Organ doses from radionuclides on the ground. Part I. Simple time dependences

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacob, P.; Paretzke, H.G.; Rosenbaum, H.

1988-06-01

Organ dose equivalents of mathematical, anthropomorphical phantoms ADAM and EVA for photon exposures from plane sources on the ground have been calculated by Monte Carlo photon transport codes and tabulated in this article. The calculation takes into account the air-ground interface and a typical surface roughness, the energy and angular dependence of the photon fluence impinging on the phantom and the time dependence of the contributions from daughter nuclides. Results are up to 35% higher than data reported in the literature for important radionuclides. This manuscript deals with radionuclides, for which the time dependence of dose equivalent rates and dosemore » equivalents may be approximated by a simple exponential. A companion manuscript treats radionuclides with non-trivial time dependences.« less

Ionisation density effects following optical excitation in LiF:Mg, Ti (TLD-100).

PubMed

Weiss, D; Horowitz, Y; Oster, L

2007-01-01

The TL signal following 5 eV photon excitation of previously irradiated and readout material has been studied as a function of ionisation density and various experimental parameters: (i) maximum temperature of the first readout; (ii) photon fluence; (iii) photon energy and (iv) beta ray dose. Following alpha particle irradiation, the ratio of the second-readout to first-readout TL signal, epsilon(alpha,) has been found to be 10-20 times higher than that following beta irradiation, indicative of the possibility of using the double ratio epsilon(alpha)/epsilon(beta) as a mixed-field discriminator. The beginning of an attempt to explain this unusual effect is offered in the framework of the track structure theory and kinetic modelling of the beta ray dose-response of the first and second readouts.

Optical dosimetry probes to validate Monte Carlo and empirical-method-based NIR dose planning in the brain.

PubMed

Verleker, Akshay Prabhu; Shaffer, Michael; Fang, Qianqian; Choi, Mi-Ran; Clare, Susan; Stantz, Keith M

2016-12-01

A three-dimensional photon dosimetry in tissues is critical in designing optical therapeutic protocols to trigger light-activated drug release. The objective of this study is to investigate the feasibility of a Monte Carlo-based optical therapy planning software by developing dosimetry tools to characterize and cross-validate the local photon fluence in brain tissue, as part of a long-term strategy to quantify the effects of photoactivated drug release in brain tumors. An existing GPU-based 3D Monte Carlo (MC) code was modified to simulate near-infrared photon transport with differing laser beam profiles within phantoms of skull bone (B), white matter (WM), and gray matter (GM). A novel titanium-based optical dosimetry probe with isotropic acceptance was used to validate the local photon fluence, and an empirical model of photon transport was developed to significantly decrease execution time for clinical application. Comparisons between the MC and the dosimetry probe measurements were on an average 11.27%, 13.25%, and 11.81% along the illumination beam axis, and 9.4%, 12.06%, 8.91% perpendicular to the beam axis for WM, GM, and B phantoms, respectively. For a heterogeneous head phantom, the measured % errors were 17.71% and 18.04% along and perpendicular to beam axis. The empirical algorithm was validated by probe measurements and matched the MC results (R²0.99), with average % error of 10.1%, 45.2%, and 22.1% relative to probe measurements, and 22.6%, 35.8%, and 21.9% relative to the MC, for WM, GM, and B phantoms, respectively. The simulation time for the empirical model was 6 s versus 8 h for the GPU-based Monte Carlo for a head phantom simulation. These tools provide the capability to develop and optimize treatment plans for optimal release of pharmaceuticals in the treatment of cancer. Future work will test and validate these novel delivery and release mechanisms in vivo.

A Photosynthesis Lab. Response of Algal Suspensions to a Gradient of Photosynthetically Active Radiation (PAR).

ERIC Educational Resources Information Center

Zee, Delmar Vander

1995-01-01

This photosynthesis exercise is intended for introductory college biology or botany courses. It is based on the principle that a closed suspension of algal cells may be expected to produce more dissolved oxygen with a greater photon fluence rate, but within limits of the photosynthetic capacity of the system. Describes materials and methods. (LZ)

Developing a treatment planning process and software for improved translation of photodynamic therapy

NASA Astrophysics Data System (ADS)

Cassidy, J.; Zheng, Z.; Xu, Y.; Betz, V.; Lilge, L.

2017-04-01

Background: The majority of de novo cancers are diagnosed in low and middle-income countries, which often lack the resources to provide adequate therapeutic options. None or minimally invasive therapies such as Photodynamic Therapy (PDT) or photothermal therapies could become part of the overall treatment options in these countries. However, widespread acceptance is hindered by the current empirical training of surgeons in these optical techniques and a lack of easily usable treatment optimizing tools. Methods: Based on image processing programs, ITK-SNAP, and the publicly available FullMonte light propagation software, a work plan is proposed that allows for personalized PDT treatment planning. Starting with, contoured clinical CT or MRI images, the generation of 3D tetrahedral models in silico, execution of the Monte Carlo simulation and presentation of the 3D fluence rate, Φ, [mWcm-2] distribution a treatment plan optimizing photon source placement is developed. Results: Permitting 1-2 days for the installation of the required programs, novices can generate their first fluence, H [Jcm-2] or Φ distribution in a matter of hours. This is reduced to 10th of minutes with some training. Executing the photon simulation calculations is rapid and not the performance limiting process. Largest sources of errors are uncertainties in the contouring and unknown tissue optical properties. Conclusions: The presented FullMonte simulation is the fastest tetrahedral based photon propagation program and provides the basis for PDT treatment planning processes, enabling a faster proliferation of low cost, minimal invasive personalized cancer therapies.

Technical Note: On maximizing Cherenkov emissions from medical linear accelerators.

PubMed

Shrock, Zachary; Yoon, Suk W; Gunasingha, Rathnayaka; Oldham, Mark; Adamson, Justus

2018-04-19

Cherenkov light during MV radiotherapy has recently found imaging and therapeutic applications but is challenged by relatively low fluence. Our purpose is to investigate the feasibility of increasing Cherenkov light production during MV radiotherapy by increasing photon energy and applying specialized beam-hardening filtration. GAMOS 5.0.0, a GEANT4-based framework for Monte Carlo simulations, was used to model standard clinical linear accelerator primary photon beams. The photon source was incident upon a 17.8 cm 3 cubic water phantom with a 94 cm source to surface distance. Dose and Cherenkov production was determined at depths of 3-9 cm. Filtration was simulated 15 cm below the photon beam source. Filter materials included aluminum, iron, and copper with thicknesses of 2-20 cm. Histories used depended on the level of attenuation from the filter, ranging from 100 million to 2 billion. Comparing average dose per history also allowed for evaluation of dose-rate reduction for different filters. Overall, increasing photon beam energy is more effective at improving Cherenkov production per unit dose than is filtration, with a standard 18 MV beam yielding 3.3-4.0× more photons than 6 MV. Introducing an aluminum filter into an unfiltered 2400 cGy/min 10 MV beam increases the Cherenkov production by 1.6-1.7×, while maintaining a clinical dose rate of 300 cGy/min, compared to increases of ~1.5× for iron and copper. Aluminum was also more effective than the standard flattening filter, with the increase over the unfiltered beam being 1.4-1.5× (maintaining 600 cGy/min dose rate) vs 1.3-1.4× for the standard flattening filter. Applying a 10 cm aluminum filter to a standard 18 MV, photon beam increased the Cherenkov production per unit dose to 3.9-4.3× beyond that of 6 MV (vs 3.3-4.0× for 18 MV with no aluminum filter). Through a combination of increasing photon energy and applying specialized beam-hardening filtration, the amount of Cherenkov photons per unit radiotherapy dose can be increased substantially. © 2018 American Association of Physicists in Medicine.

Breakdown of Bragg-Gray behaviour for low-density detectors under electronic disequilibrium conditions in small megavoltage photon fields.

PubMed

Kumar, Sudhir; Fenwick, John D; Underwood, Tracy S A; Deshpande, Deepak D; Scott, Alison J D; Nahum, Alan E

2015-10-21

In small photon fields ionisation chambers can exhibit large deviations from Bragg-Gray behaviour; the EGSnrc Monte Carlo (MC) code system has been employed to investigate this 'Bragg-Gray breakdown'. The total electron (+positron) fluence in small water and air cavities in a water phantom has been computed for a full linac beam model as well as for a point source spectrum for 6 MV and 15 MV qualities for field sizes from 0.25  ×  0.25 cm(2) to 10  ×  10 cm(2). A water-to-air perturbation factor has been derived as the ratio of total electron (+positron) fluence, integrated over all energies, in a tiny water volume to that in a 'PinPoint 3D-chamber-like' air cavity; for the 0.25  ×  0.25 cm(2) field size the perturbation factors are 1.323 and 2.139 for 6 MV and 15 MV full linac geometries respectively. For the 15 MV full linac geometry for field sizes of 1  ×  1 cm(2) and smaller not only the absolute magnitude but also the 'shape' of the total electron fluence spectrum in the air cavity is significantly different to that in the water 'cavity'. The physics of this 'Bragg-Gray breakdown' is fully explained, making reference to the Fano theorem. For the 15 MV full linac geometry in the 0.25  ×  0.25 cm(2) field the directly computed MC dose ratio, water-to-air, differs by 5% from the product of the Spencer-Attix stopping-power ratio (SPR) and the perturbation factor; this 'difference' is explained by the difference in the shapes of the fluence spectra and is also formulated theoretically. We show that the dimensions of an air-cavity with a perturbation factor within 5% of unity would have to be impractically small in these highly non-equilibrium photon fields. In contrast the dose to water in a 0.25  ×  0.25 cm(2) field derived by multiplying the dose in the single-crystal diamond dosimeter (SCDDo) by the Spencer-Attix ratio is within 2.9% of the dose computed directly in the water voxel for full linac geometry at both 6 and 15 MV, thereby demonstrating that this detector exhibits quasi Bragg-Gray behaviour over a wide range of field sizes and beam qualities.

SU-E-T-368: Evaluating Dosimetric Outcome of Modulated Photon Radiotherapy (XMRT) Optimization for Head and Neck Patients

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGeachy, P; Villarreal-Barajas, JE; Khan, R

2015-06-15

Purpose: The dosimetric outcome of optimized treatment plans obtained by modulating the photon beamlet energy and fluence on a small cohort of four Head and Neck (H and N) patients was investigated. This novel optimization technique is denoted XMRT for modulated photon radiotherapy. The dosimetric plans from XMRT for H and N treatment were compared to conventional, 6 MV intensity modulated radiotherapy (IMRT) optimization plans. Methods: An arrangement of two non-coplanar and five coplanar beams was used for all four H and N patients. Both XMRT and IMRT were subject to the same optimization algorithm, with XMRT optimization allowing bothmore » 6 and 18 MV beamlets while IMRT was restricted to 6 MV only. The optimization algorithm was based on a linear programming approach with partial-volume constraints implemented via the conditional value-at-risk method. H and N constraints were based off of those mentioned in the Radiation Therapy Oncology Group 1016 protocol. XMRT and IMRT solutions were assessed using metrics suggested by International Commission on Radiation Units and Measurements report 83. The Gurobi solver was used in conjunction with the CVX package to solve each optimization problem. Dose calculations and analysis were done in CERR using Monte Carlo dose calculation with VMC{sub ++}. Results: Both XMRT and IMRT solutions met all clinical criteria. Trade-offs were observed between improved dose uniformity to the primary target volume (PTV1) and increased dose to some of the surrounding healthy organs for XMRT compared to IMRT. On average, IMRT improved dose to the contralateral parotid gland and spinal cord while XMRT improved dose to the brainstem and mandible. Conclusion: Bi-energy XMRT optimization for H and N patients provides benefits in terms of improved dose uniformity to the primary target and reduced dose to some healthy structures, at the expense of increased dose to other healthy structures when compared with IMRT.« less

Calculation of Nuclear Particles Production at High-Energy Photon Beams from a Linac Operating at 6, 10 and 15 MV.

PubMed

Marchesini, Renato; Bettega, Daniela; Calzolari, Paola; Pignoli, Emanuele

2017-05-01

Production of photonuclear particles in a tissue-equivalent medium has been calculated for linacs at 6, 10 and 15 MV from Varian TrueBeam. Based on the knowledge of bremsstrahlung fluence spectra and linac photon beam parameters, numerical integration was performed on the cross sections for photoparticle production of the constituent elements of tissue (2H,12C,13C,16O,17O,18O,14N,15N). At 15 MV, at the depth of photon maximum dose, the total absorbed dose due to neutrons, protons, alphas and residual nuclei from photon reactions in tissue (5.5E-05 Gy per Gy of photons) is comparable to that due to neutrons from accelerator head. Results reasonably agree with data reported in the literature using Monte Carlo models simulating linac head components. This work suggests a simple method to estimate the dose contributed by the photon-induced nuclear particles for high-energy photon beams produced by linacs in use, as it might be relevant for late stochastic effects. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Dose to 'water-like' media or dose to tissue in MV photons radiotherapy treatment planning: still a matter of debate.

PubMed

Andreo, Pedro

2015-01-07

The difference between Monte Carlo Treatment Planning (MCTP) based on the assumption of 'water-like' tissues with densities obtained from CT procedures, or on tissue compositions derived from CT-determined densities, have been investigated. Stopping powers and electron fluences have been calculated for a range of media and body tissues for 6 MV photon beams, including changes in their physical data (density and stopping powers). These quantities have been used to determine absorbed doses using cavity theory. It is emphasized that tissue compositions given in ICRU or ICRP reports should not be given the standing of physical constants as they correspond to average values obtained for a limited number of human-body samples. It has been shown that mass stopping-power ratios to water are more dependent on patient-to-patient composition differences, and therefore on their mean excitation energies (I-values), than on mass density. Electron fluence in different media are also more dependent on media composition (and their I-values) than on density. However, as a consequence of the balance between fluence and stopping powers, doses calculated from their product are more constant than what the independent stopping powers and fluence variations suggest. Additionally, cancelations in dose ratios minimize the differences between the 'water-like' and 'tissue' approaches, yielding practically identical results except for bone, and to a lesser extent for adipose tissue. A priori, changing from one approach to another does not seem to be justified considering the large number of approximations and uncertainties involved throughout the treatment planning tissue segmentation and dose calculation procedures. The key issue continues to be the composition of tissues and their I-values, and as these cannot be obtained for individual patients, whatever approach is selected does not lead to significant differences from a water reference dose, the maximum of these being of the order of 5% for bone tissues. Considering, however, current developments in advanced dose calculation methods, planning in terms of dose-to-tissue should be the preferred choice, under the expectancy that progress in the field will gradually improve some of the crude approximations included in MCTP and numerical transport methods. The small differences obtained also show that a retrospective conversion from dose-to-tissue to dose-to-water, based on a widely used approach, would mostly increase the final uncertainty of the treatment planning process. It is demonstrated that, due to the difference between electron fluence distributions in water and in body tissues, the conversion requires an additional fluence correction that has so far been neglected. An improved expression for the conversion and data for the fluence correction factor are provided. These will be necessary even in a dose-to-tissue environment, for the normalization of the treatment plan to the reference dosimetry of the treatment unit, always calibrated in terms of absorbed dose to water.

Dose to ‘water-like’ media or dose to tissue in MV photons radiotherapy treatment planning: still a matter of debate

NASA Astrophysics Data System (ADS)

Andreo, Pedro

2015-01-01

The difference between Monte Carlo Treatment Planning (MCTP) based on the assumption of ‘water-like’ tissues with densities obtained from CT procedures, or on tissue compositions derived from CT-determined densities, have been investigated. Stopping powers and electron fluences have been calculated for a range of media and body tissues for 6 MV photon beams, including changes in their physical data (density and stopping powers). These quantities have been used to determine absorbed doses using cavity theory. It is emphasized that tissue compositions given in ICRU or ICRP reports should not be given the standing of physical constants as they correspond to average values obtained for a limited number of human-body samples. It has been shown that mass stopping-power ratios to water are more dependent on patient-to-patient composition differences, and therefore on their mean excitation energies (I-values), than on mass density. Electron fluence in different media are also more dependent on media composition (and their I-values) than on density. However, as a consequence of the balance between fluence and stopping powers, doses calculated from their product are more constant than what the independent stopping powers and fluence variations suggest. Additionally, cancelations in dose ratios minimize the differences between the ‘water-like’ and ‘tissue’ approaches, yielding practically identical results except for bone, and to a lesser extent for adipose tissue. A priori, changing from one approach to another does not seem to be justified considering the large number of approximations and uncertainties involved throughout the treatment planning tissue segmentation and dose calculation procedures. The key issue continues to be the composition of tissues and their I-values, and as these cannot be obtained for individual patients, whatever approach is selected does not lead to significant differences from a water reference dose, the maximum of these being of the order of 5% for bone tissues. Considering, however, current developments in advanced dose calculation methods, planning in terms of dose-to-tissue should be the preferred choice, under the expectancy that progress in the field will gradually improve some of the crude approximations included in MCTP and numerical transport methods. The small differences obtained also show that a retrospective conversion from dose-to-tissue to dose-to-water, based on a widely used approach, would mostly increase the final uncertainty of the treatment planning process. It is demonstrated that, due to the difference between electron fluence distributions in water and in body tissues, the conversion requires an additional fluence correction that has so far been neglected. An improved expression for the conversion and data for the fluence correction factor are provided. These will be necessary even in a dose-to-tissue environment, for the normalization of the treatment plan to the reference dosimetry of the treatment unit, always calibrated in terms of absorbed dose to water.

Dose specification for 192Ir high dose rate brachytherapy in terms of dose-to-water-in-medium and dose-to-medium-in-medium

NASA Astrophysics Data System (ADS)

Paiva Fonseca, Gabriel; Carlsson Tedgren, Åsa; Reniers, Brigitte; Nilsson, Josef; Persson, Maria; Yoriyaz, Hélio; Verhaegen, Frank

2015-06-01

Dose calculation in high dose rate brachytherapy with 192Ir is usually based on the TG-43U1 protocol where all media are considered to be water. Several dose calculation algorithms have been developed that are capable of handling heterogeneities with two possibilities to report dose: dose-to-medium-in-medium (Dm,m) and dose-to-water-in-medium (Dw,m). The relation between Dm,m and Dw,m for 192Ir is the main goal of this study, in particular the dependence of Dw,m on the dose calculation approach using either large cavity theory (LCT) or small cavity theory (SCT). A head and neck case was selected due to the presence of media with a large range of atomic numbers relevant to tissues and mass densities such as air, soft tissues and bone interfaces. This case was simulated using a Monte Carlo (MC) code to score: Dm,m, Dw,m (LCT), mean photon energy and photon fluence. Dw,m (SCT) was derived from MC simulations using the ratio between the unrestricted collisional stopping power of the actual medium and water. Differences between Dm,m and Dw,m (SCT or LCT) can be negligible (<1%) for some tissues e.g. muscle and significant for other tissues with differences of up to 14% for bone. Using SCT or LCT approaches leads to differences between Dw,m (SCT) and Dw,m (LCT) up to 29% for bone and 36% for teeth. The mean photon energy distribution ranges from 222 keV up to 356 keV. However, results obtained using mean photon energies are not equivalent to the ones obtained using the full, local photon spectrum. This work concludes that it is essential that brachytherapy studies clearly report the dose quantity. It further shows that while differences between Dm,m and Dw,m (SCT) mainly depend on tissue type, differences between Dm,m and Dw,m (LCT) are, in addition, significantly dependent on the local photon energy fluence spectrum which varies with distance to implanted sources.

SU-E-T-46: Application of a Twin-Detector Method for the Determination of the Mean Photon Energy Em at Points of Measurement in a Water Phantom Surrounding a GammaMed HDR 192Ir Brachytherapy Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chofor, N; Poppe, B; Nebah, F

Purpose: In a brachytherapy photon field in water the fluence-averaged mean photon energy Em at the point of measurement correlates with the radiation quality correction factor kQ of a non water-equivalent detector. To support the experimental assessment of Em, we show that the normalized signal ratio NSR of a pair of radiation detectors, an unshielded silicon diode and a diamond detector can serve to measure quantity Em in a water phantom at a Ir-192 unit. Methods: Photon fluence spectra were computed in EGSnrc based on a detailed model of the GammaMed source. Factor kQ was calculated as the ratio ofmore » the detector's spectrum-weighted responses under calibration conditions at a 60Co unit and under brachytherapy conditions at various radial distances from the source. The NSR was investigated for a pair of a p-type unshielded silicon diode 60012 and a synthetic single crystal diamond detector 60019 (both PTW Freiburg). Each detector was positioned according to its effective point of measurement, with its axis facing the source. Lateral signal profiles were scanned under complete scatter conditions, and the NSR was determined as the quotient of the signal ratio under application conditions x and that at position r-ref = 1 cm. Results: The radiation quality correction factor kQ shows a close correlation with the mean photon energy Em. The NSR of the diode/diamond pair changes by a factor of two from 0–18 cm from the source, while Em drops from 350 to 150 keV. Theoretical and measured NSR profiles agree by ± 2 % for points within 5 cm from the source. Conclusion: In the presence of the close correlation between radiation quality correction factor kQ and photon mean energy Em, the NSR provides a practical means of assessing Em under clinical conditions. Precise detector positioning is the major challenge.« less

Primary and aggregate color centers in proton irradiated LiF crystals and thin films for luminescent solid state detectors

NASA Astrophysics Data System (ADS)

Piccinini, M.; Ambrosini, F.; Ampollini, A.; Bonfigli, F.; Libera, S.; Picardi, L.; Ronsivalle, C.; Vincenti, M. A.; Montereali, R. M.

2015-04-01

Proton beams of 3 MeV energy, produced by the injector of a linear accelerator for proton therapy, were used to irradiate at room temperature lithium fluoride crystals and polycrystalline thin films grown by thermal evaporation. The irradiation fluence range was 1011-1015 protons/cm2. The proton irradiation induced the stable formation of primary and aggregate color centers. Their formation was investigated by optical absorption and photoluminescence spectroscopy. The F2 and F3+ photoluminescence intensities, carefully measured in LiF crystals and thin films, show linear behaviours up to different maximum values of the irradiation fluence, after which a quenching is observed, depending on the nature of the samples (crystals and films). The Principal Component Analysis, applied to the absorption spectra of colored crystals, allowed to clearly identify the formation of more complex aggregate defects in samples irradiated at highest fluences.

Experimental and Monte Carlo studies of fluence corrections for graphite calorimetry in low- and high-energy clinical proton beams.

PubMed

Lourenço, Ana; Thomas, Russell; Bouchard, Hugo; Kacperek, Andrzej; Vondracek, Vladimir; Royle, Gary; Palmans, Hugo

2016-07-01

The aim of this study was to determine fluence corrections necessary to convert absorbed dose to graphite, measured by graphite calorimetry, to absorbed dose to water. Fluence corrections were obtained from experiments and Monte Carlo simulations in low- and high-energy proton beams. Fluence corrections were calculated to account for the difference in fluence between water and graphite at equivalent depths. Measurements were performed with narrow proton beams. Plane-parallel-plate ionization chambers with a large collecting area compared to the beam diameter were used to intercept the whole beam. High- and low-energy proton beams were provided by a scanning and double scattering delivery system, respectively. A mathematical formalism was established to relate fluence corrections derived from Monte Carlo simulations, using the fluka code [A. Ferrari et al., "fluka: A multi-particle transport code," in CERN 2005-10, INFN/TC 05/11, SLAC-R-773 (2005) and T. T. Böhlen et al., "The fluka Code: Developments and challenges for high energy and medical applications," Nucl. Data Sheets 120, 211-214 (2014)], to partial fluence corrections measured experimentally. A good agreement was found between the partial fluence corrections derived by Monte Carlo simulations and those determined experimentally. For a high-energy beam of 180 MeV, the fluence corrections from Monte Carlo simulations were found to increase from 0.99 to 1.04 with depth. In the case of a low-energy beam of 60 MeV, the magnitude of fluence corrections was approximately 0.99 at all depths when calculated in the sensitive area of the chamber used in the experiments. Fluence correction calculations were also performed for a larger area and found to increase from 0.99 at the surface to 1.01 at greater depths. Fluence corrections obtained experimentally are partial fluence corrections because they account for differences in the primary and part of the secondary particle fluence. A correction factor, F(d), has been established to relate fluence corrections defined theoretically to partial fluence corrections derived experimentally. The findings presented here are also relevant to water and tissue-equivalent-plastic materials given their carbon content.

Frequency domain photothermoacoustic signal amplitude dependence on the optical properties of water: turbid polyvinyl chloride-plastisol system.

PubMed

Spirou, Gloria M; Mandelis, Andreas; Vitkin, I Alex; Whelan, William M

2008-05-10

Photoacoustic (more precisely, photothermoacoustic) signals generated by the absorption of photons can be related to the incident laser fluence rate. The dependence of frequency domain photoacoustic (FD-PA) signals on the optical absorption coefficient (micro(a)) and the effective attenuation coefficient (micro(eff)) of a turbid medium [polyvinyl chloride-plastisol (PVCP)] with tissuelike optical properties was measured, and empirical relationships between these optical properties and the photoacoustic (PA) signal amplitude and the laser fluence rate were derived for the water (PVCP system with and without optical scatterers). The measured relationships between these sample optical properties and the PA signal amplitude were found to be linear, consistent with FD-PA theory: micro(a)=a(A/Phi)-b and micro(eff)=c(A/Phi)+d, where Phi is the laser fluence, A is the FD-PA amplitude, and a, ...,d are empirical coefficients determined from the experiment using linear frequency-swept modulation and a lock-in heterodyne detection technique. This quantitative technique can easily be used to measure the optical properties of general turbid media using FD-PAs.

The fragmentation of 510 MeV/nucleon iron-56 in polyethylene. I. Fragment fluence spectra

NASA Technical Reports Server (NTRS)

Zeitlin, C.; Miller, J.; Heilbronn, L.; Frankel, K.; Gong, W.; Schimmerling, W.

1996-01-01

The fragmentation of 510 MeV/nucleon iron ions in several thicknesses of polyethylene has been measured. Non-interacting primary beam particles and fragments have been identified and their LETs calculated by measuring ionization energy loss in a stack of silicon detectors. Fluences, normalized to the incident beam intensity and corrected for detector effects, are presented for each fragment charge and target. Histograms of fluence as a function of LET are also presented. Some implications of these data for measurements of the biological effects of heavy ions are discussed.

Dosimetric response of variable-size cavities in photon-irradiated media and the behaviour of the Spencer-Attix cavity integral with increasing Δ.

PubMed

Kumar, Sudhir; Deshpande, Deepak D; Nahum, Alan E

2016-04-07

Cavity theory is fundamental to understanding and predicting dosimeter response. Conventional cavity theories have been shown to be consistent with one another by deriving the electron (+positron) and photon fluence spectra with the FLURZnrc user-code (EGSnrc Monte-Carlo system) in large volumes under quasi-CPE for photon beams of 1 MeV and 10 MeV in three materials (water, aluminium and copper) and then using these fluence spectra to evaluate and then inter-compare the Bragg-Gray, Spencer-Attix and 'large photon' 'cavity integrals'. The behaviour of the 'Spencer-Attix dose' (aka restricted cema), D S-A(▵), in a 1-MeV photon field in water has been investigated for a wide range of values of the cavity-size parameter ▵: D S-A(▵) decreases far below the Monte-Carlo dose (D MC) for ▵ greater than  ≈  30 keV due to secondary electrons with starting energies below ▵ not being 'counted'. We show that for a quasi-scatter-free geometry (D S-A(▵)/D MC) is closely equal to the proportion of energy transferred to Compton electrons with initial (kinetic) energies above ▵, derived from the Klein-Nishina (K-N) differential cross section. (D S-A(▵)/D MC) can be used to estimate the maximum size of a detector behaving as a Bragg-Gray cavity in a photon-irradiated medium as a function of photon-beam quality (under quasi CPE) e.g. a typical air-filled ion chamber is 'Bragg-Gray' at (monoenergetic) beam energies  ⩾260 keV. Finally, by varying the density of a silicon cavity (of 2.26 mm diameter and 2.0 mm thickness) in water, the response of different cavity 'sizes' was simulated; the Monte-Carlo-derived ratio D w/D Si for 6 MV and 15 MV photons varied from very close to the Spencer-Attix value at 'gas' densities, agreed well with Burlin cavity theory as ρ increased, and approached large photon behaviour for ρ  ≈  10 g cm(-3). The estimate of ▵ for the Si cavity was improved by incorporating a Monte-Carlo-derived correction for electron 'detours'. Excellent agreement was obtained between the Burlin 'd' factor for the Si cavity and D S-A(▵)/D MC at different (detour-corrected) ▵, thereby suggesting a further application for the D S-A(▵)/D MC ratio.

A technique for efficiently generating bimetallic clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner, R.L.; Vann, W.D.; Castleman, A.W. , Jr.

1997-08-01

Reactivities of bimetallic clusters can be controlled by varying their composition, making them potentially valuable as catalysts and for use in elucidating the reactivities of such subnanoscale surfaces. A dual rod laser vaporization source coupled to a fast flow reactor is developed for the study of bimetallic clusters and their reactions. In order to establish the versatility of the technique, the results of studies are presented in which Nb/Al clusters are formed in two plasmas induced by the second harmonic (532 nm photons) of a single Nd:YAG laser and then detected by a quadrupole mass spectrometer. The beam from themore » laser is split and then focused onto each rod, allowing the mixing ratio within the cluster to vary by altering the laser fluence on each rod. With a low fluence on the Nb rod and a high fluence on the Al rod, an Al rich cluster distribution is formed, NbAl{sub m}{sup {minus}} (m=2{endash}20), and Al{sub m}{sup {minus}} (m=5{endash}31). By increasing the fluence on the Nb rod and decreasing the fluence on the Al rod, a Nb rich cluster distribution is formed, Nb{sub n}Al{sub m}{sup {minus}} (n=3{endash}8 and m=1{endash}3), Nb{sub n}OAl{sub m}{sup {minus}} (n=3{endash}8 and m=1{endash}5), and Nb{sub n}O{sup {minus}} (n=3{endash}8). Additional characterization is also performed on V/Al clusters. {copyright} {ital 1997 American Institute of Physics.}« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Y M; Bush, K; Han, B

Purpose: Accurate and fast dose calculation is a prerequisite of precision radiation therapy in modern photon and particle therapy. While Monte Carlo (MC) dose calculation provides high dosimetric accuracy, the drastically increased computational time hinders its routine use. Deterministic dose calculation methods are fast, but problematic in the presence of tissue density inhomogeneity. We leverage the useful features of deterministic methods and MC to develop a hybrid dose calculation platform with autonomous utilization of MC and deterministic calculation depending on the local geometry, for optimal accuracy and speed. Methods: Our platform utilizes a Geant4 based “localized Monte Carlo” (LMC) methodmore » that isolates MC dose calculations only to volumes that have potential for dosimetric inaccuracy. In our approach, additional structures are created encompassing heterogeneous volumes. Deterministic methods calculate dose and energy fluence up to the volume surfaces, where the energy fluence distribution is sampled into discrete histories and transported using MC. Histories exiting the volume are converted back into energy fluence, and transported deterministically. By matching boundary conditions at both interfaces, deterministic dose calculation account for dose perturbations “downstream” of localized heterogeneities. Hybrid dose calculation was performed for water and anthropomorphic phantoms. Results: We achieved <1% agreement between deterministic and MC calculations in the water benchmark for photon and proton beams, and dose differences of 2%–15% could be observed in heterogeneous phantoms. The saving in computational time (a factor ∼4–7 compared to a full Monte Carlo dose calculation) was found to be approximately proportional to the volume of the heterogeneous region. Conclusion: Our hybrid dose calculation approach takes advantage of the computational efficiency of deterministic method and accuracy of MC, providing a practical tool for high performance dose calculation in modern RT. The approach is generalizable to all modalities where heterogeneities play a large role, notably particle therapy.« less

Track-average LET of secondary electrons generated in LiF:Mg,Ti and liquid water by 20-300 kV x-ray, 137Cs and 60Co beams.

PubMed

Cabrera-Santiago, A; Massillon-Jl, G

2016-11-21

Electrons generated in matter by photons could be a fundamental basis for an adequate analysis of radiation effects and damage. We have studied separately the 'primary electrons' generated directly by photons from the 'secondary electrons' (SE) produced by electron-electron interactions. In this work, track-average linear energy transfer, [Formula: see text], of SE in LiF:Mg,Ti and liquid water produced by twelve photon energy beams from 20 kV x-ray to 60 Co gamma rays have been investigated using the EGSnrc Monte Carlo Code. The exposure of LiF:Mg,Ti in different phantom materials has been considered. Depending on the photon energy, SE represent 40%-90% of the total electron fluence (TEF) between 1 keV and 10 keV, being higher when the photon energy increases. Independent of the medium, [Formula: see text] versus mean photon energy displays a local minimum at around 40 keV, followed by a local maximum at ~80 keV-100 keV. The [Formula: see text] of SE generated by the x-ray beams are of order of 11 keV µm -1 to 19 keV µm -1 in LiF:Mg,Ti and 5 keV µm -1 to 9 keV µm -1 in liquid water which represent 3-5 times those produced by 60 Co gamma rays in both media. These values were considerably greater than those of TEF, by factors of 3-8. Furthermore, [Formula: see text] of SE generated in liquid water by 20 kV-200 kV x-rays are similar to those of 76 MeV-120 MeV 3 He ions. Contrary to the TEF, where [Formula: see text] were independent of the phantom material, at low photon energies [Formula: see text] of SE was found to be sensitive to the surrounding medium showing higher values within the phantom than in air. This result, which agrees with published experimental results, implies the importance of the SE ionization density for an understanding of dosimeter response induced by photon beams.

WE-EF-207-06: Dedicated Cone-Beam Breast CT with Laterally-Shifted Detector: Monte Carlo Evaluation of X-Ray Scatter Distribution and Scatter-To-Primary Ratio

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, L; Vedantham, S; Karellas, A

2015-06-15

Purpose: To determine the spatial distribution of x-ray scatter and scatter-to-primary ratio (SPR) in projections during cone-beam breast CT (CBBCT) with laterally-shifted detector that results in coronal (fan-angle) truncation. Methods: We hypothesized that CBBCT with coronal truncation would lower SPR due to reduction in irradiated breast volume, and that the location of maximum x-ray scatter fluence (scatter-peak) in the detector plane can be determined from the ratio of irradiated-to-total breast volume, breast dimensions and system geometry. Monte Carlo simulations (GEANT4) reflecting a prototype CBBCT system were used to record the position-dependent primary and scatter x-ray photon fluence incident on themore » detector without coronal truncation (full fan-angle, 2f=24-degrees) and with coronal truncation (fan-angle, f+ f=12+2.7-degrees). Semi-ellipsoidal breasts (10/14/18-cm diameter, chest-wall to nipple length: 0.75xdiameter, 2%/14%/100% fibroglandular content) aligned with the axis-of-rotation (AOR) were modeled. Mono-energy photons were simulated and weighted for 2 spectra (49kVp, 1.4-mm Al HVL; 60kVp, 3.76-mm Al HVL). In addition to SPR, the scatter maps were analyzed to identify the location of the scatter-peak. Results: For CBBCT without fan-angle truncation, the scatter-peaks were aligned with the projection of the AOR onto the detector for all breasts. With truncated fan-beam, the scatter-peaks were laterally-shifted from the projection of the AOR along the fan-angle direction by 14/38/70-pixels for 10/14/18-cm diameter breasts. The corresponding theoretical shifts were 14.8/39.7/68-pixels (p=0.47, 2-tailed paired-ratio t-test). Along the cone-angle, the shift in scatter-peaks between truncated and full-fan angle CBBCT were 2/2/4 -pixels for 10/14/18-cm diameter breasts. CBBCT with fan-angle truncation reduced SPR by 14/22/28% for 10/14/18-cm diameter breasts. 60kVp reduced SPR by 21–25% compared to 49kVp. Peak SPR for CBBCT with fan-angle truncation (60kVp) were 0.09/0.25/0.73 for 10/14/18-cm diameter breasts. Conclusion: CBBCT with laterally-shifted detector geometry and with appropriate kVp/beam quality reduces SPR. If residual scatter needs correction, the location corresponding to scatter-peak can be analytically computed. This work was supported in part by NIH R01 CA128906. The contents are solely the responsibility of the authors and do not reflect the official views of the NIH or NCI.« less

Patient size and x-ray transmission in body CT.

PubMed

Ogden, Kent; Huda, Walter; Scalzetti, Ernest M; Roskopf, Marsha L

2004-04-01

Physical characteristics were obtained for 196 patients undergoing chest and abdomen computed tomography (CT) examinations. Computed tomography sections for these patients having no evident pathology were analyzed to determine patient dimensions (AP and lateral), together with the average attenuation coefficient. Patient weights ranged from approximately 3 kg to about 120 kg. For chest CT, the mean Hounsfield unit (HU) fell from about -120 HU for newborns to about -300 HU for adults. For abdominal CT, the mean HU for children and normal-sized adults was about 20 HU, but decreased to below -50 HU for adults weighing more than 100 kg. The effective photon energy and percent energy fluence transmitted through a given patient size and composition was calculated for representative x-ray spectra at 80, 100, 120, and 140 kV tube potentials. A 70-kg adult scanned at 120 kVp transmits 2.6% of the energy fluence for chest and 0.7% for abdomen CT examinations. Reducing the patient size to 10 kg increases transmission by an order of magnitude. For 70 kg patients, effective energies in body CT range from approximately 50 keV at 80 kVp to approximately 67 keV at 140 kVp; increasing patient size from 10 to 120 kg resulted in an increase in effective photon energy of approximately 4 keV. The x-ray transmission data and effective photon energy data can be used to determine CT image noise and image contrast, respectively, and information on patient size and composition can be used to determine patient doses.

Characterization of the phantom material virtual water in high-energy photon and electron beams.

PubMed

McEwen, M R; Niven, D

2006-04-01

The material Virtual Water has been characterized in photon and electron beams. Range-scaling factors and fluence correction factors were obtained, the latter with an uncertainty of around 0.2%. This level of uncertainty means that it may be possible to perform dosimetry in a solid phantom with an accuracy approaching that of measurements in water. Two formulations of Virtual Water were investigated with nominally the same elemental composition but differing densities. For photon beams neither formulation showed exact water equivalence-the water/Virtual Water dose ratio varied with the depth of measurement with a difference of over 1% at 10 cm depth. However, by using a density (range) scaling factor very good agreement (<0.2%) between water and Virtual Water at all depths was obtained. In the case of electron beams a range-scaling factor was also required to match the shapes of the depth dose curves in water and Virtual Water. However, there remained a difference in the measured fluence in the two phantoms after this scaling factor had been applied. For measurements around the peak of the depth-dose curve and the reference depth this difference showed some small energy dependence but was in the range 0.1%-0.4%. Perturbation measurements have indicated that small slabs of material upstream of a detector have a small (<0.1% effect) on the chamber reading but material behind the detector can have a larger effect. This has consequences for the design of experiments and in the comparison of measurements and Monte Carlo-derived values.

Saturable Absorption in 2D Ti3 C2 MXene Thin Films for Passive Photonic Diodes.

PubMed

Dong, Yongchang; Chertopalov, Sergii; Maleski, Kathleen; Anasori, Babak; Hu, Longyu; Bhattacharya, Sriparna; Rao, Apparao M; Gogotsi, Yury; Mochalin, Vadym N; Podila, Ramakrishna

2018-03-01

MXenes comprise a new class of 2D transition metal carbides, nitrides, and carbonitrides that exhibit unique light-matter interactions. Recently, 2D Ti 3 CNT x (T x represents functional groups such as OH and F) was found to exhibit nonlinear saturable absorption (SA) or increased transmittance at higher light fluences, which is useful for mode locking in fiber-based femtosecond lasers. However, the fundamental origin and thickness dependence of SA behavior in MXenes remain to be understood. 2D Ti 3 C 2 T x thin films of different thicknesses are fabricated using an interfacial film formation technique to systematically study their nonlinear optical properties. Using the open aperture Z-scan method, it is found that the SA behavior in Ti 3 C 2 T x MXene arises from plasmon-induced increase in the ground state absorption at photon energies above the threshold for free carrier oscillations. The saturation fluence and modulation depth of Ti 3 C 2 T x MXene is observed to be dependent on the film thickness. Unlike other 2D materials, Ti 3 C 2 T x is found to show higher threshold for light-induced damage with up to 50% increase in nonlinear transmittance. Lastly, building on the SA behavior of Ti 3 C 2 T x MXenes, a Ti 3 C 2 T x MXene-based photonic diode that breaks time-reversal symmetry to achieve nonreciprocal transmission of nanosecond laser pulses is demonstrated. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Two-photon pumped amplified spontaneous emission based on all-inorganic perovskite nanocrystals embedded with gold nanorods

NASA Astrophysics Data System (ADS)

Liu, Shaoying; Fang, Xiaohui; Wang, Yimeng; Zhang, Xinping

2018-07-01

CsPbBr3 nanocrystals have attracted great interest owing to their high fluorescence quantum efficiency, adjustable photoluminescence wavelength, and good stability. We report a device that consists of disordered gold nanorods underneath a film of CsPbBr3 nanocrystals. Two-photon pumping using femtosecond laser pulses at 800 nm enables amplified spontaneous emission (ASE) at about 523 nm. In this work, a narrow peak with linewidth of 5 nm is observed when the pump fluence reaches a low threshold of 0.65 mJ/cm2. The results show that plasmonic resonance of gold nanorods improves the emission transition rate and enables low threshold ASE.

Inferences of Shell Asymmetry in ICF Implosions using Fluence Compensated Neutron Images at the NIF

NASA Astrophysics Data System (ADS)

Casey, D.; Fittinghoff, D.; Bionta, R.; Smalyuk, V.; Grim, G.; Munro, D.; Spears, B.; Raman, K.; Clark, D.; Kritcher, A.; Hinkel, D.; Hurricane, O.; Callahan, D.; Döppner, T.; Landen, O.; Ma, T.; Le Pape, S.; Ross, S.; Meezan, N.; Pak, A.; Park, H.-S.; Volegov, P.; Merill, F.

2016-10-01

In ICF experiments, a dense shell is imploded and used to compress and heat a hotspot of DT fuel. Controlling the symmetry of this process is both important and challenging. It is therefore important to observe the symmetry of the stagnated shell assembly. The Neutron Imaging System at the NIF is used to observe the primary 14 MeV neutrons from the hotspot and the down-scattered neutrons (6-12 MeV), from the assembled shell but with a strong imprint from the primary-neutron fluence. Using a characteristic scattering angle approximation, we have compensated the image for this fluence effect, revealing information about shell asymmetry that is otherwise difficult to extract without models. Preliminary observations with NIF data show asymmetries in imploded shell, which will be compared with other nuclear diagnostics and postshot simulations. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Measurement of angularly dependent spectra of betatron gamma-rays from a laser plasma accelerator with quadrant-sectored range filters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeon, Jong Ho, E-mail: jhjeon07@ibs.re.kr; Nakajima, Kazuhisa, E-mail: naka115@dia-net.ne.jp; Rhee, Yong Joo

Measurement of angularly dependent spectra of betatron gamma-rays radiated by GeV electron beams from laser wakefield accelerators (LWFAs) are presented. The angle-resolved spectrum of betatron radiation was deconvolved from the position dependent data measured for a single laser shot with a broadband gamma-ray spectrometer comprising four-quadrant sectored range filters and an unfolding algorithm, based on the Monte Carlo code GEANT4. The unfolded gamma-ray spectra in the photon energy range of 0.1–10 MeV revealed an approximately isotropic angular dependence of the peak photon energy and photon energy-integrated fluence. As expected by the analysis of betatron radiation from LWFAs, the results indicate thatmore » unpolarized gamma-rays are emitted by electrons undergoing betatron motion in isotropically distributed orbit planes.« less

Modeling and experimental validation of angular radiance and distance-dependent radiance in a turbid medium

NASA Astrophysics Data System (ADS)

Liu, Lingling; Li, Chenxi; Zhao, Huijuan; Yi, Xi; Gao, Feng; Meng, Wei; Lu, Yiming

2014-03-01

Radiance is sensitive to the variations of tissue optical parameters, such as absorption coefficient μa, scattering coefficient μs, and anisotropy factor g. Therefore, similar to fluence, radiance can be used for tissue characterization. Compared with fluence, radiance has the advantage of offering the direction information of light intensity. Taking such advantage, the optical parameters can be determined by rotating the detector through 360 deg with only a single optode pair. Instead of the translation mode used in the fluence-based technologies, the Rotation mode has less invasiveness in the clinical diagnosis. This paper explores a new method to obtain the optical properties by measuring the distribution of light intensity in liquid phantom with only a single optode pair and the detector rotation through 360 deg. The angular radiance and distance-dependent radiance are verified by comparing experimental measurement data with Monte Carlo (MC) simulation for the short source-detector separations and diffusion approximation for the large source-detector separations. Detecting angular radiance with only a single optode pair under a certain source-detection separation will present a way for prostate diagnose and light dose calculation during the photon dynamic therapy (PDT).

Electron dynamics and prompt ablation of aluminum surface excited by intense femtosecond laser pulse

NASA Astrophysics Data System (ADS)

Ionin, A. A.; Kudryashov, S. I.; Makarov, S. V.; Seleznev, L. V.; Sinitsyn, D. V.

2014-12-01

Thin aluminum film homogeneously heated by intense IR femtosecond laser pulses exhibits on the excitation timescale consequent fluence-dependent rise and drop of the IR-pump self-reflectivity, followed by its final saturation at higher fluences F > 0.3 J/cm2. This prompt optical dynamics correlates with the initial monotonic increase in the accompanying laser-induced electron emission, which is succeeded by its non-linear (three-photon) increase for F > 0.3 J/cm2. The underlying electronic dynamics is related to the initial saturation of IR resonant interband transitions in this material, followed by its strong instantaneous electronic heating via intraband transitions during the pump pulse resulting in thermionic emission. Above the threshold fluence of 0.3 J/cm2, the surface electronic heating is balanced during the pump pulse by simultaneous cooling via intense plasma removal (prompt ablation). The relationship between the deposited volume energy density in the film and its prompt electronic temperature derived from the self-reflection measurements using a Drude model, demonstrates a kind of electron "liquid-vapor" phase transition, driven by strong cubic optical non-linearity of the photo-excited aluminum.

Some computer graphical user interfaces in radiation therapy.

PubMed

Chow, James C L

2016-03-28

In this review, five graphical user interfaces (GUIs) used in radiation therapy practices and researches are introduced. They are: (1) the treatment time calculator, superficial X-ray treatment time calculator (SUPCALC) used in the superficial X-ray radiation therapy; (2) the monitor unit calculator, electron monitor unit calculator (EMUC) used in the electron radiation therapy; (3) the multileaf collimator machine file creator, sliding window intensity modulated radiotherapy (SWIMRT) used in generating fluence map for research and quality assurance in intensity modulated radiation therapy; (4) the treatment planning system, DOSCTP used in the calculation of 3D dose distribution using Monte Carlo simulation; and (5) the monitor unit calculator, photon beam monitor unit calculator (PMUC) used in photon beam radiation therapy. One common issue of these GUIs is that all user-friendly interfaces are linked to complex formulas and algorithms based on various theories, which do not have to be understood and noted by the user. In that case, user only needs to input the required information with help from graphical elements in order to produce desired results. SUPCALC is a superficial radiation treatment time calculator using the GUI technique to provide a convenient way for radiation therapist to calculate the treatment time, and keep a record for the skin cancer patient. EMUC is an electron monitor unit calculator for electron radiation therapy. Instead of doing hand calculation according to pre-determined dosimetric tables, clinical user needs only to input the required drawing of electron field in computer graphical file format, prescription dose, and beam parameters to EMUC to calculate the required monitor unit for the electron beam treatment. EMUC is based on a semi-experimental theory of sector-integration algorithm. SWIMRT is a multileaf collimator machine file creator to generate a fluence map produced by a medical linear accelerator. This machine file controls the multileaf collimator to deliver intensity modulated beams for a specific fluence map used in quality assurance or research. DOSCTP is a treatment planning system using the computed tomography images. Radiation beams (photon or electron) with different energies and field sizes produced by a linear accelerator can be placed in different positions to irradiate the tumour in the patient. DOSCTP is linked to a Monte Carlo simulation engine using the EGSnrc-based code, so that 3D dose distribution can be determined accurately for radiation therapy. Moreover, DOSCTP can be used for treatment planning of patient or small animal. PMUC is a GUI for calculation of the monitor unit based on the prescription dose of patient in photon beam radiation therapy. The calculation is based on dose corrections in changes of photon beam energy, treatment depth, field size, jaw position, beam axis, treatment distance and beam modifiers. All GUIs mentioned in this review were written either by the Microsoft Visual Basic.net or a MATLAB GUI development tool called GUIDE. In addition, all GUIs were verified and tested using measurements to ensure their accuracies were up to clinical acceptable levels for implementations.

Microtron MT 25 as a source of neutrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kralik, M.; Solc, J.; Chvatil, D.

2012-08-15

The objective was to describe Microtron MT25 as a source of neutrons generated by bremsstrahlung induced photonuclear reactions in U and Pb targets. Bremsstrahlung photons were produced by electrons accelerated at energy 21.6 MeV. Spectral fluence of the generated neutrons was calculated with MCNPX code and then experimentally determined at two positions by means of a Bonner spheres spectrometer in which the detector of thermal neutrons was replaced by activation Mn tablets or track detectors CR-39 with a {sup 10}B radiator. The measured neutron spectral fluence and the calculated anisotropy served for the estimation of neutron yield from the targetsmore » and for the determination of ambient dose equivalent rate at the place of measurement. Microtron MT25 is intended as one of the sources for testing neutron sensitive devices which will be sent into the space.« less

Influence of laser wavelength on two-dimensional carbon nanosheet formation from laser-induced exfoliation of naphthalene

NASA Astrophysics Data System (ADS)

Qian, Min; Niu, Yue Ping; Gong, Shang Qing

2018-01-01

Pulsed Nd:YAG (532 nm) and Excimer (248 nm) lasers were employed to produce freestanding, two-dimensional (2D), carbon nanosheets (CNSs) from naphthalene, through laser-induced exfoliation. The polymer-to-carbon transition was investigated in terms of laser wavelengths, fluences, as well as target preparations. Continuous and porous CNSs of several nanometers in thickness and micrometers in size were obtained from 532 and 248 nm pulsed laser exfoliation of spin-coated naphthalene films, respectively. The porous morphology is ascribed to the photon-induced dissociation of chemical bonds dominated in 248 nm laser interaction with ablated naphthalene. With the increase of laser fluences from 1 to 5 J cm-2, amorphous carbon and ultrathin CNS structures were obtained in sequence. This work revealed a general mechanism of producing 2D structured carbon materials from pulsed laser exfoliation.

Atomic vapor laser isotope separation of lead-210 isotope

DOEpatents

Scheibner, K.F.; Haynam, C.A.; Johnson, M.A.; Worden, E.F.

1999-08-31

An isotopically selective laser process and apparatus for removal of Pb-210 from natural lead that involves a one-photon near-resonant, two-photon resonant excitation of one or more Rydberg levels, followed by field ionization and then electrostatic extraction. The wavelength to the near-resonant intermediate state is counter propagated with respect to the second wavelength required to populate the final Rydberg state. This scheme takes advantage of the large first excited state cross section, and only modest laser fluences are required. The non-resonant process helps to avoid two problems: first, stimulated Raman Gain due to the nearby F=3/2 hyperfine component of Pb-207 and, second, direct absorption of the first transition process light by Pb-207. 5 figs.

Atomic vapor laser isotope separation of lead-210 isotope

DOEpatents

Scheibner, Karl F.; Haynam, Christopher A.; Johnson, Michael A.; Worden, Earl F.

1999-01-01

An isotopically selective laser process and apparatus for removal of Pb-210 from natural lead that involves a one-photon near-resonant, two-photon resonant excitation of one or more Rydberg levels, followed by field ionization and then electrostatic extraction. The wavelength to the near-resonant intermediate state is counter propagated with respect to the second wavelength required to populate the final Rydberg state. This scheme takes advantage of the large first excited state cross section, and only modest laser fluences are required. The non-resonant process helps to avoid two problems: first, stimulated Raman Gain due to the nearby F=3/2 hyperfine component of Pb-207 and, second, direct absorption of the first transition process light by Pb-207.

Electronic excitation effects on nanoparticle formation in insulators under heavy-ion implantation

NASA Astrophysics Data System (ADS)

Kishimoto, N.; Plaksin, O. A.; Masuo, K.; Okubo, N.; Umeda, N.; Takeda, Y.

2006-01-01

Kinetic processes of nanoparticle formation by ion implantation was studied for the insulators of a-SiO2, LiNbO3, MgO · 2.4(Al2O3) and PMMA, either by changing ion flux or by using a co-irradiation technique of ions and photons. Under Cu-implantation of 60 keV Cu-, nanoparticles spontaneously formed without thermal annealing, indicating radiation-induced diffusion of implants. The high-flux implantation caused instable behaviors of nanoparticle morphology in a-SiO2, LiNbO3 and PMMA, i.e. enhanced atomic rearrangement or loss of nanoparticles. The spinel MgO · 2.4(Al2O3) also showed nanoparticle precipitation at 60 keV, but the precipitation tendency is less than the others. Combined irradiation of 3 MeV Cu ions and photons of 2.3 eV or 3.5 eV indicates that the electronic excitation during ion implantation significantly enhances nanoparticle precipitation, greatly depending on photon energy and fluence. The selectivity for photons can be applied to control nanoparticle precipitation.

Time-Resolved Imaging Study of Jetting Dynamics during Laser Printing of Viscoelastic Alginate Solutions.

PubMed

Zhang, Zhengyi; Xiong, Ruitong; Mei, Renwei; Huang, Yong; Chrisey, Douglas B

2015-06-16

Matrix-assisted pulsed-laser evaporation direct-write (MAPLE DW) has been successfully implemented as a promising laser printing technology for various fabrication applications, in particular, three-dimensional bioprinting. Since most bioinks used in bioprinting are viscoelastic, it is of importance to understand the jetting dynamics during the laser printing of viscoelastic fluids in order to control and optimize the laser printing performance. In this study, MAPLE DW was implemented to study the jetting dynamics during the laser printing of representative viscoelastic alginate bioinks and evaluate the effects of operating conditions (e.g., laser fluence) and material properties (e.g., alginate concentration) on the jet formation performance. Through a time-resolved imaging approach, it is found that when the laser fluence increases or the alginate concentration decreases, the jetting behavior changes from no material transferring to well-defined jetting to well-defined jetting with an initial bulgy shape to jetting with a bulgy shape to pluming/splashing. For the desirable well-defined jetting regimes, as the laser fluence increases, the jet velocity and breakup length increase while the breakup time and primary droplet size decrease. As the alginate concentration increases, the jet velocity and breakup length decrease while the breakup time and primary droplet size increase. In addition, Ohnesorge, elasto-capillary, and Weber number based phase diagrams are presented to better appreciate the dependence of jetting regimes on the laser fluence and alginate concentration.

SU-C-BRC-04: Efficient Dose Calculation Algorithm for FFF IMRT with a Simplified Bivariate Gaussian Source Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, F; Park, J; Barraclough, B

2016-06-15

Purpose: To develop an efficient and accurate independent dose calculation algorithm with a simplified analytical source model for the quality assurance and safe delivery of Flattening Filter Free (FFF)-IMRT on an Elekta Versa HD. Methods: The source model consisted of a point source and a 2D bivariate Gaussian source, respectively modeling the primary photons and the combined effect of head scatter, monitor chamber backscatter and collimator exchange effect. The in-air fluence was firstly calculated by back-projecting the edges of beam defining devices onto the source plane and integrating the visible source distribution. The effect of the rounded MLC leaf end,more » tongue-and-groove and interleaf transmission was taken into account in the back-projection. The in-air fluence was then modified with a fourth degree polynomial modeling the cone-shaped dose distribution of FFF beams. Planar dose distribution was obtained by convolving the in-air fluence with a dose deposition kernel (DDK) consisting of the sum of three 2D Gaussian functions. The parameters of the source model and the DDK were commissioned using measured in-air output factors (Sc) and cross beam profiles, respectively. A novel method was used to eliminate the volume averaging effect of ion chambers in determining the DDK. Planar dose distributions of five head-and-neck FFF-IMRT plans were calculated and compared against measurements performed with a 2D diode array (MapCHECK™) to validate the accuracy of the algorithm. Results: The proposed source model predicted Sc for both 6MV and 10MV with an accuracy better than 0.1%. With a stringent gamma criterion (2%/2mm/local difference), the passing rate of the FFF-IMRT dose calculation was 97.2±2.6%. Conclusion: The removal of the flattening filter represents a simplification of the head structure which allows the use of a simpler source model for very accurate dose calculation. The proposed algorithm offers an effective way to ensure the safe delivery of FFF-IMRT.« less

SU-E-T-178: Optically Stimulated Luminescence (OSL) Dosimetry: A Study of A-Al2O3:C Assessed by PENELOPE Monte Carlo Simulation.

PubMed

Nicolucci, P; Schuch, F

2012-06-01

To use the Monte Carlo code PENELOPE to study attenuation and tissue equivalence properties of a-Al2O3:C for OSL dosimetry. Mass attenuation coefficients of α-Al2O3 and α-Al2O3:C with carbon percent weight concentrations from 1% to 150% were simulated with PENELOPE Monte Carlo code and compared to mass attenuation coefficients from soft tissue for photon beams ranging from 50kV to 10MV. Also, the attenuation of primary photon beams of 6MV and 10MV and the generation of secondary electrons by α-Al2O3 :C dosimeters positioned on the entrance surface of a water phantom were studied. A difference of up to 90% was found in the mass attenuation coefficient between the pure \\agr;-A12O3 and the material with 150% weight concentration of dopant at 1.5 keV, corresponding to the K-edge photoelectric absorption of aluminum. However for energies above 80 keV the concentration of carbon does not affect the mass attenuation coefficient and the material presents tissue equivalence for the beams studied. The ratio between the mass attenuation coefficients for \\agr-A12O3:C and for soft tissue are less than unit due to the higher density of the \\agr-A12O3 (2.12 g/cm s ) and its tissue equivalence diminishes to lower concentrations of carbon and for lower energies due to the relation of the radiation interaction effects with atomic number. The larger attenuation of the primary photon beams by the dosimeter was 16% at 250 keV and the maximum increase in secondary electrons fluence to the entrance surface of the phantom was found as 91% at 2MeV. The use of the OSL dosimeters in radiation therapy can be optimized by use of PENELOPE Monte Carlo simulation to provide a study of the attenuation and response characteristics of the material. © 2012 American Association of Physicists in Medicine.

Challenges of Zinc-Specific Transrectal Fluorescence Tomography to Detect Prostate Cancer

DTIC Science & Technology

2013-12-01

swept-source and a 20mm-diameter transverse-imaging intra-lumenal applicator with 7 source and 8 detector channels placed in a liquid phantom. Higher...3. RESULTS ON PHANTOM IMAGING The performance of this system configuration is evaluated by using liquid and solid phantoms. 3.1 Experiments setup... direc - tions. For each possible future location of the detector, the photon fluence rate at that position is compared with the case in the semi

Experimental Evaluation of Turbidity Impact on the Fluence Rate Distribution in a UV Reactor Using a Microfluorescent Silica Detector.

PubMed

Li, Mengkai; Li, Wentao; Wen, Dong; Qiang, Zhimin; Blatchley, Ernest R

2017-11-21

Turbidity is a common parameter used to assess particle concentration in water using visible light. However, the fact that particles play multiple roles (e.g., scattering, refraction, and reflection) in influencing the optical properties of aqueous suspensions complicates examinations of their effects on ultraviolet (UV) photoreactor performance. To address this issue, UV fluence rate (FR) distributions in a photoreactor containing various particle suspensions (SiO 2 , MgO, and TiO 2 ) were measured using a microfluorescent silica detector (MFSD). Reflectance of solid particles, as well as transmittance and scattering properties of the suspensions were characterized at UV, visible, and infrared (IR) wavelengths. The results of these measurements indicated that the optical properties of all three particle types were similar at visible and IR wavelengths, but obvious differences were evident in the UV range. The FR results indicated that for turbidity associated with SiO 2 and MgO suspensions, the weighted average FR (WAFR) increased relative to deionized water. These increases were attributed to low particle photon absorption and strong scattering. In contrast, the WAFR values decreased with increasing turbidity for TiO 2 suspensions because of their high particle photon absorption and low scattering potential. The findings also indicate that measurements of scattering and transmittance at UV wavelengths can be used to quantify the effects of turbidity on UV FR distributions.

Creation of an atlas of filter positions for fluence field modulated CT.

PubMed

Szczykutowicz, Timothy P; Hermus, James

2015-04-01

Fluence field modulated CT (FFMCT) and volume of interest (VOI) CT imaging applications require adjustment of the profile of the x-ray fluence incident on a patient as a function of view angle. Since current FFMCT prototypes can theoretically take on an infinite number of configurations, measuring a calibration data set for all possible positions would not be feasible. The present work details a methodology for calculating an atlas of configurations that will span all likely body regions, patient sizes, patient positioning, and imaging modes. The hypothesis is that there exists a finite number of unique modulator configurations that effectively span the infinite number of possible fluence profiles with minimal loss in performance. CT images of a head, shoulder, thorax, abdominal, wrist, and leg anatomical slices were dilated and contracted to model small, medium, and large sized patients. Additionally, the images were positioned from iso-center by three different amounts. The modulator configurations required to compensate for each image were computed assuming a FFMCT prototype, digital beam attenuator, (DBA), was set to equalize the detector exposure. Each atlas configuration should be different from the other atlas configurations. The degree of difference was quantified using the sum of the absolute differences in filter thickness between configurations. Using this metric, a set of unique wedge configurations for which no two configurations have a metric value smaller than some threshold can be constructed. Differences in the total number of incident photons between the unconstrained filters and the atlas were studied as a function of the number of atlas positions for each anatomical site and size/off-centering combination. By varying the threshold used in creating the atlas, it was found that roughly 322 atlas positions provided an incident number of photons within 20% of using 19,440 unique filters (the number of atlas entries ranged from 7213 to 1). Additionally, for VOI applications implemented with a single VOI region, the number of required filter configurations was expressed in a simple closed form solution. The methodology proposed in this work will enable DBA-FFMCT and DBA-VOI imaging in the clinic without the need for patient specific air-scans to be performed. In addition, the methodology proposed here is directly applicable to other modulator designs such as piecewise linear, TomoTherapy multi leaf collimators, 2D fluid arrays, and inverse geometry CT.

The development and validation of a Monte Carlo model for calculating the out-of-field dose from radiotherapy treatments

NASA Astrophysics Data System (ADS)

Kry, Stephen

Introduction. External beam photon radiotherapy is a common treatment for many malignancies, but results in the exposure of the patient to radiation away from the treatment site. This out-of-field radiation irradiates healthy tissue and may lead to the induction of secondary malignancies. Out-of-field radiation is composed of photons and, at high treatment energies, neutrons. Measurement of this out-of-field dose is time consuming, often difficult, and is specific to the conditions of the measurements. Monte Carlo simulations may be a viable approach to determining the out-of-field dose quickly, accurately, and for arbitrary irradiation conditions. Methods. An accelerator head, gantry, and treatment vault were modeled with MCNPX and 6 MV and 18 MV beams were simulated. Photon doses were calculated in-field and compared to measurements made with an ion chamber in a water tank. Photon doses were also calculated out-of-field from static fields and compared to measurements made with thermoluminescent dosimeters in acrylic. Neutron fluences were calculated and compared to measurements made with gold foils. Finally, photon and neutron dose equivalents were calculated in an anthropomorphic phantom following intensity-modulated radiation therapy and compared to previously published dose equivalents. Results. The Monte Carlo model was able to accurately calculate the in-field dose. From static treatment fields, the model was also able to calculate the out-of-field photon dose within 16% at 6 MV and 17% at 18 MV and the neutron fluence within 19% on average. From the simulated IMRT treatments, the calculated out-of-field photon dose was within 14% of measurement at 6 MV and 13% at 18 MV on average. The calculated neutron dose equivalent was much lower than the measured value but is likely accurate because the measured neutron dose equivalent was based on an overestimated neutron energy. Based on the calculated out-of-field doses generated by the Monte Carlo model, it was possible to estimate the risk of fatal secondary malignancy, which was consistent with previous estimates except for the neutron discrepancy. Conclusions. The Monte Carlo model developed here is well suited to studying the out-of-field dose equivalent from photons and neutrons under a variety of irradiation configurations, including complex treatments on complex phantoms. Based on the calculated dose equivalents, it is possible to estimate the risk of secondary malignancy associated with out-of-field doses. The Monte Carlo model should be used to study, quantify, and minimize the out-of-field dose equivalent and associated risks received by patients undergoing radiation therapy.

Measurements of the reverse current of highly irradiated silicon sensors to determine the effective energy and current related damage rate

NASA Astrophysics Data System (ADS)

Wiehe, Moritz; Wonsak, S.; Kuehn, S.; Parzefall, U.; Casse, G.

2018-01-01

The reverse current of irradiated silicon sensors leads to self heating of the sensor and degrades the signal to noise ratio of a detector. Precise knowledge of the expected reverse current during detector operation is crucial for planning and running experiments in High Energy Physics. The dependence of the reverse current on sensor temperature and irradiation fluence is parametrized by the effective energy and the current related damage rate, respectively. In this study 18 n-in-p mini silicon strip sensors from companies Hamamatsu Photonics and Micron Semiconductor Ltd. were deployed. Measurements of the reverse current for different bias voltages were performed at temperatures of -32 ° C, -27 ° C and -23 ° C. The sensors were irradiated with reactor neutrons in Ljubljana to fluences ranging from 2 × 1014neq /cm2 to 2 × 1016neq /cm2. The measurements were performed directly after irradiation and after 10 and 30 days of room temperature annealing. The aim of the study presented in this paper is to investigate the reverse current of silicon sensors for high fluences of up to 2 × 1016neq /cm2 and compare the measurements to the parametrization models.

Development of High Fluence, High Conversion Efficiency X-Ray Sources at the National Ignition Facility

NASA Astrophysics Data System (ADS)

May, Mark

2017-10-01

Laser heated millimeter scale targets have provided recently some of the most powerful and energetic laboratory sources of x-ray photons (E = 6 - 24 keV) with high fluence and conversion efficiency (CE). These sources have included the K-shell of stainless steel (E = 5-9 keV) from cylindrical cavities having a CE of 6.8% (Etot 31 kJ), the K-shell of Kr (E = 8-20 keV) from gas pipes having a CE of 1.6% ( 20 kJ) and the L-shell of Ag (E = 3-5 keV) from novel nano-wire foam targets having a CE of 16% ( 81 kJ). The x-ray power and CE are dependent upon the peak electron temperature in the radiating plasma created from these underdense (ne < 0.25 nc) sources. The temperature can be limited by the available laser power and energy which can cause the fluence and the CE to be suboptimal especially for high Z K-shell sources. Cavity targets require several nanoseconds for the underdense plasma to fill the cavity but do have an increase in temperature and emission at late time from plasma stagnation on axis. In contrast the gas or foam targets heat volumetrically to an underdense source in less than a nanosecond which can be more efficient. Both the experimental and simulation details of these high fluence x-ray sources will be discussed. This work was done under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.

Light-stimulated cell expansion in bean (Phaseolus vulgaris L.) leaves. II. Quantity and quality of light required

NASA Technical Reports Server (NTRS)

Van Volkenburgh, E.; Cleland, R. E.; Watanabe, M.

1990-01-01

The quantity and quality of light required for light-stimulated cell expansion in leaves of Phaseolus vulgaris L. have been determined. Seedlings were grown in dim red light (RL; 4 micromoles photons m-2 s-1) until cell division in the primary leaves was completed, then excised discs were incubated in 10 mM sucrose plus 10 mM KCl in a variety of light treatments. The growth response of discs exposed to continuous white light (WL) for 16 h was saturated at 100 micromoles m-2 s-1, and did not show reciprocity. Extensive, but not continuous, illumination was needed for maximal growth. The wavelength dependence of disc expansion was determined from fluence-response curves obtained from 380 to 730 nm provided by the Okazaki Large Spectrograph. Blue (BL; 460 nm) and red light (RL; 660 nm) were most effective in promoting leaf cell growth, both in photosynthetically active and inhibited leaf discs. Far-red light (FR; 730 nm) reduced the effectiveness of RL, but not BL, indicating that phytochrome and a separate blue-light receptor mediate expansion of leaf cells.

Model for estimating the penetration depth limit of the time-reversed ultrasonically encoded optical focusing technique

PubMed Central

Jang, Mooseok; Ruan, Haowen; Judkewitz, Benjamin; Yang, Changhuei

2014-01-01

The time-reversed ultrasonically encoded (TRUE) optical focusing technique is a method that is capable of focusing light deep within a scattering medium. This theoretical study aims to explore the depth limits of the TRUE technique for biological tissues in the context of two primary constraints – the safety limit of the incident light fluence and a limited TRUE’s recording time (assumed to be 1 ms), as dynamic scatterer movements in a living sample can break the time-reversal scattering symmetry. Our numerical simulation indicates that TRUE has the potential to render an optical focus with a peak-to-background ratio of ~2 at a depth of ~103 mm at wavelength of 800 nm in a phantom with tissue scattering characteristics. This study sheds light on the allocation of photon budget in each step of the TRUE technique, the impact of low signal on the phase measurement error, and the eventual impact of the phase measurement error on the strength of the TRUE optical focus. PMID:24663917

Atomization efficiency and photon yield in laser-induced breakdown spectroscopy analysis of single nanoparticles in an optical trap

NASA Astrophysics Data System (ADS)

Purohit, Pablo; Fortes, Francisco J.; Laserna, J. Javier

2017-04-01

Laser-induced breakdown spectroscopy (LIBS) was employed for investigating the influence of particle size on the dissociation efficiency and the absolute production of photons per mass unit of airborne solid graphite spheres under single-particle regime. Particles of average diameter of 400 nm were probed and compared with 2 μm particles. Samples were first catapulted into aerosol form and then secluded in an optical trap set by a 532 nm laser. Trap stability was quantified before subjecting particles to LIBS analysis. Fine alignment of the different lines comprising the optical catapulting-optical trapping-laser-induced breakdown spectroscopy instrument and tuning of excitation parameters conditioning the LIBS signal such as fluence and acquisition delay are described in detail with the ultimate goal of acquiring clear spectroscopic data on masses as low as 75 fg. The atomization efficiency and the photon yield increase as the particle size becomes smaller. Time-resolved plasma imaging studies were conducted to elucidate the mechanisms leading to particle disintegration and excitation.

Nonequilibrium phase transitions in cuprates observed by ultrafast electron crystallography.

PubMed

Gedik, Nuh; Yang, Ding-Shyue; Logvenov, Gennady; Bozovic, Ivan; Zewail, Ahmed H

2007-04-20

Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions. The observed transient behavior displays a notable "structural isosbestic" point and a threshold effect for the dependence of c-axis expansion (Deltac) on fluence (F), with Deltac/F = 0.02 angstrom/(millijoule per square centimeter). This threshold for photon doping occurs at approximately 0.12 photons per copper site, which is unexpectedly close to the density (per site) of chemically doped carriers needed to induce superconductivity.

