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

Abstract

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

Radioxenon net count calculations revisited

“…where E is the energy detected by the β cell, n is the number of counts, and mc 2 is 511 keV [27][28][29]. The endpoint energy is then found when the function is linearly extrapolated to zero value.…”