IHNI-1中子束快中子注量率测量

摘要

To validate and determine the contamination source term of fast neutrons produced by the first in-Hospital Neutron Irradiator (IHNI-1) for boron neutron capture therapy (BNCT),a boron-covered 235U fission chamber was designed to be used for the measurement of fast neutron fluence rate.The fluence response of the fission chamber was optimized according to the calculated fluence response curve of the fission chamber covered by the boron shells with different thicknesses with the MCNP code.Consequently,a 35 mm thick B4C shell was used to shield the low energy neutrons.The fast neutron fluence rate of the thermal and epithermal neutron beams was measured with the fission chamber and compared with the simulated values.The results showed that the fast neutron component in the actual neutron beams was more than that in the simulated ones,less than the target value recommended by IAEA.%为检验和确定用于硼中子俘获治疗(BNCT)的医院中子照射器(IHNI-1)的快中子污染源项,设计了用于快中子注量率测量的包硼235U裂变电离室.利用MCNP程序对电离室的注量响应进行优化设计,计算包裹不同厚度硼壳时电离室的注量响应曲线,最终选择35 mm厚B4C壳作为低能中子屏蔽层.利用该电离室测量IHNI-1热中子和超热中子束的快中子注量率,并与模拟计算值比较.结果显示,实测的中子束比模拟计算结果具有更多的快中子成分,低于国际原子能机构(IAEA)推荐的目标值.