Rare observation of atmospheric ~(65)Zn, ~(134)Cs and ~(137)Cs with possible relation to the 12 February 2013 test announced by North Korea

摘要

Abnormal particulate radionuclides (Zn-65, Cs-134 and Cs-137) were detected at the CTBTO RN58 station which is located near North Korea between 12 and March 14, 2016. Detection ratio for caesium (Cs-134/Cs-137) shows that the product origin was nuclear explosion and dilution factors at RN58, released from DPRK test site, show clear correlation with radioactivity concentration of two samples. The detected radionuclides may be originated from the third nuclear test, February 2013. Half-life, radionuclides fractionation, MDC, and device design are attributed to no detection of other nuclides. Most of radionuclides have been decayed away and relatively long half-life nuclides might be in the third test site but they were displaced deep inside the area by fractionation during the explosion. Considering Zn-65 activity ratio to Cs-137 which is higher than historical ratios at Brunswick in 1968, there is a possibility that the third DPRK nuclear test was a "salted" nuclear bomb test using zinc as jacket instead of fissionable U-238 around the secondary stage fusion fuel.