Nuclear Reactions of Astrophysical Interest Involving Light Nuclei

Abstract

An introduction to nucleosynthesis, the creation of the elements in the big bang, in interstellar matter and in stars is given. The two--step process ${}^4$He(2n,$\gamma$)${}^6$He and the reverse photodisintegration ${}^6$He($\gamma$,2n)${}^4$He involving the halo nucleus ${}^6$He could be of importance in the $\alpha$--process in type--II supernovae. The reaction rates for the above processes are calculated using three--body methods and show an enhancement of more than three orders of magnitude compared to the previous adopted value. Direct--capture calculations give similar values for the above reaction rates. Therefore, this method was also used to calculate the reaction rates of the two--step processes ${}^6$He(2n,$\gamma$)${}^8$He and ${}^9$Li(2n,$\gamma$)${}^{11}$Li and the reverse photodisintegration of ${}^8$He and ${}^{11}$Li that could be also of importance in the $\alpha$-process.

Comments: 13 pages, using fbssuppl.sty plus 3 postscript figures available as separate uuencoded file. The postscript file with the text and 3 figures is available at ftp://is1.kph.tuwien.ac.at/pub/ohu/twostep.ps