Estimation of Electron-loss and Photon-scattering Corrections for Parallel-plate Free-air Chambers

概要

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Parallel-plate free-air ionization chambers are used for X-ray air-kerma rate standards at the National Metrology Institute of Japan (NMIJ), AIST. The electron-loss and photon-scattering correction factors are needed for the evaluation of air-kerma rate from measured current. The electron-loss correction factor (Ke) is a correction of the charge loss by giving energy to the electrode part without the high-speed electron stopping in the air area where the charges are collected. The scattering correction factor (Ksc) is for a correction of extra charges produced by scattered photons generated after an incidence photon is interactive. The electron-loss and photon-scattering correction factors for 3 different size parallel-plate free-air chambers are estimated by the EGS4 code. One chamber is used to get primary standards for absolute measurements of air kerma in beams of medium-energy X-rays and the other two are used for the same purpose in beams of low-energy X-rays. These correction factors are calculated for mono-energetic photons. It is found that electron-loss and photon-scattering correction factors depend on the chamber size, and the latter especially changes greatly depending on the size. The Ke and Ksc value for medium- and low-energy X-ray fields at AIST are estimated by averaging the energy deposition contributions over the X-ray spectrum.
一般社団法人日本原子力学会の論文
2005-12-25