质子照相中基于能量损失的密度重建

Density reconstruction based on energy loss in proton radiography

提出了一种质子能量在中高能时利用能量损失进行密度重建的方法,并利用Bethe-Bolch公式给出了利用能量损失进行密度重建的方程及条件.针对1.6 GeV的质子能量,通过定量计算常见材料的阻止本领,得出质子能量在1.45-1.6 GeV范围内时,材料的阻止本领的变化率小于1%,可近似为常数.最后,通过理论计算和Geant 4模拟,得出质子能量在1.6 GeV时,可以对面密度为113 g/cm^2的缩比法国实验客体进行密度重建.

A method of using energy loss to reconstruct the density is presented with protons at intermediate and high energy for proton radiography, and the equation and condition of density reconstruction are given based on the Bethe-Bolch formula. For the intermediate and high energy proton radiography, the stopping power of material is changed slowly within a certain energy range, and the stopping power can be approximated as a constant, then the multi-material object can be reconstructed by using the energy loss information. In this work, the protons at 1.6 GeV which can be obtained by China Spallation Neutron Source are used in the radiography, and the energy loss information is used in the reconstruction, and the Geant 4 is applied to Monte Carlo simulation. From the theoretical calculation and the Geant4 simulation, it can be seen that when the protons energy ranges from 1.45 GeV to 1.6 GeV the stopping power of material can be approximately constant, and the relative change of material stopping power is less than 1%, thus the stopping power of material is only dependent on the incident proton energy, and the density of the multimaterial object can be reconstructed by the energy loss information. The proton scanning imaging system which can avoid blurring image caused by multiple coulomb scattering at the receiving plane is used in the proton radiography to obtain the energy loss information. In the imaging system, two energy detectors are employed to record the incident energy and exit energy of protons, the object is scanned by the protons with a certain step length, and the object is rotated 180° or 360°. The energy loss distribution of the object can be obtained by the scanning imaging system, and the density of the object can be reconstructed by solving corresponding equations. The Geant 4 is used to simulate the proton scanning imaging system. In the simulation, the object is the scaling french test object（FTC） that the areal density is 113 g/cm2, the protons are monoenergetic at 1.6 GeV, the scanning interval is 0.5 mm, and the rotation angle is 0.9. The results of the density reconstruction of the scaling FTO are in good agreement with the true values.