用蒙特卡罗方法模拟直接转换X射线探测器的响应特性

Use of Monte Carlo Method to Evaluate the Response of Direct Conversion X-Ray Detectors

采用Monte Carlo方法模拟了HgI_2、非晶Se和CdTe几种直接X射线转换探测器在医用X射线范围(10—100keV)的透过谱、背向散射谱、吸收效率和光电灵敏度.对X射线和HgI_2的作用过程模拟采用了EGSmc Monte Carlo代码系统,对信号电荷的产生考虑了电荷产生的高斯噪声和材料深陷阱作用造成的部分电荷收集影响.结果表明,载流子平均自由程(Schubweg)在相对于探测材料厚度较小时,陷阱作用能很大地影响探测灵敏度.HgI_2的灵敏度是非晶Se的5倍以上,CdTe的灵敏度是非晶Se的10倍以上,采用高Z序数材料可以大大提高探测灵敏度.

The response of three semiconductor materials, polycrystalline HgI2, amorphous Se and polycrystalline CdTe, used for large area direct conversion detectors, is simulated by Monte Carlo method for X-ray photons in the diagnostic energy range （10-100keV）. The simulation involves the transmission spectra, backscatting spectra, absorption efficiency and charge sensitivity. The interaction process between X-ray photons and the conversion materials is simulated by EGSnrc Monte Carlo code system and for the generation of signal charges Gaussian noise and the collection of partial charges are taken into account. The results show that deep traps in materials can affect largely detecting sensitivity when the mean free length （Schubweg） of carriers is less than the materials thickness. The sensitivity of HgI2 is 5 times higher than that of amorphous Se and CdTe is 10 times higher than amorphous Se, it can be seen that a high Z material can improve the detecting sensitivity greatly.