Isomers in 203Tl and core excitations built on a five-nucleon-hole structure

TL;DR

This paper reports the discovery and detailed analysis of isomeric states and core excitations in $^{203}$Tl, extending the level scheme up to 11 MeV and providing insights into multi-nucleon-hole configurations and octupole excitations.

Contribution

The study identifies new isomeric states and extends the level scheme of $^{203}$Tl, combining experimental data with shell-model calculations to elucidate multi-nucleon-hole structures and core excitations.

Findings

Identification of new isomeric states with specific half-lives.

Extension of the level scheme up to 11 MeV with 25 new transitions.

Evidence for octupole excitations of the $^{208}$Pb core.

Abstract

Isomers with three- and five-nucleon-hole configurations have been established in $^{203}$Tl. These include newly identified levels with a three-nucleon structure: {\it I}$^{\pi }$ = (15/2$^{-}$) with {\it T}$_{1/2}$ = 7.9(5) ns, and {\it I}$^{\pi }$ = (35/2$^{-}$) with {\it T}$_{1/2}$ = 4.0(5) ns. In addition, five-quasiparticle states: {\it I}$^{\pi }$ = (39/2$^{-}$) with {\it T}$_{1/2}$ = 1.9(2) ns, and {\it I}$^{\pi }$ = (49/2$^{+}$) with {\it T}$_{1/2}$ = 3.4(4) ns have also been established. The previously determined long-lived decay [{\it T}$_{1/2}$ = 6.6(3) $\mu $s from this work] is associated with isomerism of the {\it I}$^{\pi }$ = (29/2$^{+}$) state. Levels above this long-lived isomer have been identified through a delayed-prompt coincidence measurement. Five-nucleon-hole states with excitation energies {\it E}$_{x}$ $\approx $ 7 MeV have been established as well as possible octupole excitations of the $^{208}$Pb core built on these levels. The level scheme of $^{203}$Tl is extended up to {\it E}$_{x}$ $\approx $ 11 MeV with the inclusion of 25 new transitions. Empirical and shell-model calculations have been performed to aid in the description of the observed states which are found to be predominantly of intrinsic character.