反应堆235U裂变源辐射防护材料的优化设计

以热中子反应堆²³⁵U裂变源为辐射源，利用MCNP程序对其能谱进行模拟并研究其辐射防护，结果表明对²³⁵U裂变源所发射的能量高于3MeV的瞬发中子，重金属具有良好的屏蔽效果，而对于能量低于1MeV的中子，轻氢材料的防护效果更好；W/LiH，W/B₄C，TiH₂/W三种复合材料当质量比满足：W：LiH=19：1，W：B₄C=9：1，W：TiH₂=3：1时材料的屏蔽效果最佳；通过遗传算法结合MCNP模拟，得到W/TiH₂/B₄C，TiH₂/Cu/Gd，TiH₂/B₄C/Gd三种复合材料的最优组分配比，源每次裂变产生的粒子穿过这三种材料后在等效组织中造成的剂量当量率（10^-11Sv·h^-1）与材料厚度呈指数下降关系，三种材料分别可近似为1.071exp（-0.187 8x），1.077exp（-0.166 2x）和1.608exp（-0.171 9x），x为材料厚度（cm）.

Optimization Design of Radiation Shielding Materials for 235U Fission Source in Reactor

With ²³⁵U fission source in thermal neutron reactor as radiation source, MCNP code is employed to simulate energy spectrum and to study shielding protect.It shows that for prompt neutron, emitting by ²³⁵U fission source, with energy more than 3 MeV, heavy metals materials have better shielding effect.However, light hydrogen materials performance better for neutrons with energy below 1MeV.For compounds-W/LiH, W/B₄C and TiH₂/W, shielding effect is best as weight ratios are W:LiH=19:1, W:B₄C=9:1, W:TiH₂=3:1.GA combined with MCNP code is employed to search optimized design of compounds, W/TiH₂/B₄C, TiH₂/Cu/Gd and TiH₂/B₄C/Gd, respectively.Weight fractions are calculated as shielding effect performance is best.Exponential decay relations between dose equivalent rate (10^-11Sv·h^-1) in tissues caused by neutron and gamma rays penetrating materials and thickness of materials can be expressed as 1.071exp (-0.187 8x), 1.077exp (-0.166 2x) and 1.608exp (-0.171 9x), respectively, where x is thickness of material in cm.