用蒙特卡罗“测量”离散程序中的参数

为了快速、精确地计算高能X射线照相中的散射光子分布，提出了将该过程中的粒子输运问题近似为一个有效的纯光子输运问题。针对该纯光子输运方程提出了一种适合于计算机计算的逐级迭代求解公式，并将该公式进行了离散化，然后编写成了计算机离散程序。用蒙特卡罗程序MCNP模拟得到了该程序所需要的参数和分布函数。最后用MCNP对该程序进行了检验。对于薄客体离散程序的计算结果与MCNP符合较好，但对于厚客体二者有较大偏离。目前可以把该程序应用于一些定性的计算分析。

“Measure” the parameters in the discretization-method using MC simulation

A new method is studied to simulate the scattered photons in high energy X-ray radiography fast and precisely. Firstly, the problem of X-ray radiography is turned into an effective pure photon transport problem, and an iterative solution to the photon transport equation is designed. Then, the solution is turned into a discrete version and realized in a computer program. After, the Monte Carlo N-particle transport code MCNP is used to “measure” the effective photon→photon scattering function and other parameters needed in our discrete method. Finally, the new computer program is compared with the MCNP in a radiography example as a check of our method. It is consistent with MCNP for the radiography of thin objects, but shows certain deviation for thick ones. The current computer program can be used in qualitative analysis.