采用蒙特卡罗程序(Monte Carlo neutron and photo transport code, MCNP)对医院中子照射器I型堆（IHNI-1）超热中子束流孔道的慢化层、反射层进行了优化设计。首先对FLUENTAL、Al等材料组成的6种慢化体方案进行了分析比较，给出了孔道出口处超热中子通量密度较大的两种设计方案；基于此两种慢化体设计方案，在保持束流孔道外框尺寸不变情况下，对慢化体周围的反射层进行了分析比较，给出了反射层的推荐方案；基于慢化体和反射层优化方案，最后给出了超热中子束流孔道出口处束流参数的空间分布。

Optimization design for the moderation layer and reflection layer of the epithermal neutron duct at in-hospital neutron irradiator mark 1(IHNI-1) reactor is carried out by using MCNP in this paper. Firstly, six moderator schemes combined with FLUENTAL are compared with Al materials, and two moderation optimization schemes which can obtain intensive epithermal neutron flux density at exit of this duct are chosen. Secondly, based on these two moderation schemes, the optimization design for reflectors around the moderator is introduced, and the recommended reflector schemes are given. Finally, based on the moderation layer and reflection layer optimization schemes, the neutron and gamma space distribution of the epithermal neutron beam at exit of this duct are detailed calculated.