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$$^{7}$$Be($$n, alpha)^{4}$$He reaction and the cosmological lithium problem; Measurement of the cross section in a wide energy range at n_TOF at CERN

n_TOF実験施設における$$^{7}$$Be($$n, alpha)^{4}$$He反応の広い中性子エネルギーに対する断面積測定とビッグバン・リチウム問題

Barbagallo, M.*; Musumarra, A.*; Cosentino, L.*; Maugeri, E.*; Heinitz, S.*; Mengoni, A.*; Dressler, R.*; Schumann, D.*; K$"a$ppeler, F.*; 原田 秀郎 ; 木村 敦; n_TOF Collaboration*; 他124名*

Barbagallo, M.*; Musumarra, A.*; Cosentino, L.*; Maugeri, E.*; Heinitz, S.*; Mengoni, A.*; Dressler, R.*; Schumann, D.*; K$"a$ppeler, F.*; Harada, Hideo; Kimura, Atsushi; n_TOF Collaboration*; 124 of others*

The energy-dependent cross section of the $$^{7}$$Be($$n, alpha)^{4}$$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. 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.

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