Re-construction and updating our understanding on the global weapons tests 137Cs fallout

Abstract

Global nuclear weapons tests fallout of ¹³⁷Cs in the northern hemisphere has been documented in the UNSCEAR (United Nations Scientific Committee on the Effect of Atomic Radiation) reports. However, many questions have arisen during the past three to four decades; e.g. the water column inventory of ¹³⁷Cs in the North Pacific Ocean was two to three time higher than the cumulative decay corrected fallout at the same latitude as stated in the UNSCEAR reports. Here we show more precise spatial distribution of global ¹³⁷Cs fallout primarily on the basis of global measurements in rain, seawater and soil, as data from 10° × 10° grids. A typical feature of geographical distribution is that two high global ¹³⁷Cs fallout areas exist in the northern hemisphere, where the highest ¹³⁷Cs fallout was observed in the globe. These areas correspond to crossovers of areas where larger precipitation amounts were expected and where higher stratosphere–troposphere exchange was expected. Our new estimate of 765 ± 79 PBq as global ¹³⁷Cs fallout for the northern hemisphere is 1.4 times higher than that of 545 PBq in the UNSCEAR reports.