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用γ射线全吸收型装置(Gamma-ray Total Absorption Facility,GTAF),可以对中子俘获反应截面进行高精度测量。为了降低实验本底,实验中需要对源中子进行准直和屏蔽,还要对被样品散射的中子进行吸收以减少它们进入探测器后所形成的干扰。采用MCNP对中子的准直器、屏蔽体和中子吸收体进行了模拟设计,中子准直屏蔽体材料选用含硼聚乙烯(BC4的质量分数为3%)和铅。准直孔直径为13 mm,长度为500mm,经准直后样品处中子束斑坪顶直径为21 mm。中子吸收体材料选用聚乙烯和碳化硼,吸收体球壳内腔半径30 mm,聚乙烯壳层厚度60 mm,碳化硼壳层厚度10 mm,被样品散射的中子经吸收体后衰减93.7%。
The Gamma-Ray Total Absorption Facility (GTAF) allows highly accurate neutron capture cross-section measurements. In order to reduce the experimental background, the experiments need to collimate and shield the source neutrons, and also absorb the neutron scattered by the sample to reduce the interference caused by them entering the detector. The neutron collimator, shield and neutron absorber were simulated by MCNP. The material of neutron collimation shield was boron-containing polyethylene (BC4 mass fraction 3%) and lead. The collimation hole has a diameter of 13 mm and a length of 500 mm. The diameter of the neutron beam spot at the collimated sample is 21 mm. Polyethylene and boron carbide were used as the material of the neutron absorber. The cavity radius of the absorber spherical shell was 30 mm. The thickness of the polyethylene shell was 60 mm. The thickness of the boron carbide shell was 10 mm. The scattered neutron was attenuated by the absorber by 93.7 %.