Perez-Nunez Delia, Braby Leslie A
Department of Nuclear Engineering, Texas A&M University, 3133 TAMU, College Station, TX 77843-3133, USA.
Health Phys. 2010 Jan;98(1):37-41. doi: 10.1097/HP.0b013e3181b8d032.
Neutrons produced from the interaction between galactic cosmic rays and spacecraft materials are responsible for a very important portion of the dose received by astronauts. The neutron energy spectrum depends on the incident charged particle spectrum and the scattering environment but generally extends to beyond 100 MeV. Tissue-equivalent proportional counters (TEPC) are used to measure the dose during the space mission, but their weight and size are very important factors for their design and construction. To achieve ideal neutron dosimetry, the wall thickness should be at least the range of a proton having the maximum energy of the neutrons to be monitored. This proton range is 0.1 cm for 10 MeV neutrons and 7.6 cm for 100 MeV neutrons. A 7.6 cm wall thickness TEPC would provide charged particle equilibrium (CPE) for neutrons up to 100 MeV, but for space applications it would not be reasonable in terms of weight and size. In order to estimate the errors in measured dose due to absence of CPE, MCNPX simulations of energy deposited by 10 MeV and 100 MeV neutrons in sites with wall thickness between 0.1 cm and 8.5 cm were performed. The results for 100 MeV neutrons show that energy deposition per incident neutron approaches a plateau as the wall thickness approaches 7.6 cm. For the 10 MeV neutrons, energy deposition per incident neutron decreases as the wall thickness increases above 0.1 cm due to attenuation.
银河系宇宙射线与航天器材料相互作用产生的中子，是宇航员所接受剂量中非常重要的一部分。中子能谱取决于入射带电粒子能谱和散射环境，但一般会延伸到100 MeV以上。组织等效正比计数器（TEPC）用于在太空任务期间测量剂量，但其重量和尺寸是其设计和制造的非常重要的因素。为了实现理想的中子剂量测定，壁厚应至少为要监测的中子最大能量的质子的射程。对于10 MeV中子，该质子射程为0.1 cm，对于100 MeV中子为7.6 cm。壁厚为7.6 cm的TEPC将为能量高达100 MeV的中子提供带电粒子平衡（CPE），但对于太空应用而言，就重量和尺寸来说是不合理的。为了估计由于缺乏CPE而导致的测量剂量误差，对能量为10 MeV和100 MeV的中子在壁厚介于0.1 cm和8.5 cm之间的位置沉积的能量进行了MCNPX模拟。100 MeV中子的结果表明，随着壁厚接近7.6 cm，每个入射中子的能量沉积接近一个平稳状态。对于10 MeV中子，由于衰减，当壁厚增加到0.1 cm以上时，每个入射中子的能量沉积会减少。
