Isomer spectroscopy at RI beam line in RCNP

Odahara, A (reprint author), Osaka Univ, Dept Phys, Osaka 5600043, Japan
Modern Physics Letters A (Impact Factor: 1.2). 07/2010; 25(21):1951-1954. DOI: 10.1142/S0217732310000721


Experiments based on the isomer-spectroscopy method were performed using the secondary beam line at RCNP, Osaka University. Recently, a new gamma-ray spectroscopy method was established using fusion reaction induced by low-energy RI beam. This method enablesus to study high-spin states of nuclei in wider mass region where it is difficult to populate them by using the combination of stable beams and stable targets. This method works well although low production of nuclei, because (1) the combination of beams and targets can be selected with large-reaction cross section and (2) high-S/N measurement can be performed by the event-by-event detection to select the events correlated with RI beam, which reduces background gamma rays, competing with gamma rays emitted from fusion products. As the first step, high-spin states of (142)Pr were studied using fusion reaction induced by low-energy (17)N RI beam. Large cross section was obtained by the (130)Te((17)N,5n) reaction with 4.9 MeV/u (17)N beam. Event selection, which was carried out by the event-by-event detection with low-beam intensity of 2x10(4) pps, enables high-S/N measurement.

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    ABSTRACT: Isomers and their roles in discovery and as probes of nuclear structure are discussed, with a focus on neutron-rich nuclei in the mass 180–190 region. Long-lived, high-K isomers are predicted in the heavy hafnium nuclei for example, some of which should be accessible by projectile fragmentation and deep-inelastic reactions. Progress with these reactions in reaching a broad range of isotopes to the right of the stability line is summarized. Recent results for isomers in the iridium and osmium isotopes produced in deep-inelastic reactions and studied with time-correlated γ -ray spectroscopy are presented as examples. These studies venture into the border region where well-deformed prolate shapes give way to soft, transitional nuclei. Prolate, oblate and triaxial structures are predicted, but with shapes that depend sensitively on the multi-particle configurations. Dynamical effects such as rotation alignment also play a significant role and produce isomeric states. In some cases, very low-lying multi-quasiparticle intrinsic states are predicted but these are possibly missed with current approaches. The prospects for the identification and characterization of such exotic isomers using new storage ring techniques, that might also provide a window into exotic states populated in their subsequent decay are outlined, as is the potential for studies with beams of isomers themselves.
    Full-text · Article · Jan 2013 · Physica Scripta