Discovery of underground argon with low level of radioactive 39Ar and possible applications to WIMP dark matter detectors

TL;DR

This study measures the low level of radioactive 39Ar in underground argon from natural gas reservoirs, demonstrating its potential for constructing large, low-background argon detectors for WIMP dark matter searches.

Contribution

First measurement of 39Ar in underground argon showing significantly reduced radioactivity suitable for dark matter detectors.

Findings

39Ar levels in underground argon are <=4x10^-17, much lower than atmospheric argon.

Underground argon can be used to build large, low-background detectors.

Potential for improved WIMP dark matter detection sensitivity.

Abstract

We report on the first measurement of 39Ar in argon from underground natural gas reservoirs. The gas stored in the US National Helium Reserve was found to contain a low level of 39Ar. The ratio of 39Ar to stable argon was found to be <=4x10-17 (84% C.L.), less than 5% the value in atmospheric argon (39Ar/Ar=8x10-16). The total quantity of argon currently stored in the National Helium Reserve is estimated at 1000 tons. 39Ar represents one of the most important backgrounds in argon detectors for WIMP dark matter searches. The findings reported demonstrate the possibility of constructing large multi-ton argon detectors with low radioactivity suitable for WIMP dark matter searches.