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Diaphragm correction factors for free-air chamber standards for air kerma in x-rays



Diaphragm correction factors for free-air chamber standards for air kerma in x-rays



Physics in Medicine and Biology 54(9): 2737-2745



At present, only a correction factor for photon transmission, k(l), is systematically applied for the entrance diaphragm of free-air chamber standards for air kerma. In the present work, the Monte Carlo code PENELOPE is used to re-evaluate k(l) for the BIPM standards and new correction factors are calculated for photon scatter and for fluorescence production in the diaphragm. An additional effect arising from electrons emitted from the diaphragm is shown to be significant at the highest photon energies. The results for the radiation qualities used for international comparisons give a combined diaphragm correction factor k(dia) = 0.9980(3) for the BIPM medium-energy standard at 250 kV. This is significantly different from the factor k(l) = 0.9996(1) in use at present and it might be concluded that differences are likely to exist for all free-air chamber standards. The effect of using a conical taper at the downstream edge of the diaphragm is shown to be negligible for these radiation qualities.

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Accession: 052590671

Download citation: RISBibTeXText

PMID: 19351980

DOI: 10.1088/0031-9155/54/9/009


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