Monte Carlo calculation of the neutron dose to a fetus at commercial flight altitudes

NASA Astrophysics Data System (ADS)

Alves, M. C.; Galeano, D. C.; Santos, W. S.; Hunt, John G.; d'Errico, Francesco; Souza, S. O.; de Carvalho Júnior, A. B.

2017-11-01

Aircrew members are exposed to primary cosmic rays as well as to secondary radiations from the interaction of cosmic rays with the atmosphere and with the aircraft. The radiation field at flight altitudes comprises neutrons, protons, electrons, positrons, photons, muons and pions. Generally, 50% of the effective dose to airplane passengers is due to neutrons. Care must be taken especially with pregnant aircrew members and frequent fliers so that the equivalent dose to the fetus will not exceed prescribed limits during pregnancy (1 mSv according to ICRP, and 5 mSv according to NCRP). Therefore, it is necessary to evaluate the equivalent dose to a fetus in the maternal womb. Up to now, the equivalent dose rate to a fetus at commercial flight altitudes was obtained using stylized pregnant-female phantom models. The aim of this study was calculating neutron fluence to dose conversion coefficients for a fetus of six months of gestation age using a new, realistic pregnant-female mesh-phantom. The equivalent dose rate to a fetus during an intercontinental flight was also calculated by folding our conversion coefficients with published spectral neutron flux data. The calculated equivalent dose rate to the fetus was 2.35 μSv.h-1, that is 1.5 times higher than equivalent dose rates reported in the literature. The neutron fluence to dose conversion coefficients for the fetus calculated in this study were 2.7, 3.1 and 3.9 times higher than those from previous studies using fetus models of 3, 6 and 9 months of gestation age, respectively. The differences between our study and data from the literature highlight the importance of using more realistic anthropomorphic phantoms to estimate doses to a fetus in pregnant aircrew members.

Correlation of Upper-Atmospheric 7-Be with Solar Energetic Particle Events

NASA Technical Reports Server (NTRS)

Phillips, G. W.; Share, G. H.; King, S. E.; August, R. A.; Tylka, A. J.; Adams, J. H., Jr.; Panasyuk, M. I.; Nymmik, R. A.; Kuzhevskij, B. M.; Kulikauskas, V. S.;

Study of surface properties of ATLAS12 strip sensors and their radiation resistance

NASA Astrophysics Data System (ADS)

Mikestikova, M.; Allport, P. P.; Baca, M.; Broughton, J.; Chisholm, A.; Nikolopoulos, K.; Pyatt, S.; Thomas, J. P.; Wilson, J. A.; Kierstead, J.; Kuczewski, P.; Lynn, D.; Hommels, L. B. A.; Ullan, M.; Bloch, I.; Gregor, I. M.; Tackmann, K.; Hauser, M.; Jakobs, K.; Kuehn, S.; Mahboubi, K.; Mori, R.; Parzefall, U.; Clark, A.; Ferrere, D.; Sevilla, S. Gonzalez; Ashby, J.; Blue, A.; Bates, R.; Buttar, C.; Doherty, F.; McMullen, T.; McEwan, F.; O'Shea, V.; Kamada, S.; Yamamura, K.; Ikegami, Y.; Nakamura, K.; Takubo, Y.; Unno, Y.; Takashima, R.; Chilingarov, A.; Fox, H.; Affolder, A. A.; Casse, G.; Dervan, P.; Forshaw, D.; Greenall, A.; Wonsak, S.; Wormald, M.; Cindro, V.; Kramberger, G.; Mandić, I.; Mikuž, M.; Gorelov, I.; Hoeferkamp, M.; Palni, P.; Seidel, S.; Taylor, A.; Toms, K.; Wang, R.; Hessey, N. P.; Valencic, N.; Hanagaki, K.; Dolezal, Z.; Kodys, P.; Bohm, J.; Stastny, J.; Bevan, A.; Beck, G.; Milke, C.; Domingo, M.; Fadeyev, V.; Galloway, Z.; Hibbard-Lubow, D.; Liang, Z.; Sadrozinski, H. F.-W.; Seiden, A.; To, K.; French, R.; Hodgson, P.; Marin-Reyes, H.; Parker, K.; Jinnouchi, O.; Hara, K.; Sato, K.; Hagihara, M.; Iwabuchi, S.; Bernabeu, J.; Civera, J. V.; Garcia, C.; Lacasta, C.; Marti i Garcia, S.; Rodriguez, D.; Santoyo, D.; Solaz, C.; Soldevila, U.

2016-09-01

A radiation hard n+-in-p micro-strip sensor for the use in the Upgrade of the strip tracker of the ATLAS experiment at the High Luminosity Large Hadron Collider (HL-LHC) has been developed by the "ATLAS ITk Strip Sensor collaboration" and produced by Hamamatsu Photonics. Surface properties of different types of end-cap and barrel miniature sensors of the latest sensor design ATLAS12 have been studied before and after irradiation. The tested barrel sensors vary in "punch-through protection" (PTP) structure, and the end-cap sensors, whose stereo-strips differ in fan geometry, in strip pitch and in edge strip ganging options. Sensors have been irradiated with proton fluences of up to 1×1016 neq/cm2, by reactor neutron fluence of 1×1015 neq/cm2 and by gamma rays from 60Co up to dose of 1 MGy. The main goal of the present study is to characterize the leakage current for micro-discharge breakdown voltage estimation, the inter-strip resistance and capacitance, the bias resistance and the effectiveness of PTP structures as a function of bias voltage and fluence. It has been verified that the ATLAS12 sensors have high breakdown voltage well above the operational voltage which implies that different geometries of sensors do not influence their stability. The inter-strip isolation is a strong function of irradiation fluence, however the sensor performance is acceptable in the expected range for HL-LHC. New gated PTP structure exhibits low PTP onset voltage and sharp cut-off of effective resistance even at the highest tested radiation fluence. The inter-strip capacitance complies with the technical specification required before irradiation and no radiation-induced degradation was observed. A summary of ATLAS12 sensors tests is presented including a comparison of results from different irradiation sites. The measured characteristics are compared with the previous prototype of the sensor design, ATLAS07.

Effects of 810 nm laser on mouse primary cortical neurons

NASA Astrophysics Data System (ADS)

Kharkwal, Gitika B.; Sharma, Sulbha K.; Huang, Ying-Ying; De Taboada, Luis; McCarthy, Thomas; Hamblin, Michael R.

2011-03-01

In the past four decades numerous studies have reported the efficacy of low level light (laser) therapy (LLLT) as a treatment for diverse diseases and injuries. Recent studies have shown that LLLT can biomodulate processes in the central nervous system and has been extensively studied as a stroke treatment. However there is still a lack of knowledge on the effects of LLLT at the cellular level in neurons. The present study aimed to study the effect of 810 nm laser on several cellular processes in primary cortical neurons cultured from mouse embryonic brains. Neurons were irradiated with light dose of 0.03, 0.3, 3, 10 and 30 J/cm2 and intracellular levels of reactive oxygen species, nitric oxide and calcium were measured. The changes in mitochondrial function in response to light were studied in terms of adenosine triphosphate (ATP) and mitochondrial membrane potential (MMP). Light induced a significant increase in calcium, ATP and MMP at lower fluences and a decrease at higher fluence. ROS was induced significantly by light at all light doses. Nitric oxide levels also showed an increase on treatment with light. The results of the present study suggest that LLLT at lower fluences is capable of inducing mediators of cell signaling process which in turn may be responsible for the biomodulatory effects of the low level laser. At higher fluences beneficial mediators are reduced but potentially harmful mediators are increased thus offering an explanation for the biphasic dose response.

Role of laser fluence in protein synthesis of cultured DRG neurons following low-level laser irradiation

NASA Astrophysics Data System (ADS)

Zheng, Liqin; Qiu, Caimin; Wang, Yuhua; Zeng, Yixiu; Yang, Hongqin; Zhang, Yanding; Xie, Shusen

2014-11-01

Low-level lasers have been used to relieve pain in clinical for many years. But the mechanism is not fully clear. In animal models, nitric oxide (NO) has been reported involving in the transmission and modulation of nociceptive signals. So the objective of this study was to establish whether low-level laser with different fluence could stimulate the production of nitric oxide synthese (NOS), which produces NO in cultured primary dorsal root ganglion neurons (DRG neurons). The primary DRG neurons were isolated from healthy Sprague Dawley rats (8-12 weeks of age) and spread on 35 mm culture dishes specially used for confocal microscopy. 24 hours after spreading, cells were irradiated with 658 nm laser for two consecutive days at the energy density of 20, 40, 60 and 80 mJ·cm-2 respectively. Control groups were not exposed to the laser, but were kept under the same conditions as the irradiated ones. The synthesis of NOS after laser irradiation was detected by immunofluorescence assay, and the changes of NOS were evaluated using confocal microscopy and Image J software. The results showed that all the laser fluence could promote the production of NOS in DRG neurons, especially the 60 mJ·cm-2 . These results demonstrated that low-level laser irradiation could modify protein synthesis in a dose- or fluence- dependent manner, and indicated that low-level laser irradiation might achieve the analgesic effect through modulation of NO production.

Some computer graphical user interfaces in radiation therapy

PubMed Central

Chow, James C L

2016-01-01

In this review, five graphical user interfaces (GUIs) used in radiation therapy practices and researches are introduced. They are: (1) the treatment time calculator, superficial X-ray treatment time calculator (SUPCALC) used in the superficial X-ray radiation therapy; (2) the monitor unit calculator, electron monitor unit calculator (EMUC) used in the electron radiation therapy; (3) the multileaf collimator machine file creator, sliding window intensity modulated radiotherapy (SWIMRT) used in generating fluence map for research and quality assurance in intensity modulated radiation therapy; (4) the treatment planning system, DOSCTP used in the calculation of 3D dose distribution using Monte Carlo simulation; and (5) the monitor unit calculator, photon beam monitor unit calculator (PMUC) used in photon beam radiation therapy. One common issue of these GUIs is that all user-friendly interfaces are linked to complex formulas and algorithms based on various theories, which do not have to be understood and noted by the user. In that case, user only needs to input the required information with help from graphical elements in order to produce desired results. SUPCALC is a superficial radiation treatment time calculator using the GUI technique to provide a convenient way for radiation therapist to calculate the treatment time, and keep a record for the skin cancer patient. EMUC is an electron monitor unit calculator for electron radiation therapy. Instead of doing hand calculation according to pre-determined dosimetric tables, clinical user needs only to input the required drawing of electron field in computer graphical file format, prescription dose, and beam parameters to EMUC to calculate the required monitor unit for the electron beam treatment. EMUC is based on a semi-experimental theory of sector-integration algorithm. SWIMRT is a multileaf collimator machine file creator to generate a fluence map produced by a medical linear accelerator. This machine file controls the multileaf collimator to deliver intensity modulated beams for a specific fluence map used in quality assurance or research. DOSCTP is a treatment planning system using the computed tomography images. Radiation beams (photon or electron) with different energies and field sizes produced by a linear accelerator can be placed in different positions to irradiate the tumour in the patient. DOSCTP is linked to a Monte Carlo simulation engine using the EGSnrc-based code, so that 3D dose distribution can be determined accurately for radiation therapy. Moreover, DOSCTP can be used for treatment planning of patient or small animal. PMUC is a GUI for calculation of the monitor unit based on the prescription dose of patient in photon beam radiation therapy. The calculation is based on dose corrections in changes of photon beam energy, treatment depth, field size, jaw position, beam axis, treatment distance and beam modifiers. All GUIs mentioned in this review were written either by the Microsoft Visual Basic.net or a MATLAB GUI development tool called GUIDE. In addition, all GUIs were verified and tested using measurements to ensure their accuracies were up to clinical acceptable levels for implementations. PMID:27027225

131I activity quantification of gamma camera planar images.

PubMed

Barquero, Raquel; Garcia, Hugo P; Incio, Monica G; Minguez, Pablo; Cardenas, Alexander; Martínez, Daniel; Lassmann, Michael

2017-02-07

A procedure to estimate the activity in target tissues in patients during the therapeutic administration of 131 I radiopharmaceutical treatment for thyroid conditions (hyperthyroidism and differentiated thyroid cancer) using a gamma camera (GC) with a high energy (HE) collimator, is proposed. Planar images are acquired for lesions of different sizes r, and at different distances d, in two HE GC systems. Defining a region of interest (ROI) on the image of size r, total counts n g are measured. Sensitivity S (cps MBq -1 ) in each acquisition is estimated as the product of the geometric G and the intrinsic efficiency η 0 . The mean fluence of 364 keV photons arriving at the ROI per disintegration G, is calculated with the MCNPX code, simulating the entire GC and the HE collimator. Intrinsic efficiency η 0 is estimated from a calibration measurement of a plane reference source of 131 I in air. Values of G and S for two GC systems-Philips Skylight and Siemens e-cam-are calculated. The total range of possible sensitivity values in thyroidal imaging in the e-cam and skylight GC measure from 7 cps MBq -1 to 35 cps MBq -1 , and from 6 cps MBq -1 to 29 cps MBq -1 , respectively. These sensitivity values have been verified with the SIMIND code, with good agreement between them. The results have been validated with experimental measurements in air, and in a medium with scatter and attenuation. The counts in the ROI can be produced by direct, scatter and penetration photons. The fluence value for direct photons is constant for any r and d values, but scatter and penetration photons show different values related to specific r and d values, resulting in the large sensitivity differences found. The sensitivity in thyroidal GC planar imaging is strongly dependent on uptake size, and distance from the GC. An individual value for the acquisition sensitivity of each lesion can significantly alleviate the level of uncertainty in the measurement of thyroid uptake activity for each patient.

131I activity quantification of gamma camera planar images

NASA Astrophysics Data System (ADS)

Barquero, Raquel; Garcia, Hugo P.; Incio, Monica G.; Minguez, Pablo; Cardenas, Alexander; Martínez, Daniel; Lassmann, Michael

2017-02-01

A procedure to estimate the activity in target tissues in patients during the therapeutic administration of 131I radiopharmaceutical treatment for thyroid conditions (hyperthyroidism and differentiated thyroid cancer) using a gamma camera (GC) with a high energy (HE) collimator, is proposed. Planar images are acquired for lesions of different sizes r, and at different distances d, in two HE GC systems. Defining a region of interest (ROI) on the image of size r, total counts n g are measured. Sensitivity S (cps MBq-1) in each acquisition is estimated as the product of the geometric G and the intrinsic efficiency η 0. The mean fluence of 364 keV photons arriving at the ROI per disintegration G, is calculated with the MCNPX code, simulating the entire GC and the HE collimator. Intrinsic efficiency η 0 is estimated from a calibration measurement of a plane reference source of 131I in air. Values of G and S for two GC systems—Philips Skylight and Siemens e-cam—are calculated. The total range of possible sensitivity values in thyroidal imaging in the e-cam and skylight GC measure from 7 cps MBq-1 to 35 cps MBq-1, and from 6 cps MBq-1 to 29 cps MBq-1, respectively. These sensitivity values have been verified with the SIMIND code, with good agreement between them. The results have been validated with experimental measurements in air, and in a medium with scatter and attenuation. The counts in the ROI can be produced by direct, scatter and penetration photons. The fluence value for direct photons is constant for any r and d values, but scatter and penetration photons show different values related to specific r and d values, resulting in the large sensitivity differences found. The sensitivity in thyroidal GC planar imaging is strongly dependent on uptake size, and distance from the GC. An individual value for the acquisition sensitivity of each lesion can significantly alleviate the level of uncertainty in the measurement of thyroid uptake activity for each patient.

Photodiode radiation hardness, lyman-alpha emitting galaxies and photon detection in liquid argon neutrino detectors

NASA Astrophysics Data System (ADS)

Baptista, Brian

2013-12-01

My dissertation is comprised of three projects: 1) studies of Lyman-alpha Emitting galaxies (LAEs), 2) radiation hardness studies of InGaAs photodiodes (PDs), and 3) scintillation photon detection in liquid argon (LAr) neutrino detectors. I began work on the project that has now become WFIRST, developing a science case that would use WFIRST after launch for the observation of LAEs. The radiation hardness of PDs was as an effort to support the WFIRST calibration team. When WFIRST was significantly delayed, I joined an R&D effort that applied my skills to work on photon detection in LAr neutrino detectors. I report results on a broadband selection method developed to detect high equivalent width (EW) LAEs. Using photometry from the CFHT-Legacy Survey Deep 2 and 3 fields, I have spectroscopically confirmed 63 z=2.5-3.5 LAEs using the WIYN/Hydra spectrograph. Using UV continuum-fitting techniques I computed properties such as EWs, internal reddening and star formation rates. 62 of my LAEs show evidence to be normal dust-free LAEs. Second, I present an investigation into the effects of ionizing proton radiation on commercial off-the-shelf InGaAs PDs. I developed a monochromator-based test apparatus that utilized NIST-calibrated reference PDs. I tested the PDs for changes to their dark current, relative responsivity as a function of wavelength, and absolute responsivity. I irradiated the test PDs using 30, 52, and 98 MeV protons at the IU Cyclotron Facility. I found the InGaAs PDs showed increased dark current as the fluence increased with no evidence of broadband response degradation at the fluences expected at an L2 orbit and a 10-year mission lifetime. Finally, I detail my efforts on technology development of both optical detector technologies and waveshifting light guide construction for LAr vacuum UV scintillation light. Cryogenic neutrino detectors use photon detection for both accelerator based science and for SNe neutrino detection and proton decay. I have developed waveshifter doped cast acrylic light guides that convert scintillation light and guide the waveshifted light to SiPMs detectors.

Mechanochemistry for shock wave energy dissipation

NASA Astrophysics Data System (ADS)

Shaw, William L.; Ren, Yi; Moore, Jeffrey S.; Dlott, Dana D.

2017-01-01

Using a laser-driven flyer-plate apparatus to launch 75 μm thick Al flyers up to 2.8 km/s, we developed a technique for detecting the attenuation of shock waves by mechanically-driven chemical reactions. The attenuating sample was spread on an ultrathin Au mirror deposited onto a glass window having a known Hugoniot. As shock energy exited the sample and passed through the mirror, into the glass, photonic Doppler velocimetry monitored the velocity profile of the ultrathin mirror. Knowing the window Hugoniot, the velocity profile could be quantitatively converted into a shock energy flux or fluence. The flux gave the temporal profile of the shock front, and showed how the shock front was reshaped by passing through the dissipative medium. The fluence, the time-integrated flux, showed how much shock energy was transmitted through the sample. Samples consisted of microgram quantities of carefully engineered organic compounds selected for their potential to undergo negative-volume chemistry. Post mortem analytical methods were used to confirm that shock dissipation was associated with shock-induced chemical reactions.

On the properties of synchrotron-like X-ray emission from laser wakefield accelerated electron beams

NASA Astrophysics Data System (ADS)

McGuffey, C.; Schumaker, W.; Matsuoka, T.; Chvykov, V.; Dollar, F.; Kalintchenko, G.; Kneip, S.; Najmudin, Z.; Mangles, S. P. D.; Vargas, M.; Yanovsky, V.; Maksimchuk, A.; Thomas, A. G. R.; Krushelnick, K.

2018-04-01

The electric and magnetic fields responsible for electron acceleration in a Laser Wakefield Accelerator (LWFA) also cause electrons to radiate x-ray photons. Such x-ray pulses have several desirable properties including short duration and being well collimated with tunable high energy. We measure the scaling of this x-ray source experimentally up to laser powers greater than 100 TW. An increase in laser power allows electron trapping at a lower density as well as with an increased trapped charge. These effects resulted in an x-ray fluence that was measured to increase non-linearly with laser power. The fluence of x-rays was also compared with that produced from K-α emission resulting from a solid target interaction for the same energy laser pulse. The flux was shown to be comparable, but the LWFA x-rays had a significantly smaller source size. This indicates that such a source may be useful as a backlighter for probing high energy density plasmas with ultrafast temporal resolution.

Pump-probe STM light emission spectroscopy for detection of photo-induced semiconductor-metal phase transition of VO2

NASA Astrophysics Data System (ADS)

Sakai, Joe; Katano, Satoshi; Kuwahara, Masashi; Uehara, Yoichi

2017-10-01

We attempted to observe pump-probe scanning tunneling microscopy (STM)-light emission (LE) from a VO2 thin film grown on a rutile TiO2(0 0 1) substrate, with an Ag tip fixed over a semiconducting domain. Laser pulses from a Ti:sapphire laser (wavelength 920 nm pulse width less than 1.5 ps) irradiated the tip-sample gap as pump and probe light sources. With a photon energy of 2.7 eV, suggesting phase transition from semiconducting monoclinic (M) to metallic rutile (R) phases in relation to the electronic band structure, faint LE was observed roughly 30 ps after the irradiation of the pump pulse, followed by retention for roughly 20 ps. The incident energy fluence of the pump pulse at the gap was five orders of magnitude lower than the threshold value for reported photo-induced M-R phase transition. The mechanism that makes it possible to reduce the threshold fluence is discussed.

Pump-probe STM light emission spectroscopy for detection of photo-induced semiconductor-metal phase transition of VO2.

PubMed

Sakai, Joe; Katano, Satoshi; Kuwahara, Masashi; Uehara, Yoichi

2017-10-11

We attempted to observe pump-probe scanning tunneling microscopy (STM)-light emission (LE) from a VO 2 thin film grown on a rutile TiO 2 (0 0 1) substrate, with an Ag tip fixed over a semiconducting domain. Laser pulses from a Ti:sapphire laser (wavelength 920 nm; pulse width less than 1.5 ps) irradiated the tip-sample gap as pump and probe light sources. With a photon energy of 2.7 eV, suggesting phase transition from semiconducting monoclinic (M) to metallic rutile (R) phases in relation to the electronic band structure, faint LE was observed roughly 30 ps after the irradiation of the pump pulse, followed by retention for roughly 20 ps. The incident energy fluence of the pump pulse at the gap was five orders of magnitude lower than the threshold value for reported photo-induced M-R phase transition. The mechanism that makes it possible to reduce the threshold fluence is discussed.

Response Funtions for Computing Absorbed Dose to Skeletal Tissues from Photon Irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eckerman, Keith F; Bolch, W E; Zankl, M

2007-01-01

The calculation of absorbed dose in skeletal tissues at radiogenic risk has been a difficult problem because the relevant structures cannot be represented in conventional geometric terms nor can they be visualised in the tomographic image data used to define the computational models of the human body. The active marrow, the tissue of concern in leukaemia induction, is present within the spongiosa regions of trabecular bone, whereas the osteoprogenitor cells at risk for bone cancer induction are considered to be within the soft tissues adjacent to the mineral surfaces. The International Commission on Radiological Protection (ICRP) recommends averaging the absorbedmore » energy over the active marrow within the spongiosa and over the soft tissues within 10 mm of the mineral surface for leukaemia and bone cancer induction, respectively. In its forthcoming recommendation, it is expected that the latter guidance will be changed to include soft tissues within 50 mm of the mineral surfaces. To address the computational problems, the skeleton of the proposed ICRP reference computational phantom has been subdivided to identify those voxels associated with cortical shell, spongiosa and the medullary cavity of the long bones. It is further proposed that the Monte Carlo calculations with these phantoms compute the energy deposition in the skeletal target tissues as the product of the particle fluence in the skeletal subdivisions and applicable fluence-to-dose response functions. This paper outlines the development of such response functions for photons.« less

ICF Gamma-Ray measurements on the NIF

NASA Astrophysics Data System (ADS)

Herrmann, Hans; Kim, Y.; Hoffman, N. M.; Batha, S. H.; Stoeffl, W.; Church, J. A.; Sayre, D. B.; Liebman, J. A.; Cerjan, C. J.; Carpenter, A. C.; Grafil, E. M.; Khater, H. Y.; Horsfield, C. J.; Rubery, M.

2013-10-01

The primary objective of the NIF Gamma Reaction History (GRH) diagnostic is to provide bang time and burn width information in order to constrain implosion simulation parameters such as shell velocity and confinement time. This is accomplished by measuring DT fusion gamma-rays with energy-thresholded Gas Cherenkov detectors that convert MeV gamma-rays into UV/visible photons for high-bandwidth optical detection. Burn-weighted CH ablator areal density is also inferred based on measurement of the 12C(n,n') gammas emitted at 4.44 MeV from DT neutrons inelastically scattering off carbon nuclei as they pass through the plastic ablator. This requires that the four independent GRH gas cells be set to differing Cherenkov thresholds (e.g., 2.9, 4.5, 8 & 10 MeV) in order to be able to unfold the primary spectral components predicted to be in the gamma ray energy spectrum (i.e., DT γ 27Al & 28Si (n,n') γ from the thermo-mechanical package (TMP); and 12C(n,n' γ from the ablator). The GRH response to 12C(n,n') γ is calibrated in-situ by placing a known areal density of carbon in the form of a puck placed ~6 cm from a DT exploding pusher implosion. Comparisons between inferred gamma fluences and simulations based on the nuclear cross sections databases will be presented. Supported by US DOE NNSA.

Characterization of the secondary neutron field produced during treatment of an anthropomorphic phantom with x-rays, protons and carbon ions

NASA Astrophysics Data System (ADS)

La Tessa, C.; Berger, T.; Kaderka, R.; Schardt, D.; Burmeister, S.; Labrenz, J.; Reitz, G.; Durante, M.

2014-04-01

Short- and long-term side effects following the treatment of cancer with radiation are strongly related to the amount of dose deposited to the healthy tissue surrounding the tumor. The characterization of the radiation field outside the planned target volume is the first step for estimating health risks, such as developing a secondary radioinduced malignancy. In ion and high-energy photon treatments, the major contribution to the dose deposited in the far-out-of-field region is given by neutrons, which are produced by nuclear interaction of the primary radiation with the beam line components and the patient’s body. Measurements of the secondary neutron field and its contribution to the absorbed dose and equivalent dose for different radiotherapy technologies are presented in this work. An anthropomorphic RANDO phantom was irradiated with a treatment plan designed for a simulated 5 × 2 × 5 cm3 cancer volume located in the center of the head. The experiment was repeated with 25 MV IMRT (intensity modulated radiation therapy) photons and charged particles (protons and carbon ions) delivered with both passive modulation and spot scanning in different facilities. The measurements were performed with active (silicon-scintillation) and passive (bubble, thermoluminescence 6LiF:Mg, Ti (TLD-600) and 7LiF:Mg, Ti (TLD-700)) detectors to investigate the production of neutral particles both inside and outside the phantom. These techniques provided the whole energy spectrum (E ⩽ 20 MeV) and corresponding absorbed dose and dose equivalent of photo neutrons produced by x-rays, the fluence of thermal neutrons for all irradiation types and the absorbed dose deposited by neutrons with 0.8 < E < 10 MeV during the treatment with scanned carbon ions. The highest yield of thermal neutrons is observed for photons and, among ions, for passively modulated beams. For the treatment with high-energy x-rays, the contribution of secondary neutrons to the dose equivalent is of the same order of magnitude as the primary radiation. In carbon therapy delivered with raster scanning, the absorbed dose deposited by neutrons in the energy region between 0.8 and 10 MeV is almost two orders of magnitude lower than charged fragments. We conclude that, within the energy range explored in this experimental work, the out-of-field dose from secondary neutrons is lowest for ions delivered by scanning, followed by passive modulation, and finally by high-energy IMRT photons.

Characterization of the secondary neutron field produced during treatment of an anthropomorphic phantom with x-rays, protons and carbon ions.

PubMed

Tessa, C La; Berger, T; Kaderka, R; Schardt, D; Burmeister, S; Labrenz, J; Reitz, G; Durante, M

2014-04-21

Short- and long-term side effects following the treatment of cancer with radiation are strongly related to the amount of dose deposited to the healthy tissue surrounding the tumor. The characterization of the radiation field outside the planned target volume is the first step for estimating health risks, such as developing a secondary radioinduced malignancy. In ion and high-energy photon treatments, the major contribution to the dose deposited in the far-out-of-field region is given by neutrons, which are produced by nuclear interaction of the primary radiation with the beam line components and the patient's body. Measurements of the secondary neutron field and its contribution to the absorbed dose and equivalent dose for different radiotherapy technologies are presented in this work. An anthropomorphic RANDO phantom was irradiated with a treatment plan designed for a simulated 5 × 2 × 5 cm³ cancer volume located in the center of the head. The experiment was repeated with 25 MV IMRT (intensity modulated radiation therapy) photons and charged particles (protons and carbon ions) delivered with both passive modulation and spot scanning in different facilities. The measurements were performed with active (silicon-scintillation) and passive (bubble, thermoluminescence ⁶LiF:Mg, Ti (TLD-600) and ⁷LiF:Mg, Ti (TLD-700)) detectors to investigate the production of neutral particles both inside and outside the phantom. These techniques provided the whole energy spectrum (E ≤ 20 MeV) and corresponding absorbed dose and dose equivalent of photo neutrons produced by x-rays, the fluence of thermal neutrons for all irradiation types and the absorbed dose deposited by neutrons with 0.8 < E < 10 MeV during the treatment with scanned carbon ions. The highest yield of thermal neutrons is observed for photons and, among ions, for passively modulated beams. For the treatment with high-energy x-rays, the contribution of secondary neutrons to the dose equivalent is of the same order of magnitude as the primary radiation. In carbon therapy delivered with raster scanning, the absorbed dose deposited by neutrons in the energy region between 0.8 and 10 MeV is almost two orders of magnitude lower than charged fragments. We conclude that, within the energy range explored in this experimental work, the out-of-field dose from secondary neutrons is lowest for ions delivered by scanning, followed by passive modulation, and finally by high-energy IMRT photons.

Characterisation of the epithermal neutron irradiation facility at the Portuguese research reactor using MCNP.

PubMed

Beasley, D G; Fernandes, A C; Santos, J P; Ramos, A R; Marques, J G; King, A

2015-05-01

The radiation field at the epithermal beamline and irradiation chamber installed at the Portuguese Research Reactor (RPI) at the Campus Tecnológico e Nuclear of Instituto Superior Técnico was characterised in the context of Prompt Gamma Neutron Activation Analysis (PGNAA) applications. Radiographic films, activation foils and thermoluminescence dosimeters were used to measure the neutron fluence and photon dose rates in the irradiation chamber. A fixed-source MCNPX model of the beamline and chamber was developed and compared to measurements in the first step towards planning a new irradiation chamber. The high photon background from the reactor results in the saturation of the detector and the current facility configuration yields an intrinsic insensitivity to various elements of interest for PGNAA. These will be addressed in future developments. Copyright © 2015 Elsevier Ltd. All rights reserved.

Excitonic lasing in solution-processed subwavelength nanosphere assemblies

DOE PAGES

Appavoo, Kannatassen; Liu, Xiaoze; Menon, Vinod; ...

2016-02-03

Lasing in solution-processed nanomaterials has gained significant interest because of the potential for low-cost integrated photonic devices. Still, a key challenge is to utilize a comprehensive knowledge of the system’s spectral and temporal dynamics to design low-threshold lasing devices. Here, we demonstrate intrinsic lasing (without external cavity) at low-threshold in an ultrathin film of coupled, highly crystalline nanospheres with overall thickness on the order of ~λ/4. The cavity-free geometry consists of ~35 nm zinc oxide nanospheres that collectively localize the in-plane emissive light fields while minimizing scattering losses, resulting in excitonic lasing with fluence thresholds at least an order ofmore » magnitude lower than previous UV-blue random and quantum-dot lasers (<75 μJ/cm 2). Fluence-dependent effects, as quantified by subpicosecond transient spectroscopy, highlight the role of phonon-mediated processes in excitonic lasing. Subpicosecond evolution of distinct lasing modes, together with three-dimensional electromagnetic simulations, indicate a random lasing process, which is in violation of the commonly cited criteria of strong scattering from individual nanostructures and an optically thick sample. Subsequently, an electron–hole plasma mechanism is observed with increased fluence. Furthermore, these results suggest that coupled nanostructures with high crystallinity, fabricated by low-cost solution-processing methods, can function as viable building blocks for high-performance optoelectronics devices.« less

Ultrafast modulation of the plasma frequency of vertically aligned indium tin oxide rods.

PubMed

Tice, Daniel B; Li, Shi-Qiang; Tagliazucchi, Mario; Buchholz, D Bruce; Weiss, Emily A; Chang, Robert P H

2014-03-12

Light-matter interaction at the nanoscale is of particular interest for future photonic integrated circuits and devices with applications ranging from communication to sensing and imaging. In this Letter a combination of transient absorption (TA) and the use of third harmonic generation as a probe (THG-probe) has been adopted to investigate the response of the localized surface plasmon resonances (LSPRs) of vertically aligned indium tin oxide rods (ITORs) upon ultraviolet light (UV) excitation. TA experiments, which are sensitive to the extinction of the LSPR, show a fluence-dependent increase in the frequency and intensity of the LSPR. The THG-probe experiments show a fluence-dependent decrease of the LSPR-enhanced local electric field intensity within the rod, consistent with a shift of the LSPR to higher frequency. The kinetics from both TA and THG-probe experiments are found to be independent of the fluence of the pump. These results indicate that UV excitation modulates the plasma frequency of ITO on the ultrafast time scale by the injection of electrons into, and their subsequent decay from, the conduction band of the rods. Increases to the electron concentration in the conduction band of ∼13% were achieved in these experiments. Computer simulation and modeling have been used throughout the investigation to guide the design of the experiments and to map the electric field distribution around the rods for interpreting far-field measurement results.

Plasma instability control toward high fluence, high energy x-ray continuum source

NASA Astrophysics Data System (ADS)

Poole, Patrick; Kirkwood, Robert; Wilks, Scott; Blue, Brent

2017-10-01

X-ray source development at Omega and NIF seeks to produce powerful radiation with high conversion efficiency for material effects studies in extreme fluence environments. While current K-shell emission sources can achieve tens of kJ on NIF up to 22 keV, the conversion efficiency drops rapidly for higher Z K-alpha energies. Pulsed power devices are efficient generators of MeV bremsstrahlung x-rays but are unable to produce lower energy photons in isolation, and so a capability gap exists for high fluence x-rays in the 30 - 100 keV range. A continuum source under development utilizes instabilities like Stimulated Raman Scattering (SRS) to generate plasma waves that accelerate electrons into high-Z converter walls. Optimizing instabilities using existing knowledge on their elimination will allow sufficiently hot and high yield electron distributions to create a superior bremsstrahlung x-ray source. An Omega experiment has been performed to investigate the optimization of SRS and high energy x-rays using Au hohlraums with parylene inner lining and foam fills, producing 10× greater x-ray yield at 50 keV than conventional direct drive experiments on the facility. Experiment and simulation details on this campaign will be presented. This work was performed under the auspices of the US DoE by LLNL under Contract No. DE-AC52-07NA27344.

Derivative-free generation and interpolation of convex Pareto optimal IMRT plans

NASA Astrophysics Data System (ADS)

Hoffmann, Aswin L.; Siem, Alex Y. D.; den Hertog, Dick; Kaanders, Johannes H. A. M.; Huizenga, Henk

2006-12-01

In inverse treatment planning for intensity-modulated radiation therapy (IMRT), beamlet intensity levels in fluence maps of high-energy photon beams are optimized. Treatment plan evaluation criteria are used as objective functions to steer the optimization process. Fluence map optimization can be considered a multi-objective optimization problem, for which a set of Pareto optimal solutions exists: the Pareto efficient frontier (PEF). In this paper, a constrained optimization method is pursued to iteratively estimate the PEF up to some predefined error. We use the property that the PEF is convex for a convex optimization problem to construct piecewise-linear upper and lower bounds to approximate the PEF from a small initial set of Pareto optimal plans. A derivative-free Sandwich algorithm is presented in which these bounds are used with three strategies to determine the location of the next Pareto optimal solution such that the uncertainty in the estimated PEF is maximally reduced. We show that an intelligent initial solution for a new Pareto optimal plan can be obtained by interpolation of fluence maps from neighbouring Pareto optimal plans. The method has been applied to a simplified clinical test case using two convex objective functions to map the trade-off between tumour dose heterogeneity and critical organ sparing. All three strategies produce representative estimates of the PEF. The new algorithm is particularly suitable for dynamic generation of Pareto optimal plans in interactive treatment planning.

Creation of an atlas of filter positions for fluence field modulated CT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szczykutowicz, Timothy P., E-mail: TSzczykutowicz@uwhealth.org; Hermus, James

2015-04-15

Purpose: Fluence field modulated CT (FFMCT) and volume of interest (VOI) CT imaging applications require adjustment of the profile of the x-ray fluence incident on a patient as a function of view angle. Since current FFMCT prototypes can theoretically take on an infinite number of configurations, measuring a calibration data set for all possible positions would not be feasible. The present work details a methodology for calculating an atlas of configurations that will span all likely body regions, patient sizes, patient positioning, and imaging modes. The hypothesis is that there exists a finite number of unique modulator configurations that effectivelymore » span the infinite number of possible fluence profiles with minimal loss in performance. Methods: CT images of a head, shoulder, thorax, abdominal, wrist, and leg anatomical slices were dilated and contracted to model small, medium, and large sized patients. Additionally, the images were positioned from iso-center by three different amounts. The modulator configurations required to compensate for each image were computed assuming a FFMCT prototype, digital beam attenuator, (DBA), was set to equalize the detector exposure. Each atlas configuration should be different from the other atlas configurations. The degree of difference was quantified using the sum of the absolute differences in filter thickness between configurations. Using this metric, a set of unique wedge configurations for which no two configurations have a metric value smaller than some threshold can be constructed. Differences in the total number of incident photons between the unconstrained filters and the atlas were studied as a function of the number of atlas positions for each anatomical site and size/off-centering combination. Results: By varying the threshold used in creating the atlas, it was found that roughly 322 atlas positions provided an incident number of photons within 20% of using 19 440 unique filters (the number of atlas entries ranged from 7213 to 1). Additionally, for VOI applications implemented with a single VOI region, the number of required filter configurations was expressed in a simple closed form solution. Conclusions: The methodology proposed in this work will enable DBA-FFMCT and DBA-VOI imaging in the clinic without the need for patient specific air-scans to be performed. In addition, the methodology proposed here is directly applicable to other modulator designs such as piecewise linear, TomoTherapy multi leaf collimators, 2D fluid arrays, and inverse geometry CT.« less

A comparison of phantom scatter from flattened and flattening filter free high-energy photon beams.

PubMed

Richmond, Neil; Allen, Vince; Daniel, Jim; Dacey, Rob; Walker, Chris

2015-01-01

Flattening filter free (FFF) photon beams have different dosimetric properties from those of flattened beams. The aim of this work was to characterize the collimator scatter (Sc) and total scatter (Scp) from 3 FFF beams of differing quality indices and use the resulting mathematical fits to generate phantom scatter (Sp) data. The similarities and differences between Sp of flattened and FFF beams are described. Sc and Scp data were measured for 3 flattened and 3 FFF high-energy photon beams (Varian 6 and 10MV and Elekta 6MV). These data were fitted to logarithmic power law functions with 4 numerical coefficients. The agreement between our experimentally determined flattened beam Sp and published data was within ± 1.2% for all 3 beams investigated and all field sizes from 4 × 4 to 40 × 40cm(2). For the FFF beams, Sp was only within 1% of the same flattened beam published data for field sizes between 6 × 6 and 14 × 14cm(2). Outside this range, the differences were much greater, reaching - 3.2%, - 4.5%, and - 4.3% for the fields of 40 × 40cm(2) for the Varian 6-MV, Varian 10-MV, and Elekta 6-MV FFF beams, respectively. The FFF beam Sp increased more slowly with increasing field size than that of the published and measured flattened beam of a similar reference field size quality index, i.e., there is less Phantom Scatter than that found with flattened beams for a given field size. This difference can be explained when the fluence profiles of the flattened and FFF beams are considered. The FFF beam has greatly reduced fluence off axis, especially as field size increases, compared with the flattened beam profile; hence, less scatter is generated in the phantom reaching the central axis. Copyright © 2015 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.

Fast simulation of yttrium-90 bremsstrahlung photons with GATE.

PubMed

Rault, Erwann; Staelens, Steven; Van Holen, Roel; De Beenhouwer, Jan; Vandenberghe, Stefaan

2010-06-01

Multiple investigators have recently reported the use of yttrium-90 (90Y) bremsstrahlung single photon emission computed tomography (SPECT) imaging for the dosimetry of targeted radionuclide therapies. Because Monte Carlo (MC) simulations are useful for studying SPECT imaging, this study investigates the MC simulation of 90Y bremsstrahlung photons in SPECT. To overcome the computationally expensive simulation of electrons, the authors propose a fast way to simulate the emission of 90Y bremsstrahlung photons based on prerecorded bremsstrahlung photon probability density functions (PDFs). The accuracy of bremsstrahlung photon simulation is evaluated in two steps. First, the validity of the fast bremsstrahlung photon generator is checked. To that end, fast and analog simulations of photons emitted from a 90Y point source in a water phantom are compared. The same setup is then used to verify the accuracy of the bremsstrahlung photon simulations, comparing the results obtained with PDFs generated from both simulated and measured data to measurements. In both cases, the energy spectra and point spread functions of the photons detected in a scintillation camera are used. Results show that the fast simulation method is responsible for a 5% overestimation of the low-energy fluence (below 75 keV) of the bremsstrahlung photons detected using a scintillation camera. The spatial distribution of the detected photons is, however, accurately reproduced with the fast method and a computational acceleration of approximately 17-fold is achieved. When measured PDFs are used in the simulations, the simulated energy spectrum of photons emitted from a point source of 90Y in a water phantom and detected in a scintillation camera closely approximates the measured spectrum. The PSF of the photons imaged in the 50-300 keV energy window is also accurately estimated with a 12.4% underestimation of the full width at half maximum and 4.5% underestimation of the full width at tenth maximum. Despite its limited accuracy, the fast bremsstrahlung photon generator is well suited for the simulation of bremsstrahlung photons emitted in large homogeneous organs, such as the liver, and detected in a scintillation camera. The computational acceleration makes it very useful for future investigations of 90Y bremsstrahlung SPECT imaging.

Periodic metallo-dielectric structure in diamond.

PubMed

Shimizu, M; Shimotsuma, Y; Sakakura, M; Yuasa, T; Homma, H; Minowa, Y; Tanaka, K; Miura, K; Hirao, K

2009-01-05

Intense ultrashort light pulses induce three dimensional localized phase transformation of diamond. Photoinduced amorphous structures have electrical conducting properties of a maximum of 64 S/m based on a localized transition from sp(3) to sp(2) in diamond. The laser parameters of fluence and scanning speed affect the resultant electrical conductivities due to recrystallization and multi-filamentation phenomena. We demonstrate that the laser-processed diamond with the periodic cylinder arrays have the characteristic transmission properties in terahertz region, which are good agreement with theoretical calculations. The fabricated periodic structures act as metallo-dielectric photonic crystal.

Dosimetric properties of a Solid Water High Equivalency (SW557) phantom for megavoltage photon beams.

PubMed

Araki, Fujio

2017-07-01

The dosimetric properties of the recently developed SW557 phantom have been investigated by comparison with those of the existing SW457 phantom in megavoltage photon beams. The electron fluence ratio φ pl w , and chamber ionization ratio k pl , of water to SW457 and water to SW557 for 4-15MV photons were calculated as a function of depth using Monte Carlo simulations, and compared with measured values. Values of φ pl w for SW457 were in the range of 1.004-1.014 for 4MV, and 1.014-1.018 for 15MV photons. The φ pl w for SW557 ranged from 1.005 to 1.008 for 4MV and from 1.010 to 1.015 for 15MV photons and the variation of φ pl w with depth for each beam energy was within ±0.5%. Values of k pl were obtained with a PTW 30013 Farmer-type ionization chamber. The k pl for SW457 ranged from 0.997 to 1.011 for 4-15MV photons. Values of k pl for SW557 were almost unity for 4 and 6MV photons, while in the case of 10 and 15MV photons they were less than 1.006, excepting the build-up region. The measured and calculated k pl values of water to SW557 were in the range of 0.997-1.002 and 1.000-1.006, respectively, for 4-15MV photons, at a depth of 10cm with a source-to-axis distance of 100cm. The measured and calculated k pl values were in agreement within their uncertainty ranges. As a water-equivalent phantom, SW557 can be used with a dosimetric difference within±0.6%, for 4-15MV photons, and is more water-equivalent than SW457 in megavoltage photon beams. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Delivery of high energy Er:YAG pulsed laser light at 2.94 µm through a silica hollow core photonic crystal fibre.

PubMed

Urich, A; Maier, R R J; Mangan, B J; Renshaw, S; Knight, J C; Hand, D P; Shephard, J D

2012-03-12

In this paper the delivery of high power Er:YAG laser pulses through a silica hollow core photonic crystal fibre is demonstrated. The Er:YAG wavelength of 2.94 µm is well beyond the normal transmittance of bulk silica but the unique hollow core guidance allows silica to guide in this regime. We have demonstrated for the first time the ability to deliver high energy pulses through an all-silica fibre at 2.94 µm. These silica fibres are mechanically and chemically robust, biocompatible and have low sensitivity to bending. A maximum pulse energy of 14 mJ at 2.94 µm was delivered through the fibre. This, to our knowledge, is the first time a silica hollow core photonic crystal fibre has been shown to transmit 2.94 μm laser light at a fluence exceeding the thresholds required for modification (e.g. cutting and drilling) of hard biological tissue. Consequently, laser delivery systems based on these fibres have the potential for the realization of novel, minimally-invasive surgical procedures.

SU-F-T-630: Energy Spectral Study On Lipiodol After Trans-Arterial Chemoembolization Using the Flattened and Unflattened Photon Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawahara, D; Medical and Dental Sciences Course, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima; Ozawa, S

Purpose: SBRT combining transarterial chemoembolization with Lipiodol is expected to improve local control. Our showed that the dose enhancement effect in the Lipiodol with 10X flattening filter free (FFF) was inserted. This study was to investigate the energy fluence variations of electron in the Lipiodol using flattened (FF) and FFF beams. Methods: FF and FFF for 6X and 10X beams by TrueBeam were used in this study. The Lipiodol (3 X 3 X 3 cm{sup 3}) was located at the depth of 5 cm in water, the dose enhancement factor (DEF) and energy fluence were calculated by Monte Carlo (MC)more » calculations (PHITS). Results: DEFs with FF and FFF of 6X were 17.1% and 24.3% at rebuild-up region in the Lipiodol (5.3cm depth), 7.0% and 17.0% at the center of Lipiodol (6.5cm depth), and −13.2% and −8.2% at behind Lipiodol (8.3cm depth). DEFs with FF and FFF of 10X were 21.7% and 15.3% at rebuild-up region, 8.2% and 10.5% at the center of Lipiodol, and −14.0% and −8.6% at behind Lipiodol. Spectral results showed that the FFF beam contained more low-energy (0–0.3MeV) component of electrons than FF beam, and FF beam contained more high-energy (over 0.3MeV) electrons than FFF beam in Lipiodol. Behind the Lipiodol, build-down effect with FF beam was larger than FFF beam because FF beam contained more high energy electrons. The difference of DEFs between FFF and FF beams for 6X were larger than for 10X. This is because 10X beam contained more high-energy electrons. Conclusion: It was found that the 6XFFF beam gives the largest change of energy fluence and the largest DEF in this study. These phenomena are mainly caused by component of low-energy electrons, and this energy is almost correspond to the boundary of photo electronic dominant and Compton scattering dominant region for photon beams.« less

SU-E-T-605: Performance Evaluation of MLC Leaf-Sequencing Algorithms in Head-And-Neck IMRT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jing, J; Lin, H; Chow, J

2015-06-15

Purpose: To investigate the efficiency of three multileaf collimator (MLC) leaf-sequencing algorithms proposed by Galvin et al, Chen et al and Siochi et al using external beam treatment plans for head-and-neck intensity modulated radiation therapy (IMRT). Methods: IMRT plans for head-and-neck were created using the CORVUS treatment planning system. The plans were optimized and the fluence maps for all photon beams determined. Three different MLC leaf-sequencing algorithms based on Galvin et al, Chen et al and Siochi et al were used to calculate the final photon segmental fields and their monitor units in delivery. For comparison purpose, the maximum intensitymore » of fluence map was kept constant in different plans. The number of beam segments and total number of monitor units were calculated for the three algorithms. Results: From results of number of beam segments and total number of monitor units, we found that algorithm of Galvin et al had the largest number of monitor unit which was about 70% larger than the other two algorithms. Moreover, both algorithms of Galvin et al and Siochi et al have relatively lower number of beam segment compared to Chen et al. Although values of number of beam segment and total number of monitor unit calculated by different algorithms varied with the head-and-neck plans, it can be seen that algorithms of Galvin et al and Siochi et al performed well with a lower number of beam segment, though algorithm of Galvin et al had a larger total number of monitor units than Siochi et al. Conclusion: Although performance of the leaf-sequencing algorithm varied with different IMRT plans having different fluence maps, an evaluation is possible based on the calculated number of beam segment and monitor unit. In this study, algorithm by Siochi et al was found to be more efficient in the head-and-neck IMRT. The Project Sponsored by the Fundamental Research Funds for the Central Universities (J2014HGXJ0094) and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.« less

Ripple coarsening on ion beam-eroded surfaces.

PubMed

Teichmann, Marc; Lorbeer, Jan; Frost, Frank; Rauschenbach, Bernd

2014-01-01

The temporal evolution of ripple pattern on Ge, Si, Al 2 O 3, and SiO 2 by low-energy ion beam erosion with Xe (+) ions is studied. The experiments focus on the ripple dynamics in a fluence range from 1.1 × 10(17) cm(-2) to 1.3 × 10(19) cm(-2) at ion incidence angles of 65° and 75° and ion energies of 600 and 1,200 eV. At low fluences a short-wavelength ripple structure emerges on the surface that is superimposed and later on dominated by long wavelength structures for increasing fluences. The coarsening of short wavelength ripples depends on the material system and angle of incidence. These observations are associated with the influence of reflected primary ions and gradient-dependent sputtering. The investigations reveal that coarsening of the pattern is a universal behavior for all investigated materials, just at the earliest accessible stage of surface evolution.

ORGAN-SPECIFIC EXTERNAL DOSE COEFFICIENTS AND PROTECTIVE APRON TRANSMISSION FACTORS FOR HISTORICAL DOSE RECONSTRUCTION FOR MEDICAL PERSONNEL

PubMed Central

Simon, Steven L.

2014-01-01

While radiation absorbed dose (Gy) to the skin or other organs is sometimes estimated for patients from diagnostic radiologic examinations or therapeutic procedures, rarely is occupationally-received radiation absorbed dose to individual organs/tissues estimated for medical personnel, e.g., radiologic technologists or radiologists. Generally, for medical personnel, equivalent or effective radiation doses are estimated for compliance purposes. In the very few cases when organ doses to medical personnel are reconstructed, the data is usually for the purpose of epidemiologic studies, e.g., a study of historical doses and risks to a cohort of about 110,000 radiologic technologists presently underway at the U.S. National Cancer Institute. While ICRP and ICRU have published organ-specific external dose conversion coefficients (DCCs), i.e., absorbed dose to organs and tissues per unit air kerma and dose equivalent per unit air kerma, those factors have been primarily published for mono-energetic photons at selected energies. This presents two related problems for historical dose reconstruction, both of which are addressed here. It is necessary to derive conversion factors values for (i) continuous distributions of energy typical of diagnostic medical x rays (bremsstrahlung radiation), and (ii) for energies of particular radioisotopes used in medical procedures, neither of which are presented in published tables. For derivation of DCCs for bremsstrahlung radiation, combinations of x-ray tube potentials and filtrations were derived for different time periods based on a review of relevant literature. Three peak tube potentials (70 kV, 80 kV, and 90 kV) with four different amounts of beam filtration were determined to be applicable for historic dose reconstruction. The probability of these machine settings were assigned to each of the four time periods (earlier than 1949, 1949-1954, 1955-1968, and after 1968). Continuous functions were fit to each set of discrete values of the ICRP/ICRU mono-energetic DCCs and the functions integrated over the air-kerma weighted photon fluence of the 12 defined x-ray spectra. The air kerma-weighted DCCs in this work were developed specifically for an irradiation geometry of anterior to posterior (AP) and for the following tissues: thyroid, breast, ovary, lens of eye, lung, colon, testes, heart, skin (anterior side only), red bone marrow (RBM), heart, and brain. In addition, a series of functional relationships to predict DT per Ka values for RBM dependent on body mass index [BMI (kg m−2) ≡ weight per height2] and average photon energy were derived from a published analysis. Factors to account for attenuation of radiation by protective lead aprons were also developed. Because lead protective aprons often worn by radiology personnel not only reduce the intensity of x-ray exposure but also appreciably harden the transmitted fluence of bremsstrahlung x rays, DCCs were separately calculated for organs possibly protected by lead aprons by considering three cases: no apron, 0.25 mm Pb apron, and 0.5 mm Pb apron. For estimation of organ doses from conducting procedures with radioisotopes, continuous functions of the reported mono-energetic values were developed and DCCs were derived by estimation of the function at relevant energies. By considering the temporal changes in primary exposure-related parameters, e.g., energy distribution, the derived DCCs and transmission factors presented here allow for more realistic historical dose reconstructions for medical personnel when monitoring badge readings are the primary data on which estimation of an individual's organ doses are based. PMID:21617389

Organ-specific external dose coefficients and protective apron transmission factors for historical dose reconstruction for medical personnel.

PubMed

Simon, Steven L

2011-07-01

While radiation absorbed dose (Gy) to the skin or other organs is sometimes estimated for patients from diagnostic radiologic examinations or therapeutic procedures, rarely is occupationally-received radiation absorbed dose to individual organs/tissues estimated for medical personnel; e.g., radiologic technologists or radiologists. Generally, for medical personnel, equivalent or effective radiation doses are estimated for compliance purposes. In the very few cases when organ doses to medical personnel are reconstructed, the data is usually for the purpose of epidemiologic studies; e.g., a study of historical doses and risks to a cohort of about 110,000 radiologic technologists presently underway at the U.S. National Cancer Institute. While ICRP and ICRU have published organ-specific external dose conversion coefficients (DCCs) (i.e., absorbed dose to organs and tissues per unit air kerma and dose equivalent per unit air kerma), those factors have been published primarily for mono-energetic photons at selected energies. This presents two related problems for historical dose reconstruction, both of which are addressed here. It is necessary to derive conversion factor values for (1) continuous distributions of energy typical of diagnostic medical x-rays (bremsstrahlung radiation), and (2) energies of particular radioisotopes used in medical procedures, neither of which are presented in published tables. For derivation of DCCs for bremsstrahlung radiation, combinations of x-ray tube potentials and filtrations were derived for different time periods based on a review of relevant literature. Three peak tube potentials (70 kV, 80 kV, and 90 kV) with four different amounts of beam filtration were determined to be applicable for historic dose reconstruction. The probabilities of these machine settings were assigned to each of the four time periods (earlier than 1949, 1949-1954, 1955-1968, and after 1968). Continuous functions were fit to each set of discrete values of the ICRP/ICRU mono-energetic DCCs and the functions integrated over the air-kerma weighted photon fluence of the 12 defined x-ray spectra. The air kerma-weighted DCCs in this work were developed specifically for an irradiation geometry of anterior to posterior (AP) and for the following tissues: thyroid, breast, ovary, lens of eye, lung, colon, testes, heart, skin (anterior side only), red bone marrow (RBM), and brain. In addition, a series of functional relationships to predict DT Ka-1 values for RBM dependent on body mass index [BMI (kg m-2) ≡ weight per height] and average photon energy were derived from a published analysis. Factors to account for attenuation of radiation by protective lead aprons were also developed. Because lead protective aprons often worn by radiology personnel not only reduce the intensity of x-ray exposure but also appreciably harden the transmitted fluence of bremsstrahlung x-rays, DCCs were separately calculated for organs possibly protected by lead aprons by considering three cases: no apron, 0.25 mm Pb apron, and 0.5 mm Pb apron. For estimation of organ doses from conducting procedures with radioisotopes, continuous functions of the reported mono-energetic values were developed, and DCCs were derived by estimation of the function at relevant energies. By considering the temporal changes in primary exposure-related parameters (e.g., energy distribution), the derived DCCs and transmission factors presented here allow for more realistic historical dose reconstructions for medical personnel when monitoring badge readings are the primary data on which estimation of an individual's organ doses are based.

Fragmentation studies of relativistic iron ions using plastic nuclear track detectors.

PubMed

Scampoli, P; Durante, M; Grossi, G; Manti, L; Pugliese, M; Gialanella, G

2005-01-01

We measured fluence and fragmentation of high-energy (1 or 5 A GeV) 56Fe ions accelerated at the Alternating Gradient Synchrotron or at the NASA Space Radiation Laboratory (Brookhaven National Laboratory, NY, USA) using solid-state CR-39 nuclear track detectors. Different targets (polyethylene, PMMA, C, Al, Pb) were used to produce a large spectrum of charged fragments. CR-39 plastics were exposed both in front and behind the shielding block (thickness ranging from 5 to 30 g/cm2) at a normal incidence and low fluence. The radiation dose deposited by surviving Fe ions and charged fragments was measured behind the shield using an ionization chamber. The distribution of the measured track size was exploited to distinguish the primary 56Fe ions tracks from the lighter fragments. Measurements of projectile's fluence in front of the shield were used to determine the dose per incident particle behind the block. Simultaneous measurements of primary 56Fe ion tracks in front and behind the shield were used to evaluate the fraction of surviving iron projectiles and the total charge-changing fragmentation cross-section. These physical measurements will be used to characterize the beam used in parallel biological experiments. c2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

Effect of Carrier Thermalization Dynamics on Light Emission and Amplification in Organometal Halide Perovskites.

PubMed

Chen, Kai; Barker, Alex J; Morgan, Francis L C; Halpert, Jonathan E; Hodgkiss, Justin M

2015-01-02

The remarkable rise of organometal halide perovskites as solar photovoltaic materials has been followed by promising developments in light-emitting devices, including lasers. Here we present unique insights into the processes leading to photon emission in these materials. We employ ultrafast broadband photoluminescence (PL) and transient absorption spectroscopies to directly link density dependent ultrafast charge dynamics to PL. We find that exceptionally strong PL at the band edge is preceded by thermalization of free charge carriers. Short-lived PL above the band gap is clear evidence of nonexcitonic emission from hot carriers, and ultrafast PL depolarization confirms that uncorrelated charge pairs are precursors to photon emission. Carrier thermalization has a profound effect on amplified stimulated emission at high fluence; the delayed onset of optical gain we resolve within the first 10 ps and the unusual oscillatory behavior are both consequences of the kinetic interplay between carrier thermalization and optical gain.

Ultrafast hole carrier relaxation dynamics in p-type CuO nanowires

PubMed Central

2011-01-01

Ultrafast hole carrier relaxation dynamics in CuO nanowires have been investigated using transient absorption spectroscopy. Following femtosecond pulse excitation in a non-collinear pump-probe configuration, a combination of non-degenerate transmission and reflection measurements reveal initial ultrafast state filling dynamics independent of the probing photon energy. This behavior is attributed to the occupation of states by photo-generated carriers in the intrinsic hole region of the p-type CuO nanowires located near the top of the valence band. Intensity measurements indicate an upper fluence threshold of 40 μJ/cm2 where carrier relaxation is mainly governed by the hole dynamics. The fast relaxation of the photo-generated carriers was determined to follow a double exponential decay with time constants of 0.4 ps and 2.1 ps. Furthermore, time-correlated single photon counting measurements provide evidence of three exponential relaxation channels on the nanosecond timescale. PMID:22151927

Predicted performance of a PG-SPECT system using CZT primary detectors and secondary Compton-suppression anti-coincidence detectors under near-clinical settings for boron neutron capture therapy

NASA Astrophysics Data System (ADS)

Hales, Brian; Katabuchi, Tatsuya; Igashira, Masayuki; Terada, Kazushi; Hayashizaki, Noriyosu; Kobayashi, Tooru

2017-12-01

A test version of a prompt-gamma single photon emission computed tomography (PG-SPECT) system for boron neutron capture therapy (BNCT) using a CdZnTe (CZT) semiconductor detector with a secondary BGO anti-Compton suppression detector has been designed. A phantom with healthy tissue region of pure water, and 2 tumor regions of 5 wt% borated polyethylene was irradiated to a fluence of 1.3 × 109 n/cm2. The number of 478 keV foreground, background, and net counts were measured for each detector position and angle. Using only experimentally measured net counts, an image of the 478 keV production from the 10B(n , α) 7Li* reaction was reconstructed. Using Monte Carlo simulation and the experimentally measured background counts, the reliability of the system under clinically accurate parameters was extrapolated. After extrapolation, it was found that the value of the maximum-value pixel in the reconstructed 478 keV γ-ray production image overestimates the simulated production by an average of 9.2%, and that the standard deviation associated with the same value is 11.4%.

Coupling Light Emitting Diodes with Photocatalyst-Coated Optical Fibers Improves Quantum Yield of Pollutant Oxidation.

PubMed

Ling, Li; Tugaoen, Heather; Brame, Jonathon; Sinha, Shahnawaz; Li, Chuanhao; Schoepf, Jared; Hristovski, Kiril; Kim, Jae-Hong; Shang, Chii; Westerhoff, Paul

2017-11-21

A photocatalyst-coated optical fiber was coupled with a 318 nm ultraviolet-A light emitting diode, which activated the photocatalysts by interfacial photon-electron excitation while minimizing photonic energy losses due to conventional photocatalytic barriers. The light delivery mechanism was explored via modeling of evanescent wave energy produced upon total internal reflection and photon refraction into the TiO 2 surface coating. This work explores aqueous phase LED-irradiated optical fibers for treating organic pollutants and for the first time proposes a dual-mechanistic approach to light delivery and photocatalytic performance. Degradation of a probe organic pollutant was evaluated as a function of optical fiber coating thickness, fiber length, and photocatalyst attachment method and compared against the performance of an equivalent catalyst mass in a completely mixed slurry reactor. Measured and simulated photon fluence through the optical fibers decreased as a function of fiber length, coating thickness, or TiO 2 mass externally coated on the fiber. Thinner TiO 2 coatings achieved faster pollutant removal rates from solution, and dip coating performed better than sol-gel attachment methods. TiO 2 attached to optical fibers achieved a 5-fold higher quantum yield compared against an equivalent mass of TiO 2 suspended in a slurry solution.

Unfolding linac photon spectra and incident electron energies from experimental transmission data, with direct independent validation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, E. S. M.; McEwen, M. R.; Rogers, D. W. O.

2012-11-15

Purpose: In a recent computational study, an improved physics-based approach was proposed for unfolding linac photon spectra and incident electron energies from transmission data. In this approach, energy differentiation is improved by simultaneously using transmission data for multiple attenuators and detectors, and the unfolding robustness is improved by using a four-parameter functional form to describe the photon spectrum. The purpose of the current study is to validate this approach experimentally, and to demonstrate its application on a typical clinical linac. Methods: The validation makes use of the recent transmission measurements performed on the Vickers research linac of National Research Councilmore » Canada. For this linac, the photon spectra were previously measured using a NaI detector, and the incident electron parameters are independently known. The transmission data are for eight beams in the range 10-30 MV using thick Be, Al and Pb bremsstrahlung targets. To demonstrate the approach on a typical clinical linac, new measurements are performed on an Elekta Precise linac for 6, 10 and 25 MV beams. The different experimental setups are modeled using EGSnrc, with the newly added photonuclear attenuation included. Results: For the validation on the research linac, the 95% confidence bounds of the unfolded spectra fall within the noise of the NaI data. The unfolded spectra agree with the EGSnrc spectra (calculated using independently known electron parameters) with RMS energy fluence deviations of 4.5%. The accuracy of unfolding the incident electron energy is shown to be {approx}3%. A transmission cutoff of only 10% is suitable for accurate unfolding, provided that the other components of the proposed approach are implemented. For the demonstration on a clinical linac, the unfolded incident electron energies and their 68% confidence bounds for the 6, 10 and 25 MV beams are 6.1 {+-} 0.1, 9.3 {+-} 0.1, and 19.3 {+-} 0.2 MeV, respectively. The unfolded spectra for the clinical linac agree with the EGSnrc spectra (calculated using the unfolded electron energies) with RMS energy fluence deviations of 3.7%. The corresponding measured and EGSnrc-calculated transmission data agree within 1.5%, where the typical transmission measurement uncertainty on the clinical linac is 0.4% (not including the uncertainties on the incident electron parameters). Conclusions: The approach proposed in an earlier study for unfolding photon spectra and incident electron energies from transmission data is accurate and practical for clinical use.« less

Perspectives for imaging single protein molecules with the present design of the European XFEL.

PubMed

Ayyer, Kartik; Geloni, Gianluca; Kocharyan, Vitali; Saldin, Evgeni; Serkez, Svitozar; Yefanov, Oleksandr; Zagorodnov, Igor

2015-07-01

The Single Particles, Clusters and Biomolecules & Serial Femtosecond Crystallography (SPB/SFX) instrument at the European XFEL is located behind the SASE1 undulator and aims to support imaging and structure determination of biological specimen between about 0.1 μm and 1 μm size. The instrument is designed to work at photon energies from 3 keV up to 16 keV. Here, we propose a cost-effective proof-of-principle experiment, aiming to demonstrate the actual feasibility of a single molecule diffraction experiment at the European XFEL. To this end, we assume self-seeding capabilities at SASE1 and we suggest to make use of the baseline European XFEL accelerator complex-with the addition of a slotted-foil setup-and of the SPB/SFX instrument. As a first step towards the realization of an actual experiment, we developed a complete package of computational tools for start-to-end simulations predicting its performance. Single biomolecule imaging capabilities at the European XFEL can be reached by exploiting special modes of operation of the accelerator complex and of the SASE1 undulator. The output peak power can be increased up to more than 1.5 TW, which allows to relax the requirements on the focusing efficiency of the optics and to reach the required fluence without changing the present design of the SPB/SFX instrument. Explicit simulations are presented using the 15-nm size RNA Polymerase II molecule as a case study. Noisy diffraction patterns were generated and they were processed to generate the 3D intensity distribution. We discuss requirements to the signal-to-background ratio needed to obtain a correct pattern orientation. When these are fulfilled, our results indicate that one can achieve diffraction without destruction with about 0.1 photons per Shannon pixel per shot at 4 Å resolution with 10(13) photons in a 4 fs pulse at 4 keV photon energy and in a 0.3 μm focus, corresponding to a fluence of 10(14) photons/μm(2). We assume negligible structured background. At this signal level, one needs only about 30 000 diffraction patterns to recover full 3D information. At the highest repetition rate manageable by detectors at European XFEL, one will be able to accumulate these data within a fraction of an hour, even assuming a relatively low hit probability of about a percent.

RPI-AM and RPI-AF, a pair of mesh-based, size-adjustable adult male and female computational phantoms using ICRP-89 parameters and their calculations for organ doses from monoenergetic photon beams

NASA Astrophysics Data System (ADS)

Zhang, Juying; Hum Na, Yong; Caracappa, Peter F.; Xu, X. George

2009-10-01

This paper describes the development of a pair of adult male and adult female computational phantoms that are compatible with anatomical parameters for the 50th percentile population as specified by the International Commission on Radiological Protection (ICRP). The phantoms were designed entirely using polygonal mesh surfaces—a Boundary REPresentation (BREP) geometry that affords the ability to efficiently deform the shape and size of individual organs, as well as the body posture. A set of surface mesh models, from Anatomium™ 3D P1 V2.0, including 140 organs (out of 500 available) was adopted to supply the basic anatomical representation at the organ level. The organ masses were carefully adjusted to agree within 0.5% relative error with the reference values provided in the ICRP Publication 89. The finalized phantoms have been designated the RPI adult male (RPI-AM) and adult female (RPI-AF) phantoms. For the purposes of organ dose calculations using the MCNPX Monte Carlo code, these phantoms were subsequently converted to voxel formats. Monoenergetic photons between 10 keV and 10 MeV in six standard external photon source geometries were considered in this study: four parallel beams (anterior-posterior, posterior-anterior, left lateral and right lateral), one rotational and one isotropic. The results are tabulated as fluence-to-organ-absorbed-dose conversion coefficients and fluence-to-effective-dose conversion coefficients and compared against those derived from the ICRP computational phantoms, REX and REGINA. A general agreement was found for the effective dose from these two sets of phantoms for photon energies greater than about 300 keV. However, for low-energy photons and certain individual organs, the absorbed doses exhibit profound differences due to specific anatomical features. For example, the position of the arms affects the dose to the lung by more than 20% below 300 keV in the lateral source directions, and the vertical position of the testes affects the dose by more than 80% below 150 keV in the PA source direction. The deformability and adjustability of organs and posture in the RPI adult phantoms may prove useful not only for average workers or patients for radiation protection purposes, but also in studies involving anatomical and posture variability that is important in future radiation protection dosimetry.

Quantitative measurement of the near-field enhancement of nanostructures by two-photon polymerization.

PubMed

Geldhauser, Tobias; Kolloch, Andreas; Murazawa, Naoki; Ueno, Kosei; Boneberg, Johannes; Leiderer, Paul; Scheer, Elke; Misawa, Hiroaki

2012-06-19

The quantitative determination of the strength of the near-field enhancement in and around nanostructures is essential for optimizing and using these structures for applications. We combine the gaussian intensity distribution of a laser profile and two-photon-polymerization of SU-8 to a suitable tool for the quantitative experimental measurement of the near-field enhancement of a nanostructure. Our results give a feedback to the results obtained by finite-difference time-domain (FDTD) simulations. The structures under investigation are gold nanotriangles on a glass substrate with 85 nm side length and a thickness of 40 nm. We compare the threshold fluence for polymerization for areas of the gaussian intensity profile with and without the near-field enhancement of the nanostructures. The experimentally obtained value of the near-field intensity enhancement is 600 ± 140, independent of the laser power, irradiation time, and spot size. The FDTD simulation shows a pointlike maximum of 2600 at the tip. In a more extended area with an approximate size close to the smallest polymerized structure of 25 nm in diameter, we find a value between 800 and 600. Using our novel approach, we determine the threshold fluence for polymerization of the commercially available photopolymerizable resin SU-8 by a femtosecond laser working at a wavelength of 795 nm and a repetition rate of 82 MHz to be 0.25 J/cm(2) almost independent of the irradiation time and the laser power used. This finding is important for future applications of the method because it enables one to use varying laser systems.

Physics of the Isotopic Dependence of Galactic Cosmic Ray Fluence Behind Shielding

NASA Technical Reports Server (NTRS)

Cucinotta, Francis A.; Saganti, Premkumar B.; Hu, Xiao-Dong; Kim, Myung-Hee Y.; Cleghorn, Timothy F.; Wilson, John W.; Tripathi, Ram K.; Zeitlin, Cary J.

