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 Musumarra, A. and Cosentino, L. and Maugeri, E. and Heinitz, S. and Mengoni, A. and Dressler, R. and Schumann, D. and Käppeler, F. and Colonna, N. and Rauscher, T. and [et al.], . (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). p. 152701.

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The energy-dependent cross section of the 7 Be (n ,α ) 4 He 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 7 Be 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 7 Be, and a specifically designed experimental setup. Coincidences between the two alpha particles have been recorded in two Si - 7 Be -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.
Faculties and Departments:05 Faculty of Science > Departement Physik > Former Organization Units Physics > Theoretische Physik Astrophysik (Thielemann)
UniBasel Contributors:Rauscher, Thomas
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Physical Society
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:20 Feb 2017 11:23
Deposited On:20 Feb 2017 11:23

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