Abstract
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 α-process building up the elements toA≈100, the4He(2n,γ)6He- and6He(α,n)9Be-reactions bridging the instability gap atA=5 andA=8 could be of relevance. We suggest a mechanism for4He(2n,γ)6He and calculate the reaction rate within the α+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 orders 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 α-process the reaction path proceeding through6He is negligible compared to4He(αn,γ)9Be.
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Communicated by B. Povh
This work was supported by the Fonds zur Förderung der wissenschaftlichen Forschung in Österreich (project P10361-PHY), by the Österreichische Nationalbank (project 5054) and by the International Science Foundation and Russian Government (grant J4M100).