中低能质子束作用下闪烁体的荧光点扩散函数研究

在质子照相中，携带客体信息的质子束通过闪烁体的荧光效应转化可见光，使用光学记录系统接收并转化为数字信号。故闪烁体上可见光分布图像直接对应于客体的面密度分布。闪烁体的点扩散性质反映点状质子束打到闪烁体上的荧光特性，因而荧光点扩散函数直接影响了成像质量，且知悉荧光点扩散函数特性是获得高质量图像反演的关键因素。导致质子在闪烁体内发生荧光点扩散是由于：1.质子在物质中经历多次库仑散射，2.是二次电子光子的传输与质子入射方向不同导致的。本课题是研究中低能质子束在闪烁体中的传输过程和荧光激发行为，使用Geant4程序进行仿真模拟，获得有限大小的质子束在闪烁体上的荧光点扩散特征。利用现有的低能质子加速器资源开展实验测量点型质子束的荧光点扩散特性工作，校验模拟的结果可靠性。

In proton Radiography, the proton beam, carrying the information of testing objects, is converted to the visible light via the scintillator, and the optical photon is collected and converted to the digital signals by the optical recording system. The distribution of the optical photon on scintillator is directly corresponding to the areal density of the object. The point spread function of the scintillator is the scintillating characteristic for a point-type proton beam, and it affects the quality of the image. To obtain the function is the key factor for the top-quality images inversion. When proton is penetrating through an object, there are two reasons to make the point spread happen, 1.proton undergo multi Coulomb Scattering, 2.the secondary electrons and secondary photons disperses. In this task, we use the Geant4 programs package to simulate the transition behavior and the scintillating characteristic of the lower energy proton beam, to obtain the scintillating character of the finite diameter proton beam. And using the existing proton accelerator, we prepare to launch the experiments to measure the scintillator's point spread function for the point type lower energy proton beam, to validate the simulating results.