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Ernesto Mainegrahing - One of the best experts on this subject based on the ideXlab platform.
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radiation attenuation by lead and nonlead materials used in radiation shielding garments
2007Co-Authors: J P Mccaffrey, B Downton, H Shen, Ernesto MainegrahingAbstract:The attenuating properties of several types of lead Pb-based and non-Pb radiation shielding materials were studied and a correlation was made of radiation attenuation, materials properties, calculated spectra and ambient dose equivalent. Utilizing the well-characterized x-Ray and Gamma Ray Beams at the National Research Council of Canada, air kerma measurements were used to compare a variety of commercial and pre-commercial radiation shielding materials over mean energy ranges from 39 to 205 keV. The EGSnrc Monte Carlo user code cavity.cpp was extended to provide computed spectra for a variety of elements that have been used as a replacement for Pb in radiation shielding garments. Computed air kerma values were compared with experimental values and with the SRS-30 catalogue of diagnostic spectra available through the Institute of Physics and Engineering in Medicine Report 78. In addition to garment materials, measurements also included pure Pb sheets, allowing direct comparisons to the common industry standards of 0.25 and 0.5 mm “lead equivalent.” The parameter “lead equivalent” is misleading, since photon attenuation properties for all materials including Pb vary significantly over the energy spectrum, with the largest variations occurring in the diagnostic imaging range. Furthermore, air kerma measurements are typically made to determine attenuation properties without reference to the measures of biological damage such as ambient dose equivalent, which also vary significantly with air kerma over the diagnostic imaging energy range. A single material or combination cannot provide optimum shielding for all energy ranges. However, appropriate choice of materials for a particular energy range can offer significantly improved shielding per unit mass over traditional Pb-based materials. DOI: 10.1118/1.2426404 I. INTRODUCTION Radiation shielding garments are commonly used to protect medical patients and workers from exposure to direct and secondary radiation during diagnostic imaging in hospitals, clinics and dental offices. Similar materials are employed for other applications such as scanner curtains used to protect personnel working in the vicinity of airport scanners or similar devices. In most of these environments, typical peak x-Ray energies range from 60 to 120 kVp, corresponding to mean energies of approximately 35– 60 keV. The photoelectric effect overwhelmingly dominates energy transfer and absorption in this energy range, so only this mechanism is discussed in this study. The effectiveness of radiation shielding varies significantly with the photoelectric attenuation coefficients of the constituent materials, the thickness of the garments, and the energy spectrum of the radiation. Historically, radiation shielding aprons and coverings have been manufactured from lead Pb powder-loaded polymer or elastomer sheets. Typical garment lifetime for these materials is approximately 10 years, although abuse can drastically shorten this period. Aging, damage, embrittlement, as well as cracking particularly of garments incorporating natural rubber results in drastically reduced lifetimes. Early studies of non-Pb materials were prompted by the desire to reduce the weight of protective garments and the possibility of improved shielding performance. 1 . The challenge
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radiation attenuation by lead and nonlead materials used in radiation shielding garments
2007Co-Authors: J P Mccaffrey, B Downton, H Shen, Ernesto MainegrahingAbstract:The attenuating properties of several types of lead (Pb)-based and non-Pb radiation shielding materials were studied and a correlation was made of radiation attenuation, materials properties, calculated spectra and ambient dose equivalent. Utilizing the well-characterized x-Ray and Gamma Ray Beams at the National Research Council of Canada, air kerma measurements were used to compare a variety of commercial and pre-commercial radiation shielding materials over mean energy ranges from 39 to 205 keV. The EGSnrc Monte Carlo user code cavity. cpp was extended to provide computed spectra for a variety of elements that have been used as a replacement for Pb in radiation shielding garments. Computed air kerma values were compared with experimental values and with the SRS-30 catalogue of diagnostic spectra available through the Institute of Physics and Engineering in Medicine Report 78. In addition to garment materials, measurements also included pure Pb sheets, allowing direct comparisons to the common industry standards of 0.25 and 0.5 mm "lead equivalent." The parameter "lead equivalent" is misleading, since photon attenuation properties for all materials (including Pb) vary significantly over the energy spectrum, with the largest variations occurring in the diagnostic imaging range. Furthermore, air kerma measurements are typically made to determine attenuation properties without reference to the measures of biological damage such as ambient dose equivalent, which also vary significantly with air kerma over the diagnostic imaging energy range. A single material or combination cannot provide optimum shielding for all energy ranges. However, appropriate choice of materials for a particular energy range can offer significantly improved shielding per unit mass over traditional Pb-based materials.
Paul S Nizin - One of the best experts on this subject based on the ideXlab platform.
