Direct Measurement of Resonances in ${}^7\mathrm{Be}(\alpha ,\gamma ){}^{11}\mathrm{C}$ Relevant to $\nu p$-Process Nucleosynthesis

We have performed the first direct measurement of two resonances of the ${}^7\mathrm{Be}(\alpha ,\gamma ){}^{11}\mathrm{C}$ reaction with unknown strengths using an intense radioactive ${}^7\mathrm{Be}$ beam and the DRAGON recoil separator. We report on the first measurement of the 1155 and 1110 keV resonance strengths of $1.73\pm 0.25(\mathrm{stat})\pm 0.40(\mathrm{syst})\mathrm{eV}$ and ${125}_{-25}^{+27}(\mathrm{stat})\pm 15(\mathrm{syst})\mathrm{meV}$, respectively. The present results have reduced the uncertainty in the ${}^7\mathrm{Be}(\alpha ,\gamma ){}^{11}\mathrm{C}$ reaction rate to $\sim 9.4\%–10.7\%$ over $T=1.5–3\mathrm{GK}$, which is relevant for nucleosynthesis in the neutrino-driven outflows of core-collapse supernovae ($\nu p$ process). We find no effect of the new, constrained reaction rate on $\nu p$-process nucleosynthesis.

Figure 1

MCP/DSSSD versus BGO/DSSSD (separator) time of flight for the recoil events for each of the resonances we studied in the present Letter. For the 1110 keV resonance, we show the two independent measurements in separate panels. Positively identified ${}^{11}\mathrm{C}$ recoils for each resonance are shown. The ovals are used to help the reader’s eye.

Figure 2

BGO position profile spectrum for the $E_r=1155\mathrm{keV}$ resonance. The black points indicate the experimental data and the gray histogram a scaled Geant simulation. The centroid of the experimental peak is at $z_r=+0.47\mathrm{cm}$ with respect to the center of the gas target.

Figure 3

Comparison between the NACRE-I [20] and NACRE-II [21] ${}^7\mathrm{Be}(\alpha ,\gamma ){}^{11}\mathrm{C}$ thermonuclear reaction rate and that of Caughlan and Fowler [35] (CF88) and the present Letter for the same temperature region.