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論文

$$^7$$Be(n,p)$$^7$$Li reaction and the cosmological lithium problem; Measurement of the cross section in a wide energy range at n_TOF at CERN

Damone, L.*; Barbagallo, M.*; Mastromarco, M.*; Cosentino, L.*; 原田 秀郎; 木村 敦; n_TOF Collaboration*; 他152名*

Physical Review Letters, 121(4), p.042701_1 - 042701_7, 2018/07

We report on the measurement of the $$^7$$Be(n,p)$$^7$$Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and they showed a large discrepancy between each other. The measurement was performed with a Si telescope and a high-purity sample produced by implantation of a $$^7$$Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with the values inferred from the time-reversal $$^7$$Li(p,n)$$^7$$Be reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. The relevance of these results on the near threshold neutron production in the p+$$^7$$Li reaction is also discussed.

論文

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

Barbagallo, M.*; Andrzejewski, J.*; Mastromarco, M.*; Perkowski, J.*; Damone, L. A.*; Gawlik, A.*; 木村 敦; n_TOF Collaboration*; 他122名*

Nuclear Instruments and Methods in Physics Research A, 887, p.27 - 33, 2018/04

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 induced 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,$$alpha$$)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.

論文

$$^7$$Be(n,$$alpha$$) and $$^7$$Be(n,p) cross-section measurement for the cosmological lithium problem at the n_TOF facility at CERN

Barbagallo, M.*; Colonna, N.*; Aberle, O.*; 原田 秀郎; 木村 敦; n_TOF Collaboration*; 他125名*

EPJ Web of Conferences (Internet), 146, p.01012_1 - 01012_4, 2017/09

 パーセンタイル:100

The Cosmological Lithium Problem refers to the large discrepancy between the abundance of primordial $$^7$$Li predicted by the standard theory of Big Bang Nucleosynthesis and the value inferred from the so-called "Spite plateau" in halo stars. A possible explanation for this longstanding puzzle in Nuclear Astrophysics is related to the incorrect estimation of the destruction rate of $$^7$$Be, which is responsible for the production of 95% of primordial Lithium. While charged-particle induced reactions have mostly been ruled out, data on the $$^7$$Be(n,$$alpha$$) and $$^7$$Be(n,p) reactions are scarce or completely missing, so that a large uncertainty still affects the abundance of $$^7$$Li predicted by the standard theory of Big Bang Nucleosynthesis. Both reactions have been measured at the n_TOF facility at CERN, providing for the first time data in a wide neutron energy range._1

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