-07-01

    Origin of (3)He in the Earth is a mystery. Lacking a production mechanism, scientists assume (3)He was trapped in the Earth, when the Earth was formed. In contrast to this assumption, we have found (3)He and (3)H concentrations in excess of the atmospheric values in the deep waters of the volcanic Lakes Pavin (France), Laacher (Germany) and Nemrut (Turkey). This paper reports the result of finding (3)H in these three volcanic lakes that appear to originate from the mantle. Because (3)H has a half-life of 12.3 years, this (3)H and the resulting (3)He must have formed recently in the mantle and not be part of a primordial reservoir. The nuclear reactions that generate tritium might be a source of "missing" energy in the interior of the Earth.

  11. A possible in situ 3H and 3He source in Earth's interior: an alternative explanation of origin of 3He in deep Earth

    NASA Astrophysics Data System (ADS)

    Jiang, Songsheng; Liu, Jing; He, Ming

    2010-07-01

    Origin of 3He in the Earth is a mystery. Lacking a production mechanism, scientists assume 3He was trapped in the Earth, when the Earth was formed. In contrast to this assumption, we have found 3He and 3H concentrations in excess of the atmospheric values in the deep waters of the volcanic Lakes Pavin (France), Laacher (Germany) and Nemrut (Turkey). This paper reports the result of finding 3H in these three volcanic lakes that appear to originate from the mantle. Because 3H has a half-life of 12.3 years, this 3H and the resulting 3He must have formed recently in the mantle and not be part of a primordial reservoir. The nuclear reactions that generate tritium might be a source of “missing” energy in the interior of the Earth.

  12. Near threshold two meson production with the pd→3Heπ+π- and pd→3HeK+K- reactions

    NASA Astrophysics Data System (ADS)

    Bellemann, F.; Berg, A.; Bisplinghoff, J.; Bohlscheid, G.; Ernst, J.; Henrich, C.; Hinterberger, F.; Ibald, R.; Jahn, R.; Jarczyk, L.; Joosten, R.; Kozela, A.; Machner, H.; Magiera, A.; Maschuw, R.; Mayer-Kuckuk, T.; Mertler, G.; Munkel, J.; von Neumann-Cosel, P.; Rosendaal, D.; von Rossen, P.; Schnitker, H.; Scho, K.; Smyrski, J.; Strzalkowski, A.; Tölle, R.; Wilkin, C.

    2000-06-01

    Near threshold two meson production via the reactions pd→3Heπ+π- and pd→3HeK+K- was measured kinematically complete with the MOMO experiment at COSY. The obtained two pion invariant mass spectra and angular distributions depict a remarkable deviation from phase space. The two kaon data are consistent with phase space topped by a clear signal of the φ meson.

  13. Thermodynamic properties of liquid 3He- 4He mixtures at zero pressure for temperatures below 250 mK and 3He concentrations below 8%

    NASA Astrophysics Data System (ADS)

    Kuerten, J. G. M.; Castelijns, C. A. M.; de Waele, A. T. A. M.; Gijsman, H. M.

    We calculated the thermodynamic quantities of dilute liquid 3He- 4He mixtures, starting from experimental values of the specific heat and the osmotic pressure. The calculations are confined to temperatures below 250 mK and 3He concentrations below 8% at zero pressure. Some results are especially useful for dilution refrigeration. Contrary to the calculations previously performed by Radebaugh, our results are in good agreement with the experimental date on both the osmotic pressure and the osmotic enthalpy.

  14. A 3He Cryostat for Scientific Measurements in Pulsed High Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Wang, Shaoliang; Li, Liang; Liu, Mengyu; Zuo, Huakun; Peng, Tao

    A top loading 3He cryostat has been developed for scientific experiments with a 60 T pulsed magnetic field facility at Wuhan National High Magnetic Field Center. The cryostat consists of a 4He bath cryostat, a 3He insert and a closed circulation system for 3He gas handling. To eliminate the eddy current heating during the pulse, the tail of the 3He insert with a vacuum space at the bottom is made from fiberglass tubing coated with epoxy. The 3He bath is separated from the 4He bath with the vacuum space. The 4He bath cryostat provides cooling power to condense 3He gas by a neck tube on top of the tail. Experimental results have shown that the sample can be cooled down to 385 mK and kept cold for more than 150 second by one-shot cooling, which is sufficiently long for an experiment in a pulsed high magnetic field.

  15. Effect of ^3He impurity on the supersolid transition of ^4He

    NASA Astrophysics Data System (ADS)

    Kim, E.; Xia, J. S.; West, J. T.; Lin, X.; Chan, M. H. W.

