Microscopic calculations for rare beta decays

In this thesis consisting of six publications and an overview part, three cases of rare beta decays are studied using microscopic nuclear models. Firstly, the half-lives and electron spectra of 113Cd and 115In fourth-forbidden nonunique ground-state-to-ground-state beta decays are studied using two closely related nuclear models: The microscopic quasiparticle-phonon model (MQPM) and the proton-neutron MQPM (pnMQPM), which has been developed as a part of this thesis work. Our results for these rare decays are compared to the available experimental data and are found to agree reasonably well. As the second application, the partial half-lives of the yet unobserved single-beta decay channels competing with the double beta decay of 96Zr are computed to estimate the possible contamination from these channels to the geochemical double-beta-decay experiments. According to our results obtained by applying the proton-neutron quasiparticle random-phase approximation (pnQRPA), the error stemming from them is still within the experimental uncertainties of the geochemical experiments. Finally, the recently discovered tiny ultra-low-Q-value decay branch of 115In has been investigated in collaboration with the JYFLTRAP group in Jyväskylä and the HADES underground laboratory in Belgium. Our pnMQPM prediction for the half-life is found to di er from the experimentally obtained result by more than an order of magnitude. The various atomic contributions possibly responsible for this discrepancy are discussed.