Stellar and Primordial Nucleosynthesis of ${}^7\mathrm{Be}$: Measurement of ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$

The ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ reaction presently represents the largest nuclear uncertainty in the predicted solar neutrino flux and has important implications on the big bang nucleosynthesis, i.e., the production of primordial ${}^7\mathrm{Li}$. We present here the results of an experiment using the recoil separator ERNA (European Recoil separator for Nuclear Astrophysics) to detect directly the ${}^7\mathrm{Be}$ ejectiles. In addition, off-beam activation and coincidence $\gamma$-ray measurements were performed at selected energies. At energies above 1 MeV a large discrepancy compared to previous results is observed both in the absolute value and in the energy dependence of the cross section. Based on the available data and models, a robust estimate of the cross section at the astrophysical relevant energies is proposed.

Figure 1

Results of the cross section measurements of the present work. The data are plotted in the form of the astrophysical $S$ factor as a function of the center-of-mass effective interaction energy. The results of previous work in the same energy range are also shown.

Figure 2

Ratio of the cascade-to-ground state transition intensities measured in this work as a function of the center-of-mass energy, compared to previous measurements.

Figure 3

Comparison of the results of the data of the present experiment and recent works with different model calculations fitted at $E\le 2000\mathrm{keV}$, see text for details. Data of the present work and 21: solid black line [36]. Data of 16, 17, 18, 20: solid grey line [32], dotted line [33].