Measurement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow/><mml:mn>7</mml:mn></mml:msup><mml:mi>Li</mml:mi><mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:mi>γ</mml:mi><mml:mo>,</mml:mo><mml:mi>t</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mn>4</mml:mn></mml:msup><mml:mi>He</mml:mi></mml:mrow></mml:math> ground-state cross section between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>E</mml:mi><mml:mi>γ</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mn>4.4</mml:mn></mml:mrow></mml:math> and 10 MeV
M. Münch, C. Matei, S. D. Pain, M. Febbraro, K. A. Chipps, H. J. Karwowski, C. Aa. Diget, A. Pappalardo, S. Chesnevskaya, G. L. Guardo, D. Walter, D. L. Balabanski, F. D. Becchetti, C. R. Brune, K. Y. Chae, J. Frost-Schenk, M. J. Kim, M. S. Kwag, M. La Cognata, D. Lattuada, R. G. Pizzone, G. G. Rapisarda, G.V. Turturică, C. A. Ur, Y. Xu
Abstract
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.