Neutron activation analysis of deposition samples in Tokai-mura, Japan and evaluation of resuspension of 137Cs

The present study assessed the effect of Cs-137 resuspention in deposition samples. Deposition samples were collected monthly in a basin; and soil samples were collected at 5 points in Tokai-mura. Cs-137 was measured using γ spectrometry. Stable elements were measured quantitatively by neutron activation analysis. Annual variations from 1984 through 1990 for the total weight of stable element depositions revealed two patterns: (1) the pattern of Na, Cl and Br depositions and (2) the pattern of Al, Sc, V, Mn, Fe, Co (except for the peak in 1989), Cs, La and Eu depositions. This seemed to attribute to the prevailing wind in Tokai-mura. Seasonal variations for the percentage of reposited Cs-137 to the total Cs-137 in depositions revealed the peak during winter when the quantity of stable cesium depositions was large and that of Cs-137 was small. The percentage of reposited Cs-137 was low in the 1970s when nuclear tests were frequently performed and became gradually higher from the 1980s when nuclear tests in the atmosphere were banned. (N.K.)