Nuclear Structure 2022

High-spin states in 212Po above the alpha-decaying (18+) isomer

Not scheduled

1m

Berkeley, CA

Poster Poster Presentations Poster Session

Speaker

Mr Luca Zago (INFN LNL and University of Padova)

Description

Due to the rather scarcity of spectroscopic data on the trans-fermium region, high-spin studies in the few-particles/holes around the Z = 82, N=126 double-shell closure, populating the same high-$j$ orbitals, can provide complementary and crucial information about the single-particle level structure of these nuclei.
A particularly rich phenomenology also arises around the lead double shell closure due to the interplay between the single-particle behaviour and the 3${}^{-}$ ${}^{208}$Pb collective vibration. This collective state lies particularly low in energy, and lowers in energy still with increasing particles added to the valence space [1]. This collective excitation can mix with the single-particle transitions between $\mathrm{\Delta }l=\mathrm{\Delta }j=3\hslash$ orbits, producing particularly fast E3 decays [2].
In this region, the ${}^{212}$Po isotope level scheme has been known up to a long-lived, $\alpha$-decaying (18${}^{+}$) state. Two new $\gamma$ rays have been observed in the excitation spectrum of this isotope using $\gamma$-decay spectroscopy with the RISING setup at GSI, Darmstadt. They have been assigned to the 23${}^{+}$ → 21${}^{-}$ → 18${}^{+}$ yrast cascade. Lifetime measurement of the two states suggests M2 and E3 assignment to the two transitions. Though with relatively low statistics, these are the first observations of high-spin states above the ${}^{212}$Po (18${}^{+}$) isomer, by virtue of the selectivity of the FRS separator obtained via ion-by-ion identification of ${}^{238}$U fragmentation products. Comparison with shell-model calculations points to shortfalls in the nuclear interactions involving high-$j$ proton and neutron orbitals.

[1] E. Caurier et al., Phys. Rev. C 67 054310 (2003)
[2] I. Bergström, B. Fant, Phys. Scr. 31 (1985)