2- States of 8Be

Abstract

The cross sections for several reactions populating sBe in the region of the 7Be+n threshold show rapid changes, which have been attributed to a 2- threshold state. An analysis of these data using R matrix theory shows that there is considerable isospin mixing in the threshold state, implying another 2 - state nearby. A two-level R matrix approximation provides a good fit to all the relevant data, with parameters consistent with shell model calculations and with properties of sLi. Proper account must be taken of the neutron threshold in order to explain the isospin mixing. The threshold state is expected to show different widths in different reactions.