|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1995 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1994 : ¥1,800,000 (Direct Cost : ¥1,800,000)
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.