Perturbation correction of a cylindrical thimble-type chamber in a graphite phantom for<sup>60</sup>Co gamma rays

Almeida, Carlos Eduardo de; Perroche-Roux, A M; Boutillon, M

doi:10.1088/0031-9155/34/10/007

Cited by 5 publications

(8 citation statements)

References 5 publications

(7 reference statements)

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“…Ferreira et al 10 also calculated the perturbation corrections for the cylindrical thimble-type standard graphite ion chamber of the Instituto de Radioproteçao e Dosimetria ͑IRD, Brazil͒ in a graphite phantom irradiated by a 60 Co beam. The results were consistent with the experimental values of de Almeida et al, 15 who measured the readings from both the IRD chamber and the BIPM chamber in the same beam thereby giving the ratio of P repl for the two chambers. Thus the measured P repl values for the IRD chamber depend upon the P repl values for the BIPM chamber.…”

Section: Introductionsupporting

confidence: 91%

“…There are no analytically calculated P repl values for the IRD chamber. Ferreira et al 10 calculated P repl values of the IRD chamber by the EGS4 Monte Carlo code and found the results agreed with the experimental values of de Almeida et al 15 However, as shown in Table III, the P repl values calculated for the IRD chamber in the present study differ from those from the measurements by about 1%. de Almeida et al 15 deduced the P repl values for the IRD chamber by comparing readings from the IRD chamber to those from the BIPM chamber.…”

Section: Iiib P Repl For Ird Chambersupporting

confidence: 81%

“…Ferreira et al 10 calculated P repl values of the IRD chamber by the EGS4 Monte Carlo code and found the results agreed with the experimental values of de Almeida et al 15 However, as shown in Table III, the P repl values calculated for the IRD chamber in the present study differ from those from the measurements by about 1%. de Almeida et al 15 deduced the P repl values for the IRD chamber by comparing readings from the IRD chamber to those from the BIPM chamber. Thus the measured P repl values for the IRD chamber are directly proportional to the P repl values of the BIPM chamber, i.e., they are not independent: If P repl values of the BIPM chamber are wrong by 1%, then so are those of the IRD chamber.…”

Section: Iiib P Repl For Ird Chambersupporting

confidence: 81%

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The replacement correction factor for the BIPM flat cavity ion chamber and the value of

Wang

Rogers

2008

Medical Physics

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A graphite flat cavity ionization chamber is used at the BIPM in France to determine the absorbed dose to graphite in a 60Co photon beam and thereby used to determine the product of the value of W/e, the average energy required to produce an ion pair in dry air, and the value of (LDelta/p)a(C), the mean restricted mass collision stopping-power ratio for graphite to air in a 60Co beam. The accuracy of the (W/e) (LDelta/p)a(C) value thus determined depends upon the accuracy of the perturbation correction factors adopted for this chamber. The perturbation effect of this chamber was accounted for by the replacement correction factor whose value was calculated by an analytical method and confirmed by an EGS4 Monte Carlo calculation. The purpose of this study is to investigate the validity of the analytical and the EGS4 calculations by using recently established methods and the EGSnrc Monte Carlo code, a much improved version of EGS4, to calculate the replacement correction factors for the graphite chamber. It is found that the replacement correction factors used for the BIPM chamber are not correct: the values used are smaller than they should be by about 1%. This leads to a 1% overestimation of the (W/e) (LDelta/p)a(C) value determined by using this chamber. This implies that 60Co air kerma standards that are directly proportional to this product need to be reduced by 1%. Based on the values of the replacement correction factors calculated in this study, and on the value of (LDelta/p)a(C) evaluated from ICRU Report No. 37 stopping power for graphite, the value of W/e determined by using the BIPM chamber should be 33.61 +/- 0.08 J/C. If a more recent value of mean excitation energy for graphite (86.8 eV) and grain density are used to evaluate the graphite stopping power, then the value obtained for W/e is 34.15 +/- 0.08 J/C.

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Section: Introductionsupporting

confidence: 91%

Section: Iiib P Repl For Ird Chambersupporting

confidence: 81%

Section: Iiib P Repl For Ird Chambersupporting

confidence: 81%

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The replacement correction factor for the BIPM flat cavity ion chamber and the value of

Wang

Rogers

2008

Medical Physics

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“…A theoretical evaluation of the perturbation corrections has been made by Boutillon (1983) for the presence of the BIPM flat cavity inside the graphite phantom for two positions of the reference plane which can be the middle plane (k pm ) or the front plane (k pf ) of the actual cavity. Niatel (1983) has confirmed these results by comparison of the absorbed dose measurements performed with the BIPM standard and the calorimeters of several national laboratories (Niatel et al 1985, Boutillon 1989.…”

Section: Theorymentioning

confidence: 60%

“…The perturbation corrections k p are defined by the relation (Boutillon 1983, de Almeida et al 1989)…”

Section: Introductionmentioning

confidence: 99%

Perturbation corrections for flat and thimble-type cylindrical standard ionization chambers for⁶⁰Co gamma rays: Monte Carlo calculations

et al. 1998

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The use of an ionization chamber for absorbed dose determinations in a medium requires one to take into account perturbation corrections due to the presence of the chamber cavity in the medium. Evaluation of these corrections for perturbation and their variation with depth in the medium has been performed for a flat cylindrical and a cylindrical (thimble-type) ionization chamber placed in a graphite phantom irradiated by a 60Co gamma beam using Monte Carlo calculations (EGS4 system with correlated sampling variance reduction technique). The results of these calculations agree with published experimental and theoretical data to better than 0.18%, with a statistical uncertainty of less than 0.17%.

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Advances in Radiation Dosimetry

Nath

Huq

1995

Radiation Therapy Physics

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Perturbation correction of a cylindrical thimble-type chamber in a graphite phantom for⁶⁰Co gamma rays

Cited by 5 publications

References 5 publications

The replacement correction factor for the BIPM flat cavity ion chamber and the value of

The replacement correction factor for the BIPM flat cavity ion chamber and the value of

Perturbation corrections for flat and thimble-type cylindrical standard ionization chambers for⁶⁰Co gamma rays: Monte Carlo calculations

Advances in Radiation Dosimetry

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Perturbation correction of a cylindrical thimble-type chamber in a graphite phantom for60Co gamma rays

Cited by 5 publications

References 5 publications

The replacement correction factor for the BIPM flat cavity ion chamber and the value of

The replacement correction factor for the BIPM flat cavity ion chamber and the value of

Perturbation corrections for flat and thimble-type cylindrical standard ionization chambers for60Co gamma rays: Monte Carlo calculations

Advances in Radiation Dosimetry

Contact Info

Product

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Perturbation correction of a cylindrical thimble-type chamber in a graphite phantom for⁶⁰Co gamma rays

Perturbation corrections for flat and thimble-type cylindrical standard ionization chambers for⁶⁰Co gamma rays: Monte Carlo calculations