Measurement of 37Ar to support technology for On-site Inspection under the Comprehensive Nuclear-Test-Ban Treaty

TL;DR

This paper describes a sensitive detection method for Argon-37, a radionuclide signature of underground nuclear tests, supporting verification efforts under the CTBT through on-site inspections.

Contribution

It introduces a low-background gas proportional counter capable of measuring Argon-37 at very low activity levels, enhancing detection capabilities for nuclear test signatures.

Findings

Achieved measurement sensitivity of 45.1 mBq/SCM for 37Ar.

Demonstrated the counter's effectiveness for on-site nuclear explosion verification.

Supports CTBT verification with improved radionuclide detection techniques.

Abstract

On-Site Inspection (OSI) is a key component of the verification regime for the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Measurements of radionuclide isotopes created by an underground nuclear explosion are a valuable signature of a Treaty violation. Argon-37 is produced from neutron interaction with calcium in soil, 40Ca(n,{\alpha})37Ar. For OSI, the 35-day half-life of 37Ar provides both high specific activity and sufficient time for completion of an inspection before decay limits sensitivity. This paper presents a low-background internal-source gas proportional counter with an 37Ar measurement sensitivity level equivalent to 45.1 mBq/SCM in whole air.