Comparison of BNM-LMRI and NBS Absorbed-Dose Standards for<sup>60</sup>Co Gamma Rays

Guiho, J.P.; Simoen, J. P.; Domen, Steve R.

doi:10.1088/0026-1394/14/2/003

Cited by 3 publications

(2 citation statements)

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“…Measurements were made with the calorimeter in air, not within a graphite phantom. Gap widths are not indicated by Guiho and Simoen in their 1975 article; however, a later article describes a calorimeter of the same external dimensions (Guiho et al 1978). Based on the data in the 1978 article, the calorimeter is simulated with a core of 3 mm thickness and of diameter 1.6 cm.…”

Section: Correction Factorsmentioning

confidence: 99%

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Re-evaluation of the product of (W/e)_airand the graphite to air stopping-power ratio for⁶⁰Co air kerma standards

Thomson

Rogers

2010

Phys. Med. Biol.

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Experiments which determine the product of (W/e)air, the average energy deposited per coulomb of charge of one sign released by an electron coming to rest in dry air, and (LDelta/rho)Ca, the Spencer-Attix mean restricted mass collision stopping-power ratio for graphite to air, in a 60Co or 137Cs beam are reanalysed. Correction factors, e.g., to account for gaps about a calorimeter core or perturbations due to a cavity's presence, are calculated using the EGSnrc Monte Carlo code system and these generally decrease the value of (W/e)air(LDelta/rho)Ca for each experiment. Stopping-power ratios are calculated for different choices of density correction and average excitation energy (I-value) for graphite. To calculate an average value (W/e)air(LBIPM/rho)Ca for the BIPM air kerma standard, each experimental result is multiplied by the ratio (LBIPM/rho)Ca/(LDelta/Rho)Ca. While individual values of (LDelta/rho)Ca are sensitive to the I-values and density corrections assumed, this ratio varies by less than 0.1% for different choices. Hence, the product (W/e)air(LBIPM/rho)Ca is relatively insensitive to these choices. The weighted mean of the updated data is (W/e)air(LBIPM/rho)Ca=33.68 J C(-1)+/-0.2%, suggesting that the accepted value of 33.97 J C(-1)+/-0.1% is 0.8% too high. This has implications for primary 60Co air kerma standards worldwide and potentially for the choice of graphite I-value and density correction for the calculation of the graphite stopping power, as well as the value of (W/e)air.

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Section: Correction Factorsmentioning

confidence: 99%

“…The 60 Co source was the one used to establish the French primary standard of exposure (air kerma). The spectrum used in simulations is taken to be that quoted by Guiho et al (1978); results are unchanged within statistics of 0.1% if 1.25 MeV is used.…”

Section: Correction Factorsmentioning

confidence: 99%