Isolation of long-lived radioisotope produced by HIroshima atomic bomb

对以往的残余放射性测量进行了精确的回顾。在地面射程超过1公里的样品中，测量和计算的同位素比值之间的差异很大。对加速器质谱仪(AMS)研究中使用的氯离子分离方法进行了改进，使之适用于分离岩石样品中的氯离子，而不需要用海盐稀释。对于超过1千米的岩石样品中的氯/氯的AMS是有用的。在获得超过1千米的岩石样品后，将进行隔离。混凝土样品的氯含量超过100ppm。用每lg样品8毫升的纯水洗涤粉状样品两次，以排除雨水中的氯离子。然而，混凝土中的AgCl样品中含有其他元素。排除该元素的工作正在进行中。超过1千米GR的瓷砖中氯含量低于20ppm，因此对氯化物样品进行AMS实验是困难的。用于^&lt；41&gt；CaAM的钙样品也是从射程超过1公里的混凝土和瓷砖中生产出来的。钙样品的测量要求提高^&lt；41&gt；钙原子吸收光谱仪的检测效率。从1公斤混凝土中分离出Eu也在进行中，以确定^&lt；152；EU/EU。初步研究表明，常规的NaI(Tl)探测器可用于测量没有天然放射性同位素的孤立Eu样品中的~&lt；152&GT；Eu伽马射线。正如我们以前的调查所显示的那样，中子注量将通过测量同位素比率和蒙特卡罗计算来评估。*)&gt；^*Ruhm，W.，Kato，K.，Korschinek，G.，Morinaga，H.，Nolte，E.(1995)从一个地点的放射性核素测量推算出广岛原子弹的中子谱和当量。国际放射生物学杂志，68，97-103。

The previous measurements of residual radioactivity were precisely reviewed. The discrepancies between measured and calculated isotope ratios are significant in samples beyond 1 km ground range (GR). The chloride isolation method used for our previous investigations of accelarator mass spectrometry (ams) has been improved, and is available for isolating chloride ions from rock sample without dilution by sea salt. It will be useful for the ams of ^<36>Cl/Cl in rock samples beyond 1 km GR.The isolations will be performed after obtaining rock samples beyond 1 km GR.Concrete samples contained chlorine more than 100 ppm. The chloride ions from rain water were excluded by washing the powdered sample by pure water of 8 ml per lg sample, twice. The AgCl samples from concrete, however contains other element. The exclusion of the element is in progerss. Tiles beyond 1 km GR contained chlorine less than 20 ppm, and hence the ams experiment for the chloride sample is difficult. Calcium samples for ^<41>Ca ams were also produced from concrete and tiles beyond 1 km range. The measurements of the calcium samples require increase of the detection efficiency in ^<41>Ca ams. Europium isolation from a 1 kg concrete is also in progress for determining ^<152>Eu/Eu. A preliminary study revealed that a conventional NaI (Tl) detector was useful for measurements of ^<152>Eu gamma rays from the isolated europium samples without natural radio isotope. The neutron fluences will be evaluated by the measurements of isotope ratios and Monte Carlo calculations, as shown in our previous investigation. ^<*)>^*Ruhm, W., Kato, K., Korschinek, G., Morinaga, H., Nolte, E.(1995) Neutron spectrum and yield of the Hiroshima A-bomb deduced from radionuclide measurements at one location. International Journal of Radiation Biology, 68,97-103.