ORIGIN OF TA-180M AND THE TEMPERATURE OF THE S-PROCESS

The origin of Ta-180m, nature's rarest isotope, represents a persisting puzzle of nuclear astrophysics. Recent studies indicate that it may be produced at a variety of nucleosynthesis sites, that is, by the s-process during stellar helium burning, or by the p- and v-processes, which occur in supernova explosions. Among these scenarios, the s-process is, at present, best suited for reliable predictions. For the quantitative discussion of a possible s-process origin of Ta-180m, the required input data were improved in two directions: (1) By photoexcitation experiments it was found that the decay of Ta-180m is not affected at typical s-process temperatures. (2) The stellar (n, gamma)-rates for Ta-179 and Ta-180m were calculated with a refined statistical model approach. The results show that the Ta-180m abundances yields a lower or an upper limit for the temperature at the s-process site, depending on whether it is produced in stellar helium burning or in supernovae.