2003-01-01

For over 25 years, NASA has supported the development of space radiation transport models for shielding applications. The NASA space radiation transport model now predicts dose and dose equivalent in Earth and Mars orbit to an accuracy of plus or minus 20%. However, because larger errors may occur in particle fluence predictions, there is interest in further assessments and improvements in NASA's space radiation transport model. In this paper, we consider the effects of the isotopic composition of the primary galactic cosmic rays (GCR) and the isotopic dependence of nuclear fragmentation cross-sections on the solution to transport models used for shielding studies. Satellite measurements are used to describe the isotopic composition of the GCR. Using NASA's quantum multiple-scattering theory of nuclear fragmentation (QMSFRG) and high-charge and energy (HZETRN) transport code, we study the effect of the isotopic dependence of the primary GCR composition and secondary nuclei on shielding calculations. The QMSFRG is shown to accurately describe the iso-spin dependence of nuclear fragmentation. The principal finding of this study is that large errors (plus or minus 100%) will occur in the mass-fluence spectra when comparing transport models that use a complete isotope grid (approximately 170 ions) to ones that use a reduced isotope grid, for example the 59 ion-grid used in the HZETRN code in the past, however less significant errors (less than 20%) occur in the elemental-fluence spectra. Because a complete isotope grid is readily handled on small computer workstations and is needed for several applications studying GCR propagation and scattering, it is recommended that they be used for future GCR studies.

Dosimetric verification of radiation therapy including intensity modulated treatments, using an amorphous-silicon electronic portal imaging device

NASA Astrophysics Data System (ADS)

Chytyk-Praznik, Krista Joy

Radiation therapy is continuously increasing in complexity due to technological innovation in delivery techniques, necessitating thorough dosimetric verification. Comparing accurately predicted portal dose images to measured images obtained during patient treatment can determine if a particular treatment was delivered correctly. The goal of this thesis was to create a method to predict portal dose images that was versatile and accurate enough to use in a clinical setting. All measured images in this work were obtained with an amorphous silicon electronic portal imaging device (a-Si EPID), but the technique is applicable to any planar imager. A detailed, physics-motivated fluence model was developed to characterize fluence exiting the linear accelerator head. The model was further refined using results from Monte Carlo simulations and schematics of the linear accelerator. The fluence incident on the EPID was converted to a portal dose image through a superposition of Monte Carlo-generated, monoenergetic dose kernels specific to the a-Si EPID. Predictions of clinical IMRT fields with no patient present agreed with measured portal dose images within 3% and 3 mm. The dose kernels were applied ignoring the geometrically divergent nature of incident fluence on the EPID. A computational investigation into this parallel dose kernel assumption determined its validity under clinically relevant situations. Introducing a patient or phantom into the beam required the portal image prediction algorithm to account for patient scatter and attenuation. Primary fluence was calculated by attenuating raylines cast through the patient CT dataset, while scatter fluence was determined through the superposition of pre-calculated scatter fluence kernels. Total dose in the EPID was calculated by convolving the total predicted incident fluence with the EPID-specific dose kernels. The algorithm was tested on water slabs with square fields, agreeing with measurement within 3% and 3 mm. The method was then applied to five prostate and six head-and-neck IMRT treatment courses (˜1900 clinical images). Deviations between the predicted and measured images were quantified. The portal dose image prediction model developed in this thesis work has been shown to be accurate, and it was demonstrated to be able to verify patients' delivered radiation treatments.

Role of Beam Spot Size in Heating Targets at Depth.

PubMed

Ross, E Victor; Childs, James

2015-12-01

Wavelength, fluence and pulse width are primary device parameters for the treatment of skin and hair conditions. Wavelength selection is based on tissue scatter and target chromophores. Pulse width is chosen to optimize target heating. Energy absorbed by a target is determined by fluence and spot size of the light source as well as the depth of the target. We conducted an in vitro skin study and simulations to compare heating of a target at a particular depth versus spot size. Porcine skin and fat tissue were prepared and separated to form a 2mm skin layer above a 1 cm thick fat layer. A 50 μm thermocouple was placed between the layers and centered beneath a 23 x 38 mm treatment window of an 805 nm diode laser device (Vectus, Cynosure, Westford, MA). Apertures provided various incident beam spot sizes and the temperature rise of the thermocouple was measured for a fixed fluence. The 2mm deep target's temperature rise versus treatment area showed two regimes with different positive slopes. The first regime up to approximately 1 cm(2) area has a greater temperature rise versus area than that for the regime greater than 1 cm(2). The slope in the second regime is nonetheless appreciable and provides a fluence reduction factor for skin safety. The same temperature rise in a target at 2 mm depth (typical hair bulb depth in some areas) is realized by increasing the area from 1 to 4 cm(2) while reducing the fluence by half. The role of spot size and in situ beam divergence is an important consideration to determine optimum fluence settings that increase skin safety when treating deeper targets.

RELATIVE DISTRIBUTIONS OF FLUENCES OF {sup 3}He AND {sup 4}He IN SOLAR ENERGETIC PARTICLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrosian, Vahe; Jiang Yanwei; Liu Siming

2009-08-10

Solar energetic particles show a rich variety of spectra and relative abundances of many ionic species and their isotopes. A long-standing puzzle has been the extreme enrichments of {sup 3}He ions. The most extreme enrichments are observed in low-fluence, the so-called impulsive, events which are believed to be produced at the flare site in the solar corona with little scattering and acceleration during transport to the Earth. In such events, {sup 3}He ions show a characteristic concave curved spectra in a log-log plot. In two earlier papers of Liu et al., we showed how such extreme enrichments and spectra canmore » result in the model developed by Petrosian and Liu, where ions are accelerated stochastically by plasma waves or turbulence. In this paper, we address the relative distributions of the fluences of {sup 3}He and {sup 4}He ions presented by Ho et al., which show that while the distribution of {sup 4}He fluence (which we believe is a good measure of the flare strength) like many other extensive characteristics of solar flare is fairly broad, the {sup 3}He fluence is limited to a narrow range. These characteristics introduce a strong anticorrelation between the ratio of the fluences and the {sup 4}He fluence. One of the predictions of our model presented in the 2006 paper was the presence of steep variation of the fluence ratio with the level of turbulence or the rate of acceleration. We show here that this feature of the model can reproduce the observed distribution of the fluences with very few free parameters. The primary reason for the success of the model in both fronts is because fully ionized {sup 3}He ion, with its unique charge-to-mass ratio, can resonantly interact with plasma modes not accessible to {sup 4}He and be accelerated more readily than {sup 4}He. Essentially in most flares, all background {sup 3}He ions are accelerated to few MeV/nucleon range, while this happens for {sup 4}He ions only in very strong events. A much smaller fraction of {sup 4}He ions reach such energies in weaker events.« less

Non-contact pumping of light emitters via non-radiative energy transfer

DOEpatents

Klimov, Victor I.; Achermann, Marc

2010-01-05

A light emitting device is disclosed including a primary light source having a defined emission photon energy output, and, a light emitting material situated near to said primary light source, said light emitting material having an absorption onset equal to or less in photon energy than the emission photon energy output of the primary light source whereby non-radiative energy transfer from said primary light source to said light emitting material can occur yielding light emission from said light emitting material.

Magnetic field effects on the energy deposition spectra of MV photon radiation.

PubMed

Kirkby, C; Stanescu, T; Fallone, B G

2009-01-21

Several groups worldwide have proposed various concepts for improving megavoltage (MV) radiotherapy that involve irradiating patients in the presence of a magnetic field-either for image guidance in the case of hybrid radiotherapy-MRI machines or for purposes of introducing tighter control over dose distributions. The presence of a magnetic field alters the trajectory of charged particles between interactions with the medium and thus has the potential to alter energy deposition patterns within a sub-cellular target volume. In this work, we use the MC radiation transport code PENELOPE with appropriate algorithms invoked to incorporate magnetic field deflections to investigate electron energy fluence in the presence of a uniform magnetic field and the energy deposition spectra within a 10 microm water sphere as a function of magnetic field strength. The simulations suggest only very minor changes to the electron fluence even for extremely strong magnetic fields. Further, calculations of the dose-averaged lineal energy indicate that a magnetic field strength of at least 70 T is required before beam quality will change by more than 2%.

An investigation of voxel geometries for MCNP-based radiation dose calculations.

PubMed

Zhang, Juying; Bednarz, Bryan; Xu, X George

2006-11-01

Voxelized geometry such as those obtained from medical images is increasingly used in Monte Carlo calculations of absorbed doses. One useful application of calculated absorbed dose is the determination of fluence-to-dose conversion factors for different organs. However, confusion still exists about how such a geometry is defined and how the energy deposition is best computed, especially involving a popular code, MCNP5. This study investigated two different types of geometries in the MCNP5 code, cell and lattice definitions. A 10 cm x 10 cm x 10 cm test phantom, which contained an embedded 2 cm x 2 cm x 2 cm target at its center, was considered. A planar source emitting parallel photons was also considered in the study. The results revealed that MCNP5 does not calculate total target volume for multi-voxel geometries. Therefore, tallies which involve total target volume must be divided by the user by the total number of voxels to obtain a correct dose result. Also, using planar source areas greater than the phantom size results in the same fluence-to-dose conversion factor.

Fluence thresholds for grazing incidence hard x-ray mirrors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aquila, A.; Ozkan, C.; Sinn, H.

2015-06-15

X-ray Free Electron Lasers (XFELs) have the potential to contribute to many fields of science and to enable many new avenues of research, in large part due to their orders of magnitude higher peak brilliance than existing and future synchrotrons. To best exploit this peak brilliance, these XFEL beams need to be focused to appropriate spot sizes. However, the survivability of X-ray optical components in these intense, femtosecond radiation conditions is not guaranteed. As mirror optics are routinely used at XFEL facilities, a physical understanding of the interaction between intense X-ray pulses and grazing incidence X-ray optics is desirable. Wemore » conducted single shot damage threshold fluence measurements on grazing incidence X-ray optics, with coatings of ruthenium and boron carbide, at the SPring-8 Angstrom compact free electron laser facility using 7 and 12 keV photon energies. The damage threshold dose limits were found to be orders of magnitude higher than would naively be expected. The incorporation of energy transport and dissipation via keV level energetic photoelectrons accounts for the observed damage threshold.« less

Implications of the focal beam profile in serial femtosecond crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galli, Lorenzo; Chapman, Henry N.; Metcalf, Peter

The photon density profile of an X-ray free-electron laser (XFEL) beam at the focal position is a critical parameter for serial femtosecond crystallography (SFX), but is difficult to measure because of the destructive power of the beam. A novel high intensity radiation induced phasing method (HIRIP) has been proposed as a general experimental approach for protein structure determination, but has proved to be sensitive to variations of the X-ray intensity, with uniform incident fluence desired for best performance. Here we show that experimental SFX data collected at the nano-focus chamber of the Coherent X-ray Imaging end-station at the Linac Coherentmore » Light Source using crystals with a limited size distribution suggests an average profile of the X-ray beam that has a large variation of intensity. We propose a new method to improve the quality of high fluence data for HI-RIP, by identifying and removing diffraction patterns from crystals exposed to the low intensity region of the beam. The method requires crystals of average size comparable to the width of the focal spot.« less

Ground Laboratory Soft X-Ray Durability Evaluation of Aluminized Teflon FEP Thermal Control Insulation

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; deGroh, Kim K.; Stueber, Thomas J.; Sechkar, Edward A.

1998-01-01

Metallized Teflon fluorinated ethylene propylene (FEP) thermal control insulation is mechanically degraded if exposed to a sufficient fluence of soft x-ray radiation. Soft x-ray photons (4-8 A in wavelength or 1.55 - 3.2 keV) emitted during solar flares have been proposed as a cause of mechanical properties degradation of aluminized Teflon FEP thermal control insulation on the Hubble Space Telescope (HST). Such degradation can be characterized by a reduction in elongation-to-failure of the Teflon FER Ground laboratory soft x-ray exposure tests of aluminized Teflon FEP were conducted to assess the degree of elongation degradation which would occur as a result of exposure to soft x-rays in the range of 3-10 keV. Tests results indicate that soft x-ray exposure in the 3-10 keV range, at mission fluence levels, does not alone cause the observed reduction in elongation of flight retrieved samples. The soft x-ray exposure facility design, mechanical properties degradation results and implications will be presented.

Ground Laboratory Soft X-Ray Durability Evaluation of Aluminized Teflon FEP Thermal Control Insulation. Revised

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; deGroh, Kim K.; Stueber, Thomas J.; Sechkar, Edward A.; Hall, Rachelle L.

1998-01-01

Metallized Teflon fluorinated ethylene propylene (FEP) thermal control insulation is mechanically degraded if exposed to a sufficient fluence of soft x-ray radiation. Soft x-ray photons (4-8 A in wavelength or 1.55 - 3.2 keV) emitted during solar flares have been proposed as a cause of mechanical properties degradation of aluminized Teflon FEP thermal control insulation on the Hubble Space Telescope (HST). Such degradation can be characterized by a reduction in elongation-to-failure of the Teflon FEP. Ground laboratory soft x-ray exposure tests of aluminized Teflon FEP were conducted to assess the degree of elongation degradation which would occur as a result of exposure to soft x-rays in the range of 3-10 keV. Tests results indicate that soft x-ray exposure in the 3-10 keV range, at mission fluence levels, does not alone cause the observed reduction in elongation of flight retrieved samples. The soft x-ray exposure facility design, mechanical properties degradation results and implications will be presented.

Damage threshold of coating materials on x-ray mirror for x-ray free electron laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koyama, Takahisa, E-mail: koyama@spring8.or.jp; Yumoto, Hirokatsu; Tono, Kensuke

2016-05-15

We evaluated the damage threshold of coating materials such as Mo, Ru, Rh, W, and Pt on Si substrates, and that of uncoated Si substrate, for mirror optics of X-ray free electron lasers (XFELs). Focused 1 μm (full width at half maximum) XFEL pulses with the energies of 5.5 and 10 keV, generated by the SPring-8 angstrom compact free electron laser (SACLA), were irradiated under the grazing incidence condition. The damage thresholds were evaluated by in situ measurements of X-ray reflectivity degradation during irradiation by multiple pulses. The measured damage fluences below the critical angles were sufficiently high compared withmore » the unfocused SACLA beam fluence. Rh coating was adopted for two mirror systems of SACLA. One system was a beamline transport mirror system that was partially coated with Rh for optional utilization of a pink beam in the photon energy range of more than 20 keV. The other was an improved version of the 1 μm focusing mirror system, and no damage was observed after one year of operation.« less

Synergistic damage effects of vacuum ultraviolet photons and O2 in SiCOH ultra-low-k dielectric films

NASA Astrophysics Data System (ADS)

Lee, J.; Graves, D. B.

2010-10-01

Damage incurred during plasma processing, leading to increases in dielectric constant k, is a persistent problem with porous ultra-low-k dielectric films, such as SiCOH. Although most of the proposed mechanisms of plasma-induced damage focus on the role of ion bombardment and radical attack, we show that plasma-generated vacuum ultraviolet (VUV) photons can play a role in creating damage leading to increases in the dielectric constant of this material. Using a vacuum beam apparatus with a calibrated VUV lamp, we show that 147 nm VUV photons impacting SiCOH results in post-exposure adsorption and reaction with water vapour from the atmosphere to form silanol bonds, thereby raising the dielectric constant. Furthermore, the level of damage increases synergistically under simultaneous exposure to VUV photons and O2. The vacuum beam photon fluences are representative of typical plasma processes, as measured in a separate plasma tool. Fourier-transform infrared (FTIR) spectroscopy (ex situ) and mass spectrometry (in situ) imply that O2 reacts with methyl radicals formed from scissioned Si-C bonds to create CO2 and H2O, the latter combining with Si dangling bonds to generate more SiOH groups than with photon exposure alone. In addition, sample near-surface diffusivity, manipulated through ion bombardment and sample heating, can be seen to affect this process. These results demonstrate that VUV photo-generated surface reactions can be potent contributors to ultra-low-k dielectric SiCOH film plasma-induced damage, and suggest that they could play analogous roles in other plasma-surface interactions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soter, J.; Bhike, M.; Finch, S. W.

Measurements of the 169Tm(n,2n) 168Tm cross section have been performed via the activation technique at 13 energies between 8.5 and 15.0 MeV. The purpose of this comprehensive data set is to provide an alternative diagnostic tool for obtaining subtle information on the neutron energy distribution produced in inertial confinement deuterium-tritium fusion experiments at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. In conclusion, the 169Tm(n,2n) 168Tm reaction not only provides the primary 14-MeV neutron fluence, but also the important down-scattered neutron fluence, the latter providing information on the density achieved in the deuterium-tritium plasma during a laser shot.

Acceleration of domain wall movement by photoirradiation in perovskite-type cobaltite

NASA Astrophysics Data System (ADS)

Okimoto, Y.; Kurashima, M.; Seko, K.; Ishikawa, T.; Onda, K.; Koshihara, S.; Kyomen, T.; Itoh, M.

2011-04-01

Femtosecond reflection spectroscopy was performed on a perovskite-type cobalt oxide, namely, Pr0.5Ca0.5CoO3, that undergoes a photoinduced spin-state transition. After photoirradiation at 30 K, the time profile of the reflectance change shows a broad peak reflecting the propagation of the photodomain (about 60 Co sites per one photon). Analysis of the peak position indicates the sudden increase of the velocity of the propagation with increasing the excitation intensity. Such acceleration with increase in fluence originates from an abrupt sound velocity change driven by a cooperative photoinduced structural transition.

Laser Ablation of Poly(methylmethacrylate) Doped with Aromatic Compounds: Laser Intensity Dependence of Absorption Coefficient

NASA Astrophysics Data System (ADS)

Wang, Jun; Niino, Hiroyuki; Yabe, Akira

1999-02-01

We developed a novel method of obtaining an absorption coefficient which depends on the laser intensity, since a single-photon absorption coefficient of a polymer could not be applied to laser ablation. The relationship between the nonlinear absorption coefficient and the laser intensity was derived from experimental data of transmission and incident laser intensities. Using the nonlinear absorption coefficient of poly(methylmethacrylate) doped with benzil and pyrene, we succeeded in fitting the relationship of etch depth and laser intensity, obtained experimentally, and discussed the energy absorbed by the polymer at the threshold fluence.

X-ray spectrometer with a low-cost SiC photodiode

NASA Astrophysics Data System (ADS)

Zhao, S.; Lioliou, G.; Barnett, A. M.

2018-04-01

A low-cost Commercial-Off-The-Shelf (COTS) 4H-SiC 0.06 mm2 UV p-n photodiode was coupled to a low-noise charge-sensitive preamplifier and used as photon counting X-ray spectrometer. The photodiode/spectrometer was investigated at X-ray energies from 4.95 keV to 21.17 keV: a Mo cathode X-ray tube was used to fluoresce eight high-purity metal foils to produce characteristic X-ray emission lines which were used to characterise the instrument. The energy resolution (full width at half maximum, FWHM) of the spectrometer was found to be 1.6 keV to 1.8 keV, across the energy range. The energy linearity of the detector/spectrometer (i.e. the detector's charge output per photon as a function of incident photon energy across the 4.95 keV to 21.17 keV energy range), as well as the count rate linearity of the detector/spectrometer (i.e. number of detected photons as a function of photon fluence at a specific energy) were investigated. The energy linearity of the detector/spectrometer was linear with an error < ± 0.7 %; the count rate linearity of the detector/spectrometer was linear with an error < ± 2 %. The use of COTS SiC photodiodes as detectors for X-ray spectrometers is attractive for nanosatellite/CubeSat applications (including solar flare monitoring), and for cost sensitive industrial uses.

The Lunar Regolith as a Remote Sensing Target for the Lunar Reconnaissance Orbiter (LRO)

NASA Technical Reports Server (NTRS)

Mendell, Wendell W.

2009-01-01

Of the 6 instruments and one technology demonstration aboard the LRO, only CRaTER does not measure some kind of interaction of particles with the lunar regolith. LEND detects neutron fluence that contains information about the number density of protons in the upper regolith. To infer the presence of protons, the PI must assume a model that characterizes the surface as a collection of atoms. Thus, LEND does not sense the regolith as a structure. LROC, LOLA, and LAMP sense reflected photons whose wavelength is much shorter than the median particle size in the regolith. The photons interact with electrons, either in atomic shells or in chemical bonds. These interactions occur within a nanometer or so of the surface of a particle. Thus, the particles are macroscopic objects and models of the reflection process invoke ray-tracing optics. DIVINER senses photons that have been emitted by surface particles through thermal phonon processes. The wavelengths detected by the instrument are of the same order as the median particle size, and the photons contain information on particle dimensions as well as the molecular bonds in the constituent compounds. The Mini-RF synthetic aperture radar generates and detects photons of a few centimeters wavelength that interact with the regolith as a dielectric, the dielectric properties of the particulate component being described through effective medium theory. However, the interaction with rocks (macroscopic objects of interest to geologists) can be characterized using Fresnel or Mie models of electromagnetic properties.

Low intensity, continuous wave photodoping of ZnO quantum dots - photon energy and particle size effects.

PubMed

Aguirre, Matías E; Municoy, S; Grela, M A; Colussi, A J

2017-02-08

The unique properties of semiconductor quantum dots (QDs) have found application in the conversion of solar to chemical energy. How the relative rates of the redox processes that control QD photon efficiencies depend on the particle radius (r) and photon energy (E λ ), however, is not fully understood. Here, we address these issues and report the quantum yields (Φs) of interfacial charge transfer and electron doping in ZnO QDs capped with ethylene glycol (EG) as a function of r and E λ in the presence and absence of methyl viologen (MV 2+ ) as an electron acceptor, respectively. We found that Φs for the oxidation of EG are independent of E λ and photon fluence (φ λ ), but markedly increase with r. The independence of Φs on φ λ ensures that QDs are never populated by more than one electron-hole pair, thereby excluding Auger-type terminations. We show that these findings are consistent with the operation of an interfacial redox process that involves thermalized carriers in the Marcus inverted region. In the absence of MV 2+ , QDs accumulate electrons up to limiting volumetric densities ρ e,∞ that depend sigmoidally on excess photon energy E* = E λ - E BG (r), where E BG (r) is the r-dependent bandgap energy. The maximum electron densities: ρ ev,∞ ∼ 4 × 10 20 cm -3 , are reached at E* > 0.5 eV, independent of the particle radius.

Production of clinically useful positron emitter beams during carbon ion deceleration.

PubMed

Lazzeroni, M; Brahme, A

2011-03-21

In external beam radiation therapy, radioactive beams offer the best clinical solution to simultaneously treat and in vivo monitor the dose delivery and tumor response using PET or PET-CT imaging. However, difficulties mainly linked to the low production efficiency have so far limited their use. This study is devoted to the analysis of the production of high energy (11)C fragments, preferably by projectile fragmentation of a stable monodirectional and monoenergetic primary (12)C beam in different absorbing materials (decelerators) in order to identify the optimal elemental composition. The study was performed using the Monte Carlo code SHIELD-HIT07. The track length and fluence of generated secondary particles were scored in a uniform absorber of 300 cm length and 10 cm radius, divided into slices of 1 cm thickness. The (11)C fluence build-up and mean energy variation with increasing decelerator depth are presented. Furthermore, the fluence of the secondary (11)C beam was studied as a function of its mean energy and the corresponding remaining range in water. It is shown that the maximum (11)C fluence build-up is high in compounds where the fraction by weight of hydrogen is high, being the highest in liquid hydrogen. Furthermore, a cost effective alternative solution to the single medium initially envisaged is presented: a two-media decelerator that comprises a first liquid hydrogen section followed by a second decelerating section made of a hydrogen-rich material, such as polyethylene (C(2)H(4)). The purpose of the first section is to achieve a fast initial (11)C fluence build-up, while the second section is primarily designed to modulate the mean energy of the generated (11)C beam in order to reach the tumor depth. Finally, it was demonstrated that, if the intensity of the primary (12)C beam can be increased by an order of magnitude, a sufficient intensity of the secondary (11)C beam is achieved for therapy and subsequent therapeutic PET imaging sessions. Such an increase in the intensity might be easily achieved with a superconducting cyclotron.

Three-Dimensional Electron Beam Dose Calculations.

NASA Astrophysics Data System (ADS)

Shiu, Almon Sowchee

The MDAH pencil-beam algorithm developed by Hogstrom et al (1981) has been widely used in clinics for electron beam dose calculations for radiotherapy treatment planning. The primary objective of this research was to address several deficiencies of that algorithm and to develop an enhanced version. Two enhancements have been incorporated into the pencil-beam algorithm; one models fluence rather than planar fluence, and the other models the bremsstrahlung dose using measured beam data. Comparisons of the resulting calculated dose distributions with measured dose distributions for several test phantoms have been made. From these results it is concluded (1) that the fluence-based algorithm is more accurate to use for the dose calculation in an inhomogeneous slab phantom, and (2) the fluence-based calculation provides only a limited improvement to the accuracy the calculated dose in the region just downstream of the lateral edge of an inhomogeneity. The source of the latter inaccuracy is believed primarily due to assumptions made in the pencil beam's modeling of the complex phantom or patient geometry. A pencil-beam redefinition model was developed for the calculation of electron beam dose distributions in three dimensions. The primary aim of this redefinition model was to solve the dosimetry problem presented by deep inhomogeneities, which was the major deficiency of the enhanced version of the MDAH pencil-beam algorithm. The pencil-beam redefinition model is based on the theory of electron transport by redefining the pencil beams at each layer of the medium. The unique approach of this model is that all the physical parameters of a given pencil beam are characterized for multiple energy bins. Comparisons of the calculated dose distributions with measured dose distributions for a homogeneous water phantom and for phantoms with deep inhomogeneities have been made. From these results it is concluded that the redefinition algorithm is superior to the conventional, fluence-based, pencil-beam algorithm, especially in predicting the dose distribution downstream of a local inhomogeneity. The accuracy of this algorithm appears sufficient for clinical use, and the algorithm is structured for future expansion of the physical model if required for site specific treatment planning problems.

Pixel response-based EPID dosimetry for patient specific QA.

PubMed

Han, Bin; Ding, Aiping; Lu, Minghui; Xing, Lei

2017-01-01

Increasing use of high dose rate, flattening filter free (FFF), and/or small-sized field beams presents a significant challenge to the medical physics community. In this work, we develop a strategy of using a high spatial resolution and high frame rate amorphous silicon flat panel electronic portal imaging device (EPID) for dosimetric measurements of these challenging cases, as well as for conventional external beam therapy. To convert a series of raw EPID-measured radiation field images into water-based dose distribution, a pixel-to-pixel dose-response function of the EPID specific to the linac is essential. The response function was obtained by using a Monte Carlo simulation of the photon transport in the EPID with a comprehensive calibration. After the raw image was converted into the primary incident photon fluence, the fluence was further convolved into a water-based dose distribution of the dynamic field by using a pregenerated pencil-beam kernel. The EPID-based dosimetric measurement technique was validated using beams with and without flattening filter of all energies available in Varian TrueBeam STx™. Both regularly and irregularly shaped fields measured using a PTW 729 ion chamber array in plastic water phantom. The technique was also applied to measure the distribution for a total of 23 treatment plans of different energies to evaluate the accuracy of the proposed approach. The EPID measurements of square fields of 4 × 4 cm 2 to 20 × 20 cm 2 , circular fields of 2-15 cm diameters, rectangular fields of various sizes, and irregular MLC fields were in accordance with measurements using a Farmer chamber and/or ion chamber array. The 2D absolute dose maps generated from EPID raw images agreed with ion chamber measurements to within 1.5% for all fields. For the 23 patient cases examined in this work, the average γ-index passing rate were found to be 99.2 ± 0.6%, 97.4 ± 2.4%, and 72.6 ± 8.4%, respectively, for criterions of 3 mm/3%, 2 mm/2%, and 1 mm/1%. The high spatial resolution and high frame rate EPID provides an accurate and efficient dosimetric tool for QA of modern radiation therapy. Accurate absolute 2D dose maps can be generated from the system for an independent dosimetric verification of treatment delivery. © 2016 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

Monte Carlo simulations for angular and spatial distributions in therapeutic-energy proton beams

NASA Astrophysics Data System (ADS)

Lin, Yi-Chun; Pan, C. Y.; Chiang, K. J.; Yuan, M. C.; Chu, C. H.; Tsai, Y. W.; Teng, P. K.; Lin, C. H.; Chao, T. C.; Lee, C. C.; Tung, C. J.; Chen, A. E.

2017-11-01

The purpose of this study is to compare the angular and spatial distributions of therapeutic-energy proton beams obtained from the FLUKA, GEANT4 and MCNP6 Monte Carlo codes. The Monte Carlo simulations of proton beams passing through two thin targets and a water phantom were investigated to compare the primary and secondary proton fluence distributions and dosimetric differences among these codes. The angular fluence distributions, central axis depth-dose profiles, and lateral distributions of the Bragg peak cross-field were calculated to compare the proton angular and spatial distributions and energy deposition. Benchmark verifications from three different Monte Carlo simulations could be used to evaluate the residual proton fluence for the mean range and to estimate the depth and lateral dose distributions and the characteristic depths and lengths along the central axis as the physical indices corresponding to the evaluation of treatment effectiveness. The results showed a general agreement among codes, except that some deviations were found in the penumbra region. These calculated results are also particularly helpful for understanding primary and secondary proton components for stray radiation calculation and reference proton standard determination, as well as for determining lateral dose distribution performance in proton small-field dosimetry. By demonstrating these calculations, this work could serve as a guide to the recent field of Monte Carlo methods for therapeutic-energy protons.

Is energy pooling necessary in ultraviolet matrix-assisted laser desorption/ionization?

PubMed

Lin, Hou-Yu; Song, Botao; Lu, I-Chung; Hsu, Kuo-Tung; Liao, Chih-Yu; Lee, Yin-Yu; Tseng, Chien-Ming; Lee, Yuan-Tseh; Ni, Chi-Kung

2014-01-15

Energy pooling has been suggested as the key process for generating the primary ions during ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI). In previous studies, decreases in fluorescence quantum yields as laser fluence increased for 2-aminobenzoic acid, 2,5-dihydroxybenzoic acid (2,5-DHB), and 3-hydroxypicolinic acid were used as evidence of energy pooling. This work extends the research to other matrices and addresses whether energy pooling is a universal property in UV-MALDI. Energy pooling was investigated in a time-resolved fluorescence experiment by using a short laser pulse (355 nm, 20 ps pulse width) for excitation and a streak camera (1 ps time resolution) for fluorescence detection. The excited-state lifetime of 2,5-DHB decreased with increases in laser fluence. This suggests that a reaction occurs between two excited molecules, and that energy pooling may be one of the possible reactions. However, the excited-state lifetime of 2,4,6-trihydroxyacetophenone (THAP) did not change with increases in laser fluence. The upper limit of the energy pooling rate constant for THAP is estimated to be approximately 100-500 times smaller than that of 2,5-DHB. The small energy pooling rate constant for THAP indicates that the potential contribution of the energy pooling mechanism to the generation of THAP matrix primary ions should be reconsidered. Copyright © 2013 John Wiley & Sons, Ltd.

Using measured 30-150 kVp polychromatic tungsten x-ray spectra to determine ion chamber calibration factors, Nx (Gy C(-1)).

PubMed

Mercier, J R; Kopp, D T; McDavid, W D; Dove, S B; Lancaster, J L; Tucker, D M

2000-10-01

Two methods for determining ion chamber calibration factors (Nx) are presented for polychromatic tungsten x-ray beams whose spectra differ from beams with known Nx. Both methods take advantage of known x-ray fluence and kerma spectral distributions. In the first method, the x-ray tube potential is unchanged and spectra of differing filtration are measured. A primary standard ion chamber with known Nx for one beam is used to calculate the x-ray fluence spectrum of a second beam. Accurate air energy absorption coefficients are applied to the x-ray fluence spectra of the second beam to calculate actual air kerma and Nx. In the second method, two beams of differing tube potential and filtration with known Nx are used to bracket a beam of unknown Nx. A heuristically derived Nx interpolation scheme based on spectral characteristics of all three beams is described. Both methods are validated. Both methods improve accuracy over the current half value layer Nx estimating technique.

SU-E-T-67: A Quality Assurance Procedure for VMAT Delivery Technique with Multiple Verification Metric Using TG-119 Protocol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katsuta, Y; Kadoya, N; Shimizu, E

2015-06-15

Purpose: A successful VMAT plan delivery includes precise modulations of dose rate, gantry rotational and multi-leaf collimator shapes. The purpose of this research is to construct routine QA protocol which focuses on VMAT delivery technique and to obtain a baseline including dose error, fluence distribution and mechanical accuracy during VMAT. Methods: The mock prostate, head and neck (HN) cases supplied from AAPM were used in this study. A VMAT plans were generated in Monaco TPS according to TG-119 protocol. Plans were created using 6 MV and 10 MV photon beams for each case. The phantom based measurement, fluence measurement andmore » log files analysis were performed. The dose measurement was performed using 0.6 cc ion chamber, which located at isocenter. The fluence distribution were acquired using the MapCHECK2 mounted in the MapPHAN. The trajectory log files recorded inner 20 leaf pairs and gantry angle positions at every 0.25 sec interval were exported to in-house software developed by MATLAB and determined those RMS values. Results: The dose difference is expressed as a ratio of the difference between measured and planned doses. The dose difference for 6 MV was 0.91%, for 10 MV was 0.67%. In turn, the fluence distribution using gamma criteria of 2%/2 mm with a 50% minimum dose threshold for 6 MV was 98.8%, for 10 MV was 97.5%, respectively. The RMS values of MLC for 6 MV and 10 MV were 0.32 mm and 0.37 mm, of gantry were 0.33 degree and 0.31 degree. Conclusion: In this study, QA protocol to assess VMAT delivery accuracy is constructed and results acquired in this study are used as a baseline of VMAT delivery performance verification.« less

SU-F-J-214: Dose Reduction by Spatially Optimized Image Quality Via Fluence Modulated Proton CT (FMpCT)

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Angelis, L; Landry, G; Dedes, G

Purpose: Proton CT (pCT) is a promising imaging modality for reducing range uncertainty in image-guided proton therapy. Range uncertainties partially originate from X-ray CT number conversion to stopping power ratio (SPR) and are limiting the exploitation of the full potential of proton therapy. In this study we explore the concept of spatially dependent fluence modulated proton CT (FMpCT), for achieving optimal image quality in a clinical region of interest (ROI), while reducing significantly the imaging dose to the patient. Methods: The study was based on simulated ideal pCT using pencil beam (PB) scanning. A set of 250 MeV protons PBsmore » was used to create 360 projections of a cylindrical water phantom and a head and neck cancer patient. The tomographic images were reconstructed using a filtered backprojection (FBP) as well as an iterative algorithm (ITR). Different fluence modulation levels were investigated and their impact on the image was quantified in terms of SPR accuracy as well as noise within and outside selected ROIs, as a function of imaging dose. The unmodulated image served as reference. Results: Both FBP reconstruction and ITR without total variation (TV) yielded image quality in the ROIs similar to the reference images, for modulation down to 0.1 of the full proton fluence. The average dose was reduced by 75% for the water phantom and by 40% for the patient. FMpCT does not improve the noise for ITR with TV and modulation 0.1. Conclusion: This is the first work proposing and investigating FMpCT for producing optimal image quality for treatment planning and image guidance, while simultaneously reducing imaging dose. Future work will address spatial resolution effects and the impact of FMpCT on the quality of proton treatment plans for a prototype pCT scanner capable of list mode data acquisition. Acknowledgement: DFG-MAP DFG - Munich-Centre for Advanced Photonics (MAP)« less

Impacts of side chain and excess energy on the charge photogeneration dynamics of low-bandgap copolymer-fullerene blends

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huo, Ming-Ming, E-mail: hithuomm@163.com; Zhang, Jian-Ping, E-mail: jpzhang@chem.ruc.edu.cn, E-mail: hjhzlz@iccas.ac.cn; Department of Chemistry, Renmin University of China, Beijing 100872

2014-02-28

Primary charge photogeneration dynamics in neat and fullerene-blended films of a pair of alternating benzo[1,2-b:4,5-b{sup ′}]dithiophene (BDT) and thieno[3,4-b]thiophene (TT) copolymers are comparatively studied by using near-infrared, time-resolved absorption (TA) spectroscopy under low excitation photon fluence. PBDTTT-E and PBDTTT-C, differed merely in the respective TT-substituents of ester (-E) and carbonyl (-C), show distinctly different charge photogeneration dynamics. The pair of neat PBDTTT films show exciton lifetimes of ∼0.1 ns and fluorescence quantum yields below 0.2%, as well as prominent excess-energy enhanced exciton dissociation. In addition, PBDTTT-C gives rise to >50% higher P{sup •+} yield than PBDTTT-E does irrespective to themore » excitation photon energy. Both PBDTTT-E:PC{sub 61}BM and PBDTTT-C:PC{sub 61}BM blends show subpicosecond exciton lifetimes and nearly unitary fluorescence quenching efficiency and, with respect to the former blend, the latter one shows substantially higher branching ratio of charge separated (CS) state over interfacial charge transfer (ICT) state, and hence more efficient exciton-to-CS conversion. For PBDTTT-C:PC{sub 61}BM, the ultrafast charge dynamics clearly show the processes of ICT-CS interconversion and P{sup •+} migration, which are possibly influenced by the ICT excess energy. However, such processes are relatively indistinctive in the case of PBDTTT-E:PC{sub 61}BM. The results strongly prove the importance of ICT dissociation in yielding free charges, and are discussed in terms of the film morphology and the precursory solution-phase macromolecular conformation.« less

Validation and uncertainty analysis of a pre-treatment 2D dose prediction model

NASA Astrophysics Data System (ADS)

Baeza, Jose A.; Wolfs, Cecile J. A.; Nijsten, Sebastiaan M. J. J. G.; Verhaegen, Frank

2018-02-01

Independent verification of complex treatment delivery with megavolt photon beam radiotherapy (RT) has been effectively used to detect and prevent errors. This work presents the validation and uncertainty analysis of a model that predicts 2D portal dose images (PDIs) without a patient or phantom in the beam. The prediction model is based on an exponential point dose model with separable primary and secondary photon fluence components. The model includes a scatter kernel, off-axis ratio map, transmission values and penumbra kernels for beam-delimiting components. These parameters were derived through a model fitting procedure supplied with point dose and dose profile measurements of radiation fields. The model was validated against a treatment planning system (TPS; Eclipse) and radiochromic film measurements for complex clinical scenarios, including volumetric modulated arc therapy (VMAT). Confidence limits on fitted model parameters were calculated based on simulated measurements. A sensitivity analysis was performed to evaluate the effect of the parameter uncertainties on the model output. For the maximum uncertainty, the maximum deviating measurement sets were propagated through the fitting procedure and the model. The overall uncertainty was assessed using all simulated measurements. The validation of the prediction model against the TPS and the film showed a good agreement, with on average 90.8% and 90.5% of pixels passing a (2%,2 mm) global gamma analysis respectively, with a low dose threshold of 10%. The maximum and overall uncertainty of the model is dependent on the type of clinical plan used as input. The results can be used to study the robustness of the model. A model for predicting accurate 2D pre-treatment PDIs in complex RT scenarios can be used clinically and its uncertainties can be taken into account.

A gamma-ray burst with a high-energy spectral component inconsistent with the synchrotron shock model.

PubMed

González, M M; Dingus, B L; Kaneko, Y; Preece, R D; Dermer, C D; Briggs, M S

2003-08-14

Gamma-ray bursts are among the most powerful events in nature. These events release most of their energy as photons with energies in the range from 30 keV to a few MeV, with a smaller fraction of the energy radiated in radio, optical, and soft X-ray afterglows. The data are in general agreement with a relativistic shock model, where the prompt and afterglow emissions correspond to synchrotron radiation from shock-accelerated electrons. Here we report an observation of a high-energy (multi-MeV) spectral component in the burst of 17 October 1994 that is distinct from the previously observed lower-energy gamma-ray component. The flux of the high-energy component decays more slowly and its fluence is greater than the lower-energy component; it is described by a power law of differential photon number index approximately -1 up to about 200 MeV. This observation is difficult to explain with the standard synchrotron shock model, suggesting the presence of new phenomena such as a different non-thermal electron process, or the interaction of relativistic protons with photons at the source.

Optical flashes from internal pairs formed in gamma-ray burst afterglows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panaitescu, A.

We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV–TeV photons. For gamma-ray burst (GRB) afterglows, this formalism is more suitable if the relativistic reverse shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the Fermi-LAT fluence), the unknown source Lorentz factor, and the unmeasured peak energy of the LAT spectral component. We show synchrotron and inverse-Compton light curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of GRB optical counterparts. Pairs formed in bright LAT afterglows with a Lorentz factor in the few hundreds may produce bright optical counterparts (more » $$R\\lt 10$$) lasting for up to one hundred seconds. As a result, the number of internal pairs formed from unscattered seed photons decreases very strongly with the source Lorentz factor, thus bright GRB optical counterparts cannot arise from internal pairs if the afterglow Lorentz factor is above several hundreds.« less

LETTER TO THE EDITOR: Comments on 'The influence of a novel transmission detector on 6 MV x-ray beam characteristics'

NASA Astrophysics Data System (ADS)

Harder, Dietrich

2010-02-01

In their recent paper (Venkataraman et al 2009 Phys. Med. Biol. 54 3173-83) the authors reported on photon beam attenuation and secondary electron production in the novel transmission detector COMPASS, to be placed in the accessory holder of the linac treatment head. In the interest of IMRT patient safety, space-resolved measurements by transmission detectors analysing the MLC-shaped photon fluence pattern in real time are in fact an urgent item for equipment designers. However, there are some constraints for the construction of such devices. The COMPASS system, at its present stage of development, has difficulties in complying with the constraints that the spatial sampling rate should fit the desired task and that the enhanced secondary electron contamination of the photon beam due to the presence of the device should be minimized. The authors also missed to mention a forerunner in this field, the DAVID transmission detector (Poppe et al 2006 Phys. Med. Biol. 51 1237-48), serving for the real-time supervision of the MLC aperture during patient treatment and ever since proven in clinical practice. The DAVID system, a transparent multiwire ionization chamber placed in the accessory holder, will be shortly described.

Vacuum ultra-violet damage and damage mitigation for plasma processing of highly porous organosilicate glass dielectrics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marneffe, J.-F. de, E-mail: marneffe@imec.be; Lukaszewicz, M.; Porter, S. B.

2015-10-07

Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition,more » the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.« less

Optical flashes from internal pairs formed in gamma-ray burst afterglows

DOE PAGES

Panaitescu, A.

2015-06-09

We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV–TeV photons. For gamma-ray burst (GRB) afterglows, this formalism is more suitable if the relativistic reverse shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the Fermi-LAT fluence), the unknown source Lorentz factor, and the unmeasured peak energy of the LAT spectral component. We show synchrotron and inverse-Compton light curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of GRB optical counterparts. Pairs formed in bright LAT afterglows with a Lorentz factor in the few hundreds may produce bright optical counterparts (more » $$R\\lt 10$$) lasting for up to one hundred seconds. As a result, the number of internal pairs formed from unscattered seed photons decreases very strongly with the source Lorentz factor, thus bright GRB optical counterparts cannot arise from internal pairs if the afterglow Lorentz factor is above several hundreds.« less

Macroscopic singlet oxygen modeling for dosimetry of Photofrin-mediated photodynamic therapy: an in-vivo study

NASA Astrophysics Data System (ADS)

Qiu, Haixia; Kim, Michele M.; Penjweini, Rozhin; Zhu, Timothy C.

2016-08-01

Although photodynamic therapy (PDT) is an established modality for cancer treatment, current dosimetric quantities, such as light fluence and PDT dose, do not account for the differences in PDT oxygen consumption for different fluence rates (φ). A macroscopic model was adopted to evaluate using calculated reacted singlet oxygen concentration ([) to predict Photofrin-PDT outcome in mice bearing radiation-induced fibrosarcoma tumors, as singlet oxygen is the primary cytotoxic species responsible for cell death in type II PDT. Using a combination of fluences (50, 135, 200, and 250 J/cm2) and φ (50, 75, and 150 mW/cm2), tumor regrowth rate, k, was determined for each condition. A tumor cure index, CI=1-k/k, was calculated based on the k between PDT-treated groups and that of the control, k. The measured Photofrin concentration and light dose for each mouse were used to calculate PDT dose and [, while mean optical properties (μa=0.9 cm-1, μs‧=8.4 cm-1) were used to calculate φ for all mice. CI was correlated to the fluence, PDT dose, and [ with R2=0.35, 0.79, and 0.93, respectively. These results suggest that [ serves as a better dosimetric quantity for predicting PDT outcome.

A comparison of phantom scatter from flattened and flattening filter free high-energy photon beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richmond, Neil, E-mail: neil.richmond@stees.nhs.uk; Allen, Vince; Daniel, Jim

2015-04-01

Flattening filter free (FFF) photon beams have different dosimetric properties from those of flattened beams. The aim of this work was to characterize the collimator scatter (S{sub c}) and total scatter (S{sub cp}) from 3 FFF beams of differing quality indices and use the resulting mathematical fits to generate phantom scatter (S{sub p}) data. The similarities and differences between S{sub p} of flattened and FFF beams are described. S{sub c} and S{sub cp} data were measured for 3 flattened and 3 FFF high-energy photon beams (Varian 6 and 10 MV and Elekta 6 MV). These data were fitted to logarithmicmore » power law functions with 4 numerical coefficients. The agreement between our experimentally determined flattened beam S{sub p} and published data was within ± 1.2% for all 3 beams investigated and all field sizes from 4 × 4 to 40 × 40 cm{sup 2}. For the FFF beams, S{sub p} was only within 1% of the same flattened beam published data for field sizes between 6 × 6 and 14 × 14 cm{sup 2}. Outside this range, the differences were much greater, reaching − 3.2%, − 4.5%, and − 4.3% for the fields of 40 × 40 cm{sup 2} for the Varian 6-MV, Varian 10-MV, and Elekta 6-MV FFF beams, respectively. The FFF beam S{sub p} increased more slowly with increasing field size than that of the published and measured flattened beam of a similar reference field size quality index, i.e., there is less Phantom Scatter than that found with flattened beams for a given field size. This difference can be explained when the fluence profiles of the flattened and FFF beams are considered. The FFF beam has greatly reduced fluence off axis, especially as field size increases, compared with the flattened beam profile; hence, less scatter is generated in the phantom reaching the central axis.« less

Magnetic field influences on the lateral dose response functions of photon-beam detectors: MC study of wall-less water-filled detectors with various densities.

PubMed

Looe, Hui Khee; Delfs, Björn; Poppinga, Daniela; Harder, Dietrich; Poppe, Björn

2017-06-21

The distortion of detector reading profiles across photon beams in the presence of magnetic fields is a developing subject of clinical photon-beam dosimetry. The underlying modification by the Lorentz force of a detector's lateral dose response function-the convolution kernel transforming the true cross-beam dose profile in water into the detector reading profile-is here studied for the first time. The three basic convolution kernels, the photon fluence response function, the dose deposition kernel, and the lateral dose response function, of wall-less cylindrical detectors filled with water of low, normal and enhanced density are shown by Monte Carlo simulation to be distorted in the prevailing direction of the Lorentz force. The asymmetric shape changes of these convolution kernels in a water medium and in magnetic fields of up to 1.5 T are confined to the lower millimetre range, and they depend on the photon beam quality, the magnetic flux density and the detector's density. The impact of this distortion on detector reading profiles is demonstrated using a narrow photon beam profile. For clinical applications it appears as favourable that the magnetic flux density dependent distortion of the lateral dose response function, as far as secondary electron transport is concerned, vanishes in the case of water-equivalent detectors of normal water density. By means of secondary electron history backtracing, the spatial distribution of the photon interactions giving rise either directly to secondary electrons or to scattered photons further downstream producing secondary electrons which contribute to the detector's signal, and their lateral shift due to the Lorentz force is elucidated. Electron history backtracing also serves to illustrate the correct treatment of the influences of the Lorentz force in the EGSnrc Monte Carlo code applied in this study.

Topography evolution of 500 keV Ar(4+) ion beam irradiated InP(100) surfaces - formation of self-organized In-rich nano-dots and scaling laws.

PubMed

Sulania, Indra; Agarwal, Dinesh C; Kumar, Manish; Kumar, Sunil; Kumar, Pravin

2016-07-27

We report the formation of self-organized nano-dots on the surface of InP(100) upon irradiating it with a 500 keV Ar(4+) ion beam. The irradiation was carried out at an angle of 25° with respect to the normal at the surface with 5 different fluences ranging from 1.0 × 10(15) to 1.0 × 10(17) ions per cm(2). The morphology of the ion-irradiated surfaces was examined by atomic force microscopy (AFM) and the formation of the nano-dots on the irradiated surfaces was confirmed. The average size of the nano-dots varied from 44 ± 14 nm to 94 ± 26 nm with increasing ion fluence. As a function of the ion fluence, the variation in the average size of the nano-dots has a great correlation with the surface roughness, which changes drastically up to the ion fluence of 1.0 × 10(16) ions per cm(2) and attains almost a saturation level for further irradiation. The roughness and the growth exponent values deduced from the scaling laws suggest that the kinetic sputtering and the large surface diffusion steps of the atoms are the primary reasons for the formation of the self-organized nanodots on the surface. X-ray photo-electron spectroscopy (XPS) studies show that the surface stoichiometry changes with the ion fluence. With irradiation, the surface becomes more indium (In)-rich owing to the preferential sputtering of the phosphorus atoms (P) and the pure metallic In nano-dots evolve at the highest ion fluence. The cross-sectional scanning electron microscopy (SEM) analysis of the sample irradiated with the highest fluence showed the absence of the nanostructuring beneath the surface. The surface morphological changes at this medium energy ion irradiation are discussed in correlation with the low and high energy experiments to shed more light on the mechanism of the well separated nano-dot formation.

Variations in energy spectra and water-to-material stopping-power ratios in three-dimensional conformal and intensity-modulated photon fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jang, Si Young; Liu, H. Helen; Mohan, Radhe

Because of complex dose distributions and dose gradients that are created in three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiation therapy (IMRT), photon- and electron-energy spectra might change significantly with spatial locations and doses. This study examined variations in photon- and electron-energy spectra in 3D-CRT and IMRT photon fields. The effects of spectral variations on water-to-material stopping-power ratios used in Monte Carlo treatment planning systems and the responses of energy-dependent dosimeters, such as thermoluminescent dosimeters (TLDs) and radiographic films were further studied. The EGSnrc Monte Carlo code was used to simulate megavoltage 3D-CRT and IMRT photon fields. The photon- and electron-energymore » spectra were calculated in 3D water phantoms and anthropomorphic phantoms based on the fluence scored in voxel grids. We then obtained the water-to-material stopping-power ratios in the local voxels using the Spencer-Attix cavity theory. Changes in the responses of films and TLDs were estimated based on the calculated local energy spectra and published data on the dosimeter energy dependency. Results showed that the photon-energy spectra strongly depended on spatial positions and doses in both the 3D-CRT and IMRT fields. The relative fraction of low-energy photons (<100 keV) increased inversely with the photon dose in low-dose regions of the fields. A similar but smaller effect was observed for electrons in the phantoms. The maximum variation of the water-to-material stopping-power ratio over the range of calculated dose for both 3D-CRT and IMRT was negligible (<1.0%) for ICRU tissue, cortical bone, and soft bone and less than 3.6% for dry air and lung. Because of spectral softening at low doses, radiographic films in the phantoms could over-respond to dose by more than 30%, whereas the over-response of TLDs was less than 10%. Thus, spatial variations of the photon- and electron-energy spectra should be considered as important factors in 3D-CRT and IMRT dosimetry.« less

Photonic jet subwavelength etching using a shaped optical fiber tip.

PubMed

Zelgowski, Julien; Abdurrochman, Andri; Mermet, Frederic; Pfeiffer, Pierre; Fontaine, Joël; Lecler, Sylvain

2016-05-01

We demonstrate that photonic jets (PJs) can be obtained in the vicinity of a shaped optical fiber and that they can be used to achieve subwavelength etchings. Only 10% of the power of a 30 W, 100 ns, near-infrared (1064 nm) Nd:YAG laser, commonly used for industrial laser processing, has been required. Etchings on a silicon wafer with a lateral feature size close to half-laser wavelength have been achieved using a shaped-tip optical fiber. This breakthrough has been carried out in ambient air by using a multimode 100/140 μm silica fiber with a shaped tip that generates a concentrated beam at their vicinity, a phenomenon referred to as a PJ, obtained for the first time without using microspheres. PJ achieved with a fiber tip, easier to manipulate, opens far-reaching benefits for all PJ applications. The roles of parameters such as laser fluence, tip shape, and mode excitation are discussed. A good correlation has been observed between the computed PJ intensity distribution and the etched marks' sizes.

Fermi-LAT observations of the gamma-ray burst GRB 130427A.

PubMed

Ackermann, M; Ajello, M; Asano, K; Atwood, W B; Axelsson, M; Baldini, L; Ballet, J; Barbiellini, G; Baring, M G; Bastieri, D; Bechtol, K; Bellazzini, R; Bissaldi, E; Bonamente, E; Bregeon, J; Brigida, M; Bruel, P; Buehler, R; Burgess, J Michael; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Cecchi, C; Chaplin, V; Charles, E; Chekhtman, A; Cheung, C C; Chiang, J; Chiaro, G; Ciprini, S; Claus, R; Cleveland, W; Cohen-Tanugi, J; Collazzi, A; Cominsky, L R; Connaughton, V; Conrad, J; Cutini, S; D'Ammando, F; de Angelis, A; DeKlotz, M; de Palma, F; Dermer, C D; Desiante, R; Diekmann, A; Di Venere, L; Drell, P S; Drlica-Wagner, A; Favuzzi, C; Fegan, S J; Ferrara, E C; Finke, J; Fitzpatrick, G; Focke, W B; Franckowiak, A; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gehrels, N; Germani, S; Gibby, M; Giglietto, N; Giles, M; Giordano, F; Giroletti, M; Godfrey, G; Granot, J; Grenier, I A; Grove, J E; Gruber, D; Guiriec, S; Hadasch, D; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Horan, D; Hughes, R E; Inoue, Y; Jogler, T; Jóhannesson, G; Johnson, W N; Kawano, T; Knödlseder, J; Kocevski, D; Kuss, M; Lande, J; Larsson, S; Latronico, L; Longo, F; Loparco, F; Lovellette, M N; Lubrano, P; Mayer, M; Mazziotta, M N; McEnery, J E; Michelson, P F; Mizuno, T; Moiseev, A A; Monzani, M E; Moretti, E; Morselli, A; Moskalenko, I V; Murgia, S; Nemmen, R; Nuss, E; Ohno, M; Ohsugi, T; Okumura, A; Omodei, N; Orienti, M; Paneque, D; Pelassa, V; Perkins, J S; Pesce-Rollins, M; Petrosian, V; Piron, F; Pivato, G; Porter, T A; Racusin, J L; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Ritz, S; Roth, M; Ryde, F; Sartori, A; Parkinson, P M Saz; Scargle, J D; Schulz, A; Sgrò, C; Siskind, E J; Sonbas, E; Spandre, G; Spinelli, P; Tajima, H; Takahashi, H; Thayer, J G; Thayer, J B; Thompson, D J; Tibaldo, L; Tinivella, M; Torres, D F; Tosti, G; Troja, E; Usher, T L; Vandenbroucke, J; Vasileiou, V; Vianello, G; Vitale, V; Winer, B L; Wood, K S; Yamazaki, R; Younes, G; Yu, H-F; Zhu, S J; Bhat, P N; Briggs, M S; Byrne, D; Foley, S; Goldstein, A; Jenke, P; Kippen, R M; Kouveliotou, C; McBreen, S; Meegan, C; Paciesas, W S; Preece, R; Rau, A; Tierney, D; van der Horst, A J; von Kienlin, A; Wilson-Hodge, C; Xiong, S; Cusumano, G; La Parola, V; Cummings, J R

2014-01-03

The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest γ-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

Nanowire–quantum-dot lasers on flexible membranes

NASA Astrophysics Data System (ADS)

Tatebayashi, Jun; Ota, Yasutomo; Ishida, Satomi; Nishioka, Masao; Iwamoto, Satoshi; Arakawa, Yasuhiko

2018-06-01

We demonstrate lasing in a single nanowire with quantum dots as an active medium embedded on poly(dimethylsiloxane) membranes towards application in nanowire-based flexible nanophotonic devices. Nanowire laser structures with 50 quantum dots are grown on patterned GaAs(111)B substrates and then transferred from the as-grown substrates on poly(dimethylsiloxane) transparent flexible organosilicon membranes, by means of spin-casting and curing processes. We observe lasing oscillation in the transferred single nanowire cavity with quantum dots at 1.425 eV with a threshold pump pulse fluence of ∼876 µJ/cm2, which enables the realization of high-performance multifunctional NW-based flexible photonic devices.

Shift in room-temperature photoluminescence of low-fluence Si+-implanted SiO2 films subjected to rapid thermal annealing.

PubMed

Fu, Ming-Yue; Tsai, Jen-Hwan; Yang, Cheng-Fu; Liao, Chih-Hsiung

2008-12-01

We experimentally demonstrate the effect of the rapid thermal annealing (RTA) in nitrogen flow on photoluminescence (PL) of SiO 2 films implanted by different doses of Si + ions. Room-temperature PL from 400-nm-thick SiO 2 films implanted to a dose of 3×10 16 cm -2 shifted from 2.1 to 1.7 eV upon increasing RTA temperature (950-1150 °C) and duration (5-20 s). The reported approach of implanting silicon into SiO 2 films followed by RTA may be effective for tuning Si-based photonic devices.

Shift in room-temperature photoluminescence of low-fluence Si+-implanted SiO2 films subjected to rapid thermal annealing

PubMed Central

Fu, Ming-Yue; Tsai, Jen-Hwan; Yang, Cheng-Fu; Liao, Chih-Hsiung

2008-01-01

We experimentally demonstrate the effect of the rapid thermal annealing (RTA) in nitrogen flow on photoluminescence (PL) of SiO2 films implanted by different doses of Si+ ions. Room-temperature PL from 400-nm-thick SiO2 films implanted to a dose of 3×1016 cm−2 shifted from 2.1 to 1.7 eV upon increasing RTA temperature (950–1150 °C) and duration (5–20 s). The reported approach of implanting silicon into SiO2 films followed by RTA may be effective for tuning Si-based photonic devices. PMID:27878029

Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A

DOE PAGES

Ackermann, M.; Ajello, M.; Asano, K.; ...

2013-11-21

The Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources using the observations of the exceptionally bright gamma-ray burst (GRB) 130427A. We found that GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest γ-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A

NASA Technical Reports Server (NTRS)

Ackermann, M.; Ajello, M.; Asano, K.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.;

Primary inhibition of hypocotyl growth and phototropism depend differently on phototropin-mediated increases in cytoplasmic calcium induced by blue light.

PubMed

Folta, Kevin M; Lieg, Erin J; Durham, Tessa; Spalding, Edgar P

2003-12-01

The phototropin photoreceptors transduce blue-light signals into several physiological and developmental responses in plants. A transient rise in cytoplasmic calcium (Ca2+) that begins within seconds of phototropin 1 (phot1) excitation is believed to be an important element in the transduction pathways leading to one or more of the phot1-dependent responses. The goal of the present work was to determine whether the Ca2+ response was necessary for (a). the inhibition of hypocotyl elongation that develops within minutes of the irradiation, and (b). hypocotyl phototropism (curved growth of the stem in response to asymmetric illumination). After determining that pulses of light delivering photon fluences of between 1 and 1000 micromol m-2 induced growth inhibition mediated by phot1 without significant interference from other photosensory pathways, the effect of blocking the Ca2+ rise was assessed. Treatment of seedlings with a Ca2+ chelator prevented the rise in cytoplasmic Ca2+ and prevented phot1-mediated growth inhibition. However, the same chelator treatment did not impair phot1-mediated phototropism. Thus, it appears that the early, transient rise in cytoplasmic Ca2+ is an important intermediary process in at least one but not all phot1-signaling pathways.

Primary Inhibition of Hypocotyl Growth and Phototropism Depend Differently on Phototropin-Mediated Increases in Cytoplasmic Calcium Induced by Blue Light1

PubMed Central

Folta, Kevin M.; Lieg, Erin J.; Durham, Tessa; Spalding, Edgar P.

2003-01-01

The phototropin photoreceptors transduce blue-light signals into several physiological and developmental responses in plants. A transient rise in cytoplasmic calcium (Ca2+) that begins within seconds of phototropin 1 (phot1) excitation is believed to be an important element in the transduction pathways leading to one or more of the phot1-dependent responses. The goal of the present work was to determine whether the Ca2+ response was necessary for (a) the inhibition of hypocotyl elongation that develops within minutes of the irradiation, and (b) hypocotyl phototropism (curved growth of the stem in response to asymmetric illumination). After determining that pulses of light delivering photon fluences of between 1 and 1,000 μmol m-2 induced growth inhibition mediated by phot1 without significant interference from other photosensory pathways, the effect of blocking the Ca2+ rise was assessed. Treatment of seedlings with a Ca2+ chelator prevented the rise in cytoplasmic Ca2+ and prevented phot1-mediated growth inhibition. However, the same chelator treatment did not impair phot1-mediated phototropism. Thus, it appears that the early, transient rise in cytoplasmic Ca2+ is an important intermediary process in at least one but not all phot1-signaling pathways. PMID:14645723

Looking for Dust-Scattering Light Echoes

NASA Astrophysics Data System (ADS)

Mills, Brianna; Heinz, Sebastian; Corrales, Lia

2018-01-01

Galactic X-ray transient sources such as neutron stars or black holes sometimes undergo an outburst in X-rays. Ring structures have been observed around three such sources, produced by the X-ray photons being scattered by interstellar dust grains along our line of sight. These dust-scattering light echoes have proven to be a useful tool for measuring and constraining Galactic distances, mapping the dust structure of the Milky Way, and determining the dust composition in the clouds producing the echo. Detectable light echoes require a sufficient quantity of dust along our line of sight, as well as bright, short-lived Galactic X-ray flares. Using data from the Monitor of All-Sky X-ray Image (MAXI) on-board the International Space Station, we ran a peak finding algorithm in Python to look for characteristic flare events. Each flare was characterized by its fluence, the integrated flux of the flare over time. We measured the distribution of flare fluences to show how many observably bright flares were recorded by MAXI. This work provides a parent set for dust echo searches in archival X-ray data and will inform observing strategies with current and future X-ray missions such as Athena and Lynx.

Measurement of the main and critical parameters for optimal laser treatment of heart disease

NASA Astrophysics Data System (ADS)

Kabeya, FB; Abrahamse, H.; Karsten, AE

2017-10-01

Laser light is frequently used in the diagnosis and treatment of patients. As in traditional treatments such as medication, bypass surgery, and minimally invasive ways, laser treatment can also fail and present serious side effects. The true reason for laser treatment failure or the side effects thereof, remains unknown. From the literature review conducted, and experimental results generated we conclude that an optimal laser treatment for coronary artery disease (named heart disease) can be obtained if certain critical parameters are correctly measured and understood. These parameters include the laser power, the laser beam profile, the fluence rate, the treatment time, as well as the absorption and scattering coefficients of the target treatment tissue. Therefore, this paper proposes different, accurate methods for the measurement of these critical parameters to determine the optimal laser treatment of heart disease with a minimal risk of side effects. The results from the measurement of absorption and scattering properties can be used in a computer simulation package to predict the fluence rate. The computing technique is a program based on the random number (Monte Carlo) process and probability statistics to track the propagation of photons through a biological tissue.

Laser-driven formation of a high-pressure phase in amorphous silica.

PubMed

Salleo, Alberto; Taylor, Seth T; Martin, Michael C; Panero, Wendy R; Jeanloz, Raymond; Sands, Timothy; Génin, François Y

2003-12-01

Because of its simple composition, vast availability in pure form and ease of processing, vitreous silica is often used as a model to study the physics of amorphous solids. Research in amorphous silica is also motivated by its ubiquity in modern technology, a prominent example being as bulk material in transmissive and diffractive optics for high-power laser applications such as inertial confinement fusion (ICF). In these applications, stability under high-fluence laser irradiation is a key requirement, with optical breakdown occurring when the fluence of the beam is higher than the laser-induced damage threshold (LIDT) of the material. The optical strength of polished fused silica transmissive optics is limited by their surface LIDT. Surface optical breakdown is accompanied by densification, formation of point defects, cratering, material ejection, melting and cracking. Through a combination of electron diffraction and infrared reflectance measurements we show here that synthetic vitreous silica transforms partially into a defective form of the high-pressure stishovite phase under high-intensity (GW cm(-2)) laser irradiation. This phase transformation offers one suitable mechanism by which laser-induced damage grows catastrophically once initiated, thereby dramatically shortening the service lifetime of optics used for high-power photonics.

Inversion of gravitropism by symmetric blue light on the clinostat.

PubMed

Sailer, H; Nick, P; Schafer, E

1990-02-01

Gravitropic stimulation of maize (Zea mays L.) seedlings resulted in a continuous curvature of the coleoptiles in a direction opposing the vector of gravity when the seedlings were rotated on a horizontal clinostat. The orientation of this response, however, was reversed when the gravitropic stimulation was preceded by symmetric preirradiation with blue light (12.7 micromoles photons m-2). The fluence-response curve of this blue light exhibited a lower threshold at 0.5 micromole m-2, and could be separated into two parts: fluences exceeding 5 micromoles m-2 reversed the direction of the gravitropic response, whereas for a range between the threshold and 4 micromoles m-2 a split population was obtained. In all cases a very strong curvature resulted either in the direction of gravity or in the opposite orientation. A minor fraction of seedlings, however, curved towards the caryopsis. Furthermore, the capacity of blue light to reverse the direction of the gravitropic response disappeared with the duration of gravitropic stimulation and it depended on the delay time between both stimulations. This tonic blue-light influence appears to be transient, which is in contrast to the stability observed for tropistic blue-light effects.

Radiation damage and waste management options for the SOMBRERO final focus system and neutron dumps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Latkowski, J F; Meier, W R; Reyes, S

1999-08-09

Previous studies of the safety and environmental aspects of the SOMBRERO inertial fusion energy (IFE) power plant design did not completely address the issues associated with the final focus system. While past work calculated neutron fluences for a grazing incidence metal mirror (GIMM) and a final focus mirror, scattering off of the final optical component was not included, and thus, fluences in the final focus mirror were significantly underestimated. In addition, past work did not consider neutron-induced gamma-rays. Finally, power plant lifetime waste volumes may have been underestimated as neutron activation of the neutron dumps and building structure were notmore » addressed. In the present work, a modified version of the SOMBRERO target building is presented where a significantly larger open solid-angle fraction (5%) is used to enhance beam smoothing of a diode-pumped solid-state laser (DPSSL). The GIMMs are replaced with transmissive fused silica wedges and have been included in three -dimensional neutron and photon transport calculations. This work shows that a power plant with a large open solid-angle fraction, needed for beam smoothing with a DPSSL, is acceptable from tritium breeding, and neutron activation points-of-view.« less

Role of root UV-B sensing in Arabidopsis early seedling development.

PubMed

Tong, Hongyun; Leasure, Colin D; Hou, Xuewen; Yuen, Gigi; Briggs, Winslow; He, Zheng-Hui

2008-12-30

All sun-exposed organisms are affected by UV-B [(UVB) 280-320 nm], an integral part of sunlight. UVB can cause stresses or act as a developmental signal depending on its fluence levels. In plants, the mechanism by which high-fluence-rate UVB causes damages and activates DNA-repair systems has been extensively studied. However, little is known about how nondamaging low-fluence-rate UVB is perceived to regulate plant morphogenesis and development. Here, we report the identification of an Arabidopsis mutant, root UVB sensitive 1 (rus1), whose primary root is hypersensitive to very low-fluence-rate (VLF) UVB. Under standard growth-chamber fluorescent white light, rus1 displays stunted root growth and fails to form postembryonic leaves. Experiments with different monochromatic light sources showed that rus1 phenotypes can be rescued if the seedlings are allowed to grow in light conditions with minimum UVB. We determined that roots, not other organs, perceive the UVB signal. Genetic and molecular analyses confirmed that the root light-sensitive phenotypes are independent of all other known plant photoreceptors. Three rus1 alleles have been identified and characterized. A map-based approach was used to identify the RUS1 locus. RUS1 encodes a protein that contains DUF647 (domain of unknown function 647), a domain highly conserved in eukaryotes. Our results demonstrate a root VLF UVB-sensing mechanism that is involved in Arabidopsis early seedling morphogenesis and development.

A correction scheme for a simplified analytical random walk model algorithm of proton dose calculation in distal Bragg peak regions

NASA Astrophysics Data System (ADS)

Yao, Weiguang; Merchant, Thomas E.; Farr, Jonathan B.

2016-10-01

The lateral homogeneity assumption is used in most analytical algorithms for proton dose, such as the pencil-beam algorithms and our simplified analytical random walk model. To improve the dose calculation in the distal fall-off region in heterogeneous media, we analyzed primary proton fluence near heterogeneous media and propose to calculate the lateral fluence with voxel-specific Gaussian distributions. The lateral fluence from a beamlet is no longer expressed by a single Gaussian for all the lateral voxels, but by a specific Gaussian for each lateral voxel. The voxel-specific Gaussian for the beamlet of interest is calculated by re-initializing the fluence deviation on an effective surface where the proton energies of the beamlet of interest and the beamlet passing the voxel are the same. The dose improvement from the correction scheme was demonstrated by the dose distributions in two sets of heterogeneous phantoms consisting of cortical bone, lung, and water and by evaluating distributions in example patients with a head-and-neck tumor and metal spinal implants. The dose distributions from Monte Carlo simulations were used as the reference. The correction scheme effectively improved the dose calculation accuracy in the distal fall-off region and increased the gamma test pass rate. The extra computation for the correction was about 20% of that for the original algorithm but is dependent upon patient geometry.

Electron-positron pair production by ultrarelativistic electrons in a soft photon field

NASA Technical Reports Server (NTRS)

Mastichiadis, A.; Marscher, A. P.; Brecher, K.

1986-01-01

The fully differential cross section for photon-electron pair production is integrated numerically over phase space. Results are obtained for the astrophysically interesting case in which the interaction between an ultrarelativistic electron and a soft photon results in electron-positron pair production. The positron spectrum is a function of the energies of both the photon and the electron, as well as the angle of interaction. It is found that the energy at which the positron distribution peaks is inversely proportional to the photon energy and independent of the electron energy. The positron spectrum is integrated once more over initial electron energies for a power-law energy distribution of primary electrons. The same procedure is repeated for the recoil particle; it is shown that the peak of the recoil energy distribution depends linearly on the energy of the primary electron. Finally, semianalytical expressions are obtained for the energy losses of the primary electrons.

Growth mechanisms of multiscale, mound-like surface structures on titanium by femtosecond laser processing

NASA Astrophysics Data System (ADS)

Peng, Edwin; Bell, Ryan; Zuhlke, Craig A.; Wang, Meiyu; Alexander, Dennis R.; Gogos, George; Shield, Jeffrey E.

