Neutron capture cross section measurements for nuclear astrophysics at CERN n_TOF

Abstract

A series of neutron capture cross section measurements of interest to nuclear astrophysics have been recently performed at n TOF, the neutron spallation source operating at CERN. The low repetition frequency of the proton beam driver, the extremely high instantaneous neutron flux, and the low background conditions in the experimental area are optimal for capture cross section measurements on low-mass or radioactive samples. An overview of the measurements performed during the two experimental campaigns in 2002 and 2003 is presented with special emphasis on the measurement of the capture cross sections of the Os isotopes relevant for the cosmochronology based on the Re/Os clock.

Experimental nuclear astrophysics in Italy

“…THM is a powerful indirect method, which requires normalization to high energy data but which allows for the exploration of the very low energy region also removing the electron screening effect. Results are expected in the near future by LUNA on 2 H(p,γ) 3 He and by AsFiN with the THM on 3 He(α,γ) 7 Be, 3 He(n,p) 3 H, 7 Be(n,α) 4 He and 7 Be(n,p) 7 Li. Another series of key experiments for BBN studies has been carried out at n TOF, the neutron Time-of-Flight facility at CERN, where the 7 Be(n,p) 7 Li and 7 Be(n,α) 4 He reactions have been directly measured for the first time in a wide energy range, providing additional constrains for the reaction rates used in BBN.…”

“…A minimal nuclear network for BBN calculations includes about 8 isotopes and 12 reactions. Two of these reactions have been studied in the underground Gran Sasso Laboratory (LNGS) by LUNA (Laboratory for Underground Nuclear Astrophysics) inside the energy region of astrophysical interest taking advantage of the background suppression: 3 He(α,γ) 7 Be and 2 H(α,γ) 6 Li. The former has also been studied by ERNA (European Recoil separator for Nuclear Astrophysics) at higher energies.…”

“…The former has also been studied by ERNA (European Recoil separator for Nuclear Astrophysics) at higher energies. Moreover, the reactions 2 H( 2 H,p) 3 H, 2 H( 2 H,n) 3 He, 3 He( 2 H,p) 4 He and 7 Li(p,α) 4 He have been studied by AsFiN with the Trojan Horse Method (THM). THM is a powerful indirect method, which requires normalization to high energy data but which allows for the exploration of the very low energy region also removing the electron screening effect.…”

“…The published results of all these experimental efforts have excluded the nuclear solution to the controversial cosmological 6 Li problem and have ruled out the neutron-induced reactions as potential explanation of the cosmological 7 Li problem. Furthermore, 2 H( 2 H,p) 3 H and 2 H( 2 H,n) 3 He are presently studied after cluster Coulomb explosion in laser-induced plasma by AsFiN. Finally, anti-nuclei production is studied by ALICE at CERN LHC and it will be refined in the future.…”

“…Its cross section is too low to be measured in laboratory conditions, so that theoretical estimations are currently used in stellar models calculations. However, measurements are possible for other reactions of the pp chain, which are of primary interest to understand the solar-neutrino flux at Earth and for the nucleosynthesis of some light isotopes, such as 3 He and 7 Li (see, e.g., [11]). Concerning the CNO cycle, the leading reaction is 14 N(p,γ) 15 O, which has been studied at LUNA.…”