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on absorbed dose in narrow 60co Gamma Ray Beams and dosimetry of the Gamma knife
1998Co-Authors: Paul S NizinAbstract:Using separate analytical functions describing primary dose, P0(dm,r), collimator scatter, Sc(r), and phantom scatter, TAR(d,r), an expression for absorbed dose in narrow 60Co Gamma-Ray Beams is developed and each function is quantified: D(d,r) = P0(dm,r) Sc(r) TAR(d,r). The absorbed dose is calculated in Beams as narrow as 0.2 cm in radius. Analytical and experimental results are compared using measured dose data for the Gamma Knife. Close agreement with experimental data is observed.
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tissue air ratios for narrow 60co Gamma Ray Beams
1998Co-Authors: Paul S Nizin, R B MooijAbstract:This study introduces a table of tissue-air ratios (TAR) for narrow 60Co Gamma-Ray Beams. The table is consistent with recently published TAR data for broad 60Co Gamma-Ray Beams [Table 4.1, Br. J. Radiol. Suppl. 25 (1996)]. Narrow-beam TARs are derived analytically from broad-beam data of Table 4.1 and are tabulated for circular fields ranging from 0.2 to 2.2 cm in radius--an approximate equivalent of a 0.4 cm x 0.4 cm to 4 cm x 4 cm square-field range. The extent of depth is from 0.5 to 30 cm in water.
Pedro Andreo - One of the best experts on this subject based on the ideXlab platform.
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performance analysis and determination of the p wall correction factor for 60co Gamma Ray Beams for wellhofer roos type plane parallel chambers
2002Co-Authors: Asa Palm, Ladislav Czap, Pedro Andreo, Olof MattssonAbstract:The wall perturbation correction factor pwall in 60Co for Wellhofer Roos-type plane-parallel ionization chambers is determined experimentally and compared with the results of a previous study using PTW–Roos chambers (Palm et al 2000 Phys. Med. Biol. 45 971–81). Five ionization chambers of the type Wellhofer PPC-35 (or its equivalent PPC-40) are used for the analysis. Wall perturbation correction factors are obtained by assuming ND,air chamber factors determined by cross-calibration in a high-energy electron and in a 60Co γ-Ray beam to be equal, and by assigning any differences to the wall perturbation factor. The procedure yields a pwall value of 1.018 (uc = 0.010), which is slightly higher than the value 1.014 (uc = 0.010) formerly obtained for the PTW–Roos chambers using the ND,air method. The chamber-to-chamber variation in pwall for the Wellhofer–Roos chambers is found to be very small, with a maximum difference of 0.3%. The effect of using new pcav values for graphite-walled Farmer-type chambers used in water in electron Beams is to decrease pwall by approximately 0.5%. The long- and short-term stability of the Roos-type chambers manufactured by Wellhofer is investigated by measurements at the IAEA Dosimetry Laboratory in Vienna, Austria, and at the Sahlgrenska University Hospital in Goteborg, Sweden. Calibrations made at the IAEA over several months show variations in the ND,w calibration factors larger than expected, based on previous experiences with PTW–Roos chambers. Measurements of the short-term stability of the Wellhofer–Roos chambers show a marked increase in chamber response for the time the chambers are immersed in water, pointing to a possible problem in the chamber design. As a consequence of these findings, Wellhofer is currently working on a re-design of the chamber to solve the stability problem.
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calibration of plane parallel chambers and determination of p wall for the nacp and roos chambers for 60co Gamma Ray Beams
2000Co-Authors: Asa Palm, Olof Mattsson, Pedro AndreoAbstract:Procedures for the calibration and use of plane-parallel ionization chambers in high-energy electron and photon Beams have been given in the international code of practice IAEA TRS-381. In the present work, plane-parallel ionization chambers of the type PTW-34001 Roos and Scanditronix NACP02 have been calibrated using two NK -based procedures. For the NACP chamber the difference between the N D ,air chamber factors determined in an electron beam and in a 60 Co -Ray beam, respectively, is of the same magnitude as the experimental uncertainty. Results for the PTW Roos chambers, however, do not agree, in accordance with recent findings of other authors. The value determined in a 60 Co -Ray beam is questioned and the reason for the discrepancy assigned to the correction factor for the perturbation due to the chamber wall, p wall . New values of p wall have been experimentally determined by comparing absorbed dose measurements based on air-kerma and absorbed dose to water calibration procedures. A new p wall factor for the Roos chamber in 60 Co -Ray Beams in water (1.009±0.6%) was derived as the weighted average of the different determinations. The value is not significantly higher than the p wall factor given in TRS-381 (1.003±1.5%), but the combined standard uncertainty is reduced. The chamber to chamber variation for six commercial PTW Roos chambers and a Roos prototype was found to be very small.
Christoph H Keitel - One of the best experts on this subject based on the ideXlab platform.