2017-10-01

Femtosecond laser surface processing (FLSP) can be used to functionalize many surfaces, imparting specialized properties such as increased broadband optical absorption or super-hydrophobicity/-hydrophilicity. In this study, the subsurface microstructure of a series of mound-like FLSP structures formed on commercially pure titanium using five combinations of laser fluence and cumulative pulse counts was studied. Using a dual beam Scanning Electron Microscope with a Focused Ion Beam, the subsurface microstructure for each FLSP structure type was revealed by cross-sectioning. The microstructure of the mounds formed using the lowest fluence value consists of the original Ti grains. This is evidence that preferential laser ablation is the primary formation mechanism. However, the underlying microstructure of mounds produced using higher fluence values was composed of a distinct smaller-grained α-Ti region adjacent to the original larger Ti grains remaining deeper beneath the surface. This layer was attributed to resolidification of molten Ti from the hydrodynamic Marangoni effect driven fluid flow of molten Ti, which is the result of the femtosecond pulse interaction with the material.

Ultraviolet Laser-induced ignition of RDX single crystal

PubMed Central

Yan, Zhonghua; Zhang, Chuanchao; Liu, Wei; Li, Jinshan; Huang, Ming; Wang, Xuming; Zhou, Guorui; Tan, Bisheng; Yang, Zongwei; Li, Zhijie; Li, Li; Yan, Hongwei; Yuan, Xiaodong; Zu, Xiaotao

2016-01-01

The RDX single crystals are ignited by ultraviolet laser (355 nm, 6.4 ns) pulses. The laser-induced damage morphology consisted of two distinct regions: a core region of layered fracture and a peripheral region of stripped material surrounding the core. As laser fluence increases, the area of the whole crack region increases all the way, while both the area and depth of the core region increase firstly, and then stay stable over the laser fluence of 12 J/cm2. The experimental details indicate the dynamics during laser ignition process. Plasma fireball of high temperature and pressure occurs firstly, followed by the micro-explosions on the (210) surface, and finally shock waves propagate through the materials to further strip materials outside and yield in-depth cracks in larger surrounding region. The plasma fireball evolves from isotropic to anisotropic under higher laser fluence resulting in the damage expansion only in lateral direction while maintaining the fixed depth. The primary insights into the interaction dynamics between laser and energetic materials can help developing the superior laser ignition technique. PMID:26847854

SU-F-T-376: The Efficiency of Calculating Photonuclear Reaction On High-Energy Photon Therapy by Monte Carlo Method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirayama, S; Fujibuchi, T

Purpose: Secondary-neutrons having harmful influences to a human body are generated by photonuclear reaction on high-energy photon therapy. Their characteristics are not known in detail since the calculation to evaluate them takes very long time. PHITS(Particle and Heavy Ion Transport code System) Monte Carlo code since versions 2.80 has the new parameter “pnimul” raising the probability of occurring photonuclear reaction forcibly to make the efficiency of calculation. We investigated the optimum value of “pnimul” on high-energy photon therapy. Methods: The geometry of accelerator head based on the specification of a Varian Clinac 21EX was used for PHITS ver. 2.80. Themore » phantom (30 cm * 30 cm * 30 cm) filled the composition defined by ICRU(International Commission on Radiation Units) was placed at source-surface distance 100 cm. We calculated the neutron energy spectra in the surface of ICRU phantom with “pnimal” setting 1, 10, 100, 1000, 10000 and compared the total calculation time and the behavior of photon using PDD(Percentage Depth Dose) and OCR(Off-Center Ratio). Next, the cutoff energy of photon, electron and positron were investigated for the calculation efficiency with 4, 5, 6 and 7 MeV. Results: The calculation total time until the errors of neutron fluence become within 1% decreased as increasing “pnimul”. PDD and OCR showed no differences by the parameter. The calculation time setting the cutoff energy like 4, 5, 6 and 7 MeV decreased as increasing the cutoff energy. However, the errors of photon become within 1% did not decrease by the cutoff energy. Conclusion: The optimum values of “pnimul” and the cutoff energy were investigated on high-energy photon therapy. It is suggest that using the optimum “pnimul” makes the calculation efficiency. The study of the cutoff energy need more investigation.« less

SU-E-T-238: Monte Carlo Estimation of Cerenkov Dose for Photo-Dynamic Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chibani, O; Price, R; Ma, C

Purpose: Estimation of Cerenkov dose from high-energy megavoltage photon and electron beams in tissue and its impact on the radiosensitization using Protoporphyrine IX (PpIX) for tumor targeting enhancement in radiotherapy. Methods: The GEPTS Monte Carlo code is used to generate dose distributions from 18MV Varian photon beam and generic high-energy (45-MV) photon and (45-MeV) electron beams in a voxel-based tissueequivalent phantom. In addition to calculating the ionization dose, the code scores Cerenkov energy released in the wavelength range 375–425 nm corresponding to the pick of the PpIX absorption spectrum (Fig. 1) using the Frank-Tamm formula. Results: The simulations shows thatmore » the produced Cerenkov dose suitable for activating PpIX is 4000 to 5500 times lower than the overall radiation dose for all considered beams (18MV, 45 MV and 45 MeV). These results were contradictory to the recent experimental studies by Axelsson et al. (Med. Phys. 38 (2011) p 4127), where Cerenkov dose was reported to be only two orders of magnitude lower than the radiation dose. Note that our simulation results can be corroborated by a simple model where the Frank and Tamm formula is applied for electrons with 2 MeV/cm stopping power generating Cerenkov photons in the 375–425 nm range and assuming these photons have less than 1mm penetration in tissue. Conclusion: The Cerenkov dose generated by high-energy photon and electron beams may produce minimal clinical effect in comparison with the photon fluence (or dose) commonly used for photo-dynamic therapy. At the present time, it is unclear whether Cerenkov radiation is a significant contributor to the recently observed tumor regression for patients receiving radiotherapy and PpIX versus patients receiving radiotherapy only. The ongoing study will include animal experimentation and investigation of dose rate effects on PpIX response.« less

Measurements of the 169Tm(n ,2 n )168Tm cross section from threshold to 15 MeV

NASA Astrophysics Data System (ADS)

Soter, J.; Bhike, M.; Finch, S. W.; Krishichayan, Tornow, W.

2017-12-01

Measurements of the 169Tm(n ,2 n )168Tm cross section have been performed via the activation technique at 13 energies between 8.5 and 15.0 MeV. The purpose of this comprehensive data set is to provide an alternative diagnostic tool for obtaining subtle information on the neutron energy distribution produced in inertial confinement deuterium-tritium fusion experiments at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. The 169Tm(n ,2 n )168Tm reaction not only provides the primary 14-MeV neutron fluence, but also the important down-scattered neutron fluence, the latter providing information on the density achieved in the deuterium-tritium plasma during a laser shot.

Theoretical and experimental study of the dark signal in CMOS image sensors affected by neutron radiation from a nuclear reactor

NASA Astrophysics Data System (ADS)

Xue, Yuanyuan; Wang, Zujun; He, Baoping; Yao, Zhibin; Liu, Minbo; Ma, Wuying; Sheng, Jiangkun; Dong, Guantao; Jin, Junshan

2017-12-01

The CMOS image sensors (CISs) are irradiated with neutron from a nuclear reactor. The dark signal in CISs affected by neutron radiation is studied theoretically and experimentally. The Primary knock-on atoms (PKA) energy spectra for 1 MeV incident neutrons are simulated by Geant4. And the theoretical models for the mean dark signal, dark signal non-uniformity (DSNU) and dark signal distribution versus neutron fluence are established. The results are found to be in good agreement with the experimental outputs. Finally, the dark signal in the CISs under the different neutron fluence conditions is estimated. This study provides the theoretical and experimental evidence for the displacement damage effects on the dark signal CISs.

Tailoring molybdenum nanostructure evolution by low-energy He+ ion irradiation

NASA Astrophysics Data System (ADS)

Tripathi, J. K.; Novakowski, T. J.; Hassanein, A.

2015-10-01

Mirror-finished polished molybdenum (Mo) samples were irradiated with 100 eV He+ ions as a function of ion fluence (using a constant flux of 7.2 × 1020 ions m-2 s-1) at normal incidence and at 923 K. Mo surface deterioration and nanoscopic fiber-form filament ("Mo fuzz") growth evolution were monitored by using field emission (FE) scanning electron (SEM) and atomic force (AFM) microscopy studies. Those studies confirm a reasonably clean and flat surface, up to several micrometer scales along with a few mechanical-polishing-induced scratches. However, He+ ion irradiation deteriorates the surface significantly even at 2.1 × 1023 ions m-2 fluence (about 5 min. irradiation time) and leads to evolution of homogeneously populated ∼75-nm-long Mo nanograins having ∼8 nm intergrain width. The primary stages of Mo fuzz growth, i.e., elongated half-cylindrical ∼70 nm nanoplatelets, and encapsulated bubbles of 20-45 nm in diameter and preferably within the grain boundaries of sub-micron-sized grains, were observed after 1.3 × 1024 ions m-2 fluence irradiation. Additionally, a sequential enhancement in the sharpness, density, and protrusions of Mo fuzz at the surface with ion fluence was also observed. Fluence- and flux-dependent studies have also been performed at 1223 K target temperature (beyond the temperature window for Mo fuzz formation). At a constant fluence of 2.6 × 1024 ions m-2, 7.2 × 1020 ions m-2 s-1 flux generates a homogeneous layered and stacked nanodiscs of ∼70 nm diameter. On the other hand, 1.2 × 1021 ions m-2 s-1 flux generates a combination of randomly patched netlike nanomatrix networked structure, mostly with ∼105 nm nanostructure wall width, various-shaped pores, and self-organized nano arrays. While the observed netlike nanomatrix network structures for 8.6 × 1024 ions m-2 fluence (at a constant flux of 1.2 × 1021 ions m-2 s-1) is quite similar to those for 2.6 × 1024 ions m-2 fluence, the nanostructure wall width extends up to ∼45 nm more and has a quite different nanostructured surface. Ex-situ X-ray photoelectron spectroscopy studies show a sequential reduction in at.% of Mo 3d doublets with fluence, leading to the complete depletion of 2.6 × 1024 ions m-2 at 973 K. For 2.6 × 1024 ions m-2 fluence irradiation at 973 K, only MoO3 3d doublets were observed. However, the Mo 3d doublets reappear at 1273 K irradiation, where a variety of nanostructures were observed with relatively much lower density than that of Mo fuzz. As in the microscopy studies, the reflectivity measurements also show a sequential reduction with ion fluence, leading to almost zero reflectivity value for fully grown fuzzy structures. The study is significant in the understanding of fuzz formation on high-Z refractory metals for fusion applications; in addition, the observed MoO3 fuzz has potential application in solar power concentration technology and in water splitting for hydrogen production.

Dose evaluation of Grid Therapy using a 6 MV flattening filter-free (FFF) photon beam: A Monte Carlo study.

PubMed

Martínez-Rovira, Immaculada; Puxeu-Vaqué, Josep; Prezado, Yolanda

2017-10-01

Spatially fractionated radiotherapy is a strategy to overcome the main limitation of radiotherapy, i.e., the restrained normal tissue tolerances. A well-known example is Grid Therapy, which is currently performed at some hospitals using megavoltage photon beams delivered by Linacs. Grid Therapy has been successfully used in the management of bulky abdominal tumors with low toxicity. The aim of this work was to evaluate whether an improvement in therapeutic index in Grid Therapy can be obtained by implementing it in a flattening filter-free (FFF) Linac. The rationale behind is that the removal of the flattening filter shifts the beam energy spectrum towards lower energies and increase the photon fluence. Lower energies result in a reduction of lateral scattering and thus, to higher peak-to-valley dose ratios (PVDR) in normal tissues. In addition, the gain in fluence might allow using smaller beams leading a more efficient exploitation of dose-volume effects, and consequently, a better normal tissue sparing. Monte Carlo simulations were used to evaluate realistic dose distributions considering a 6 MV FFF photon beam from a standard medical Linac and a cerrobend mechanical collimator in different configurations: grid sizes of 0.3 × 0.3 cm 2 , 0.5 × 0.5 cm 2 , and 1 × 1 cm 2 and a corresponding center-to-center (ctc) distance of 0.6, 1, and 2 cm, respectively (total field size of 10 × 10 cm 2 ). As figure of merit, peak doses in depth, PVDR, output factors (OF), and penumbra values were assessed. Dose at the entrance is slightly higher than in conventional Grid Therapy. However, it is compensated by the large PVDR obtained at the entrance, reaching a maximum of 35 for a grid size of 1 × 1 cm 2 . Indeed, this grid size leads to very high PVDR values at all depths (≥ 10), which are much higher than in standard Grid Therapy. This may be beneficial for normal tissues but detrimental for tumor control, where a lower PVDR might be requested. In that case, higher valley doses in the tumor could be achieved by using an interlaced approach and/or adapting the ctc distance. The smallest grid size (0.3 × 0.3 cm 2 ) leads to low PVDR at all depths, comparable to standard Grid Therapy. However, the use of very thin beams might increase the normal tissue tolerances with respect to the grid size commonly used (1 × 1 cm 2 ). The gain in fluence provided by FFF implies that the important OF reduction (0.6) will not increase treatment time. Finally, the intermediate configuration (0.5 × 0.5 cm 2 ) provides high PVDR in the first 5 cm, and comparable PVDR to previous Grid Therapy works at depth. Therefore, this configuration might allow increasing the normal tissue tolerances with respect to Grid Therapy thanks to the higher PVDR and thinner beams, while a similar tumor control could be expected. The implementation of Grid Therapy in an FFF photon beam from medical Linac might lead to an improvement of the therapeutic index. Among the cases evaluated, a grid size of 0.5 × 0.5 cm 2 (1-cm-ctc) is the most advantageous configuration from the physics point of view. Radiobiological experiments are needed to fully explore this new avenue and to confirm our results. © 2017 American Association of Physicists in Medicine.

Numeric spectral radiation hydrodynamic calculations of supernova shock breakouts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sapir, Nir; Halbertal, Dorri

2014-12-01

We present here an efficient numerical scheme for solving the non-relativistic one-dimensional radiation-hydrodynamics equations including inelastic Compton scattering, which is not included in most codes and is crucial for solving problems such as shock breakout. The devised code is applied to the problems of a steady-state planar radiation mediated shock (RMS) and RMS breakout from a stellar envelope. The results are in agreement with those of a previous work on shock breakout, in which Compton equilibrium between matter and radiation was assumed and the 'effective photon' approximation was used to describe the radiation spectrum. In particular, we show that themore » luminosity and its temporal dependence, the peak temperature at breakout, and the universal shape of the spectral fluence derived in this earlier work are all accurate. Although there is a discrepancy between the spectral calculations and the effective photon approximation due to the inaccuracy of the effective photon approximation estimate of the effective photon production rate, which grows with lower densities and higher velocities, the difference in peak temperature reaches only 30% for the most discrepant cases of fast shocks in blue supergiants. The presented model is exemplified by calculations for supernova 1987A, showing the detailed evolution of the burst spectrum. The incompatibility of the stellar envelope shock breakout model results with observed properties of X-ray flashes (XRFs) and the discrepancy between the predicted and observed rates of XRFs remain unexplained.« less

A mathematical deconvolution formulation for superficial dose distribution measurement by Cerenkov light dosimetry.

PubMed

Brost, Eric Edward; Watanabe, Yoichi

2018-06-01

Cerenkov photons are created by high-energy radiation beams used for radiation therapy. In this study, we developed a Cerenkov light dosimetry technique to obtain a two-dimensional dose distribution in a superficial region of medium from the images of Cerenkov photons by using a deconvolution method. An integral equation was derived to represent the Cerenkov photon image acquired by a camera for a given incident high-energy photon beam by using convolution kernels. Subsequently, an equation relating the planar dose at a depth to a Cerenkov photon image using the well-known relationship between the incident beam fluence and the dose distribution in a medium was obtained. The final equation contained a convolution kernel called the Cerenkov dose scatter function (CDSF). The CDSF function was obtained by deconvolving the Cerenkov scatter function (CSF) with the dose scatter function (DSF). The GAMOS (Geant4-based Architecture for Medicine-Oriented Simulations) Monte Carlo particle simulation software was used to obtain the CSF and DSF. The dose distribution was calculated from the Cerenkov photon intensity data using an iterative deconvolution method with the CDSF. The theoretical formulation was experimentally evaluated by using an optical phantom irradiated by high-energy photon beams. The intensity of the deconvolved Cerenkov photon image showed linear dependence on the dose rate and the photon beam energy. The relative intensity showed a field size dependence similar to the beam output factor. Deconvolved Cerenkov images showed improvement in dose profiles compared with the raw image data. In particular, the deconvolution significantly improved the agreement in the high dose gradient region, such as in the penumbra. Deconvolution with a single iteration was found to provide the most accurate solution of the dose. Two-dimensional dose distributions of the deconvolved Cerenkov images agreed well with the reference distributions for both square fields and a multileaf collimator (MLC) defined, irregularly shaped field. The proposed technique improved the accuracy of the Cerenkov photon dosimetry in the penumbra region. The results of this study showed initial validation of the deconvolution method for beam profile measurements in a homogeneous media. The new formulation accounted for the physical processes of Cerenkov photon transport in the medium more accurately than previously published methods. © 2018 American Association of Physicists in Medicine.

Conversion from dose-to-graphite to dose-to-water in an 80 MeV/A carbon ion beam.

PubMed

Rossomme, S; Palmans, H; Shipley, D; Thomas, R; Lee, N; Romano, F; Cirrone, P; Cuttone, G; Bertrand, D; Vynckier, S

2013-08-21

Based on experiments and numerical simulations, a study is carried out pertaining to the conversion of dose-to-graphite to dose-to-water in a carbon ion beam. This conversion is needed to establish graphite calorimeters as primary standards of absorbed dose in these beams. It is governed by the water-to-graphite mass collision stopping power ratio and fluence correction factors, which depend on the particle fluence distributions in each of the two media. The paper focuses on the experimental and numerical determination of this fluence correction factor for an 80 MeV/A carbon ion beam. Measurements have been performed in the nuclear physics laboratory INFN-LNS in Catania (Sicily, Italy). The numerical simulations have been made with a Geant4 Monte Carlo code through the GATE simulation platform. The experimental data are in good agreement with the simulated results for the fluence correction factors and are found to be close to unity. The experimental values increase with depth reaching 1.010 before the Bragg peak region. They have been determined with an uncertainty of 0.25%. Different numerical results are obtained depending on the level of approximation made in calculating the fluence correction factors. When considering carbon ions only, the difference between measured and calculated values is maximal just before the Bragg peak, but its value is less than 1.005. The numerical value is close to unity at the surface and increases to 1.005 near the Bragg peak. When the fluence of all charged particles is considered, the fluence correction factors are lower than unity at the surface and increase with depth up to 1.025 before the Bragg peak. Besides carbon ions, secondary particles created due to nuclear interactions have to be included in the analysis: boron ions ((10)B and (11)B), beryllium ions ((7)Be), alpha particles and protons. At the conclusion of this work, we have the conversion of dose-to-graphite to dose-to-water to apply to the response of a graphite calorimeter in an 80 MeV/A carbon ion beam. This conversion consists of the product of two contributions: the water-to-graphite electronic mass collision stopping power ratio, which is equal to 1.115, and the fluence correction factor which varies linearly with depth, as k(fl, all) = 0.9995 + 0.0048(zw-eq). The latter has been determined on the basis of experiments and numerical simulations.

Photolysis of Pure Solid O3 and O2 Films at 193nm

NASA Technical Reports Server (NTRS)

Raut, U.; Loeffler, M. J.; Fama, M.; Baragiola, R. A.

2011-01-01

We studied quantitatively the photochemistry of solid O3 and O2 films at 193 nm and 22 K with infrared spectroscopy and microgravimetry. Photolysis of pure ozone destroyed O3, but a small amount of ozone remained in the film at high fluence. Photolysis of pure O2 produced O3 in an amount that increased with photon fluence to a stationary level. For both O2 and O3 films, the O3:O2 ratio at large fluences is ?0.07, about two orders of magnitude larger than those obtained in gas phase photolysis. This enhancement is attributed to the increased photodissociation of O2 due to photoabsorption by O2 dimers, a process significant at solid-state densities. We obtain initial quantum yield for ozone synthesis from solid oxygen, phi (O3) = 0.24 0.06, and quantum yields for destruction of O3 and O2 in their parent solids, phi(-O3) = 1.0 0.2 and phi(-O2) = 0.36 0.1. Combined with known photoabsorption cross sections, we estimate probabilities for geminate recombination of 0.5 0.1 for O3 fragments and 0.88 0.03 for oxygen atoms from O2 dissociation. Using a single parameter kinetic model, we deduce the ratio of reaction cross sections for an O atom with O2 vs. O3 to be 0.1 0.2. The general good agreement of the model with the data suggests the validity of the central assumption of efficient energy and spin relaxation of photofragments in the solid prior to their reactions with other species.

The Effect of Photobiomodulation on the Sea Urchin Paracentrotus lividus (Echinodermata) Using Higher-Fluence on Fertilization, Embryogenesis, and Larval Development: An In Vitro Study.

PubMed

Amaroli, Andrea; Gambardella, Chiara; Ferrando, Sara; Hanna, Reem; Benedicenti, Alberico; Gallus, Lorenzo; Faimali, Marco; Benedicenti, Stefano

2017-03-01

The aim of this study was to investigate the photobiomodulation (PBM) effect of the 808 nm diode laser irradiation on spermatozoa, eggs, fertilized eggs, embryos, and larvae of Paracentrotus lividus, using two different power settings. Studies have shown the possible use of PBM in artificial insemination. These have shown the potential effect of low-power laser irradiation on spermatozoa, while there are few studies on the effect of laser photonic energy on oocytes and almost no reports on the influence of lasers in embryogenesis. P. lividus gametes, zygotes, embryos, and larvae were irradiated using the 808 nm diode laser (fluence 64 J/cm 2 using 1 W or 192 J/cm 2 with 3 W) with a flat-top hand-piece delivery, compared to a control without laser irradiation (0 J/cm 2 -0 W). The fertilization rate and the early developmental stages were investigated. The fertilization ability was not affected by the sperm/egg irradiation. At the gastrula stage, no significant differences were observed compared with the control samples. In the late pluteus stage, there were no differences in the developmental percentage observed between the control and the treated samples (1 W), with the exception of larvae from gastrulae and larvae, which were irradiated at 3 W. This study has demonstrated that both the 64 J/cm 2 -1 W and the 192 J/cm 2 -3 W do not induce morphological damage on the irradiated P. lividus gametes whose zygotes generate normal embryos and larvae. Our data therefore support the assumption to use higher fluence in preliminary studies on in vitro fertilization.

A systematic Chandra study of Sgr A⋆: II. X-ray flare statistics

NASA Astrophysics Data System (ADS)

Yuan, Qiang; Wang, Q. Daniel; Liu, Siming; Wu, Kinwah

2018-01-01

The routinely flaring events from Sgr A⋆ trace dynamic, high-energy processes in the immediate vicinity of the supermassive black hole. We statistically study temporal and spectral properties, as well as fluence and duration distributions, of the flares detected by the Chandra X-ray Observatory from 1999 to 2012. The detection incompleteness and bias are carefully accounted for in determining these distributions. We find that the fluence distribution can be well characterized by a power law with a slope of 1.73^{+0.20}_{-0.19}, while the durations (τ in seconds) by a lognormal function with a mean log (τ)=3.39^{+0.27}_{-0.24} and an intrinsic dispersion σ =0.28^{+0.08}_{-0.06}. No significant correlation between the fluence and duration is detected. The apparent positive correlation, as reported previously, is mainly due to the detection bias (i.e. weak flares can be detected only when their durations are short). These results indicate that the simple self-organized criticality model has difficulties in explaining these flares. We further find that bright flares usually have asymmetric light curves with no statistically evident difference/preference between the rising and decaying phases in terms of their spectral/timing properties. Our spectral analysis shows that although a power-law model with a photon index of 2.0 ± 0.4 gives a satisfactory fit to the joint spectra of strong and weak flares, there is weak evidence for a softer spectrum of weaker flares. This work demonstrates the potential to use statistical properties of X-ray flares to probe their trigger and emission mechanisms, as well as the radiation propagation around the black hole.

Photolysis of pure solid O{sub 3} and O{sub 2} films at 193 nm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raut, U.; Loeffler, M. J.; Fama, M.

2011-05-21

We studied quantitatively the photochemistry of solid O{sub 3} and O{sub 2} films at 193 nm and 22 K with infrared spectroscopy and microgravimetry. Photolysis of pure ozone destroyed O{sub 3}, but a small amount of ozone remained in the film at high fluence. Photolysis of pure O{sub 2} produced O{sub 3} in an amount that increased with photon fluence to a stationary level. For both O{sub 2} and O{sub 3} films, the O{sub 3}:O{sub 2} ratio at large fluences is {approx}0.07, about two orders of magnitude larger than those obtained in gas phase photolysis. This enhancement is attributed tomore » the increased photodissociation of O{sub 2} due to photoabsorption by O{sub 2} dimers, a process significant at solid-state densities. We obtain initial quantum yield for ozone synthesis from solid oxygen, {Phi}(O{sub 3}) = 0.24 {+-} 0.06, and quantum yields for destruction of O{sub 3} and O{sub 2} in their parent solids, {Phi}(-O{sub 3}) = 1.0 {+-} 0.2 and {Phi}(-O{sub 2}) = 0.36 {+-} 0.1. Combined with known photoabsorption cross sections, we estimate probabilities for geminate recombination of 0.5 {+-} 0.1 for O{sub 3} fragments and 0.88 {+-} 0.03 for oxygen atoms from O{sub 2} dissociation. Using a single parameter kinetic model, we deduce the ratio of reaction cross sections for an O atom with O{sub 2} vs. O{sub 3} to be 0.1-0.2. The general good agreement of the model with the data suggests the validity of the central assumption of efficient energy and spin relaxation of photofragments in the solid prior to their reactions with other species.« less

Poster — Thur Eve — 01: The effect of the number of projections on MTF and CNR in Compton scatter tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chighvinadze, T; Pistorius, S; CancerCare Manitoba, Winnipeg, MB

2014-08-15

Purpose: To investigate the dependence of the reconstructed image quality on the number of projections in multi-projection Compton scatter tomography (MPCST). The conventional relationship between the projection number used for reconstruction and reconstructed image quality pertained to CT does not necessarily apply to MPCST, which can produce images from a single projection if the detectors have sufficiently high energy and spatial resolution. Methods: The electron density image was obtained using filtered-backprojection of the scatter signal over circular arcs formed using Compton equation. The behavior of the reconstructed image quality as a function of the projection number was evaluated through analyticalmore » simulations and characterized by CNR and MTF. Results: The increase of the projection number improves the contrast with this dependence being a function of fluence. The number of projections required to approach the asymptotic maximum contrast decreases as the fluence increases. Increasing projection number increases the CNR but not spatial resolution. Conclusions: For MPCST using a 500eV energy resolution and a 2×2mm{sup 2} size detector, an adequate image quality can be obtained with a small number of projections provided the incident fluence is high enough. This is conceptually different from conventional CT where a minimum number of projections is required to obtain an adequate image quality. While increasing projection number, even for the lowest dose value, the CNR increases even though the number of photons per projection decreases. The spatial resolution of the image is improved by increasing the sampling within a projection rather than by increasing the number of projections.« less

A simulation study on few parameters of Cherenkov photons in extensive air showers of different primaries incident at various zenith angles over a high altitude observation level

NASA Astrophysics Data System (ADS)

Das, G. S.; Hazarika, P.; Goswami, U. D.

2018-07-01

We have studied the distribution patterns of lateral density, arrival time and angular position of Cherenkov photons generated in Extensive Air Showers (EASs) initiated by γ-ray, proton and iron primaries incident with various energies and at various zenith angles. This study is the extension of our earlier work [1] to cover a wide energy range of ground based γ-ray astronomy with a wide range of zenith angles (≤40°) of primary particles, as well as the extension to study the angular distribution patterns of Cherenkov photons in EASs. This type of study is important for distinguishing the γ-ray initiated showers from the hadronic showers in the ground based γ-ray astronomy, where Atmospheric Cherenkov Technique (ACT) is being used. Importantly, such study gives an insight on the nature of γ-ray and hadronic showers in general. In this work, the CORSIKA 6.990 simulation code is used for generation of EASs. Similarly to the case of Ref. [1], this study also revealed that, the lateral density and arrival time distributions of Cherenkov photons vary almost in accordance with the functions: ρch(r) =ρ0e-βr and tch(r) =t0eΓ/rλ respectively by taking different values of the parameters of functions for the type, energy and zenith angle of the primary particle. The distribution of Cherenkov photon's angular positions with respect to shower axis shows distinctive features depending on the primary type, its energy and the zenith angle. As a whole this distribution pattern for the iron primary is noticeably different from those for γ-ray and proton primaries. The value of the angular position at which the maximum number of Cherenkov photons are concentrated, increases with increase in energy of vertically incident primary, but for inclined primary it lies within a small value (≤1°) for almost all energies and primary types. No significant difference in the results obtained by using the high energy hadronic interaction models, viz., QGSJETII and EPOS has been observed.

Electron fluence correction factors for various materials in clinical electron beams.

PubMed

Olivares, M; DeBlois, F; Podgorsak, E B; Seuntjens, J P

2001-08-01

Relative to solid water, electron fluence correction factors at the depth of dose maximum in bone, lung, aluminum, and copper for nominal electron beam energies of 9 MeV and 15 MeV of the Clinac 18 accelerator have been determined experimentally and by Monte Carlo calculation. Thermoluminescent dosimeters were used to measure depth doses in these materials. The measured relative dose at dmax in the various materials versus that of solid water, when irradiated with the same number of monitor units, has been used to calculate the ratio of electron fluence for the various materials to that of solid water. The beams of the Clinac 18 were fully characterized using the EGS4/BEAM system. EGSnrc with the relativistic spin option turned on was used to optimize the primary electron energy at the exit window, and to calculate depth doses in the five phantom materials using the optimized phase-space data. Normalizing all depth doses to the dose maximum in solid water stopping power ratio corrected, measured depth doses and calculated depth doses differ by less than +/- 1% at the depth of dose maximum and by less than 4% elsewhere. Monte Carlo calculated ratios of doses in each material to dose in LiF were used to convert the TLD measurements at the dose maximum into dose at the center of the TLD in the phantom material. Fluence perturbation correction factors for a LiF TLD at the depth of dose maximum deduced from these calculations amount to less than 1% for 0.15 mm thick TLDs in low Z materials and are between 1% and 3% for TLDs in Al and Cu phantoms. Electron fluence ratios of the studied materials relative to solid water vary between 0.83+/-0.01 and 1.55+/-0.02 for materials varying in density from 0.27 g/cm3 (lung) to 8.96 g/cm3 (Cu). The difference in electron fluence ratios derived from measurements and calculations ranges from -1.6% to +0.2% at 9 MeV and from -1.9% to +0.2% at 15 MeV and is not significant at the 1sigma level. Excluding the data for Cu, electron fluence correction factors for open electron beams are approximately proportional to the electron density of the phantom material and only weakly dependent on electron beam energy.

Monte Carlo and analytical calculations for characterization of gas bremsstrahlung in ILSF insertion devices

NASA Astrophysics Data System (ADS)

Salimi, E.; Rahighi, J.; Sardari, D.; Mahdavi, S. R.; Lamehi Rachti, M.

2014-12-01

Gas bremsstrahlung is generated in high energy electron storage rings through interaction of the electron beam with the residual gas molecules in vacuum chamber. In this paper, Monte Carlo calculation has been performed to evaluate radiation hazard due to gas bremsstrahlung in the Iranian Light Source Facility (ILSF) insertion devices. Shutter/stopper dimensions is determined and dose rate from the photoneutrons via the giant resonance photonuclear reaction which takes place inside the shutter/stopper is also obtained. Some other characteristics of gas bremsstrahlung such as photon fluence, energy spectrum, angular distribution and equivalent dose in tissue equivalent phantom have also been investigated by FLUKA Monte Carlo code.

Characterization and performances of DOSION, a dosimetry equipment dedicated to radiobiology experiments taking place at GANIL

NASA Astrophysics Data System (ADS)

Boissonnat, Guillaume; Fontbonne, Jean-Marc; Balanzat, Emmanuel; Boumard, Frederic; Carniol, Benjamin; Cassimi, Amine; Colin, Jean; Cussol, Daniel; Etasse, David; Fontbonne, Cathy; Frelin, Anne-Marie; Hommet, Jean; Salvador, Samuel

2017-06-01

Currently, radiobiology experiments using heavy ions at GANIL (Grand Accélérateur National d‧Ions Lourds) are conducted under the supervision of the CIMAP (Center for research on Ions, MAterials and Photonics). In this context, a new beam monitoring equipment named DOSION has been developed. It allows to perform measurements of accurate fluence and dose maps in near real time for each biological sample irradiated. In this paper, we present the detection system, its design, performances, calibration protocol and measurements performed during radiobiology experiments. This setup is currently available for any radiobiology experiments if one wishes to correlate one's own sample analysis to state-of-the-art dosimetric references.

Light fluence dosimetry in lung-simulating cavities

NASA Astrophysics Data System (ADS)

Zhu, Timothy C.; Kim, Michele M.; Padawer, Jonah; Dimofte, Andreea; Potasek, Mary; Beeson, Karl; Parilov, Evgueni

2018-02-01

Accurate light dosimery is critical to ensure consistent outcome for pleural photodynamic therapy (pPDT). Ellipsoid shaped cavities with different sizes surrounded by turbid medium are used to simulate the intracavity lung geometry. An isotropic light source is introduced and surrounded by turbid media. Direct measurements of light fluence rate were compared to Monte Carlo simulated values on the surface of the cavities for various optical properties. The primary component of the light was determined by measurements performed in air in the same geometry. The scattered component was found by submerging the air-filled cavity in scattering media (Intralipid) and absorbent media (ink). The light source was located centrally with the azimuthal angle, but placed in two locations (vertically centered and 2 cm below the center) for measurements. Light fluence rate was measured using isotropic detectors placed at various angles on the ellipsoid surface. The measurements and simulations show that the scattered dose is uniform along the surface of the intracavity ellipsoid geometries in turbid media. One can express the light fluence rate empirically as φ =4S/As*Rd/(1- Rd), where Rd is the diffuse reflectance, As is the surface area, and S is the source power. The measurements agree with this empirical formula to within an uncertainty of 10% for the range of optical properties studied. GPU voxel-based Monte-Carlo simulation is performed to compare with measured results. This empirical formula can be applied to arbitrary geometries, such as the pleural or intraperitoneal cavity.

Measurements of the Tm 169 ( n , 2 n ) Tm 168 cross section from threshold to 15 MeV

DOE PAGES

Soter, J.; Bhike, M.; Finch, S. W.; ...

2017-12-27

Measurements of the 169Tm(n,2n) 168Tm cross section have been performed via the activation technique at 13 energies between 8.5 and 15.0 MeV. The purpose of this comprehensive data set is to provide an alternative diagnostic tool for obtaining subtle information on the neutron energy distribution produced in inertial confinement deuterium-tritium fusion experiments at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. In conclusion, the 169Tm(n,2n) 168Tm reaction not only provides the primary 14-MeV neutron fluence, but also the important down-scattered neutron fluence, the latter providing information on the density achieved in the deuterium-tritium plasma during a laser shot.

A brachytherapy photon radiation quality index Q(BT) for probe-type dosimetry.

PubMed

Quast, Ulrich; Kaulich, Theodor W; Álvarez-Romero, José T; Carlsson Tedgren, Sa; Enger, Shirin A; Medich, David C; Mourtada, Firas; Perez-Calatayud, Jose; Rivard, Mark J; Zakaria, G Abu

2016-06-01

In photon brachytherapy (BT), experimental dosimetry is needed to verify treatment plans if planning algorithms neglect varying attenuation, absorption or scattering conditions. The detector's response is energy dependent, including the detector material to water dose ratio and the intrinsic mechanisms. The local mean photon energy E¯(r) must be known or another equivalent energy quality parameter used. We propose the brachytherapy photon radiation quality indexQ(BT)(E¯), to characterize the photon radiation quality in view of measurements of distributions of the absorbed dose to water, Dw, around BT sources. While the external photon beam radiotherapy (EBRT) radiation quality index Q(EBRT)(E¯)=TPR10(20)(E¯) is not applicable to BT, the authors have applied a novel energy dependent parameter, called brachytherapy photon radiation quality index, defined as Q(BT)(E¯)=Dprim(r=2cm,θ0=90°)/Dprim(r0=1cm,θ0=90°), utilizing precise primary absorbed dose data, Dprim, from source reference databases, without additional MC-calculations. For BT photon sources used clinically, Q(BT)(E¯) enables to determine the effective mean linear attenuation coefficient μ¯(E) and thus the effective energy of the primary photons Eprim(eff)(r0,θ0) at the TG-43 reference position Pref(r0=1cm,θ0=90°), being close to the mean total photon energy E¯tot(r0,θ0). If one has calibrated detectors, published E¯tot(r) and the BT radiation quality correction factor [Formula: see text] for different BT radiation qualities Q and Q0, the detector's response can be determined and Dw(r,θ) measured in the vicinity of BT photon sources. This novel brachytherapy photon radiation quality indexQ(BT) characterizes sufficiently accurate and precise the primary photon's penetration probability and scattering potential. Copyright © 2016. Published by Elsevier Ltd.

Comparison of photon organ and effective dose coefficients for PIMAL stylized phantom in bent positions in standard irradiation geometries.

PubMed

Dewji, Shaheen; Reed, K Lisa; Hiller, Mauritius

2017-08-01

Computational phantoms with articulated arms and legs have been constructed to enable the estimation of radiation dose in different postures. Through a graphical user interface, the Phantom wIth Moving Arms and Legs (PIMAL) version 4.1.0 software can be employed to articulate the posture of a phantom and generate a corresponding input deck for the Monte Carlo N-Particle (MCNP) radiation transport code. In this work, photon fluence-to-dose coefficients were computed using PIMAL to compare organ and effective doses for a stylized phantom in the standard upright position with those for phantoms in realistic work postures. The articulated phantoms represent working positions including fully and half bent torsos with extended arms for both the male and female reference adults. Dose coefficients are compared for both the upright and bent positions across monoenergetic photon energies: 0.05, 0.1, 0.5, 1.0, and 5.0 MeV. Additionally, the organ doses are compared across the International Commission on Radiological Protection's standard external radiation exposure geometries: antero-posterior, postero-anterior, left and right lateral, and isotropic (AP, PA, LLAT, RLAT, and ISO). For the AP and PA irradiation geometries, differences in organ doses compared to the upright phantom become more profound with increasing bending angles and have doses largely overestimated for all organs except the brain in AP and bladder in PA. In LLAT and RLAT irradiation geometries, energy deposition for organs is more likely to be underestimated compared to the upright phantom, with no overall change despite increased bending angle. The ISO source geometry did not cause a significant difference in absorbed organ dose between the different phantoms, regardless of position. Organ and effective fluence-to-dose coefficients are tabulated. In the AP geometry, the effective dose at the 45° bent position is overestimated compared to the upright phantom below 1 MeV by as much as 27% and 82% in the 90° position. The effective dose in the 45° bent position was comparable to that in the 90° bent position for the LLAT and RLAT irradiation geometries. However, the upright phantom underestimates the effective dose to PIMAL in the LLAT and RLAT geometries by as much as 30% at 50 keV.

A stochastic convolution/superposition method with isocenter sampling to evaluate intrafraction motion effects in IMRT.

PubMed

Naqvi, Shahid A; D'Souza, Warren D

2005-04-01

Current methods to calculate dose distributions with organ motion can be broadly classified as "dose convolution" and "fluence convolution" methods. In the former, a static dose distribution is convolved with the probability distribution function (PDF) that characterizes the motion. However, artifacts are produced near the surface and around inhomogeneities because the method assumes shift invariance. Fluence convolution avoids these artifacts by convolving the PDF with the incident fluence instead of the patient dose. In this paper we present an alternative method that improves the accuracy, generality as well as the speed of dose calculation with organ motion. The algorithm starts by sampling an isocenter point from a parametrically defined space curve corresponding to the patient-specific motion trajectory. Then a photon is sampled in the linac head and propagated through the three-dimensional (3-D) collimator structure corresponding to a particular MLC segment chosen randomly from the planned IMRT leaf sequence. The photon is then made to interact at a point in the CT-based simulation phantom. Randomly sampled monoenergetic kernel rays issued from this point are then made to deposit energy in the voxels. Our method explicitly accounts for MLC-specific effects (spectral hardening, tongue-and-groove, head scatter) as well as changes in SSD with isocentric displacement, assuming that the body moves rigidly with the isocenter. Since the positions are randomly sampled from a continuum, there is no motion discretization, and the computation takes no more time than a static calculation. To validate our method, we obtained ten separate film measurements of an IMRT plan delivered on a phantom moving sinusoidally, with each fraction starting with a random phase. For 2 cm motion amplitude, we found that a ten-fraction average of the film measurements gave an agreement with the calculated infinite fraction average to within 2 mm in the isodose curves. The results also corroborate the existing notion that the interfraction dose variability due to the interplay between the MLC motion and breathing motion averages out over typical multifraction treatments. Simulation with motion waveforms more representative of real breathing indicate that the motion can produce penumbral spreading asymmetric about the static dose distributions. Such calculations can help a clinician decide to use, for example, a larger margin in the superior direction than in the inferior direction. In the paper we demonstrate that a 15 min run on a single CPU can readily illustrate the effect of a patient-specific breathing waveform, and can guide the physician in making informed decisions about margin expansion and dose escalation.

Time-resolved photoion imaging spectroscopy: Determining energy distribution in multiphoton absorption experiments

NASA Astrophysics Data System (ADS)

Qian, D. B.; Shi, F. D.; Chen, L.; Martin, S.; Bernard, J.; Yang, J.; Zhang, S. F.; Chen, Z. Q.; Zhu, X. L.; Ma, X.

2018-04-01

We propose an approach to determine the excitation energy distribution due to multiphoton absorption in the case of excited systems following decays to produce different ion species. This approach is based on the measurement of the time-resolved photoion position spectrum by using velocity map imaging spectrometry and an unfocused laser beam with a low fluence and homogeneous profile. Such a measurement allows us to identify the species and the origin of each ion detected and to depict the energy distribution using a pure Poisson's equation involving only one variable which is proportional to the absolute photon absorption cross section. A cascade decay model is used to build direct connections between the energy distribution and the probability to detect each ionic species. Comparison between experiments and simulations permits the energy distribution and accordingly the absolute photon absorption cross section to be determined. This approach is illustrated using C60 as an example. It may therefore be extended to a wide variety of molecules and clusters having decay mechanisms similar to those of fullerene molecules.

Flash-Bang Detector to Model the Attenuation of High-Energy Photons

NASA Astrophysics Data System (ADS)

Pagsanjan, N., III; Kelley, N. A.; Smith, D. M.; Sample, J. G.

2015-12-01

It has been known for years that lightning and thunderstorms produce gamma rays and x-rays. Terrestrial gamma-ray flashes (TGFs) are extremely bright bursts of gamma rays originating from thunderstorms. X-ray stepped leaders are bursts of x-rays coming from the lightning channel. It is known that the attenuation of these high-energy photons is a function of distance, losing energy and intensity at larger distances. To complement gamma-ray detectors on the ground it would be useful to measure the distance to the flash. Knowing the distance would allow for the true source fluence of gamma rays or x-rays to be modeled. A flash-bang detector, which uses a micro-controller, a photodiode, a microphone and temperature sensor will be able to detect the times at which lightning and thunder occurs. Knowing the speed of sound as function of temperature and the time difference between the flash and the thunder, the range to the lightning can be calculated. We will present the design of our detector as well as some preliminary laboratory test results.

Measurement of the vacuum-ultraviolet absorption spectrum of low-k dielectrics using X-ray reflectivity

NASA Astrophysics Data System (ADS)

Choudhury, F. A.; Nguyen, H. M.; King, S. W.; Lee, C. H.; Lin, Y. H.; Fung, H. S.; Chen, C. C.; Li, W.; Benjamin, D.; Blatz, J. M.; Nishi, Y.; Shohet, J. L.

2018-02-01

During plasma processing, low-k dielectrics are exposed to high levels of vacuum ultraviolet (VUV) radiation that can cause severe damage to dielectric materials. The degree and nature of VUV-induced damage depend on the VUV photon energies and fluence. In this work, we examine the VUV-absorption spectrum of low-k organosilicate glass using specular X-ray reflectivity (XRR). Low-k SiCOH films were exposed to synchrotron VUV radiation with energies ranging from 7 to 21 eV, and the density vs. depth profile of the VUV-irradiated films was extracted from fitting the XRR experimental data. The results show that the depth of the VUV-induced damage layer is a function of the photon energy. Between 7 and 11 eV, the depth of the damaged layer decreases sharply from 110 nm to 60 nm and then gradually increases to 85 nm at 21 eV. The maximum VUV absorption in low-k films occurs between 11 and 15 eV. The depth of the damaged layer was found to increase with film porosity.

Isotopic Dependence of GCR Fluence behind Shielding

NASA Technical Reports Server (NTRS)

Cucinotta, Francis A.; Wilson, John W.; Saganti, Premkumar; Kim, Myung-Hee Y.; Cleghorn, Timothy; Zeitlin, Cary; Tripathi, Ram K.

2006-01-01

In this paper we consider the effects of the isotopic composition of the primary galactic cosmic rays (GCR), nuclear fragmentation cross-sections, and isotopic-grid on the solution to transport models used for shielding studies. Satellite measurements are used to describe the isotopic composition of the GCR. For the nuclear interaction data-base and transport solution, we use the quantum multiple-scattering theory of nuclear fragmentation (QMSFRG) and high-charge and energy (HZETRN) transport code, respectively. The QMSFRG model is shown to accurately describe existing fragmentation data including proper description of the odd-even effects as function of the iso-spin dependence on the projectile nucleus. The principle finding of this study is that large errors (+/-100%) will occur in the mass-fluence spectra when comparing transport models that use a complete isotopic-grid (approx.170 ions) to ones that use a reduced isotopic-grid, for example the 59 ion-grid used in the HZETRN code in the past, however less significant errors (<+/-20%) occur in the elemental-fluence spectra. Because a complete isotopic-grid is readily handled on small computer workstations and is needed for several applications studying GCR propagation and scattering, it is recommended that they be used for future GCR studies.

Nanosecond multiple pulse measurements and the different types of defects

NASA Astrophysics Data System (ADS)

Wagner, Frank R.; Natoli, Jean-Yves; Beaudier, Alexandre; Commandré, Mireille

2017-11-01

Laser damage measurements with multiple pulses at constant fluence (S-on-1 measurements) are of high practical importance for design and validation of high power photonic instruments. Using nanosecond lasers, it has been recognized long ago that single pulse laser damage is linked to fabrication related defects. Models describing the laser damage probability as the probability of encounter between the high fluence region of the laser beam and the fabrication related defects are thus widely used to analyze the measurements. Nanosecond S-on-1 tests often reveal the "fatigue effect", i.e. a decrease of the laser damage threshold with increasing pulse number. Most authors attribute this effect to cumulative material modifications operated by the first pulses. In this paper we discuss the different situations that are observed upon nanosecond S-on-1 measurements of several different materials using different wavelengths and speak in particular about the defects involved in the laser damage mechanism. These defects may be fabrication-related or laser-induced, stable or evolutive, cumulative or of short lifetime. We will show that the type of defect that is dominating an S-on-1 experiment depends on the wavelength and the material under test and give examples from measurements of nonlinear optical crystals, fused silica and oxide mixture coatings.

Controllable Si (100) micro/nanostructures by chemical-etching-assisted femtosecond laser single-pulse irradiation

NASA Astrophysics Data System (ADS)

Li, Xiaowei; Xie, Qian; Jiang, Lan; Han, Weina; Wang, Qingsong; Wang, Andong; Hu, Jie; Lu, Yongfeng

2017-05-01

In this study, silicon micro/nanostructures of controlled size and shape are fabricated by chemical-etching-assisted femtosecond laser single-pulse irradiation, which is a flexible, high-throughput method. The pulse fluence is altered to create various laser printing patterns for the etching mask, resulting in the sequential evolution of three distinct surface micro/nanostructures, namely, ring-like microstructures, flat-top pillar microstructures, and spike nanostructures. The characterized diameter of micro/nanostructures reveals that they can be flexibly tuned from the micrometer (˜2 μm) to nanometer (˜313 nm) scales by varying the laser pulse fluence in a wide range. Micro-Raman spectroscopy and transmission electron microscopy are utilized to demonstrate that the phase state changes from single-crystalline silicon (c-Si) to amorphous silicon (a-Si) after single-pulse femtosecond laser irradiation. This amorphous layer with a lower etching rate then acts as a mask in the wet etching process. Meanwhile, the on-the-fly punching technique enables the efficient fabrication of large-area patterned surfaces on the centimeter scale. This study presents a highly efficient method of controllably manufacturing silicon micro/nanostructures with different single-pulse patterns, which has promising applications in the photonic, solar cell, and sensors fields.

A deterministic electron, photon, proton and heavy ion transport suite for the study of the Jovian moon Europa

NASA Astrophysics Data System (ADS)

Badavi, Francis F.; Blattnig, Steve R.; Atwell, William; Nealy, John E.; Norman, Ryan B.

2011-02-01

A Langley research center (LaRC) developed deterministic suite of radiation transport codes describing the propagation of electron, photon, proton and heavy ion in condensed media is used to simulate the exposure from the spectral distribution of the aforementioned particles in the Jovian radiation environment. Based on the measurements by the Galileo probe (1995-2003) heavy ion counter (HIC), the choice of trapped heavy ions is limited to carbon, oxygen and sulfur (COS). The deterministic particle transport suite consists of a coupled electron photon algorithm (CEPTRN) and a coupled light heavy ion algorithm (HZETRN). The primary purpose for the development of the transport suite is to provide a means to the spacecraft design community to rapidly perform numerous repetitive calculations essential for electron, photon, proton and heavy ion exposure assessment in a complex space structure. In this paper, the reference radiation environment of the Galilean satellite Europa is used as a representative boundary condition to show the capabilities of the transport suite. While the transport suite can directly access the output electron and proton spectra of the Jovian environment as generated by the jet propulsion laboratory (JPL) Galileo interim radiation electron (GIRE) model of 2003; for the sake of relevance to the upcoming Europa Jupiter system mission (EJSM), the JPL provided Europa mission fluence spectrum, is used to produce the corresponding depth dose curve in silicon behind a default aluminum shield of 100 mils (˜0.7 g/cm2). The transport suite can also accept a geometry describing ray traced thickness file from a computer aided design (CAD) package and calculate the total ionizing dose (TID) at a specific target point within the interior of the vehicle. In that regard, using a low fidelity CAD model of the Galileo probe generated by the authors, the transport suite was verified versus Monte Carlo (MC) simulation for orbits JOI-J35 of the Galileo probe extended mission. For the upcoming EJSM mission with an expected launch date of 2020, the transport suite is used to compute the depth dose profile for the traditional aluminum silicon as a standard shield target combination, as well as simulating the shielding response of a high charge number (Z) material such as tantalum (Ta). Finally, a shield optimization algorithm is discussed which can guide the instrument designers and fabrication personnel with the choice of graded-Z shield selection and analysis.

A novel algorithm for the reconstruction of an entrance beam fluence from treatment exit patient portal dosimetry images

NASA Astrophysics Data System (ADS)

Sperling, Nicholas Niven

The problem of determining the in vivo dosimetry for patients undergoing radiation treatment has been an area of interest since the development of the field. Most methods which have found clinical acceptance work by use of a proxy dosimeter, e.g.: glass rods, using radiophotoluminescence; thermoluminescent dosimeters (TLD), typically CaF or LiF; Metal Oxide Silicon Field Effect Transistor (MOSFET) dosimeters, using threshold voltage shift; Optically Stimulated Luminescent Dosimeters (OSLD), composed of Carbon doped Aluminum Dioxide crystals; RadioChromic film, using leuko-dye polymers; Silicon Diode dosimeters, typically p-type; and ion chambers. More recent methods employ Electronic Portal Image Devices (EPID), or dosimeter arrays, for entrance or exit beam fluence determination. The difficulty with the proxy in vivo dosimetery methods is the requirement that they be placed at the particular location where the dose is to be determined. This precludes measurements across the entire patient volume. These methods are best suited where the dose at a particular location is required. The more recent methods of in vivo dosimetry make use of detector arrays and reconstruction techniques to determine dose throughout the patient volume. One method uses an array of ion chambers located upstream of the patient. This requires a special hardware device and places an additional attenuator in the beam path, which may not be desirable. A final approach is to use the existing EPID, which is part of most modern linear accelerators, to image the patient using the treatment beam. Methods exist to deconvolve the detector function of the EPID using a series of weighted exponentials. Additionally, this method has been extended to determine in vivo dosimetry. The method developed here employs the use of EPID images and an iterative deconvolution algorithm to reconstruct the impinging primary beam fluence on the patient. This primary fluence may then be employed to determine dose through the entire patient volume. The method requires patient specific information, including a CT for deconvolution/dose reconstruction. With the large-scale adoption of Cone Beam CT (CBCT) systems on modern linear accelerators, a treatment time CT is readily available for use in this deconvolution and in dose representation.

The effect of low-energy electrons on the response of ion chambers to ionizing photon beams

NASA Astrophysics Data System (ADS)

La Russa, Daniel J.

Cavity ionization chambers are one of the most popular and widely used devices for quantifying ionizing photon beams. This popularity originates from the precision of these devices and the relative ease with which ionization measurements are converted to quantities of interest in therapeutic radiology or radiation protection, collectively referred to as radiation dosimetry. The formalisms used for these conversions, known as cavity theory, make several assumptions about the electron spectrum in the low-energy range resulting from the incident photon beam. These electrons often account for a significant fraction of the ion chamber response. An inadequate treatment of low-energy electrons can therefore significantly effect calculated quantities of interest. This thesis sets out to investigate the effect of low-energy electrons on (1) the use of Spencer-Attix cavity theory with 60Co beams; and (2) the standard temperature-pressure correction factor, P TP, used to relate the measured ionization to a set of reference temperature and pressure conditions for vented ion chambers. Problems with the PTP correction are shown to arise when used with kilovoltage x rays, where ionization measurements are due primarily to electrons that do not have enough energy to cross the cavity. A combination of measurements and Monte Carlo calculations using the EGSnrc Monte Carlo code demonstrate the breakdown of PTP in these situations when used with non-air-equivalent chambers. The extent of the breakdown is shown to depend on cavity size, energy of the incident photons, and the composition of the chamber. In the worst case, the standard P TP factor overcorrects the response of an aluminum chamber by ≈12% at an air density typical of Mexico City. The response of a more common graphite-walled chamber with similar dimensions at the same air density is undercorrected by ≈ 2%. The EGSnrc Monte Carlo code is also used to investigate Spencer-Attix cavity theory as it is used in the formalism to determine the air kerma for a 60Co beam. Following a comparison with measurements in the literature, the air kerma formalism is shown to require a fluence correction factor, Kfl, to ensure the accuracy of the formalism regardless of chamber composition and cavity size. The need for such a correction stems from the fact that the cavity clearly distorts the fluence for mismatched cavity and wall materials, and the inability to select the appropriate "cut-off" energy, Delta, in the Spencer-Attix stopping-power ratio. A discussion of this issue is followed by detailed calculations of K fl values for several of the graphite ionization chambers used at national metrology institutes, which range between 0.9999 and 0.9994 with a one standard deviation uncertainty of +/- 0.0002.

Backscatter dose effects for high atomic number materials being irradiated in the presence of a magnetic field: A Monte Carlo study for the MRI linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmad, Syed Bilal

Purpose: To quantify and explain the backscatter dose effects for clinically relevant high atomic number materials being irradiated in the presence of a 1.5 T transverse magnetic field. Methods: Interface effects were investigated using Monte Carlo simulation techniques. We used GPUMCD (v5.1) and GEANT4 (v10.1) for this purpose. GPUMCD is a commercial software written for the Elekta AB, MRI linac. Dose was scored using GPUMCD in cubic voxels of side 1 and 0.5 mm, in two different virtual phantoms of dimensions 20 × 20 × 20 cm and 5 × 5 × 13.3 cm, respectively. A photon beam was generatedmore » from a point 143.5 cm away from the isocenter with energy distribution sampled from a histogram representing the true Elekta, MRI linac photon spectrum. A slab of variable thickness and position containing either bone, aluminum, titanium, stainless steel, or one of the two different dental filling materials was inserted as an inhomogeneity in the 20 × 20 × 20 cm phantom. The 5 × 5 × 13.3 cm phantom was used as a clinical test case in order to explain the dose perturbation effects for a head and neck cancer patient. The back scatter dose factor (BSDF) was defined as the ratio of the doses at a given depth with and without the presence of the inhomogeneity. Backscattered electron fluence was calculated at the inhomogeneity interface using GEANT4. A 1.5 T magnetic field was applied perpendicular to the direction of the beam in both phantoms, identical to the geometry in the Elekta MRI linac. Results: With the application of a 1.5 T magnetic field, all the BSDF’s were reduced by 12%–47%, compared to the no magnetic field case. The corresponding backscattered electron fluence at the interface was also reduced by 45%–64%. The reduction in the BSDF at the interface, due to the application of the magnetic field, is manifested in a different manner for each material. In the case of bone, the dose drops at the interface contrary to the expected increase when no magnetic field is applied. In the case of aluminum, the dose at the interface is the same with and without the presence of the aluminum. For all of the other materials the dose increases at the interface. Conclusions: The reduction in dose at the interface, in the presence of the magnetic field, is directly related to the reduction in backscattered electron fluence. This reduction occurs due to two different reasons. First, the electron spectrum hitting the interface is changed when the magnetic field is turned on, which results in changes in the electron scattering probability. Second, some electrons that have curved trajectories due to the presence of the magnetic field are absorbed by the higher density side of the interface and no longer contribute to the backscattered electron fluence.« less

NE-213-scintillator-based neutron detection system for diagnostic measurements of energy spectra for neutrons having energies greater than or equal to 0.8 MeV created during plasma operations at the Princeton Tokamak Fusion Test Reactor

NASA Astrophysics Data System (ADS)

Dickens, J. K.; Hill, N. W.; Hou, F. S.; McConnell, J. W.; Spencer, R. R.; Tsang, F. Y.

1985-08-01

A system for making diagnostic measurements of the energy spectra of greater than or equal to 0.8-MeV neutrons produced during plasma operations of the Princeton Tokamak Fusion Test Reactor (TFTR) has been fabricated and tested and is presently in operation in the TFTR Test Cell Basement. The system consists of two separate detectors, each made up of cells containing liquid NE-213 scintillator attached permanently to RCA-8850 photomultiplier tubes. Pulses obtained from each photomultiplier system are amplified and electronically analyzed to identify and separate those pulses due to neutron-induced events in the detector from those due to photon-induced events in the detector. Signals from each detector are routed to two separate Analog-to-Digital Converters, and the resulting digitized information, representing: (1) the raw neutron-spectrum data; and (2) the raw photon-spectrum data, are transmited to the CICADA data-acquisition computer system of the TFTR. Software programs have been installed on the CICADA system to analyze the raw data to provide moderate-resolution recreations of the energy spectrum of the neutron and photon fluences incident on the detector during the operation of the TFTR. A complete description of, as well as the operation of, the hardware and software is given in this report.

Characterization of fast photoelectron packets in weak and strong laser fields in ultrafast electron microscopy.

PubMed

Plemmons, Dayne A; Tae Park, Sang; Zewail, Ahmed H; Flannigan, David J

2014-11-01

The development of ultrafast electron microscopy (UEM) and variants thereof (e.g., photon-induced near-field electron microscopy, PINEM) has made it possible to image atomic-scale dynamics on the femtosecond timescale. Accessing the femtosecond regime with UEM currently relies on the generation of photoelectrons with an ultrafast laser pulse and operation in a stroboscopic pump-probe fashion. With this approach, temporal resolution is limited mainly by the durations of the pump laser pulse and probe electron packet. The ability to accurately determine the duration of the electron packets, and thus the instrument response function, is critically important for interpretation of dynamics occurring near the temporal resolution limit, in addition to quantifying the effects of the imaging mode. Here, we describe a technique for in situ characterization of ultrashort electron packets that makes use of coupling with photons in the evanescent near-field of the specimen. We show that within the weakly-interacting (i.e., low laser fluence) regime, the zero-loss peak temporal cross-section is precisely the convolution of electron packet and photon pulse profiles. Beyond this regime, we outline the effects of non-linear processes and show that temporal cross-sections of high-order peaks explicitly reveal the electron packet profile, while use of the zero-loss peak becomes increasingly unreliable. Copyright © 2014 Elsevier B.V. All rights reserved.

An update on the clinical trial of BNCT at the BMRR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, R.; Capala, J.; Chanana, A.D.

1999-09-01

Boron neutron capture therapy (BNCT) was proposed more than six decades ago. It is a binary treatment modality that requires selective delivery of a {sup 10}B-labeled compound to a tumor and slow neutron irradiation of the tumor-bearing tissues. In order to improve the penetration of the neutron beam, an epithermal neutron beam was developed at the Brookhaven Medical Research Reactor (BMRR). This epithermal neutron beam can deliver relatively high thermal neutron fluence at depth without severe skin damage. Boronophenylalanine-fructose (BPA-F), a nontoxic boron carrier, was found to preferentially accumulate in tumor cells following intravenous infusion in patients with GBM. Inmore » preclinical BNCT studies in rats bearing 9L gliosarcoma, BPA-mediated BNCT was shown to be more efficacious than photon irradiation. In 1994, improvements in the neutron beam and in the understanding of the radiobiology of BPA-mediated BNCT led to the initiation of BNCT trials for human GBM at BMRR using BPA-F and epithermal neutrons. The primary objective of the phase I/II clinical trial of BPA-mediated BNCT at BMRR is to evaluate the safety of the BPA-F-mediated BNCT using epithermal neutrons in patients with GBM at a series of escalating BNCT doses. An incidental objective is to evaluate the therapeutic effectiveness of BNCT at each dose level. For each dose escalation group, the average brain dose (ABD) is escalated, as well as the minimum tumor dose. In summary, the BNCT procedure employed in the phase I/II clinical trial of BPA-F-mediated BNCT for GBM at BNL was found to be safe in all patients. The palliation afforded by a single session of BNCT compares favorably with palliation provided by fractionated photon therapy and adjuvant chemotherapy. If no evidence of radiation-induced brain toxicity is found in the current protocol, BNCT radiation dose will be further escalated.« less

EPR/PTFE dosimetry for test reactor environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vehar, D.W.; Griffin, P.J.; Quirk, T.J.

2011-07-01

The use of Electron Paramagnetic Resonance (EPR) spectroscopy with materials such as alanine is well established as a technique for measurement of ionizing radiation absorbed dose in photon and electron fields such as Co-60, high-energy bremsstrahlung and electron-beam fields [1]. In fact, EPR/Alanine dosimetry has become a routine transfer standard for national standards bodies such as NIST and NPL. In 1992 the Radiation Metrology Laboratory (RML) at Sandia National Laboratories implemented EPR/Alanine capabilities for use in routine and calibration activities at its Co-60 and pulsed-power facilities. At that time it also investigated the usefulness of the system for measurement ofmore » absorbed dose in the mixed neutron/photon environments of reactors such as the Sandia Pulsed Reactor and the Annular Core Research Reactor used for hardness testing of electronics. The RML concluded that the neutron response of alanine was a sufficiently high fraction of the overall dosimeter response that the resulting uncertainties in the photon dose would be unacceptably large for silicon-device testing. However, it also suggested that non-hydrogenous materials such as polytetrafluoroethylene (PTFE) would exhibit smaller neutron response and might be useful in mixed environments. Preliminary research with PTFE in photon environments indicated considerable promise, but further development was not pursued at that time. Because of renewed interest in absorbed dose measurements that could better define the individual contributions of photon and neutron components to the overall dose delivered to a test object, the RML has re-initiated the development of an EPR/PTFE dosimetry system. This effort consists of three stages: 1) Identification of PTFE materials that may be suitable for dosimetry applications. It was speculated that the inconsistency of EPR signatures in the earlier samples may have been due to variability in PTFE manufacturing processes. 2) Characterization of dosimetry in photon-only environments. This is necessary to establish requirements for sample preparation, operating parameters and limitations for use in well-defined and predictable environments prior to deployment in the less well-defined mixed environments of test reactors. 3) Characterization of the EPR responses obtained with PTFE in mixed neutron/photon fields. This includes evaluation of the neutron and photon contributions to response, determination of applicable of neutron fluence and photon dose ranges. This paper presents a summary of the research, a description of the EPR/PTFE dosimetry system, and recommendations for preparation and fielding of the dosimetry in photon and mixed neutron/photon environments. (authors)« less

A TPS kernel for calculating survival vs. depth: distributions in a carbon radiotherapy beam, based on Katz's cellular Track Structure Theory.

PubMed

Waligórski, M P R; Grzanka, L; Korcyl, M; Olko, P

2015-09-01

An algorithm was developed of a treatment planning system (TPS) kernel for carbon radiotherapy in which Katz's Track Structure Theory of cellular survival (TST) is applied as its radiobiology component. The physical beam model is based on available tabularised data, prepared by Monte Carlo simulations of a set of pristine carbon beams of different input energies. An optimisation tool developed for this purpose is used to find the composition of pristine carbon beams of input energies and fluences which delivers a pre-selected depth-dose distribution profile over the spread-out Bragg peak (SOBP) region. Using an extrapolation algorithm, energy-fluence spectra of the primary carbon ions and of all their secondary fragments are obtained over regular steps of beam depths. To obtain survival vs. depth distributions, the TST calculation is applied to the energy-fluence spectra of the mixed field of primary ions and of their secondary products at the given beam depths. Katz's TST offers a unique analytical and quantitative prediction of cell survival in such mixed ion fields. By optimising the pristine beam composition to a published depth-dose profile over the SOBP region of a carbon beam and using TST model parameters representing the survival of CHO (Chinese Hamster Ovary) cells in vitro, it was possible to satisfactorily reproduce a published data set of CHO cell survival vs. depth measurements after carbon ion irradiation. The authors also show by a TST calculation that 'biological dose' is neither linear nor additive. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Frequency Agile Microwave Photonic Notch Filter in a Photonic Chip

DTIC Science & Technology

2016-10-21

AFRL-AFOSR-JP-TR-2016-0087 Frequency Agile Microwave Photonic Notch Filter in a Photonic Chip Benjamin Eggleton UNIVERSITY OF SYDNEY Final Report 10...REPORT TYPE      Final 3.  DATES COVERED (From - To)      14 May 2014 to 13 May 2016 4.  TITLE AND SUBTITLE Frequency Agile Microwave Photonic Notch Filter ...primary objective is to explore a novel class microwave photonic (MWP) notch filter with a very narrow isolation bandwidth, an ultrahigh stopband

TCPD: A micropattern photon detector hybrid for RICH applications

NASA Astrophysics Data System (ADS)

Hamar, G.; Varga, D.

2017-03-01

A micropattern and wire chamber hybrid has been constructed for UV photon detection, and its performance evaluated. It is revealed that such combination retains some key advantages of both the Thick-GEM primary and CCC secondary amplification stages, and results in a high gain gaseous photon detector with outstanding stability. Key features such as MIP suppression, detection efficiency and photon cluster size are discussed. The capability of the detector for UV photon detection has been established and proven with Cherenkov photons in particle beam tests.

Formation of isolated Zn vacancies in ZnO single crystals by absorption of ultraviolet radiation: a combined study using positron annihilation, photoluminescence, and mass spectroscopy.

PubMed

Khan, Enamul H; Weber, Marc H; McCluskey, Matthew D

2013-07-05

Positron annihilation spectra reveal isolated zinc vacancy (V(Zn)) creation in single-crystal ZnO exposed to 193-nm radiation at 100 mJ/cm(2) fluence. The appearance of a photoluminescence excitation peak at 3.18 eV in irradiated ZnO is attributed to an electronic transition from the V(Zn) acceptor level at ~100 meV to the conduction band. The observed V(Zn) density profile and hyperthermal Zn(+) ion emission support zinc vacancy-interstitial Frenkel pair creation by exciting a wide 6.34 eV Zn-O antibonding state at 193-nm photon-a novel photoelectronic process for controlled V(Zn) creation in ZnO.

A common fluence threshold for first positive and second positive phototropism in Arabidopsis thaliana

NASA Technical Reports Server (NTRS)

Janoudi, A.; Poff, K. L.

1990-01-01

The relationship between the amount of light and the amount of response for any photobiological process can be based on the number of incident quanta per unit time (fluence rate-response) or on the number of incident quanta during a given period of irradiation (fluence-response). Fluence-response and fluence rate-response relationships have been measured for second positive phototropism by seedlings of Arabidopsis thaliana. The fluence-response relationships exhibit a single limiting threshold at about 0.01 micromole per square meter when measured at fluence rates from 2.4 x 10(-5) to 6.5 x 10(-3) micromoles per square meter per second. The threshold values in the fluence rate-response curves decrease with increasing time of irradiation, but show a common fluence threshold at about 0.01 micromole per square meter. These thresholds are the same as the threshold of about 0.01 micromole per square meter measured for first positive phototropism. Based on these data, it is suggested that second positive curvature has a threshold in time of about 10 minutes. Moreover, if the times of irradiation exceed the time threshold, there is a single limiting fluence threshold at about 0.01 micromole per square meter. Thus, the limiting fluence threshold for second positive phototropism is the same as the fluence threshold for first positive phototropism. Based on these data, we suggest that this common fluence threshold for first positive and second positive phototropism is set by a single photoreceptor pigment system.

Evidence for Secondary Emission as the Origin of Hard Spectra in TeV Blazars

NASA Astrophysics Data System (ADS)

Zheng, Y. G.; Kang, T.

2013-02-01

We develop a model for the possible origin of hard, very high energy (VHE) spectra from a distant blazar. In the model, both the primary photons produced in the source and secondary photons produced outside it contribute to the observed high-energy γ-ray emission. That is, the primary photons are produced through the synchrotron self-Compton process, and the secondary photons are produced through high-energy proton interactions with background photons along the line of sight. We apply the model to a characteristic case of VHE γ-ray emission in the distant blazar 1ES 1101-232. Assuming suitable electron and proton spectra, we obtain excellent fits to the observed spectra of this blazar. This indicated that the surprisingly low attenuation of the high-energy γ-rays, especially the shape of the VHE γ-ray tail of the observed spectra, can be explained by secondary γ-rays produced in interactions of cosmic-ray protons with background photons in intergalactic space.

