Study on the evaluation of fast-neutron energy spectrum of the Hiroshima atomic bomb

在1986年剂量测定系统（DS 86）中给出了与距震源距离相关的中子能谱。迄今为止，除了早期的^ P测量外，还没有关于广岛原子弹快中子的实验结果报道<32>。对热中子俘获反应产生的几种核的详细分析表明，导出的广岛原子弹的中子谱比DS 86给出的谱硬得多。~（12）Eu和~（12）Co的测量<152><60>也表明，DS 86中子能谱存在系统误差。最近对<36>广岛、长崎和反应堆实验的^ Cl测量表明，广岛原子弹的中子源可能不同于DS 86中给出的中子源。在本工作中，<63><63>使用东北大学快中子实验室（FNL）的Dynamitron加速器测量了^ Cu（n，p）^ Ni的反应截面，这是评估中子能谱所必需的基本核数据。中子辐照后，<63>通过电解、阴离子交换和溶剂萃取等化学方法分离镍。用<63>液体闪烁计数法测定~（13）Ni。结果发现了激发函数中的精细结构，并从反应机理的角度探讨了其原因。此外，<63>通过相同的化学程序从广岛铜样品中提取了^ Ni。^<63>Ni计数仍在进行中。

The neutron spectra correlated to the distance from the hypocenter are given in the Dosimetry System 1986 (DS86). So far no experimental results for the fast neutrons have been reported for the Hiroshima atomic bomb except for the early measurement of ^<32>P.The detailed analysis of several nuclei produced by the thermal-neutron capture reaction suggests that the derived neutron spectrum for the Hiroshima atomic bomb is much harder than the spectrum given in DS86. The measurement of ^<152>Eu and ^<60>Co also suggests that systematic errors exist in the DS86 neutron spectrum. The recent measurements of ^<36>Cl for Hiroshima, Nagasaki and the reactor experiment have shown that the source neutrons for the Hiroshima atomic bomb could be different from the one given in DS86. Thus the direct measurement of the fast neutrons for the Hiroshima atomic bomb is particularly desirable.In the present work, the reaction cross sections for ^<63>Cu(n, p)^<63>Ni were measured using the Dynamitron accelerator at the Fast Neutron Laboratory (FNL) of Tohoku University, which is indispensable as a basic nuclear data for the evaluation of neutron energy spectrum. After neutron irradiation, the ^<63>Ni was chemically separated by electrolysis, anion exchange and solvent extraction. The ^<63>Ni was determined by liquid scintillation counting. As a result, the fine structure in the excitation function was found, whose cause is investigated in the relation to the reaction mechanism. Also, ^<63>Ni was extracted from the Hiroshima copper samples by the same chemical procedure. The ^<63>Ni counting is still under way.