Bond J E, Nath R, Schulz R J
Med Phys. 1978 Sep-Oct;5(5):422-5. doi: 10.1118/1.594439.
The application of cavity-ionization chambers to the standadization of 60Co gamma-ray beams, in terms of exposure, requires that the specific ionization of air Jg, be corrected for the attenuation and scatter of the incident rays by the wall, central electrode, and supporting stem of the chamber. A Monte Carlo photon-electron transport code has been developed for the purpose of calculating this correction for spherical and cylindrical chambers. The code has been applied to a spherical graphite chamber having dimensions typical of the chambers used by the NBS, the calculated wall-correction factor is in close agreement with the average of the NBS factors which were determined experimentally. The code was also used to calculate Aeq, which is central to the determination of tissue-air ratios. The calculated value, 0.989 +/- 0.003, is very close to the generally accepted value, 0.985.
就照射量而言，将空腔电离室应用于60Coγ射线束的标准化，需要针对电离室壁、中心电极和支撑杆对入射射线的衰减和散射，对空气比电离Jg进行校正。为计算球形和圆柱形电离室的这种校正，已开发了一种蒙特卡罗光子-电子输运代码。该代码已应用于尺寸具有美国国家标准局（NBS）所用电离室典型特征的球形石墨电离室，计算得到的壁校正因子与通过实验确定的NBS因子的平均值密切吻合。该代码还用于计算Aeq，它对于组织空气比的确定至关重要。计算值为0.989±0.003，与普遍接受的值0.985非常接近。
