Speaker
Description
Odd-mass, neutron-deficient nuclei in the vicinity of the Z = 82 closed shell are currently the subject of extensive experimental investigation due to the frequent occurrence of shape coexistence and nuclear isomerism in this region. In 2022, a new isomeric state in ¹⁷⁹Au was identified at an excitation energy of 1743(17) keV, with spin and parity of 19/2⁺ and a half-life of 2.16(8) µs. Due to limited data statistics, only four decay branches could be established [1]. This isomeric state, not yet observed in neighbouring odd-mass isotopes, has proven to be a valuable probe for accessing multiple non-yrast excited states. This initiated a new dedicated experiment at the JYFL-ACCLAB in Finland, employing the RITU separator and a nonstandard focal-plane setup with two multiwire proportional counters. Preliminary results from this ongoing analysis will be presented.
The earlier experiment also revealed a low-lying 11/2⁻ isomer with a half-life of 196(15) ns at E = 181(17) keV, interpreted as arising from a πh11/2 proton-hole configuration. One of its feeding transitions, originating from a newly identified 11/2⁻ band-head state, was deduced to have mixed E0 + M1(+E2) multipolarity, suggesting the shape change. The presence of the E0 component was reinvestigated using the new dataset.
References
[1] M. Balogh et al., Phys. Rev. C 106 (2022) 064324