γ-ray spectroscopy of the Neutron-rich ¹⁸⁸٫¹⁸⁹Ta isomeric decay

Since the discovery of the atomic nucleus and nuclear forces, particularly the strong interaction that holds the components of the nucleus together, physicists have been trying to explain the properties of this strong interaction and its mechanism, as well as the general properties of the nucleus. This pursuit led to the development of experimental techniques through which the properties of exotic nuclei can be investigated. One of the world’s leading accelerator complexes capable of producing heavy exotic nuclei is the GSI Helmholtzzentrum für Schwerionenforschung, located in Darmstadt, Germany. In March 2021, the S452 experiment was conducted at the GSI facility to investigate the nuclear structure of nuclei far from the line of stability. Heavy, neutron-rich isotopes in the mass number range A ∼ 190 were produced via fragmentation at 1 GeV/u with primary beams of ²⁰⁸Pb impinging on a ⁹Be target. The nuclei of interest were then identified on an event-by-event basis by determining the atomic number Z and the mass-to-charge ratio, A/Q. The selected isotopes were then delivered to the DESPEC setup for nuclear structure studies, where the ions were stopped by a stack of silicon layers in the AIDA setup. The isomeric decay of the odd-odd nucleus ¹⁸⁸Ta and the odd-even nucleus ¹⁸⁹Ta was investigated using γ-ray spectroscopy. The study was carried out using two EUROBALL clusters, each containing seven encapsulated HPGe crystals, placed in a forward position with respect to AIDA. Additionally, 36 ultra-fast LaBr₃(Ce) detectors from the FATIMA setup were arranged in three rings around the AIDA setup. Results obtained from the experimental data revealed the existence of new isomeric states in both the ¹⁸⁸Ta and ¹⁸⁹Ta isotopes. Lifetime measurements of the new isomeric states are presented in this work, as well as the previously reported isomeric states with improved precision. In the case of the ¹⁸⁸Ta isotope, the isomeric ratio of both the newly discovered and previously reported isomeric states is also presented. New spectroscopic results have been obtained for the ¹⁸⁹Ta isotope. Three high-K isomeric states have been identified in this work, one of which was already reported in earlier studies. The information obtained, such as γ−γ coincidences and relative intensities Iγ from our study, allows us to establish a partial level scheme for ¹⁸⁹Ta. Theoretical calculations (TRS) were performed for one-quasiparticle states and three-quasiparticle states in ¹⁸⁹Ta to explain the new experimental results and to characterize the isomeric states. Additionally, a second partial level scheme is proposed based on spectroscopic comparisons between the ¹⁸⁹Ta and the ¹⁸⁵,¹⁸⁷Ta isotopes.