A Deterministic Electron, Photon, Proton and Heavy Ion Radiation Transport Suite for the Study of the Jovian System

NASA Technical Reports Server (NTRS)

Norman, Ryan B.; Badavi, Francis F.; Blattnig, Steve R.; Atwell, William

2011-01-01

A deterministic suite of radiation transport codes, developed at NASA Langley Research Center (LaRC), which describe the transport of electrons, photons, protons, and heavy ions in condensed media is used to simulate exposures from spectral distributions typical of electrons, protons and carbon-oxygen-sulfur (C-O-S) trapped heavy ions in the Jovian radiation environment. The particle transport suite consists of a coupled electron and photon deterministic transport algorithm (CEPTRN) and a coupled light particle and heavy ion deterministic transport algorithm (HZETRN). The primary purpose for the development of the transport suite is to provide a means for the spacecraft design community to rapidly perform numerous repetitive calculations essential for electron, proton and heavy ion radiation exposure assessments in complex space structures. In this paper, the radiation environment of the Galilean satellite Europa is used as a representative boundary condition to show the capabilities of the transport suite. While the transport suite can directly access the output electron spectra of the Jovian environment as generated by the Jet Propulsion Laboratory (JPL) Galileo Interim Radiation Electron (GIRE) model of 2003; for the sake of relevance to the upcoming Europa Jupiter System Mission (EJSM), the 105 days at Europa mission fluence energy spectra provided by JPL is used to produce the corresponding dose-depth curve in silicon behind an aluminum shield of 100 mils ( 0.7 g/sq cm). The transport suite can also accept ray-traced thickness files from a computer-aided design (CAD) package and calculate the total ionizing dose (TID) at a specific target point. In that regard, using a low-fidelity CAD model of the Galileo probe, the transport suite was verified by comparing with Monte Carlo (MC) simulations for orbits JOI--J35 of the Galileo extended mission (1996-2001). For the upcoming EJSM mission with a potential launch date of 2020, the transport suite is used to compute the traditional aluminum-silicon dose-depth calculation as a standard shield-target combination output, as well as the shielding response of high charge (Z) shields such as tantalum (Ta). Finally, a shield optimization algorithm is used to guide the instrument designer with the choice of graded-Z shield analysis.

Excitation of photosystem I by 760 nm femtosecond laser pulses: transient absorption spectra and intermediates

NASA Astrophysics Data System (ADS)

Cherepanov, Dmitry A.; Shelaev, Ivan V.; Gostev, Fedor E.; Mamedov, Mahir D.; Petrova, Anastasia A.; Aybush, Arseniy V.; Shuvalov, Vladimir A.; Semenov, Alexey Yu; Nadtochenko, Victor A.

2017-09-01

Excitation of photosystem I (PS I) by a femtosecond 760 nm pump leads to one- and two-photon absorption. The one-photon excitation produces intermediates with transient absorption spectra similar to the spectra of the primary [{{{P}}700}+{{{A}}0}-{{A}}1] and secondary [{{{P}}700}+{{A}}0{{{A}}1}-] ion-radical pairs in the PS I reaction center. The two-photon absorption generates the upper level excited states of chlorophyll (Chl) and carotenoid molecules in the antenna. These excited states are converted into the long-lived intermediates and can be tentatively attributed to the excited and charge-transfer ion-radical states of Chl molecules and to the excited states of carotenoids in the antenna. The transient spectra of intermediates generated by two-photon excitation differ from the transient one-photon spectra of the primary and secondary ion-radical pairs.

Experimental and simulation-based investigation of He, Ne and Ar irradiation of polymers for ion microscopy

PubMed Central

Rzeznik, Lukasz; Fleming, Yves; Wirtz, Tom

2016-01-01

Summary Secondary ion mass spectrometry (SIMS) on the helium ion microscope (HIM) promises higher lateral resolution than on classical SIMS instruments. However, full advantage of this new technique can only be obtained when the interaction of He+ or Ne+ primary ions with the sample is fully controlled. In this work we investigate how He+ and Ne+ bombardment influences roughness formation and preferential sputtering for polymer samples and how they compare to Ar+ primary ions used in classical SIMS by combining experimental techniques with Molecular Dynamics (MD) simulations and SD_TRIM_SP modelling. The results show that diffusion coefficients for He, Ne and Ar in polymers are sufficiently high to prevent any accumulation of rare gas atoms in the polymers which could lead to some swelling and bubble formation. Roughness formation was also not observed. Preferential sputtering is more of a problem, with enrichment of carbon up to surface concentrations above 80%. In general, the preferential sputtering is largely depending on the primary ion species and the impact energies. For He+ bombardment, it is more of an issue for low keV impact energies and for the heavier primary ion species the preferential sputtering is sample dependent. For He+ steady state conditions are reached for fluences much higher than 1018 ions/cm2. For Ne+ and Ar+, the transient regime extends up to fluences of 1017–1018 ions/cm2. Hence, preferential sputtering needs to be taken into account when interpreting images recorded under He+ or Ne+ bombardment on the HIM. PMID:27547629

A Common Fluence Threshold for First Positive and Second Positive Phototropism in Arabidopsis thaliana1

PubMed Central

Janoudi, Abdul; Poff, Kenneth L.

1990-01-01

The relationship between the amount of light and the amount of response for any photobiological process can be based on the number of incident quanta per unit time (fluence rate-response) or on the number of incident quanta during a given period of irradiation (fluence-response). Fluence-response and fluence rate-response relationships have been measured for second positive phototropism by seedlings of Arabidopsis thaliana. The fluence-response relationships exhibit a single limiting threshold at about 0.01 micromole per square meter when measured at fluence rates from 2.4 × 10−5 to 6.5 × 10−3 micromoles per square meter per second. The threshold values in the fluence rateresponse curves decrease with increasing time of irradiation, but show a common fluence threshold at about 0.01 micromole per square meter. These thresholds are the same as the threshold of about 0.01 micromole per square meter measured for first positive phototropism. Based on these data, it is suggested that second positive curvature has a threshold in time of about 10 minutes. Moreover, if the times of irradiation exceed the time threshold, there is a single limiting fluence threshold at about 0.01 micromole per square meter. Thus, the limiting fluence threshold for second positive phototropism is the same as the fluence threshold for first positive phototropism. Based on these data, we suggest that this common fluence threshold for first positive and second positive phototropism is set by a single photoreceptor pigment system. PMID:11537470

Neutron Fluence and Energy Reconstruction with the LNE-IRSN/MIMAC Recoil Detector MicroTPC at 27 keV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maire, D.; Lebreton, L.; Querre, Ph.

2015-07-01

The French Institute for Radiation protection and Nuclear Safety (IRSN), designated by the French Metrology Institute (LNE) for neutron metrology, is developing a time projection chamber using a Micromegas anode: microTPC. This work is carried out in collaboration with the Laboratory of Subatomic Physics and Cosmology (LPSC). The aim is to characterize the energy distribution of neutron fluence in the energy range 8 keV - 5 MeV with a primary procedure. The time projection chambers are gaseous detectors able to measure charged particles energy and to reconstruct their track if a pixelated anode is used. In our case, the gasmore » is used as a (n, p) converter in order to detect neutrons down to few keV. Coming from elastic collisions with neutrons, recoil protons lose a part of their kinetic energy by ionizing the gas. The ionization electrons are drifted toward a pixelated anode (2D projection), read at 50 MHz by a self-triggered electronic system to obtain the third track dimension. The neutron energy is reconstructed event by event thanks to proton scattering angle and proton energy measurements. The scattering angle is deduced from the 3D track. The proton energy is obtained by charge collection measurements, knowing the ionization quenching factor (i.e. the part of proton kinetic energy lost by ionizing the gas). The fluence is calculated thanks to the detected events number and the simulation of the detector response. The μTPC is a new reliable detector able to measure energy distribution of the neutron fluence without unfolding procedure or prior neutron calibration contrary to usual gaseous counters. The microTPC is still being developed and measurements have been carried out at the AMANDE facility, with neutrons energies going from 8 keV to 565 keV. After the context and the μ-TPC working principle presentation, measurements of the neutron energy and fluence at 27 keV and 144 keV are shown and compared to the complete detector response simulation. This work shows the first direct reconstruction of neutron energy and fluence, simultaneously, at 27.2 keV in a continuous irradiation mode. (authors)« less

Neutron fluence and energy reconstruction with the IRSN recoil detector μ-TPC at 27 keV, 144 keV and 565 keV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maire, D.; Lebreton, L.; Richer, J.P.

2015-07-01

The French Institute for Radioprotection and Nuclear Safety (IRSN), associated to the French Metrology Institute (LNE), is developing a time projection chamber using a Micromegas anode: μ-TPC. This work is carried out in collaboration with the Laboratory of Subatomic Physics and Cosmology (LPSC). The aim is to characterize with a primary procedure the energy distribution of neutron fluence in the energy range 8 keV - 1 MeV. The time projection chambers are gaseous detectors, which are able to measure charged particles energy and to reconstruct their track if a pixelated anode is used. In our case, the gas is usedmore » as a (n, p) converter in order to detect neutrons down to few keV. Coming from elastic collisions with neutrons, recoil protons lose a part of their kinetic energy by ionizing the gas. The ionization electrons are drifted toward a pixelated anode (2D projection), read at 50 MHz by a self-triggered electronic system to obtain the third track dimension. The neutron energy is reconstructed event by event thanks to proton scattering angle and proton energy measurements. The scattering angle is deduced from the 3D track. The proton energy is obtained by charge collection measurements, knowing the ionization quenching factor (i.e. the part of proton kinetic energy lost by ionizing the gas). The fluence is calculated thanks to the detected events number and the simulated detector response. The μ-TPC is a new reliable detector which enables to measure energy distribution of the neutron fluence without deconvolution or neutron calibration contrary to usual gaseous counters. The μ-TPC is still being developed and measurements have been carried out at the AMANDE facility, with neutrons energies going from 8 keV to 565 keV. After the context and the μ-TPC working principle presentation, measurements of the neutron energy and fluence at 27.2 keV, 144 keV and 565 keV are shown and compared to the complete detector simulation. This work shows the first direct reconstruction of neutron energy and fluence, simultaneously, at 27.2 keV in a continuous irradiation mode. (authors)« less

Amplification of effects of photons on wound healing

NASA Astrophysics Data System (ADS)

Dyson, Mary

2009-02-01

Following the absorption of photons by cells either resident in or in transit through the skin at and around a wound site, healing can be modulated. This is due to the primary, secondary and tertiary cellular effects of the photons. The main primary effect of phototherapy is photon absorption. This initiates secondary effects within the cells that have absorbed the photons. Secondary effects are restricted to cells that have absorbed a suprathreshold quantity of photonic energy. Photon absorption can lead to an increase in ATP synthesis and the release of reactive oxygen species that can activate specific transcription factors resulting in changes in synthesis of the enzymes needed for cellular proliferation, migration, phagocytosis and protein synthesis, all essential for wound healing. The amount of ATP production is limited in each cell by the availability of ADP and phosphate. Spatial and temporal amplification of the effects of photon absorption increases the range and duration of phototherapy. It may be caused in part by tertiary effects initiated in cells that have not absorbed photons by regulatory proteins such as cytokines secreted by cells that have absorbed photons. Amplification may also be due to changes induced by photons in immune cells, stem cells and soluble protein mediators while in transit through the dermal capillaries. The peripheral location of these capillaries makes their contents readily accessible to photons. The longer the duration of treatment, the greater will be the number of cells in transit that can be affected by photons. Depth of effect may be increased by transduction of electromagnetic energy into mechanical energy. For a treatment to be clinically effective on wound healing, its duration and power may each be important. Components of the immune system, endocrine system and nervous system may also amplify the effects of photons on wound healing.

Femtosecond laser-induced subwavelength ripples formed by asymmetrical grating splitting

NASA Astrophysics Data System (ADS)

Feng, Pin; Jiang, Lan; Li, Xin; Zhang, Kaihu; Shi, Xuesong; Li, Bo; Lu, Yongfeng

2016-05-01

The formation process and mechanism of subwavelength ripples were studied upon irradiation of ZnO by a femtosecond laser (800 nm, 50 fs, 1 kHz). An abnormally asymmetrical grating-splitting phenomenon was discovered. At relatively high laser fluences (F = 0.51-0.63 J/cm2), near-wavelength ripples were split asymmetrically to create subwavelength laser-induced periodic surface structures (LIPSS) with dual gaps (˜230 nm and ˜430 nm) on the primary grooves. At relatively low laser fluences (F = 0.4-0.45 J/cm2), near-wavelength ripples were split symmetrically, leading to the formation of uniform subwavelength structures with a period of ˜340 nm. The splitting phenomena are related to the varying laser beam dose induced by the overlapping during line scanning. The two grating-splitting types further imply that the dominated mechanism for LIPSS formation may be changed under different processing conditions.

Solid-state track recorder dosimetry device to measure absolute reaction rates and neutron fluence as a function of time

DOEpatents

Gold, Raymond; Roberts, James H.

1989-01-01

A solid state track recording type dosimeter is disclosed to measure the time dependence of the absolute fission rates of nuclides or neutron fluence over a period of time. In a primary species an inner recording drum is rotatably contained within an exterior housing drum that defines a series of collimating slit apertures overlying windows defined in the stationary drum through which radiation can enter. Film type solid state track recorders are positioned circumferentially about the surface of the internal recording drum to record such radiation or its secondary products during relative rotation of the two elements. In another species both the recording element and the aperture element assume the configuration of adjacent disks. Based on slit size of apertures and relative rotational velocity of the inner drum, radiation parameters within a test area may be measured as a function of time and spectra deduced therefrom.

WE-E-18A-05: Bremsstrahlung of Laser-Plasma Interaction at KeV Temperature: Forward Dose and Attenuation Factors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saez-Beltran, M; Fernandez Gonzalez, F

2014-06-15

Purpose: To obtain an analytical empirical formula for the photon dose source term in forward direction from bremsstrahlung generated from laser-plasma accelerated electron beams in aluminum solid targets, with electron-plasma temperatures in the 10–100 keV energy range, and to calculate transmission factors for iron, aluminum, methacrylate, lead and concrete and air, materials most commonly found in vacuum chamber labs. Methods: Bremsstrahlung fluence is calculated from the convolution of thin-target bremsstrahlung spectrum for monoenergetic electrons and the relativistic Maxwell-Juettner energy distribution for the electron-plasma. Unattenuatted dose in tissue is calculated by integrating the photon spectrum with the mass-energy absorption coefficient. Formore » the attenuated dose, energy dependent absorption coefficient, build-up factors and finite shielding correction factors were also taken into account. For the source term we use a modified formula from Hayashi et al., and we fitted the proportionality constant from experiments with the aid of the previously calculated transmission factors. Results: The forward dose has a quadratic dependence on electron-plasma temperature: 1 joule of effective laser energy transferred to the electrons at 1 m in vacuum yields 0,72 Sv per MeV squared of electron-plasma temperature. Air strongly filters the softer part of the photon spectrum and reduce the dose to one tenth in the first centimeter. Exponential higher energy tail of maxwellian spectrum contributes mainly to the transmitted dose. Conclusion: A simple formula for forward photon dose from keV range temperature plasma is obtained, similar to those found in kilovoltage x-rays but with higher dose per dissipated electron energy, due to thin target and absence of filtration.« less

Sci-Fri PM: Planning-10: The replacement correction factors for cylindrical chambers in megavoltage beams.

PubMed

Wang, L; Rogers, Dwo

2008-07-01

The replacement correction factor (P repl ) in ion chamber dosimetry accounts for the effects of the medium being replaced by the air cavity of the chamber. In TG-21, P repl was conceptually separated into two components: fluence correction, P fl , and gradient correction, P gr . In TG-51, for electron beams, the calibration is at d ref where P gr is required for cylindrical chambers and P fl is unknown and assumed to be the same as that for a beam having the same mean electron energy at d max . For cylindrical chambers in high-energy photon beams, P repl also represents a major uncertainty in current dosimetry protocols. In this study, P repl is calculated with high precision (<0.1%) by the Monte Carlo method as the ratio of the dose in a phantom to the dose scored in water-walled cylindrical cavities of various radii (with the center of the cavity being the point of measurement) in both high energy photon and electron beams. It is found that, for electron beams, the mean electron energy at depth is a good beam quality specifier for P fl ; and TG-51's adoption of P fl at d max with the same mean electron energy for use at d ref is proven to be accurate. For Farmer chambers in photon beams, there is essentially no beam quality dependence for P repl values. In a Co photon beam, the calculated P repl is about 0.4-0.6% higher than the TG-21 value, indicating TG-21 (and TG-51) used incorrect values of P repl for cylindrical chambers. © 2008 American Association of Physicists in Medicine.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 insteadmore » 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)« less

WE-E-18A-06: To Remove Or Not to Remove: Comfort Pads From Beneath Neonates for Radiography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, X; Baad, M; Reiser, I

2014-06-15

Purpose: To obtain an analytical empirical formula for the photon dose source term in forward direction from bremsstrahlung generated from laser-plasma accelerated electron beams in aluminum solid targets, with electron-plasma temperatures in the 10–100 keV energy range, and to calculate transmission factors for iron, aluminum, methacrylate, lead and concrete and air, materials most commonly found in vacuum chamber labs. Methods: Bremsstrahlung fluence is calculated from the convolution of thin-target bremsstrahlung spectrum for monoenergetic electrons and the relativistic Maxwell-Juettner energy distribution for the electron-plasma. Unattenuatted dose in tissue is calculated by integrating the photon spectrum with the mass-energy absorption coefficient. Formore » the attenuated dose, energy dependent absorption coefficient, build-up factors and finite shielding correction factors were also taken into account. For the source term we use a modified formula from Hayashi et al., and we fitted the proportionality constant from experiments with the aid of the previously calculated transmission factors. Results: The forward dose has a quadratic dependence on electron-plasma temperature: 1 joule of effective laser energy transferred to the electrons at 1 m in vacuum yields 0,72 Sv per MeV squared of electron-plasma temperature. Air strongly filters the softer part of the photon spectrum and reduce the dose to one tenth in the first centimeter. Exponential higher energy tail of maxwellian spectrum contributes mainly to the transmitted dose. Conclusion: A simple formula for forward photon dose from keV range temperature plasma is obtained, similar to those found in kilovoltage x-rays but with higher dose per dissipated electron energy, due to thin target and absence of filtration.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lane, Taylor; Parma, Edward J.

Delayed fission gamma-rays play an important role in determining the time dependent ioniz- ing dose for experiments in the central irradiation cavity of the Annular Core Research Reactor (ACRR). Delayed gamma-rays are produced from both fission product decay and from acti- vation of materials in the core, such as cladding and support structures. Knowing both the delayed gamma-ray emission rate and the time-dependent gamma-ray energy spectrum is nec- essary in order to properly determine the dose contributions from delayed fission gamma-rays. This information is especially important when attempting to deconvolute the time-dependent neutron, prompt gamma-ray, and delayed gamma-ray contribution tomore » the response of a diamond photo-conducting diode (PCD) or fission chamber in time frames of milliseconds to seconds following a reactor pulse. This work focused on investigating delayed gamma-ray character- istics produced from fission products from thermal, fast, and high energy fission of Th-232, U-233, U-235, U-238, and Pu-239. This work uses a modified version of CINDER2008, a transmutation code developed at Los Alamos National Laboratory, to model time and energy dependent photon characteristics due to fission. This modified code adds the capability to track photon-induced transmutations, photo-fission, and the subsequent radiation caused by fission products due to photo-fission. The data is compared against previous work done with SNL- modified CINDER2008 [ 1 ] and experimental data [ 2 , 3 ] and other published literature, includ- ing ENDF/B-VII.1 [ 4 ]. The ability to produce a high-fidelity (7,428 group) energy-dependent photon fluence at various times post-fission can improve the delayed photon characterization for radiation effects tests at research reactors, as well as other applications.« less

Laser ablation of ceramic Al2O3 at 193 nm and 248 nm: The importance of single-photon ionization processes

NASA Astrophysics Data System (ADS)

Peláez, R. J.; Afonso, C. N.; Bator, M.; Lippert, T.

2013-06-01

The aim of this work is to demonstrate that single-photon photoionization processes make a significant difference in the expansion and temperature of the plasma produced by laser ablation of ceramic Al2O3 in vacuum as well as to show their consequences in the kinetic energy distribution of the species that eventually will impact on the film properties produced by pulsed laser deposition. This work compares results obtained by mass spectrometry and optical spectroscopy on the composition and features of the plasma produced by laser ablation at 193 nm and 248 nm, i.e., photon energies that are, respectively, above and below the ionization potential of Al, and for fluences between threshold for visible plasma and up to ≈2 times higher. The results show that the ionic composition and excitation of the plasma as well as the ion kinetic energies are much higher at 193 nm than at 248 nm and, in the latter case, the population of excited ions is even negligible. The comparison of Maxwell-Boltzmann temperature, electron temperatures, and densities of the plasmas produced with the two laser wavelengths suggests that the expansion of the plasma produced at 248 nm is dominated by a single population. Instead, the one produced at 193 nm is consistent with the existence of two populations of cold and hot species, the latter associated to Al+ ions that travel at the forefront and produced by single photon ionization as well as Al neutrals and double ionized ions produced by electron-ion impact. The results also show that the most energetic Al neutrals in the plasma produced at the two studied wavelengths are in the ground state.

Effects of laser fluence non-uniformity on ambient-temperature soot measurements using the auto-compensating laser-induced incandescence technique

NASA Astrophysics Data System (ADS)

Liu, Fengshan; Rogak, Steven; Snelling, David R.; Saffaripour, Meghdad; Thomson, Kevin A.; Smallwood, Gregory J.

2016-11-01

Multimode pulsed Nd:YAG lasers are commonly used in auto-compensating laser-induced incandescence (AC-LII) measurements of soot in flames and engine exhaust as well as black carbon in the atmosphere. Such lasers possess a certain degree of fluence non-uniformity across the laser beam even with the use of beam shaping optics. Recent research showed that the measured volume fraction of ambient-temperature soot using AC-LII increases significantly, by about a factor of 5-8, with increasing the laser fluence in the low-fluence regime from a very low fluence to a relatively high fluence of near sublimation. The causes of this so-called soot volume fraction anomaly are currently not understood. The effects of laser fluence non-uniformity on the measured soot volume fraction using AC-LII were investigated. Three sets of LII experiments were conducted in the exhaust of a MiniCAST soot generator under conditions of high elemental carbon using Nd:YAG lasers operated at 1064 nm. The laser beams were shaped and relay imaged to achieve a relatively uniform fluence distribution in the measurement volume. To further homogenize the laser fluence, one set of LII experiments was conducted by using a diffractive optical element. The measured soot volume fractions in all three sets of LII experiments increase strongly with increasing the laser fluence before a peak value is reached and then start to decrease at higher fluences. Numerical calculations were conducted using the experimental laser fluence histograms. Laser fluence non-uniformity is found partially responsible for the soot volume fraction anomaly, but is insufficient to explain the degree of soot volume fraction anomaly observed experimentally. Representing the laser fluence variations by a histogram derived from high-resolution images of the laser beam energy profile gives a more accurate definition of inhomogeneity than a simple averaged linear profile across the laser beam.

Experimental derivation of the fluence non-uniformity correction for air kerma near brachytherapy linear sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vianello, E. A.; Almeida, C. E. de

2008-07-15

In brachytherapy, one of the elements to take into account for measurements free in air is the non-uniformity of the photon fluence due to the beam divergence that causes a steep dose gradient near the source. The correction factors for this phenomenon have been usually evaluated by two available theories by Kondo and Randolph [Radiat. Res. 13, 37-60 (1960)] and Bielajew [Phys. Med. Biol. 35, 517-538 (1990)], both conceived for point sources. This work presents the experimental validation of the Monte Carlo calculations made by Rodriguez and deAlmeida [Phys. Med. Biol. 49, 1705-1709 (2004)] for the non-uniformity correction specifically formore » a Cs-137 linear source measured using a Farmer type ionization chamber. The experimental values agree very well with the Monte Carlo calculations and differ from the results predicted by both theoretical models widely used. This result confirms that for linear sources there are some important differences at short distances from the source and emphasizes that those theories should not be used for linear sources. The data provided in this study confirm the limitations of the mentioned theories when linear sources are used. Considering the difficulties and uncertainties associated with the experimental measurements, it is recommended to use the Monte Carlo data to assess the non-uniformity factors for linear sources in situations that require this knowledge.« less

Size-Dependent Coherent-Phonon Plasmon Modulation and Deformation Characterization in Gold Bipyramids and Nanojavelins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirschner, Matthew S.; Lethiec, Clotilde M.; Lin, Xiao-Min

2016-04-04

Localized surface plasmon resonances (LSPRs) arising from metallic nanoparticles offer an array of prospective applications that range from chemical sensing to biotherapies. Bipyramidal particles exhibit particularly narrow ensemble LSPR resonances that reflect small dispersity of size and shape but until recently were only synthetically accessible over a limited range of sizes with corresponding aspect ratios. Narrow size dispersion offers the opportunity to examine ensemble dynamical phenomena such as coherent phonons that induce periodic oscillations of the LSPR energy. Here, we characterize transient optical behavior of a large range of gold bipyramid sizes, as well as higher aspect ratio nanojavelin ensemblesmore » with specific attention to the lowest-order acoustic phonon mode of these nanoparticles. We report coherent phonon-driven oscillations of the LSPR position for particles with resonances spanning 670 to 1330 nm. Nanojavelins were shown to behave similarly to bipyramids but offer the prospect of separate control over LSPR energy and coherent phonon oscillation period. We develop a new methodology for quantitatively measuring mechanical expansion caused by photogenerated coherent phonons. Using this method, we find an elongation of approximately 1% per photon absorbed per unit cell and that particle expansion along the lowest frequency acoustic phonon mode is linearly proportional to excitation fluence for the fluence range studied. These characterizations provide insight regarding means to manipulate phonon period and transient mechanical deformation.« less

The sensitivity of normal brain and intracranially implanted VX2 tumour to interstitial photodynamic therapy.

PubMed Central

Lilge, L.; Olivo, M. C.; Schatz, S. W.; MaGuire, J. A.; Patterson, M. S.; Wilson, B. C.

1996-01-01

The applicability and limitations of a photodynamic threshold model, used to describe quantitatively the in vivo response of tissues to photodynamic therapy, are currently being investigated in a variety of normal and malignant tumour tissues. The model states that tissue necrosis occurs when the number of photons absorbed by the photosensitiser per unit tissue volume exceeds a threshold. New Zealand White rabbits were sensitised with porphyrin-based photosensitisers. Normal brain or intracranially implanted VX2 tumours were illuminated via an optical fibre placed into the tissue at craniotomy. The light fluence distribution in the tissue was measured by multiple interstitial optical fibre detectors. The tissue concentration of the photosensitiser was determined post mortem by absorption spectroscopy. The derived photodynamic threshold values for normal brain are significantly lower than for VX2 tumour for all photosensitisers examined. Neuronal damage is evident beyond the zone of frank necrosis. For Photofrin the threshold decreases with time delay between photosensitiser administration and light treatment. No significant difference in threshold is found between Photofrin and haematoporphyrin derivative. The threshold in normal brain (grey matter) is lowest for sensitisation by 5 delta-aminolaevulinic acid. The results confirm the very high sensitivity of normal brain to porphyrin photodynamic therapy and show the importance of in situ light fluence monitoring during photodynamic irradiation. Images Figure 1 Figure 4 Figure 5 Figure 6 Figure 7 PMID:8562339

SU-F-T-326: Diode Array Transmission Detector Systems Evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffman, D; Dyer, B; Kumaran Nair, C

2016-06-15

Purpose: A new transmission detector, Delta4 Discover, developed by Scandidos (Uppsala, Sweden) was evaluated for external photon beam verification and quality assurance. The device is an array of 4040 diodes designed to be mounted on the linac accessory tray to measure photon field shape, position and fluence during patient treatment. Interfractional measurements are compared to a baseline measurement made during delivery quality assurance. The aim of this work is to evaluate the stability of the device and its effect on the shape and magnitude of the treatment beam. Methods: Beam profiles, percent depth dose, and beam attenuation was measured formore » 6, 10, and 15 MV photon beams with and without the device in place for 1×1 and 30×30 cm2 fields. Changes in profile and percent depth dose was quantified to evaluate the need to recommission the treatment beam, or account for the device with a tray factor. The stability of the radiation measurements was evaluated by measuring the deviation of each diode measurement during repeated prostate VMAT treatment delivery. Results: Photon beam profiles changed by < 1.25% in the nonpenumbra regions of the 30×30 cm2 beam. Percent depth dose curves show a 5–7% increased dose at depths < 2.5cm, but agreed within 1% at depths > 2.5cm. This indicates increased skin dose, similar to the use of a physical beam wedge. The device attenuated 6, 10, and 15 MV photon beams by 1.71±0.02%, 1.36±0.03%, and 1.17±0.03%, respectively. The diode array reproduced dosimetric measurements within 0.5% standard deviation for repeated prostate VMAT measurement. Conclusion: The device demonstrated stabile radiation measurements, while not changing the treatment beam shape in a clinically significantly manner. Use of this device can be accounted for with a tray factor, as opposed to recommissioning the treatment beam.« less

A comparison between the processing of Titan aerosols analogs by ionizing photons and energetic cosmic rays.

NASA Astrophysics Data System (ADS)

De Araujo Vasconcelos, Fredson; Pilling, Sergio; Boduch, Philippe; Alexandre Souza Bergantini, M.; Ding, M. Jingjie J.; Rothard, Hermann; Robson Rocha, Will

Titan, the largest satellite of Saturn, has an atmosphere mainly made of N_{2} and CH_{4} and includes traces of several simple organic compounds. This atmosphere also partly consists of haze and erosol particles which during the last 4.5 gigayears have been processed by electric discharges, ions, and ionizing photons, being slowly deposited over Titańs surface. In this work, we investigate the possible effects produced by ionizing photons (vacuum ultraviolet and soft X-rays) and cosmic ray analogs (15.7 MeV (16) O (+5) ) on Titan aerosol analogs in an attempt to simulate some prebiotic photochemistry. For photons, the experiments have been performed using a high vacuum portable chamber from the Laboratorio de Astroquimica e Astrobiologia (LASA/UNIVAP) coupled to the the Brazilian Synchrotron Light Source (LNLS) in Campinas, Brazil. For ions, the investigation was performed at the Grand Accelerateur National d’Ions Lourds (GANIL) Caen, France. In-situ sample analyses were performed by a Fourier transform infrared spectrometer at different fluences. During the sample processing, the infrared spectra have presented several new organic molecules, including nitriles, HCN and aromatic CN compounds. The processing of the sample by fast ions has enhanced the formation of daughter species in the Titan aerosol sample when compared with the products from the employing VUV and soft X-rays photons. The destruction cross section of the parent species was determined, as well as, the formation cross section for some selected daughter species. Molecular Half-lives were extrapolated to the Titańs environment. This investigation confirms previous results which showed that the organic chemistry on frozen moons inside Solar system can be very complex and extremely rich in prebiotic compounds. Authors would like to tanks the agencies FAPESP (JP-2009/18304-0), CAPES-Cofecub (569/2007), INCT-A and CNPq for the financial support.

The effect of fluence on the magnetic properties of superparamagnetic iron-nickel nanoparticles in SiO2 made by dual Ni and Fe low energy ion implantation

NASA Astrophysics Data System (ADS)

Williams, G. V. M.; Prakash, T.; Kennedy, J.

2017-10-01

Superparamagnetic Ni1-yFey nanoparticles were made in a SiO2 film by 10 keV ion beam implantation of Ni followed by Fe with a Ni fluence of 4 × 1016 at.cm-2 and a Fe fluence fraction of 0.47. Nearly all of the moments magnetically ordered, which was not reported for an implanted film made with a Fe fluence fraction of 0.56 and half the Ni fluence. The temperature dependence of the saturation moment is remarkably similar for low and high Ni fluences where there is also the presence of very thin spin-disordered shells. The higher Ni fluence leads to a significant enhancement of the susceptibility by a factor of 9 when compared with the lower fluence sample. This enhancement is likely to be due to a larger magnetically ordered volume fraction.

A multiscale filter for noise reduction of low-dose cone beam projections.

PubMed

Yao, Weiguang; Farr, Jonathan B

2015-08-21

The Poisson or compound Poisson process governs the randomness of photon fluence in cone beam computed tomography (CBCT) imaging systems. The probability density function depends on the mean (noiseless) of the fluence at a certain detector. This dependence indicates the natural requirement of multiscale filters to smooth noise while preserving structures of the imaged object on the low-dose cone beam projection. In this work, we used a Gaussian filter, exp(-x2/2σ(2)(f)) as the multiscale filter to de-noise the low-dose cone beam projections. We analytically obtained the expression of σ(f), which represents the scale of the filter, by minimizing local noise-to-signal ratio. We analytically derived the variance of residual noise from the Poisson or compound Poisson processes after Gaussian filtering. From the derived analytical form of the variance of residual noise, optimal σ(2)(f)) is proved to be proportional to the noiseless fluence and modulated by local structure strength expressed as the linear fitting error of the structure. A strategy was used to obtain the reliable linear fitting error: smoothing the projection along the longitudinal direction to calculate the linear fitting error along the lateral direction and vice versa. The performance of our multiscale filter was examined on low-dose cone beam projections of a Catphan phantom and a head-and-neck patient. After performing the filter on the Catphan phantom projections scanned with pulse time 4 ms, the number of visible line pairs was similar to that scanned with 16 ms, and the contrast-to-noise ratio of the inserts was higher than that scanned with 16 ms about 64% in average. For the simulated head-and-neck patient projections with pulse time 4 ms, the visibility of soft tissue structures in the patient was comparable to that scanned with 20 ms. The image processing took less than 0.5 s per projection with 1024   ×   768 pixels.

Neutron Radiation Shielding For The NIF Streaked X-Ray Detector (SXD) Diagnostic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, P; Holder, J; Young, B

2006-11-02

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) is preparing for the National Ignition Campaign (NIC) scheduled in 2010. The NIC is comprised of several ''tuning'' physics subcampaigns leading up to a demonstration of Inertial Confinement Fusion (ICF) ignition. In some of these experiments, time-resolved x-ray imaging of the imploding capsule may be required to measure capsule trajectory (shock timing) or x-ray ''bang-time''. A capsule fueled with pure tritium (T) instead of a deutriun-tritium (DT) mixture is thought to offer useful physics surrogacy, with reduced yields of up to 5e14 neutrons. These measurements will require the usemore » of the NIF streak x-ray detector (SXD). The resulting prompt neutron fluence at the planned SXD location ({approx}1.7 m from the target) would be {approx}1.4e9/cm{sup 2}. Previous measurements suggest the onset of significant background at a neutron fluence of {approx} 1e8/cm{sup 2}. The radiation damage and operational upsets which starts at {approx}1e8 rad-Si/sec must be factored into an integrated experimental campaign plan. Monte Carlo analyses were performed to predict the neutron and gamma/x-ray fluences and radiation doses for the proposed diagnostic configuration. A possible shielding configuration is proposed to mitigate radiation effects. The primary component of this shielding is an 80 cm thickness of Polyethylene (PE) between target chamber center (TCC) and the SXD diagnostic. Additionally, 6-8 cm of PE around the detector provide from the large number of neutrons that scatter off the inside of the target chamber. This proposed shielding configuration reduces the high-energy neutron fluence at the SXD by approximately a factor {approx}50.« less

Diaphragm correction factors for the FAC-IR-300 free-air ionization chamber.

PubMed

Mohammadi, Seyed Mostafa; Tavakoli-Anbaran, Hossein

2018-02-01

A free-air ionization chamber FAC-IR-300, designed by the Atomic Energy Organization of Iran, is used as the primary Iranian national standard for the photon air kerma. For accurate air kerma measurements, the contribution from the scattered photons to the total energy released in the collecting volume must be eliminated. One of the sources of scattered photons is the chamber's diaphragm. In this paper, the diaphragm scattering correction factor, k dia , and the diaphragm transmission correction factor, k tr , were introduced. These factors represent corrections to the measured charge (or current) for the photons scattered from the diaphragm surface and the photons penetrated through the diaphragm volume, respectively. The k dia and k tr values were estimated by Monte Carlo simulations. The simulations were performed for the mono-energetic photons in the energy range of 20 - 300keV. According to the simulation results, in this energy range, the k dia values vary between 0.9997 and 0.9948, and k tr values decrease from 1.0000 to 0.9965. The corrections grow in significance with increasing energy of the primary photons. Copyright © 2017 Elsevier Ltd. All rights reserved.

Peer-to-peer Monte Carlo simulation of photon migration in topical applications of biomedical optics

NASA Astrophysics Data System (ADS)

Doronin, Alexander; Meglinski, Igor

2012-09-01

In the framework of further development of the unified approach of photon migration in complex turbid media, such as biological tissues we present a peer-to-peer (P2P) Monte Carlo (MC) code. The object-oriented programming is used for generalization of MC model for multipurpose use in various applications of biomedical optics. The online user interface providing multiuser access is developed using modern web technologies, such as Microsoft Silverlight, ASP.NET. The emerging P2P network utilizing computers with different types of compute unified device architecture-capable graphics processing units (GPUs) is applied for acceleration and to overcome the limitations, imposed by multiuser access in the online MC computational tool. The developed P2P MC was validated by comparing the results of simulation of diffuse reflectance and fluence rate distribution for semi-infinite scattering medium with known analytical results, results of adding-doubling method, and with other GPU-based MC techniques developed in the past. The best speedup of processing multiuser requests in a range of 4 to 35 s was achieved using single-precision computing, and the double-precision computing for floating-point arithmetic operations provides higher accuracy.

Peer-to-peer Monte Carlo simulation of photon migration in topical applications of biomedical optics.

PubMed

Doronin, Alexander; Meglinski, Igor

2012-09-01

In the framework of further development of the unified approach of photon migration in complex turbid media, such as biological tissues we present a peer-to-peer (P2P) Monte Carlo (MC) code. The object-oriented programming is used for generalization of MC model for multipurpose use in various applications of biomedical optics. The online user interface providing multiuser access is developed using modern web technologies, such as Microsoft Silverlight, ASP.NET. The emerging P2P network utilizing computers with different types of compute unified device architecture-capable graphics processing units (GPUs) is applied for acceleration and to overcome the limitations, imposed by multiuser access in the online MC computational tool. The developed P2P MC was validated by comparing the results of simulation of diffuse reflectance and fluence rate distribution for semi-infinite scattering medium with known analytical results, results of adding-doubling method, and with other GPU-based MC techniques developed in the past. The best speedup of processing multiuser requests in a range of 4 to 35 s was achieved using single-precision computing, and the double-precision computing for floating-point arithmetic operations provides higher accuracy.

Monte Carlo simulation of near-infrared light propagation in realistic adult head models with hair follicles

NASA Astrophysics Data System (ADS)

Pan, Boan; Fang, Xiang; Liu, Weichao; Li, Nanxi; Zhao, Ke; Li, Ting

2018-02-01

Near infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS) has been used to measure brain activation, which are clinically important. Monte Carlo simulation has been applied to the near infrared light propagation model in biological tissue, and has the function of predicting diffusion and brain activation. However, previous studies have rarely considered hair and hair follicles as a contributing factor. Here, we attempt to use MCVM (Monte Carlo simulation based on 3D voxelized media) to examine light transmission, absorption, fluence, spatial sensitivity distribution (SSD) and brain activation judgement in the presence or absence of the hair follicles. The data in this study is a series of high-resolution cryosectional color photograph of a standing Chinse male adult. We found that the number of photons transmitted under the scalp decreases dramatically and the photons exported to detector is also decreasing, as the density of hair follicles increases. If there is no hair follicle, the above data increase and has the maximum value. Meanwhile, the light distribution and brain activation have a stable change along with the change of hair follicles density. The findings indicated hair follicles make influence of NIRS in light distribution and brain activation judgement.

On the Time Evolution of Gamma-Ray Burst Pulses: A Self-Consistent Description.

PubMed

Ryde; Svensson

2000-01-20

For the first time, the consequences of combining two well-established empirical relations that describe different aspects of the spectral evolution of observed gamma-ray burst (GRB) pulses are explored. These empirical relations are (1) the hardness-intensity correlation and (2) the hardness-photon fluence correlation. From these we find a self-consistent, quantitative, and compact description for the temporal evolution of pulse decay phases within a GRB light curve. In particular, we show that in the case in which the two empirical relations are both valid, the instantaneous photon flux (intensity) must behave as 1&solm0;&parl0;1+t&solm0;tau&parr0;, where tau is a time constant that can be expressed in terms of the parameters of the two empirical relations. The time evolution is fully defined by two initial constants and two parameters. We study a complete sample of 83 bright GRB pulses observed by the Compton Gamma-Ray Observatory and identify a major subgroup of GRB pulses ( approximately 45%) which satisfy the spectral-temporal behavior described above. In particular, the decay phase follows a reciprocal law in time. It is unclear what physics causes such a decay phase.

Plasmon-resonant nanorods as multimodal agents for two-photon luminescent imaging and photothermal therapy

NASA Astrophysics Data System (ADS)

Huff, Terry B.; Hansen, Matthew N.; Tong, Ling; Zhao, Yan; Wang, Haifeng; Zweifel, Daniel A.; Cheng, Ji-Xin; Wei, Alexander

2007-02-01

Plasmon-resonant gold nanorods have outstanding potential as multifunctional agents for image-guided therapies. Nanorods have large absorption cross sections at near-infrared (NIR) frequencies, and produce two-photon luminescence (TPL) when excited by fs-pulsed laser irradiation. The TPL signals can be detected with single-particle sensitivity, enabling nanorods to be imaged in vivo while passing through blood vessels at subpicomolar concentrations. Furthermore, cells labeled with nanorods become highly susceptible to photothermal damage when irradiated at plasmon resonance, often resulting in a dramatic blebbing of the cell membrane. However, the straightforward application of gold nanorods for cell-specific labeling is obstructed by the presence of CTAB, a cationic surfactant carried over from nanorod synthesis which also promotes their nonspecific uptake into cells. Careful exchange and replacement of CTAB can be achieved by introducing oligoethyleneglycol (OEG) units capable of chemisorption onto nanorod surfaces by in situ dithiocarbamate formation, a novel method of surface functionalization. Nanorods with a dense coating of methyl-terminated OEG chains are shielded from nonspecific cell uptake, whereas nanorods functionalized with folate-terminated OEG chains accumulate on the surface of tumor cells overexpressing their cognate receptor, with subsequent delivery of photoinduced cell damage at low laser fluence.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Groetz, J.-E., E-mail: jegroetz@univ-fcomte.fr; Mavon, C.; Fromm, M.

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 airmore » 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.« less

Monte Carlo modeling of a conventional X-ray computed tomography scanner for gel dosimetry purposes.

PubMed

Hayati, Homa; Mesbahi, Asghar; Nazarpoor, Mahmood

2016-01-01

Our purpose in the current study was to model an X-ray CT scanner with the Monte Carlo (MC) method for gel dosimetry. In this study, a conventional CT scanner with one array detector was modeled with use of the MCNPX MC code. The MC calculated photon fluence in detector arrays was used for image reconstruction of a simple water phantom as well as polyacrylamide polymer gel (PAG) used for radiation therapy. Image reconstruction was performed with the filtered back-projection method with a Hann filter and the Spline interpolation method. Using MC results, we obtained the dose-response curve for images of irradiated gel at different absorbed doses. A spatial resolution of about 2 mm was found for our simulated MC model. The MC-based CT images of the PAG gel showed a reliable increase in the CT number with increasing absorbed dose for the studied gel. Also, our results showed that the current MC model of a CT scanner can be used for further studies on the parameters that influence the usability and reliability of results, such as the photon energy spectra and exposure techniques in X-ray CT gel dosimetry.

Measurements of high energy photons in Z-pinch experiments on primary test stand

NASA Astrophysics Data System (ADS)

Si, Fenni; Zhang, Chuanfei; Xu, Rongkun; Yuan, Xi; Huang, Zhanchang; Xu, Zeping; Ye, Fan; Yang, Jianlun; Ning, Jiamin; Hu, Qingyuan; Zhu, Xuebin

2015-08-01

High energy photons are measured for the first time in wire-array Z-pinch experiments on the Primary Test Stand (PTS) which delivers a current up to 8 MA with a rise time of 70 ns. A special designed detecting system composed of three types of detectors is used to measure the average energy, intensity, and pulse waveform of high energy photons. Results from Pb-TLD (thermoluminescence dosimeter) detector indicate that the average energy is 480 keV (±15%). Pulse shape of high energy photons is measured by the photodiode detector consisted of scintillator coupled with a photodiode, and it is correlated with soft x-ray power by the same timing signal. Intensity is measured by both TLD and the photodiode detector, showing good accordance with each other, and it is 1010 cm-2 (±20%) at 2 m in the horizontal direction. Measurement results show that high energy photons are mainly produced in pinch regions due to accelerated electrons. PTS itself also produces high energy photons due to power flow electrons, which is one order smaller in amplitude than those from pinch region.

Measurements of high energy photons in Z-pinch experiments on primary test stand.

PubMed

Si, Fenni; Zhang, Chuanfei; Xu, Rongkun; Yuan, Xi; Huang, Zhanchang; Xu, Zeping; Ye, Fan; Yang, Jianlun; Ning, Jiamin; Hu, Qingyuan; Zhu, Xuebin

2015-08-01

High energy photons are measured for the first time in wire-array Z-pinch experiments on the Primary Test Stand (PTS) which delivers a current up to 8 MA with a rise time of 70 ns. A special designed detecting system composed of three types of detectors is used to measure the average energy, intensity, and pulse waveform of high energy photons. Results from Pb-TLD (thermoluminescence dosimeter) detector indicate that the average energy is 480 keV (±15%). Pulse shape of high energy photons is measured by the photodiode detector consisted of scintillator coupled with a photodiode, and it is correlated with soft x-ray power by the same timing signal. Intensity is measured by both TLD and the photodiode detector, showing good accordance with each other, and it is 10(10) cm(-2) (±20%) at 2 m in the horizontal direction. Measurement results show that high energy photons are mainly produced in pinch regions due to accelerated electrons. PTS itself also produces high energy photons due to power flow electrons, which is one order smaller in amplitude than those from pinch region.

NE-213-scintillator-based neutron detection system for diagnostic measurements of energy spectra for neutrons having energies greater than or equal to 0. 8 MeV created during plasma operations at the Princeton Tokamak Fusion Test Reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dickens, J.K.; Hill, N.W.; Hou, F.S.

1985-08-01

A system for making diagnostic measurements of the energy spectra of greater than or equal to 0.8-MeV neutrons produced during plasma operations of the Princeton Tokamak Fusion Test Reactor (TFTR) has been fabricated and tested and is presently in operation in the TFTR Test Cell Basement. The system consists of two separate detectors, each made up of cells containing liquid NE-213 scintillator attached permanently to RCA-8850 photomultiplier tubes. Pulses obtained from each photomultiplier system are amplified and electronically analyzed to identify and separate those pulses due to neutron-induced events in the detector from those due to photon-induced events in themore » detector. Signals from each detector are routed to two separate Analog-to-Digital Converters, and the resulting digitized information, representing: (1) the raw neutron-spectrum data; and (2) the raw photon-spectrum data, are transmited to the CICADA data-acquisition computer system of the TFTR. Software programs have been installed on the CICADA system to analyze the raw data to provide moderate-resolution recreations of the energy spectrum of the neutron and photon fluences incident on the detector during the operation of the TFTR. A complete description of, as well as the operation of, the hardware and software is given in this report.« less

Synthesis, characterization and two-photon PDT efficacy studies of triads incorporating tumor targeting and imaging components

NASA Astrophysics Data System (ADS)

Spangler, C. W.; Starkey, J.; Rebane, A.; Drobizhev, M.; Meng, F.; Gong, A.

2008-02-01

Over the past three years we have described the rationale for using new photosensitizers (PS) with greatly enhanced multi-photon absorption. In particular, we have synthesized new porphyrin-based photosensitizers that also incorporate small molecule targeting agents that direct the ensemble to over-expressed tumor receptor sites, as well as Near-infrared imaging agents that will allow practical image-guided two-photon PDT in the tissue transparency window (750-1000 nm) at laser fluences that are harmless to surrounding healthy tissue. We have previously shown (PW2006) successful treatment of human breast cancer models (MDA-MB-231) in SCID mice, and have recently extended these studies to the treatment of both human small cell (SC) (NCI-H69) and non-small cell (NSC) (A-459) models in SCID mice. We have demonstrated that lung cancer xenografts can be successfully treated by irradiating from the side of the mouse opposite the implanted tumor, thereby passing through ca. 2 cm of mouse skin, tissue and organs before encountering the bulk tumor. These results suggest that this technology can be used to treat deep subcutaneous spontaneous tumors in larger animal models (e.g. canine). We would also emphasize that the synthetic route to these triads attaches the targeting moiety in the last step of the synthesis, and can be easily changed, thus allowing a myriad of targeting agents to be employed, opening the door to the possibility of patient-specific PDT.

Secondary neutron spectrum from 250-MeV passively scattered proton therapy: measurement with an extended-range Bonner sphere system.

PubMed

Howell, Rebecca M; Burgett, E A

2014-09-01

Secondary neutrons are an unavoidable consequence of proton therapy. While the neutron dose is low compared to the primary proton dose, its presence and contribution to the patient dose is nonetheless important. The most detailed information on neutrons includes an evaluation of the neutron spectrum. However, the vast majority of the literature that has reported secondary neutron spectra in proton therapy is based on computational methods rather than measurements. This is largely due to the inherent limitations in the majority of neutron detectors, which are either not suitable for spectral measurements or have limited response at energies greater than 20 MeV. Therefore, the primary objective of the present study was to measure a secondary neutron spectrum from a proton therapy beam using a spectrometer that is sensitive to neutron energies over the entire neutron energy spectrum. The authors measured the secondary neutron spectrum from a 250-MeV passively scattered proton beam in air at a distance of 100 cm laterally from isocenter using an extended-range Bonner sphere (ERBS) measurement system. Ambient dose equivalent H*(10) was calculated using measured fluence and fluence-to-ambient dose equivalent conversion coefficients. The neutron fluence spectrum had a high-energy direct neutron peak, an evaporation peak, a thermal peak, and an intermediate energy continuum between the thermal and evaporation peaks. The H*(10) was dominated by the neutrons in the evaporation peak because of both their high abundance and the large quality conversion coefficients in that energy interval. The H*(10) 100 cm laterally from isocenter was 1.6 mSv per proton Gy (to isocenter). Approximately 35% of the dose equivalent was from neutrons with energies ≥20 MeV. The authors measured a neutron spectrum for external neutrons generated by a 250-MeV proton beam using an ERBS measurement system that was sensitive to neutrons over the entire energy range being measured, i.e., thermal to 250 MeV. The authors used the neutron fluence spectrum to demonstrate experimentally the contribution of neutrons with different energies to the total dose equivalent and in particular the contribution of high-energy neutrons (≥20 MeV). These are valuable reference data that can be directly compared with Monte Carlo and experimental data in the literature.

Secondary neutron spectrum from 250-MeV passively scattered proton therapy: Measurement with an extended-range Bonner sphere system

PubMed Central

Howell, Rebecca M.; Burgett, E. A.

2014-01-01

Purpose: Secondary neutrons are an unavoidable consequence of proton therapy. While the neutron dose is low compared to the primary proton dose, its presence and contribution to the patient dose is nonetheless important. The most detailed information on neutrons includes an evaluation of the neutron spectrum. However, the vast majority of the literature that has reported secondary neutron spectra in proton therapy is based on computational methods rather than measurements. This is largely due to the inherent limitations in the majority of neutron detectors, which are either not suitable for spectral measurements or have limited response at energies greater than 20 MeV. Therefore, the primary objective of the present study was to measure a secondary neutron spectrum from a proton therapy beam using a spectrometer that is sensitive to neutron energies over the entire neutron energy spectrum. Methods: The authors measured the secondary neutron spectrum from a 250-MeV passively scattered proton beam in air at a distance of 100 cm laterally from isocenter using an extended-range Bonner sphere (ERBS) measurement system. Ambient dose equivalent H*(10) was calculated using measured fluence and fluence-to-ambient dose equivalent conversion coefficients. Results: The neutron fluence spectrum had a high-energy direct neutron peak, an evaporation peak, a thermal peak, and an intermediate energy continuum between the thermal and evaporation peaks. The H*(10) was dominated by the neutrons in the evaporation peak because of both their high abundance and the large quality conversion coefficients in that energy interval. The H*(10) 100 cm laterally from isocenter was 1.6 mSv per proton Gy (to isocenter). Approximately 35% of the dose equivalent was from neutrons with energies ≥20 MeV. Conclusions: The authors measured a neutron spectrum for external neutrons generated by a 250-MeV proton beam using an ERBS measurement system that was sensitive to neutrons over the entire energy range being measured, i.e., thermal to 250 MeV. The authors used the neutron fluence spectrum to demonstrate experimentally the contribution of neutrons with different energies to the total dose equivalent and in particular the contribution of high-energy neutrons (≥20 MeV). These are valuable reference data that can be directly compared with Monte Carlo and experimental data in the literature. PMID:25186404

Atomistic three-dimensional coherent x-ray imaging of nonbiological systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ho, Phay J.; Knight, Chris; Tegze, Miklos

We computationally study the resolution limits for three-dimensional coherent x-ray diffractive imaging of heavy, nonbiological systems using Ar clusters as a prototype. We treat electronic and nuclear dynamics on an equal footing and remove the frozen-lattice approximation often used in electronic damage studies. We explore the achievable resolution as a function of pulse parameters (fluence level, pulse duration, and photon energy) and particle size. The contribution of combined lattice and electron dynamics is not negligible even for 2 fs pulses, and the Compton scattering is less deleterious than in biological systems for atomic-scale imaging. Although free-electron scattering represents a significantmore » background, we find that recovery of the original structure is in principle possible with 3 angstrom resolution for particles of 11 nm diameter.« less

Atomistic three-dimensional coherent x-ray imaging of nonbiological systems

DOE PAGES

Ho, Phay J.; Knight, Chris; Tegze, Miklos; ...

2016-12-12

We computationally study the resolution limits for three-dimensional coherent x-ray diffractive imaging of heavy, nonbiological systems using Ar clusters as a prototype. We treat electronic and nuclear dynamics on an equal footing and remove the frozen-lattice approximation often used in electronic damage studies. We explore the achievable resolution as a function of pulse parameters (fluence level, pulse duration, and photon energy) and particle size. The contribution of combined lattice and electron dynamics is not negligible even for 2 fs pulses, and the Compton scattering is less deleterious than in biological systems for atomic-scale imaging. Although free-electron scattering represents a significantmore » background, we find that recovery of the original structure is in principle possible with 3 angstrom resolution for particles of 11 nm diameter.« less

Permanent fine tuning of silicon microring devices by femtosecond laser surface amorphization and ablation.

PubMed

Bachman, Daniel; Chen, Zhijiang; Fedosejevs, Robert; Tsui, Ying Y; Van, Vien

2013-05-06

We demonstrate the fine tuning capability of femtosecond laser surface modification as a permanent trimming mechanism for silicon photonic components. Silicon microring resonators with a 15 µm radius were irradiated with single 400 nm wavelength laser pulses at varying fluences. Below the laser ablation threshold, surface amorphization of the crystalline silicon waveguides yielded a tuning rate of 20 ± 2 nm/J · cm(-2)with a minimum resonance wavelength shift of 0.10nm. Above that threshold, ablation yielded a minimum resonance shift of -1.7 nm. There was some increase in waveguide loss for both trimming mechanisms. We also demonstrated the application of the method by using it to permanently correct the resonance mismatch of a second-order microring filter.

Population inversion in monolayer and bilayer graphene

NASA Astrophysics Data System (ADS)

Gierz, Isabella; Mitrano, Matteo; Petersen, Jesse C.; Cacho, Cephise; Turcu, I. C. Edmond; Springate, Emma; Stöhr, Alexander; Köhler, Axel; Starke, Ulrich; Cavalleri, Andrea

2015-04-01

The recent demonstration of saturable absorption and negative optical conductivity in the Terahertz range in graphene has opened up new opportunities for optoelectronic applications based on this and other low dimensional materials. Recently, population inversion across the Dirac point has been observed directly by time- and angle-resolved photoemission spectroscopy (tr-ARPES), revealing a relaxation time of only ∼130 femtoseconds. This severely limits the applicability of single layer graphene to, for example, Terahertz light amplification. Here we use tr-ARPES to demonstrate long-lived population inversion in bilayer graphene. The effect is attributed to the small band gap found in this compound. We propose a microscopic model for these observations and speculate that an enhancement of both the pump photon energy and the pump fluence may further increase this lifetime.

SU-E-T-439: An Improved Formula of Scatter-To-Primary Ratio for Photon Dose Calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, T

2014-06-01

Purpose: Scatter-to-primary ratio (SPR) is an important dosimetric quantity that describes the contribution from the scatter photons in an external photon beam. The purpose of this study is to develop an improved analytical formula to describe SPR as a function of circular field size (r) and depth (d) using Monte Carlo (MC) simulation. Methods: MC simulation was performed for Mohan photon spectra (Co-60, 4, 6, 10, 15, 23 MV) using EGSNRC code. Point-spread scatter dose kernels in water are generated. The scatter-to-primary ratio (SPR) is also calculated using MC simulation as a function of field size for circular field sizemore » with radius r and depth d. The doses from forward scatter and backscatter photons are calculated using a convolution of the point-spread scatter dose kernel and by accounting for scatter photons contributing to dose before (z'd) reaching the depth of interest, d, where z' is the location of scatter photons, respectively. The depth dependence of the ratio of the forward scatter and backscatter doses is determined as a function of depth and field size. Results: We are able to improve the existing 3-parameter (a, w, d0) empirical formula for SPR by introducing depth dependence for one of the parameter d0, which becomes 0 for deeper depths. The depth dependence of d0 can be directly calculated as a ratio of backscatter-to-forward scatter doses for otherwise the same field and depth. With the improved empirical formula, we can fit SPR for all megavoltage photon beams to within 2%. Existing 3-parameter formula cannot fit SPR data for Co-60 to better than 3.1%. Conclusion: An improved empirical formula is developed to fit SPR for all megavoltage photon energies to within 2%.« less

On-Site Determination and Monitoring of Real-Time Fluence Delivery for an Operating UV Reactor Based on a True Fluence Rate Detector.

PubMed

Li, Mengkai; Li, Wentao; Qiang, Zhimin; Blatchley, Ernest R

2017-07-18

At present, on-site fluence (distribution) determination and monitoring of an operating UV system represent a considerable challenge. The recently developed microfluorescent silica detector (MFSD) is able to measure the approximate true fluence rate (FR) at a fixed position in a UV reactor that can be compared with a FR model directly. Hence it has provided a connection between model calculation and real-time fluence determination. In this study, an on-site determination and monitoring method of fluence delivery for an operating UV reactor was developed. True FR detectors, a UV transmittance (UVT) meter, and a flow rate meter were used for fundamental measurements. The fluence distribution, as well as reduction equivalent fluence (REF), 10th percentile dose in the UV fluence distribution (F 10 ), minimum fluence (F min ), and mean fluence (F mean ) of a test reactor, was calculated in advance by the combined use of computational fluid dynamics and FR field modeling. A field test was carried out on the test reactor for disinfection of a secondary water supply. The estimated real-time REF, F 10 , F min , and F mean decreased 73.6%, 71.4%, 69.6%, and 72.9%, respectively, during a 6-month period, which was attributable to lamp output attenuation and sleeve fouling. The results were analyzed with synchronous data from a previously developed triparameter UV monitoring system and water temperature sensor. This study allowed demonstration of an accurate method for on-site, real-time fluence determination which could be used to enhance the security and public confidence of UV-based water treatment processes.

Photon sieve telescope

NASA Astrophysics Data System (ADS)

Andersen, Geoff; Tullson, Drew

2006-06-01

In designing next-generation, ultra-large (>20m) apertures for space, many current concepts involve compactable, curved membrane reflectors. Here we present the idea of using a flat diffractive element that requires no out-of-plane deformation and so is much simpler to deploy. The primary is a photon sieve - a diffractive element consisting of a large number of precisely positioned holes distributed according to an underlying Fresnel Zone Plate (FZP) geometry. The advantage of the photon sieve over the FZP is that all the regions are connected, so the membrane substrate under simple tension can avoid buckling. Also, the hole distribution can be varied to generate any conic or apodization for specialized telescope requirements such as exo-solar planet detection. We have designed and tested numerous photon sieves as telescope primaries. Some of these have over 10 million holes in a 0.1 m diameter aperture and all of them give diffraction limited imaging. While photon sieves are diffractive elements and thus suffer from dispersion, we will present two successful solutions to this problem.

Radiation damage studies of soft magnetic metallic glasses irradiated with high-energy heavy ions

NASA Astrophysics Data System (ADS)

Pavlovič, Márius; Miglierini, Marcel; Mustafin, Edil; Ensinger, Wolfgang; Šagátová, Andrea; Šoka, Martin

2015-01-01

Some soft magnetic metallic glasses are considered for use in magnetic cores of accelerator radio frequency cavities. Due to losses of the circulating ion beam, they may be exposed to irradiation by different ions at different energies. This paper presents data and review results of irradiation experiments concerning the influence of high-energy heavy ions on magnetic susceptibility of VITROPERM®-type metallic glasses. Samples of the VITROPERM® magnetic ribbons were irradiated by Au, Xe and U ions at 11.1 MeV/A (per nucleon) and 5.9 MeV/A, respectively. Irradiation fluences from 1 × 1011 up to 1 × 1013 ions/cm2 were applied. In case of the Au and U ions, the total fluence was accumulated in one beamtime, whereas two separate beamtimes were used to accumulate the final fluence in case of the Xe ions. Relative change in the samples' magnetic susceptibility after and before irradiation was evaluated as a function of the irradiation fluence. The irradiation experiments were performed with the UNILAC accelerator at GSI Helmholtzzentrum für Schwerionenforschung GmbH. They were simulated in SRIM2010 in order to obtain ionization densities (electronic stopping, dE/dx) and dpa (displacements per atom) caused by the ion beams in the sample material. This paper focuses mainly on the results collected in experiments with the Xe ions and compares them with data obtained in earlier experiments using Au and U ions. Radiation hardness of VITROPERM® is compared with radiation hardness of VITROVAC® that was studied in previous experiments. The VITROPERM® samples showed less drop in magnetic susceptibility in comparison with the VITROVAC® ones, and this drop occurred at higher fluences. This indicates higher radiation hardness of VITROPERM® compared with VITROVAC®. In addition, heavier ions cause bigger change in magnetic susceptibility than the lighter ones. The effect can be roughly scaled with electronic stopping, which suggests that the main mechanism of radiation damage is associated with swift electrons generated in the material via ionization by primary heavy ions.

Validation of a method for in vivo 3D dose reconstruction for IMRT and VMAT treatments using on-treatment EPID images and a model-based forward-calculation algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Uytven, Eric, E-mail: eric.vanuytven@cancercare.mb.ca; Van Beek, Timothy; McCowan, Peter M.

2015-12-15

Purpose: Radiation treatments are trending toward delivering higher doses per fraction under stereotactic radiosurgery and hypofractionated treatment regimens. There is a need for accurate 3D in vivo patient dose verification using electronic portal imaging device (EPID) measurements. This work presents a model-based technique to compute full three-dimensional patient dose reconstructed from on-treatment EPID portal images (i.e., transmission images). Methods: EPID dose is converted to incident fluence entering the patient using a series of steps which include converting measured EPID dose to fluence at the detector plane and then back-projecting the primary source component of the EPID fluence upstream of themore » patient. Incident fluence is then recombined with predicted extra-focal fluence and used to calculate 3D patient dose via a collapsed-cone convolution method. This method is implemented in an iterative manner, although in practice it provides accurate results in a single iteration. The robustness of the dose reconstruction technique is demonstrated with several simple slab phantom and nine anthropomorphic phantom cases. Prostate, head and neck, and lung treatments are all included as well as a range of delivery techniques including VMAT and dynamic intensity modulated radiation therapy (IMRT). Results: Results indicate that the patient dose reconstruction algorithm compares well with treatment planning system computed doses for controlled test situations. For simple phantom and square field tests, agreement was excellent with a 2%/2 mm 3D chi pass rate ≥98.9%. On anthropomorphic phantoms, the 2%/2 mm 3D chi pass rates ranged from 79.9% to 99.9% in the planning target volume (PTV) region and 96.5% to 100% in the low dose region (>20% of prescription, excluding PTV and skin build-up region). Conclusions: An algorithm to reconstruct delivered patient 3D doses from EPID exit dosimetry measurements was presented. The method was applied to phantom and patient data sets, as well as for dynamic IMRT and VMAT delivery techniques. Results indicate that the EPID dose reconstruction algorithm presented in this work is suitable for clinical implementation.« less

Light parameters influence cell viability in antifungal photodynamic therapy in a fluence and rate fluence-dependent manner

NASA Astrophysics Data System (ADS)

Prates, Renato A.; da Silva, Eriques G.; Yamada, Aécio M.; Suzuki, Luis C.; Paula, Claudete R.; Ribeiro, Martha S.

2009-05-01

The aim of this study was to investigate the influence of light parameters on yeast cells. It has been proposed for many years that photodynamic therapy (PDT) can inactivate microbial cells. A number of photosensitizer and light sources were reported in different light parameters and in a range of dye concentrations. However, much more knowledge concerning the importance of fluence, fluence rate and exposure time are required for a better understanding of the photodynamic efficiency. Suspensions (106 CFU/mL) of Candida albicans, Candida krusei, and Cryptococcus neoformans var. grubii were used. Two fluence rates, 100 and 300 mW/cm2 were compared at 3, 6, and 9 min of irradiation, resulting fluences from 18 to 162 J/cm2. The light source was a laser emitting at λ = 660 nm with output power adjusted at 30 and 90 mW. As photosensitizer, one hundred-μM methylene blue was used. Temperature was monitored to verify possible heat effect and reactive oxygen species (ROS) formation was evaluated. The same fluence in different fluence rates showed dissimilar levels of inactivation on yeast cells as well as in ROS formation. In addition, the increase of the fluence rate showed an improvement on cell photoinactivation. PDT was efficient against yeast cells (6 log reduction), and no significant temperature increase was observed. Fluence per se should not be used as an isolate parameter to compare photoinactivation effects on yeast cells. The higher fluence rate was more effective than the lower one. Furthermore, an adequate duration of light exposure cannot be discarded.

Bowtie filters for dedicated breast CT: Analysis of bowtie filter material selection.

PubMed

Kontson, Kimberly; Jennings, Robert J

2015-09-01

For a given bowtie filter design, both the selection of material and the physical design control the energy fluence, and consequently the dose distribution, in the object. Using three previously described bowtie filter designs, the goal of this work is to demonstrate the effect that different materials have on the bowtie filter performance measures. Three bowtie filter designs that compensate for one or more aspects of the beam-modifying effects due to the differences in path length in a projection have been designed. The nature of the designs allows for their realization using a variety of materials. The designs were based on a phantom, 14 cm in diameter, composed of 40% fibroglandular and 60% adipose tissue. Bowtie design #1 is based on single material spectral matching and produces nearly uniform spectral shape for radiation incident upon the detector. Bowtie design #2 uses the idea of basis-material decomposition to produce the same spectral shape and intensity at the detector, using two different materials. With bowtie design #3, it is possible to eliminate the beam hardening effect in the reconstructed image by adjusting the bowtie filter thickness so that the effective attenuation coefficient for every ray is the same. Seven different materials were chosen to represent a range of chemical compositions and densities. After calculation of construction parameters for each bowtie filter design, a bowtie filter was created using each of these materials (assuming reasonable construction parameters were obtained), resulting in a total of 26 bowtie filters modeled analytically and in the penelope Monte Carlo simulation environment. Using the analytical model of each bowtie filter, design profiles were obtained and energy fluence as a function of fan-angle was calculated. Projection images with and without each bowtie filter design were also generated using penelope and reconstructed using FBP. Parameters such as dose distribution, noise uniformity, and scatter were investigated. Analytical calculations with and without each bowtie filter show that some materials for a given design produce bowtie filters that are too large for implementation in breast CT scanners or too small to accurately manufacture. Results also demonstrate the ability to manipulate the energy fluence distribution (dynamic range) by using different materials, or different combinations of materials, for a given bowtie filter design. This feature is especially advantageous when using photon counting detector technology. Monte Carlo simulation results from penelope show that all studied material choices for bowtie design #2 achieve nearly uniform dose distribution, noise uniformity index less than 5%, and nearly uniform scatter-to-primary ratio. These same features can also be obtained using certain materials with bowtie designs #1 and #3. With the three bowtie filter designs used in this work, the selection of material is an important design consideration. An appropriate material choice can improve image quality, dose uniformity, and dynamic range.

Bowtie filters for dedicated breast CT: Analysis of bowtie filter material selection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kontson, Kimberly, E-mail: Kimberly.Kontson@fda.hhs.gov; Jennings, Robert J.

Purpose: For a given bowtie filter design, both the selection of material and the physical design control the energy fluence, and consequently the dose distribution, in the object. Using three previously described bowtie filter designs, the goal of this work is to demonstrate the effect that different materials have on the bowtie filter performance measures. Methods: Three bowtie filter designs that compensate for one or more aspects of the beam-modifying effects due to the differences in path length in a projection have been designed. The nature of the designs allows for their realization using a variety of materials. The designsmore » were based on a phantom, 14 cm in diameter, composed of 40% fibroglandular and 60% adipose tissue. Bowtie design #1 is based on single material spectral matching and produces nearly uniform spectral shape for radiation incident upon the detector. Bowtie design #2 uses the idea of basis-material decomposition to produce the same spectral shape and intensity at the detector, using two different materials. With bowtie design #3, it is possible to eliminate the beam hardening effect in the reconstructed image by adjusting the bowtie filter thickness so that the effective attenuation coefficient for every ray is the same. Seven different materials were chosen to represent a range of chemical compositions and densities. After calculation of construction parameters for each bowtie filter design, a bowtie filter was created using each of these materials (assuming reasonable construction parameters were obtained), resulting in a total of 26 bowtie filters modeled analytically and in the PENELOPE Monte Carlo simulation environment. Using the analytical model of each bowtie filter, design profiles were obtained and energy fluence as a function of fan-angle was calculated. Projection images with and without each bowtie filter design were also generated using PENELOPE and reconstructed using FBP. Parameters such as dose distribution, noise uniformity, and scatter were investigated. Results: Analytical calculations with and without each bowtie filter show that some materials for a given design produce bowtie filters that are too large for implementation in breast CT scanners or too small to accurately manufacture. Results also demonstrate the ability to manipulate the energy fluence distribution (dynamic range) by using different materials, or different combinations of materials, for a given bowtie filter design. This feature is especially advantageous when using photon counting detector technology. Monte Carlo simulation results from PENELOPE show that all studied material choices for bowtie design #2 achieve nearly uniform dose distribution, noise uniformity index less than 5%, and nearly uniform scatter-to-primary ratio. These same features can also be obtained using certain materials with bowtie designs #1 and #3. Conclusions: With the three bowtie filter designs used in this work, the selection of material is an important design consideration. An appropriate material choice can improve image quality, dose uniformity, and dynamic range.« less

SU-F-T-425: Head-Scatter Off-Axis for FFF Megavoltage Photon Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, T; Penjweini, R; Dimofte, A

Purpose: Head-scatter photons inside a clinical accelerator cause the output to change with collimator setting. On the central-axis, this contribution is well-described by output factor in air (or head-scatter factor). However, a few studies have examined this component at off-axis points. Methods: We define the head-scatter off-axis ratio, HOA, as the ratio of the water kerma in air due to head-scatter photons at the off-axis position x to the water kerma from direct primary photons on the central axis: HOA(cx,cy,xy) = (Q(cx,cy,x) – QP(cx,cy,x))/QP(cx,cy,0), where Q(cx, cy,x), QP(cx,cy,x) are charges measured by an ionization chamber in a miniphantom for collimatormore » setting cx × cy and cx × 3 cm, respectively, at off-axis point x. “Direct primary” is those photons that come from the source without interactions in the intervening structures. Results: We measured HOA for two energies (6XFFF and 6X) along X and Y jaw directions for various collimator settings. The shape of HOA has well defined penumbra for collimator setting larger than 10 × 10 cm2. Conclusion: The narrow gaussian component is interpreted as the source of photons scattered in the flattening filter and the primary collimator. The broad component is attributed to photons scattered in the secondary (variable) collimators. By a direct comparison between 6X and 6XFFF beams, we can confirm that the second component is indeed coming from collimator jaws and identify the parts coming from the primary collimator and the flattening filter, respectively.« less

Comparison of anisotropic aperture based intensity modulated radiotherapy with 3D-conformal radiotherapy for the treatment of large lung tumors.

