Experimental Nuclear Astrophysics With the Light Elements Li, Be and B: A Review

G.G Rapisarda,L Lamia,Chengbo Li,S Degl’Innocenti,R.G Pizzone,S Romano,Qungang Wen,S Palmerini,C Spitaleri,E Tognelli,R Depalo,A Caciolli

doi:10.3389/fspas.2020.589240

Abstract

Light elements offer a unique opportunity for studying several astrophysical scenarios from Big Bang Nucleosynthesis to stellar physics. Understanding the stellar abundances of light elements is key to obtaining information on internal stellar structures and mixing phenomena in different evolutionary phases, such as the pre-main-sequence, main-sequence or red-giant branch. In such a case, light elements, i.e., lithium, beryllium and boron, are usually burnt at temperatures of the order of 2–5 × 106 K. Consequently, the astrophysical S(E)-factor and the reaction rate of the nuclear reactions responsible for the burning of such elements must be measured and evaluated at ultra-low energies (between 0 and 10 keV). The Trojan Horse Method (THM) is an experimental technique that allows us to perform this kind of measurements avoiding uncertainties due to the extrapolation and electron screening effects on direct data. A long Trojan Horse Method research program has been devoted to the measurement of light element burning cross sections at astrophysical energies. In addition, dedicated direct measurements have been performed using both in-beam spectroscopy and the activation technique. In this review we will report the details of these experimental measurements and the results in terms of S(E)-factor, reaction rate and electron screening potential. A comparison between astrophysical reaction rates evaluated here and the literature will also be given.

Highlights

Lithium, beryllium and boron are carriers of important information in several domain of astrophysics, from primordial Big Bang Nucleosynthesis (BBN) to cosmic ray nucleosyntheis (GCR nucleosynthesis) and stellar nucleosynthesis.Experimental Nuclear Astrophysics with LiBeBPrimordial nucleosynthesis is one of the three pillars of the Big Bang theory together with Hubble expansion and the relic Cosmic Microwave Background (CMB) radiation
The Trojan Horse Method (THM) has been used in order to extract the bare-nucleus S(E)-factor of the 9Be(p,α)6Li reaction at astrophysical energies avoiding extrapolations free of Coulomb suppression and electron screening effect
Indirect low-energy measurements of the 10B(p,α)7Be cross section performed with the THM are pivotal to disentangling the two components and avoiding possible uncertainty due to the extrapolation procedure

Summary

INTRODUCTION

Beryllium and boron (hereafter LiBeB, for simplicity) are carriers of important information in several domain of astrophysics, from primordial Big Bang Nucleosynthesis (BBN) to cosmic ray nucleosyntheis (GCR nucleosynthesis) and stellar nucleosynthesis (both for quiescent and explosive scenarios). Several efforts have been made within pure nuclear physics in the recent years to alleviate this deviation, as in the case of the recent cross section measurements of the 7Be(n,p) 7Li and 7Be(n,α) 4He neutron-induced reactions (Barbagallo et al, 2016; Lamia et al, 2017; Damone et al, 2018; Lamia et al, 2019), which affect the total 7Li primordial abundance Despite these efforts or new physics in BBN models [see e.g. The BBN calculations of (Coc et al, 2012) allow us to get the primordial abundances of boron (11B), N(11B)/N(H) ≈ 3 × 10−16 and beryllium N(9Be)/N(H) ≈ 3 × 10−18 at very low values with respect the ones observed up to now in halo-stars (Tan et al, 2009; Primas, 2010; Boesgaard et al, 2011). Lithium and boron abundances could be used to constrain neutrino driven nucleosynthesis, as recently suggested by Kusakabe et al (2019)

THE ROLE OF THE TROJAN HORSE METHOD IN NUCLEAR ASTROPHYSICS

STUDY CASES

Trojan Horse Method Measurements

Findings

CONCLUSIONS