7Be(n,p) cross section measurement for the Cosmological Lithium Problem at the n_TOF facility at CERN

Damone Lucia Anna,J Andrzejewski,N Colonna,P Finocchiaro,L Cosentino,M Barbagallo,M Mastromarco

doi:10.1051/epjconf/201818402004

Abstract

One of the most puzzling problems in Nuclear Astrophysics is the "Cosmological Lithium Problem", i.e the discrepancy between the primordial abundance of 7Li observed in metal poor halo stars [1], and the one predicted by Big Bang Nucleosynthesis (BBN). One of the reactions that could have an impact on the problem is 7Be(n,p)7Li. 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, an accurate measurement of 7Be(n,p) cross section has been recently performed at n_TOF, with a pure 7Be target produced by implantation of a 7Be beam at ISOLDE. The experimental procedure, the setup used in the measurement and the results obtained so far will be here presented.

Highlights

Theoretical models of the Big Bang Nucleosynthesis (BBN), i.e. the production of light elements in the first few minutes of the life of the Universe, correctly predict the abundance of all primordial elements except for 7Li that is overestimated by a factor of 3-5
This significant discrepancy between observation and predictions is known as the cosmological lithium problem (CLiP) [2]
9th European Summer School on Experimental Nuclear Astrophysics to the existing one consists in a flux up to 40 times higher

Summary

Introduction

Theoretical models of the Big Bang Nucleosynthesis (BBN), i.e. the production of light elements in the first few minutes of the life of the Universe, correctly predict the abundance of all primordial elements except for 7Li that is overestimated by a factor of 3-5. Since 95% of the primordial 7Li is produced by the electron capture decay of 7Be, a higher destruction rate of 7Be can solve or at least partially explain the CLiP In this scenario, reactions induced by neutrons on 7Be, in particular the 7Be(n,α)4He and the 7Be(n,p)7Li reactions, could play an important role in explaining this discrepancy. The recent construction of a second experimental area (EAR2) at n_TOF (Neutron Time of Flight) characterized by an extremely high instantaneous neutron flux (108 n/cm2/pulse), a good energy resolution and a low repetition rate, offered the unique opportunity to perform time-of-flight measurements of 7Be(n,p)7Li and 7Be(n,α)4He cross sections over a wide energy range (from thermal up to 1 GeV), covering the one of interest for the Big Bang Nucleosynthesis Results on the latter reaction have already been published [3]. Preliminary results on the (n,p) reaction are here reported

Experimental Setup

Data analysis

Findings

Conclusions