电子直线加速器机房中子辐射屏蔽估算与评价

Calculation and evaluation on the shielding of neutron irradiation in electron linear accelerator rooms

目的探讨基于"避免防护过度"和"辐射防护最优化"原则的屏蔽防护门2种设计方案下电子直线加速器机房中子辐射屏蔽估算方法,评价屏蔽效果。方法以25 Me V电子直线加速器机房为研究对象,依据美国辐射防护和测量委员会(NCRP)151号报告建议书(NCRP 151号报告)相关建议和要求,采用2种设计方案对屏蔽防护门进行辐射屏蔽,典型设计方案为在迷道入口处安装50 mm铅当量加12.00 cm的含硼聚乙烯(BPE)屏蔽防护门,优化设计方案为在迷道内增加10.00 cm的BPE屏蔽防护门和在迷道入口处安装8 mm铅当量屏蔽防护门,采用相应的公式和参数对2种设计方案的屏蔽效果进行估算和分析。结果采用典型设计方案和优化设计方案时,迷道入口M点处总的每周剂量当量分别为3 662.000和564.345μSv/周,屏蔽防护门外总的剂量当量率分别为1.820和0.391μSv/h,均小于2.500μSv/h。优化设计方案总的剂量当量率仅为典型设计方案的21.43%,无论从屏蔽效果还是从屏蔽用材方面均优于典型设计方案。结论采用优化设计方案在迷道入口内部安装BPE屏蔽防护门的屏蔽方案合理可行,可作为电子直线加速器机房中子辐射防护评价方法。

Objective To discuss the methods for calculating neutron irradiation dose with two designs on protective door of the electron linear accelerator room and evaluate their shielding effect,based on the principles of“Avoiding excessive protection”and“Optimization of protection”. Methods A 25 MeV electron linear accelerator was selected as the study object to assess the optimizing design and typical design of protective door,according to the recommendation and require-ment of NCRP Report No. 151 with the corresponding formulas and the actual parameters of the accelerator. The typical design was a protective door of 50 mm lead equivalent plus 12. 00 cm BPE at the entrance of maze. The optimizing design was 10. 00 cm BPE protective door in maze and 8 mm lead equivalent protective door at the entrance. The shielding effects of the two kinds of design schemes were analyzed and estimated by the corresponding formula and parameters. Results In the typical design,week dose equivalent of entrance（ M point ） and the total dose equivalent rate were 3 662. 000μSv/week and 1. 820 μSv/h,while in the optimizing design they were 564. 345μSv/week and 0. 391μSv/h respectively. The total dose equivalent rate in the optimizing design was only 21. 43% of the typical design. The optimizing design was better not only on the shielding effect but also on the shielding material. Conclusion The optimizing design of the protec-tive door is reasonable and feasible,which can be used as the method of neutron protection of electron linear accelerator rooms.