High-spin spectroscopy in ${}^{207}$At: Evidence of a 29/2${}^{+}$ isomeric state

Abstract

Yrast and near-yrast states above the known 25/2${}^{+}$ isomer in ${}^{207}$At are established for the first time. The level scheme is extended up to 47/2$\hslash$ and 6.5 MeV with the addition of about 60 new ${\hat{I}}^3$-ray transitions. The half-life of the 25/2${}^{+}$ isomer is revisited and a value of $T_{1/2}$ = 107.5(9) ns is deduced. Evidence of a hitherto unobserved 29/2${}^{+}$ isomer in ${}^{207}$At is presented. A systematic study of $B(E3)$ values for the transitions de-exciting the 29/2${}^{+}$ isomer in the neighboring odd-$A$ At isotopes suggests a half-life in the 2$-$4.5 $\hat{I}¼$s range for this state in ${}^{207}$At. The experimental results are compared with large-scale shell-model calculations performed using the KHM3Y effective interaction in the $Z$ = 50$-$126, $N$ = 82$-$184 model space and an overall good agreement is noted between the theory and the experiment. A qualitative comparison of the excited states and the isomers with analogous states in neighboring nuclei provides further insight into the structure of ${}^{207}$At.

16 pages, 14 figures