    2007-03-01

    The supersolid phase of ^4He was reported by a series of torsional oscillator experiments [1]. One of the most striking features of the supersolid transition is the intriguing ^3He impurity effect. The addition of an extremely small amount of ^3He impurity broadens the transition and enhances the transition temperature Tc. This effect is very different from that in helium film and that in `bulk' superfluid helium. We have studied the influence of ^3He impurity on the supersolid transition systematically by progressively diluting isotopically-pure ^4He (^3He impurity less than 2ppb) with ^3He. The transition temperature is monotonically enhanced with increasing ^3He concentration and the supersolid fraction shows a broad maximum around 0.2 ppm. [1] E. Kim and M. H. W. Chan, Science 305, 1941 (2004); Nature 425, 227 (2004); J. Low Temp. Phys. 138, 859 (2005); Phys. Rev. Lett. 97, 115302 (2006).

  16. 3He immersion cell for ultralow temperature study of amorphous solids

    NASA Astrophysics Data System (ADS)

    Rogge, Sven; Natelson, Douglas; Osheroff, D. D.

    1997-04-01

    We have constructed a 3He immersion cell for dielectric measurements of insulating amorphous solids in a nuclear demagnetization cryostat at temperatures between 500 μK and 150 mK. The samples are directly immersed in 3He with two heat exchangers per electrode which are thermally isolated from each other and have a very low capacitance to ground. The cell incorporates a 195Pt pulsed NMR thermometer with a novel superconducting magnet and a 3He viscometer for calibration.

  17. SU-E-T-225: Correction Matrix for PinPoint Ionization Chamber for Dosimetric Measurements in the Newly Released Incise™ Multileaf Collimator Shaped Small Field for CyberKnife M6™ Machine

    SciTech Connect

    Zhang, Y; Li, T; Heron, D; Huq, M

    2015-06-15

    Purpose: For small field dosimetry, such as measurements of output factors for cones or MLC-shaped irregular small fields, ion chambers often Result in an underestimation of the dose, due to both the volume averaging effect and the lack of lateral charged particle equilibrium. This work presents a mathematical model for correction matrix for a PTW PinPoint ionization chamber for dosimetric measurements made in the newly released Incise™ Multileaf collimator fields of the CyberKnife M6™ machine. Methods: A correction matrix for a PTW 0.015cc PinPoint ionization chamber was developed by modeling its 3D dose response in twelve cone-shaped circular fields created using the 5mm, 7.5mm, 10mm, 12.5mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 50mm, 60mm cones in a CyberKnife M6™ machine. For each field size, hundreds of readings were recorded for every 2mm chamber shift in the horizontal plane. The contribution of each dose pixel to a measurement point depended on the radial distance and the angle to the chamber axis. These readings were then compared with the theoretical dose as obtained with Monte Carlo calculation. A penalized least-square optimization algorithm was developed to generate the correction matrix. After the parameter fitting, the mathematical model was validated for MLC-shaped irregular fields. Results: The optimization algorithm used for parameter fitting was stable and the resulted response factors were smooth in spatial domain. After correction with the mathematical model, the chamber reading matched with the calculation for all the tested fields to within 2%. Conclusion: A novel mathematical model has been developed for PinPoint chamber for dosimetric measurements in small MLC-shaped irregular fields. The correction matrix is dependent on detector, treatment unit and the geometry of setup. The model can be applied to non-standard composite fields and provides an access to IMRT point dose validation.

  18. Transport in very dilute solutions of 3He in superfluid 4He

    NASA Astrophysics Data System (ADS)

    Baym, Gordon; Beck, D. H.; Pethick, C. J.

    2013-07-01

    Motivated by a proposed experimental search for the electric dipole moment of the neutron (nEDM) utilizing neutron-3He capture in a dilute solution of 3He in superfluid 4He, we derive the transport properties of dilute solutions in the regime where the 3He are classically distributed and rapid 3He-3He scatterings keep the 3He in equilibrium. Our microscopic framework takes into account phonon-phonon, phonon-3He, and 3He-3He scatterings. We then apply these calculations to measurements by Rosenbaum [J. Low Temp. Phys.JLTPAC0022-229110.1007/BF00655864 16, 131 (1974)] and by Lamoreaux [Europhys. Lett.EULEEJ0295-507510.1209/epl/i2002-00408-4 58, 718 (2002)] of dilute solutions in the presence of a heat flow. We find satisfactory agreement of theory with the data, serving to confirm our understanding of the microscopics of the helium in the future nEDM experiment.

  19. (3)He-MRI in follow-up of lung transplant recipients.

