The First Excited State of 9B

Abstract

The energy of the ! + first excited state of 9B is derived from the measured energy of the analogue state in 9Be together with calculated values of the Coulomb displacement energy. The latter include contributions from the internal Coulomb interaction, the electromagnetic spin-orbit interaction and the different external wavefunctions in 9Be and 9B. The ! + excitation energy is predicted to be greater in 9B than in 9Be,arising from an inverted Thomas-Ehrman shift, due to the 9Be state being above the 8 Be(g.s.) + s-wave neutron threshold. This result is in conflict with a recently published calculation (Sherr and Bertsch 1985), which was based on a single-particle potential model.