On the internal bremsstrahlung accompanying β-decay and its potential relevance in the application of radioactive sources

An in-depth analysis of the decay process for beta-emitting radionuclides highlights, for some ofthem, the existence of high-order effects usually not taken into account in literature asconsidered negligible in terms of energy and yield, and referred to as Internal Bremsstrahlung(IB). This set of beta-radionuclides presents, besides their beta spectrum, a continuous gamma emissiondue to the Coulomb field braking action on the emitted electron following the decaying nucleus.In this work, we review the theoretical and experimental studies on the IB process focusing onits actual importance for the pure beta emitters. It emerges that there is no satisfactory model ableto reproduce the experimental IB distribution for most of the investigated beta emitters and theseveral measurements are sometimes at odds with each other. Moreover, as recentlydemonstrated, the IB process can give a relevant contribution to the physics of beta emitters thusrequiring its inclusion in the physics of the beta decay. A discussion on the importance ofconsidering IB process in both applicative fields such as nuclear medicine, industrialapplications, and research or calibration laboratories, and in other relevant fields of particlephysics or astrophysics, such as the research on dark matter or neutrino mass, is presented.