Background: The He3(α,γ)Be7 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 He3(α,γ)Be7 reaction cross sections above 3.1-MeV center-of-mass energy. Recently, a previously unobserved resonance in the Li6(p,γ)Be7 reaction suggested a new level in Be7, which would also have an impact on the He3(α,γ)Be7 reaction in the energy range above 4.0 MeV. The aim of the present experiment is to measure the He3(α,γ)Be7 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 He3 gas was irradiated using an α beam. The Be7 produced was implanted into the exit foil. The Be7 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=4.0and4.4 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 Be7 proton separation energy. An upper limit of 45 neV for the strength of a He3(α,γ)Be7 resonance is derived.
ASJC Scopus subject areas
- Nuclear and High Energy Physics