7Li(p→,γ)8Bereaction atEp=80–0 keV

The ${}^7\mathrm{Li}(p\to ,\gamma {)}^8\mathrm{Be}$ reaction has been studied in the laboratory energy range $E_p=80\mathrm{}$–0 keV. The vector analyzing powers $A_y\left(\theta \right)$ and the angular distributions of the cross section $d\sigma /d\Omega \left(\theta \right)$ for capture to the ground, first-, and third-excited states are reported. Additionally, the absolute cross section ${\sigma }_T\mathrm{}\left(E\right)\mathrm{}$ and (equivalently) the astrophysical $S$ factor $S\left(E\right)\mathrm{}$ have been measured for capture to the third-excited state. Calculations have been performed for all three transitions using the direct capture model to which the known nearby $M$1 resonances were added. While they predict the angular distribution observed for the cross section and analyzing power in the case of both the first and third-excited states of ${}^8$Be, they do not reproduce those for the ground state. These calculations predict negligible $M$1 strength below 80 keV for capture to the third-excited state ${(2\mathrm{}}^{+}$, $T=0+1\mathrm{}$, 16.6 MeV), and we therefore conclude that the extrapolation of the astrophysical $S$ factor for the ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ reaction, which has been performed previously by assuming pure $E$1 capture, is valid with regard to the neglect of any significant $p$-wave capture strength.