Development of a low background liquid scintillation counter for a shallow underground laboratory

TL;DR

This paper describes the design and background evaluation of a low-background liquid scintillation counter developed for a shallow underground laboratory to enhance detection sensitivity of radioactive isotopes.

Contribution

It introduces a new low-background liquid scintillation counter optimized for shallow underground environments, including its design and background assessment.

Findings

Simulations show effective background reduction in the underground setting

Design achieves low background levels suitable for sensitive isotope detection

Counter enhances measurement capabilities for charged particle emitting isotopes

Abstract

Pacific Northwest National Laboratory has recently opened a shallow underground laboratory intended for measurement of low-concentration levels of radioactive isotopes in samples collected from the environment. The development of a low-background liquid scintillation counter is currently underway to further augment the measurement capabilities within this underground laboratory. Liquid scintillation counting is especially useful for measuring charged particle (e.g., $\beta$, $\alpha$) emitting isotopes with no (or very weak) gamma-ray yields. The combination of high-efficiency detection of charged particle emission in a liquid scintillation cocktail coupled with the low-background environment of an appropriately-designed shield located in a clean underground laboratory provides the opportunity for increased-sensitivity measurements of a range of isotopes. To take advantage of the 35 meters-water-equivalent overburden of the underground laboratory, a series of simulations have evaluated the scintillation counter's shield design requirements to assess the possible background rate achievable. This report presents the design and background evaluation for a shallow underground, low background liquid scintillation counter design for sample measurements.