Speaker
Description
Shape coexistence is a phenomenon in which multiple shapes occur within the same nucleus. Although this phenomenon has been proposed to exist in various regions of the nuclear chart [1], neutron‑deficient Pb isotopes near the N=104 mid‑shell have been a primary focus of study for several decades. Notably, the neutron‑deficient $^{186}$Pb isotope exhibits three distinct shapes [2–5] at low excitation energy. In the shell‑model picture, these three shapes are associated with 0p–0h (spherical), 2p–2h (oblate), and 4p–4h (prolate) multiproton–multihole configurations. Performing fusion–evaporation experiments beyond the mid‑shell becomes increasingly challenging due to the decreasing production cross‑sections and the rising fission cross‑section.
The most recent results at Jyväskylä focused on $^{184}$Pb, utilising the recoil‑decay‑tagging method in conjunction with the JUROGAM II germanium‑detector array [6]. This experiment led to the identification of non‑yrast structures in $^{184}$Pb for the first time. Observing non‑yrast structures in this nucleus is currently at the limit of experimental feasibility. The systematic behaviour of structures in neutron‑deficient Pb isotopes will be discussed.
Another topic of this presentation concerns the mid‑shell nucleus $^{186}$Pb, studied using the combined gamma‑ray and conversion‑electron spectrometer SAGE. The results of this experiment enabled an assessment of the mixing between yrast and non‑yrast configurations and revealed the $2_1^+\rightarrow0_2^+$ collective transition.
This presentation will focus on the most recent results for $^{184}$Pb [6], as well as findings from combined gamma‑ray and conversion‑electron spectroscopy of $^{186}$Pb [5], and will compare these results. Both experiments were performed at the Accelerator Laboratory of Jyväskylä. Future prospects will also be outlined in this presentation.