基于Benjamin结构的球形组织等效正比计数器气体放大倍数的模拟与实验研究

Simulation and experimental study of the gas gain in Benjamin type tissue equivalent proportional counter

充分了解气体放大倍数特性对正比计数器的设计和使用非常重要。球形组织等效正比计数器(Tissue Equivalent Proportional Counter,TEPC)在辐射防护领域具有广泛应用,有必要对TEPC气体放大倍数进行分析,以指导探测器的设计和运行。本文设计了Benjamin结构的TEPC,采用有限元法分析该球形TEPC内的电场分布,验证了Benjamin结构TEPC具有均匀的电场分布和气体放大倍数分布。利用Garfield程序和ANSYS软件模拟计算了一定工作条件下TEPC的绝对气体放大倍数。使用Benjamin结构的球形TEPC和内置241Amα源进行了放大倍数实验测量并与模拟进行了对比。结果表明,Garfield程序和ANSYS相结合模拟计算的TEPC绝对气体放大倍数结果与实验测量结果符合较好,可用于TEPC探测器气体放大倍数计算,为探测器的设计和运行提供参考。

Background： A good knowledge of gas gain properties is of importance for the development and operation of proportional counters. Spherical tissue equivalent proportional counters （TEPC） have been widely used in the protection dosimetry applications, thus it is necessary to investigate the gas gain characterization in TEPC detectors. Because of the extremely low pressure, gas gain in the TEPC is significantly influenced by the gradient of the electric field around the anode wire. Gradient-field model was proved to be accurate enough to predict the gas gain in the TEPC. However, the formula based on the gradient-field model comprises three gas dependent constants which make it impractical for TEPC design and applications. Purpose： This work aims to develop a technical routine for the simulation of the TEPC gas gain and implement validations of the simulated results. Methods： In this work, a Benjamin type TEPC was firstly developed, then ANSYS was employed to solve the electric field strength in the detector. Garfield was used to simulate the gas gain properties in the Benjamin type TEPC with different bias voltage. At last, an internal 241Amα source was adopted to measure the absolute gas amplification factor in the TEPC. Results： It is found that, Benjamin type TEPC has a uniform electric field intensity distribution along the anode wire, which could be employed in TEPC design. Garfield simulated results agreed well with the experimental values. The deviation between the measured and simulated values increases with the applied bias of the detector. Conclusion： Given the fact that the TEPC was usually operated with gas gain to be about 40, the Garfield simulation method could be used as reference in the TEPC development and operation.