Creation and survival of 180Ta in stellar environments plus a brief overview of nuclear research at the ANU
Mercredi 11 octobre 2017 11:00
- Duree : 1 heure
Lieu : Seminar Room 7/8 - ILL 1, 71 avenue des Martyrs, Grenoble
Orateur : Gregory LANE (Australian National University, Acton ACT 2601,Australia)
180Ta is nature’s rarest isotope and also the only naturally occurring isomer, existing in an excited nuclear state at 77 keV with a half-life of >4.5x10^16 years, whereas the ground state has a half-life of only 8.15 hours. Isolated by the stable isobars 180W and 180Hf, it is bypassed by the main r- and s-processes and hence the location and mode of its nucleosynthesis is an open question. The problem is further complicated by the fact that resonant photoabsorption has been shown to transmute the long-lived isomer into the shorter-lived ground state, suggesting that 180Ta may be destroyed in the photon bath of a star.
Specific laboratory observations of photon resonances that mediate the transmutation have been tentatively associated with particular excited states in 180Ta. This has led to predictions for the strengths of "back-decay" transitions that would connect the resonance states back to the long-lived isomer. I will report on a search for these "back-decays" from an experiment that used the 180Hf(d,2n) reaction, 14UD Pelletron accelerator and CAESAR gamma-ray detector array, at the Australian National University (ANU). Stringent limits on the possible gamma-ray branches have been obtained and the implications for the creation and survival of 180Ta will be discussed.
In addition, aspects of the broader ANU research program will be presented, especially details of SABRE, our planned dark matter experiment. SABRE will operate identical detectors in both Gran Sasso in the northern hemisphere and in the Stawell Underground Physics Laboratory (SUPL) that hopes to be the first deep-underground laboratory in the southern hemisphere. The goal of SABRE is to make a definitive test of DAMA/LIBRA, an experiment that has observed modulations of the signal in their detector over 13 annual cycles that appear to correlate with expectations for how dark matter interactions should modulate due to the motion of the earth through the galactic dark matter halo.
Contact : tellier@ill.fr
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