关键词: 
能量沉积 /
X射线 /
MCNP /
放射医

摘要: MCNP程序提供了计算光子沉积能的两种方法， 分别是F6和*F8。 当次级电子射程与网格尺度比较接近时， *F8的精度比F6高， 但计算效率比F6低很多。 分析比较了几种提高计算效率的技巧， 分别是： 网格大于10倍电子射程用F6； F6与*F8的联合使用； 改变电子能量子步数； 关掉δ电子； 次级电子自适应截断等。 数值模拟表明， F6与*F8的联合使用以及次级电子自适应截断这两种技巧对精度与效率兼顾得很好。 F6 and *F8 are two methods to calculate energy deposition of photon by MCNP program. If the dimension of grid is almost the same long as the range of secondary electron， the precision of *F8 is higher than that of F6， but the efficiency of F6 is greatly higher than that of *F8. This paper presents five techniques to increase the efficiency，namely: F6 is use to the model with grid dimension bigger than 10 ranges of secondary electron; combination of F6 and *F8; change the substeps of electron; turn off knock on electron; selfadaption cutoff secondary electron. The two techniques， combination of F6 and *F8，selfadaption cutoff secondary electron， can provide a good precision and efficiency.