High-spin states of $$^{204}$$At: isomeric states and shears band structure

Abstract

High-spin states of neutron-deficient trans-lead nucleus \(^{204}\hbox {At}\) were populated up to \(\sim 8\,\mathrm{MeV}\) excitation through the \(^{12}\hbox {C} + ^{197}\hbox {Au}\) fusion evaporation reaction. Decay of the associated levels through prompt and delayed \(\gamma \)-ray emissions were studied to evaluate the underlying nuclear structure. The level scheme, which was partly known, was extended further. An isomeric \(16^+\) level with observed mean lifetime \(\tau =52 \pm 5\, \mathrm{ns}\), was established from our measurements. Attempts were made to interpret the excited states based on multi quasiparticle and hole structures involving \(2f_{5/2}\), \(1h_{9/2}\), and \(1i_{13/2}\) shell model states, along with moderate core excitation. Magnetic dipole band structure over the spin parity range: \(16^+\)–\(23^+\) was confirmed and evaluated in more detail, including the missing cross-over E2 transitions. Band-crossing along the shears band was observed and compared with the evidence of similar phenomena in the neighbouring \(^{202}\hbox {Bi}\), \(^{205}\hbox {Rn}\) isotones and the \(^{203}\hbox {At}\) isotope. Based on comparison of the measured B(M1)/B(E2) values for transitions along the band with the semiclassical model based estimates, the shears band of \(^{204}\hbox {At}\) was established along with the level scheme.