Investigation of the direct-capture reaction, He^3(α,γ)Be^7

The absolute cross section for the reaction, He^3(α,γ) Be^7, has been measured over the range of energies 181 ≤ E_(cm) ≤ 2493 keV, using a gas target behind a thin nickel entrance foil. Calibrated NaI(Tl) crystals were used to detect the prompt capture radiation. Over the entire energy region the measured total cross section and branching ratio confirm theoretical predictions based on calculations neglecting the contributions to the matrix elements from the region inside the nuclear radius. These cross-section measurements have been used to obtain a new value for the low-energy cross-section factor, S_o, for this reaction (S_o = 0.47 ± .07 keY barns), and this value has been used to reevaluate the importance of the He^3(α,γ) Be^7 reaction in the termination of the proton-proton chain in nuclear astrophysics.