Rühm W, Kato K, Korschinek G, Morinaga H, Nolte E
Suzugamine Women's College, Hirosima, Japan.
Int J Radiat Biol. 1995 Jul;68(1):97-103. doi: 10.1080/09553009514550971.
In this paper measurements of the radionuclides of 36Cl, 41Ca, 60Co, 152Eu and 154Eu in samples from Hiroshima, which were exposed to neutrons of the A-bomb explosion, are interpreted. In order to calculate the neutron spectrum at the sample site, neutron transport calculations using Monte Carlo techniques were carried out. Activation profiles in a granite mock-up irradiated with reactor neutrons could be reproduced by this method using DS86 input parameters. The calculated neutron spectrum at the sample site for non-thermal neutrons is identical to that obtained in DS86, but contains some 50% more thermal neutrons. The influence of parameters like soil composition, source terms and air humidity on the activation of these radioisotopes is discussed. The granite-covered earth at the sample site, for example, hardens the spectrum in comparison with DS86 values. Even when using a fission spectrum pointing downward and neglecting air humidity one cannot explain our 36Cl measurements. If the effective thermal neutron fluences, that have a similar ratio of resonance integral to thermal neutron capture cross sections obtained from 36Cl, 41Ca and 152Eu, are averaged, a bomb yield of about 16 kt is deduced in agreement with a bomb yield of (15 +/- 3) kt estimated in DS86.
本文对广岛原子弹爆炸中子照射样本中36Cl、41Ca、60Co、152Eu和154Eu等放射性核素的测量结果进行了解释。为了计算样本位置的中子能谱，采用蒙特卡罗技术进行了中子输运计算。利用DS86输入参数，通过该方法可以重现反应堆中子照射的花岗岩模型中的活化分布。样本位置非热中子的计算能谱与DS86中获得的能谱相同，但热中子含量多出约50%。讨论了土壤成分、源项和空气湿度等参数对这些放射性同位素活化的影响。例如，与DS86值相比，样本位置覆盖花岗岩的地表使能谱变硬。即使使用向下指向的裂变能谱并忽略空气湿度，也无法解释我们对36Cl的测量结果。如果对具有从36Cl、41Ca和152Eu获得的类似共振积分与热中子俘获截面比值的有效热中子注量进行平均，推导出的炸弹当量约为16千吨，这与DS86中估计的(15±3)千吨炸弹当量一致。
