基于90Sr源β射线的外推电离室入射窗修正因子

为实现外推电离室对β辐射吸收剂量的准确测量，对影响外推电离室入射窗修正因子k_wi的主要量进行了研究。实验测量了外推电离室不同极间距和不同源 探距（源到外推电离室入射窗表面的距离）下的k_wi。研究结果表明，在源 探距不变的条件下，k_wi随电离室极间距的增大而减小；在电离室极间距为3 mm的条件下，k_wi随源-探距的增大而减小。利用蒙特卡罗模拟计算出不带展平过滤器、源 探距为30 cm、电离室极间距为3 mm时，k_wi为1.0845，与实验测量结果比较，其相对偏差为0.11%。因此，在给出k_wi的同时，应提供相应的源-探距和电离室极间距。

Extrapolation Chamber Entrance Window Correction Factor on 90Sr β Ray Radiation Field

In order to achieve accurate measurement of the absorbed dose of beta radiation, the main influence factors of the extrapolation chamber entrance window correction factor k_wi were studied.k_wi at different cavity lengths and different source detection distances was measured by experiments. The results show that the correction factork_wi with the same source-detection distance decreases with the increase of the cavity length. Andk_wi decreases with the increase of the source-detection distance when the cavity length is 3 mm. The calculatedk_wi without flattened filter at source-detection distance of 30 cm and cavity length of 3 mm was simulated using Monte Carlo method. The simulation result is 1.084 5, which differs from the experiment result by 0.11%. Therefore, in addition to the correction factork_wi, corresponding source-detection distance and cavity length should be supplied.