³H(α,γ)⁷Li reaction at low energies

The absolute cross section of the ³H(α,γ)⁷Li reaction has been measured for 50≤E_c.m.≤1200 keV. Specially prepared ³H targets were bombarded with an α⁺ beam, and γ rays were detected using an 85% high-purity germanium detector. Total S factors and the branching ratios for radiative capture to the two final bound states are reported for the entire energy range. Angular distributions of the capture γ rays were measured for nine energies in the range 115≤E_c.m.≤1200 keV. Legendre coefficients extracted from fits to the angular distributions are also reported. The energy dependence of the measured S factors is found to be in agreement with existing theoretical calculations. The new results are used to calculate the thermonuclear reaction rate for temperatures below 10 GK, required for computing the ⁷Li abundance in primordial nucleosynthesis.