Heavy Ion Discussion Group, March 21, 2023, 9:00 a.m. CDT

Title: Isomers from collective and intrinsic modes in Z=80-83 nuclei
Name: Saket Suman
Affiliation: UM-DAE Centre for Excellence in Basic Sciences, Mumbai

The competition between collective and intrinsic modes of excitation has been explored through the study of isomers in Hg, Tl, Pb and Bi isotopes in the A ≈ 200 region. Isotopes on the proton-rich side exhibit collective behavior whereas heavier ones display single-particle excitations. Their proximity to the line of stability poses challenges in accessing these nuclei through fusion evaporation reactions involving heavy beams. Therefore, multi-nucleon transfer reactions using highly-energetic, ²⁰⁷Pb and ²⁰⁹Bi beams, with above-barrier energies, incident on a ¹⁹⁷Au target, were used to populate highly-excited levels. The Gammasphere detector array and pulsed beams in different intervals ranging from < 1 μs to several seconds, were used to study isomers with a wide range of half-lives. The evolution of collectivity in ^198,200,202Hg (Z=80) has been studied through a measurement of the half-lives of the 7^-, 9^- and 12⁺ states and their associated transition probabilities. In Tl (Z=81) isotopes, the moderately deformed ¹⁹⁹Tl is found to exhibit significant contributions from rotation-aligned angular momentum, while in ²⁰⁰Tl, a 6-quasiparticle isomer arising from intrinsic excitations is found to be yrast. One of the important results is the identification of the three longest-lived nuclear states across the nuclear chart above an excitation energy of 7 MeV, in ²⁰⁴Pb and ^205,206Bi. Additionally, the Indian National Gamma Array (INGA) facility was used to study high-K states in Yb isotopes. A brief glimpse of one of the in-house measurements, using a HPGe detector and a DSP system, for a high-precision lifetime measurement will also be presented.