7Be(n, α)4He Reaction and the Cosmological Lithium Problem: Measurement of the Cross Section in a Wide Energy Range at n_TOF at CERN

Barbagallo, M. and Bosnar, Damir and Žugec, Petar (n_TOF Collaboration) (2016) 7Be(n, α)4He Reaction and the Cosmological Lithium Problem: Measurement of the Cross Section in a Wide Energy Range at n_TOF at CERN. Physical Review Letters, 117 (15). pp. 152701-7. ISSN 0031-9007

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The energy-dependent cross section of the 7Be(n, α)4He reaction, of interest for the so-called cosmological lithium problem in big bang nucleosynthesis, has been measured for the first time from 10 meV to 10 keV neutron energy. The challenges posed by the short half-life of 7Be and by the low reaction cross section have been overcome at n_TOF thanks to an unprecedented combination of the extremely high luminosity and good resolution of the neutron beam in the new experimental area (EAR2) of the n_TOF facility at CERN, the availability of a sufficient amount of chemically pure 7Be, and a specifically designed experimental setup. Coincidences between the two alpha particles have been recorded in two Si-7Be-Si arrays placed directly in the neutron beam. The present results are consistent, at thermal neutron energy, with the only previous measurement performed in the 1960s at a nuclear reactor. The energy dependence reported here clearly indicates the inadequacy of the cross section estimates currently used in BBN calculations. Although new measurements at higher neutron energy may still be needed, the n_TOF results hint at a minor role of this reaction in BBN, leaving the long-standing cosmological lithium problem unsolved.

Item Type: Article
Keywords: 7Be(n, α)4He reaction, neutron time of flight, n_TOF, Cosmological Lithium Problem
Date: October 2016
Subjects: NATURAL SCIENCES > Physics
Additional Information: © 2016 American Physical Society. This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Received 22 June 2016; revised manuscript received 12 August 2016; published 3 October 2016.
Divisions: Faculty of Science > Department of Physics
Project code: HRZZ-IP-11-2013-1680
Publisher: American Physical Society
Depositing User: Gordana Stubičan Ladešić
Date Deposited: 29 Nov 2016 19:51
Last Modified: 29 Nov 2017 16:38
URI: http://digre.pmf.unizg.hr/id/eprint/5360

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