Production and survival of 99Tc in He-shell recurrent thermal pulses

After a brief introduction to the present state of art of nuclear beta-decay studies in astrophysics, we report our recent work on the long-standing 99Tc problem. Having combined a detailed study of the recurrent He-shell thermal-pulse, third dredge-up episodes in a 2.25 M/sub solar/ star and an s-process network calculation, we show that a substantial amount of 99Tc can be produced by the s-process and can survive to be dredged up to the stellar surface. We stress that the factual observation of 99Tc at the surface of certain stars does not necessarily preclude the 22Ne(α,n)25Mg reaction from remaining as the neutron source for the s-process. The calculated surface abundances of 99Tc and elements with neighboring atomic numbers are compared with observations. 43 refs., 5 figs