Cross section of He3(α,γ)Be7 around the Be

Abstract

Background: The 3 He(α, γ ) 7 Be reaction is a widely studied nuclear reaction; however, it is still not understood with the required precision. It has a great importance both in Big Bang nucleosynthesis and in solar hydrogen burning. The low mass number of the reaction partners makes it also suitable for testing microscopic calculations. Purpose: Despite the high number of experimental studies, none of them addresses the 3 He(α, γ ) 7 Be reaction cross sections above 3.1-MeV center-of-mass energy. Recently, a previously unobserved resonance in the 6 Li(p, γ ) 7 Be reaction suggested a new level in 7 Be, which would also have an impact on the 3 He(α, γ ) 7 Be reaction in the energy range above 4.0 MeV. The aim of the present experiment is to measure the 3 He(α, γ ) 7 Be reaction cross section in the energy range of the proposed level. Method: For this investigation the activation technique was used. A thin window gas-cell target confining 3 He gas was irradiated using an α beam. The 7 Be produced was implanted into the exit foil. The 7 Be activity was determined by counting the γ rays following its decay by a well-shielded high-purity germanium detector. Results: Reaction cross sections have been determined between E cm = 4.0 and 4.4 MeV with 0.04-MeV steps covering the energy range of the proposed nuclear level. One lower-energy cross-section point was also determined to be able to compare the results with previous studies. Conclusions: A constant cross section of around 10.5 μb was observed around the 7 Be proton separation energy. An upper limit of 45 neV for the strength of a 3 He(α, γ ) 7 Be resonance is derived.

Underground measurement at LUNA found no evidence for a low-energy resonance in the 6Li(p, γ)7Be reaction

“…No evidence for such a resonance was found in the 3 He( 4 He,γ) 7 Be reaction at E c.m. = 4210 keV as reported in recent comprehensive study [13].…”

Underground experimental study finds no evidence of low-energy resonance in theLi6(p,γ)Be7reaction

“…The new 7 Be excited state can potentially contribute as a resonance in the 3 He( 4 He,γ) 7 Be reaction at centerof-mass energy E ≈ 4210 keV and affect the extrapolation of the cross section to solar energies. However, a recent 3 He( 4 He,γ) 7 Be cross section measurement found no evidence for such resonance [29].…”

3He(α,γ)7Be cross section measurement around7Be known energy levels

“…Then the arrangement is modified by placing the entrance foil between the alpha source and the detector, and a collimator is placed along the source-foil-Figure 1. The new preliminary data compared to literature values [7,11]. The total uncertainty of the data is shown.…”

“…In 2019, the reaction cross section was measured around the proton separation energy of the compound 7 Be nucleus in E c.m. = 4.0−4.4 MeV [11].…”