Scattered Radiation from Large Cs137 Sources

Costrell, Louis

doi:10.1097/00004032-196210000-00002

Cited by 8 publications

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“…Smaller values of W are obtained for smaller values of A since more energy is deposited from more isotropically distributed 6-rays. For a typical 6oCo incident photon spectrum (Rogers et a1 1988), U was calculated to be 1.058~0.0011, and for a typical 13'Cs spectrum (Costrell 1962) the value 0.975_+0.006 was obtained. Having determined the size of one's chamber in terms of A, one should use the U-value from figure 4 in conjunction with the appropriate expressions from the previous section or the K-factors depicted in figure 1.…”

Section: (The Unbound Compton Distribution Was Takenmentioning

confidence: 96%

An analytic theory of the point-source nonuniformity correction factor for thick-walled ionisation chambers in photon beams

Bielajew

1990

Phys. Med. Biol.

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In exposure and air kerma measurements, axial and radial nonuniformity perturbation correction factors are used to account for the nonuniformity of the incident photon field in the vicinity of the ionisation chamber cavity. An analytic theory for calculating the point source nonuniformity correction factor for thick-walled ionisation chambers is developed. The theory developed herein is compared with Monte Carlo calculations for chambers with pancake, cylindrical and spherical geometries similar in size to the instruments employed by Standards laboratories. The perturbations, which differ from those calculated or measured by some Standards laboratories, suggest that corrections of the order of 0.3% should be applied to typical pancake geometries, smaller corrections of the order of 0.05% or less for typical Farmer-type chambers, and no correction for spherical chambers.

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Section: (The Unbound Compton Distribution Was Takenmentioning

confidence: 96%

An analytic theory of the point-source nonuniformity correction factor for thick-walled ionisation chambers in photon beams

Bielajew

1990

Phys. Med. Biol.

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“…The method of choice is to use Monte Carlo calculations to simulate all parts of the irradiation facility that might influence the photon spectrum, notably the finite source, its encapsulation and the collimating system. Such calculations have been carried out mainly for 60 Co therapy units [38][39][40] and only a small number for 137 Cs units [41] and 192 Ir sources [42,43]. Examples of calculated spectra are shown in figure 5.…”

Section: Photon Spectra For Different Gamma-ray Sourcesmentioning

confidence: 99%

Air-kerma cavity standards

Büermann

Burns

2009

Metrologia

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This paper reviews the current status of air-kerma cavity standards for gamma rays from 60Co, 137Cs and 192Ir sources. It describes the basic principles and the theories to determine the air-kerma rate from the ionization current of graphite-walled cavity ionization chambers. A typical design of a cavity chamber is shown and described. The various correction factors to be applied to the standards and their determination by experimental and Monte Carlo methods are discussed. A typical uncertainty budget for a cavity standard is presented and the results of comparisons between primary standards are summarized and discussed. Finally, conclusions are drawn and proposals made for topics to be addressed in future studies.

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“…Spectra for 137 Cs gamma-ray beams are given by Costrell [ 22 ], measured for eight different source geometries. For the purposes of this report, his spectra were combined (when similar) and adjusted to form five spectra with scattered-photon contributions of 15 %, 20 %, 25 %, 30 %, and 35 %, in addition to a single-line spectrum of monoenergetic 0.662 MeV photons.…”

Section: Assumed Photon Spectra For Nist Gamma-ray Sourcesmentioning

confidence: 99%

“… Incident photon spectra assumed for NBS-NIST 137 Co calibrating beams. The legend gives the scatter contribution of the spectra derived from results of Costrell [ 22 ]. The vertical arrow indicates a δ -function at the photon energy 0.662 MeV.…”

Section: Figmentioning

confidence: 99%

Changes in the US primary standards for the air kerma from gamma-ray beams

Seltzer

Bergstrom

2003

J. Res. Natl. Inst. Stand. Technol.

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Monte Carlo photon-electron transport calculations have been done to derive new wall corrections for the six NBS-NIST standard graphite-wall, air-ionization cavity chambers that serve as the U.S. national primary standard for air kerma (and exposure) for gamma rays from 60Co, 137Cs, and 192Ir sources. The data developed for and from these calculations have also been used to refine a number of other factors affecting the standards. The largest changes are due to the new wall corrections, and the total changes are +0.87 % to +1.11 % (depending on the chamber) for 60Co beams, +0.64 % to +1.07 % (depending on the chamber) for 137Cs beams, and −0.06 % for the single chamber used in the measurement of the standardized 192Ir source. The primary standards for air kerma will be adjusted in the near future to reflect the changes in factors described in this work.

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Scattered Radiation from Large Cs137 Sources

Cited by 8 publications

References 0 publications

An analytic theory of the point-source nonuniformity correction factor for thick-walled ionisation chambers in photon beams

An analytic theory of the point-source nonuniformity correction factor for thick-walled ionisation chambers in photon beams

Air-kerma cavity standards

Changes in the US primary standards for the air kerma from gamma-ray beams

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