Deposition of90Sr and plutonium isotopes derived from the Chernobyl accident in Japan

Abstract

To clarify environmental effects of the Chemobyl radionuclides, long-lived Chernobyl radioactivity (239,240Pu,238Pu,241Pu and90Sr) in deposition samples in May 1986 was measured at 11 stations in Japan. Temporal variation of weekly deposition of90Sr differed from that of volatile radionuclides such as131I and137Cs, which may reflect the released process at Chernobyl. On the other hand, the geographical distributions of the monthly deposition of long-lived radionuclides were similar to those of volatile radionuclides, in which maximum deposits of90Sr and plutonium were observed in Akita, a northwestern Japan Sea coast site of Honshu Island. Higher241Pu deposition in most of the stations, as well as high238Pu/239,240Pu activity ratios were observed. The241Pu/238Pu activity ratios in deposition samples were nearly equal to that in the total release, which is clear evidence that Chernobyl-derived plutonium was transported to Japan in May 1986 together with volatile radionuclides although the contribution of Chernobyl Pu was about three orders of magnitude lower than137Cs.