    PubMed

    Gast, Klaus Kurt; Zaporozhan, Julia; Ley, Sebastian; Biedermann, Alexander; Knitz, Frank; Eberle, Balthasar; Schmiedeskamp, Joerg; Heussel, Claus-Peter; Mayer, Eckhard; Schreiber, Wolfgang Günter; Thelen, Manfred; Kauczor, Hans-Ulrich

    2004-01-01

    The aim of this study was to evaluate the possible contribution of (3)He-MRI to detect obliterative bronchiolitis (OB) in the follow-up of lung transplant recipients. Nine single- and double-lung transplanted patients were studied by an initial and a follow-up (3)He-MRI study. Images were evaluated subjectively by estimation of ventilation defect area and quantitatively by individually adapted threshold segmentation and subsequent calculation of ventilated lung volume. Bronchiolitis obliterans syndrome (BOS) was diagnosed using pulmonary function tests. At (3)He-MRI, OB was suspected if ventilated lung volume had decreased by 10% or more at the follow-up MRI study compared with the initial study. General accordance between pulmonary function testing and (3)He-MRI was good, although subjective evaluation of (3)He-MRI underestimated improvement in ventilation as obtained by pulmonary function tests. The (3)He-MRI indicated OB in 6 cases. According to pulmonary function tests, BOS was diagnosed in 5 cases. All diagnoses of BOS were also detected by (3)He-MRI. In 2 of these 5 cases, (3)He-MRI indicated OB earlier than pulmonary function tests. The results support the hypothesis that (3)He-MRI may be sensitive for early detection of OB and emphasize the need for larger prospective follow-up studies.

  20. Cluster folding model analysis of 3He elastic and inelastic scattering from 12C

    NASA Astrophysics Data System (ADS)

    Khallaf, S. A. E.; Nossair, A. M. A.; Ebrahim, A. A.; Ebraheem, Awad A.

    2003-02-01

    Angular distributions of differential cross sections for the 12C( 3He, 3He) 12C, 12C( 3He, 3He) 12C ∗ reactions at E=72 MeV have been analyzed with a double folding cluster model DFC based on five sets of the effective N-N interaction of Gaussian form with different parameters. The transition to the (2 +; 4.44 MeV) state in 12C is studied and the deformation length δ2 is extracted. It is found that the extracted deformation length is sensitive to the nuclear model used and it is similar to the corresponding value found in the literature.

  1. Ion Implantation of 3He in Tantalum for Use in a Low Energy Deuteron Polarization Analyzer

    DTIC Science & Technology

    1994-01-01

    depends on aAzz2 where a and A are the cross section and analyzing power, respectively. The cross section of the 3He ( d ,p) reaction below 978 keV appears...protons from the 3He ( d ,p) 4He reaction would be more visible. The statistics were poor, but a definite implant in all the targets on the order of 1017 3He ...accelerator and a polarimeter using the 3He ( d ,p)4 He reaction . (Figure 8) During the experiment Pzz was measured at the beginning, and twice during the tests

  2. The influence of restricted geometry of diamagnetic nanoporous media on 3He relaxation

    NASA Astrophysics Data System (ADS)

    Alakshin, E. M.; Gazizulin, R. R.; Zakharov, M. Yu.; Klochkov, A. V.; Morozov, E. V.; Salikhov, T. M.; Safin, T. R.; Safiullin, K. R.; Tagirov, M. S.; Shabanova, O. B.

    2015-01-01

    This is an experimental study of the spin kinetics of 3He in contact with diamagnetic samples of inverse opals SiO2, and LaF3 nanopowder. It is demonstrated that the nuclear magnetic relaxation of the absorbed 3He occurs due to the modulation of dipole-dipole interaction by the quantum motion in the two-dimensional film. It is found that the relaxation of liquid 3He occurs through a spin diffusion to the absorption layer, and that the restricted geometry of diamagnetic nanoporous media has an influence on the 3He relaxation.

  3. 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.

  4. Practical method for determination of air kerma by use of an ionization chamber toward construction of a secondary X-ray field to be used in clinical examination rooms.

