Alpha radioactivity deep-underground as a probe of axion dark matter

TL;DR

This paper proposes a novel underground radioisotope decay experiment to detect axion dark matter by observing time variations in alpha decay rates, covering a wide axion mass range with competitive sensitivity.

Contribution

It introduces a theoretical framework linking axion dark matter to alpha decay half-life modulation and presents a prototype experiment at Gran Sasso to test this method.

Findings

Predicted alpha decay rate modulation due to axion oscillations.

Constructed underground setup for sensitive alpha decay measurements.

Projected limits on axion decay constant across a broad mass range.

Abstract

We propose to investigate the time modulation of radioisotope decays deep underground as a method to explore axion dark matter. In this work, we focus on the $\alpha$-decay of heavy isotopes and develop a theoretical description for the $\theta$-dependence of $\alpha$-decay half-lives, which enables us to predict the time variation of $\alpha$-radioactivity in response to an oscillating axion dark matter background. To probe this scenario, we have recently constructed and installed a setup deep underground at the Gran Sasso Laboratory, based on the $\alpha$-decay of Americium-241. This prototype experiment, named RadioAxion-$\alpha$, will allow us to explore a broad range of oscillation's periods, from a micro-second up to one year, thus providing competitive limits on the axion decay constant across 13 orders of magnitude in the axion mass, ranging from $10^{-9}$ eV to $10^{-20}$ eV after one month of data collection, and down to $10^{-22}$ eV after three years.