Competition between the neutron-proton pair break-ups delineating the level structure of 202Po

TL;DR

This study extends the level scheme of $^{202}$Po up to 8 MeV and 27ħ, revealing new gamma transitions and sequences, and uses shell model calculations to explain the nuclear structure and isomeric states.

Contribution

The paper provides a comprehensive high-spin level scheme for $^{202}$Po with new transitions and sequences, supported by shell model calculations that clarify the structure of isomeric states.

Findings

Extended level scheme up to 8 MeV and 27ħ.

Identification of 57 new gamma-ray transitions.

Shell model calculations explain isomeric states and missing decays.

Abstract

High-spin spectroscopic study of $^{202}$Po ($Z$ = 84, $N$ = 118) has been carried out using the $^{195}$Pt($^{12}$C, 5n)$^{202}$Po fusion-evaporation reaction. An extended level scheme has been proposed up to an excitation energy of $E_x\approx$ 8 MeV and angular momentum of 27$\hbar$, with the addition of 57 newly observed $\gamma$-ray transitions, along with the revisions in the placement of 8 already known transitions and the multipolarities of 4 of these transitions. The energy of the unobserved 8$^+ \rightarrow 6^+$ transition has been proposed to be 9.0(5) keV, which resolves the uncertainty in the excitation energy of the levels above the 6$^{+}$ state. Three new sequences of $M1$ transitions have also been identified in the high excitation energy regime and included in the proposed level scheme. The large-scale shell model calculations for $Z>82$ and $N<126$ valence space have been carried out using PBPOP interaction which explained the overall level scheme for both the positive and negative parity states. The calculations successfully reproduced the purity of the proton $\pi h_{9/2}$ dominated $8^+$ isomeric state, and also explained the missing $E2$ decay of the ${12}^+$ isomeric state in terms of changing nucleonic configurations.