Cross section of 3He(α, γ)7Be around the 7Be proton separation threshold

Szücs, T. and Kiss, G. and Gyürky, Gy. and Halász, Z. and Szegedi, T. and Fülöp, Zs. (2019) Cross section of 3He(α, γ)7Be around the 7Be proton separation threshold. PHYSICAL REVIEW C, 99. No.-055804. ISSN 0556-2813

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Abstract

Background: The 3He(α, γ )7Be 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 3He(α, γ )7Be reaction cross sections above 3.1-MeV center-of-mass energy. Recently, a previously unobserved resonance in the 6Li(p, γ )7Be reaction suggested a new level in 7Be, which would also have an impact on the 3He(α, γ )7Be reaction in the energy range above 4.0 MeV. The aim of the present experiment is to measure the 3He(α, γ )7Be 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 3He gas was irradiated using an α beam. The 7Be produced was implanted into the exit foil. The 7Be 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 Ecm = 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 7Be proton separation energy. An upper limit of 45 neV for the strength of a 3He(α, γ )7Be resonance is derived.

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