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The level structure of the transitional nucleus $\mathrm{^{217}Ra}$ has been extended with the addition of around 20 new transitions. The discrepancies between the placements of several transitions reported in the earlier studies are resolved. The newly-established negative-parity sequence at low excitation energies hints at the expected parity-doublet structures in this nucleus. The properties of the observed simplex bands are compared with that of similar bands in neighboring nuclei. Since the presence of parity-doublet structures reflect octupole correlations, theoretical calculations using reflection-asymmetric triaxial particle rotor model (RAT-PRM) have been performed. A comparison of the observed features of the simplex bands with the predictions of the RAT-PRM calculations suggests that $\mathrm{^{217}Ra}$ exhibits an intermediate the behavior between the extremes of spherical and octupole-deformed nuclei. The termination of the simplex bands at intermediate energies and the structures lying above reflect the dominance of the single-particle excitations at higher excitation energies., Comment: 15 pages, 16 figures

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$\hbar$ and 6.5 MeV with the addition of about 60 new $\gamma$-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 $\mu$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., Comment: 16 pages, 14 figures

Metastable states with T$_{1/2}$ = 8(2) ms in $^{205}$Bi and T$_{1/2}$ = 0.22(2) ms in $^{204}$Pb, with $\approx $ 8 MeV excitation energy and angular momentum $\ge $ 22 $\hbar $, have been established. These represent, by up to two orders of magnitude, the longest-lived nuclear states above an excitation energy of 7 MeV, ever identified in the nuclear chart. Additionally, the half-life of the 10.17 MeV state in $^{206}$Bi has been determined to be 0.027(2) ms, the next highest value in this highly excited regime. These observations indicate the emergence of an island of extreme nuclear isomerism arising from core-excited configurations at high excitation in the vicinity of the doubly closed-shell nucleus $^{208}$Pb. These results are expected to provide discriminating tests of the effective interactions used in current large-scale shell-model calculations., Comment: 17 pages, 5 figures