结合光学模拟的塑料闪烁体探测器能量刻度

Energy Calibration of Plastic Scintillator Detector Combined with Optical Simulation

由于高能γ射线全能峰的缺失,导致塑料闪烁体探测器难以进行能量刻度,为此本文提出了一种结合光学模拟的塑料闪烁体探测器能量刻度方法。使用GEANT4建立了塑料闪烁体探测器的光学模型,模拟了闪烁荧光在闪烁体内的传输、收集以及在光电倍增管上的光电转换和光电子倍增的过程,实现了对实验测量能谱的精确模拟。通过计算低能γ射线全能峰的位置刻度了模拟能谱,由此得到了实验测量能谱的康普顿峰位置。使用^(137)Cs和^(60)Co的康普顿峰完成了对塑料闪烁体探测器的能量刻度,二者的模拟能谱与实验能谱的康普顿峰能量分辨率的相对误差均小于1%,验证了蒙特卡罗模拟能谱与实验测量能谱的一致性,也证明了能量刻度结果是可靠的。

Plastic scintillator detectors are widely utilized in radiation measurement due to their unique characteristics such as fast decay time,low production cost,availability for large-scale production,and tissue equivalence.However,their limited photoelectric absorption cross-section and poor energy resolution make it challenging to accurately detectγ-ray photopeaks.The absence of high-energyγ-ray photopeaks poses a challenge in the energy calibration of plastic scintillator detectors,which is the foundation for radiation energy detection.Nevertheless,it is feasible to calibrate a plastic scintillator detector using the Compton peaks.Numerous studies on the plastic scintillator detector energy calibration based on the Monte Carlo method were reported,but most of them cannot directly simulate energy spectra or calculate the energy values of Compton peaks.An energy calibration method combined with optical simulation was proposed to overcome this obstacle in this paper.This method describes physical processes in plastic scintillator detectors more comprehensively than energy calibration methods based on the regular Monte Carlo simulation.Furthermore,it does not rely on empirical formulas to determine energy resolution.An optical model of the plastic scintillator detector built with GEANT410.7 was used to describe the scintillation properties of the plastic scintillator,the properties of optical surfaces,and the photoelectric conversion and photoelectron multiplication processes of the photomultiplier tube.Thus,this model could accurately simulate the energy deposition ofγ-rays,the transportation and collection of the scintillation light in the scintillator,as well as the photoelectric conversion process of the scintillation light and photoelectron multiplication process at the photomultiplier tube.These allow for an accurate simulation of the experimental energy spectrum.The simulated energy spectra were calibrated using the photopeaks of low-energyγ-rays.Since the simulated energy spectra are reasonable approximations of experimental energy spectra,the energy values of the Compton peaks in the experimental spectra are the same as Compton peaks in the calibrated simulated energy spectra.Two radiation sources of ^(137)Cs and ^(60)Co were used to calibrate the plastic scintillator detector in the experiment based on this method,and the energy calibration of the plastic scintillator detector was completed using Compton peaks of ^(137)Cs and ^(60)Co.The relative error of the Compton peak energy resolution for ^(137 )Cs between the simulated energy spectrum and the calibrated experimental energy spectrum is 0.70%.For ^(60 )Co,the value is 0.91%.Either value is less than 1%,which in turn verifies the agreement between simulated energy spectra and experimental energy spectra,and also demonstrates the reliability of the energy calibration result.