Nahum A E
Phys Med Biol. 1978 Jan;23(1):24-38. doi: 10.1088/0031-9155/23/1/002.
Water/air mass stopping power ratios have been calculated for 5, 10, 20 and 30 MeV electron beams and various photon beams from 60Co to 31 MV betatron. The stopping power ratios have been evaluated by applying a modified version of the Spencer-Attix theory to depth-dependent electron flux spectra computed by the Monte Carlo method. Results are presented for three values of the cavity size parameter delta, 0.001, 0.01 and 0.1 MeV, and also for a Bragg-Gray cavity. For the electron beams, the results are compared to Berger's comprehensive computations. In the case of the photon beams, such a rigorous evaluation of the stopping power ratio has not been carried out previously. It is shown that the currently used approximate Bragg-Gray ratios are as much as 2% too low for high energy photon beams, and that there is a difference of about 1% between values for betatron (thin target) and linac (thick target) beams of the same maximum photon energy.
已计算出5、10、20和30兆电子伏电子束以及从60钴到31兆伏电子感应加速器的各种光子束的水/气质量阻止本领比。通过将斯宾塞 - 阿蒂克斯理论的修正版本应用于由蒙特卡罗方法计算的深度相关电子通量谱来评估阻止本领比。给出了腔尺寸参数δ为0.001、0.01和0.1兆电子伏的三个值以及布拉格 - 格雷腔的结果。对于电子束，将结果与伯杰的综合计算进行了比较。对于光子束，以前尚未对阻止本领比进行如此严格的评估。结果表明，对于高能光子束，目前使用的近似布拉格 - 格雷比低达2%，并且相同最大光子能量的电子感应加速器（薄靶）束和直线加速器（厚靶）束的值之间存在约1%的差异。
