No abstract

The exposure of the population of Utah to external gamma-radiation from the fallout from nuclear weapons tests carried out between 1951 and 1958 at the Nevada Test Site has been reconstructed from recent measurements of residual cesium-137 and plutonium in soil. Although the highest exposures were found in the extreme southwest part of Utah, as expected, the residents of the populous northern valleys around Provo, Salt Lake City, and Ogden received a higher mean dose and a significantly greater population dose (person-rads) than did the residents of most counties closer to the test site. However, population doses from external exposure throughout Utah were far too low to result in any statistically observable health effects.

Mass spectrometric analyses of soil samples collected around Denver, GO permit the identification of plutonium contamination from the Rocky Flats plant as low as 0.2 mCi/km2 which represents 10% of global fallout. The areal extent of the plutonium contamination followed an inverse power function of the soil concentration. Integrating this equation indicates that 3.4 f 0.9 Ci of 2se-2aoPu from Rocky Flats were deposited on public and private land.

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The stratospheric inventory of the plutonium-238 resulting from the disintegration of a nuclear auxiliary power generator (SNAP-9A) in early 1966 accounts for essentially all the plutonium present in the original generator that reentered the atmosphere. Consequently, the pyrophoric (238)Pu must have completely burned up during reentry and ablated into small particles. The arithmetic mean of the distribution of the (238)Pu particle size was estimated to be 10 millimicrons, which confirms this conclusion.