Low-lying levels of 79Br

Abstract

The properties of the low-lying levels of 79Br were investigated by means of the Coulomb excitation process which was effected by the bombardment of a thick target of PbBr 2 (isotopically enriched to 95.1% in 79Br) with 2.5 to 7.0 MeV alpha particles and with 36 MeV oxygen ions. In the ensuing singles and coincidence gamma-ray spectra, peaks attributed to 79Br were observed at 43±3, 136.1±1.1, 208.4±0.6, 217.3±0.3, 238.6±0.4, 261.5±0.3, 299.4±0.7, 306.4±0.3, ≈ 307 or ≈ 216, 389.1±0.6, 397.2±0.3, 522.8±0.3, 544.0±0.4, 605.4±0.5 and 760.5±0.8 keV. The changes in gamma-ray yields with alpha-particle energy were compatible with those predicted for E2 Coulomb excitation. The ifB(E2) ex values were determined from these yields. Angular anisotropies were measured for the stronger transitions to aid in the assignment of spins. Additional information was obtained about the 79Br level properties through an investigation of gamma rays following the decay of 79Kr. The energies, spins, parities and reduced E2 transition probabilities for the levels of 79Br consistent with this investigation are E Iπ B( E2) ex (KeV) (e 2fm 4 217.2±0.3 5 2 − 395± 33 261.4±0.3 3 2 − 70± 6 306.4±0.3 1 2 , 3 2 − 211± 18 397.2±0.3 3 2 − 33± 5 522.8±0.3 5 2 − 950± 90 605.9±0.2 3 2 − 152± 23 761.2±0.4 5 2 , 7 2 − 1280±220 831.6±0.4 1 2 , 3 2 − <60 1332.3±0.3 3 2 − The B(M1) values which were estimated for 16 of the gamma-ray transitions, had values ranging from 0.002 to ≈ 0.5 (e h ̵ /2Mc) 2 .