Nuclear Seminar - Mgr. Ovidiu Nitescu (30.10.2024)
Wednesday 30.10.2024 at 14:00, Lecture room F1/364
Mgr. Ovidiu Nitescu (doktorand KJFB):
Nuclear beta and double beta decay studies for neutrino physics
Abstract:
We investigate the atomic exchange effect between the final atom's bound electrons and those emitted in the allowed β decay and 2νββ decay of the initial nucleus. The electron wave functions are obtained with the Dirac-Hartree-Fock-Slater self-consistent method, and we ensure the orthogonality between the continuum and bound electron states of the final atom by modifying the last iteration of the self-consistent method. We argue that our findings can solve the mismatch between the predictions and experimental measurements in the low-energy region of the β spectrum. The relevance of exchange corrections is also analyzed in the context of one of the most promising candidates for determining the neutrino mass scale: the unique first forbidden β transition of 187Re. Additionally, we examine the contribution of all s-wave electrons available for capture in the two-neutrino double electron capture (2νECEC) processes, going beyond the K and L1 orbitals considered in prior studies. A systematic study is conducted for all nuclei undergoing 2νECEC process, and more details and improvements are presented for the recently measured 2νECEC process of 124Xe. Finally, based on the observation that the effective nuclear matrix elements (NMEs) of two-neutrino double beta decay in both neutron-rich and proton-rich nuclei span similar ranges, we propose a semi-empirical formula (SEF) for calculating the NMEs. Compared with the previous phenomenological and nuclear models, the SEF yields the best agreement with the experimental NMEs. Its stability and predictive power are cross-validated, and predictions are provided for nuclear systems of experimental interest.