    PubMed

    Maehata, Itsumi; Hayashi, Hiroaki; Kimoto, Natsumi; Takegami, Kazuki; Okino, Hiroki; Kanazawa, Yuki; Tominaga, Masahide

    2016-07-01

    We propose a new practical method for the construction of an accurate secondary X-ray field using medical diagnostic X-ray equipment. For accurate measurement of the air kerma of an X-ray field, it is important to reduce and evaluate the contamination rate of scattered X-rays. To determine the rate quantitatively, we performed the following studies. First, we developed a shield box in which an ionization chamber could be set at an inner of the box to prevent detection of the X-rays scattered from the air. In addition, we made collimator plates which were placed near the X-ray source for estimation of the contamination rate by scattered X-rays from the movable diaphragm which is a component of the X-ray equipment. Then, we measured the exposure dose while changing the collimator plates, which had diameters of 25-90 mm(ϕ). The ideal value of the exposure dose was derived mathematically by extrapolation to 0 mm(ϕ). Tube voltages ranged from 40 to 130 kV. Under these irradiation conditions, we analyzed the contamination rate by the scattered X-rays. We found that the contamination rates were less than 1.7 and 2.3 %, caused by air and the movable diaphragm, respectively. The extrapolated value of the exposure dose has been determined to have an uncertainty of 0.7 %. The ionization chamber used in this study was calibrated with an accuracy of 5 %. Using this kind of ionization chamber, we can construct a secondary X-ray field with an uncertainty of 5 %.

  5. Calculation of reactivities using ionization chamber currents with different sets of kinetic parameters for reduced scram system efficiency in the VVER-1000 of the third unit of the Kalinin nuclear power plant at the stage of physical start-up

    SciTech Connect

    Zizin, M. N.; Zizina, S. N.; Kryakvin, L. V.; Pitilimov, V. A.; Tereshonok, V. A.

    2011-12-15

    The effectiveness of the VVER-1000 reactor scram system is analyzed using ionization chamber currents with different sets of kinetic parameters with allowance for the isotopic composition in the calculation of these parameters. The most 'correct, aesthetically acceptable' results are obtained using the eight-group constants of the ROSFOND (BNAB-RF) library. The difference between the maximum and minimum values of the scram system effectiveness calculated with different sets of kinetic parameters slightly exceeds 2{beta}. The problems of introducing corrections due to spatial effects are not considered in this study.

  6. SU‐C‐105‐05: Reference Dosimetry of High‐Energy Electron Beams with a Farmer‐Type Ionization Chamber

    SciTech Connect

    Muir, B; Rogers, D

    2013-06-15

    Purpose: To investigate gradient effects and provide Monte Carlo calculated beam quality conversion factors to characterize the Farmer‐type NE2571 ion chamber for high‐energy reference dosimetry of clinical electron beams. Methods: The EGSnrc code system is used to calculate the absorbed dose to water and to the gas in a fully modeled NE2571 chamber as a function of depth in a water phantom. Electron beams incident on the surface of the phantom are modeled using realistic BEAMnrc accelerator simulations and electron beam spectra. Beam quality conversion factors are determined using calculated doses to water and to air in the chamber in high‐energy electron beams and in a cobalt‐60 reference field. Calculated water‐to‐air stopping power ratios are employed for investigation of the overall ion chamber perturbation factor. Results: An upstream shift of 0.3–0.4 multiplied by the chamber radius, r-cav, both minimizes the variation of the overall ion chamber perturbation factor with depth and reduces the difference between the beam quality specifier (R{sub 5} {sub 0}) calculated using ion chamber simulations and that obtained with simulations of dose‐to‐water in the phantom. Beam quality conversion factors are obtained at the reference depth and gradient effects are optimized using a shift of 0.2r-cav. The photon‐electron conversion factor, k-ecal, amounts to 0.906 when gradient effects are minimized using the shift established here and 0.903 if no shift of the data is used. Systematic uncertainties in beam quality conversion factors are investigated and amount to between 0.4 to 1.1% depending on assumptions used. Conclusion: The calculations obtained in this work characterize the use of an NE2571 ion chamber for reference dosimetry of high‐energy electron beams. These results will be useful as the AAPM continues to review their reference dosimetry protocols.

  7. Temperature Measurements of Fusion Plasmas Produced by Laser-Irradiated D2-3 He or CD4-3 He Clustering Gases

    NASA Astrophysics Data System (ADS)

    Bang, W.; Ditmire, T.; Quevedo, H.; Dyer, G.; Bernstein, A. C.; Donovan, M.; Gaul, E.; Barbui, M.; Bonasera, A.; Hagel, K.; Natowitz, J. B.

