508. 核爆発による放射性塵の測定および分析

Abstract

The radioactive airborne debris that reached the sky over Japan in the wake of the 7th Chinese nuclear test explosion of December 24, 1967 were collected with the use of an airborne dust sampler mounted on aircraft and subjected to gross β-activity measurement, γ-ray spectrometry and mass spectrometry. The concentration of radioactive debris in the air stood at about 18, 000pCi/m3 on December 25, from where it decreased gradually to reach a level below 1pCi/m3 on December 28, the level prevalent before the test explosion. Short-lived rodionuclides such as 239Np, 143Ce, 132l and 99Mo were clearly detected by γ-ray spectrometry, but the presence of 237U was not confirmed. The elementary composition of the debris collected shortly after the explosion was not substantially different from those collected at normal times. The content of lithium however, was about 120 times as high as the level before the test explosion. The isotopic abundance ratio of 6Li was 14.6%, about twice the natural isotopic abundance ratio.