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arXiv · nucl-th/9602033

Reaction rate for two--neutron capture by $^4$He

V. D. Efros·W. Balogh·H. Herndl·R. Hofinger·H. Oberhummer
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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 to $A \approx 100$, the $^4$He(2n,$γ$)$^6$He-- and $^6$He($α$,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,$γ$)$^6$He 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 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 $α$--process the reaction path proceeding through $^6$He is negligible compared to $^4$He($α$n,$γ$)$^9$Be.

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V. D. Efros, W. Balogh, H. Herndl, R. Hofinger, H. Oberhummer. 1996-02-27. Reaction rate for two--neutron capture by $^4$He. https://doi.org/10.1007/s002180050084

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