Beam Quality Determination of Ultra High Energy Neutrons

由于在筑波大学帕姆斯建造了超高能中子设施，以产生在剂量分布方面优于现代直线加速器产生的X射线束的中子束。这是利用高能物理实验室助推同步加速器500 MeV质子束轰击厚铀靶的反应实现的。在20 mV左右，剂量率为每分钟15cGy时，该中子束的深度剂量百分比与X射线相当。用HMV-I细胞系评价了该中子束的相对生物学效应。经中子照射后的细胞存活曲线为肩峰，n=8，dq=2.3Gy.目前的中子在10^2存活水平时的RBE值为1.24，与^&lt；137&gt；Cs伽马射线相比。结果表明，当中子的深度剂量分布优于高能直线加速器X射线时，高能中子的生物效应实际上还不够大。

As ultra high energy neutron facility was constructed at PARMS, University of Tsukuba, to produce a neutron beam superior to an X ray beam generated by a modern linac in terms of dose distribution. This has been achieved using the reaction on a thick uranium target struck by 500 MeV proton beam from the booster-synchrotron of High Energy Physics Laboratory. The percent depth dose of this neutron beam is nearly equivalent to that of X-rays at around 20 MV and the dose rate of 15cGy per minute. Relative biological effectiveness of this neutron beam has been estimated on the cell killing effect by the use of HMV-I cell line. Resultant survival curve of cells after the neutron irradiation shows the shoulder with n and Dq of 8 and 2.3 Gy, respectively. RBE value at 10 ^2 survival level for the present neutron, compared with ^<137> Cs gamma -rays is 1.24. The result suggests that the biological effects of high energy neutrons are not practically large enough whenever the depth dose distri bution of neutrons becomes superior to high energy linac X-rays.