Cosmogenic activation of xenon and copper

TL;DR

This study investigates the production of long-lived radioactive isotopes in xenon and copper due to cosmic ray exposure, highlighting potential background sources for dark matter experiments and comparing observed activation rates with predictions.

Contribution

First dedicated measurement of cosmogenic activation of xenon and copper at high altitude, providing data for background modeling in rare event searches.

Findings

Detected specific isotopes in xenon and copper after cosmic exposure.

Observed discrepancies between measured activation rates and software predictions.

Identified 125Sb as a potential background source in xenon for dark matter detection.

Abstract

Rare event search experiments using liquid xenon as target and detection medium require ultra-low background levels to fully exploit their physics potential. Cosmic ray induced activation of the detector components and, even more importantly, of the xenon itself during production, transportation and storage at the Earth's surface, might result in the production of radioactive isotopes with long half-lives, with a possible impact on the expected background. We present the first dedicated study on the cosmogenic activation of xenon after 345 days of exposure to cosmic rays at the Jungfraujoch research station at 3470m above sea level, complemented by a study of copper which has been activated simultaneously. We have directly observed the production of 7Be, 101Rh, 125Sb, 126I and 127Xe in xenon, out of which only 125Sb could potentially lead to background for a multi-ton scale dark matter search. The production rates for five out of eight studied radioactive isotopes in copper are in agreement with the only existing dedicated activation measurement, while we observe lower rates for the remaining ones. The specific saturation activities for both samples are also compared to predictions obtained with commonly used software packages, where we observe some underpredictions, especially for xenon activation.