176Lu-An s-Process Thermometer

Details 176Lu-An s-Process Thermometer 176Lu-An s-Process Thermometer

Oct 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991aipc..238..850k&link_type=abstract

Capture gamma-ray spectroscopy. AIP Conference Proceedings, Volume 238, pp. 850-859 (1991).

Physics

Gamma Transitions And Level Energies, Radiative Capture, 2H-Induced Reactions, 150<=A<=189

Scientific paper

The use of 176Lu as a cosmic clock has been in question since the possibility of a thermal coupling between the long-lived ground state (t1/2=41.109 yr) and the beta unstable isomer with 3.68 hr half-life was considered. This coupling requires induced transitions to higher lying states because direct transitions are highly forbidden by selection rules. First experimental evidence for the enhancement of the overall decay rate by that mechanism was provided via photoactivation measurements, but a quantitative discussion became possible only after the level scheme of 176Lu had been carefully established in two recent investigations. These studies identified an 1π=5- state at 838.6 keV to be the most efficient mediating level for the coupling of ground state and isomer. As a consequence, the half-life of 176Lu is drastically reduced above 1.5.108 K, i.e., at conditions typical for the production of 176Lu in the s-process during the helium burning phase of stellar evolution. Hence, any interpretation of 176Lu as a cosmic clock is strongly dependent on the conditions at the stellar site, a problem that cannot be solved reliably enough with present stellar models. Instead, the strong temperature dependence of the 176Lu half-life makes it a sensitive tool for constraining the s-process temperature to the range between 2.4.108 to 3.6.108 K.

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