    2014-10-01

    We report on experiments in which a mixture of D2 or CD4 clusters and 3He gas was irradiated by a petawatt-laser pulse, generating nuclear fusion reactions such as D(d, 3He) n, D(d, t) p , and 3He(d, p)4He. We measured the yields of fusion neutrons and protons from these reactions and found them to agree with yields based on a simple cylindrical plasma model. The plasma temperature was determined by two different methods. In the first, it was derived from time-of-flight data of deuterium ions ejected from exploding D2 or CD4 clusters. In the second, it was measured from the ratio of neutron yield to proton yield from D(d, 3He) n and 3He(d, p)4He reactions, respectively. The temperatures determined by these two methods agree well, indicating (i) the ion energy distribution is not significantly distorted when ions travel in the disassembling plasma; (ii) the kinetic energy of deuterium ions, especially the hottest part responsible for nuclear fusion, is well described by a near-Maxwellian distribution.

  8. Type 3 solar radio bursts and 3HE-rich events

    NASA Technical Reports Server (NTRS)

    Reames, D. V.; Stone, R. G.

    1985-01-01

    The kilometric radio data for 3He-rich events during the 1979 to 82 time period were investigated. Type 3 bursts are present for each event as expected from the prevous electron 3He-event association. A list of identified solar events is presented.

  9. Fusion product studies via fast ion D-D and D-3He fusion on JET

    NASA Astrophysics Data System (ADS)

    Sharapov, S. E.; Hellsten, T.; Kiptily, V. G.; Craciunescu, T.; Eriksson, J.; Fitzgerald, M.; Girardo, J.-B.; Goloborod'ko, V.; Hellesen, C.; Hjalmarsson, A.; Johnson, T.; Kazakov, Y.; Koskela, T.; Mantsinen, M.; Monakhov, I.; Nabais, F.; Nocente, M.; Perez von Thun, C.; Rimini, F.; Santala, M.; Schneider, M.; Tardocchi, M.; Tsalas, M.; Yavorskij, V.; Zoita, V.; Contributors, JET

    2016-11-01

    Dedicated fast ion D-D and D-3He fusion experiments were performed on JET with carbon wall (2008) and ITER-like wall (2014) for testing the upgraded neutron and energetic ion diagnostics of fusion products. Energy spectrum of D-D neutrons was the focus of the studies in pure deuterium plasmas. A significant broadening of the energy spectrum of neutrons born in D-D fast fusion was observed, and dependence of the maximum D and D-D neutron energies on plasma density was established. Diagnostics of charged products of aneutronic D-3He fusion reactions, 3.7 MeV alpha-particles similar to those in D-T fusion, and 14.6 MeV protons, were the focus of the studies in D-3He plasmas. Measurements of 16.4 MeV gamma-rays born in the weak secondary branch of D(3He, γ)5Li reaction were used for assessing D-3He fusion power. For achieving high yield of D-D and D-3He reactions at relatively low levels of input heating power, an acceleration of D beam up to the MeV energy range was used employing 3rd harmonic (f=3{{f}CD} ) ICRH technique. These results were compared to the techniques of D beam injection into D-3He mixture, and 3He-minority ICRH in D plasmas.

  10. Measurement of fast minority /sub 3/He/sup + +/ energy distribution during ICRF heating

    DOEpatents

    Post, D.E. Jr.; Grisham, L.R.; Medley, S.S.

    A method and means for measuring the fast /sub 3/He/sup + +/ distribution during /sub 3/He/sup + +/ minority Ion Cyclotron Resonance Frequency (ICRF) heating is disclosed. The present invention involves the use of 10 to 100 keV beams of neutral helium atoms to neutralize the fast /sub 3/He/sup + +/ ions in a heated plasma by double charge exchange (/sub 3/He/sup + +/ + /sub 4/He/sup 0/ ..-->.. /sub 3/He/sup 0/ + /sub 4/He/sup + +/). The neutralized fast /sub 3/He/sup 0/ atoms then escape from the hot plasma confined by a magnetic field and are detected by conventional neutral particle analyzing means. This technique permits the effectiveness of the coupling of the ion cyclotron waves to the /sub 3/He/sup + +/ minority ions to be accurately measured. The present invention is particularly adapted for use in evaluating the effectiveness of the intermediate coupling between the RF heating and the /sub 3/He/sup + +/ in an energetic toroidal plasma.

  11. On the connection between the 3HE-enrichment and spectral index of solar energetic particles

    NASA Technical Reports Server (NTRS)

    Kocharov, L. G.; Dvoryanchikov, Y. V.

    1985-01-01

    A model is presented which explains the observed tendency of events with large 3He/4He ratios to have steeper spectra. In this model preferential injection of 3He, acceleration by Alfven waves and Coulomb deceleration of ions are considered simultaneously. The observed tendency may be obtained as a result of competition between injection and acceleration processes.

