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

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 α-decay of heavy isotopes and develop a theoretical description for the θ-dependence of α-decay half-lives, which enables us to predict the time variation of α-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 α-decay of Americium-241. This prototype experiment, named RadioAxion-α, 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.