High-spin states of 204 At: isomeric states and shears band structure

Abstract

High-spin states of neutron-deficient trans-lead nucleus 204At were populated up to ∼8MeV excitation through the 12C + 197Au fusion evaporation reaction. Decay of the associated levels through prompt and delayed γ-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 τ=52±5ns, was established from our measurements. Attempts were made to interpret the excited states based on multi quasiparticle and hole structures involving 2 f5 / 2, 1 h9 / 2, and 1 i13 / 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 202Bi , 205Rn isotones and the 203At 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 204At was established along with the level scheme.