Measurement of the 7 Li ( γ , t ) 4 He ground-state cross section between E γ = 4.4 and 10 MeV

The $^{7}\\mathrm{Li}(\\ensuremath{\\gamma},t)^{4}\\mathrm{He}$ ground state cross section was measured for the first time using monoenergetic $\\ensuremath{\\gamma}$ rays with energies between 4.4 and 10 MeV at the High Intensity Gamma-ray Source. The reaction is important for the primordial Li problem and for testing our understanding of the mirror $\\ensuremath{\\alpha}$-capture reactions $^{3}\\mathrm{H}(\\ensuremath{\\alpha},\\ensuremath{\\gamma})^{7}\\mathrm{Li}$ and $^{3}\\mathrm{He}(\\ensuremath{\\alpha},\\ensuremath{\\gamma})^{7}\\mathrm{Be}$. Although over the last 30 years most measurements of the $^{3}\\mathrm{H}(\\ensuremath{\\alpha},\\ensuremath{\\gamma})^{7}\\mathrm{Li}$ reaction have concentrated in an energy range below ${E}_{\\ensuremath{\\gamma}}=3.65$ MeV, measurements at higher energies could potentially restrict the extrapolation to astrophysically important energies. The experimental arrangement for measuring the $^{7}\\mathrm{Li}(\\ensuremath{\\gamma},t)^{4}\\mathrm{He}$ reaction included a large-area silicon detector array and several beam characterization instruments. The experimental astrophysical $S$ factor of $^{3}\\mathrm{H}(\\ensuremath{\\alpha},\\ensuremath{\\gamma})$ calculated from the present data was fitted using the $R$-matrix formalism. The results are in disagreement with previous experimental measurements in the same energy range but the extrapolated $S$ factor agrees with the potential model calculation and lower energy experimental data.