부산대학교 도서관

High-spin states of neutron-deficient trans-lead nucleus 204 At were populated up to ∼ 8 MeV excitation through the 12 C + 197 Au 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 ± 5 ns , was established from our measurements. Attempts were made to interpret the excited states based on multi quasiparticle and hole structures involving 2 f 5 / 2 , 1 h 9 / 2 , and 1 i 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 Bi , 205 Rn isotones and the 203 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 At was established along with the level scheme. [ABSTRACT FROM AUTHOR]