Study of beta decay of exotic nuclei interesting for fundamental and applied physics with Total Absorption Gamma-Ray Spectroscopy (TAGS) technique: the case of 85 Se

par Julien Pépin (Equipe S.E.N.)

jeudi 11 juin 2026, 14:00 → 16:00 Europe/Paris

Amphi Besse (Subatech IMT Atlantique)

The precise knowledge of beta-decay properties of neutron rich nuclei impacts several fields of fundamental and applied physics, such as nuclear structure and astrophysics, reactor antineutrino emission estimation and decay heat calculations. 

The beta decay databases suffer of a bias called “Pandemonium effect” which is a distortion in the attribution of feeding probability in beta decay level schemes due to the low efficiency of high-resolution Germanium detectors. This low efficiency penalize the detection of high energy gammas and gamma cascades and then the attribution of the feeding to low energy levels in beta decay scheme. The solution to this problem is the Total Absorption Gamma Ray Spectroscopy (TAGS) technique which is based on high efficiency detectors. This PhD work presents the realization and analysis of a new TAGS measurement realized in September 2022 at the Jyväskylä accelerator in Finland. The data analysis process is presented from detector calibration to subtraction of contaminants as well as the improvement of the GEANT4 simulation of the detector. The extraction of the beta feeding from the new dataset is presented for one nucleus, the ⁸⁵Se. These new results are criticized and compared with previous measurements. Their impact on beta strength and mean energies calculation is assessed.