Japan Atomic Energy Agency, Tokai, Naka, Ibaraki, 319-1195 Japan.
Health Phys. 2010 Apr;98(4):591-6. doi: 10.1097/HP.0b013e3181c80ea9.
It has been sometimes necessary for personnel to work in areas where low-energy heavy ions interact with targets or with beam transport equipment and thereby produce significant levels of radiation. Methods to predict doses and to assist shielding design are desirable. The Particle and Heavy Ion Transport code System (PHITS) has been typically used to predict radiation levels around high-energy (above 100 MeV amu(-1)) heavy ion accelerator facilities. However, predictions by PHITS of radiation levels around low-energy (around 10 MeV amu(-1)) heavy ion facilities to our knowledge have not yet been investigated. The influence of the "switching time" in PHITS calculations of low-energy heavy ion reactions, defined as the time when the JAERI Quantum Molecular Dynamics model (JQMD) calculation stops and the Generalized Evaporation Model (GEM) calculation begins, was studied using neutron energy spectra from 6.25 MeV amu(-1) and 10 MeV amu(-1) (12)C ions and 10 MeV amu(-1) (16)O ions incident on a copper target. Using a value of 100 fm c(-1) for the switching time, calculated neutron energy spectra obtained agree well with the experimental data. PHITS was then used with the switching time of 100 fm c(-1) to simulate an experimental study by Ohnesorge et al. by calculating neutron dose equivalent rates produced by 3 MeV amu(-1) to 16 MeV amu(-1) (12)C, (14)N, (16)O, and (20)Ne beams incident on iron, nickel and copper targets. The calculated neutron dose equivalent rates agree very well with the data and follow a general pattern which appears to be insensitive to the heavy ion species but is sensitive to the target material.
有时需要工作人员在低能重离子与靶或束流传输设备相互作用从而产生大量辐射的区域工作。需要有预测剂量和协助屏蔽设计的方法。粒子与重离子输运代码系统（PHITS）通常用于预测高能（超过 100 MeV amu(-1))重离子加速器设施周围的辐射水平。然而，据我们所知，PHITS 尚未对低能（约 10 MeV amu(-1))重离子设施周围的辐射水平进行预测。研究了 PHITS 计算低能重离子反应中“切换时间”的影响，切换时间定义为 JAERI 量子分子动力学模型（JQMD）计算停止和广义蒸发模型（GEM）计算开始的时间。使用 6.25 MeV amu(-1)和 10 MeV amu(-1)（12)C 离子以及 10 MeV amu(-1)（16)O 离子入射到铜靶的中子能谱研究了这一影响。使用切换时间为 100 fm c(-1)，计算得到的中子能谱与实验数据吻合较好。然后，使用切换时间为 100 fm c(-1)，PHITS 模拟了 Ohnesorge 等人的实验研究，计算了 3 MeV amu(-1)至 16 MeV amu(-1)（12)C、（14)N、（16)O 和（20)Ne 束入射到铁、镍和铜靶时产生的中子剂量当量率。计算得到的中子剂量当量率与数据非常吻合，遵循一种似乎对重离子种类不敏感但对靶材料敏感的一般模式。
