Measurements of Argon-39 at the U20az underground nuclear explosion site

Publication date: November 2017
Source:Journal of Environmental Radioactivity, Volumes 178–179
Author(s): J.I. McIntyre, C.E. Aalseth, T.R. Alexander, H.O. Back, B.J. Bellgraph, T.W. Bowyer, V. Chipman, M.W. Cooper, A.R. Day, S. Drellack, M.P. Foxe, B.G. Fritz, J.C. Hayes, P. Humble, M.E. Keillor, R.R. Kirkham, E.J. Krogstad, J.D. Lowrey, E.K. Mace, M.F. Mayer, B.D. Milbrath, A. Misner, S.M. Morley, M.E. Panisko, K.B. Olsen, M.D. Ripplinger, A. Seifert, R. Suarez
Pacific Northwest National Laboratory reports on the detection of ³⁹Ar at the location of an underground nuclear explosion on the Nevada Nuclear Security Site. The presence of ³⁹Ar was not anticipated at the outset of the experimental campaign but results from this work demonstrated that it is present, along with ³⁷Ar and ⁸⁵Kr in the subsurface at the site of an underground nuclear explosion. Our analysis showed that by using state-of-the-art technology optimized for radioargon measurements, it was difficult to distinguish ³⁹Ar from the fission product ⁸⁵Kr. Proportional counters are currently used for high-sensitivity measurement of ³⁷Ar and ³⁹Ar. Physical and chemical separation processes are used to separate argon from air or soil gas, yielding pure argon with contaminant gases reduced to the parts-per-million level or below. However, even with purification at these levels, the beta decay signature of ⁸⁵Kr can be mistaken for that of ³⁹Ar, and the presence of either isotope increases the measurement background level for the measurement of ³⁷Ar. Measured values for the ³⁹Ar measured at the site ranged from 36,000 milli- Becquerel/standard-cubic-meter-of-air (mBq/SCM) for shallow bore holes to 997,000 mBq/SCM from the rubble chimney from the underground nuclear explosion.



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