Other
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.3309h&link_type=abstract
American Astronomical Society, 185th AAS Meeting, #33.09; Bulletin of the American Astronomical Society, Vol. 26, p.1363
Other
Scientific paper
Recent studies of the nucleosynthesis that occurs in the neutrino-driven wind following the delayed explosion of a Type II or Ib supernova have provided a promising site for the synthesis of the r-process isotopes. One worrisome aspect of such models has been a large overproduction of N=50 (closed neutron shell) nuclei. The conditions in the wind that favor production of these nuclei, Y_e ~ 0.45 - 0.46, S/N_Ak ~ 50 - 100, arise in about 0.01 M\sun \ of the ejecta at early times ( ~ 2 s). The overproductions are so great that, if these results were typical of all such supernovae, essentially no heavy element production (other than these rare nuclei) could occur. However, a successful r-process, which gives an appropriate total r-abundance ejecta per event, and reproduces the solar isotopic r-abundance distribution, does emerge from the same model at later times ( ~ 10 - 20 s) when the entropy is higher ( ~ 400) and Y_e is lower ( ~ 0.40). We have re-explored the nucleosynthesis in the same supernova model and included nu_e and bar nu_e capture reactions on free nucleons and heavy nuclei during the freeze out from nuclear statistical equilibrium. For only slightly larger ( ~ 5%) values of Y_e (i.e., Y_e ~ 0.485 instead of 0.46), the problematic nucleosynthesis disappears and is replaced by the moderate production of some long sought p-process nuclei, (74) Se, (78) Kr, (84) Sr, (92) Mo, and (96) Ru, thus turning the principal failure of this model into a success. The necessary minor adjustments to Y_e can probably be accounted for by small corrections to the electron and anti-electron neutrino fluences and temperatures in the model at early times without adversely altering the r-process that occurs at a later time. It is interesting that both r- and p-process nuclei can be produced in such close proximity. They would probably be mixed in the explosion.
Fuller George M.
Hoffman Robert D.
Meyer Bradley S.
Woosley Stan E.
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