Ratios of cross sections for ${}_{}{}^7{}_{}{}^{}\mathrm{Li}(p, n){}_{}{}^7{}_{}{}^{}\mathrm{Be}$ leading to the ground and first excited states of ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ have been measured at 24.8, 35, and 45 MeV. An analysis of these ratios yields the ratio of spin-flip to spin-nonflip strength, ${\left|\frac{V_{\sigma \tau }}{V_{\tau }}\right|}^2$, free of many of the uncertainties usually associated with distorted wave analyses for such light nuclei. The ratio increases by about 60% in the observed energy range. A comparison with known values of $V_{\tau }$ yields $V_{\sigma \tau }$. The isovector tensor force is also obtained.

• Received 14 January 1980

DOI:https://doi.org/10.1103/PhysRevLett.44.972