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

摘要

Pacific Northwest National Laboratory reports on the detection of Ar-39 at the location of an underground nuclear explosion on the Nevada Nuclear Security Site. The presence of Ar-39 was not anticipated at the outset of the experimental campaign but results from this work demonstrated that it is present, along with Ar-37 and Kr-85 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 Ar-39 from the fission product Kr-85. Proportional counters are currently used for high-sensitivity measurement of Ar-37 and Ar-39. 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 Kr-85 can be mistaken for that of Ar-39, and the presence of either isotope increases the measurement background level for the measurement of Ar-37. Measured values for the Ar-39 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. Published by Elsevier Ltd.