Experimental setup and procedure for the measurement of the 7Be(n,p)7Li reaction at n_TOF

Abstract

Following the completion of the second neutron beam line and the related experimental area (EAR2) at the n_TOF spallation neutron source at CERN, several experiments were planned and performed. The high instantaneous neutron flux available in EAR2 allows to investigate neutron indiced reactions with charged particles in the exit channel even employing targets made out of small amounts of short-lived radioactive isotopes. After the successful measurement of the 7 Be(n,α)α cross section, the 7 Be(n,p) 7 Li reaction was studied in order to provide still missing cross section data of relevance for Big Bang Nucleosynthesis (BBN), in an attempt to find a solution to the cosmological Lithium abundance problem. This paper describes the experimental setup employed in such a measurement and its characterization.

n + 7Be Cross-Sections of Astrophysical Interest at the CERN n_TOF Facility

“…Figure 5. The 6 Li(n, t) 4 He cross-section (circles) measured during the validation test, compared with the international standard (dashed line) [19].…”

Study of a data analysis method for the angle resolving silicon telescope

“…A new, highly sophisticated silicon telescope (SITE) has recently been introduced at n_TOF for measurements of the neutron induced reactions with charged particles in the exit channel [7]. It consists of two separate and segmented layers of 16 silicon strips, 5 cm × 3 mm each, placed in (a) (b) Figure 1: (a) Experimental setup housing the segmented silicon telescope (SITE), originally used for the measurement of the 7 Be(n, p) reaction.…”

“…Excellent particle discrimination capabilities of this silicon telescope have been clearly demonstrated [7] and it has already been successfully used in the challenging measurement of the 7 Be(n, p) reaction cross section, highly relevant for the long-standing Cosmological Lithium Problem [8]. This measurement has also been accompanied by the measurement of the 7 Be(n, α) reaction cross section [9], employing a similar type of silicon sandwich detector [10].…”

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

“…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 7 Li 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].…”

“…This significant discrepancy between observation and predictions is known as the cosmological lithium problem (CLiP) [2]. Since 95% of the primordial 7 Li is produced by the electron capture decay of 7 Be, a higher destruction rate of 7 Be can solve or at least partially explain the CLiP. In this scenario, reactions induced by neutrons on 7 Be, in particular the 7 Be(n,α) 4 He and the 7 Be(n,p) 7 Li reactions, could play an important role in explaining this discrepancy.…”