Monthly Deposition of ¹³⁷Cs in the Period from 1964 through 1971 at Osaka, Japan

Abstract

Monthly deposition of ¹³⁷Cs at Osaka was measured in the period of 7 years from July 1964 through July 1971. Gamma-ray spectra of the samples collected monthly by the basin method were measured with a large volume Ge(Li) detector shielded with 20 cm iron in order to determine their ¹³⁷Cs activities. On close examination of the variation of monthly ¹³⁷Cs deposition, it is noted that, besides the seasonal variation of so-called “spring maximum”, there appeared many peaks, each of which can be assumed to have been caused by the influence of a nuclear explosion. Yearly ¹³⁷Cs depositions during the period were also estimated and compared with those measured by another institute.