Measurement of d+Be7 Cross Sections for Big-Bang Nucleosynthesis

Abstract

The cross sections of nuclear reactions between the radioisotope 7 Be and deuterium, a possible mechanism of reducing the production of mass-7 nuclides in Big-Bang nucleosynthesis, were measured at center-of-mass energies between 0.2 MeV and 1.5 MeV. The measured cross sections are dominated by the (d, α) reaction channel, towards which prior experiments were mostly insensitive. A new resonance at 0.36(5) MeV with a strength of ωγ = 1.7(5) keV was observed inside the relevant Gamow window. Calculations of nucleosynthesis outcomes based on the experimental cross section show that the resonance reduces the predicted abundance of primordial 7 Li, but not sufficiently to solve the primordial lithium problem.

Comment on "Measurement of d + 7Be Cross Sections for Big-Bang Nucleosynthesis"

“…Indeed, when switching this reaction on and off in our BBN codes using the FSU rate we obtain a decrease in the final 7 Li/H of 0.7%, in conflict with the 1.4-8.1% decrease reported in Ref. [2]. It is worth noting that the Erratum underestimates the fractional reduction in primordial Li according to its own calculations.…”

“…These numbers imply an absurdly small uncertainty in the primordial Li abundance prediction when the 7 Be+d rate is neglected. They also imply that by the authors' own calculations the reduction in Li/H for the upper limit of the Rijal et al reaction rate is 9.3%, not the 8.1% given in the Erratum [2].…”

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In a recent Letter entitled "Measurement of d + 7 Be Cross Sections for Big-Bang Nucleosynthesis", Rijal et al [1] describe the results of an experiment that put the 7 Be + d reaction rate on firmer ground. The erratum [2] claims that including this reaction rate in big bang nucleosynthesis (BBN) brings a significant reduction of up to 8.1% of lithium production relative to calculations that exclude this reaction. In contrast, using several well tested BBN codes, we confirm earlier studies showing that the effect is less than 1%, so that this measurement cannot alleviate the cosmological lithium problem.

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Progress in nuclear astrophysics of east and southeast Asia

“…Their contributions were found to be quite minor [158,159]. An important report from Florida group [160] is that the 7 Be(d,α) reaction might make a remarkable effect on destruction of 7 Be. All other reactions however need to be revisited before making a definite conclusion.…”

Cross-section Measurement of the Cosmologically Relevant 7Be(n, α)4He Reaction over a Broad Energy Range in a Single Experiment

“…Furthermore, the destructive 7 Be(d, p)2α channel has also been investigated without any significant impact on the lithium problem solution (see Pitrou et al 2018 for details). Most recently, the measurement of Rijal et al (2018) evaluated the impact of a new resonance at ∼360 keV; although it increases the total 7 Be(d, p)2α reaction rate, its contribution is not sufficient for solving the lithium problem. Additional solutions have been proposed, such as the recent study of Hartos et al (2018) to investigate the role of the 11 C levels intervening in the 7 Be(α, γ) 11 C; they concluded that these channels play a minor role in the lithium problem.…”