Endo S, Stevens D L, Bonner P, Hill M A, Nikjoo H, Dalla Vecchia M, Komatsu K, Hoshi M, Goodhead D T
Research Institute for Radiation Biology and Medicine, Hiroshima University, Japan.
Phys Med Biol. 1999 May;44(5):1207-18. doi: 10.1088/0031-9155/44/5/009.
Gamma-rays contribute 33% of the absorbed dose from an unfiltered 252Cf fission neutron source. To reduce this gamma-ray component and to enable radiobiological experiments at as high a dose rate as possible, Monte Carlo calculations for several filter materials (Al, Fe, Pb and concrete) have been made using MCNP neutron and photon transport code version 4a. A lead filter of thickness 4 cm was found to reduce the gamma-ray component to 6.7% of the total dose whilst reducing the neutron dose by only about 10%. Such a filter was installed at the MRC 252Cf neutron irradiation facility and dosimetric measurements were made using a TE-TE chamber and a 7LiF(Mg, Cu, P) TLD. Monte Carlo simulations agree with experimental measurements of neutron and gamma-ray doses within 6%. V79-4 Chinese hamster cells were irradiated with lead-filtered and unfiltered neutrons and also with 60Co gamma-rays at two dose rates. The survival fraction obtained for each radiation was consistent with the reduced gamma-ray dose. The relative biological effectiveness for neutrons alone, corrected for gamma-ray effects, was found to be 9.2 +/- 3.4 from the initial slopes and 3.1 +/- 0.5 at 10% survival, both relative to the acute gamma-rays.
伽马射线在未加过滤的²⁵²Cf裂变中子源产生的吸收剂量中占33%。为了减少这种伽马射线成分，并尽可能在高剂量率下进行放射生物学实验，使用MCNP中子和光子输运代码版本4a对几种过滤材料（铝、铁、铅和混凝土）进行了蒙特卡罗计算。发现厚度为4厘米的铅滤器可将伽马射线成分降低至总剂量的6.7%，同时仅使中子剂量降低约10%。这样一个滤器安装在了医学研究委员会的²⁵²Cf中子辐照设施中，并使用TE-TE室和⁷LiF（Mg，Cu，P）热释光剂量计进行了剂量测量。蒙特卡罗模拟与中子和伽马射线剂量的实验测量结果在6%的误差范围内相符。V79-4中国仓鼠细胞分别用经过铅滤器过滤和未经过滤的中子以及在两种剂量率下的⁶⁰Co伽马射线进行辐照。每种辐射获得的存活分数与降低后的伽马射线剂量一致。经伽马射线效应校正后，仅中子的相对生物效能从初始斜率来看为9.2±3.4，在10%存活时为3.1±0.5，两者均相对于急性伽马射线。