  12. 4 He adsorption on a 3He-plated graphite surface

    NASA Astrophysics Data System (ADS)

    Kwon, Yongkyung; Ahn, Jeonghwan

    Path-integral Monte Carlo (PIMC) calculations have been performed for 4He atoms on top of the 3He first layer on graphite. For this we ignore Fermi statistics of solidified 3He adatoms while Bose statistics of 4He atoms are fully incorporated. We first find that the first 3He layer exhibits a 7/12 commensurate solid structure at the areal density of 0.111 Å-2, which turns out to be identical to the experimental value for its completion density. Additional adsorption of 4He atoms above the complete first 3He layer is found to sustain the underlying 3He commensurate structure and the second 4He layer is observed to display the 4/7 commensurate structure with respect to the first-layer commensurate 3He solid at the areal density of 0.0636 Å-2. Furthermore, it is found that the 4/7 commensurate structure of the second-layer 4He atoms can be formed above a mixture of the first-layer 3He and 4He atoms on graphite. These PIMC results suggest that the 4/7 commensurate structure of the second-layer 4He atoms on graphite, whose existence on top of the first 4He layer has long been in dispute, may be realized on a 3He-plated graphite surface. This could lead to a new approach to observe two-dimensional supersolidity in 4He on graphite.

  13. Surface Specific Heat of {sup 3}He and Andreev Bound States

    SciTech Connect

    Choi, H.; Davis, J. P.; Pollanen, J.; Halperin, W.P.

    2006-03-31

    High resolution measurements of the specific heat of liquid {sup 3}He in the presence of a silver surface have been performed at temperatures near the superfluid transition in the pressure range of 1-29 bar. The surface contribution to the heat capacity is identified with Andreev bound states of {sup 3}He quasiparticles that have a range of half a coherence length.

  14. Nuclear georeactor origin of oceanic basalt 3He/4He, evidence, and implications

    PubMed Central

    Herndon, J. Marvin

    2003-01-01

    Nuclear georeactor numerical simulation results yield substantial 3He and 4He production and 3He/4He ratios relative to air (RA) that encompass the entire 2-SD (2σ) confidence level range of tabulated measured 3He/4He ratios of basalts from along the global spreading ridge system. Georeactor-produced 3He/4He ratios are related to the extent of actinide fuel consumption at time of production and are high near the end of the georeactor lifetime. Georeactor numerical simulation results and the observed high 3He/4He ratios measured in Icelandic and Hawaiian oceanic basalts indicate that the demise of the georeactor is approaching. Within the present level of uncertainty, one cannot say precisely when georeactor demise will occur, whether in the next century, in a million years, or in a billion years from now. PMID:12615991

  15. Variational calculations for ground state properties of liquid 3He injected in a carbon nanotube

    NASA Astrophysics Data System (ADS)

    Bordbar, G. H.; Rastkhadiv, M. A.

    2017-09-01

    Liquid 3He injected in a carbon nanotube is of high interests due to different behavior of the liquid helium in the quasi-one-dimensional systems. In this work, a variational approach has been performed to calculate some thermodynamic properties of this quantum system. In order to do so, a single-walled carbon nanotube containing liquid 3He is considered, applying the Lennard-Jones and Stan-Cole potentials for 3He-3He and 3He-C interactions, respectively. Finally the total energy, equation of state and incompressibility of the system have been calculated. Our calculations show the high values for the incompressibility at high densities, especially for high radii.

  16. Development of a polarized 3He neutron spin filter for POLANO at J-PARC

    NASA Astrophysics Data System (ADS)

    Ino, T.; Ohkawara, M.; Ohoyama, K.; Yokoo, T.; Itoh, S.; Nambu, Y.; Fujita, M.; Kira, H.; Hayashida, H.; Hiroi, K.; Sakai, K.; Oku, T.; Kakurai, K.

    2017-06-01

    We have developed a polarized 3He neutron spin filter (NSF) for a new polarized neutron spectrometer, POLANO, at the Japan Proton Accelerator Research Complex (J-PARC). POLANO aims to utilize high energy neutrons polarized by a 3He NSF and spin analyzed by an array of magnetic supermirrors for inelastic neutron scattering. The 3He gas is continuously polarized in-situ by spin-exchange optical pumping to provide a highly and stably polarized neutron beam. The POLANO 3He NSF is designed to polarize neutrons with energies as high as 200 meV and fit in a restricted space. It is equipped with adiabatic fast passage NMR that enables one to flip the 3He spins, and consequently, the neutron spins.

