Search for the Ga73 ground-state doublet splitting in the β decay of Zn73

Abstract

The existence of two close-lying nuclear states in 73 Ga has recently been experimentally determined: a 1/2 − spin-parity for the ground state was measured in a laser spectroscopy experiment, while a J π = 3/2 − level was observed in transfer reactions. This scenario is supported by Coulomb excitation studies, which set a limit for the energy splitting of 0.8 keV. In this work, we report on the study of the excited structure of 73 Ga populated in the β decay of 73 Zn produced at ISOLDE, CERN. Using β-gated, γ -ray singles, and γ -γ coincidences, we have searched for energy differences to try to delimit the ground-state energy splitting, providing a more stringent energy difference limit. Three new half-lives of excited states in 73 Ga have been measured using the fast-timing method with LaBr 3 (Ce) detectors. From our study, we help clarify the excited structure of 73 Ga and we extend the existing 73 Zn decay to 73 Ga with 8 new energy levels and 35 γ transitions. We observe a 195-keV transition consistent with a γ ray de-exciting a short-lived state in the β-decay parent 73 Zn.

Investigating the large deformation of the 5/2+ isomeric state in Zn73 : An indicator for triaxiality

“…Our non observation of this state is consistent with the conclusion from the recent measurement of the beta-decay of 73 Zn [21] and also with the earlier β-decay study of 73 Cu to 73 Zn [22]. The recently reported abnormally large quadrupole moment for 73 Zn [19] was reinvestigated by using shell model calculations with the JUN45 and A3DA-m interactions, and by a T-plot analysis which reveals a triaxial shape of the state.…”

“…1(b2). This confirms the isomer half-life to be of the order of 10 ms, thus consistent with the isomer observed in the previous studies [21,22].…”

“…The latter work proposed a 13 ms isomeric state to exist in 73 Zn with a tentative spin-parity assignment of 5/2 + at 195 keV. The lifetime and decay energy of this isomeric state were also confirmed in a recent β-decay study of a 73 Zn beam produced via laser ionization [22]. Thus, the existence of a 5.8 s isomer and its decaying transitions remains unconfirmed.…”

“…Although it has been the subject of numerous experimental investigations in this region, detailed spectroscopic information for the mid-shell isotope 73 Zn remains inconclusive [20][21][22]37]. Here, we may further compare available states of 73 Zn with those calculated using the shell model.…”

Fast-timing study of Ga81 from the β decay of Zn81

“…The present experiment was performed at the ISOLDE CERN facility in the framework of a systematic fast-timing investigation of neutron-rich nuclei populated following the decay of Zn isotopes [25][26][27]. The selectivity and efficiency for the production of Zn ion beams had been previously optimized [28] in order to enhance the beam purity for 77−82 Zn ions.…”