2−Threshold State inBe8

Abstract

The ${2}^{\ensuremath{-}}$ level in $^{8}\mathrm{Be}$ at the threshold for the reaction $^{7}\mathrm{Li}(p,n)^{7}\mathrm{Be}$ is shown to be a virtual state relative to threshold. A description of the state as an $S$-matrix pole in the scattering-length approximation gives a good account of its properties as observed in different reaction channels, and, in particular, removes an apparent contradiction about its width as observed through particle and $\ensuremath{\gamma}$-ray channels. The width of the ${2}^{\ensuremath{-}}$ state is found to be about 50 keV.