Abstract
One of the most puzzling problems in Nuclear Astrophysics is the “Cosmological Lithium Problem”, i.e the discrepancy between the primordial abundance of \(^{7}\)Li observed in metal poor halo stars (Asplund et al. in Astrophys J 644:229–259, 2006, [1]), and the one predicted by Big Bang Nucleosynthesis (BBN). One of the reactions that could have an impact on the problem is \(^{7}\)Be(n,p)\(^{7}\)Li. Despite of the importance of this reaction in BBN, the cross-section has never been directly measured at the energies of interest for BBN. Taking advantage of the innovative features of the second experimental area at the n\(\_\)TOF facility at CERN (Sabate-Gilarte et al. in Eur Phys J A 53:210, 2017, [2]; Weiss et al. in NIMA 799:90, 2015, [3]), an accurate measurement of \(^{7}\)Be(n,p) cross section has been recently performed at n\(\_\)TOF, with a pure \(^{7}\)Be target produced by implantation of a \(^{7}\)Be beam at ISOLDE. The mesurement started in April 2016 and lasted for two months. The experimental procedure, the setup used in the measurement and the results obtained so far will be here presented.
Highlights
The innovative neutron time-of-flight facility n TOF based on a neutron spallation source, was built at CERN with the aim of addressing the request of high accuracy nuclear data for Nuclear Astrophysics and for advanced nuclear energy systems [1]
The Cosmological Lithium Problem refers to the large discrepancy between the abundance of primordial 7Li predicted by the standard theory of Big Bang Nucleosynthesis and the value inferred from the so-called “Spite plateau” in halo stars
A possible explanation for this longstanding puzzle in Nuclear Astrophysics is related to the incorrect estimation of the destruction rate of 7Be, which is responsible for the production of 95% of primordial Lithium
Summary
The innovative neutron time-of-flight facility n TOF based on a neutron spallation source, was built at CERN with the aim of addressing the request of high accuracy nuclear data for Nuclear Astrophysics and for advanced nuclear energy systems [1]. In particular Nuclear Astrophysics presents many cases that require high precision neutron induced reaction data, for example to improve modelling of stellar Nucleosynthesis and Big Bang Nucleosynthesis. One of the most important unresolved problems in Nuclear Astrophysics is the so-called “Cosmological Lithium problem” (CLiP) [2] It refers to the large discrepancy (factor 2–3) between the abundance of primordial 7Li predicted by the standard theory of Big Bang Nucleosynthesis (BBN) and the value inferred from the so-called “Spite plateau” in halo stars. Concerning 7Be(n,α) reaction cross-section, only one measurement exists, performed at thermal energy in the 60’s [3]. The two measurements, performed with two different silicon detection systems, provide for the first time nuclear data on 7Be(n,α) and 7Be(n,p) cross-section in a wide neutron energy range, allowing to clarify the role of these reactions in Nuclear Astrophysics
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