屏蔽材料γ射线积累因子的MCNP模拟

MCNP simulation for gamma-ray buildup factors of shielding material

在γ射线的屏蔽设计中,选择合适的积累因子对屏蔽效果至关重要。目前,在设计屏蔽材料时,使用单层材料时考虑了轫致辐射的影响,而使用复合材料时并没有考虑。为了提高屏蔽厚度计算的准确性,在考虑轫致辐射的情况下,采用蒙特卡罗(Monte Carlo)方法对单层材料、多层组合材料的积累因子进行研究,模拟了不同γ射线能量和不同屏蔽材料厚度时的积累因子,同时对有无轫致辐射时积累因子的差别进行了对比。结果表明:对于单层材料和组合材料,轫致辐射对积累因子的贡献在低能和薄屏蔽厚度时较低,在高能和高屏蔽厚度时比较明显;积累因子随γ射线能量的增加呈现出下降的趋势,随着屏蔽厚度的增加呈现出增加的趋势。为实际情况中高能γ射线的屏蔽设计提供了积累因子的参考值以及计算方法。

[Background]In the shielding design ofγ-ray,it is very important to select the appropriate buildup factor for the shielding effect.As far as the current data are concerned,when designing the shielding material,the effect of bremsstrahlung is considered for the single-layer materials,but not for composite materials.[Purpose]This study aims to improve the accuracy of the shielding thickness calculation with the consideration ofγ-ray buildup factors by simulation.[Methods]The Monte Carlo method was used to simulate the buildup factors in differentγ-ray energies and different shielding material thickness.Buildup factors of single-layer materials and multilayer composite materials were calculated with the consideration of bremsstrahlung and compared with those without bremsstrahlung.[Results]Simulation results show that the contribution of bremsstrahlung to the buildup factor is lower at low energies and thin shielding thicknesses for single-layer materials and composite materials,but it is more obvious at high energies and high shielding thicknesses.The buildup factors show a decreasing trend with the increase ofγ-ray energy,and show an increasing trend with the increase of shielding thickness.[Conclusions]This study provides a reference and calculation method for the buildup factor for shielding design of high-energyγ-ray in actual situations.