Tungsten-185 in Precipitation and the Seasonal Variations in Fall-out

Abstract

THE introduction of tungsten during the U.S. ‘Hardtack’ nuclear test series in 1958 provided a unique opportunity of identifying nuclear debris of known origin. From June 1958 until August 1959, tungsten-185 (half-life, 74 days), the tungsten isotope of most interest, was detected in precipitation occurring at Westwood, New Jersey and other stations¹. Data on both tungsten-185 and strontium-90, and other short-lived isotopes such as barium-140 and strontium-89, in rain-water cast light on the mechanism of stratospheric fall-out, and if suitable corrections for radioactive decay of the short-lived isotopes are made the fraction of debris from ‘Hardtack’ tests may be estimated. An initial activity ratio tungsten-185/strontium-90 of 500 on July 15, 1958, as suggested by Lockhart et al. ², has been used in this work.