Neutron capture nucleosynthesis in the universe

Abstract

First, the nucleosynthesis in the universe was reviewed. In particular, the neutron capture nucleosyntheses in the Big-Bang and the s-and r-processes were reviewed in detail. It was pointed out that keV-neutron capture cross sections were important for the study on the neutron capture nucleosynthesis. Second, our measurement of keV-neutron capture cross sections was explained briefly, and the results on 7 Li, 12 C, and 16 O were shown and compared with previous experimental values and the predicted values from the 1/v law and the thermal neutron capture cross sections. The results at 30 keV on 12 C and 16 O were much larger than the 1/v predictions, while the result at 30 keV on 7 Li was in good agreement with the 1/v prediction. The large values for 12 C and 16 O were ascribed to the non-resonant p-wave neutron capture from the analysis of observed capture g-ray spectra and the neutron energy dependence of derived partial capture cross sections. As for 7 Li, the good agreement was ascribed to the peculiarity of bound states of its residual nucleus, which strongly suppresses the non-resonant p-wave neutron capture. Finally, it was shown that the non-resonant p-wave neutron capture is predominant in the neutron capture nucleosynthesis of light nuclei in the universe. q

RADIATIVE NEUTRON CAPTURE ON 9Be, 14C, 14N, 15N AND 16O AT THERMAL AND ASTROPHYSICAL ENERGIES

“…Therefore, continuing the analysis of the radiative capture of neutrons by light atomic nuclei, which is part of the different thermonuclear cycles [17][18][19][20] and take part in one of the variants of reaction chains for inhomogeneous Big Bang models [21][22][23][24][25] this allow to the synthesis of heavy elements via the next chain of neutron capture reactions 1 H(n, γ) 2 H(n, γ) 3 H( 2 H, n) 4 He( 3 H, γ) 7 Li(n, γ) 8 Li( 4 He, n) 11 B(n, γ) 12 B(β − ) 12 C(n, γ) 13 C(n, γ) 14 C(n, γ) 15 …”

The 7Li (n,γ)8Li radiative capture at astrophysical energies

“…For example, it is believed that the primordial nucleosynthesis followed the basic reaction chain of the form [6]: Furthermore, the reaction under consideration is the mirror reaction to the 7 Be(p, ) 8 B capture process, where 8 В decays into 8 Ве+e + + due to the weak interaction. Neutrinos from this reaction have rather high energy and have been registered on Earth over several decades, but the unstable 8 Ве nucleus decays into two -particles.…”

“…However, previous work [24] for the n 6 Li system showed that it is possible to use the allowed scheme {42} for 6 Li without taking into account its forbidden configuration {6}. Therefore, we will further consider the second variant of the FS structure and potentials with the allowed scheme {43} for 7 Li as the main variant of the classification of FS and AS in such a system.…”

Radiative n 10B Capture at Thermal and Astrophysical Energies

“…(31), because the 3 S 1 potential equals zero, completely determines the slope and location of the line in Fig. 7, shown the calculated cross section of the 3 Let us turn now to analysis of the total cross sections of 11 B(n, γ) 12 B reaction in the energy range 1-1000 keV and pay special attention to the signature of the resonances at 21 and 430 keV. In Fig.…”

“…The study of the reaction 11 B(n, ) 12 B, from the astrophysical point of view, may play a definite role in reaction chains in the so-called inhomogeneous Big Bang models 1,2,3,4,5 that allow to the synthesis of heavy elements via the next chain of neutron capture reactions: 1 H(n,) 2 H(n,) 3 H( 2 Н,n) 4 He( 3 Н,) 7 Li(n,) 8 Li( 4 Не,n) 11 B(n,) 12 B( -) 12 C(n,) 13 C(n,) 14 С(n,) 15 C( -) 15 N(n,) 16 N( -) 16 О(n,) 17 О(n, 4 He) 14 C… (1) While, the study of the reaction 10 B(n, ) 11 B, from the astrophysical point of view, is not so interesting because this capture channel will be negligible, as opposed to 7 Li(, ) 11 B, for production of 11 B for reaction chains of Eq. (1).…”