PubMed

Simeonova, Anna; Abo-Madyan, Yasser; El-Haddad, Mostafa; Welzel, Grit; Polednik, Martin; Boggula, Ramesh; Wenz, Frederik; Lohr, Frank

2012-02-01

IMRT allows dose escalation for large lung tumors, but respiratory motion may compromise delivery. A treatment plan that modulates fluence predominantly in the transversal direction and leaves the fluence identical in the direction of the breathing motion may reduce this problem. Planning-CT-datasets of 20 patients with Stage I-IV non small cell lung cancer (NSCLC) formed the basis of this study. A total of two IMRT plans and one 3D plan were created for each patient. Prescription dose was 60 Gy to the CTV and 70 Gy to the GTV. For the 3D plans an energy of 18 MV photons was used. IMRT plans were calculated for 6 MV photons with 13 coplanar and with 17 noncoplanar beams. Robustness of the used method of anisotropic modulation toward breathing motion was tested in a 13-field IMRT plan. As a consequence of identical prescription doses, mean target doses were similar for 3D and IMRT. Differences between 3D and 13- and 17-field IMRT were significant for CTV Dmin (43 Gy vs. 49.1 Gy vs. 48.6 Gy; p<0.001) and CTV D(95) (53.2 Gy vs. 55.0 Gy vs. 55.4 Gy; p=0.001). The D(mean) of the contralateral lung was significantly lower in the 17-field plans (17-field IMRT vs. 13- vs. 3D: 12.5 Gy vs. 14.8 Gy vs. 15.8 Gy: p<0.05). The spinal cord dose limit of 50 Gy was always respected in IMRT plans and only in 17 of 20 3D-plans. Heart D(max) was only marginally reduced with IMRT (3D vs. 13- vs. 17-field IMRT: 38.2 Gy vs. 36.8 Gy vs. 37.8 Gy). Simulated breathing motion caused only minor changes in the IMRT dose distribution (~0.5-1 Gy). Anisotropic modulation of IMRT improves dose delivery over 3D-RT and renders IMRT plans robust toward breathing induced organ motion, effectively preventing interplay effects. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

Proton NMR spectral study of UV treated live Escherichia coli Bacteria

NASA Astrophysics Data System (ADS)

Sorokopud, Michael

The lethal effects of ultraviolet radiation on microorganisms have been known and utilized for many years. In sufficiently high photon fluences, light and in particular, UV light, is an effective and subtle means of killing or at least immobilizing most, if not all cells and micro-organisms. Because of their small size, light can penetrate the enclosing protective walls and enter the inner volumes where it can break organic bonds in components that are vital to cell function. Despite the fact that a very low dose of UV light (1-9 mJ/cm2) has been shown to inactivate many micro-organisms, there remains a dearth of biological information about light induced effects in molecules and their interactions within living microbial systems. The use of 1H NMR as a spectroscopic tool was chosen to undertake an examination of the possible effects resulting from exposing E. coli to lethal fluencies of UV radiation. Once sample preparation, treatment, and NMR mounting methods were optimized, the high sensitivity and high resolution capabilities of the method produced reproducible results for a series of experiments. These results reveal significant changes in the ratio of the 1H NMR spectra of the treated to untreated E.coli samples when the treated sample was exposed to a lethal fluence of 275nm light. Photons at the 275nm wavelength, used in this study, have enough energy to break all of the principle bonds in an organic molecule. The difference spectrum between treated to untreated samples appears to be fitted well using specific component spectra from these groups of compounds. Increases in NMR peak amplitudes are observed and appear to be correlated with the spectral locations of several amino acids, membrane components and several sugars/saccharides. Increases in peak intensities of 4-8% were observed in the 0.8-1.1 ppm chemical shift region, characteristic of lipid and amino acid groups. A 3.5-4% increase was observed in the 2 ppm and 3.4-4 ppm region characteristic of various sugars and possibly amino acid components.

Dependence of the phototropic response of Arabidopsis thaliana on fluence rate and wavelength

DOE Office of Scientific and Technical Information (OSTI.GOV)

Konjevic, R.; Steinitz, B.; Poff, K.L.

1989-12-01

In the phototropic response of Arabidopsis thaliana seedlings, the shape of the fluence-response relation depends on fluence rate and wavelength. At low fluence rates, the response to 450-nm light is characterized by a single maximum at about 0.3 {mu}mol{center dot}m{sup {minus}2}. At higher fluence rates, the response shows two distinct maxima, I and II, at 0.3 and 3.5 {mu}mol{center dot}m{sup {minus}2}, respectively. The response to 500-nm light shows a single maximum at 2 {mu}mol{center dot}m{sup {minus}2}, and the response to 510-nm light shows a single maximum at 4.5 {mu}mol{center dot}m{sup {minus}2}, independent of fluence rate. The response to 490-nm lightmore » shows a maximal at 4.5 {mu}mol{center dot}m{sup {minus}2} and a shoulder at about 0.6 {mu}mol{center dot}m{sup {minus}2}. Preirradiation with high-fluence 510-nm light from above, immediately followed by unilateral 450-nm light, eliminates maximum II but not maximum I. Preirradiation with high-fluence 450-nm light from above eliminates the response to subsequent unilateral irradiation with either 450-nm or 510-nm light. The recovery of the response following high-fluence 450-nm light is considerably slower than the recovery following high-fluence 510-nm light. Unilateral irradiation with low-fluence 510-nm light followed by 450-nm light results in curvature that is approximately the sum of those produced by either irradiation alone. Based on these results, it is proposed that phototropism in A. thaliana seedlings is mediated by at least two blue-light photoreceptor pigments.« less

Comprehensive studies of ultrashort laser pulse ablation of tin target at terawatt power

NASA Astrophysics Data System (ADS)

Elsied, Ahmed M.; Diwakar, Prasoon K.; Hassanein, Ahmed

2018-01-01

The fundamental properties of ultrashort laser interactions with metals using up to terawatt power were comprehensively studied, i.e., specifically mass ablation, nanoparticle formation, and ion dynamics using multitude of diagnostic techniques. Results of this study can be useful in many fields of research including spectroscopy, micromachining, thin film fabrication, particle acceleration, physics of warm dense matter, and equation-of-state determination. A Ti:Sapphire femtosecond laser system (110 mJ maximum energy, 40 fs, 800 nm, P-polarized, single pulse mode) was used, which delivered up to 3 terawatt laser power to ablate 1 mm tin film in vacuum. The experimental analysis includes the effect of the incident laser fluence on the ablated mass, size of the ablated area, and depth of ablation using white light profilometer. Atomic force microscope was used to measure the emitted particles size distribution at different laser fluence. Faraday cup (FC) detector was used to analyze the emitted ions flux by measuring the velocity, and the total charge of the emitted ions. The study shows that the size of emitted particles follows log-normal distribution with peak shifts depending on incident laser fluence. The size of the ablated particles ranges from 20 to 80 nm. The nanoparticles deposited on the wafer tend to aggregate and to be denser as the incident laser fluence increases as shown by AFM images. Laser ablation depth was found to increase logarithmically with laser fluence then leveling off at laser fluence > 400 J/cm2. The total ablated mass tends to increase logarithmically with laser fluence up to 60 J/cm2 while, increases gradually at higher fluence due to the increase in the ablated area. The measured ion emitted flux shows a linear dependence on laser fluence with two distinct regimes. Strong dependence on laser fluence was observed at fluences < 350 J/cm2. Also, a slight enhancement in ion velocity was observed with increasing laser fluence up to 350 J/cm2.

Proton Particle Test Fluence: What's the Right Number?

NASA Technical Reports Server (NTRS)

LaBel, Kenneth A.; Ladbury, Raymond

2015-01-01

While we have been utilizing standard fluence levels such as those listed in the JESD57 document, we have begun revisiting what an appropriate test fluence is when it comes to qualifying a device for single events. Instead of a fixed fluence level or until a specific number of events occurs, a different thought process is required.

Particle Test Fluence: What's the Right Number?

NASA Technical Reports Server (NTRS)

LaBel, Kenneth A.

2014-01-01

While we have been utilizing standard fluence levels such as those listed in the JESD57 document, we have begun revisiting what an appropriate test fluence is when it comes to qualifying a device for single events. Instead of a fixed fluence level or until a specific number of events occurs, a different thought process is required.

Experimental Overview of Direct Photon Results in Heavy Ion Collisions

NASA Astrophysics Data System (ADS)

Novitzky, Norbert

2016-07-01

Direct photons are color blind probes and thus they provide unique opportunities to study the colored medium created in heavy ion collisions. There are many different sources of direct photons each probing different physics processes as the system evolves. In basic 2 → 2 processes the prompt photons from primary hard scatterings offer the most precise measurements of the outgoing parton energy in the opposite direction. In heavy ion collisions the created medium emits photons as thermal radiation, whose rate and anisotropies provide a unique prospective on the properties and evolution of the system. Recent results on direct photons from the LHC and RHIC experiments are briefly summarized in this paper.

Fγ: A new observable for photon-hadron discrimination in hybrid air shower events

NASA Astrophysics Data System (ADS)

Niechciol, M.; Risse, M.; Ruehl, P.; Settimo, M.; Younk, P. W.; Yushkov, A.

2018-01-01

To search for ultra-high-energy photons in primary cosmic rays, air shower observables are needed that allow a good separation between primary photons and primary hadrons. We present a new observable, Fγ, which can be extracted from ground-array data in hybrid events, where simultaneous measurements of the longitudinal and the lateral shower profile are performed. The observable is based on a template fit to the lateral distribution measured by the ground array with the template taking into account the complementary information from the measurement of the longitudinal profile, i.e. the primary energy and the geometry of the shower. Fγ shows a very good photon-hadron separation, which is even superior to the separation given by the well-known Xmax observable (the atmospheric depth of the shower maximum). At energies around 1 EeV (10 EeV), Fγ provides a background rejection better than 97.8 % (99.9 %) at a signal efficiency of 50 %. Advantages of the observable Fγ are its technical stability with respect to irregularities in the ground array (i.e. missing or temporarily non-operating stations) and that it can be applied over the full energy range accessible to the air shower detector, down to its threshold energy. Furthermore, Fγ complements nicely to Xmax such that both observables can well be combined to achieve an even better discrimination power, exploiting the rich information available in hybrid events.

Sacral chordomas: Impact of high-dose proton/photon-beam radiation therapy combined with or without surgery for primary versus recurrent tumor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Lily; De Laney, Thomas F.; Liebsch, Norbert J.

2006-08-01

Purpose: To assess the efficacy of definitive treatment of sacral chordoma by high-dose proton/photon-beam radiation therapy alone or combined with surgery. Methods and Materials: The records of 16 primary and 11 recurrent sacral chordoma patients treated from November 1982 to November 2002 by proton/photon radiation therapy alone (6 patients) or combined with surgery (21 patients) have been analyzed for local control, survival, and treatment-related morbidity. The outcome analysis is based on follow-up information as of 2005. Results: Outcome results show a large difference in local failure rate between patients treated for primary and recurrent chordomas. Local control results by surgerymore » and radiation were 12/14 vs. 1/7 for primary and recurrent lesions. For margin-positive patients, local control results were 10 of 11 and 0 of 5 in the primary and recurrent groups, respectively; the mean follow-up on these locally controlled patients was 8.8 years (4 at 10.3, 12.8, 17, and 21 years). Radiation alone was used in 6 patients, 4 of whom received {>=}73.0 Gy (E); local control was observed in 3 of these 4 patients for 2.9, 4.9, and 7.6 years. Conclusion: These data indicate a high local control rate for surgical and radiation treatment of primary (12 of 14) as distinct from recurrent (1 of 7) sacral chordomas. Three of 4 chordomas treated by {>=}73.0 Gy (E) of radiation alone had local control; 1 is at 91 months. This indicates that high-dose proton/photon therapy offers an effective treatment option.« less

Enhanced dielectric-wall linear accelerator

DOEpatents

Sampayan, S.E.; Caporaso, G.J.; Kirbie, H.C.

1998-09-22

A dielectric-wall linear accelerator is enhanced by a high-voltage, fast e-time switch that includes a pair of electrodes between which are laminated alternating layers of isolated conductors and insulators. A high voltage is placed between the electrodes sufficient to stress the voltage breakdown of the insulator on command. A light trigger, such as a laser, is focused along at least one line along the edge surface of the laminated alternating layers of isolated conductors and insulators extending between the electrodes. The laser is energized to initiate a surface breakdown by a fluence of photons, thus causing the electrical switch to close very promptly. Such insulators and lasers are incorporated in a dielectric wall linear accelerator with Blumlein modules, and phasing is controlled by adjusting the length of fiber optic cables that carry the laser light to the insulator surface. 6 figs.

Enhanced dielectric-wall linear accelerator

DOEpatents

Sampayan, Stephen E.; Caporaso, George J.; Kirbie, Hugh C.

1998-01-01

A dielectric-wall linear accelerator is enhanced by a high-voltage, fast e-time switch that includes a pair of electrodes between which are laminated alternating layers of isolated conductors and insulators. A high voltage is placed between the electrodes sufficient to stress the voltage breakdown of the insulator on command. A light trigger, such as a laser, is focused along at least one line along the edge surface of the laminated alternating layers of isolated conductors and insulators extending between the electrodes. The laser is energized to initiate a surface breakdown by a fluence of photons, thus causing the electrical switch to close very promptly. Such insulators and lasers are incorporated in a dielectric wall linear accelerator with Blumlein modules, and phasing is controlled by adjusting the length of fiber optic cables that carry the laser light to the insulator surface.

Vacuum-surface flashover switch with cantilever conductors

DOEpatents

Caporaso, George J.; Sampayan, Stephen E.; Kirbie, Hugh C.

2001-01-01

A dielectric-wall linear accelerator is improved by a high-voltage, fast rise-time switch that includes a pair of electrodes between which are laminated alternating layers of isolated conductors and insulators. A high voltage is placed between the electrodes sufficient to stress the voltage breakdown of the insulator on command. A light trigger, such as a laser, is focused along at least one line along the edge surface of the laminated alternating layers of isolated conductors and insulators extending between the electrodes. The laser is energized to initiate a surface breakdown by a fluence of photons, thus causing the electrical switch to close very promptly. Such insulators and lasers are incorporated in a dielectric wall linear accelerator with Blumlein modules, and phasing is controlled by adjusting the length of fiber optic cables that carry the laser light to the insulator surface.

Enhanced nonlinear optical responses in donor-acceptor ionic complexes via photo induced energy transfer.

PubMed

Mamidala, Venkatesh; Polavarapu, Lakshminarayana; Balapanuru, Janardhan; Loh, Kian Ping; Xu, Qing-Hua; Ji, Wei

2010-12-06

By complexion of donor and acceptor using ionic interactions, the enhanced nonlinear optical responses of donor-acceptor ionic complexes in aqueous solution were studied with 7-ns laser pulses at 532 nm. The optical limiting performance of negatively charged gold nanoparticles or graphene oxide (Acceptor) was shown to be improved significantly when they were mixed with water-soluble, positively-charged porphyrin (Donor) derivative. In contrast, no enhancement was observed when mixing with negatively-charged porphyrin. Transient absorption studies of the donor-acceptor complexes confirmed that the addition of energy transfer pathway were responsible for excited-state deactivation, which results in the observed enhancement. Fluence, angle-dependent scattering and time correlated single photon counting measurements suggested that the enhanced nonlinear scattering due to faster nonradiative decay should play a major role in the enhanced optical limiting responses.

Exciton–exciton annihilation and biexciton stimulated emission in graphene nanoribbons

PubMed Central

Soavi, Giancarlo; Dal Conte, Stefano; Manzoni, Cristian; Viola, Daniele; Narita, Akimitsu; Hu, Yunbin; Feng, Xinliang; Hohenester, Ulrich; Molinari, Elisa; Prezzi, Deborah; Müllen, Klaus; Cerullo, Giulio

2016-01-01

Graphene nanoribbons display extraordinary optical properties due to one-dimensional quantum-confinement, such as width-dependent bandgap and strong electron–hole interactions, responsible for the formation of excitons with extremely high binding energies. Here we use femtosecond transient absorption spectroscopy to explore the ultrafast optical properties of ultranarrow, structurally well-defined graphene nanoribbons as a function of the excitation fluence, and the impact of enhanced Coulomb interaction on their excited states dynamics. We show that in the high-excitation regime biexcitons are formed by nonlinear exciton–exciton annihilation, and that they radiatively recombine via stimulated emission. We obtain a biexciton binding energy of ≈250 meV, in very good agreement with theoretical results from quantum Monte Carlo simulations. These observations pave the way for the application of graphene nanoribbons in photonics and optoelectronics. PMID:26984281

Ultrafast laser-induced reproducible nano-gratings on a molybdenum surface

NASA Astrophysics Data System (ADS)

Dar, Mudasir H.; Saad, Nabil A.; Sahoo, Chakradhar; Naraharisetty, Sri Ram G.; Rao Desai, Narayana

2017-02-01

Wavelength-dependent reproducible nano-gratings were produced on a bulk molybdenum surface upon irradiation with femtosecond laser pulses at near normal incidence in ambient air and water environments. The surface morphology of the irradiated surfaces was characterized by field emission scanning electron microscopy. The ripple spacing was observed to decrease by half when the surface was irradiated with the second harmonic of the fundamental 800 nm radiation. Careful choice of the laser parameters such as fluence, scanning speed, polarization and wavelength were observed to be important for the formation of smooth periodic ripples. The mechanism of formation of polarization-dependent periodic ripples is explained based on the interference model. We also demonstrated the use of a laser direct writing technique for the fabrication of periodic subwavelength structures that have potential applications in photonic devices.

Studies of uniformity of 50 μm low-gain avalanche detectors at the Fermilab test beam

NASA Astrophysics Data System (ADS)

Apresyan, A.; Xie, S.; Pena, C.; Arcidiacono, R.; Cartiglia, N.; Carulla, M.; Derylo, G.; Ferrero, M.; Flores, D.; Freeman, P.; Galloway, Z.; Ghassemi, A.; Al Ghoul, H.; Gray, L.; Hidalgo, S.; Kamada, S.; Los, S.; Mandurrino, M.; Merlos, A.; Minafra, N.; Pellegrini, G.; Quirion, D.; Ronzhin, A.; Royon, C.; Sadrozinski, H.; Seiden, A.; Sola, V.; Spiropulu, M.; Staiano, A.; Uplegger, L.; Yamamoto, K.; Yamamura, K.

2018-07-01

In this paper we report measurements of the uniformity of time resolution, signal amplitude, and charged particle detection efficiency across the sensor surface of low-gain avalanche detectors (LGAD). Comparisons of the performance of sensors with different doping concentrations and different active thicknesses are presented, as well as their temperature dependence and radiation tolerance up to 6 × 1014 n/cm2. Results were obtained at the Fermilab test beam facility using 120 GeV proton beams, and a high precision pixel tracking detector. LGAD sensors manufactured by the Centro Nacional de Microelectrónica (CNM) and Hamamatsu Photonics (HPK) were studied. The uniformity of the sensor response in pulse height before irradiation was found to have a 2% spread. The signal detection efficiency and timing resolution in the sensitive areas before irradiation were found to be 100% and 30-40 ps, respectively. A "no-response" area between pads was measured to be about 130 μm for CNM and 170 μm for HPK sensors. After a neutron fluence of 6 × 1014 n/cm2 the CNM sensor exhibits a large gain variation of up to a factor of 2.5 when comparing metalized and non-metalized sensor areas. An irradiated CNM sensor achieved a time resolution of 30 ps for the metalized area and 40 ps for the non-metalized area, while a HPK sensor irradiated to the same fluence achieved a 30 ps time resolution.

Experimental evaluation of dual multiple aperture devices for fluence field modulated x-ray computed tomography

NASA Astrophysics Data System (ADS)

Mathews, A. J.; Gang, G.; Levinson, R.; Zbijewski, W.; Kawamoto, S.; Siewerdsen, J. H.; Stayman, J. W.

2017-03-01

Acquisition of CT images with comparable diagnostic power can potentially be achieved with lower radiation exposure than the current standard of care through the adoption of hardware-based fluence-field modulation (e.g. dynamic bowtie filters). While modern CT scanners employ elements such as static bowtie filters and tube-current modulation, such solutions are limited in the fluence patterns that they can achieve, and thus are limited in their ability to adapt to broad classes of patient morphology. Fluence-field modulation also enables new applications such as region-of-interest imaging, task specific imaging, reducing measurement noise or improving image quality. The work presented in this paper leverages a novel fluence modulation strategy that uses "Multiple Aperture Devices" (MADs) which are, in essence, binary filters, blocking or passing x-rays on a fine scale. Utilizing two MAD devices in series provides the capability of generating a large number of fluence patterns via small relative motions between the MAD filters. We present the first experimental evaluation of fluence-field modulation using a dual-MAD system, and demonstrate the efficacy of this technique with a characterization of achievable fluence patterns and an investigation of experimental projection data.

Desensitization and recovery of phototropic responsiveness in Arabidopsis thaliana

NASA Technical Reports Server (NTRS)

Janoudi, A. K.; Poff, K. L.

1993-01-01

Phototropism is induced by blue light, which also induces desensitization, a partial or total loss of phototropic responsiveness. The fluence and fluence-rate dependence of desensitization and recovery from desensitization have been measured for etiolated and red light (669-nm) preirradiated Arabidopsis thaliana seedlings. The extent of desensitization increased as the fluence of the desensitizing 450-nm light was increased from 0.3 to 60 micromoles m-2 s-1. At equal fluences, blue light caused more desensitization when given at a fluence rate of 1.0 micromole m-2 s-1 than at 0.3 micromole m-2 s-1. In addition, seedlings irradiated with blue light at the higher fluence rate required a longer recovery time than seedlings irradiated at the lower fluence rate. A red light preirradiation, probably mediated via phytochrome, decreased the time required for recovery from desensitization. The minimum time for detectable recovery was about 65 s, and the maximum time observed was about 10 min. It is proposed that the descending arm of the fluence-response relationship for first positive phototropism is a consequence of desensitization, and that the time threshold for second positive phototropism establishes a period during which recovery from desensitization occurs.

Construction of 144, 565 keV and 5.0 MeV monoenergetic neutron calibration fields at JAERI.

PubMed

Tanimura, Y; Yoshizawa, M; Saegusa, J; Fujii, K; Shimizu, S; Yoshida, M; Shibata, Y; Uritani, A; Kudo, K

2004-01-01

Monoenergetic neutron calibration fields of 144, 565 keV and 5.0 MeV have been developed at the Facility of Radiation Standards of JAERI using a 4 MV Pelletron accelerator. The 7Li(p,n)7Be and 2H(d,n)3He reactions are employed for neutron production. The neutron energy was measured by the time-of-flight method with a liquid scintillation detector and calculated with the MCNP-ANT code. A long counter is employed as a neutron monitor because of the flat response. The monitor is set up where the influence of inscattered neutrons from devices and their supporting materials at a calibration point is as small as possible. The calibration coefficients from the monitor counts to the neutron fluence at a calibration point were obtained from the reference fluence measured with the transfer instrument of the primary standard laboratory (AIST), a 24.13 cm phi Bonner sphere counter. The traceability of the fields to AIST was established through the calibration.

Summary of Workshop on InP: Status and Prospects

NASA Technical Reports Server (NTRS)

Walters, R. J.; Weinberg, I.

1994-01-01

The primary objective of most of the programs in InP solar cells is the development of the most radiation hard solar cell technology. In the workshop, it was generally agreed that the goal is a cell which displays high radiation tolerance in a radiation environment equivalent to a 1 MeV electron fluence of about 10(exp 16)/sq cm. Furthermore, it is desired that the radiation response of the cell be essentially flat out to this fluence - i.e. that the power output of the cell not decrease from its beginning of life (BOL) value in this radiation environment. It was also agreed in the workshop that the manufacturability of InP solar cells needs to be improved. In particular, since InP wafers are relatively dense and brittle, alternative substrates need to be developed. Research on hetero-epitaxial InP cells grown on Si, Ge, and GaAs substrates is currently underway. The ultimate goal is to develop hetero-epitaxial InP solar cells using a cheap, strong, and lightweight substrate.

Enhanced structural stability of nanoporous zirconia under irradiation of He

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Tengfei; Huang, Xuejun; Wang, Chenxu

2012-01-01

This work reports a greatly enhanced tolerance for He irradiation-induced swelling in nanocrystalline zirconia film with interconnected nanoporous structure (hereinafter referred as to NC-C). Compared to bulk yttria-stabilized zirconia (YSZ) and another nanocrystalline zirconia film only with discrete nano voids (hereinafter referred as to NC-V), the NC-C film reveals good tolerance for irradiation of high-fluence He. No appreciable surface blistering can be found even at the highest fluence of 6 1017 cm2 in NCC film. From TEM analysis of as-irradiated samples, the enhanced tolerance for volume swelling in NCC film is attributed to the enhanced diffusion mechanism of deposited Hemore » via widely distributed nano channels. Furthermore, the growth of grain size is quite small for both nanocrystalline zirconia films after irradiation, which is ascribed to the decreasing of area of grain boundary due to loose structure and low energy of primary knock-on atoms for He ions.« less

Correlation of proton irradiation induced threshold voltage shifts to deep level traps in AlGaN/GaN heterostructures

NASA Astrophysics Data System (ADS)

Zhang, Z.; Cardwell, D.; Sasikumar, A.; Kyle, E. C. H.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; Speck, J. S.; Arehart, A. R.; Ringel, S. A.

2016-04-01

The impact of proton irradiation on the threshold voltage (VT) of AlGaN/GaN heterostructures is systematically investigated to enhance the understanding of a primary component of the degradation of irradiated high electron mobility transistors. The value of VT was found to increase monotonically as a function of 1.8 MeV proton fluence in a sub-linear manner reaching 0.63 V at a fluence of 1 × 1014 cm-2. Silvaco Atlas simulations of VT shifts caused by GaN buffer traps using experimentally measured introduction rates, and energy levels closely match the experimental results. Different buffer designs lead to different VT dependences on proton irradiation, confirming that deep, acceptor-like defects in the GaN buffer are primarily responsible for the observed VT shifts. The proton irradiation induced VT shifts are found to depend on the barrier thickness in a linear fashion; thus, scaling the barrier thickness could be an effective way to reduce such degradation.

SU-F-T-507: Modeling Cerenkov Emissions From Medical Linear Accelerators: A Monte Carlo Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shrock, Z; Oldham, M; Adamson, J

2016-06-15

Purpose: Cerenkov emissions are a natural byproduct of MV radiotherapy but are typically ignored as inconsequential. However, Cerenkov photons may be useful for activation of drugs such as psoralen. Here, we investigate Cerenkov radiation from common radiotherapy beams using Monte Carlo simulations. Methods: GAMOS, a GEANT4-based framework for Monte Carlo simulations, was used to model 6 and 18MV photon beams from a Varian medical linac. Simulations were run to track Cerenkov production from these beams when irradiating a 50cm radius sphere of water. Electron contamination was neglected. 2 million primary photon histories were run for each energy, and values scoredmore » included integral dose and total track length of Cerenkov photons between 100 and 400 nm wavelength. By lowering process energy thresholds, simulations included low energy Bremsstrahlung photons to ensure comprehensive evaluation of UV production in the medium. Results: For the same number of primary photons, UV Cerenkov production for 18MV was greater than 6MV by a factor of 3.72 as determined by total track length. The total integral dose was a factor of 2.31 greater for the 18MV beam. Bremsstrahlung photons were a negligibly small component of photons in the wavelength range of interest, comprising 0.02% of such photons. Conclusion: Cerenkov emissions in water are 1.6x greater for 18MV than 6MV for the same integral dose. Future work will expand the analysis to include optical properties of tissues, and to investigate strategies to maximize Cerenkov emission per unit dose for MV radiotherapy.« less

Wavelength dependence of femtosecond laser-induced damage threshold of optical materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gallais, L., E-mail: laurent.gallais@fresnel.fr; Douti, D.-B.; Commandré, M.

2015-06-14

An experimental and numerical study of the laser-induced damage of the surface of optical material in the femtosecond regime is presented. The objective of this work is to investigate the different processes involved as a function of the ratio of photon to bandgap energies and compare the results to models based on nonlinear ionization processes. Experimentally, the laser-induced damage threshold of optical materials has been studied in a range of wavelengths from 1030 nm (1.2 eV) to 310 nm (4 eV) with pulse durations of 100 fs with the use of an optical parametric amplifier system. Semi-conductors and dielectrics materials, in bulk or thinmore » film forms, in a range of bandgap from 1 to 10 eV have been tested in order to investigate the scaling of the femtosecond laser damage threshold with the bandgap and photon energy. A model based on the Keldysh photo-ionization theory and the description of impact ionization by a multiple-rate-equation system is used to explain the dependence of laser-breakdown with the photon energy. The calculated damage fluence threshold is found to be consistent with experimental results. From these results, the relative importance of the ionization processes can be derived depending on material properties and irradiation conditions. Moreover, the observed damage morphologies can be described within the framework of the model by taking into account the dynamics of energy deposition with one dimensional propagation simulations in the excited material and thermodynamical considerations.« less

Development of a fast and feasible spectrum modeling technique for flattening filter free beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, Woong; Bush, Karl; Mok, Ed

Purpose: To develop a fast and robust technique for the determination of optimized photon spectra for flattening filter free (FFF) beams to be applied in convolution/superposition dose calculations. Methods: A two-step optimization method was developed to derive optimal photon spectra for FFF beams. In the first step, a simple functional form of the photon spectra proposed by Ali ['Functional forms for photon spectra of clinical linacs,' Phys. Med. Biol. 57, 31-50 (2011)] is used to determine generalized shapes of the photon spectra. In this method, the photon spectra were defined for the ranges of field sizes to consider the variationsmore » of the contributions of scattered photons with field size. Percent depth doses (PDDs) for each field size were measured and calculated to define a cost function, and a collapsed cone convolution (CCC) algorithm was used to calculate the PDDs. In the second step, the generalized functional form of the photon spectra was fine-tuned in a process whereby the weights of photon fluence became the optimizing free parameters. A line search method was used for the optimization and first order derivatives with respect to the optimizing parameters were derived from the CCC algorithm to enhance the speed of the optimization. The derived photon spectra were evaluated, and the dose distributions using the optimized spectra were validated. Results: The optimal spectra demonstrate small variations with field size for the 6 MV FFF beam and relatively large variations for the 10 MV FFF beam. The mean energies of the optimized 6 MV FFF spectra were decreased from 1.31 MeV for a 3 Multiplication-Sign 3 cm{sup 2} field to 1.21 MeV for a 40 Multiplication-Sign 40 cm{sup 2} field, and from 2.33 MeV at 3 Multiplication-Sign 3 cm{sup 2} to 2.18 MeV at 40 Multiplication-Sign 40 cm{sup 2} for the 10 MV FFF beam. The developed method could significantly improve the agreement between the calculated and measured PDDs. Root mean square differences on the optimized PDDs were observed to be 0.41% (3 Multiplication-Sign 3 cm{sup 2}) down to 0.21% (40 Multiplication-Sign 40 cm{sup 2}) for the 6 MV FFF beam, and 0.35% (3 Multiplication-Sign 3 cm{sup 2}) down to 0.29% (40 Multiplication-Sign 40 cm{sup 2}) for the 10 MV FFF beam. The first order derivatives from the functional form were found to improve the speed of computational time up to 20 times compared to the other techniques. Conclusions: The derived photon spectra resulted in good agreements with measured PDDs over the range of field sizes investigated. The suggested method is easily applicable to commercial radiation treatment planning systems since it only requires measured PDDs as input.« less

Atomic Oxygen Fluence Monitor

NASA Technical Reports Server (NTRS)

Banks, Bruce A.

2011-01-01

This innovation enables a means for actively measuring atomic oxygen fluence (accumulated atoms of atomic oxygen per area) that has impinged upon spacecraft surfaces. Telemetered data from the device provides spacecraft designers, researchers, and mission managers with real-time measurement of atomic oxygen fluence, which is useful for prediction of the durability of spacecraft materials and components. The innovation is a compact fluence measuring device that allows in-space measurement and transmittance of measured atomic oxygen fluence as a function of time based on atomic oxygen erosion yields (the erosion yield of a material is the volume of material that is oxidized per incident oxygen atom) of materials that have been measured in low Earth orbit. It has a linear electrical response to atomic oxygen fluence, and is capable of measuring high atomic oxygen fluences (up to >10(exp 22) atoms/sq cm), which are representative of multi-year low-Earth orbital missions (such as the International Space Station). The durability or remaining structural lifetime of solar arrays that consist of polymer blankets on which the solar cells are attached can be predicted if one knows the atomic oxygen fluence that the solar array blanket has been exposed to. In addition, numerous organizations that launch space experiments into low-Earth orbit want to know the accumulated atomic oxygen fluence that their materials or components have been exposed to. The device is based on the erosion yield of pyrolytic graphite. It uses two 12deg inclined wedges of graphite that are over a grit-blasted fused silica window covering a photodiode. As the wedges erode, a greater area of solar illumination reaches the photodiode. A reference photodiode is also used that receives unobstructed solar illumination and is oriented in the same direction as the pyrolytic graphite covered photodiode. The short-circuit current from the photodiodes is measured and either sent to an onboard data logger, or transmitted to a receiving station on Earth. By comparison of the short-circuit currents from the fluence-measuring photodiode and the reference photodiode, one can compute the accumulated atomic oxygen fluence arriving in the direction that the fluence monitor is pointing. The device produces a signal that is linear with atomic oxygen fluence using a material whose atomic oxygen erosion yield has been measured over a period of several years in low-Earth orbit.

Materials International Space Station Experiment-6 (MISSE-6) Atomic Oxygen Fluence Monitor Experiment

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; Miller, Sharon K.; Waters, Deborah L.

2010-01-01

An atomic oxygen fluence monitor was flown as part of the Materials International Space Station Experiment-6 (MISSE-6). The monitor was designed to measure the accumulation of atomic oxygen fluence with time as it impinged upon the ram surface of the MISSE 6B Passive Experiment Container (PEC). This was an active experiment for which data was to be stored on a battery-powered data logger for post-flight retrieval and analysis. The atomic oxygen fluence measurement was accomplished by allowing atomic oxygen to erode two opposing wedges of pyrolytic graphite that partially covered a photodiode. As the wedges of pyrolytic graphite erode, the area of the photodiode that is illuminated by the Sun increases. The short circuit current, which is proportional to the area of illumination, was to be measured and recorded as a function of time. The short circuit current from a different photodiode, which was oriented in the same direction and had an unobstructed view of the Sun, was also to be recorded as a reference current. The ratio of the two separate recorded currents should bear a linear relationship with the accumulated atomic oxygen fluence and be independent of the intensity of solar illumination. Ground hyperthermal atomic oxygen exposure facilities were used to evaluate the linearity of the ratio of short circuit current to the atomic oxygen fluence. In flight, the current measurement circuitry failed to operate properly, thus the overall atomic oxygen mission fluence could only be estimated based on the physical erosion of the pyrolytic graphite wedges. The atomic oxygen fluence was calculated based on the knowledge of the space atomic oxygen erosion yield of pyrolytic graphite measured from samples on the MISSE 2. The atomic oxygen fluence monitor, the expected result and comparison of mission atomic oxygen fluence based on the erosion of the pyrolytic graphite and Kapton H atomic oxygen fluence witness samples are presented in this paper.

A Nanowire-Based Plasmonic Quantum Dot Laser.

PubMed

Ho, Jinfa; Tatebayashi, Jun; Sergent, Sylvain; Fong, Chee Fai; Ota, Yasutomo; Iwamoto, Satoshi; Arakawa, Yasuhiko

2016-04-13

Quantum dots enable strong carrier confinement and exhibit a delta-function like density of states, offering significant improvements to laser performance and high-temperature stability when used as a gain medium. However, quantum dot lasers have been limited to photonic cavities that are diffraction-limited and further miniaturization to meet the demands of nanophotonic-electronic integration applications is challenging based on existing designs. Here we introduce the first quantum dot-based plasmonic laser to reduce the cross-sectional area of nanowire quantum dot lasers below the cutoff limit of photonic modes while maintaining the length in the order of the lasing wavelength. Metal organic chemical vapor deposition grown GaAs-AlGaAs core-shell nanowires containing InGaAs quantum dot stacks are placed directly on a silver film, and lasing was observed from single nanowires originating from the InGaAs quantum dot emission into the low-loss higher order plasmonic mode. Lasing threshold pump fluences as low as ∼120 μJ/cm(2) was observed at 7 K, and lasing was observed up to 125 K. Temperature stability from the quantum dot gain, leading to a high characteristic temperature was demonstrated. These results indicate that high-performance, miniaturized quantum dot lasers can be realized with plasmonics.

Validation of the MCNP6 electron-photon transport algorithm: multiple-scattering of 13- and 20-MeV electrons in thin foils

NASA Astrophysics Data System (ADS)

Dixon, David A.; Hughes, H. Grady

2017-09-01

This paper presents a validation test comparing angular distributions from an electron multiple-scattering experiment with those generated using the MCNP6 Monte Carlo code system. In this experiment, a 13- and 20-MeV electron pencil beam is deflected by thin foils with atomic numbers from 4 to 79. To determine the angular distribution, the fluence is measured down range of the scattering foil at various radii orthogonal to the beam line. The characteristic angle (the angle for which the max of the distribution is reduced by 1/e) is then determined from the angular distribution and compared with experiment. Multiple scattering foils tested herein include beryllium, carbon, aluminum, copper, and gold. For the default electron-photon transport settings, the calculated characteristic angle was statistically distinguishable from measurement and generally broader than the measured distributions. The average relative difference ranged from 5.8% to 12.2% over all of the foils, source energies, and physics settings tested. This validation illuminated a deficiency in the computation of the underlying angular distributions that is well understood. As a result, code enhancements were made to stabilize the angular distributions in the presence of very small substeps. However, the enhancement only marginally improved results indicating that additional algorithmic details should be studied.

Optimization of dual-wavelength intravascular photoacoustic imaging of atherosclerotic plaques using Monte Carlo optical modeling

NASA Astrophysics Data System (ADS)

Dana, Nicholas; Sowers, Timothy; Karpiouk, Andrei; Vanderlaan, Donald; Emelianov, Stanislav

2017-10-01

Coronary heart disease (the presence of coronary atherosclerotic plaques) is a significant health problem in the industrialized world. A clinical method to accurately visualize and characterize atherosclerotic plaques is needed. Intravascular photoacoustic (IVPA) imaging is being developed to fill this role, but questions remain regarding optimal imaging wavelengths. We utilized a Monte Carlo optical model to simulate IVPA excitation in coronary tissues, identifying optimal wavelengths for plaque characterization. Near-infrared wavelengths (≤1800 nm) were simulated, and single- and dual-wavelength data were analyzed for accuracy of plaque characterization. Results indicate light penetration is best in the range of 1050 to 1370 nm, where 5% residual fluence can be achieved at clinically relevant depths of ≥2 mm in arteries. Across the arterial wall, fluence may vary by over 10-fold, confounding plaque characterization. For single-wavelength results, plaque segmentation accuracy peaked at 1210 and 1720 nm, though correlation was poor (<0.13). Dual-wavelength analysis proved promising, with 1210 nm as the most successful primary wavelength (≈1.0). Results suggest that, without flushing the luminal blood, a primary and secondary wavelength near 1210 and 1350 nm, respectively, may offer the best implementation of dual-wavelength IVPA imaging. These findings could guide the development of a cost-effective clinical system by highlighting optimal wavelengths and improving plaque characterization.

Out-of-field neutron and leakage photon exposures and the associated risk of second cancers in high-energy photon radiotherapy: current status.

PubMed

Takam, R; Bezak, E; Marcu, L G; Yeoh, E

2011-10-01

Determination and understanding of out-of-field neutron and photon doses in accelerator-based radiotherapy is an important issue since linear accelerators operating at high energies (>10 MV) produce secondary radiations that irradiate parts of the patient's anatomy distal to the target region, potentially resulting in detrimental health effects. This paper provides a compilation of data (technical and clinical) reported in the literature on the measurement and Monte Carlo simulations of peripheral neutron and photon doses produced from high-energy medical linear accelerators and the reported risk and/or incidence of second primary cancer of tissues distal to the target volume. Information in the tables facilitates easier identification of (1) the various methods and measurement techniques used to determine the out-of-field neutron and photon radiations, (2) reported linac-dependent out-of-field doses, and (3) the risk/incidence of second cancers after radiotherapy due to classic and modern treatment methods. Regardless of the measurement technique and type of accelerator, the neutron dose equivalent per unit photon dose ranges from as low as 0.1 mSv/Gy to as high as 20.4 mSv/Gy. This radiation dose potentially contributes to the induction of second primary cancer in normal tissues outside the treated area.

Single-Walled Carbon Nanotubes, Carbon Nanofibers and Laser-Induced Incandescence

NASA Technical Reports Server (NTRS)

Schubert, Kathy (Technical Monitor); VanderWal, Randy L.; Ticich, Thomas M.; Berger, Gordon M.; Patel, Premal D.

2004-01-01

Laser induced incandescence applied to a heterogeneous, multi-element reacting flows is characterized by a) temporally resolved emission spectra, time-resolved emission at selected detection wavelengths and fluence dependence. Laser fluences above 0.6 Joules per square centimeter at 1064 nm initiate laser-induced vaporization, yielding a lower incandescence intensity, as found through fluence dependence measurements. Spectrally derived temperatures show that values of excitation laser fluence beyond this value lead to a super-heated plasma, well above the vaporization of temperature of carbon. The temporal evolution of the emission signal at these fluences is consistent with plasma dissipation processes, not incandescence from solid-like structures.

Heavy Ion Irradiation Fluence Dependence for Single-Event Upsets of NAND Flash Memory

NASA Technical Reports Server (NTRS)

Chen, Dakai; Wilcox, Edward; Ladbury, Raymond; Kim, Hak; Phan, Anthony; Seidleck, Christina; LaBel, Kenneth

2016-01-01

We investigated the single-event effect (SEE) susceptibility of the Micron 16 nm NAND flash, and found the single-event upset (SEU) cross section varied inversely with fluence. The SEU cross section decreased with increasing fluence. We attribute the effect to the variable upset sensitivities of the memory cells. The current test standards and procedures assume that SEU follow a Poisson process and do not take into account the variability in the error rate with fluence. Therefore, heavy ion irradiation of devices with variable upset sensitivity distribution using typical fluence levels may underestimate the cross section and on-orbit event rate.

Temperature, illumination, and fluence dependence of current and voltage in electron irradiated solar cells

NASA Technical Reports Server (NTRS)

Faith, T. J.; Obenschain, A. F.

1974-01-01

Empirical equations have been derived from measurements of solar cell photovoltaic characteristics relating light-generated current and open circuit voltage to cell temperature, intensity of illumination and 1-MeV electron fluence. Both 2-ohm-cm and 10-ohm-cm cells were tested over the temperature range from 120 to 470 K, the illumination intensity range from 5 to 1830 mW/sq cm, and the electron fluence range from 1 x 10 to the 13th to 1 x 10 to the 16th electrons/sq cm. The normalized temperature coefficient of the light generated current varies as the 0.18 power of the fluence for temperatures above approximately 273 K and is independent of fluence at lower temperatures. At 140 mW/sq cm, a power law expression was derived which shows that the light-generated current decreases at a rate proportional to the 0.153 power of the fluence for both resistivities. The coefficient of the expression is larger for 2-ohm-cm cells; consequently, the advantage for 10-ohm-cm cells increased with increasing fluence.

Photoluminescence and reflectivity of polymethylmethacrylate implanted by low-energy carbon ions at high fluences

NASA Astrophysics Data System (ADS)

Wang, Jun; Zhu, Fei; Zhang, Bei; Liu, Huixian; Jia, Guangyi; Liu, Changlong

2012-11-01

Polymethylmethacrylate (PMMA) specimens were implanted with 30 keV carbon ions in a fluence range of 1 × 1016 to 2 × 1017 cm-2, and photoluminescence (PL) and reflectivity of the implanted samples were examined. A luminescent band with one peak was found in PL spectra excited by 480 nm line, but its intensity did not vary in parallel with ion fluence. The strongest PL occurred at the fluence of 5 × 1016 cm-2. Results from visible-light-excited micro-Raman spectra indicated that the formation of hydrogenated amorphous carbon structures in subsurface layer and their evolutions with ion fluence could be responsible for the observed PL responses. Measurements of the small-angle reflectance spectra from both the implanted and rear surfaces of samples in the ultraviolet-visible (UV-vis) range demonstrated a kind of both fluence-dependent and wavelength-related reflectivity variations, which were attributed to the structural changes induced by ion implantation. A noticeable reflectivity modification, which may be practically used, could be found at the fluence of 1 × 1016 cm-2.

Surface modifications of ultra-thin gold films by swift heavy ion irradiation

NASA Astrophysics Data System (ADS)

Dash, P.; Mallick, P.; Rath, H.; Dash, B. N.; Tripathi, A.; Prakash, Jai; Avasthi, D. K.; Satyam, P. V.; Mishra, N. C.

2010-10-01

Gold films of thickness 10 and 20 nm grown on float glass substrate by thermal evaporation technique were irradiated with 107 MeV Ag8+ and 58 MeV Ni5+ ions at different fluences and characterized by Grazing Incidence X-ray Diffraction (GIXRD) and Atomic Force Microscopy (AFM). The pristine films were continuous and no island structures were found even at these small thicknesses. The surface roughness estimated from AFM data did not show either monotonic increase or decrease with ion fluences. Instead, it increased at low fluences and decreased at high fluences for 20 nm thick film. In the 10 nm film roughness first increased with ion fluence, then decreased and again increased at higher fluences. The pattern of variation, however, was identical for Ni and Ag beams. Both the beams led to the formation of cracks on the film surface at intermediate fluences. The observed ion-irradiation induced thickness dependent topographic modification is explained by the spatial confinement of the energy deposited by ions in the reduced dimension of the films.

Regimes of Pulsar Pair Formation and Particle Energetics

NASA Technical Reports Server (NTRS)

Harding, Alice K.; Muslimov, Alexander G.; Zhang, Bing; White, Nicholas E. (Technical Monitor)

2002-01-01

We investigate the conditions required for the production of electron-positron pairs above a pulsar polar cap (PC) and the influence of pair production on the energetics of the primary particle acceleration. Assuming space-charge limited flow acceleration including the inertial frame-dragging effect, we allow both one-photon and two-photon pair production by either curvature radiation (CR) photons or photons resulting from inverse-Compton scattering of thermal photons from the PC by primary electrons. We find that,, while only the younger pulsars can produce pairs through CR, nearly all known radio pulsars are capable of producing pairs through non-resonant inverse-Compton scatterings. The effect of the neutron star equations of state on the pair death lines is explored. We show that pair production is facilitated in more compact stars and more a massive stars. Therefore accretion of mass by pulsars in binary systems may allow pair production in most of the millisecond purser population. We also find that two-photon pair production may be important in millisecond pursers if their surface temperatures are above approx. or equal to three million degrees K. Pursers that produce pairs through CRT wilt have their primary acceleration limited by the effect of screening of the electric field. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sup 1/2, sub rot) dependence. The acceleration voltage drop in pursers that produce pairs only through inverse-Compton emission will not be limited by electric field screening. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sub rot) dependence. Thus, older pursers will have significantly lower gamma-ray luminosity.

Multiple scattering theory for total skin electron beam design.

PubMed

Antolak, J A; Hogstrom, K R

1998-06-01

The purpose of this manuscript is to describe a method for designing a broad beam of electrons suitable for total skin electron irradiation (TSEI). A theoretical model of a TSEI beam from a linear accelerator with a dual scattering system has been developed. The model uses Fermi-Eyges theory to predict the planar fluence of the electron beam after it has passed through various materials between the source and the treatment plane, which includes scattering foils, monitor chamber, air, and a plastic diffusing plate. Unique to this model is its accounting for removal of the tails of the electron beam profile as it passes through the primary x-ray jaws. A method for calculating the planar fluence profile for an obliquely incident beam is also described. Off-axis beam profiles and percentage depth doses are measured with ion chambers, film, and thermoluminescent dosimeters (TLD). The measured data show that the theoretical model can accurately predict beam energy and planar fluence of the electron beam at normal and oblique incidence. The agreement at oblique angles is not quite as good but is sufficiently accurate to be of predictive value when deciding on the optimal angles for the clinical TSEI beams. The advantage of our calculational approach for designing a TSEI beam is that many different beam configurations can be tested without having to perform time-consuming measurements. Suboptimal configurations can be quickly dismissed, and the predicted optimal solution should be very close to satisfying the clinical specifications.

A new Recoil Proton Telescope for energy and fluence measurement of fast neutron fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lebreton, Lena; Bachaalany, Mario; Husson, Daniel

The spectrometer ATHENA (Accurate Telescope for High Energy Neutron metrology Applications), is being developed at the IRSN / LMDN (Institut de Radioprotection et de Surete nucleaire / Laboratoire de Metrologie et de dosimetrie des neutrons) and aims at characterizing energy and fluence of fast neutron fields. The detector is a Recoil Proton Telescope and measures neutron fields in the range of 5 to 20 MeV. This telescope is intended to become a primary standard for both energy and fluence measurements. The neutron detection is achieved by a polyethylene radiator for n-p conversion, three 50{sub m} thick silicon sensors that usemore » CMOS technology for the proton tracking and a 3 mm thick silicon diode to measure the residual proton energy. This first prototype used CMOS sensors called MIMOSTAR, initially developed for heavy ion physics. The use of CMOS sensors and silicon diode increases the intrinsic efficiency of the detector by a factor of ten compared with conventional designs. The first prototype has already been done and was a successful study giving the results it offered in terms of energy and fluence measurements. For mono energetic beams going from 5 to 19 MeV, the telescope offered an energy resolution between 5 and 11% and fluence difference going from 5 to 7% compared to other home standards. A second and final prototype of the detector is being designed. It will hold upgraded CMOS sensors called FastPixN. These CMOS sensors are supposed to run 400 times faster than the older version and therefore give the telescope the ability to support neutron flux in the order of 107 to 108cm{sup 2}:s{sup 1}. The first prototypes results showed that a 50 m pixel size is enough for a precise scattering angle reconstruction. Simulations using MCNPX and GEANT4 are already in place for further improvements. A DeltaE diode will replace the third CMOS sensor and will be installed right before the silicon diode for a better recoil proton selection. The final prototype with its new geometry will increase the telescopes efficiency by a factor of 1.5. It will also cover some of the most important points in metrology; repeatability, reproducibility and sustainability. (authors)« less

The perturbation correction factors for cylindrical ionization chambers in high-energy photon beams.

PubMed

Yoshiyama, Fumiaki; Araki, Fujio; Ono, Takeshi

2010-07-01

In this study, we calculated perturbation correction factors for cylindrical ionization chambers in high-energy photon beams by using Monte Carlo simulations. We modeled four Farmer-type cylindrical chambers with the EGSnrc/Cavity code and calculated the cavity or electron fluence correction factor, P (cav), the displacement correction factor, P (dis), the wall correction factor, P (wall), the stem correction factor, P (stem), the central electrode correction factor, P (cel), and the overall perturbation correction factor, P (Q). The calculated P (dis) values for PTW30010/30013 chambers were 0.9967 +/- 0.0017, 0.9983 +/- 0.0019, and 0.9980 +/- 0.0019, respectively, for (60)Co, 4 MV, and 10 MV photon beams. The value for a (60)Co beam was about 1.0% higher than the 0.988 value recommended by the IAEA TRS-398 protocol. The P (dis) values had a substantial discrepancy compared to those of IAEA TRS-398 and AAPM TG-51 at all photon energies. The P (wall) values were from 0.9994 +/- 0.0020 to 1.0031 +/- 0.0020 for PTW30010 and from 0.9961 +/- 0.0018 to 0.9991 +/- 0.0017 for PTW30011/30012, in the range of (60)Co-10 MV. The P (wall) values for PTW30011/30012 were around 0.3% lower than those of the IAEA TRS-398. Also, the chamber response with and without a 1 mm PMMA water-proofing sleeve agreed within their combined uncertainty. The calculated P (stem) values ranged from 0.9945 +/- 0.0014 to 0.9965 +/- 0.0014, but they are not considered in current dosimetry protocols. The values were no significant difference on beam qualities. P (cel) for a 1 mm aluminum electrode agreed within 0.3% with that of IAEA TRS-398. The overall perturbation factors agreed within 0.4% with those for IAEA TRS-398.

Measured Thermal and Fast Neutron Fluence Rates for ATF-1 Holders During ATR Cycle 157D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Larry Don; Miller, David Torbet

This report contains the thermal (2200 m/s) and fast (E>1MeV) neutron fluence rate data for the ATF-1 holders located in core for ATR Cycle 157D which were measured by the Radiation Measurements Laboratory (RML) as requested by the Power Reactor Programs (ATR Experiments) Radiation Measurements Work Order. This report contains measurements of the fluence rates corresponding to the particular elevations relative to the 80-ft. core elevation. The data in this report consist of (1) a table of the ATR power history and distribution, (2) a hard copy listing of all thermal and fast neutron fluence rates, and (3) plots ofmore » both the thermal and fast neutron fluence rates. The fluence rates reported are for the average power levels given in the table of power history and distribution.« less

Non-Thermal Spectra from Pulsar Magnetospheres in the Full Electromagnetic Cascade Scenario

NASA Astrophysics Data System (ADS)

Peng, Qi-Yong; Zhang, Li

2008-08-01

We simulated non-thermal emission from a pulsar magnetosphere within the framework of a full polar-cap cascade scenario by taking the acceleration gap into account, using the Monte Carlo method. For a given electric field parallel to open field lines located at some height above the surface of a neutron star, primary electrons were accelerated by parallel electric fields and lost their energies by curvature radiation; these photons were converted to electron-positron pairs, which emitted photons through subsequent quantum synchrotron radiation and inverse Compton scattering, leading to a cascade. In our calculations, the acceleration gap was assumed to be high above the stellar surface (about several stellar radii); the primary and secondary particles and photons emitted during the journey of those particles in the magnetosphere were traced using the Monte Carlo method. In such a scenario, we calculated the non-thermal photon spectra for different pulsar parameters and compared the model results for two normal pulsars and one millisecond pulsar with the observed data.

A multiscale filter for noise reduction of low-dose cone beam projections

NASA Astrophysics Data System (ADS)

Yao, Weiguang; Farr, Jonathan B.

2015-08-01

The Poisson or compound Poisson process governs the randomness of photon fluence in cone beam computed tomography (CBCT) imaging systems. The probability density function depends on the mean (noiseless) of the fluence at a certain detector. This dependence indicates the natural requirement of multiscale filters to smooth noise while preserving structures of the imaged object on the low-dose cone beam projection. In this work, we used a Gaussian filter, \\text{exp}≤ft(-{{x}2}/2σ f2\\right) as the multiscale filter to de-noise the low-dose cone beam projections. We analytically obtained the expression of {σf} , which represents the scale of the filter, by minimizing local noise-to-signal ratio. We analytically derived the variance of residual noise from the Poisson or compound Poisson processes after Gaussian filtering. From the derived analytical form of the variance of residual noise, optimal σ f2 is proved to be proportional to the noiseless fluence and modulated by local structure strength expressed as the linear fitting error of the structure. A strategy was used to obtain the reliable linear fitting error: smoothing the projection along the longitudinal direction to calculate the linear fitting error along the lateral direction and vice versa. The performance of our multiscale filter was examined on low-dose cone beam projections of a Catphan phantom and a head-and-neck patient. After performing the filter on the Catphan phantom projections scanned with pulse time 4 ms, the number of visible line pairs was similar to that scanned with 16 ms, and the contrast-to-noise ratio of the inserts was higher than that scanned with 16 ms about 64% in average. For the simulated head-and-neck patient projections with pulse time 4 ms, the visibility of soft tissue structures in the patient was comparable to that scanned with 20 ms. The image processing took less than 0.5 s per projection with 1024   ×   768 pixels.

Simultaneous X-Ray, Gamma-Ray, and Radio Observations of the Repeating Fast Radio Burst FRB 121102

NASA Astrophysics Data System (ADS)

Scholz, P.; Bogdanov, S.; Hessels, J. W. T.; Lynch, R. S.; Spitler, L. G.; Bassa, C. G.; Bower, G. C.; Burke-Spolaor, S.; Butler, B. J.; Chatterjee, S.; Cordes, J. M.; Gourdji, K.; Kaspi, V. M.; Law, C. J.; Marcote, B.; McLaughlin, M. A.; Michilli, D.; Paragi, Z.; Ransom, S. M.; Seymour, A.; Tendulkar, S. P.; Wharton, R. S.

2017-09-01

We undertook coordinated campaigns with the Green Bank, Effelsberg, and Arecibo radio telescopes during Chandra X-ray Observatory and XMM-Newton observations of the repeating fast radio burst FRB 121102 to search for simultaneous radio and X-ray bursts. We find 12 radio bursts from FRB 121102 during 70 ks total of X-ray observations. We detect no X-ray photons at the times of radio bursts from FRB 121102 and further detect no X-ray bursts above the measured background at any time. We place a 5σ upper limit of 3 × 10‑11 erg cm‑2 on the 0.5–10 keV fluence for X-ray bursts at the time of radio bursts for durations < 700 ms, which corresponds to a burst energy of 4 × 1045 erg at the measured distance of FRB 121102. We also place limits on the 0.5–10 keV fluence of 5 × 10‑10 and 1 × 10‑9 erg cm‑2 for bursts emitted at any time during the XMM-Newton and Chandra observations, respectively, assuming a typical X-ray burst duration of 5 ms. We analyze data from the Fermi Gamma-ray Space Telescope Gamma-ray Burst Monitor and place a 5σ upper limit on the 10–100 keV fluence of 4 × 10‑9 erg cm‑2 (5 × 1047 erg at the distance of FRB 121102) for gamma-ray bursts at the time of radio bursts. We also present a deep search for a persistent X-ray source using all of the X-ray observations taken to date and place a 5σ upper limit on the 0.5–10 keV flux of 4 × 10‑15 erg s‑1 cm‑2 (3 × 1041 erg s‑1 at the distance of FRB 121102). We discuss these non-detections in the context of the host environment of FRB 121102 and of possible sources of fast radio bursts in general.

Clinical application of intense pulsed light depilation technology in total auricular reconstruction.

PubMed

Guo, Ying; Shan, Jing; Zhang, Tianyu

2017-08-01

Although ear reconstruction technology has been highly developed in recent years, hair growth on the reconstructed ear has plagued both surgeons and patients. In this paper, the authors introduce a clinical application of intense pulsed light depilation in total auricular reconstruction. From August 2012 to August 2013, 27 patients (28 ears) suffering from congenital microtia were treated by intense pulsed light depilation (650-950-nm filter, initial fluence of 14-16 J/cm 2 and gradually increased, pulse width of 30-50 ms, spot size of 20 × 30 mm 2 , intervals of 6-8 weeks, a total of four sessions) either before or after auricular reconstruction. According to the treatment situation at diagnosis, the patients were divided into two groups: the preoperative group and the postoperative group. There were no differences between the two groups in terms of age or initial fluence for hair removal; however, there were less treatments in the former than in the latter group (preoperative group 4.1 ± 0.3, postoperative group 4.7 ± 0.7, F = 9.10, P = 0.006), and the maximum fluence used for hair removal was lower in the former than in the latter group (preoperative group 18-20 J/cm 2 , postoperative group 19-22 J/cm 2 , F = 22.31, P < 0.001). After follow-up for ≥4-6 months, the effective rate was 100% in the preoperative group, and the effective rate was 80% in the postoperative group. Intense pulsed light depilation technology is a reasonable complementary approach to total auricular reconstruction. And preoperative depilation is recommended over postoperative depilation. The non-invasive modern photonic technology can resolve the problem of postoperative residual hair on the reconstructed auricle, improving auricular shape and increasing patient satisfaction. In addition, an adequately set preoperative hair removal area can provide surface skin that is most similar to normal auricle skin for auricular reconstruction.

SU-E-T-644: Evaluation of Angular Dependence Correction for 2D Array Detector Using for Quality Assurance of Volumetric Modulated Arc Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karthikeyan, N; Ganesh, K M; Vikraman, S

2014-06-15

Purpose: To evaluate the angular dependence correction for Matrix Evolution 2D array detector in quality assurance of volumetric modulated arc therapy(VMAT). Methods: Total ten patients comprising of different sites were planned for VMAT and taken for the study. Each plan was exposed on Matrix Evolution 2D array detector with Omnipro IMRT software based on the following three different methods using 6MV photon beams from Elekta Synergy linear accelerator. First method, VMAT plan was delivered on Matrix Evolution detector as it gantry mounted with dedicated holder with build-up of 2.3cm. Second, the VMAT plan was delivered with the static gantry anglemore » on to the table mounted setup. Third, the VMAT plan was delivered with actual gantry angle on Matrix Evolution detector fixed in Multicube phantom with gantry angle sensor and angular dependence correction were applied to quantify the plan quality. For all these methods, the corresponding QA plans were generated in TPS and the dose verification was done for both point and 2D fluence analysis with pass criteria of 3% dose difference and 3mm distance to agreement. Results: The measured point dose variation for the first method was observed as 1.58±0.6% of mean and SD with TPS calculated. For second and third method, the mean and standard deviation(SD) was observed as 1.67±0.7% and 1.85±0.8% respectively. The 2D fluence analysis of measured and TPS calculated has the mean and SD of 97.9±1.1%, 97.88±1.2% and 97.55±1.3% for first, second and third methods respectively. The calculated two-tailed Pvalue for point dose and 2D fluence analysis shows the insignificance with values of 0.9316 and 0.9015 respectively, among the different methods of QA. Conclusion: The qualitative evaluation of angular dependence correction for Matrix Evolution 2D array detector shows its competency in accuracy of quality assurance measurement of composite dose distribution of volumetric modulated arc therapy.« less

On the wall perturbation correction for a parallel-plate NACP-02 chamber in clinical electron beams.

PubMed

Zink, K; Wulff, J

2011-02-01

In recent years, several Monte Carlo studies have been published concerning the perturbation corrections of a parallel-plate chamber in clinical electron beams. In these studies, a strong depth dependence of the relevant correction factors (p(wall) and P(cav)) for depth beyond the reference depth is recognized and it has been shown that the variation with depth is sensitive to the choice of the chamber's effective point of measurement. Recommendations concerning the positioning of parallel-plate ionization chambers in clinical electron beams are not the same for all current dosimetry protocols. The IAEA TRS-398 as well as the IPEM protocol and the German protocol DIN 6800-2 interpret the depth of measurement within the phantom as the water equivalent depth, i.e., the nonwater equivalence of the entrance window has to be accounted for by shifting the chamber by an amount deltaz. This positioning should ensure that the primary electrons traveling from the surface of the water phantom through the entrance window to the chamber's reference point sustain the same energy loss as the primary electrons in the undisturbed phantom. The objective of the present study is the determination of the shift deltaz for a NACP-02 chamber and the calculation of the resulting wall perturbation correction as a function of depth. Moreover, the contributions of the different chamber walls to the wall perturbation correction are identified. The dose and fluence within the NACP-02 chamber and a wall-less air cavity is calculated using the Monte Carlo code EGSnrc in a water phantom at different depths for different clinical electron beams. In order to determine the necessary shift to account for the nonwater equivalence of the entrance window, the chamber is shifted in steps deltaz around the depth of measurement. The optimal shift deltaz is determined from a comparison of the spectral fluence within the chamber and the bare cavity. The wall perturbation correction is calculated as the ratio between doses for the complete chamber and a wall-less air cavity. The high energy part of the fluence spectra within the chamber strongly varies even with small chamber shifts, allowing the determination of deltaz within micrometers. For the NACP-02 chamber a shift deltaz = -0.058 cm results. This value is independent of the energy of the primary electrons as well as of the depth within the phantom and it is in good agreement with the value recommended in the German dosimetry protocol. Applying this shift, the calculated wall perturbation correction as a function of depth is varying less than 1% from zero up to the half value depth R50 for electron energies in the range of 6-21 MeV. The remaining depth dependence can mainly be attributed to the scatter properties of the entrance window. When neglecting the nonwater equivalence of the entrance window, the variation of p(wall) with depth is up to 10% and more, especially for low electron energies. The variation of the wall perturbation correction for the NACP-02 chamber in clinical electron beams strongly depends on the positioning of the chamber. Applying a shift deltaz = -0.058 cm toward the focus ensures that the primary electron spectrum within the chamber bears the largest resemblance to the fluence of a wall-less cavity. Hence, the influence of the chamber walls on the perturbation correction can be separated out and the residual variation of p(wall) with depth is minimized.

On the predictive potential of Pc5 ULF waves to forecast relativistic electrons based on their relationships over two solar cycles

NASA Astrophysics Data System (ADS)

Lam, Hing-Lan

2017-01-01

A statistical study of relativistic electron (>2 MeV) fluence derived from geosynchronous satellites and Pc5 ultralow frequency (ULF) wave power computed from a ground magnetic observatory data located in Canada's auroral zone has been carried out. The ground observations were made near the foot points of field lines passing through the GOESs from 1987 to 2009 (cycles 22 and 23). We determine statistical relationships between the two quantities for different phases of a solar cycle and validate these relationships in two different cycles. There is a positive linear relationship between log fluence and log Pc5 power for all solar phases; however, the power law indices vary for different phases of the cycle. High index values existed during the descending phase. The Pearson's cross correlation between electron fluence and Pc5 power indicates fluence enhancement 2-3 days after strong Pc5 wave activity for all solar phases. The lag between the two quantities is shorter for extremely high fluence (due to high Pc5 power), which tends to occur during the declining phases of both cycles. Most occurrences of extremely low fluence were observed during the extended solar minimum of cycle 23. The precursory attribute of Pc5 power with respect to fluence and the enhancement of fluence due to rising Pc5 power both support the notion of an electron acceleration mechanism by Pc5 ULF waves. This precursor behavior establishes the potential of using Pc5 power to predict relativistic electron fluence.

Optimizing fluence and debridement effects on cutaneous resurfacing carbon dioxide laser surgery.

PubMed

Weisberg, N K; Kuo, T; Torkian, B; Reinisch, L; Ellis, D L

1998-10-01

To develop methods to compare carbon dioxide (CO2) resurfacing lasers, fluence, and debridement effects on tissue shrinkage and histological thermal denaturation. In vitro human or in vivo porcine skin samples received up to 5 passes with scanner or short-pulsed CO2 resurfacing lasers. Fluences ranging from 2.19 to 17.58 J/cm2 (scanner) and 1.11 to 5.56 J/cm2 (short pulsed) were used to determine each laser's threshold energy for clinical effect. Variable amounts of debridement were also studied. Tissue shrinkage was evaluated by using digital photography to measure linear distance change of the treated tissue. Tissue histological studies were evaluated using quantitative computer image analysis. Fluence-independent in vitro tissue shrinkage was seen with the scanned and short-pulsed lasers above threshold fluence levels of 5.9 and 2.5 J/cm2, respectively. Histologically, fluence-independent thermal depths of damage of 77 microns (scanner) and 25 microns (pulsed) were observed. Aggressive debridement of the tissue increased the shrinkage per pass of the laser, and decreased the fluence required for the threshold effect. In vivo experiments confirmed the in vitro results, although the in vivo threshold fluence level was slightly higher and the shrinkage obtained was slightly lower per pass. Our methods allow comparison of different resurfacing lasers' acute effects. We found equivalent laser tissue effects using lower fluences than those currently accepted clinically. This suggests that the morbidity associated with CO2 laser resurfacing may be minimized by lowering levels of tissue input energy and controlling for tissue debridement.

Practical new method of measuring thermal-neutron fluence

NASA Technical Reports Server (NTRS)

Siebold, J. R.; Warman, E. A.

1967-01-01

Thermoluminescence dosimeter technique measures thermal-neutron fluence by encapsulating lithium flouride phosphor powder and exposing it to a neutron environment. The capsule is heated in a dosimeter reader, which results in light emission proportional to the neutron fluence.

Fluence correction factors for graphite calorimetry in a low-energy clinical proton beam: I. Analytical and Monte Carlo simulations.

PubMed

Palmans, H; Al-Sulaiti, L; Andreo, P; Shipley, D; Lühr, A; Bassler, N; Martinkovič, J; Dobrovodský, J; Rossomme, S; Thomas, R A S; Kacperek, A

2013-05-21

The conversion of absorbed dose-to-graphite in a graphite phantom to absorbed dose-to-water in a water phantom is performed by water to graphite stopping power ratios. If, however, the charged particle fluence is not equal at equivalent depths in graphite and water, a fluence correction factor, kfl, is required as well. This is particularly relevant to the derivation of absorbed dose-to-water, the quantity of interest in radiotherapy, from a measurement of absorbed dose-to-graphite obtained with a graphite calorimeter. In this work, fluence correction factors for the conversion from dose-to-graphite in a graphite phantom to dose-to-water in a water phantom for 60 MeV mono-energetic protons were calculated using an analytical model and five different Monte Carlo codes (Geant4, FLUKA, MCNPX, SHIELD-HIT and McPTRAN.MEDIA). In general the fluence correction factors are found to be close to unity and the analytical and Monte Carlo codes give consistent values when considering the differences in secondary particle transport. When considering only protons the fluence correction factors are unity at the surface and increase with depth by 0.5% to 1.5% depending on the code. When the fluence of all charged particles is considered, the fluence correction factor is about 0.5% lower than unity at shallow depths predominantly due to the contributions from alpha particles and increases to values above unity near the Bragg peak. Fluence correction factors directly derived from the fluence distributions differential in energy at equivalent depths in water and graphite can be described by kfl = 0.9964 + 0.0024·zw-eq with a relative standard uncertainty of 0.2%. Fluence correction factors derived from a ratio of calculated doses at equivalent depths in water and graphite can be described by kfl = 0.9947 + 0.0024·zw-eq with a relative standard uncertainty of 0.3%. These results are of direct relevance to graphite calorimetry in low-energy protons but given that the fluence correction factor is almost solely influenced by non-elastic nuclear interactions the results are also relevant for plastic phantoms that consist of carbon, oxygen and hydrogen atoms as well as for soft tissues.

Increase of bulk optical damage threshold fluences of KDP crystals by laser irradiation and heat treatment

DOEpatents

Swain, J.E.; Stokowski, S.E.; Milam, D.; Kennedy, G.C.; Rainer, F.