  17. Nuclear georeactor origin of oceanic basalt 3He/4He, evidence, and implications.

    PubMed

    Herndon, J Marvin

    2003-03-18

    Nuclear georeactor numerical simulation results yield substantial (3)He and (4)He production and (3)He(4)He ratios relative to air (R(A)) that encompass the entire 2-SD (2sigma) confidence level range of tabulated measured (3)He(4)He ratios of basalts from along the global spreading ridge system. Georeactor-produced (3)He(4)He ratios are related to the extent of actinide fuel consumption at time of production and are high near the end of the georeactor lifetime. Georeactor numerical simulation results and the observed high (3)He(4)He ratios measured in Icelandic and Hawaiian oceanic basalts indicate that the demise of the georeactor is approaching. Within the present level of uncertainty, one cannot say precisely when georeactor demise will occur, whether in the next century, in a million years, or in a billion years from now.

  18. Application of Sol-Gel Technology to High Pressure Polarized 3HE Nuclear Targets

    NASA Astrophysics Data System (ADS)

    Tobias, W. A.; Cates, G. D.; Chaput, J.; Deur, A.; Rohrbaugh, S.; Singh, J.

    2003-01-01

    High-purity sol-gel solutions have been developed to coat the interior surface of glass vessels used for polarizing 3He by spin-exchange optical pumping. Such cells have been shown to exhibit 3He longitudinal lifetimes T1 in excess of 350 hours1. The sol-gel technique was designed to minimize spin-relaxation due to wall collisions so that only dipole-dipole interactions between colliding 3He atoms dominate in the relaxation process. Until now, sol-gel technology had not been applied to high pressure 3He gas targets used in nuclear scattering experiments. A description of the sol-gel technique and recent developments on its integration into the production of 3He targets will be presented.

  19. T(T,4He)2n and 3He(3He,4He)2p Reactions and the Energy Dependence of Their Mechanisms

    NASA Astrophysics Data System (ADS)

    Bacher, Andrew; McNabb, Dennis; Brune, Carl; Sayre, Dan; Hale, Gerry; Frenje, Johan; Gatu Johnson, Maria

    2015-10-01

    We have studied the T(T,alpha)2n reaction because it is the charge symmetric analog to the 3He(3He,alpha)2p reaction which completes the most direct mode of the p-p chain in stellar interiors. These reactions lead to three-body final states whose energy spectrum shapes are dominated by the strong nucleon-alpha interaction and the weaker nucleon-nucleon interaction. These experiments were done at OMEGA at the University of Rochester and at the NIF at Lawrence Livermore Lab. We will focus on two features: (1) the excitation energy dependence of the reaction mechanism and (2) the center-of-mass energy dependence of the reaction mechanism. At stellar energies (OMEGA and the NIF) we find that the shape of the neutron spectrum peaks in the middle. The n-alpha 1/2-excited state is about two times stronger than the n-alpha 3/2-ground state. For the 3He+3He reaction (at CalTech), the proton spectrum peaks at the high end. The p-alpha 3/2-state is about two times stronger than the 1/2-state. This difference in the spectrum shape is explained by theoretical models which include the interference between the two identical fermions in the final state. At CalTech we have angular distributions of the 3He+3He reaction from 2 MeV to 18 MeV. We see the p-wave strength increasing.

  20. The Solar injection of ten electron/3He-rich SEP events

    NASA Astrophysics Data System (ADS)

    Wang, L.; Krucker, S.; Mason, G. M.; Li, G.

    2016-12-01

    We have derived the particle injections at the Sun for ten good electron/3He-rich solar energetic particle (SEP) events, using a 1.2 AU particle path length (suggested by analysis of the velocity dispersion). The inferred solar injections of high-energy ( 10 to 300 keV) electrons and of ˜MeV/nucleon ions (carbon and heavier) start with a delay of 17 ± 3 min and 75 ± 14 min, respectively, after the injection of low-energy ( 0.4 to 9 keV) electrons. The injection duration (averaged over energy) ranges from 200 to 550 min for ions, from 90 to 160 min for low-energy electrons, and from 10 to 30 min for high-energy electrons. Most of the selected events have no reported Hα flares or GOES SXR bursts, but all have type III radio bursts that typically start after the onset of a low-energy electron injection. All nine events with SOHO/LASCO coverage have a relatively fast (>570 km s-1), mostly narrow (< 30°), west-limb coronal mass ejection (CME) that launches near the start of the low-energy electron injection, and reaches an average altitude of 1.0 and 4.7 RS, respectively, at the start of the high-energy electron injection and of the ion injection. The electron energy spectra show a continuous power law extending across the transition from low to high energies, suggesting that the low-energy electron injection may provide seed electrons for the delayed high-energy electron acceleration. The delayed ion injections and high ionization states may suggest an ion acceleration along the lower altitude flanks, rather than at the nose of the CMEs.

