High Throughput Argon-37 Field System
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Pure and Applied Geophysics
High Throughput Argon-37 Field System JAMES C. HAYES,1 CRAIG AALSETH,1 THOMAS ALEXANDER,1 HENNING BACK,1 ERIC CHURCH,1 MICHAEL FOXE,1 TODD HOSSBACH,1 PAUL HUMBLE,1 LANCE LIDEY,1 EMILY MACE,1 KERRY MEINHARDT,1 JENNIFER MENDEZ,1 JUSTIN MCINTYRE,1 CORY OVERMAN,1 ROBIN RIEMANN,1 ALLEN SEIFERT,1 KURT SILVERS,1 DAVID STEPHENSON,1 REYNOLD SUAREZ,1 and GREG WHYATT1 Abstract—Pacific Northwest National Laboratory (PNNL) has developed a unique fieldable 37Ar measurement system designed to measure 37Ar activity concentrations from soil gas samples to detect above ground and underground nuclear explosions. The Argon-37 Field System is modular in design to accommodate both chemical processing and nuclear detection. The system can be packed into shipping crates and shipped to a location near where the sampling is taking place. The system can process six 2-m3 whole-air samples in 24 h and can measure the 37Ar activity in each of the samples using six proportional counters. The proportional counters, designed and built at PNNL, are surrounded with both active and passive shielding to reduce background and can achieve a minimum detection concentration of 10 mBq/m3 of 37Ar in whole-air equivalent. The Argon-37 Field System has undergone extensive testing against rigorous requirements to assure the system meets the needs of the noble gas nuclear explosion monitoring community. Keywords: CTBT, Argon-37, Radioxenon, nuclear explosion monitoring.
1. Introduction Detection of radionuclides from an above ground or underground nuclear explosion is a critical component of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) verification regime (UN 1996). The CTBT calls for both atmospheric sampling for radionuclides to detect above ground and vented releases from an underground nuclear explosion and allows for soil gas sampling for radionuclides in certain circumstances.
1
Pacific Northwest National Laboratory, Richland, WA, USA. E-mail: [email protected]
Effectively collecting and measuring short-lived radioactive gases from the soil near a suspected subsurface nuclear explosion can yield clear evidence of a recent nuclear explosion. The relatively long half-life of 37Ar (35d) is attractive because it provides enough time for field teams to begin work and provides a detectable signal near the surface for many months. Argon-37 is produced from in-situ neutron activation of calcium in the soil through the 40 Ca(n,a)37Ar reaction. The dominant 37Ar nuclear decay signature consists of five low-energy Auger electrons with a total energy of 2.8 keV. The amount of 37Ar generated from a nuclear event depends upon the number of neutrons produced and the amount of Ca in the surrounding geology. In a well contained test, most fission and activation products from an underground event will be contained within the explosion cavity; however, the chemically inert nature of Ar and Xe can result in these two gases migrating through the subsurface to ground level (Carrigan et al. 2019; Lowrey et al. 2016; Johnson et al. 2019). Whil
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