1982-07-07

The bulk optical damage threshold fluence of potassium dihydrogen phosphate (KDP) crystals is increased by irradiating the crystals with laser pulses of duration 1 to 20 nanoseconds of increasing fluence, below the optical damage threshold fluence for untreated crystals, or by baking the crystals for times of the order of 24 hours at temperatures of 110 to 165/sup 0/C, or by a combination of laser irradiation and baking.

Desensitization and recovery of phototropic responsiveness in Arabidopsis thaliana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janoudi, A.K.; Poff, K.L.

1993-04-01

Phototropism is induced by blue light, which also induces desensitization, a partial or total loss of phototropic responsiveness. The fluence and fluence-rate dependence of densensitization and recovery from desensitization have been measured for etiolated and red light (669-nm) preirradiated Arabidopsis thaliana seedlings. The extent of desensitization increased as the fluence of the desensitizing 450-nm light was increased from 0.3 to 60 [mu]mol m[sup [minus]2] s[sup [minus]1]. At equal fluences, blue light caused more desensitization when given at a fluence rate of 1.0 [mu]mol m[sup [minus]2] s[sup [minus]1] than at 0.3 [mu]mol m[sup [minus]2] s[sup [minus]1]. In addition, seedlings irradiated withmore » blue light at the higher fluence rate required a longer recovery time than seedlings irradiated at the lower fluence rate. A red light preirradiation, probably mediated via phytochrome, decreased the time required for recovery from desensitization. The minimum time for detectable recovery was about 65 s, and the maximum time observed was about 10 min. It is proposed that the descending arm of the fluence-response relationship for first positive phototropism is a consequence of desensitization, and that the time threshold for second positive phototropism establishes a period during which recovery from desensitization occurs. 11 refs., 6 figs.« less

Fluence Rate Differences in Photodynamic Therapy Efficacy and Activation of Epidermal Growth Factor Receptor after Treatment of the Tumor-Involved Murine Thoracic Cavity

PubMed Central

Grossman, Craig E.; Carter, Shirron L.; Czupryna, Julie; Wang, Le; Putt, Mary E.; Busch, Theresa M.

2016-01-01

Photodynamic therapy (PDT) of the thoracic cavity can be performed in conjunction with surgery to treat cancers of the lung and its pleura. However, illumination of the cavity results in tissue exposure to a broad range of fluence rates. In a murine model of intrathoracic PDT, we studied the efficacy of 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH; Photochlor®)-mediated PDT in reducing the burden of non-small cell lung cancer for treatments performed at different incident fluence rates (75 versus 150 mW/cm). To better understand a role for growth factor signaling in disease progression after intrathoracic PDT, the expression and activation of epidermal growth factor receptor (EGFR) was evaluated in areas of post-treatment proliferation. The low fluence rate of 75 mW/cm produced the largest reductions in tumor burden. Bioluminescent imaging and histological staining for cell proliferation (anti-Ki-67) identified areas of disease progression at both fluence rates after PDT. However, increased EGFR activation in proliferative areas was detected only after treatment at the higher fluence rate of 150 mW/cm. These data suggest that fluence rate may affect the activation of survival factors, such as EGFR, and weaker activation at lower fluence rate could contribute to a smaller tumor burden after PDT at 75 mW/cm. PMID:26784170

Fluence Rate Differences in Photodynamic Therapy Efficacy and Activation of Epidermal Growth Factor Receptor after Treatment of the Tumor-Involved Murine Thoracic Cavity.

PubMed

Grossman, Craig E; Carter, Shirron L; Czupryna, Julie; Wang, Le; Putt, Mary E; Busch, Theresa M

2016-01-14

Photodynamic therapy (PDT) of the thoracic cavity can be performed in conjunction with surgery to treat cancers of the lung and its pleura. However, illumination of the cavity results in tissue exposure to a broad range of fluence rates. In a murine model of intrathoracic PDT, we studied the efficacy of 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH; Photochlor(®))-mediated PDT in reducing the burden of non-small cell lung cancer for treatments performed at different incident fluence rates (75 versus 150 mW/cm). To better understand a role for growth factor signaling in disease progression after intrathoracic PDT, the expression and activation of epidermal growth factor receptor (EGFR) was evaluated in areas of post-treatment proliferation. The low fluence rate of 75 mW/cm produced the largest reductions in tumor burden. Bioluminescent imaging and histological staining for cell proliferation (anti-Ki-67) identified areas of disease progression at both fluence rates after PDT. However, increased EGFR activation in proliferative areas was detected only after treatment at the higher fluence rate of 150 mW/cm. These data suggest that fluence rate may affect the activation of survival factors, such as EGFR, and weaker activation at lower fluence rate could contribute to a smaller tumor burden after PDT at 75 mW/cm.

Surface morphology correlated with field emission properties of laser irradiated nickel

NASA Astrophysics Data System (ADS)

Jalil, S. A.; Bashir, S.; Akram, M.; Ahmed, Q. S.; Haq, F. U.

2017-08-01

The effect of laser fluence on the surface morphology and field emission properties of nickel (Ni) has been investigated. Circular shaped Ni targets are irradiated with Nd:YAG laser (1064 nm, 10 Hz, 10 ns) at various fluences ranging from 5.2 to 26 J/cm2 in air. For low fluence ranging from 5.2 to 10.4 J/cm2, SEM analysis reveals the growth of unorganized channels, grains, droplets, and ridges. Whereas, at moderate fluence of 15.6 J/cm2, the formation of ridges and cones along with few number of holes are observed. However, at high fluence regime ranging from 20 to 26 J/cm2, a sharp transition in morphology from ridges to holes has been observed. The laser structured Ni targets are also investigated for field emission properties by recording their I-V characteristics and Fowler-Nordheim (F-N) plots. The enhancement in field emission factor (β) and the reduction in turn on field are found to be dependent upon the laser fluence and morphology of the grown structures. For samples treated at low and moderate fluences, the growth of cones, channels and ridges is responsible for enhancement of β factor ranging from 121 to 178. Whereas, for samples treated at high fluence region, the formation of pores and holes is responsible for significant field convergence and consequently resulting in substantial enhancement in β factor to 276.

The performance of diphoton primary vertex reconstruction methods in H → γγ+Met channel of ATLAS experiment

NASA Astrophysics Data System (ADS)

Tomiwa, K. G.

2017-09-01

The search for new physics in the H → γγ+met relies on how well the missing transverse energy is reconstructed. The Met algorithm used by the ATLAS experiment in turns uses input variables like photon and jets which depend on the reconstruction of the primary vertex. This document presents the performance of di-photon vertex reconstruction algorithms (hardest vertex method and Neural Network method). Comparing the performance of these algorithms for the nominal Standard Model sample and the Beyond Standard Model sample, we see the overall performance of the Neural Network method of primary vertex selection performed better than the Hardest vertex method.

A 60 Meter Delay Stabilized Microwave Fiber Optic Link for 5.3 GHz Reference Signal Distribution on the Shuttle Radar Topography Mapper

NASA Technical Reports Server (NTRS)

Lutes, G.; Tu, M.; McWatters, D.

1999-01-01

The Photonic Systems for Antenna Applications Symposium (PSAA) is the primary conference devoted exclusively to the exchange of information on the technology and application of photonics in antenna, phased array, and sensor systems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sweezy, Jeremy Ed

A photon next-event fluence estimator at a point has been implemented in the Monte Carlo Application Toolkit (MCATK). The next-event estimator provides an expected value estimator for the flux at a point due to all source and collision events. An advantage of the next-event estimator over track-length estimators, which are normally employed in MCATK, is that flux estimates can be made in locations that have no random walk particle tracks. The next-event estimator allows users to calculate radiographs and estimate response for detectors outside of the modeled geometry. The next-event estimator is not yet accessable through the MCATK FlatAPI formore » C and Fortran. The next-event estimator in MCATK has been tested against MCNP6 using 5 suites of test problems. No issues were found in the MCATK implementation. One issue was found in the exclusion radius approximation in MCNP6. The theory, implementation, and testing are described in this document.« less

COMPILATION OF CONVERSION COEFFICIENTS FOR THE DOSE TO THE LENS OF THE EYE

PubMed Central

2017-01-01

Abstract A compilation of fluence-to-absorbed dose conversion coefficients for the dose to the lens of the eye is presented. The compilation consists of both previously published data and newly calculated values: photon data (5 keV–50 MeV for both kerma approximation and full electron transport), electron data (10 keV–50 MeV), and positron data (1 keV–50 MeV) – neutron data will be published separately. Values are given for angles of incidence from 0° up to 90° in steps of 15° and for rotational irradiation. The data presented can be downloaded from this article's website and they are ready for use by Report Committee (RC) 26. This committee has been set up by the International Commission on Radiation Units and Measurements (ICRU) and is working on a ‘proposal for a redefinition of the operational quantities for external radiation exposure’. PMID:27542816

First-principles calculation of the polarization-dependent force driving the Eg mode in bismuth under optical excitation.

NASA Astrophysics Data System (ADS)

Murray, Eamonn; Fahy, Stephen

2014-03-01

Using first principles electronic structure methods, we calculate the induced force on the Eg (zone centre transverse optical) phonon mode in bismuth immediately after absorption of polarized light. When radiation with polarization perpendicular to the c-axis is absorbed in bismuth, the distribution of excited electrons and holes breaks the three-fold rotational symmetry and leads to a net force on the atoms in the direction perpendicular to the axis. We calculate the initial excited electronic distribution as a function of photon energy and polarization and find the resulting transverse and longitudinal forces experienced by the atoms. Using the measured, temperature-dependent rate of decay of the transverse force[2], we predict the approximate amplitude of induced atomic motion in the Eg mode as a function of temperature and optical fluence. This work is supported by Science Foundation Ireland and a Marie Curie International Incoming Fellowship.

A Monte Carlo model for photoneutron generation by a medical LINAC

NASA Astrophysics Data System (ADS)

Sumini, M.; Isolan, L.; Cucchi, G.; Sghedoni, R.; Iori, M.

2017-11-01

For an optimal tuning of the radiation protection planning, a Monte Carlo model using the MCNPX code has been built, allowing an accurate estimate of the spectrometric and geometrical characteristics of photoneutrons generated by a Varian TrueBeam Stx© medical linear accelerator. We considered in our study a device working at the reference energy for clinical applications of 15 MV, stemmed from a Varian Clinac©2100 modeled starting from data collected thanks to several papers available in the literature. The model results were compared with neutron and photon dose measurements inside and outside the bunker hosting the accelerator obtaining a complete dose map. Normalized neutron fluences were tallied in different positions at the patient plane and at different depths. A sensitivity analysis with respect to the flattening filter material were performed to enlighten aspects that could influence the photoneutron production.

Marshall Space Flight Center's Solar Wind Facility

NASA Technical Reports Server (NTRS)

Wright, K. H.; Schneider, T. A.; Vaughn, J. A.; Whittlesey, P. L.

2017-01-01

Historically, NASA's Marshall Space Flight Center (MSFC) has operated a Solar Wind Facility (SWF) to provide long term particle and photon exposure to material samples. The requirements on the particle beam details were not stringent as the cumulative fluence level is the test goal. Motivated by development of the faraday cup instrument on the NASA Solar Probe Plus (SPP) mission, the MSFC SWF has been upgraded to included high fidelity particle beams providing broadbeam ions, broadbeam electrons, and narrow beam protons or ions, which cover a wide dynamic range of solar wind velocity and flux conditions. The large vacuum chamber with integrated cryo-shroud, combined with a 3-axis positioning system, provides an excellent platform for sensor development and qualification. This short paper provides some details of the SWF charged particle beams characteristics in the context of the Solar Probe Plus program requirements. Data will be presented on the flux and energy ranges as well as beam stability.

Exciton–exciton annihilation and biexciton stimulated emission in graphene nanoribbons

DOE PAGES

Soavi, Giancarlo; Dal Conte, Stefano; Manzoni, Cristian; ...

2016-03-17

Graphene nanoribbons display extraordinary optical properties due to one-dimensional quantum-confinement, such as width-dependent bandgap and strong electron–hole interactions, responsible for the formation of excitons with extremely high binding energies. Here we use femtosecond transient absorption spectroscopy to explore the ultrafast optical properties of ultranarrow, structurally well-defined graphene nanoribbons as a function of the excitation fluence, and the impact of enhanced Coulomb interaction on their excited states dynamics. We show that in the high-excitation regime biexcitons are formed by nonlinear exciton–exciton annihilation, and that they radiatively recombine via stimulated emission. We obtain a biexciton binding energy of ≈250meV, in very goodmore » agreement with theoretical results from quantum Monte Carlo simulations. As a result, these observations pave the way for the application of graphene nanoribbons in photonics and optoelectronics.« less

Development and validation of a GEANT4 radiation transport code for CT dosimetry

PubMed Central

Carver, DE; Kost, SD; Fernald, MJ; Lewis, KG; Fraser, ND; Pickens, DR; Price, RR; Stabin, MG

2014-01-01

We have created a radiation transport code using the GEANT4 Monte Carlo toolkit to simulate pediatric patients undergoing CT examinations. The focus of this paper is to validate our simulation with real-world physical dosimetry measurements using two independent techniques. Exposure measurements were made with a standard 100-mm CT pencil ionization chamber, and absorbed doses were also measured using optically stimulated luminescent (OSL) dosimeters. Measurements were made in air, a standard 16-cm acrylic head phantom, and a standard 32-cm acrylic body phantom. Physical dose measurements determined from the ionization chamber in air for 100 and 120 kVp beam energies were used to derive photon-fluence calibration factors. Both ion chamber and OSL measurement results provide useful comparisons in the validation of our Monte Carlo simulations. We found that simulated and measured CTDI values were within an overall average of 6% of each other. PMID:25706135

Development and validation of a GEANT4 radiation transport code for CT dosimetry.

PubMed

Carver, D E; Kost, S D; Fernald, M J; Lewis, K G; Fraser, N D; Pickens, D R; Price, R R; Stabin, M G

2015-04-01

The authors have created a radiation transport code using the GEANT4 Monte Carlo toolkit to simulate pediatric patients undergoing CT examinations. The focus of this paper is to validate their simulation with real-world physical dosimetry measurements using two independent techniques. Exposure measurements were made with a standard 100-mm CT pencil ionization chamber, and absorbed doses were also measured using optically stimulated luminescent (OSL) dosimeters. Measurements were made in air with a standard 16-cm acrylic head phantom and with a standard 32-cm acrylic body phantom. Physical dose measurements determined from the ionization chamber in air for 100 and 120 kVp beam energies were used to derive photon-fluence calibration factors. Both ion chamber and OSL measurement results provide useful comparisons in the validation of the Monte Carlo simulations. It was found that simulated and measured CTDI values were within an overall average of 6% of each other.

DANCE : Device for Measurement of (n.g.) Reactions on radioactive Species /

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chamberlin, E. P.; Dragowsky, M.; Fowler, Malcolm M.

2001-01-01

DANCE (Device for Advanced Neutron Capture Experiments) is a 4{pi} 162 element BaF{sub 2} array under development at Los Alamos National Laboratory. It is designed to provide high granularity, fast timing and high photon detection efficiency. It will be located at the Los Alamos Neutron Scattering Center where neutrons are produced using 800 MeV proton induced spallation reactions on heavy element production targets. Using the pulsed high neutron fluence available at this facility combined with time of flight techniques it will be possible to make neutron capture measurements in the neutron energy range from eV to 100's of keV onmore » rare and radioactive target material at the milligram and below level. These measurements will provide critically needed data for the interpretation of the astrophysical s-process 'branching point' nuclei as well as information for reactions needed in understanding transmutation processes of radioactive species.« less

Quantum beats from the coherent interaction of hole states with surface state in near-surface quantum well

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khan, Salahuddin; Jayabalan, J., E-mail: jjaya@rrcat.gov.in; Chari, Rama

2014-08-18

We report tunneling assisted beating of carriers in a near-surface single GaAsP/AlGaAs quantum well using transient reflectivity measurement. The observed damped oscillating signal has a period of 120 ± 6 fs which corresponds to the energy difference between lh1 and hh2 hole states in the quantum well. Comparing the transient reflectivity signal at different photon energies and with a buried quantum well sample, we show that the beating is caused by the coherent coupling between surface state and the hole states (lh1 and hh2) in the near-surface quantum well. The dependence of decay of coherence of these tunneling carriers on the excitationmore » fluence is also reported. This observation on the coherent tunneling of carrier is important for future quantum device applications.« less

NuSTAR observations of GRB 130427A establish a single component synchrotron afterglow origin for the late optical to multi-GEV emission

DOE PAGES

Kouveliotou, Chryssa; Granot, J.; Racusin, J. L.; ...

2013-11-21

Here, GRB 130427A occurred in a relatively nearby galaxy; its prompt emission had the largest GRB fluence ever recorded. The afterglow of GRB 130427A was bright enough for the Nuclear Spectroscopic Telescope ARray ( NuSTAR) to observe it in the 3-79 keV energy range long after its prompt emission (~1.5 and 5 days). This range, where afterglow observations were previously not possible, bridges an important spectral gap. Combined with Swift, Fermi, and ground-based optical data, NuSTAR observations unambiguously establish a single afterglow spectral component from optical to multi-GeV energies a day after the event, which is almost certainly synchrotron radiation.more » Such an origin of the late-time Fermi/Large Area Telescope >10 GeV photons requires revisions in our understanding of collisionless relativistic shock physics.« less

Harmonic Quantum Coherence of Multiple Excitons in PbS/CdS Core-Shell Nanocrystals

NASA Astrophysics Data System (ADS)

Tahara, Hirokazu; Sakamoto, Masanori; Teranishi, Toshiharu; Kanemitsu, Yoshihiko

2017-12-01

The generation and recombination dynamics of multiple excitons in nanocrystals (NCs) have attracted much attention from the viewpoints of fundamental physics and device applications. However, the quantum coherence of multiple exciton states in NCs still remains unclear due to a lack of experimental support. Here, we report the first observation of harmonic dipole oscillations in PbS/CdS core-shell NCs using a phase-locked interference detection method for transient absorption. From the ultrafast coherent dynamics and excitation-photon-fluence dependence of the oscillations, we found that multiple excitons cause the harmonic dipole oscillations with ω , 2 ω , and 3 ω oscillations, even though the excitation pulse energy is set to the exciton resonance frequency, ω . This observation is closely related to the quantum coherence of multiple exciton states in NCs, providing important insights into multiple exciton generation mechanisms.

Femtosecond laser fluence based nanostructuring of W and Mo in ethanol

NASA Astrophysics Data System (ADS)

Bashir, Shazia; Rafique, Muhammad Shahid; Nathala, Chandra Sekher; Ajami, Ali Asghar; Husinsky, Wolfgang

2017-05-01

The effect of femtosecond laser fluence on nanostructuring of Tungsten (W) and Molybdenum (Mo) has been investigated after ablation in ethanol environment. A Ti: Sapphire laser (800 nm, 30 fs) at fluences ranging from 0.6 to 5.7 J cm-2 was employed to ablate targets. The growth of structures on the surface of irradiated targets is investigated by Field Emission Scanning Electron Microscope (FESEM) analysis. The SEM was performed for both central as well as the peripheral ablated regions. It is observed that both the development and shape of nanoscale features is dependent upon deposited energies to the target surface as well as nature of material. Nanostructures grown on Mo are more distinct and well defined as compared to W. At central ablated areas of W, unorganized Laser Induced Periodic Surface Structures (LIPSS) are grown at low fluences, whereas, nonuniform melting along with cracking is observed at higher fluences. In case of Mo, well-defined and organized LIPSS are observed for low fluences. With increasing fluence, LIPSS become unorganized and broken with an appearance of cracks and are completely vanished with the formation of nanoscale cavities and conical structures. In case of peripheral ablated areas broken and bifurcated LIPSS are grown for all fluences for both materials. The, ablated diameter, ablation depth, ablation rate and the dependence of periodicity of LIPSS on the laser fluence are also estimated for both W and Mo. Parametric instabilities of laser-induced plasma along with generation and scattering of surface plasmons is considered as a possible cause for the formation of LIPSS. For ethanol assisted ablation, the role of bubble cavitation, precipitation, confinement and the convective flow is considered to be responsible for inducing increased hydrodynamic instabilities at the liquid-solid interface.

Linoleic Acid-Induced Ultra-Weak Photon Emission from Chlamydomonas reinhardtii as a Tool for Monitoring of Lipid Peroxidation in the Cell Membranes

PubMed Central

Prasad, Ankush; Pospíšil, Pavel

2011-01-01

Reactive oxygen species formed as a response to various abiotic and biotic stresses cause an oxidative damage of cellular component such are lipids, proteins and nucleic acids. Lipid peroxidation is considered as one of the major processes responsible for the oxidative damage of the polyunsaturated fatty acid in the cell membranes. Various methods such as a loss of polyunsaturated fatty acids, amount of the primary and the secondary products are used to monitor the level of lipid peroxidation. To investigate the use of ultra-weak photon emission as a non-invasive tool for monitoring of lipid peroxidation, the involvement of lipid peroxidation in ultra-weak photon emission was studied in the unicellular green alga Chlamydomonas reinhardtii. Lipid peroxidation initiated by addition of exogenous linoleic acid to the cells was monitored by ultra-weak photon emission measured with the employment of highly sensitive charged couple device camera and photomultiplier tube. It was found that the addition of linoleic acid to the cells significantly increased the ultra-weak photon emission that correlates with the accumulation of lipid peroxidation product as measured using thiobarbituric acid assay. Scavenging of hydroxyl radical by mannitol, inhibition of intrinsic lipoxygenase by catechol and removal of molecular oxygen considerably suppressed ultra-weak photon emission measured after the addition of linoleic acid. The photon emission dominated at the red region of the spectrum with emission maximum at 680 nm. These observations reveal that the oxidation of linoleic acid by hydroxyl radical and intrinsic lipoxygenase results in the ultra-weak photon emission. Electronically excited species such as excited triplet carbonyls are the likely candidates for the primary excited species formed during the lipid peroxidation, whereas chlorophylls are the final emitters of photons. We propose here that the ultra-weak photon emission can be used as a non-invasive tool for the detection of lipid peroxidation in the cell membranes. PMID:21799835

Analysis of multiple photoreceptor pigments for phototropism in a mutant of Arabidopsis thaliana

NASA Technical Reports Server (NTRS)

Konjevic, R.; Khurana, J. P.; Poff, K. L.

1992-01-01

The shape of the fluence-response relationship for the phototropic response of the JK224 strain of Arabidopsis thaliana depends on the fluence rate and wavelength of the actinic light. At low fluence rate (0.1 micromole m-2 s-1), the response to 450-nm light is characterized by a single maximum at about 9 micromoles m-2. At higher fluence rate (0.4 micromole m-2 s-1), the response shows two maxima, at 4.5 and 9 micromoles m-2. The response to 510-nm light shows a single maximum at 4.5 micromoles m-2. Unilateral preirradiation with high fluence rate (25 micromoles m-2 s-1) 510-nm light eliminates the maximum at 4.5 micromoles m-2 in the fluence response curve to a subsequent unilateral 450-nm irradiation, while the second maximum at 9 micromoles m-2 is unaffected. Based on these results, it is concluded that a single photoreceptor pigment has been altered in the JK224 strain of Arabidopsis thaliana.

Space Environment Effects: Model for Emission of Solar Protons (ESP): Cumulative and Worst Case Event Fluences

NASA Technical Reports Server (NTRS)

Xapsos, M. A.; Barth, J. L.; Stassinopoulos, E. G.; Burke, E. A.; Gee, G. B.

1999-01-01

The effects that solar proton events have on microelectronics and solar arrays are important considerations for spacecraft in geostationary and polar orbits and for interplanetary missions. Designers of spacecraft and mission planners are required to assess the performance of microelectronic systems under a variety of conditions. A number of useful approaches exist for predicting information about solar proton event fluences and, to a lesser extent, peak fluxes. This includes the cumulative fluence over the course of a mission, the fluence of a worst-case event during a mission, the frequency distribution of event fluences, and the frequency distribution of large peak fluxes. Naval Research Laboratory (NRL) and NASA Goddard Space Flight Center, under the sponsorship of NASA's Space Environments and Effects (SEE) Program, have developed a new model for predicting cumulative solar proton fluences and worst-case solar proton events as functions of mission duration and user confidence level. This model is called the Emission of Solar Protons (ESP) model.

Space Environment Effects: Model for Emission of Solar Protons (ESP)--Cumulative and Worst-Case Event Fluences

NASA Technical Reports Server (NTRS)

Xapsos, M. A.; Barth, J. L.; Stassinopoulos, E. G.; Burke, Edward A.; Gee, G. B.

1999-01-01

The effects that solar proton events have on microelectronics and solar arrays are important considerations for spacecraft in geostationary and polar orbits and for interplanetary missions. Designers of spacecraft and mission planners are required to assess the performance of microelectronic systems under a variety of conditions. A number of useful approaches exist for predicting information about solar proton event fluences and, to a lesser extent, peak fluxes. This includes the cumulative fluence over the course of a mission, the fluence of a worst-case event during a mission, the frequency distribution of event fluences, and the frequency distribution of large peak fluxes. Naval Research Laboratory (NRL) and NASA Goddard Space Flight Center, under the sponsorship of NASA's Space Environments and Effects (SEE) Program, have developed a new model for predicting cumulative solar proton fluences and worst-case solar proton events as functions of mission duration and user confidence level. This model is called the Emission of Solar Protons (ESP) model.

Temperature, illumination and fluence dependence of current and voltage in electron irradiated solar cells

NASA Technical Reports Server (NTRS)

Obenschain, A. F.; Faith, T. J.

1973-01-01

Emperical equations have been derived from measurements of solar cell photovoltaic characteristics relating light generated current, IL, and open circuit voltage, VO, to cell temperature, T, intensity of illumination, W, and 1 Mev electron fluence, phi both 2 ohm-cm and 10 ohm-cm cells were tested. The temperature dependency of IL is similar for both resistivities at 140mw/sq cm; at high temperature the coefficient varies with fluence as phi 0.18, while at low temperatures the coefficient is relatively independent of fluence. Fluence dependent degration causes a decrease in IL at a rate proportional to phi 0.153 for both resistivities. At all intensities other than 560 mw/sq cm, a linear dependence of IL on illumination was found. The temperature coefficient of voltage was, to a good approximation, independent of both temperature and illumination for both resistivities. Illumination dependence of VOC was logarithmic, while the decrease with fluence of VOC varied as phi 0.25 for both resistivities.

Investigation of the Stability and 1.0 MeV Proton Radiation Resistance of Commercially Produced Hydrogenated Amorphous Silicon Alloy Solar Cells

NASA Technical Reports Server (NTRS)

Lord, Kenneth R., II; Walters, Michael R.; Woodyard, James R.

1994-01-01

The radiation resistance of commercial solar cells fabricated from hydrogenated amorphous silicon alloys is reported. A number of different device structures were irradiated with 1.0 MeV protons. The cells were insensitive to proton fluences below 1E12 sq cm. The parameters of the irradiated cells were restored with annealing at 200 C. The annealing time was dependent on proton fluence. Annealing devices for one hour restores cell parameters for fluences below 1E14 sq cm fluences above 1E14 sq cm require longer annealing times. A parametric fitting model was used to characterize current mechanisms observed In dark I-V measurements. The current mechanism were explored with irradiation fluence, and voltage and light soaking times. The thermal generation current density and quality factor increased with proton fluence. Device simulation shows the degradation in cell characteristics may be explained by the reduction of the electric field in the intrinsic layer.

Equivalent electron fluence for solar proton damage in GaAs shallow junction cells

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Stock, L. V.

1984-01-01

The short-circuit current reduction in GaAs shallow junction heteroface solar cells was calculated according to a simplified solar cell damage model in which the nonuniformity of the damage as a function of penetration depth is treated explicitly. Although the equivalent electron fluence was not uniquely defined for low-energy monoenergetic proton exposure, an equivalent electron fluence is found for proton spectra characteristic of the space environment. The equivalent electron fluence ratio was calculated for a typical large solar flare event for which the proton spectrum is PHI(sub p)(E) = A/E(p/sq. cm) where E is in MeV. The equivalent fluence ratio is a function of the cover glass shield thickness or the corresponding cutoff energy E(sub c). In terms of the cutoff energy, the equivalent 1 MeV electron fluence ratio is r(sub p)(E sub c) = 10(9)/E(sub c)(1.8) where E(sub c) is in units of KeV.

Multiple phytochromes are involved in red-light-induced enhancement of first-positive phototropism in arabidopsis thaliana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janoudi, A.K.; Gordon, W.R.; Poff, K.L.

1997-03-01

The amplitude of phototropic curvature to blue light is enhanced by a prior exposure of seedlings to red light. This enhancement is mediated by phytochrome. Fluence-response relationships have been constructed for red-light-induced enhancement in the phytochrome A (phyA) null mutant, the phytochrome B- (phyB) deficient mutant, and in two transgenic lines of Arabidopsis thaliana that overexpress either phyA or phyB. These fluence-response relationships demonstrate the existence of two responses in enhancement, a response in the very-low-to-low-fluence range, and a response in the high-fluence range. Only the response in the high-fluence range is present in the phyA null mutant. In contrast,more » the phyB-deficient mutant is indistinguishable from the wild-type parent in red-light responsiveness. These data indicate that phyA is necessary for the very-low-to-low but not the high-fluence response, and that phyB is not necessary for either response range. Based on these results, the high-fluence response, if controlled by a single phytochrome, must be controlled by a phytochrome other than phyA or phyB. Overexpression of phyA has a negative effect and overexpression of phyB has an enhancing effect in the high fluence range. These results suggest that overexpression of either phytochrome perturbs the function of the endogenous photoreceptor system in unpreditable fashion. 25 refs., 3 figs.« less

Visualizing and quantifying dose distribution in a UV reactor using three-dimensional laser-induced fluorescence.

PubMed

Gandhi, Varun N; Roberts, Philip J W; Kim, Jae-Hong

2012-12-18

Evaluating the performance of typical water treatment UV reactors is challenging due to the complexity in assessing spatial and temporal variation of UV fluence, resulting from highly unsteady, turbulent nature of flow and variation in UV intensity. In this study, three-dimensional laser-induced fluorescence (3DLIF) was applied to visualize and quantitatively analyze a lab-scale UV reactor consisting of one lamp sleeve placed perpendicular to flow. Mapping the spatial and temporal fluence delivery and MS2 inactivation revealed the highest local fluence in the wake zone due to longer residence time and higher UV exposure, while the lowest local fluence occurred in a region near the walls due to short-circuiting flow and lower UV fluence rate. Comparing the tracer based decomposition between hydrodynamics and IT revealed similar coherent structures showing the dependency of fluence delivery on the reactor flow. The location of tracer injection, varying the height and upstream distance from the lamp center, was found to significantly affect the UV fluence received by the tracer. A Lagrangian-based analysis was also employed to predict the fluence along specific paths of travel, which agreed with the experiments. The 3DLIF technique developed in this study provides new insight on dose delivery that fluctuates both spatially and temporally and is expected to aid design and optimization of UV reactors as well as validate computational fluid dynamics models that are widely used to simulate UV reactor performances.

Epidermal protection with cryogen spray cooling during high fluence pulsed dye laser irradiation: an ex vivo study.

PubMed

Tunnell, J W; Nelson, J S; Torres, J H; Anvari, B

2000-01-01

Higher laser fluences than currently used in therapy (5-10 J/cm(2)) are expected to result in more effective treatment of port wine stain (PWS) birthmarks. However, higher incident fluences increase the risk of epidermal damage caused by absorption of light by melanin. Cryogen spray cooling offers an effective method to reduce epidermal injury during laser irradiation. The objective of this study was to determine whether high laser incident fluences (15-30 J/cm(2)) could be used while still protecting the epidermis in ex vivo human skin samples. Non-PWS skin from a human cadaver was irradiated with a Candela ScleroPlus Laser (lambda = 585 nm; pulse duration = 1.5 msec) by using various incident fluences (8-30 J/cm(2)) without and with cryogen spray cooling (refrigerant R-134a; spurt durations: 40-250 msec). Assessment of epidermal damage was based on histologic analysis. Relatively short spurt durations (40-100 msec) protected the epidermis for laser incident fluences comparable to current therapeutic levels (8-10 J/cm(2)). However, longer spurt durations (100-250 msec) increased the fluence threshold for epidermal damage by a factor of three (up to 30 J/cm(2)) in these ex vivo samples. Results of this ex vivo study show that epidermal protection from high laser incident fluences can be achieved by increasing the cryogen spurt duration immediately before pulsed laser exposure. Copyright 2000 Wiley-Liss, Inc.

An 808-nm Diode Laser with a Flat-Top Handpiece Positively Photobiomodulates Mitochondria Activities.

PubMed

Amaroli, Andrea; Ravera, Silvia; Parker, Steven; Panfoli, Isabella; Benedicenti, Alberico; Benedicenti, Stefano

2016-11-01

Photobiomodulation is proposed as a non-linear process. Only the action of light at a low intensity and fluence is assumed to have stimulation on cells; whereas a higher light intensity and fluence generates negative effects, exhausting the cell's energy reserve as a consequence of a too strong stimulation. In our work, we detected the photobiomodulatory effect of an 808-nm higher-fluence diode laser [64 J/cm 2 -1 W, continuous wave (CW)] irradiated by a flat-top handpiece on mitochondria activities, such as oxygen consumption, activity of mitochondria complexes I, II, III, and IV, and cytochrome c as well as ATP synthesis. The experiments are performed by standard procedure on mitochondria purified from bovine liver. Our higher-fluence diode laser positively photobiomodulates the mitochondria oxygen consumption, the activity of the complexes III and IV, and the ATP production, with a P/O = 2.6. The other activities are not influenced. Our data show for the first time that even the higher fluences (64 J/cm 2 -1 W), similar to the low fluences, can photobiostimulate the mitochondria respiratory chain without uncoupling them and can induce an increment in the ATP production. These results suggest that the negative effects of higher fluences observed to date are not unequivocally due to higher fluence per se but might be a consequence of the irradiation carried by handpieces with a Gaussian profile.

Charge collection and field profile studies of heavily irradiated strip sensors for the ATLAS inner tracker upgrade

NASA Astrophysics Data System (ADS)

Hara, K.; Allport, P. P.; Baca, M.; Broughton, J.; Chisholm, A.; Nikolopoulos, K.; Pyatt, S.; Thomas, J. P.; Wilson, J. A.; Kierstead, J.; Kuczewski, P.; Lynn, D.; Arratia, M.; Hommels, L. B. A.; Ullan, M.; Bloch, I.; Gregor, I. M.; Tackmann, K.; Trofimov, A.; Yildirim, E.; Hauser, M.; Jakobs, K.; Kuehn, S.; Mahboubi, K.; Mori, R.; Parzefall, U.; Clark, A.; Ferrere, D.; Gonzalez Sevilla, S.; Ashby, J.; Blue, A.; Bates, R.; Buttar, C.; Doherty, F.; McMullen, T.; McEwan, F.; O'Shea, V.; Kamada, S.; Yamamura, K.; Ikegami, Y.; Nakamura, K.; Takubo, Y.; Unno, Y.; Takashima, R.; Chilingarov, A.; Fox, H.; Affolder, A. A.; Casse, G.; Dervan, P.; Forshaw, D.; Greenall, A.; Wonsak, S.; Wormald, M.; Cindro, V.; Kramberger, G.; Mandić, I.; Mikuž, M.; Gorelov, I.; Hoeferkamp, M.; Palni, P.; Seidel, S.; Taylor, A.; Toms, K.; Wang, R.; Hessey, N. P.; Valencic, N.; Hanagaki, K.; Dolezal, Z.; Kodys, P.; Bohm, J.; Mikestikova, M.; Bevan, A.; Beck, G.; Milke, C.; Domingo, M.; Fadeyev, V.; Galloway, Z.; Hibbard-Lubow, D.; Liang, Z.; Sadrozinski, H. F.-W.; Seiden, A.; To, K.; French, R.; Hodgson, P.; Marin-Reyes, H.; Parker, K.; Jinnouchi, O.; Hara, K.; Sato, K.; Sato, K.; Hagihara, M.; Iwabuchi, S.; Bernabeu, J.; Civera, J. V.; Garcia, C.; Lacasta, C.; Marti i. Garcia, S.; Rodriguez, D.; Santoyo, D.; Solaz, C.; Soldevila, U.

2016-09-01

The ATLAS group has evaluated the charge collection in silicon microstrip sensors irradiated up to a fluence of 1 ×1016 neq/cm2, exceeding the maximum of 1.6 ×1015 neq/cm2 expected for the strip tracker during the high luminosity LHC (HL-LHC) period including a safety factor of 2. The ATLAS12, n+-on-p type sensor, which is fabricated by Hamamatsu Photonics (HPK) on float zone (FZ) substrates, is the latest barrel sensor prototype. The charge collection from the irradiated 1×1 cm2 barrel test sensors has been evaluated systematically using penetrating β-rays and an Alibava readout system. The data obtained at different measurement sites are compared with each other and with the results obtained from the previous ATLAS07 design. The results are very consistent, in particular, when the deposit charge is normalized by the sensor's active thickness derived from the edge transient current technique (edge-TCT) measurements. The measurements obtained using β-rays are verified to be consistent with the measurements using an electron beam. The edge-TCT is also effective for evaluating the field profiles across the depth. The differences between the irradiated ATLAS07 and ATLAS12 samples have been examined along with the differences among the samples irradiated with different radiation sources: neutrons, protons, and pions. The studies of the bulk properties of the devices show that the devices can yield a sufficiently large signal for the expected fluence range in the HL-LHC, thereby acting as precision tracking sensors.

Characterisation of an accelerator-based neutron source for BNCT versus beam energy

NASA Astrophysics Data System (ADS)

Agosteo, S.; Curzio, G.; d'Errico, F.; Nath, R.; Tinti, R.

2002-01-01

Neutron capture in 10B produces energetic alpha particles that have a high linear energy transfer in tissue. This results in higher cell killing and a higher relative biological effectiveness compared to photons. Using suitably designed boron compounds which preferentially localize in cancerous cells instead of healthy tissues, boron neutron capture therapy (BNCT) has the potential of providing a higher tumor cure rate within minimal toxicity to normal tissues. This clinical approach requires a thermal neutron source, generally a nuclear reactor, with a fluence rate sufficient to deliver tumorcidal doses within a reasonable treatment time (minutes). Thermal neutrons do not penetrate deeply in tissue, therefore BNCT is limited to lesions which are either superficial or otherwise accessible. In this work, we investigate the feasibility of an accelerator-based thermal neutron source for the BNCT of skin melanomas. The source was designed via MCNP Monte Carlo simulations of the thermalization of a fast neutron beam, generated by 7 MeV deuterons impinging on a thick target of beryllium. The neutron field was characterized at several deuteron energies (3.0-6.5 MeV) in an experimental structure installed at the Van De Graaff accelerator of the Laboratori Nazionali di Legnaro, in Italy. Thermal and epithermal neutron fluences were measured with activation techniques and fast neutron spectra were determined with superheated drop detectors (SDD). These neutron spectrometry and dosimetry studies indicated that the fast neutron dose is unacceptably high in the current design. Modifications to the current design to overcome this problem are presented.

Lower Ionosphere Sensitivity to Solar X-ray Flares Over a Complete Solar Cycle Evaluated From VLF Signal Measurements

NASA Astrophysics Data System (ADS)

Macotela, Edith L.; Raulin, Jean-Pierre; Manninen, Jyrki; Correia, Emília; Turunen, Tauno; Magalhães, Antonio

2017-12-01

The daytime lower ionosphere behaves as a solar X-ray flare detector, which can be monitored using very low frequency (VLF) radio waves that propagate inside the Earth-ionosphere waveguide. In this paper, we infer the lower ionosphere sensitivity variation over a complete solar cycle by using the minimum X-ray fluence (FXmin) necessary to produce a disturbance of the quiescent ionospheric conductivity. FXmin is the photon energy flux integrated over the time interval from the start of a solar X-ray flare to the beginning of the ionospheric disturbance recorded as amplitude deviation of the VLF signal. FXmin is computed for ionospheric disturbances that occurred in the time interval of December-January from 2007 to 2016 (solar cycle 24). The computation of FXmin uses the X-ray flux in the wavelength band below 0.2 nm and the amplitude of VLF signals transmitted from France (HWU), Turkey (TBB), and U.S. (NAA), which were recorded in Brazil, Finland, and Peru. The main result of this study is that the long-term variation of FXmin is correlated with the level of solar activity, having FXmin values in the range (1 - 12) × 10-7 J/m2. Our result suggests that FXmin is anticorrelated with the lower ionosphere sensitivity, confirming that the long-term variation of the ionospheric sensitivity is anticorrelated with the level of solar activity. This result is important to identify the minimum X-ray fluence that an external source of ionization must overcome in order to produce a measurable ionospheric disturbance during daytime.

Role of defects in laser-induced modifications of silica coatings and fused silica using picosecond pulses at 1053 nm: II Scaling laws and the density of precursors

DOE PAGES

Laurence, T. A.; Negres, R. A.; Ly, S.; ...

2017-06-22

Here, we investigate the role of defects in laser-induced damage of fused silica and of silica coatings produced by e-beam and PIAD processes which are used in damage resistant, multi-layer dielectric, reflective optics. We perform experiments using 1053 nm, 1–60 ps laser pulses with varying beam size, number of shots, and pulse widths in order to understand the characteristics of defects leading to laser-induced damage. This pulse width range spans a transition in mechanisms from intrinsic material ablation for short pulses to defect-dominated damage for longer pulses. We show that for pulse widths as short as 10 ps, laser-induced damagemore » properties of fused silica and silica films are dominated by isolated absorbers. The density of these precursors and their fluence dependence of damage initiation suggest a single photon process for initial energy absorption in these precursors. Higher density precursors that initiate close to the ablation threshold at shorter pulse widths are also observed in fused silica, whose fluence and pulse width scaling suggest a multiphoton initiation process. We also show that these initiated damage sites grow with subsequent laser pulses. We show that scaling laws obtained in more conventional ways depend on the beam size and on the definition of damage for ps pulses. For this reason, coupling scaling laws with the density of precursors are critical to understanding the damage limitations of optics in the ps regime.« less

Role of defects in laser-induced modifications of silica coatings and fused silica using picosecond pulses at 1053 nm: II Scaling laws and the density of precursors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laurence, T. A.; Negres, R. A.; Ly, S.

Here, we investigate the role of defects in laser-induced damage of fused silica and of silica coatings produced by e-beam and PIAD processes which are used in damage resistant, multi-layer dielectric, reflective optics. We perform experiments using 1053 nm, 1–60 ps laser pulses with varying beam size, number of shots, and pulse widths in order to understand the characteristics of defects leading to laser-induced damage. This pulse width range spans a transition in mechanisms from intrinsic material ablation for short pulses to defect-dominated damage for longer pulses. We show that for pulse widths as short as 10 ps, laser-induced damagemore » properties of fused silica and silica films are dominated by isolated absorbers. The density of these precursors and their fluence dependence of damage initiation suggest a single photon process for initial energy absorption in these precursors. Higher density precursors that initiate close to the ablation threshold at shorter pulse widths are also observed in fused silica, whose fluence and pulse width scaling suggest a multiphoton initiation process. We also show that these initiated damage sites grow with subsequent laser pulses. We show that scaling laws obtained in more conventional ways depend on the beam size and on the definition of damage for ps pulses. For this reason, coupling scaling laws with the density of precursors are critical to understanding the damage limitations of optics in the ps regime.« less

Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event

DOE PAGES

Kadler, M.; Krauß, F.; Mannheim, K.; ...

2016-04-18

The astrophysical sources of the extraterrestrial, very high-energy neutrinos detected by the IceCube collaboration remain to be identified. Gamma-ray (γ-ray) blazars have been predicted to yield a cumulative neutrino signal exceeding the atmospheric background above energies of 100 TeV, assuming that both the neutrinos and the γ-ray photons are produced by accelerated protons in relativistic jets. As the background spectrum falls steeply with increasing energy, the individual events with the clearest signature of being of extraterrestrial origin are those at petaelectronvolt energies. Inside the large positional-uncertainty fields of the first two petaelectronvolt neutrinos detected by IceCube, the integrated emission ofmore » the blazar population has a sufficiently high electromagnetic flux to explain the detected IceCube events, but fluences of individual objects are too low to make an unambiguous source association. In this paper, we report that a major outburst of the blazar PKS B1424–418 occurred in temporal and positional coincidence with a third petaelectronvolt-energy neutrino event (HESE-35) detected by IceCube. On the basis of an analysis of the full sample of γ-ray blazars in the HESE-35 field, we show that the long-term average γ-ray emission of blazars as a class is in agreement with both the measured all-sky flux of petaelectronvolt neutrinos and the spectral slope of the IceCube signal. Finally, the outburst of PKS B1424–418 provides an energy output high enough to explain the observed petaelectronvolt event, suggestive of a direct physical association.« less

An unconventional adaptation of a classical Gaussian plume dispersion scheme for the fast assessment of external irradiation from a radioactive cloud

NASA Astrophysics Data System (ADS)

Pecha, Petr; Pechova, Emilie

2014-06-01

This article focuses on derivation of an effective algorithm for the fast estimation of cloudshine doses/dose rates induced by a large mixture of radionuclides discharged into the atmosphere. A certain special modification of the classical Gaussian plume approach is proposed for approximation of the near-field dispersion problem. Specifically, the accidental radioactivity release is subdivided into consecutive one-hour Gaussian segments, each driven by a short-term meteorological forecast for the respective hours. Determination of the physical quantity of photon fluence rate from an ambient cloud irradiation is coupled to a special decomposition of the Gaussian plume shape into the equivalent virtual elliptic disks. It facilitates solution of the formerly used time-consuming 3-D integration and provides advantages with regard to acceleration of the computational process on a local scale. An optimal choice of integration limit is adopted on the basis of the mean free path of γ-photons in the air. An efficient approach is introduced for treatment of a wide range of energetic spectrum of the emitted photons when the usual multi-nuclide approach is replaced by a new multi-group scheme. The algorithm is capable of generating the radiological responses in a large net of spatial nodes. It predetermines the proposed procedure such as a proper tool for online data assimilation analysis in the near-field areas. A specific technique for numerical integration is verified on the basis of comparison with a partial analytical solution. Convergence of the finite cloud approximation to the tabulated semi-infinite cloud values for dose conversion factors was validated.

Response functions for computing absorbed dose to skeletal tissues from photon irradiation—an update

NASA Astrophysics Data System (ADS)

Johnson, Perry B.; Bahadori, Amir A.; Eckerman, Keith F.; Lee, Choonsik; Bolch, Wesley E.

2011-04-01

A comprehensive set of photon fluence-to-dose response functions (DRFs) is presented for two radiosensitive skeletal tissues—active and total shallow marrow—within 15 and 32 bone sites, respectively, of the ICRP reference adult male. The functions were developed using fractional skeletal masses and associated electron-absorbed fractions as reported for the UF hybrid adult male phantom, which in turn is based upon micro-CT images of trabecular spongiosa taken from a 40 year male cadaver. The new DRFs expand upon both the original set of seven functions produced in 1985, and a 2007 update calculated under the assumption of secondary electron escape from spongiosa. In this study, it is assumed that photon irradiation of the skeleton will yield charged particle equilibrium across all spongiosa regions at energies exceeding 200 keV. Kerma coefficients for active marrow, inactive marrow, trabecular bone and spongiosa at higher energies are calculated using the DRF algorithm setting the electron-absorbed fraction for self-irradiation to unity. By comparing kerma coefficients and DRF functions, dose enhancement factors and mass energy-absorption coefficient (MEAC) ratios for active marrow to spongiosa were derived. These MEAC ratios compared well with those provided by the NIST Physical Reference Data Library (mean difference of 0.8%), and the dose enhancement factors for active marrow compared favorably with values calculated in the well-known study published by King and Spiers (1985 Br. J. Radiol. 58 345-56) (mean absolute difference of 1.9 percentage points). Additionally, dose enhancement factors for active marrow were shown to correlate well with the shallow marrow volume fraction (R2 = 0.91). Dose enhancement factors for the total shallow marrow were also calculated for 32 bone sites representing the first such derivation for this target tissue.

High-rate x-ray spectroscopy in mammography with a CdTe detector: a digital pulse processing approach.

PubMed

Abbene, L; Gerardi, G; Principato, F; Del Sordo, S; Ienzi, R; Raso, G

2010-12-01

Direct measurement of mammographic x-ray spectra under clinical conditions is a difficult task due to the high fluence rate of the x-ray beams as well as the limits in the development of high resolution detection systems in a high counting rate environment. In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate x-ray spectroscopy in mammography. The DPP system performs a digital pile-up inspection and a digital pulse height analysis of the detector signals, digitized through a 14-bit, 100 MHz digitizer, for x-ray spectroscopy even at high photon counting rates. We investigated on the response of the digital detection system both at low (150 cps) and at high photon counting rates (up to 500 kcps) by using monoenergetic x-ray sources and a nonclinical molybdenum anode x-ray tube. Clinical molybdenum x-ray spectrum measurements were also performed by using a pinhole collimator and a custom alignment device. The detection system shows excellent performance up to 512 kcps with an energy resolution of 4.08% FWHM at 22.1 keV. Despite the high photon counting rate (up to 453 kcps), the molybdenum x-ray spectra, measured under clinical conditions, are characterized by a low number of pile-up events. The agreement between the attenuation curves and the half value layer values, obtained from the measured spectra, simulated spectra, and from the exposure values directly measured with an ionization chamber, also shows the accuracy of the measurements. These results make the proposed detection system a very attractive tool for both laboratory research and advanced quality controls in mammography.

Analyzing non-LTE Kr plasmas produced in high energy density experiments: from the Z machine to the National Ignition Facility

NASA Astrophysics Data System (ADS)

Dasgupta, Arati

2015-11-01

Designing high fluence photon sources above 10 keV are a challenge for High Energy Density plasmas. This has motivated radiation source development investigations of Kr with K-shell energies around 13 keV. Recent pulsed power driven gas-puff experiments on the refurbished Z machine at Sandia have produced intense X-rays in the multi-keV photon energy range. K-shell radiative yields and efficiencies are very high for Ar, but rapidly decrease for higher atomic number (ZA) elements such as Kr. It has been suggested that an optimum exists corresponding to a trade-off between the increase of photon energy for higher ZA elements and the corresponding fall off in radiative power. However the conversion efficiency on NIF, where the drive, energy deposition process, and target dynamics are different, does not fall off with higher ZA as rapidly as on Z. We have developed detailed atomic structure and collisional data for the full K-, L- and partial M-shell of Kr using the Flexible Atomic Code (FAC). Our non-LTE atomic model includes all collisional and recombination processes, including state-specific dielectronic recombination (DR), that significantly affect ionization balance and spectra of Kr plasmas at the temperatures and densities of concern. The model couples ionization physics, radiation production and transport, and magnetohydrodynamics. In this talk, I will give a detailed description of the model and discuss 1D Kr simulations employing a multifrequency radiation transport scheme. Synthetic K- and L-shell spectra will be compared with available experimental data. This talk will analyze experimental data indicative of the differences between Z and NIF experimental data and discuss how they affect the K-shell radiative output of Kr plasma. Work supported by DOE/NNSA.

Skeletal dosimetry in the MAX06 and the FAX06 phantoms for external exposure to photons based on vertebral 3D-microCT images

NASA Astrophysics Data System (ADS)

Kramer, R.; Khoury, H. J.; Vieira, J. W.; Kawrakow, I.

2006-12-01

3D-microCT images of vertebral bodies from three different individuals have been segmented into trabecular bone, bone marrow and bone surface cells (BSC), and then introduced into the spongiosa voxels of the MAX06 and the FAX06 phantoms, in order to calculate the equivalent dose to the red bone marrow (RBM) and the BSC in the marrow cavities of trabecular bone with the EGSnrc Monte Carlo code from whole-body exposure to external photon radiation. The MAX06 and the FAX06 phantoms consist of about 150 million 1.2 mm cubic voxels each, a part of which are spongiosa voxels surrounded by cortical bone. In order to use the segmented 3D-microCT images for skeletal dosimetry, spongiosa voxels in the MAX06 and the FAX06 phantom were replaced at runtime by so-called micro matrices representing segmented trabecular bone, marrow and BSC in 17.65, 30 and 60 µm cubic voxels. The 3D-microCT image-based RBM and BSC equivalent doses for external exposure to photons presented here for the first time for complete human skeletons are in agreement with the results calculated with the three correction factor method and the fluence-to-dose response functions for the same phantoms taking into account the conceptual differences between the different methods. Additionally the microCT image-based results have been compared with corresponding data from earlier studies for other human phantoms. This article is dedicated to Prof. Dr Guenter Drexler from the Laboratório de Ciências Radiológicas, State University of Rio de Janeiro, on the occasion of his 70th birthday.

Response functions for computing absorbed dose to skeletal tissues from photon irradiation--an update.

PubMed

Johnson, Perry B; Bahadori, Amir A; Eckerman, Keith F; Lee, Choonsik; Bolch, Wesley E

2011-04-21

A comprehensive set of photon fluence-to-dose response functions (DRFs) is presented for two radiosensitive skeletal tissues-active and total shallow marrow-within 15 and 32 bone sites, respectively, of the ICRP reference adult male. The functions were developed using fractional skeletal masses and associated electron-absorbed fractions as reported for the UF hybrid adult male phantom, which in turn is based upon micro-CT images of trabecular spongiosa taken from a 40 year male cadaver. The new DRFs expand upon both the original set of seven functions produced in 1985, and a 2007 update calculated under the assumption of secondary electron escape from spongiosa. In this study, it is assumed that photon irradiation of the skeleton will yield charged particle equilibrium across all spongiosa regions at energies exceeding 200 keV. Kerma coefficients for active marrow, inactive marrow, trabecular bone and spongiosa at higher energies are calculated using the DRF algorithm setting the electron-absorbed fraction for self-irradiation to unity. By comparing kerma coefficients and DRF functions, dose enhancement factors and mass energy-absorption coefficient (MEAC) ratios for active marrow to spongiosa were derived. These MEAC ratios compared well with those provided by the NIST Physical Reference Data Library (mean difference of 0.8%), and the dose enhancement factors for active marrow compared favorably with values calculated in the well-known study published by King and Spiers (1985 Br. J. Radiol. 58 345-56) (mean absolute difference of 1.9 percentage points). Additionally, dose enhancement factors for active marrow were shown to correlate well with the shallow marrow volume fraction (R(2) = 0.91). Dose enhancement factors for the total shallow marrow were also calculated for 32 bone sites representing the first such derivation for this target tissue.

RESPONSE FUNCTIONS FOR COMPUTING ABSORBED DOSE TO SKELETAL TISSUES FROM PHOTON IRRADIATION – AN UPDATE

PubMed Central

Johnson, Perry; Bahadori, Amir; Eckerman, Keith; Lee, Choonsik; Bolch, Wesley E.

2014-01-01

A comprehensive set of photon fluence-to-dose response functions (DRFs) are presented for two radiosensitive skeletal tissues – active and total shallow marrow – within 15 and 32 bones sites, respectively, of the ICRP reference adult male. The functions were developed using fractional skeletal masses and associated electron absorbed fractions as reported for the UF hybrid adult male phantom, which in turn is based upon microCT images of trabecular spongiosa taken from a 40-year male cadaver. The new DRFs expand upon both the original set of seven functions produced in 1985, as well as a 2007 update calculated under the assumption of secondary electron escape from spongiosa. In the present study, it is assumed that photon irradiation of the skeleton will yield charged particle equilibrium across all spongiosa regions at energies exceeding 200 keV. Kerma factors for active marrow, inactive marrow, trabecular bone, and spongiosa at higher energies are calculated using the DRF algorithm setting the electron absorbed fraction for self-irradiation to unity. By comparing kerma factors and DRF functions, dose enhancement factors and mass energy-absorption coefficient (MEAC) ratios for active marrow to spongiosa were derived. These MEAC ratios compared well with those provided by the NIST Physical Reference Data Library (mean difference of 0.8%), and the dose enhancement factors for active marrow compared favorably with values calculated in the well-known study published by King and Spiers (1985) (mean absolute difference of 1.9 percentage points). Additionally, dose enhancement factors for active marrow were shown to correlate well with the shallow marrow volume fraction (R2 = 0.91). Dose enhancement factors for the total shallow marrow were also calculated for 32 bone sites PMID:21427484

GRO/OSSE Observations of Nuclear Line Emission from the Intense Flares of June 1991

NASA Astrophysics Data System (ADS)

Murphy, R. J.; Share, G. H.; Johnson, W. N.; Kinzer, R. L.; Kroeger, R.; Kurfess, J. D.; Strickman, M. S.; Grove, J. E.; Cameron, R.; Jung, G.; Grabelsky, D.; Matz, S. M.; Purcell, W.; Ulmer, M. P.; Frye, G.; Jenkins, T.; Jensen, C.

1992-05-01

The Oriented Scintillation Spectroscopy Experiment (OSSE) on the Compton Gamma Ray Observatory is comprised of 4 independently-oriented large-area ( ~ 500 cm(2) /detector at 511 keV) NaI detectors covering the energy range from 0.050 to 10 MeV. Solar observations are typically performed with two of the detectors staring at the Sun and two alternating between viewing the Sun and viewing background regions on two-minute timescales. In June of 1991, OSSE observed 4 of the X10+ flares from Active Region 6659. Intense gamma-ray line emission at 0.511 MeV (positron annihilation) and 2.223 MeV (neutron capture), and from several deexcitation lines of carbon and oxygen were recorded. Using a combination of data from sunward-pointing and off-pointing detectors to avoid saturation effects during the intense portions of the flares, background-subtracted spectra have been obtained. These spectra were fit to derive photon fluxes for the above-mentioned gamma-ray lines. Preliminary lower limits to the integrated fluxes in the 2.223 MeV line (not accounting for saturation effects and based on data collected only during the OSSE observation times) are about 300, 200, 30 and 100 photons/cm(2) for the June 4, 6, 9 and 11 flares, respectively. This is to be compared to a fluence of about 300 photons/cm(2) for the 1982 June 3 flare observed by the SMM Gamma-Ray Spectrometer. Integrated fluxes for the other lines will be presented and compared to line flux measurements of flares obtained with the SMM/GRS. This work is supported under NASA contract S10987C.

Development of a compact laser-produced plasma soft X-ray source for radiobiology experiments

NASA Astrophysics Data System (ADS)

Adjei, Daniel; Ayele, Mesfin Getachew; Wachulak, Przemyslaw; Bartnik, Andrzej; Wegrzynski, Łukasz; Fiedorowicz, Henryk; Vyšín, Luděk; Wiechec, Anna; Lekki, Janusz; Kwiatek, Wojciech M.; Pina, Ladislav; Davídková, Marie; Juha, Libor

2015-12-01

A desk-top laser-produced plasma (LPP) source of soft X-rays (SXR) has been developed for radiobiology research. The source is based on a double-stream gas puff target, irradiated with the focused beam of a commercial Nd:YAG laser. The source has been optimized to get a maximum photon emission from LPP in the X-ray "water window" spectral wavelength range from 2.3 nm (i.e., an absorption edge of oxygen) to 4.4 nm (i.e., an absorption edge of carbon) (280-540 eV in photon energy units) by using argon gas-puff target and spectral filtering by free-standing thin foils. The present source delivers nanosecond pulses of soft X-rays at a fluence of about 4.2 × 103 photons/μm2/pulse on a sample placed inside the vacuum chamber. In this paper, the source design, radiation output characterization measurements and initial irradiation experiments are described. The source can be useful in addressing observations related to biomolecular, cellular and organisms' sensitivity to pulsed radiation in the "water window", where carbon atoms absorb X-rays more strongly than the oxygen, mostly present in water. The combination of the SXR source and the radiobiology irradiation layout, reported in this article, make possible a systematic investigation of relationships between direct and indirect action of ionizing radiation, an increase of a local dose in carbon-rich compartments of the cell (e.g., lipid membranes), an experimental estimation of a particular role of the Auger effect (in particular in carbon atoms) in the damage to biological systems, and the study of ionization/excitation-density (LET - Linear Energy Transfer) and dose-rate effects in radiobiology.

The effect of energy spectrum change on DNA damage in and out of field in 10-MV clinical photon beams.

PubMed

Ezzati, A O; Xiao, Y; Sohrabpour, M; Studenski, M T

2015-01-01

The aim of this study was to quantify the DNA damage induced in a clinical megavoltage photon beam at various depths in and out of the field. MCNPX was used to simulate 10 × 10 and 20 × 20 cm(2) 10-MV photon beams from a clinical linear accelerator. Photon and electron spectra were collected in a water phantom at depths of 2.5, 12.5 and 22.5 cm on the central axis and at off-axis points out to 10 cm. These spectra were used as an input to a validated microdosimetric Monte Carlo code, MCDS, to calculate the RBE of induced DSB in DNA at points in and out of the primary radiation field at three depths. There was an observable difference in the energy spectra for photons and electrons for points in the primary radiation field and those points out of field. In the out-of-field region, the mean energy for the photon and electron spectra decreased by a factor of about six and three from the in-field mean energy, respectively. Despite the differences in spectra and mean energy, the change in RBE was <1 % from the in-field region to the out-of-field region at any depth. There was no significant change in RBE regardless of the location in the phantom. Although there are differences in both the photon and electron spectra, these changes do not correlate with a change in RBE in a clinical MV photon beam as the electron spectra are dominated by electrons with energies >20 keV.

Pulse fluence dependent nanograting inscription on the surface of fused silica

NASA Astrophysics Data System (ADS)

Liang, Feng; Vallée, Réal; Leang Chin, See

2012-06-01

Pulse fluence dependent nanograting inscription on the surface of fused silica is investigated. The nanograting period is found to decrease with the increase of the incident pulse fluence. Local intensity distribution and incubation effect are responsible for the change of the nanograting period.

Deuterium trapping in tungsten

NASA Astrophysics Data System (ADS)

Poon, Michael

Tungsten is one of the primary material candidates being investigated for use in the first-wall of a magnetic confinement fusion reactor. An ion accelerator was used to simulate the type of ion interaction that may occur at a plasma-facing material. Thermal desorption spectroscopy (TDS) was the primary tool used to analyze the effects of the irradiation. Secondary ion mass spectroscopy (SIMS) was used to determine the distribution of trapped D in the tungsten specimen. The tritium migration analysis program (TMAP) was used to simulate thermal desorption profiles from the D depth distributions. Fitting of the simulated thermal desorption profiles with the measured TDS results provided values of the D trap energies. Deuterium trapping in single crystal tungsten was studied as a function of the incident ion fluence, ion flux, irradiation temperature, irradiation history, and surface impurity levels during irradiation. The results show that deuterium was trapped at vacancies and voids. Two deuterium atoms could be trapped at a tungsten vacancy, with trapping energies of 1.4 eV and 1.2 eV for the first and second D atoms, respectively. In a tungsten void, D is trapped as atoms adsorbed on the inner walls of the void with a trap energy of 2.1 eV, or as D2 molecules inside the void with a trap energy of 1.2 eV. Deuterium trapping in polycrystalline tungsten was also studied as a function of the incident fluence, irradiation temperature, and irradiation history. Deuterium trapping in polycrystalline tungsten also occurs primarily at vacancies and voids with the same trap energies as in single crystal tungsten; however, the presence of grain boundaries promotes the formation of large surface blisters with high fluence irradiations at 500 K. In general, D trapping is greater in polycrystalline tungsten than in single crystal tungsten. To simulate mixed materials comprising of carbon (C) and tungsten, tungsten specimens were pre-irradiated with carbon ions prior to D irradiation. Deuterium trapping could be characterized by three regimes: (i) enhanced D retention in a graphitic film formed by the C+ irradiation; (ii) decreased D retention in a modified tungsten-carbon layer; and (iii) D retention in pure tungsten.

F γ: A new observable for photon-hadron discrimination in hybrid air shower events

DOE Office of Scientific and Technical Information (OSTI.GOV)

Niechciol, M.; Risse, M.; Ruehl, P.

To semore » arch for ultra-high-energy photons in primary cosmic rays, air shower observables are needed that allow a good separation between primary photons and primary hadrons. In this paper, we present a new observable, F γ, which can be extracted from ground-array data in hybrid events, where simultaneous measurements of the longitudinal and the lateral shower profile are performed. The observable is based on a template fit to the lateral distribution measured by the ground array with the template taking into account the complementary information from the measurement of the longitudinal profile, i.e. the primary energy and the geometry of the shower. F γ shows a very good photon-hadron separation, which is even superior to the separation given by the well-known X max observable (the atmospheric depth of the shower maximum). At energies around 1 EeV (10 EeV), F γ provides a background rejection better than 97.8 % (99.9 %) at a signal efficiency of 50 %. Advantages of the observable F γ are its technical stability with respect to irregularities in the ground array (i.e. missing or temporarily non-operating stations) and that it can be applied over the full energy range accessible to the air shower detector, down to its threshold energy. Finally and furthermore, F γ complements nicely to X max such that both observables can well be combined to achieve an even better discrimination power, exploiting the rich information available in hybrid events.« less

F γ: A new observable for photon-hadron discrimination in hybrid air shower events

DOE PAGES

Niechciol, M.; Risse, M.; Ruehl, P.; ...

2017-10-21

To semore » arch for ultra-high-energy photons in primary cosmic rays, air shower observables are needed that allow a good separation between primary photons and primary hadrons. In this paper, we present a new observable, F γ, which can be extracted from ground-array data in hybrid events, where simultaneous measurements of the longitudinal and the lateral shower profile are performed. The observable is based on a template fit to the lateral distribution measured by the ground array with the template taking into account the complementary information from the measurement of the longitudinal profile, i.e. the primary energy and the geometry of the shower. F γ shows a very good photon-hadron separation, which is even superior to the separation given by the well-known X max observable (the atmospheric depth of the shower maximum). At energies around 1 EeV (10 EeV), F γ provides a background rejection better than 97.8 % (99.9 %) at a signal efficiency of 50 %. Advantages of the observable F γ are its technical stability with respect to irregularities in the ground array (i.e. missing or temporarily non-operating stations) and that it can be applied over the full energy range accessible to the air shower detector, down to its threshold energy. Finally and furthermore, F γ complements nicely to X max such that both observables can well be combined to achieve an even better discrimination power, exploiting the rich information available in hybrid events.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flechsig, U.; Nolting, F.; Fraile Rodriguez, A.

The Surface/Interface: Microscopy beamline of the Swiss Light Source started operation in 2001. In 2007 the beamline has been significantly upgraded with a second refocusing section and a blazed grating optimized for high photon flux. Two Apple II type undulators with a plane grating monochromator using the collimated light scheme deliver photons with an energy from 90eV to about 2keV with variable polarization for the photoemission electron microscope (PEEM) as the primary user station. We measured a focus of (45x60) {mu}m({nu}xh) and a photon flux > 10{sup 12} photon/s for all gratings. Polarization switching within a few seconds is realizedmore » with the small bandpass of the monochromator and a slight detuning of the undulator.« less

Borexino's search for low-energy neutrino and antineutrino signals correlated with gamma-ray bursts

NASA Astrophysics Data System (ADS)

Agostini, M.; Altenmüller, K.; Appel, S.; Atroshchenko, V.; Bellini, G.; Benziger, J.; Bick, D.; Bonfini, G.; Bravo, D.; Caccianiga, B.; Calaprice, F.; Caminata, A.; Carlini, M.; Cavalcante, P.; Chepurnov, A.; Choi, K.; D'Angelo, D.; Davini, S.; de Kerret, H.; Derbin, A.; Di Noto, L.; Drachnev, I.; Etenko, A.; Fomenko, K.; Franco, D.; Gabriele, F.; Galbiati, C.; Ghiano, C.; Giammarchi, M.; Goeger-Neff, M.; Goretti, A.; Gromov, M.; Hagner, C.; Hungerford, E.; Ianni, Aldo; Ianni, Andrea; Jany, A.; Jedrzejczak, K.; Jeschke, D.; Kobychev, V.; Korablev, D.; Korga, G.; Kryn, D.; Laubenstein, M.; Lehnert, B.; Litvinovich, E.; Lombardi, F.; Lombardi, P.; Ludhova, L.; Lukyanchenko, G.; Machulin, I.; Manecki, S.; Maneschg, W.; Manuzio, G.; Marcocci, S.; Meroni, E.; Meyer, M.; Miramonti, L.; Misiaszek, M.; Montuschi, M.; Mosteiro, P.; Muratova, V.; Neumair, B.; Oberauer, L.; Obolensky, M.; Ortica, F.; Pallavicini, M.; Papp, L.; Pocar, A.; Ranucci, G.; Razeto, A.; Re, A.; Romani, A.; Roncin, R.; Rossi, N.; Schönert, S.; Semenov, D.; Skorokhvatov, M.; Smirnov, O.; Sotnikov, A.; Sukhotin, S.; Suvorov, Y.; Tartaglia, R.; Testera, G.; Thurn, J.; Toropova, M.; Unzhakov, E.; Vishneva, A.; Vogelaar, R. B.; von Feilitzsch, F.; Wang, H.; Weinz, S.; Winter, J.; Wojcik, M.; Wurm, M.; Yokley, Z.; Zaimidoroga, O.; Zavatarelli, S.; Zuber, K.; Zuzel, G.; Borexino Collaboration

2017-01-01

A search for neutrino and antineutrino events correlated with 2350 gamma-ray bursts (GRBs) is performed with Borexino data collected between December 2007 and November 2015. No statistically significant excess over background is observed. We look for electron antineutrinos (νbare) that inverse beta decay on protons with energies from 1.8 MeV to 15 MeV and set the best limit on the neutrino fluence from GRBs below 8 MeV. The signals from neutrinos and antineutrinos from GRBs that scatter on electrons are also searched for, a detection channel made possible by the particularly radio-pure scintillator of Borexino. We obtain currently the best limits on the neutrino fluence of all flavors and species below 7 MeV. Finally, time correlations between GRBs and bursts of events are investigated. Our analysis combines two semi-independent data acquisition systems for the first time: the primary Borexino readout optimized for solar neutrino physics up to a few MeV, and a fast waveform digitizer system tuned for events above 1 MeV.

Anomalous Kinetics of Diffusion-Controlled Defect Annealing in Irradiated Ionic Solids.

PubMed

Kotomin, Eugene; Kuzovkov, Vladimir; Popov, Anatoli I; Maier, Joachim; Vila, Rafael

2018-01-11

The annealing kinetics of the primary electronic F-type color centers (oxygen vacancies with trapped one or two electrons) is analyzed for three ionic materials (Al 2 O 3 , MgO, and MgF 2 ) exposed to intensive irradiation by electrons, neutrons, and heavy swift ions. Phenomenological theory of diffusion-controlled recombination of the F-type centers with much more mobile interstitial ions (complementary hole centers) allows us to extract from experimental data the migration energy of interstitials and pre-exponential factor of diffusion. The obtained migration energies are compared with available first-principles calculations. It is demonstrated that with the increase of radiation fluence both the migration energy and pre-exponent are decreasing in all three materials, irrespective of the type of irradiation. Their correlation satisfies the Meyer-Neldel rule observed earlier in glasses, liquids, and disordered materials.The origin of this effect is discussed. This study demonstrates that in the quantitative analysis of the radiation damage of real materials the dependence of the defect migration parameters on the radiation fluence plays an important role and cannot be neglected.

