Origin of Ta-180m and the temperature of the s-process

Abstract

The origin of 180m Ta, 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 180m Ta, the required input data were improved in two directions : (1) By photoexcitation experiments it was found that the decay of 180m Ta is not affected at typical s-process temperatures. (2) The stellar (n, γ)-rates for 179 Ta and 180m Ta were calculated with a refined statistical model approach. The results show that the 180m Ta abundances yields a lower or an upper limit for the temperature at the s-process sire, depending on whether it is produced in stellar helium burning or in supernovae