Unbound states studied by direct reactions
Résumé
The t(6He,8He)p t(8He,10He)p reactions were studied in experiments with 25A MeV 6He beam and 27.4A MeV 8He beams and an unique tritium gas target. Results on the 8He and 10He excitation energy spectra are presented. The 8He spectrum exhibits 3 states, apart of the ground state and known (2+) state at 3.6 MeV, the third state is seen at 5.4 MeV. A tentative assignment 1+ is proposed for this structure. The 10He spectrum shows no event at the excitation energy below 3 MeV what is in contradiction with the earlier reports on this nucleus. A high statistics of α-n coincidence events collected for the 8He beam run has been subjected to analysis in order search for the bound tetraneutron. The search produced a negative result.