Light quality influences indigo precursors production and seed germination in Isatis tinctoria L. and Isatis indigotica Fort.

PubMed

Tozzi, Sabrina; Lercari, Bartolomeo; Angelini, Luciana G

2005-01-01

Isatis tinctoria L. and Isatis indigotica Fort. are biennial herbaceous plants belonging to the family of Cruciferae that are used as a source of natural indigo and show several morphological and genetic differences. Production of indigo (indigotin) precursors, indican (indoxyl beta-D glucoside) and isatan B (indoxyl ketogluconate), together with seed germination ability were compared in Isatis tinctoria and Isatis indigotica grown under six different light conditions (darkness, white, red, far red, blue, yellow light) at 25 degrees C. Light quality influenced both germination and production of indigo precursors in the two Isatis species. Different responsiveness to far red and blue light was observed. Indeed, a detrimental effect on germination by blue and far red light was found in I. tinctoria only. Different amounts of isatan B were produced under red and far red light in the two Isatis species. In I. tinctoria, the level of main indigo precursor isatan B was maximal under red light and minimal under far red light. Whereas in I. indigotica far red light promoted a large accumulation of isatan B. The photon fluence rate dependency for white and yellow light responses showed that the accumulation of indigo precursors was differently influenced in the two Isatis species. In particular, both white and yellow light enhanced above 40 micromol m(-2) s(-1) the production of isatan B in I. indigotica while only white light showed a photon fluence dependency in I. tinctoria. These results suggest a different role played by the labile and stable phytochrome species (phyA and phyB) in the isatan B production in I. tinctoria and I. indigotica. I. indigotica, whose germination percentage was not influenced by light quality, demonstrated higher germination capability compared with I. tinctoria. In fact, I. tinctoria showed high frequency of germination in darkness and under light sources that establish high phytochrome photoequilibrium (red, white and yellow light). Germination in I. tinctoria was negatively affected by far red and blue light. I. indigotica seeds appear to be indifferent to canopy-like light (far red). Our results provide further insights on the distinct behaviour of I. tinctoria and I. indigotica that belong to two different genetic clusters and different original environments.

Measurement of trapped proton fluences in main stack of P0006 experiment

NASA Technical Reports Server (NTRS)

Nefedov, N.; Csige, I.; Benton, E. V.; Henke, R. P.; Benton, E. R.; Frigo, L. A.

1995-01-01

We have measured directional distribution and Eastward directed mission fluence of trapped protons at two different energies with plastic nuclear track detectors (CR-39 with DOP) in the main stack of the P0006 experiment on LDEF. Results show arriving directions of trapped protons have very high anisotropy with most protons arriving from the West direction. Selecting these particles we have determined the mission fluence of Eastward directed trapped protons. We found experimental fluences are slightly higher than results of the model calculations of Armstrong and Colborn.

Individual Members of the Cab Gene Family Differ Widely in Fluence Response.

PubMed Central

White, M. J.; Kaufman, L. S.; Horwitz, B. A.; Briggs, W. R.; Thompson, W. F.

1995-01-01

Chlorophyll a/b-binding protein genes (Cab genes) can be extremely sensitive to light. Transcript accumulation following a red light pulse increases with fluence over 8 orders of magnitude (L.S. Kaufman, W.F. Thompson, W.R. Briggs [1984] Science 226: 1447-1449). We have constructed fluence-response curves for individual Cab genes. At least two Cab genes (Cab-8 and AB96) show a very low fluence response to a single red light pulse. In contrast, two other Cab genes (AB80 and AB66) fail to produce detectable transcript following a single pulse of either red or blue light but are expressed in continuous red light. Thus, very low fluence responses and high irradiance responses occur in the same gene family. PMID:12228352

Low versus High Fluence Parameters in the Treatment of Facial Laceration Scars with a 1,550 nm Fractional Erbium-Glass Laser

PubMed Central

Shim, Hyung-Sup; Jun, Dai-Won; Kim, Sang-Wha; Jung, Sung-No; Kwon, Ho

2015-01-01

Purpose. Early postoperative fractional laser treatment has been used to reduce scarring in many institutions, but the most effective energy parameters have not yet been established. This study sought to determine effective parameters in the treatment of facial laceration scars. Methods. From September 2012 to September 2013, 57 patients were enrolled according to the study. To compare the low and high fluence parameters of 1,550 nm fractional erbium-glass laser treatment, we virtually divided the scar of each individual patient in half, and each half was treated with a high and low fluence setting, respectively. A total of four treatment sessions were performed at one-month intervals and clinical photographs were taken at every visit. Results. Results were assessed using the Vancouver Scar Scale (VSS) and global assessment of the two portions of each individual scar. Final evaluation revealed that the portions treated with high fluence parameter showed greater difference compared to pretreatment VSS scores and global assessment values, indicating favorable cosmetic results. Conclusion. We compared the effects of high fluence and low fluence 1,550 nm fractional erbium-glass laser treatment for facial scarring in the early postoperative period and revealed that the high fluence parameter was more effective for scar management. PMID:26236738

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, C; Kim, J; Park, S

Purpose: Photon beams with energy higher than 10 MV interact with metal material in the primary barriers, where lead or steel have been widely used, neutrons can be generated. Monte Carlo simulations were performed to simulate the production of photoneutrons and the neutron shielding effect. Methods: For two photon beam energies, 15 MV and 18 MV, we simulated to strike metal sheets (steel and lead), and the ambient dose equivalents were calculated at the isocenter (in the patient plane) while delivering 1 Gy to the patient. For these cases, the thickness of the neutron shielding materials (Borated polyethylene (BPE) andmore » concrete) were simulated to reduce the patient exposure by neutron doses. Results: When 18 MV photons interact with the metal sheets in the primary barrier, the evaluated neutron doses at the isocenter inside the treatment vault were 48.7 µSv and 7.3 µSv for lead and steel, respectively. In case of 15 MV photons, the calculated neutron doses were 18.6 µSv and 0.6 µSv for lead and steel, respectively. The neutron dose delivered to the patient can be reduced to negligible levels by including a 10 cm thick sheet of BPE or 22 cm thick sheet of concrete. Conclusion: When bunker shielding is designed with a primary barrier including a metal sheet inside the wall for a high energy machine, proper neutron shielding should be constructed to avoid undesirable extra dose.« less

Comparison of big event with calculations of the air shower development

NASA Technical Reports Server (NTRS)

Niwa, M.; Misaki, A.; Matano, T.

1985-01-01

The incidence of high energy hadrons and electron-photons in air showers at various stages of development is calculated. Numerical calculation is used to solve the diffusion equation for a nuclear cascade and analytical calculation for cascade shower induced gamma rays. From these calculations, one can get the longitudinal development of the high energy hadron and electron-photon components, and the energy spectra of these components at various depths of air shower development. The total number of hadrons (N sub H) and electron-photon components (N sub gamma) are related according to stages of the air shower development and primary energy. The relation of the total energy of hadron and electron-photon component above the threshold energy is given. The energy balance between both components is also a useful parameter to study high energy events accompanying air showers. The relation of N sub H and fractional hadronic energy E (sum E sub H sup gamma/sum E sub H sup gamma + Sum E sub gamma) is calculated. This relation is helpful to understand the stage of air shower development(t) and primary energy (E sub p).

SU-F-T-258: Efficacy of Exit Fluence-Based Dose Calculation for Prostate Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siebers, J; Gardner, J; Neal, B

Purpose: To investigate the efficacy of exit-fluence-based dose computation for prostate radiotherapy by determining if it estimates true dose more accurately than the original planning dose. Methods: Virtual exit-fluencebased dose computation was performed for 19 patients, each with 9–12 repeat CT images. For each patient, a 78 Gy treatment plan was created utilizing 5 mm CTV-to-PTV and OAR-to-PRV margins. A Monte Carlo framework was used to compute dose and exit-fluence images for the planning image and for each repeat CT image based on boney-anatomyaligned and prostate-centroid-aligned CTs. Identical source particles were used for the MC dose-computations on the planning andmore » repeat CTs to maximize correlation. The exit-fluence-based dose and image were computed by multiplying source particle weights by FC(x,y)=FP(x,y)/FT(x,y), where (x,y) are the source particle coordinates projected to the exit-fluence plane and we denote the dose/fluence from the plan by (DP,FP), from the repeat-CT as (DT,FT), and the exit-fluence computation by (DFC,FFC). DFC mimics exit-fluence backprojection through the planning image as FT=FFC. Dose estimates were intercompared to judge the efficacy of exit-fluence-based dose computation. Results: Boney- and prostate-centroid aligned results are combined as there is no statistical difference between them, yielding 420 dose comparisons per dose-volume metric. DFC is more accurate than DP for 46%, 33%, and 44% of cases in estimating CTV D98, D50, and D2 respectively. DFC improved rectum D50 and D2 estimates 54% and 49% respectively and bladder D50 and D2 47 and 49% respectively. While averaged over all patients and images DFC and DP were within 3.1% of DT, they differed from DT by as much as 22% for GTV D98, 71% for the Bladder D50, 17% for Bladder D2, 19% for Rectum D2. Conclusion: Exit-fluence based dose computations infrequently improve CTV or OAR dose estimates and should be used with caution. Research supported in part by Varian Medical Systems.« less

Light dosimetry and dose verification for pleural PDT

NASA Astrophysics Data System (ADS)

Dimofte, Andreea; Sharikova, Anna V.; Meo, Julia L.; Simone, Charles B.; Friedberg, Joseph S.; Zhu, Timothy C.

2013-03-01

In-vivo light dosimetry for patients undergoing photodynamic therapy (PDT) is critical for predicting PDT outcome. Patients in this study are enrolled in a Phase I clinical trial of HPPH-mediated PDT for the treatment of non-small cell lung cancer with pleural effusion. They are administered 4mg per kg body weight HPPH 48 hours before the surgery and receive light therapy with a fluence of 15-45 J/cm2 at 661 and 665nm. Fluence rate (mW/cm2) and cumulative fluence (J/cm2) are monitored at 7 sites during the light treatment delivery using isotropic detectors. Light fluence (rate) delivered to patients is examined as a function of treatment time, volume and surface area. In a previous study, a correlation between the treatment time and the treatment volume and surface area was established. However, we did not include the direct light and the effect of the shape of the pleural surface on the scattered light. A real-time infrared (IR) navigation system was used to separate the contribution from the direct light. An improved expression that accurately calculates the total fluence at the cavity wall as a function of light source location, cavity geometry and optical properties is determined based on theoretical and phantom studies. The theoretical study includes an expression for light fluence rate in an elliptical geometry instead of the spheroid geometry used previously. The calculated light fluence is compared to the measured fluence in patients of different cavity geometries and optical properties. The result can be used as a clinical guideline for future pleural PDT treatment.

Safety and efficacy of low fluence, high repetition rate versus high fluence, low repetition rate 810-nm diode laser for axillary hair removal in Chinese women.

PubMed

Li, Wenhai; Liu, Chengyi; Chen, Zhou; Cai, Lin; Zhou, Cheng; Xu, Qianxi; Li, Houmin; Zhang, Jianzhong

2016-11-01

High-fluence diode lasers with contact cooling have emerged as the gold standard to remove unwanted hair. Lowering the energy should result in less pain and could theoretically affect the efficacy of the therapy. To compare the safety and efficacy of a low fluence high repetition rate 810-nm diode laser to those of a high fluence, low repetition rate diode laser for permanent axillary hair removal in Chinese women. Ninety-two Chinese women received four axillae laser hair removal treatments at 4-week intervals using the low fluence, high repetition rate 810-nm diode laser in super hair removal (SHR) mode on one side and the high fluence, low repetition rate diode laser in hair removal (HR) mode on the other side. Hair counts were done at each follow-up visit and 6-month follow-up after the final laser treatment using a "Hi Quality Hair Analysis Program System"; the immediate pain score after each treatment session was recorded by a visual analog scale. The overall median reduction of hair was 90.2% with the 810-nm diode laser in SHR mode and 87% with the same laser in HR mode at 6-month follow-up. The median pain scores in SHR mode and in HR mode were 2.75 and 6.75, respectively. Low fluence, high repetition rate diode laser can efficiently remove unwanted hair but also significantly improve tolerability and reduce adverse events during the course of treatment.

A quality assurance program for clinical PDT

NASA Astrophysics Data System (ADS)

Dimofte, Andreea; Finlay, Jarod; Ong, Yi Hong; Zhu, Timothy C.

2018-02-01

Successful outcome of Photodynamic therapy (PDT) depends on accurate delivery of prescribed light dose. A quality assurance program is necessary to ensure that light dosimetry is correctly measured. We have instituted a QA program that include examination of long term calibration uncertainty of isotropic detectors for light fluence rate, power meter head intercomparison for laser power, stability of the light-emitting diode (LED) light source integrating sphere as a light fluence standard, laser output and calibration of in-vivo reflective fluorescence and absorption spectrometers. We examined the long term calibration uncertainty of isotropic detector sensitivity, defined as fluence rate per voltage. We calibrate the detector using the known calibrated light fluence rate of the LED light source built into an internally baffled 4" integrating sphere. LED light sources were examined using a 1mm diameter isotropic detector calibrated in a collimated beam. Wavelengths varying from 632nm to 690nm were used. The internal LED method gives an overall calibration accuracy of +/- 4%. Intercomparison among power meters was performed to determine the consistency of laser power and light fluence rate measured among different power meters. Power and fluence readings were measured and compared among detectors. A comparison of power and fluence reading among several power heads shows long term consistency for power and light fluence rate calibration to within 3% regardless of wavelength. The standard LED light source is used to calibrate the transmission difference between different channels for the diffuse reflective absorption and fluorescence contact probe as well as isotropic detectors used in PDT dose dosimeter.

Visualization of laser tattoo removal treatment effects in a mouse model by two-photon microscopy

PubMed Central

Jang, Won Hyuk; Yoon, Yeoreum; Kim, Wonjoong; Kwon, Soonjae; Lee, Seunghun; Song, Duke; Choi, Jong Woon; Kim, Ki Hean

2017-01-01

Laser tattoo removal is an effective method of eliminating tattoo particles in the skin. However, laser treatment cannot always remove the unwanted tattoo completely, and there are risks of either temporary or permanent side effects. Studies using preclinical animal models could provide detailed information on the effects of laser treatment in the skin, and might help to minimize side effects in clinical practices. In this study, two-photon microscopy (TPM) was used to visualize the laser treatment effects on tattoo particles in both phantom specimens and in vivo mouse models. Fluorescent tattoo ink was used for particle visualization by TPM, and nanosecond (ns) and picosecond (ps) lasers at 532 nm were used for treatment. In phantom specimens, TPM characterized the fragmentation of individual tattoo particles by tracking them before and after the laser treatment. These changes were confirmed by field emission scanning electron microscopy (FE-SEM). TPM was used to measure the treatment efficiency of the two lasers at different laser fluences. In the mouse model, TPM visualized clusters of tattoo particles in the skin and detected their fragmentation after the laser treatment. Longitudinal TPM imaging observed the migration of cells containing tattoo particles after the laser treatment. These results show that TPM may be useful for the assessment of laser tattoo removal treatment in preclinical studies. PMID:28856046

Dynamics of sonoluminescing bubbles within a liquid hammer device.

PubMed

Urteaga, Raúl; García-Martínez, Pablo Luis; Bonetto, Fabián J

2009-01-01

We studied the dynamics of a single sonoluminescing bubble (SBSL) in a liquid hammer device. In particular, we investigated the phosphoric acid-xenon system, in which pulses up to four orders of magnitude brighter than SBSL in water systems (about 10;{12} photons per pulse) have been previously reported [Chakravarty, Phys. Rev. E 69, 066317 (2004)]. We used stroboscopic photography and a Mie scattering technique in order to measure the radius evolution of the bubbles. Under adequate conditions we may position a bubble at the bottom of the tube (cavity) and a second bubble trapped at the middle of the tube (upper bubble). During its collapse, the cavity produces the compression of the liquid column. This compression drives impulsively the dynamics of the upper bubble. Our measurements reveal that the observed light emissions produced by the upper bubble are generated at its second collapse. We employed a simple numerical model to investigate the conditions that occur during the upper bubble collapse. We found good agreement between numerical and experimental values for the light intensity (fluence) and light pulse widths. Results from the model show that the light emission is increased mainly due to an increase in noble gas ambient radius and not because the maximum temperature increases. Even for the brightest pulses obtained ( 2x10;{13} photons, about 20W of peak power) the maximum temperatures computed for the upper bubble are always lower than 20000K .

Excimer Laser Curing Of Polymer Coatings

NASA Astrophysics Data System (ADS)

Klick, David; Akerman, M. Alfred; Paul, George L.; Supurovic, Darko; Tsuda, Haruki

1988-12-01

The use of the excimer laser as a source of energy for photo-assisted curing of industrial polymeric coatings was investigated. Presently, UV lamps are sometimes used to excite a photoinitiating molecule mixed with the starting monomers and oligomers of a coating. The resulting polymeric chain reaction multiplies the effect of the initial photons, making economical use of the light source. The high cost of laser photons may thus be justifiable if lasers provide advantages over lamps. A series of visibly transparent 7 μm coatings (a typical thickness for 'slick' magazine coatings) with various photoinitiators, monomers, and oligomers was illuminated with excimer laser light of various wavelengths, fluences, and pulse repetition rates. For the optimum parameters, it was found that the laser had large advantages in curing speed over existing UV lamp processes, due to its monochromaticity. Pigmented coatings (20 μm TiO2 mixtures typical of appliance or automotive finishes) are not easily cured with UV lamps due to the inability of light to penetrate the absorbing and scattering pigmented layer. However, economically-viable cure rates were achieved with certain photoinitiators using a tunable excimer-pumped dye laser. A prototype of such a laser suitable for factory use was built and used to cure these coatings. Results are scaled to a factory situation, and costs are calculated to show the advantages of the laser method over currently used processes.

Impact of Mg-ion implantation with various fluence ranges on optical properties of n-type GaN

NASA Astrophysics Data System (ADS)

Tsuge, Hirofumi; Ikeda, Kiyoji; Kato, Shigeki; Nishimura, Tomoaki; Nakamura, Tohru; Kuriyama, Kazuo; Mishima, Tomoyoshi

2017-10-01

Optical characteristics of Mg-ion implanted GaN layers with various fluence ranges were evaluated. Mg ion implantation was performed twice at energies of 30 and 60 keV on n-GaN layers. The first implantation at 30 keV was performed with three different fluence ranges of 1.0 × 1014, 1.0 × 1015 and 5.0 × 1015 cm-2. The second implantation at an energy of 60 keV was performed with a fluence of 6.5 × 1013 cm-2. After implantation, samples were annealed at 1250 °C for 1 min under N2 atmosphere. Photoluminescence (PL) spectrum of the GaN layer with the Mg ion implantation at the fluence range of 1.0 × 1014 cm-2 at 30 keV was similar to the one of Mg-doped p-GaN layers grown by MOVPE (Metal-Organic Vapor Phase Epitaxy) on free-standing GaN substrates and those at the fluence ranges over 1.0 × 1015 cm-2 were largely degraded.

Laser fluence dependence on emission dynamics of ultrafast laser induced copper plasma

DOE PAGES

Anoop, K. K.; Harilal, S. S.; Philip, Reji; ...

2016-11-14

The characteristic emission features of a laser-produced plasma strongly depend strongly on the laser fluence. We investigated the spatial and temporal dynamics of neutrals and ions in femtosecond laser (800 nm, ≈ 40 fs, Ti:Sapphire) induced copper plasma in vacuum using both optical emission spectroscopy (OES) and spectrally resolved two-dimensional (2D) imaging methods over a wide fluence range of 0.5 J/cm 2-77.5 J/cm 2. 2D fast gated monochromatic images showed distinct plume splitting between the neutral and ions especially at moderate to higher fluence ranges. OES studies at low to moderate laser fluence regime confirm intense neutral line emission overmore » the ion emission whereas this trend changes at higher laser fluence with dominance of the latter. This evidences a clear change in the physical processes involved in femtosecond laser matter interaction at high input laser intensity. The obtained ion dynamics resulting from the OES, and spectrally resolved 2D imaging are compared with charged particle measurement employing Faraday cup and Langmuir probe and results showed good correlation.« less

Lymphatic Drainage from Renal Tumors In Vivo: A Prospective Sentinel Node Study Using SPECT/CT Imaging.

PubMed

Kuusk, Teele; De Bruijn, Roderick; Brouwer, Oscar R; De Jong, Jeroen; Donswijk, Maarten; Grivas, Nikolaos; Hendricksen, Kees; Horenblas, Simon; Prevoo, Warner; Valdés Olmos, Renato A; Van Der Poel, Henk G; Van Rhijn, Bas W G; Wit, Esther M; Bex, Axel

2018-06-01

Lymphatic drainage from renal tumors is unpredictable. In vivo drainage studies of primary lymphatic landing sites may reveal the variability and dynamics of lymphatic connections. The purpose of this study was to investigate the lymphatic drainage pattern of renal tumors in vivo with single photon emission/computerized tomography after intratumor radiotracer injection. We performed a phase II, prospective, single arm study to investigate the distribution of sentinel nodes from renal tumors on single photon emission/computerized tomography. Patients with cT1-3 (less than 10 cm) cN0M0 renal tumors of any subtype were enrolled in analysis. After intratumor ultrasound guided injection of 0.4 ml 99m Tc-nanocolloid we performed preoperative imaging of sentinel nodes with lymphoscintigraphy and single photon emission/computerized tomography. Sentinel and locoregional nonsentinel nodes were resected with a γ probe combined with a mobile γ camera. The primary study end point was the location of sentinel nodes outside the locoregional retroperitoneal templates on single photon emission/computerized tomography. Using a Simon minimax 2-stage design to detect a 25% extralocoregional retroperitoneal template location of sentinel nodes on imaging at α = 0.05 and 80% power at least 40 patients with sentinel node imaging on single photon emission/computerized tomography were needed. Of the 68 patients 40 underwent preoperative single photon emission/computerized tomography of sentinel nodes and were included in primary end point analysis. Lymphatic drainage outside the locoregional retroperitoneal templates was observed in 14 patients (35%). Eight patients (20%) had supradiaphragmatic sentinel nodes. Sentinel nodes from renal tumors were mainly located in the respective locoregional retroperitoneal templates. Simultaneous sentinel nodes were located outside the suggested lymph node dissection templates, including supradiaphragmatic sentinel nodes in more than a third of the patients. Copyright © 2018 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

Study of the effects of neutron irradiation on silicon strip detectors

NASA Astrophysics Data System (ADS)

Guibellino, P.; Panizza, G.; Hall, G.; Sotthibandhu, S.; Ziock, H. J.; Ferguson, P.; Sommer, W. F.; Edwards, M.; Cartiglia, N.; Hubbard, B.; Lesloe, J.; Pitzl, D.; O'Shaughnessy, K.; Rowe, W.; Sadoziski, H. F.-W.; Seiden, A.; Spencer, E.

1992-05-01

Silicon strip detectors and test structures were exposed to neutron fluences up to Φ = 6.1 × 10 14 n/cm 2, using the ISIS neutron source at the Rutherford Appleton Laboratory (UK). In this paper we report some of our results concerning the effects of displacement damage, with a comparison of devices made of silicon of different resistivity. The various samples exposed showed a very similar dependence of the leakage current on the fluence received. We studied the change of effective doping concentration, and observed a behaviour suggesting the onset of type inversion at a fluence of ˜ 2.0 × 10 13 n/cm 2, a value which depends on the initial doping concentration. The linear increase of the depletion voltage for fluences higher than the inversion point could eventually determine the maximum fluence tolerable by silicon detectors.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, Anne A.; Katoh, Yutai; Snead, Mary A.

A new, fine-grain nuclear graphite, grade G347A from Tokai Carbon Co., Ltd., has been irradiated in the High Flux Isotope Reactor at Oak Ridge National Laboratory to study the materials property changes that occur when exposed to neutron irradiation at temperatures of interest for Generation-IV nuclear reactor applications. Specimen temperatures ranged from 290°C to 800 °C with a maximum neutron fluence of 40 × 10 25 n/m 2 [E > 0.1 MeV] (~30dpa). Lastly, observed behaviors include: anisotropic behavior of dimensional change in an isotropic graphite, Young's modulus showing parabolic fluence dependence, electrical resistivity increasing at low fluence and additionalmore » increase at high fluence, thermal conductivity rapidly decreasing at low fluence followed by continued degradation, and a similar plateau value of the mean coefficient of thermal expansion for all irradiation temperatures.« less

Anisotropy of the neutron fluence from a plasma focus.

NASA Technical Reports Server (NTRS)

Lee, J. H.; Shomo, L. P.; Kim, K. H.

1972-01-01

The fluence of neutrons from a plasma focus was measured by gamma spectrometry of an activated silver target. This method results in a significant increase in accuracy over the beta-counting method. Multiple detectors were used in order to measure the anisotropy of the fluence of neutrons. The fluence was found to be concentrated in a cone with a half-angle of 30 deg about the axis, and to drop off rapidly outside of this cone; the anisotropy was found to depend upon the total yield of neutrons. This dependence was strongest on the axis. Neither the axial concentration of the fluence of neutrons nor its dependence on the total yield of neutrons is explained by any of the currently proposed models. Some other explanations, including the possibility of an axially distributed source, are considered.

System and Method for Determining Fluence of a Substance

NASA Technical Reports Server (NTRS)

Banks, Bruce A. (Inventor)

2016-01-01

A system and method for measuring a fluence of gas are disclosed. The system has a first light detector capable of outputting an electrical signal based on an amount of light received. A barrier is positionable adjacent the first light detector and is susceptible to a change in dimension from the fluence of the gas. The barrier permits a portion of light from being received by the first light detector. The change in the dimension of the barrier changes the electrical signal output from the first light detector. A second light detector is positionable to receive light representative of the first light detector without the barrier. The system and method have broad application to detect fluence of gas that may cause erosion chemical reaction causing erosive deterioration. One application is in low orbit Earth for detecting the fluence of atomic oxygen.

SWIMRT: A graphical user interface using the sliding window algorithm to construct a fluence map machine file

PubMed Central

Chow, James C.L.; Grigorov, Grigor N.; Yazdani, Nuri

2006-01-01

A custom‐made computer program, SWIMRT, to construct “multileaf collimator (MLC) machine” file for intensity‐modulated radiotherapy (IMRT) fluence maps was developed using MATLAB® and the sliding window algorithm. The user can either import a fluence map with a graphical file format created by an external treatment‐planning system such as Pinnacle3 or create his or her own fluence map using the matrix editor in the program. Through comprehensive calibrations of the dose and the dimension of the imported fluence field, the user can use associated image‐processing tools such as field resizing and edge trimming to modify the imported map. When the processed fluence map is suitable, a “MLC machine” file is generated for our Varian 21 EX linear accelerator with a 120‐leaf Millennium MLC. This machine file is transferred to the MLC console of the LINAC to control the continuous motions of the leaves during beam irradiation. An IMRT field is then irradiated with the 2D intensity profiles, and the irradiated profiles are compared to the imported or modified fluence map. This program was verified and tested using film dosimetry to address the following uncertainties: (1) the mechanical limitation due to the leaf width and maximum traveling speed, and (2) the dosimetric limitation due to the leaf leakage/transmission and penumbra effect. Because the fluence map can be edited, resized, and processed according to the requirement of a study, SWIMRT is essential in studying and investigating the IMRT technique using the sliding window algorithm. Using this program, future work on the algorithm may include redistributing the time space between segmental fields to enhance the fluence resolution, and readjusting the timing of each leaf during delivery to avoid small fields. Possible clinical utilities and examples for SWIMRT are given in this paper. PACS numbers: 87.53.Kn, 87.53.St, 87.53.Uv PMID:17533330

WE-AB-209-10: Optimizing the Delivery of Sequential Fluence Maps for Efficient VMAT Delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Craft, D; Balvert, M

2016-06-15

Purpose: To develop an optimization model and solution approach for computing MLC leaf trajectories and dose rates for high quality matching of a set of optimized fluence maps to be delivered sequentially around a patient in a VMAT treatment. Methods: We formulate the fluence map matching problem as a nonlinear optimization problem where time is discretized but dose rates and leaf positions are continuous variables. For a given allotted time, which is allocated across the fluence maps based on the complexity of each fluence map, the optimization problem searches for the best leaf trajectories and dose rates such that themore » original fluence maps are closely recreated. Constraints include maximum leaf speed, maximum dose rate, and leaf collision avoidance, as well as the constraint that the ending leaf positions for one map are the starting leaf positions for the next map. The resulting model is non-convex but smooth, and therefore we solve it by local searches from a variety of starting positions. We improve solution time by a custom decomposition approach which allows us to decouple the rows of the fluence maps and solve each leaf pair individually. This decomposition also makes the problem easily parallelized. Results: We demonstrate method on a prostate case and a head-and-neck case and show that one can recreate fluence maps to high degree of fidelity in modest total delivery time (minutes). Conclusion: We present a VMAT sequencing method that reproduces optimal fluence maps by searching over a vast number of possible leaf trajectories. By varying the total allotted time given, this approach is the first of its kind to allow users to produce VMAT solutions that span the range of wide-field coarse VMAT deliveries to narrow-field high-MU sliding window-like approaches.« less

Solar cell radiation handbook

NASA Technical Reports Server (NTRS)

Tada, H. Y.; Carter, J. R., Jr.

1977-01-01

Solar cell theory cells are manufactured, and how they are modeled mathematically is reviewed. The interaction of energetic charged particle radiation with solar cells is discussed in detail and the concept of 1 MeV equivalent electron fluence is introduced. The space radiation environment is described and methods of calculating equivalent fluences for the space environment are developed. A computer program was written to perform the equivalent fluence calculations and a FORTRAN listing of the program is included. Finally, an extensive body of data detailing the degradation of solar cell electrical parameters as a function of 1 MeV electron fluence is presented.

Equivalent electron fluence for space qualification of shallow junction heteroface GaAs solar cells

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Stock, L. V.

1984-01-01

It is desirable to perform qualification tests prior to deployment of solar cells in space power applications. Such test procedures are complicated by the complex mixture of differing radiation components in space which are difficult to simulate in ground test facilities. Although it has been shown that an equivalent electron fluence ratio cannot be uniquely defined for monoenergetic proton exposure of GaAs shallow junction cells, an equivalent electron fluence test can be defined for common spectral components of protons found in space. Equivalent electron fluence levels for the geosynchronous environment are presented.

Monopolar radiofrequency facial tightening: a retrospective analysis of efficacy and safety in over 600 treatments.

PubMed

Weiss, Robert A; Weiss, Margaret A; Munavalli, Girish; Beasley, Karen L

2006-09-01

Monopolar radiofrequency skin heating coupled with cryogen cooling of facial skin for skin tightening has been utilized on over 10,000 patients since 2002. In order to establish the actual rate and degree of side effects in our clinical experience, a retrospective chart review was performed. Charts and clinical images of over 600 consecutive patient treatments between May 2002 and June 2006 using a monopolar radiofrequency device (Thermacool, Thermage, Haywood, CA) for skin tightening at the Maryland Laser, Skin and Vein Institute were retrospectively reviewed. The primary presentation for treatment was skin laxity of the lower face. Treatment was delivered with a 1-cm2 standard tip at fluences of 81 to 124 J/cm2 (level of 12.5 to 15), a 1-cm2 "fast" tip at fluences of 62 to 109 J/cm2 (level of 72.0 to 76.0), a 1.5-cm2 "big fast" tip at fluences of 75 to 130 J/cm2 (level of 61.5 to 65), and a 3-cm2 "bigger" tip at equivalent fluences as each became available. As treatment algorithms evolved over 4 years, the algorithm of multiple passes at lower fluence associated with better clinical outcomes and greater patient acceptance has been adopted. The most common immediate and expected clinical effects were erythema and edema lasting less than 24 hours, although 6 patients reported edema lasting for up to 1 week. There were no permanent side effects. In total, 2.7% of treatments resulted in temporary side effects, the most significant of which was a slight depression on the cheek (n = 1), which completely resolved within 3.5 months. Other side effects included localized areas of acneiform subcutaneous erythematous papules (n = 4) and a linear superficial crust (n = 1) with the original tip, all of which resolved within 1 week. One patient reported small erythematous subcutaneous nodules resolving in 17 days. Tenderness of the neck lasting from 2 weeks (n = 2) to 3 weeks (n = 1) was also reported. Our data, obtained in an office setting without injectable anesthetic or i.v. sedation, indicate that monopolar RF for skin tightening is a very safe procedure. The treatment algorithm and tips have evolved over several years leading to increased safety and efficacy. Side effects are infrequent, self-limited, and minor, comparing favorably to other nonablative devices utilized for facial rejuvenation.

Out-of-field in vivo dosimetry using TLD in SABR for primary kidney cancer involving mixed photon fields.

PubMed

Lonski, P; Keehan, S; Siva, S; Pham, D; Franich, R D; Taylor, M L; Kron, T

2017-05-01

To assess out-of-field dose using three different variants of LiF thermoluminescence dosimeters (TLD) for ten patients who underwent stereotactic ablative body radiotherapy (SABR) for primary renal cell carcinoma (RCC) and compare with treatment planning system (TPS) dose calculations. Thermoluminescent dosimeter (TLD) measurements were conducted at 20, 30, 40 and 50cm from isocentre on ten patients undergoing SABR for primary RCC. Three types of high-sensitivity LiF:Mg,Cu,P TLD material with different 6 Li/ 7 Li isotope ratios were used. Patient plans were calculated using Eclipse Anisotropic Analytical Algorithm (AAA) for clinical evaluation and recalculated using Pencil Beam Convolution (PBC) algorithm for comparison. Both AAA and PBC showed diminished accuracy for photon doses at increasing distance out-of-field. At 50cm, measured photon dose was 0.3cGy normalised to a 10Gy prescription on average with only small variation across all patients. This is likely due to the leakage component of the out-of-field dose. The 6 Li-enriched TLD materials showed increased signal attributable to additional neutron contribution. LiF:Mg,Cu,P TLD containing 6 Li is sensitive enough to measure out-of-field dose 50cm from isocentre however will over-estimate the photon component of out-of-field dose in high energy treatments due to the presence of thermal neutrons. 7 Li enriched materials which are insensitive to neutrons are therefore required for accurate photon dosimetry. Neutron signal has been shown here to increase with MUs and is higher for patients treated using certain non coplanar beam arrangements. Further work is required to convert this additional neutron signal to dose. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

The Effect of Low Energy Nitrogen Ion Implantation on Graphene Nanosheets

NASA Astrophysics Data System (ADS)

Mishra, Mukesh; Alwarappan, Subbiah; Kanjilal, Dinakar; Mohanty, Tanuja

2018-03-01

Herein, we report the effect 50 keV nitrogen ion implantation at varying fluence on the optical properties of graphene nanosheets (number of layers < 5). Initially, graphene nanosheets synthesized by the direct liquid exfoliation of graphite layers were deposited on a cleaned Si-substrate by drop cast method. These graphene nanosheets are implanted with 50 keV nitrogen-ion beam at six different fluences. Raman spectroscopic results show that the D, D' and G peak get broadened up to the nitrogen ion fluence of 1 × 1015 ions/cm2, while 2D peak of graphene nanosheets disappeared for nitrogen-ions have fluence more than 1014 ions/cm2. However, further increase of fluence causes the indistinguishable superimposition of D, D' and G peaks. Surface contact potential value analysis for ion implanted graphene nanosheets shows the increase in defect concentration from 1.15 × 1012 to 1.98 × 1014 defects/cm2 with increasing the nitrogen ion fluence, which resembles the Fermi level shift towards conduction band. XRD spectra confirmed that the crystallinity of graphene nanosheets was found to tamper with increasing fluence. These results revealed that the limit of nitrogen ion implantation resistant on the vibrational behaviors for graphene nanosheets was 1015 ions/cm2 that opens up the scope of application of graphene nanosheets in device fabrication for ion-active environment and space applications.

Adaptive treatment-length optimization in spatiobiologically integrated radiotherapy

NASA Astrophysics Data System (ADS)

Ajdari, Ali; Ghate, Archis; Kim, Minsun

2018-04-01

Recent theoretical research on spatiobiologically integrated radiotherapy has focused on optimization models that adapt fluence-maps to the evolution of tumor state, for example, cell densities, as observed in quantitative functional images acquired over the treatment course. We propose an optimization model that adapts the length of the treatment course as well as the fluence-maps to such imaged tumor state. Specifically, after observing the tumor cell densities at the beginning of a session, the treatment planner solves a group of convex optimization problems to determine an optimal number of remaining treatment sessions, and a corresponding optimal fluence-map for each of these sessions. The objective is to minimize the total number of tumor cells remaining (TNTCR) at the end of this proposed treatment course, subject to upper limits on the biologically effective dose delivered to the organs-at-risk. This fluence-map is administered in future sessions until the next image is available, and then the number of sessions and the fluence-map are re-optimized based on the latest cell density information. We demonstrate via computer simulations on five head-and-neck test cases that such adaptive treatment-length and fluence-map planning reduces the TNTCR and increases the biological effect on the tumor while employing shorter treatment courses, as compared to only adapting fluence-maps and using a pre-determined treatment course length based on one-size-fits-all guidelines.

Real-time simulator for designing electron dual scattering foil systems.

PubMed

Carver, Robert L; Hogstrom, Kenneth R; Price, Michael J; LeBlanc, Justin D; Pitcher, Garrett M

2014-11-08

The purpose of this work was to develop a user friendly, accurate, real-time com- puter simulator to facilitate the design of dual foil scattering systems for electron beams on radiotherapy accelerators. The simulator allows for a relatively quick, initial design that can be refined and verified with subsequent Monte Carlo (MC) calculations and measurements. The simulator also is a powerful educational tool. The simulator consists of an analytical algorithm for calculating electron fluence and X-ray dose and a graphical user interface (GUI) C++ program. The algorithm predicts electron fluence using Fermi-Eyges multiple Coulomb scattering theory with the reduced Gaussian formalism for scattering powers. The simulator also estimates central-axis and off-axis X-ray dose arising from the dual foil system. Once the geometry of the accelerator is specified, the simulator allows the user to continuously vary primary scattering foil material and thickness, secondary scat- tering foil material and Gaussian shape (thickness and sigma), and beam energy. The off-axis electron relative fluence or total dose profile and central-axis X-ray dose contamination are computed and displayed in real time. The simulator was validated by comparison of off-axis electron relative fluence and X-ray percent dose profiles with those calculated using EGSnrc MC. Over the energy range 7-20 MeV, using present foils on an Elekta radiotherapy accelerator, the simulator was able to reproduce MC profiles to within 2% out to 20 cm from the central axis. The central-axis X-ray percent dose predictions matched measured data to within 0.5%. The calculation time was approximately 100 ms using a single Intel 2.93 GHz processor, which allows for real-time variation of foil geometrical parameters using slider bars. This work demonstrates how the user-friendly GUI and real-time nature of the simulator make it an effective educational tool for gaining a better understanding of the effects that various system parameters have on a relative dose profile. This work also demonstrates a method for using the simulator as a design tool for creating custom dual scattering foil systems in the clinical range of beam energies (6-20 MeV). 

MO-FG-CAMPUS-TeP1-05: Rapid and Efficient 3D Dosimetry for End-To-End Patient-Specific QA of Rotational SBRT Deliveries Using a High-Resolution EPID

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Y M; Han, B; Xing, L

2016-06-15

Purpose: EPID-based patient-specific quality assurance provides verification of the planning setup and delivery process that phantomless QA and log-file based virtual dosimetry methods cannot achieve. We present a method for EPID-based QA utilizing spatially-variant EPID response kernels that allows for direct calculation of the entrance fluence and 3D phantom dose. Methods: An EPID dosimetry system was utilized for 3D dose reconstruction in a cylindrical phantom for the purposes of end-to-end QA. Monte Carlo (MC) methods were used to generate pixel-specific point-spread functions (PSFs) characterizing the spatially non-uniform EPID portal response in the presence of phantom scatter. The spatially-variant PSFs weremore » decomposed into spatially-invariant basis PSFs with the symmetric central-axis kernel as the primary basis kernel and off-axis representing orthogonal perturbations in pixel-space. This compact and accurate characterization enables the use of a modified Richardson-Lucy deconvolution algorithm to directly reconstruct entrance fluence from EPID images without iterative scatter subtraction. High-resolution phantom dose kernels were cogenerated in MC with the PSFs enabling direct recalculation of the resulting phantom dose by rapid forward convolution once the entrance fluence was calculated. A Delta4 QA phantom was used to validate the dose reconstructed in this approach. Results: The spatially-invariant representation of the EPID response accurately reproduced the entrance fluence with >99.5% fidelity with a simultaneous reduction of >60% in computational overhead. 3D dose for 10{sub 6} voxels was reconstructed for the entire phantom geometry. A 3D global gamma analysis demonstrated a >95% pass rate at 3%/3mm. Conclusion: Our approach demonstrates the capabilities of an EPID-based end-to-end QA methodology that is more efficient than traditional EPID dosimetry methods. Displacing the point of measurement external to the QA phantom reduces the necessary complexity of the phantom itself while offering a method that is highly scalable and inherently generalizable to rotational and trajectory based deliveries. This research was partially supported by Varian.« less

Structural and magnetic fluence dependence in cobalt titanate thin films synthesized by pulse laser deposition

NASA Astrophysics Data System (ADS)

Prisbrey, Shon Thomas

Knowledge of the fundamental structure and magnetic characteristics of dilute magnetic semiconductors (DMSs) is an essential step towards the development of spin-polarized electronics (spintronics). Recently (2001), the report of ferromagnetism in cobalt-doped anatase titania films synthesized by pulse laser deposition (PLD) elicited interest as a possible DMS oxide. Other investigations of the CoxTi1-xO2-delta material system, utilizing a myriad of deposition techniques, yielded conflicting results as to the source of magnetism and the local environment of the deposited cobalt. No complete characterization of PLD synthesized films has been reported. This dissertation quantifies the effect of laser fluence on film morphology, structure, and magnetic properties by fully characterizing CoxTi1-x O2-delta films grown under optimal PLD deposition conditions that were identified separately in prior published work. The construction of a custom PLD system that provided repeatable laser/target interaction via a combination of fluence and target movement is addressed. A brief outline of magnetism and its relation to structure is also given. The remainder of the dissertation details the effect of laser fluence on Co0.049Ti0.951O2-delta and Co 0.038Ti0.962O2-delta films. Film structure, morphology, and magnetic properties were determined for illumination conditions corresponding to laser fluences varying from 0.57 to 1.37 J/cm2. The local cobalt environment is strongly correlated with laser fluence. Cobalt in 4.9% concentration films grown with a laser fluence between 0.7 and 0.93 J/cm2 were octahedrally coordinated, as were 3.8% films grown with a fluence less than 0.93 J/cm2. Departure of the laser fluence from these ranges results in a multitude of cobalt environments in the films. The film magnetization is observed to be a function of laser fluence with a maximum moment of ˜3.19 muB per cobalt atom occurring at 0.93 J/cm2 in the 4.9% films and ˜1.9 muB per cobalt atom at 0.57 J/cm2 in the 3.8% films. There is no evidence of cobalt segregation and subsequent formation of metallic cobalt in the high moment films. A departure in laser fluence from the maximum moment conditions results in a drop in moment to ˜1 muB. An appendix detailing previous work that investigated iridium as an oxidation resistant capping layer is also included.

N+ ion-target interactions in PPO polymer: A structural characterization

NASA Astrophysics Data System (ADS)

Das, A.; Dhara, S.; Patnaik, A.

1999-01-01

N + ion beam induced effects on the spin coated amorphous poly(2,6-dimethyl phenylene oxide) (PPO) films in terms of chemical structure and electronic and vibrational properties were investigated using Fourier Transform Infrared spectroscopy (FTIR) and Ultraviolet-Visible (UV-VIS) spectroscopy. Both techniques revealed that the stability of PPO was very weak towards 100 keV N + ions revealing the threshold fluence to be 10 14 ions/cm 2 for fragmentation of the polymer. FTIR analysis showed disappearance of all characteristic IR bands at a total fluence of 10 14 ions/cm 2 except for the band CC at 1608 cm -1 which was found to shift to a lower wave number along with an enhancement in the full width half maximum (FWHM) value with increasing fluence. A new bond appeared due to oxidation as a shoulder at 1680 cm -1 in FTIR spectra indicating the presence of CO type bond as a result of N + implantation on PPO films. The optical band gap ( Eg) deduced from absorption spectra, was observed to decrease from 4.4 to 0.5 eV with fluence. The implantation induced carbonaceous clusters, determined using Robertson's formula for the optical band gap, were found to consist of ˜160 fused hexagonal aromatic rings at the maximum energy fluence. An enhanced absorption coefficient as a function of fluence indicated incorporation of either much larger concentration of charge carriers or their mobility than that of the pristine sample. Calculated band tail width from Urbach band tail region for the implanted samples pointed the band edge sharpness to be strongly dependent on fluence indicating an increased disorder with increasing fluence.

Use of Atomic Oxygen for Increased Water Contact Angles of Various Polymers for Biomedical Applications

NASA Technical Reports Server (NTRS)

deGroh, Kim; Berger, Lauren; Roberts, Lily

2009-01-01

The purpose of this study was to determine the effect of atomic oxygen (AO) exposure on the hydrophilicity of nine different polymers for biomedical applications. Atomic oxygen treatment can alter the chemistry and morphology of polymer surfaces, which may increase the adhesion and spreading of cells on Petri dishes and enhance implant growth. Therefore, nine different polymers were exposed to atomic oxygen and water-contact angle, or hydrophilicity, was measured after exposure. To determine whether hydrophilicity remains static after initial atomic oxygen exposure, or changes with higher fluence exposures, the contact angles between the polymer and water droplet placed on the polymer s surface were measured versus AO fluence. The polymers were exposed to atomic oxygen in a 100-W, 13.56-MHz radio frequency (RF) plasma asher, and the treatment was found to significantly alter the hydrophilicity of non-fluorinated polymers. Pristine samples were compared with samples that had been exposed to AO at various fluence levels. Minimum and maximum fluences for the ashing trials were set based on the effective AO erosion of a Kapton witness coupon in the asher. The time intervals for ashing were determined by finding the logarithmic values of the minimum and maximum fluences. The difference of these two values was divided by the desired number of intervals (ideally 10). The initial desired fluence was then multiplied by this result (2.37), as was each subsequent desired fluence. The flux in the asher was determined to be approximately 3.0 x 10(exp 15) atoms/sq cm/sec, and each polymer was exposed to a maximum fluence of 5.16 x 10(exp 20) atoms/sq cm.

Platelet adhesion and plasma protein adsorption control of collagen surfaces by He + ion implantation

NASA Astrophysics Data System (ADS)

Kurotobi, K.; Suzuki, Y.; Nakajima, H.; Suzuki, H.; Iwaki, M.

2003-05-01

He + ion implanted collagen-coated tubes with a fluence of 1 × 10 14 ions/cm 2 were exhibited antithrombogenicity. To investigate the mechanisms of antithrombogenicity of these samples, plasma protein adsorption assay and platelet adhesion experiments were performed. The adsorption of fibrinogen (Fg) and von Willebrand factor (vWf) was minimum on the He + ion implanted collagen with a fluence of 1 × 10 14 ions/cm 2. Platelet adhesion (using platelet rich plasma) was inhibited on the He + ion implanted collagen with a fluence of 1 × 10 14 ions/cm 2 and was accelerated on the untreated collagen and ion implanted collagen with fluences of 1 × 10 13, 1 × 10 15 and 1 × 10 16 ions/cm 2. Platelet activation with washed platelets was observed on untreated collagen and He + ion implanted collagen with a fluence of 1 × 10 14 ions/cm 2 and was inhibited with fluences of 1 × 10 13, 1 × 10 15 and 1 × 10 16 ions/cm 2. Generally, platelets can react with a specific ligand inside the collagen (GFOGER sequence). The results of platelets adhesion experiments using washed platelets indicated that there were no ligands such as GFOGER on the He + ion implanted collagen over a fluence of 1 × 10 13 ions/cm 2. On the 1 × 10 14 ions/cm 2 implanted collagen, no platelet activation was observed due to the influence of plasma proteins. From the above, it is concluded that the decrease of adsorbed Fg and vWf caused the antithrombogenicity of He + ion implanted collagen with a fluence of 1 × 10 14 ions/cm 2 and that plasma protein adsorption took an important role repairing the graft surface.

Nanosecond laser-metal ablation at different ambient conditions

NASA Astrophysics Data System (ADS)

Elsied, Ahmed M.; Dieffenbach, Payson C.; Diwakar, Prasoon K.; Hassanein, Ahmed

2018-05-01

Ablation of metals under different ambient conditions and laser fluences, was investigated through series of experiments. A 1064 nm, 6 ns Nd:YAG laser was used to ablate 1 mm thick metal targets with laser energy ranging from 2 mJ to 300 mJ. The experiments were designed to study the effect of material properties, laser fluence, ambient gas, and ambient pressure on laser-metal ablation. The first experiment was conducted under vacuum to study the effect of laser fluence and material properties on metal ablation, using a wide range of laser fluences (2 J/cm2 up to 300 J/cm2) and two different targets, Al and W. The second experiment was conducted at atmospheric pressure using two different ambient gases air and argon, to understand the effect of ambient gas on laser-metal ablation process. The third experiment was conducted at two different pressures (10 Torr and 760 Torr) using the same ambient gas to investigate the effect of ambient pressure on laser-metal ablation. To compare the different ablation processes, the amount of mass ablated, ablation depth, crater profile and melt formation were measured using White Light Profilometer (WLP). The experimental results show that at low laser fluence: the ablated mass, ablation depth, and height of molten layer follow a logarithmic function of the incident laser fluence. While, at high laser fluence they follow a linear function. This dependence on laser fluence was found to be independent on ambient conditions and irradiated material. The effect of ambient pressure was more pronounced than the effect of ambient gas type. Plasma shielding effect was found to be very pronounced in the presence of ambient gas and led to significant reduction in the total mass ablation.

Photoaggregation of crystallins (main proteins of eye lens) under the effect of XeCl laser radiation

NASA Astrophysics Data System (ADS)

Soustov, Lev V.; Chelnokov, Evgeny V.; Bityurin, Nikita M.; Kiselev, A. L.; Nemov, V. V.; Sergeev, Yu. V.; Ostrovsky, Michail A.

2004-07-01

UV light is one of primary factors associated with cataract formation in the eye lens. α-, β-, γ-Crystallins maintain lens transparency, and damage to these proteins plays a major role in cataract formation. The effect of XeCl laser radiation (308 nm) on βL-crystallin solution is studied. The strong dependence of protein aggregation kinetics on both laser fluence (w) and repetition rate (F) is investigated. The kinetics features are similar to those of carbonic anhydrase photoaggregation studied previously.

Re-crystallization of ITO films after carbon irradiation

NASA Astrophysics Data System (ADS)

Usman, Muhammad; Khan, Shahid; Khan, Majid; Abbas, Turab Ali

2017-01-01

2.0 MeV carbon ion irradiation effects on Indium Tin Oxide (ITO) thin films on glass substrate are investigated. The films are irradiated with carbon ions in the fluence range of 1 × 1013 to 1 × 1015 ions/cm2. The irradiation induced effects in ITO are compared before and after ion bombardment by systematic study of structural, optical and electrical properties of the films. The XRD results show polycrystalline nature of un-irradiated ITO films which turns to amorphous state after 1 × 1013 ions/cm2 fluence of carbon ions. Further increase in ion fluence to 1 × 1014 ions/cm2 re-crystallizes the structure and retains for even higher fluences. A gradual decrease in the electrical conductivity and transmittance of irradiated samples is observed with increasing ion fluence. The band gap of the films is observed to be decreased after carbon irradiation.

Radiation Resistance Studies of Amorphous Silicon Alloy Photovoltaic Materials

NASA Technical Reports Server (NTRS)

Woodyard, James R.

1994-01-01

The radiation resistance of commercial solar cells fabricated from hydrogenated amorphous silicon alloys was investigated. A number of different device structures were irradiated with 1.0 MeV protons. The cells were insensitive to proton fluences below 1E12 sq cm. The parameters of the irradiated cells were restored with annealing at 200 C. The annealing time was dependent on proton fluence. Annealing devices for one hour restores cell parameters for fluences below lE14 sq cm require longer annealing times. A parametric fitting model was used to characterize current mechanisms observed in dark I-V measurements. The current mechanisms were explored with irradiation fluence, and voltage and light soaking times. The thermal generation current density and quality factor increased with proton fluence. Device simulation shows the degradation in cell characteristics may be explained by the reduction of the electric field in the intrinsic layer.

Investigation of the stability and 1.0 MeV proton radiation resistance of commercially produced hydrogenated amorphous silicon alloy solar cells

NASA Technical Reports Server (NTRS)

Lord, Kenneth R., II; Walters, Michael R.; Woodyard, James R.

1994-01-01

The radiation resistance of commercial solar cells fabricated from hydrogenated amorphous silicon alloys is reported. A number of different device structures were irradiated with 1.0 MeV protons. The cells were annealing at 200 C. The annealing time was dependent on proton fluence. Annealing devices for one hour restores cell parameters or fluences below 1(exp 14) cm(exp -2); fluences above 1(exp 14) cm(exp -2) require longer annealing times. A parametric fitting model was used to characterize current mechanisms observed in dark I-V measurements. The current mechanisms were explored with irradiation fluence, and voltage and light soaking times. The thermal generation current density and quality factor increased with proton fluence. Device simulation shows the degradation in cell characteristics may be explained by the reduction of the electric field in the intrinsic layer.

Epoxy-paint stripping using TEA CO2 laser: Determination of threshold fluence and the process parameters

NASA Astrophysics Data System (ADS)

Kumar, Manoj; Bhargava, P.; Biswas, A. K.; Sahu, Shasikiran; Mandloi, V.; Ittoop, M. O.; Khattak, B. Q.; Tiwari, M. K.; Kukreja, L. M.

2013-03-01

It is shown that the threshold fluence for laser paint stripping can be accurately estimated from the heat of gasification and the absorption coefficient of the epoxy-paint. The threshold fluence determined experimentally by stripping of the epoxy-paint on a substrate using a TEA CO2 laser matches closely with the calculated value. The calculated threshold fluence and the measured absorption coefficient of the paint allowed us to determine the epoxy paint thickness that would be removed per pulse at a given laser fluence even without experimental trials. This was used to predict the optimum scan speed required to strip the epoxy-paint of a given thickness using a high average power TEA CO2 laser. Energy Dispersive X-Ray Fluorescence (EDXRF) studies were also carried out on laser paint-stripped concrete substrate to show high efficacy of this modality.

Property changes of G347A graphite due to neutron irradiation

DOE PAGES

Campbell, Anne A.; Katoh, Yutai; Snead, Mary A.; ...

2016-08-18

A new, fine-grain nuclear graphite, grade G347A from Tokai Carbon Co., Ltd., has been irradiated in the High Flux Isotope Reactor at Oak Ridge National Laboratory to study the materials property changes that occur when exposed to neutron irradiation at temperatures of interest for Generation-IV nuclear reactor applications. Specimen temperatures ranged from 290°C to 800 °C with a maximum neutron fluence of 40 × 10 25 n/m 2 [E > 0.1 MeV] (~30dpa). Lastly, observed behaviors include: anisotropic behavior of dimensional change in an isotropic graphite, Young's modulus showing parabolic fluence dependence, electrical resistivity increasing at low fluence and additionalmore » increase at high fluence, thermal conductivity rapidly decreasing at low fluence followed by continued degradation, and a similar plateau value of the mean coefficient of thermal expansion for all irradiation temperatures.« less

Internal photon and electron dosimetry of the newborn patient—a hybrid computational phantom study

NASA Astrophysics Data System (ADS)

Wayson, Michael; Lee, Choonsik; Sgouros, George; Treves, S. Ted; Frey, Eric; Bolch, Wesley E.

2012-03-01

Estimates of radiation absorbed dose to organs of the nuclear medicine patient are a requirement for administered activity optimization and for stochastic risk assessment. Pediatric patients, and in particular the newborn child, represent that portion of the patient population where such optimization studies are most crucial owing to the enhanced tissue radiosensitivities and longer life expectancies of this patient subpopulation. In cases where whole-body CT imaging is not available, phantom-based calculations of radionuclide S values—absorbed dose to a target tissue per nuclear transformation in a source tissue—are required for dose and risk evaluation. In this study, a comprehensive model of electron and photon dosimetry of the reference newborn child is presented based on a high-resolution hybrid-voxel phantom from the University of Florida (UF) patient model series. Values of photon specific absorbed fraction (SAF) were assembled for both the reference male and female newborn using the radiation transport code MCNPX v2.6. Values of electron SAF were assembled in a unique and time-efficient manner whereby the collisional and radiative components of organ dose--for both self- and cross-dose terms—were computed separately. Dose to the newborn skeletal tissues were assessed via fluence-to-dose response functions reported for the first time in this study. Values of photon and electron SAFs were used to assemble a complete set of S values for some 16 radionuclides commonly associated with molecular imaging of the newborn. These values were then compared to those available in the OLINDA/EXM software. S value ratios for organ self-dose ranged from 0.46 to 1.42, while similar ratios for organ cross-dose varied from a low of 0.04 to a high of 3.49. These large discrepancies are due in large part to the simplistic organ modeling in the stylized newborn model used in the OLINDA/EXM software. A comprehensive model of internal dosimetry is presented in this study for the newborn nuclear medicine patient based upon the UF hybrid computational phantom. Photon dose response functions, photon and electron SAFs, and tables of radionuclide S values for the newborn child--both male and female--are given in a series of four electronic annexes available at stacks.iop.org/pmb/57/1433/mmedia. These values can be applied to optimization studies of image quality and stochastic risk for this most vulnerable class of pediatric patients.

Implementation and validation of collapsed cone superposition for radiopharmaceutical dosimetry of photon emitters

NASA Astrophysics Data System (ADS)

Sanchez-Garcia, Manuel; Gardin, Isabelle; Lebtahi, Rachida; Dieudonné, Arnaud

2015-10-01

Two collapsed cone (CC) superposition algorithms have been implemented for radiopharmaceutical dosimetry of photon emitters. The straight CC (SCC) superposition method uses a water energy deposition kernel (EDKw) for each electron, positron and photon components, while the primary and scatter CC (PSCC) superposition method uses different EDKw for primary and once-scattered photons. PSCC was implemented only for photons originating from the nucleus, precluding its application to positron emitters. EDKw are linearly scaled by radiological distance, taking into account tissue density heterogeneities. The implementation was tested on 100, 300 and 600 keV mono-energetic photons and 18F, 99mTc, 131I and 177Lu. The kernels were generated using the Monte Carlo codes MCNP and EGSnrc. The validation was performed on 6 phantoms representing interfaces between soft-tissues, lung and bone. The figures of merit were γ (3%, 3 mm) and γ (5%, 5 mm) criterions corresponding to the computation comparison on 80 absorbed doses (AD) points per phantom between Monte Carlo simulations and CC algorithms. PSCC gave better results than SCC for the lowest photon energy (100 keV). For the 3 isotopes computed with PSCC, the percentage of AD points satisfying the γ (5%, 5 mm) criterion was always over 99%. A still good but worse result was found with SCC, since at least 97% of AD-values verified the γ (5%, 5 mm) criterion, except a value of 57% for the 99mTc with the lung/bone interface. The CC superposition method for radiopharmaceutical dosimetry is a good alternative to Monte Carlo simulations while reducing computation complexity.

Implementation and validation of collapsed cone superposition for radiopharmaceutical dosimetry of photon emitters.

PubMed

Sanchez-Garcia, Manuel; Gardin, Isabelle; Lebtahi, Rachida; Dieudonné, Arnaud

2015-10-21

Two collapsed cone (CC) superposition algorithms have been implemented for radiopharmaceutical dosimetry of photon emitters. The straight CC (SCC) superposition method uses a water energy deposition kernel (EDKw) for each electron, positron and photon components, while the primary and scatter CC (PSCC) superposition method uses different EDKw for primary and once-scattered photons. PSCC was implemented only for photons originating from the nucleus, precluding its application to positron emitters. EDKw are linearly scaled by radiological distance, taking into account tissue density heterogeneities. The implementation was tested on 100, 300 and 600 keV mono-energetic photons and (18)F, (99m)Tc, (131)I and (177)Lu. The kernels were generated using the Monte Carlo codes MCNP and EGSnrc. The validation was performed on 6 phantoms representing interfaces between soft-tissues, lung and bone. The figures of merit were γ (3%, 3 mm) and γ (5%, 5 mm) criterions corresponding to the computation comparison on 80 absorbed doses (AD) points per phantom between Monte Carlo simulations and CC algorithms. PSCC gave better results than SCC for the lowest photon energy (100 keV). For the 3 isotopes computed with PSCC, the percentage of AD points satisfying the γ (5%, 5 mm) criterion was always over 99%. A still good but worse result was found with SCC, since at least 97% of AD-values verified the γ (5%, 5 mm) criterion, except a value of 57% for the (99m)Tc with the lung/bone interface. The CC superposition method for radiopharmaceutical dosimetry is a good alternative to Monte Carlo simulations while reducing computation complexity.

Solar cell radiation handbook

NASA Technical Reports Server (NTRS)

Tada, H. Y.; Carter, J. R., Jr.; Anspaugh, B. E.; Downing, R. G.

1982-01-01

The handbook to predict the degradation of solar cell electrical performance in any given space radiation environment is presented. Solar cell theory, cell manufacturing and how they are modeled mathematically are described. The interaction of energetic charged particles radiation with solar cells is discussed and the concept of 1 MeV equivalent electron fluence is introduced. The space radiation environment is described and methods of calculating equivalent fluences for the space environment are developed. A computer program was written to perform the equivalent fluence calculations and a FORTRAN listing of the program is included. Data detailing the degradation of solar cell electrical parameters as a function of 1 MeV electron fluence are presented.

Femtosecond laser ablation of dentin and enamel: relationship between laser fluence and ablation efficiency.

PubMed

Chen, Hu; Liu, Jing; Li, Hong; Ge, Wenqi; Sun, Yuchun; Wang, Yong; Lü, Peijun

2015-02-01

The objective was to study the relationship between laser fluence and ablation efficiency of a femtosecond laser with a Gaussian-shaped pulse used to ablate dentin and enamel for prosthodontic tooth preparation. A diode-pumped thin-disk femtosecond laser with wavelength of 1025 nm and pulse width of 400 fs was used for the ablation of dentin and enamel. The laser spot was guided in a line on the dentin and enamel surfaces to form a groove-shaped ablation zone under a series of laser pulse energies. The width and volume of the ablated line were measured under a three-dimensional confocal microscope to calculate the ablation efficiency. Ablation efficiency for dentin reached a maximum value of 0.020 mm3∕J when the laser fluence was set at 6.51 J∕cm2. For enamel, the maximum ablation efficiency was 0.009 mm3∕J at a fluence of 7.59 J∕cm2.Ablation efficiency of the femtosecond laser on dentin and enamel is closely related to the laser fluence and may reach a maximum when the laser fluence is set to an appropriate value. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Formation of porous networks on polymeric surfaces by femtosecond laser micromachining

NASA Astrophysics Data System (ADS)

Assaf, Youssef; Kietzig, Anne-Marie

2017-02-01

In this study, porous network structures were successfully created on various polymer surfaces by femtosecond laser micromachining. Six different polymers (poly(tetrafluoroethylene) (PTFE), poly(methyl methacrylate) (PMMA), high density poly(ethylene) (HDPE), poly(lactic acid) (PLA), poly(carbonate) (PC), and poly(ethylene terephthalate) (PET)) were machined at different fluences and pulse numbers, and the resulting structures were identified and compared by lacunarity analysis. At low fluence and pulse numbers, porous networks were confirmed to form on all materials except PLA. Furthermore, all networks except for PMMA were shown to bundle up at high fluence and pulse numbers. In the case of PC, a complete breakdown of the structure at such conditions was observed. Operation slightly above threshold fluence and at low pulse numbers is therefore recommended for porous network formation. Finally, the thickness over which these structures formed was measured and compared to two intrinsic material dependent parameters: the single pulse threshold fluence and the incubation coefficient. Results indicate that a lower threshold fluence at operating conditions favors material removal over structure formation and is hence detrimental to porous network formation. Favorable machining conditions and material-dependent parameters for the formation of porous networks on polymer surfaces have thus been identified.

Extracting the distribution of laser damage precursors on fused silica surfaces for 351 nm, 3 ns laser pulses at high fluences (20-150 J/cm2).

PubMed

Laurence, Ted A; Bude, Jeff D; Ly, Sonny; Shen, Nan; Feit, Michael D

2012-05-07

Surface laser damage limits the lifetime of optics for systems guiding high fluence pulses, particularly damage in silica optics used for inertial confinement fusion-class lasers (nanosecond-scale high energy pulses at 355 nm/3.5 eV). The density of damage precursors at low fluence has been measured using large beams (1-3 cm); higher fluences cannot be measured easily since the high density of resulting damage initiation sites results in clustering. We developed automated experiments and analysis that allow us to damage test thousands of sites with small beams (10-30 µm), and automatically image the test sites to determine if laser damage occurred. We developed an analysis method that provides a rigorous connection between these small beam damage test results of damage probability versus laser pulse energy and the large beam damage results of damage precursor densities versus fluence. We find that for uncoated and coated fused silica samples, the distribution of precursors nearly flattens at very high fluences, up to 150 J/cm2, providing important constraints on the physical distribution and nature of these precursors.

Fast approximate delivery of fluence maps for IMRT and VMAT

NASA Astrophysics Data System (ADS)

Balvert, Marleen; Craft, David

2017-02-01

In this article we provide a method to generate the trade-off between delivery time and fluence map matching quality for dynamically delivered fluence maps. At the heart of our method lies a mathematical programming model that, for a given duration of delivery, optimizes leaf trajectories and dose rates such that the desired fluence map is reproduced as well as possible. We begin with the single fluence map case and then generalize the model and the solution technique to the delivery of sequential fluence maps. The resulting large-scale, non-convex optimization problem was solved using a heuristic approach. We test our method using a prostate case and a head and neck case, and present the resulting trade-off curves. Analysis of the leaf trajectories reveals that short time plans have larger leaf openings in general than longer delivery time plans. Our method allows one to explore the continuum of possibilities between coarse, large segment plans characteristic of direct aperture approaches and narrow field plans produced by sliding window approaches. Exposing this trade-off will allow for an informed choice between plan quality and solution time. Further research is required to speed up the optimization process to make this method clinically implementable.

Protocol for Determining Ultraviolet Light Emitting Diode (UV-LED) Fluence for Microbial Inactivation Studies.

PubMed

Kheyrandish, Ataollah; Mohseni, Madjid; Taghipour, Fariborz

2018-06-15

Determining fluence is essential to derive the inactivation kinetics of microorganisms and to design ultraviolet (UV) reactors for water disinfection. UV light emitting diodes (UV-LEDs) are emerging UV sources with various advantages compared to conventional UV lamps. Unlike conventional mercury lamps, no standard method is available to determine the average fluence of the UV-LEDs, and conventional methods used to determine the fluence for UV mercury lamps are not applicable to UV-LEDs due to the relatively low power output, polychromatic wavelength, and specific radiation profile of UV-LEDs. In this study, a method was developed to determine the average fluence inside a water suspension in a UV-LED experimental setup. In this method, the average fluence was estimated by measuring the irradiance at a few points for a collimated and uniform radiation on a Petri dish surface. New correction parameters were defined and proposed, and several of the existing parameters for determining the fluence of the UV mercury lamp apparatus were revised to measure and quantify the collimation and uniformity of the radiation. To study the effect of polychromatic output and radiation profile of the UV-LEDs, two UV-LEDs with peak wavelengths of 262 and 275 nm and different radiation profiles were selected as the representatives of typical UV-LEDs applied to microbial inactivation. The proper setup configuration for microorganism inactivation studies was also determined based on the defined correction factors.

Two solar proton fluence models based on ground level enhancement observations

NASA Astrophysics Data System (ADS)

Raukunen, Osku; Vainio, Rami; Tylka, Allan J.; Dietrich, William F.; Jiggens, Piers; Heynderickx, Daniel; Dierckxsens, Mark; Crosby, Norma; Ganse, Urs; Siipola, Robert

2018-01-01

Solar energetic particles (SEPs) constitute an important component of the radiation environment in interplanetary space. Accurate modeling of SEP events is crucial for the mitigation of radiation hazards in spacecraft design. In this study we present two new statistical models of high energy solar proton fluences based on ground level enhancement (GLE) observations during solar cycles 19-24. As the basis of our modeling, we utilize a four parameter double power law function (known as the Band function) fits to integral GLE fluence spectra in rigidity. In the first model, the integral and differential fluences for protons with energies between 10 MeV and 1 GeV are calculated using the fits, and the distributions of the fluences at certain energies are modeled with an exponentially cut-off power law function. In the second model, we use a more advanced methodology: by investigating the distributions and relationships of the spectral fit parameters we find that they can be modeled as two independent and two dependent variables. Therefore, instead of modeling the fluences separately at different energies, we can model the shape of the fluence spectrum. We present examples of modeling results and show that the two methodologies agree well except for a short mission duration (1 year) at low confidence level. We also show that there is a reasonable agreement between our models and three well-known solar proton models (JPL, ESP and SEPEM), despite the differences in both the modeling methodologies and the data used to construct the models.

Detector, collimator and real-time reconstructor for a new scanning-beam digital x-ray (SBDX) prototype.

PubMed

Speidel, Michael A; Tomkowiak, Michael T; Raval, Amish N; Dunkerley, David A P; Slagowski, Jordan M; Kahn, Paul; Ku, Jamie; Funk, Tobias

Scanning-beam digital x-ray (SBDX) is an inverse geometry fluoroscopy system for low dose cardiac imaging. The use of a narrow scanned x-ray beam in SBDX reduces detected x-ray scatter and improves dose efficiency, however the tight beam collimation also limits the maximum achievable x-ray fluence. To increase the fluence available for imaging, we have constructed a new SBDX prototype with a wider x-ray beam, larger-area detector, and new real-time image reconstructor. Imaging is performed with a scanning source that generates 40,328 narrow overlapping projections from 71 × 71 focal spot positions for every 1/15 s scan period. A high speed 2-mm thick CdTe photon counting detector was constructed with 320×160 elements and 10.6 cm × 5.3 cm area (full readout every 1.28 μs), providing an 86% increase in area over the previous SBDX prototype. A matching multihole collimator was fabricated from layers of tungsten, brass, and lead, and a multi-GPU reconstructor was assembled to reconstruct the stream of captured detector images into full field-of-view images in real time. Thirty-two tomosynthetic planes spaced by 5 mm plus a multiplane composite image are produced for each scan frame. Noise equivalent quanta on the new SBDX prototype measured 63%-71% higher than the previous prototype. X-ray scatter fraction was 3.9-7.8% when imaging 23.3-32.6 cm acrylic phantoms, versus 2.3-4.2% with the previous prototype. Coronary angiographic imaging at 15 frame/s was successfully performed on the new SBDX prototype, with live display of either a multiplane composite or single plane image.