Experimental Evidence For Subshell Closure In He-8 And Indication Of A Resonant State In He-7 Below 1 Mev

The spectroscopy of the unstable He-8 and unbound He-7 nuclei is investigated via the p(He-8, d) transfer reaction with a 15.7A MeV He-8 beam from the SPIRAL facility. The emitted deuterons were detected by the telescope array MUST. The results are analyzed within the coupled-channels Born approximation framework, and a spectroscopic factor (CS)-S-2=4.4 +/- 1.3 for neutron pickup to the He-7(g.s.) is deduced. This value is consistent with a full p3/2 subshell for He-8. Tentative evidence for the first excited state of He-7 is found at E-*=0.9 +/- 0.5 MeV (width Gamma=1.0 +/- 0.9 MeV). The second one is observed at a position compatible with previous measurements, E-*=2.9 +/- 0.1 MeV. Both are in agreement with previous separate measurements. The reproduction of the first excited state below 1 MeV would be a challenge for the most sophisticated nuclear theories.