Experimental searches for rare alpha and beta decays

Abstract.

The current status of the experimental searches for rare alpha and beta decays is reviewed. Several interesting observations of alpha and beta decays, previously unseen due to their large half-lives ($10^{15}$ - $10^{20}$ yr), have been achieved during the last years thanks to the improvements in the experimental techniques and to the underground locations of experiments that allows to suppress backgrounds. In particular, the list includes first observations of alpha decays of ¹⁵¹Eu , ¹⁸⁰W (both to the ground state of the daughter nuclei), ¹⁹⁰Pt (to excited state of the daughter nucleus), ²⁰⁹Bi (to the ground and excited states of the daughter nucleus). The isotope ²⁰⁹Bi has the longest known half-life of $T_{1/2} \approx 10^{19}$ yr relatively to alpha decay. The beta decay of ¹¹⁵In to the first excited state of ¹¹⁵Sn ($E_{\mathrm{exc}} = 497.334$ keV), recently observed for the first time, has the $Q_{\beta}$ value of only $(147 \pm 10)$ eV, which is the lowest $Q_{\beta}$ value known to-date. Searches and investigations of other rare alpha and beta decays ( ⁴⁸Ca , ⁵⁰V, ⁹⁶Zr, ¹¹³Cd, ¹²³Te, ^178m2H, ^180mTa and others) are also discussed.