Search

Fusion-fission reactions were induced by bombarding a thick 27Al target with 178Hf projectiles at a laboratory energy of 1150 MeV using the ATLAS accelerator at Argonne National Laboratory. The subsequent γ-ray decays were measured using the GAMMASPHERE germanium detector array. The beam was pulsed at two different ON/OFF cycles of 82.5/825 ns and 25/75 μs in order to observe the γ rays from the decay of isomeric states. In 121Sb 2721+Δ keV, Iπ=(25/2+) and 2434 keV, Iπ=19/2- states have measured half-lives of T1/2=200(30) μs and 8.2(2) ns respectively. The 2614+Δ keV, Iπ=(27/2+) and 2486 keV, Iπ=19/2+ states in 123Sb have measured half-lives of T1/2=52(3) μs and 7.9(4) ns respectively. The positive parity isomers in these nuclei correspond to a πd5/2 or πg7/2 configuration, in 121Sb and 123Sb respectively, coupled to aligned (h11/2)2 neutrons. The Iπ=19/2- isomeric state in 121Sb is proposed to have a νh11/2 x νd3/2 x πd5/2 configuration. A previously unobserved isomer has been identified in 99Mo at an energy of 3010 keV, decaying with T1/2=18(5) ns. This state is interpreted as an energetically favoured 3 quasi-particle alignment of ν (d5/2 g7/2) x π(g9/2)2 configuration which is observed systematically in the even-Z N=57 isotones. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The depopulation of the quasistable isomer (J[sup π]=9[sup -], E[sub x]=75 keV) in [sup 180]Ta through resonant photoabsorption was studied with intense bremsstrahlung. The results show evidence for a deexciting level with an energy of 1.085 MeV or below, leading to a dramatic acceleration of the isomer decay to the short-lived J[sup π]=1[sup +] ground state under stellar s-process conditions. Consequences for a possible nucleosynthesis of nature’s rarest isotope [sup 180]Ta within the s process are discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]