Radiative Pion Capture inLi6

Abstract

The photon spectrum from the reaction ${}_{}{}^6{}_{}{}^{}\mathrm{Li}({\pi }^{-},\gamma )$ was measured with high resolution in the 50- to 150-MeV region by using an electron-positron pair spectrometer. The total fraction of pions absorbed radiatively is 4.4 ± 0.6% with branching ratios to the ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ ground state of 0.31 ± 0.04% and to the 1.8-MeV state of 0.15 ± 0.03%, in disagreement with previous experimental results, but in qualitative agreement with theoretical predictions. Evidence for higher excitations is observed in addition to quasifree capture accompanied by neutron emission.