  1. The injection of ten electron/3He-rich SEP events

    NASA Astrophysics Data System (ADS)

    Wang, Linghua; Krucker, Säm; Mason, Glenn; Li, Gang

    2017-04-01

    We have derived the particle injections at the Sun for ten good electron/3He-rich solar energetic particle (SEP) events, using a 1.2 AU particle path length (suggested by analysis of the velocity dispersion). The inferred solar injections of high-energy (˜10 to 300 keV) electrons and of ˜MeV/nucleon ions (carbon and heavier) start with a delay of 17±3 minutes and 75±14 minutes, respectively, after the injection of low-energy (˜0.4 to 9 keV) electrons. The injection duration (averaged over energy) ranges from ˜200 to 550 minutes for ions, from ˜90 to 160 minutes for low-energy electrons, and from ˜10 to 30 minutes for high-energy electrons. Most of the selected events have no reported Hα flares or GOES SXR bursts, but all have type III radio bursts that typically start after the onset of a low-energy electron injection. All nine events with SOHO/LASCO coverage have a relatively fast (>570km/s), mostly narrow (≲30°), west-limb coronal mass ejection (CME) that launches near the start of the low-energy electron injection, and reaches an average altitude of ˜1.0 and 4.7 RS, respectively, at the start of the high-energy electron injection and of the ion injection. The electron energy spectra show a continuous power law extending across the transition from low to high energies, suggesting that the low-energy electron injection may provide seed electrons for the delayed high-energy electron acceleration. The delayed ion injections and high ionization states may suggest an ion acceleration along the lower altitude flanks, rather than at the nose of the CMEs.

  2. The injection of ten electron/3He-rich SEP events

    NASA Astrophysics Data System (ADS)

    Wang, Linghua; Mason, Glenn; Krucker, Samuel; Li, Gang

    2016-07-01

    We have derived the particle injections at the Sun for ten good electron/ ^{3}He-rich solar energetic particle (SEP) events, using a 1.2 AU particle path length (suggested by analysis of the velocity dispersion). The inferred solar injections of high-energy (˜10 to 300 keV) electrons and of ˜MeV/nucleon ions (carbon and heavier) start with a delay of 17±3 minutes and 75±±14 minutes, respectively, after the injection of low-energy (˜0.4 to 9 keV) electrons. The injection duration (averaged over energy) ranges from ˜200 to 550 minutes for ions, from ˜90 to 160 minutes for low-energy electrons, and from ˜10 to 30 minutes for high-energy electrons. Most of the selected events have no reported H_{α} flares or GOES SXR bursts, but all have type III radio bursts that typically start after the onset of a low-energy electron injection. All nine events with SOHO/LASCO coverage have a relatively fast (>570km/s), mostly narrow (≲30°), west-limb coronal mass ejection (CME) that launches near the start of the low-energy electron injection, and reaches an average altitude of ˜1.0 and 4.7 R _{S} , respectively, at the start of the high-energy electron injection and of the ion injection. The electron energy spectra show a continuous power law extending across the transition from low to high energies, suggesting that the low-energy electron injection may provide seed electrons for the delayed high-energy electron acceleration. The delayed ion injections and high ionization states may suggest an ion acceleration along the lower altitude flanks, rather than at the nose of the CMEs.

  3. Interpretation of the Processes 3He(e,e'p)2H and 3He(e,e'p)(pn) at High Missing Momenta

    NASA Astrophysics Data System (ADS)

    Ciofi Degli Atti, C.; Kaptari, L. P.

    2005-07-01

    Using realistic three-body wave functions corresponding to the AV18 interaction, it is shown that the effects of the final state interaction in the exclusive processes 3He(e,e'p)2H and 3He(e,e'p)(pn), can be successfully treated in terms of a generalized eikonal approximation based upon the direct calculation of the Feynman diagrams describing the rescattering of the struck nucleon. The relevant role played by the double rescattering contribution at high values of the missing momentum is illustrated.

  4. Interpretation of the processes 3He(e,e'p)2H and 3He(e,e'p)(pn) at high missing momenta.

    PubMed

    Ciofi degli Atti, C; Kaptari, L P

    2005-07-29

    Using realistic three-body wave functions corresponding to the AV18 interaction, it is shown that the effects of the final state interaction in the exclusive processes 3He(e,e'p)2H and 3He(e,e'p)(pn), can be successfully treated in terms of a generalized eikonal approximation based upon the direct calculation of the Feynman diagrams describing the rescattering of the struck nucleon. The relevant role played by the double rescattering contributio