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γ Ray Beams with large orbital angular momentum via nonlinear compton scattering with radiation reaction
2018Co-Authors: Yueyue Chen, Karen Zaven Hatsagortsyan, Christoph H KeitelAbstract:Gamma-Ray Beams with a large angular momentum may affect astrophysical phenomena, which calls for appropriate earth-based experimental investigations. For this purpose, we investigate the generation of well-collimated γ-Ray Beams with a very large orbital angular momentum using nonlinear Compton scattering of a strong laser pulse of twisted photons at ultrarelativistic electrons. Angular momentum conservation among absorbed laser photons, quantum radiation, and electrons is numerically demonstrated in the quantum radiation-dominated regime. We point out that the angular momentum of the absorbed laser photons is not solely transferred to the emitted γ photons, but due to radiation reaction shared between the γ photons and interacting electrons. The efficiency of the angular momentum transfer is optimized with respect to the laser and electron beam parameters. The accompanying process of electron-positron pair production is furthermore shown to enhance the orbital angular momentum gained by the γ-Ray beam.
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laser driven thomson scattering for the generation of ultra bright multi mev Gamma Ray Beams
2015Co-Authors: G Sarri, Darragh J Corvan, J M Cole, W Schumaker, Antonino Di Piazza, H Ahmed, M Yeung, Zu Zhao, Christopher Harvey, Christoph H KeitelAbstract:Compact γ-Ray sources are of key importance not only for fundamental research but also for paramount practical applications such as cancer radiotherapy, active interrogation of materials, and high-energy radiography. Particular characteristics are required for meaningful implementation: multi-MeV energies per photon, a high degree of collimation, and a high peak brilliance. Laser-driven sources are theoretically expected to deliver such capabilities but experiments to date have reported either sub-MeV photon energies, or relatively low brilliance. By entering the non-linear regime of Thomson scattering, we report here on the first experimental realisation of a compact laser-driven γ-Ray source that simultaneously ensures ultra-high brilliance (≈1019 photons s-1 mm-2 mrad-2 0.1% BW), low divergence (≈ mrad), and high photon energy (up to 18 MeV). The reported brilliance exceeds by two orders of magnitudes those of alternative mechanisms and it is the highest ever achieved in the multi-MeV regime in a laboratory experiment.
Ladislav Czap - One of the best experts on this subject based on the ideXlab platform.
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comparison of the air kerma standards for 137cs and 60co Gamma Ray Beams between the iaea and the nist
2011Co-Authors: Ronaldo Minniti, Ladislav CzapAbstract:A comparison of the air kerma standards for 137Cs and 60Co Gamma-Ray Beams was performed between the NIST and the IAEA. Two reference class ionization chambers owned by the IAEA were used as part of this comparison and were calibrated at each facility. The calibration coefficients, NK, were determined for both chambers and in both Gamma-Ray Beams. The measurements were performed at the IAEA and NIST facilities starting in the fall of 2009 and were completed in 2010. The comparison ratio of the calibration coefficients for each chamber, NK,IAEA/NK,NIST, between the IAEA and NIST was 0.999 and 0.997 for the 137Cs and 60Co Gamma-Ray Beams respectively. The relative standard uncertainty for each of these ratios is 0.5%. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by SIM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
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performance analysis and determination of the p wall correction factor for 60co Gamma Ray Beams for wellhofer roos type plane parallel chambers
2002Co-Authors: Asa Palm, Ladislav Czap, Pedro Andreo, Olof MattssonAbstract:The wall perturbation correction factor pwall in 60Co for Wellhofer Roos-type plane-parallel ionization chambers is determined experimentally and compared with the results of a previous study using PTW–Roos chambers (Palm et al 2000 Phys. Med. Biol. 45 971–81). Five ionization chambers of the type Wellhofer PPC-35 (or its equivalent PPC-40) are used for the analysis. Wall perturbation correction factors are obtained by assuming ND,air chamber factors determined by cross-calibration in a high-energy electron and in a 60Co γ-Ray beam to be equal, and by assigning any differences to the wall perturbation factor. The procedure yields a pwall value of 1.018 (uc = 0.010), which is slightly higher than the value 1.014 (uc = 0.010) formerly obtained for the PTW–Roos chambers using the ND,air method. The chamber-to-chamber variation in pwall for the Wellhofer–Roos chambers is found to be very small, with a maximum difference of 0.3%. The effect of using new pcav values for graphite-walled Farmer-type chambers used in water in electron Beams is to decrease pwall by approximately 0.5%. The long- and short-term stability of the Roos-type chambers manufactured by Wellhofer is investigated by measurements at the IAEA Dosimetry Laboratory in Vienna, Austria, and at the Sahlgrenska University Hospital in Goteborg, Sweden. Calibrations made at the IAEA over several months show variations in the ND,w calibration factors larger than expected, based on previous experiences with PTW–Roos chambers. Measurements of the short-term stability of the Wellhofer–Roos chambers show a marked increase in chamber response for the time the chambers are immersed in water, pointing to a possible problem in the chamber design. As a consequence of these findings, Wellhofer is currently working on a re-design of the chamber to solve the stability problem.
