Physics – Nuclear Physics – Nuclear Theory
Scientific paper
1996-02-21
Physics
Nuclear Physics
Nuclear Theory
13 pages, 4 postscript figures, to appear in "Zeitschrift f. Physik A", changed internet address and filename, the uuencoded p
Scientific paper
10.1007/s002180050084
Recent investigations suggest that the neutrino--heated hot bubble between the nascent neutron star and the overlying stellar mantle of a type--II supernova may be the site of the r--process. In the preceding $\alpha$--process building up the elements to $A \approx 100$, the $^4$He(2n,$\gamma$)$^6$He-- and $^6$He($\alpha$,n)$^9$Be--reactions bridging the instability gap at $A=5$ and $A=8$ could be of relevance. We suggest a mechanism for $^4$He(2n,$\gamma$)$^6$He and calculate the reaction rate within the $\alpha$+n+n approach. The value obtained is about a factor 1.6 smaller than the one obtained recently in the simpler direct--capture model, but is at least three order of magnitude enhanced compared to the previously adopted value. Our calculation confirms the result of the direct--capture calculation that under representative conditions in the $\alpha$--process the reaction path proceeding through $^6$He is negligible compared to $^4$He($\alpha$n,$\gamma$)$^9$Be.
Balogh W.
Efros Victor D.
Herndl H.
Hofinger R.
Oberhummer Heinz
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