The missing 1 2+ mirror state in 9B

Abstract

The status of the mirror state in 9B of the first excited 1 2+ 1.68 MeV state in 9Be is reviewed. The experimental evidence is inconclusive except for an apparent peak recently reported in a spectrum from the 9Be(6Li, 6He)9B reaction. This reaction has been reinvestigated at the same energy and angle but with substantially improved resolution and statistics, and the present results provide no evidence for the previously reported peak. Spectra obtained at other energies and angles have very low background and yet similarly fail to exhibit a peak. In addition, no evidence for population of the mirror state is found in spectra taken for the reaction 10B(9Be, 10Be)9B at two bombarding energies. The energy and width of the expected 1 2+ state in 9B remain open questions for which several different theoretical descriptions offer quite different predictions. Show more