Fission product radioactivity in the air along the 80th meridian (west) during 1959

Abstract

The program of measurement of the fission product concentration in the air at ground level at sites along the 80th meridian was continued during 1959. During this period no fresh nuclear debris was added to the atmosphere, with the result that seasonal changes in deposition rates from stratospheric sources were more apparent. The radioactivity levels in the northern hemisphere reached the highest average during the operation of this network (started May 1956) in the spring of 1959. Radiochemical analyses indicated that the bulk of this debris was introduced into the stratosphere during the October 1958 series of high-yield nuclear tests held in the arctic region of the Soviet Union. Evidence has been obtained of a definite seasonal dependence for stratospheric deposition, with debris in the arctic stratosphere being more strongly influenced than that in the tropic stratosphere. No such definite conclusions can be made from radioactivity collected in the southern hemisphere. Evidence is presented that mixing of the stratospheric sources in the northern hemisphere was not complete by the end of 1959; and though radioactivity levels in the two hemispheres were approaching unity in late 1959, the isotopic composition of the collections indicated that the average age of the debris in the southern hemisphere was much greater.