250~600 kV X射线石墨空腔电离室壁修正因子及物理常数的蒙卡模拟

Simulation of the Wall Correction Factors and Physical Constants of 250~600 kV X-ray Graphite Cavity Ionization Chamber

石墨空腔电离室由于对较高能量段有较好的能量响应,广泛应用于137Cs(有效能量为662keV)、60Co(有效能量为1250keV)以及平均能量为350keV的192Irγ射线空气比释动能的测量。运用EGSnrc程序模拟自制石墨空腔电离室在250~600kV窄谱辐射质下量值复现过程中的壁修正因子及物理常数。结果显示,石墨与空气的阻止本领比、空气与石墨的质能吸收系数之比、韧致辐射份额常数均与平均能量间有比较明显的关系可循,壁修正因子随着X射线能量的增加,则会有先变大后减小的趋势。蒙特卡洛模拟的结果为建立250~600kVX射线空气比释动能国家基准、实现量值复现提供了技术数据,达到了复现结果测量不确定度的预期要求。

Graphite cavity ionization chamber due to higher energy has good energy response, is widely used in 137 Cs(effective energy of 662 keV), 60 Co (effective energy of 1 250 keV) and average energy is 350 keV 192 Ir gamma ray air kerma.The EGSnrc program was used to simulate the wall correction factor and physical constant of the self-made graphite cavity ionization chamber in the process of quantitative reconstruction under 250~400 kV narrow spectrum radiative mass. The results showed that there was a significant relationship between the blocking power ratio of graphite and air, the mass energy absorption coefficient of air and graphite, and the proportion constant of toughened radiation, and the average energy. With the increase of X-ray energy, the wall correction factor had a tendency of first increasing and then decreasing, and it could not determine the future trend. The results of monte carlo simulation provide technical data for establishing 250~600 kV X-ray air kerma national benchmark and realizing the reappearance of measurement values, and meet the expected requirements of the uncertainty of measurement of the reappearance results.