Speaker
Description
The cosmological lithium problem [1] remains one of the major unresolved issues in nuclear astrophysics. It is related to the production and destruction channels of primordial $^{7}$Be, the main source of $^{7}$Li. Though the production channels of $^{7}$Be are well studied [2], improved measurements are required in the destruction reactions. The dominant neutron-induced destruction channels, $^{7}$Be$(n,p)^{7}$Li, $^{7}$Be$(n,p_{1})^{7}$Li$^{}(0.478)$, and $^{7}$Be$(n,\alpha)\alpha$, were previously investigated using the Trojan Horse Method (THM) through measurements of the $^{7}$Be + $d$ reaction at 3.16 MeV/u [3]. This resulted in a 10% reduction of the lithium discrepancy. Later, an indirect study of the $^{7}$Be$(n,p_{1})$ channel by Iwasa et al. [4] reported a significantly smaller cross section, implying a smaller contribution of this channel to the cosmological lithium problem than that inferred in Ref. [3]. In this work, we make a detailed study of the destruction channels of $^{7}$Be with neutrons via indirect methods. The experiment was carried out at HIE-ISOLDE, CERN, with a 5 MeV/u $^{7}$Be beam on a CD$2$ target [5]. The $^{7}$Be$(n,\alpha)\alpha$ reaction is studied via the THM, while the $^{7}$Be$(n,p_{1})$ cross section is derived from the $\Gamma_{p_{1}}/\Gamma_{p_{0}}$ ratios extracted from the $^{7}$Be$(d,p)^{8}$Be$^{}(p)^{7}$Li$^{*}$ reaction, as the $\Gamma_{p_{0}}$ values of the relevant excited states in $^{8}$Be are well known [6]. The present results lead to a few percent improvement in the lithium discrepancy. In addition, the $\Gamma_{p_{1}}/\Gamma_{p_{0}}$ ratios for the 20.9 MeV $(4^{-})$ and 21.5 MeV $(3^{+})$ states in $^{8}$Be are determined for the first time.
References:
1. A. Coc et al., Astrophys. J. Lett. 600, 544 (2004).
2. Carmona-Gallardo et al., Phys. Rev. C 86, 032801 (2012) (R).
3. S. Hayakawa et al., Astrophys. J. Lett. 915, L13 (2021).
4. N. Iwasa et al., Phys. Rev. C 112, 035801 (2025).
5. Sk M. Ali et al., Phys. Rev. Lett. 128, 252701 (2022).
6. L. Damone et al., Phys. Rev. Lett. 121, 042701 (2018).
| Category | Experiment |
|---|