Properties of very n -rich He isotopes

Low-energy spectra of the 8, 10 He nuclei were investigated in the ( t , p ) -type reactions at small centre-of-mass angles using ∼ 25 AMeV beams of 6 He and 8 He nuclei. The 0 + ground state (g.s.) of 8 He and excited states, 2 + at 3.6-3.9MeV and (1 + ) at 5.3-5.5MeV, were populated with cross-sections of 200, 100-250, and 90-125μb/sr, respectively. To account for a near-threshold anomaly observed in the 8 He spectrum the population of a 1 - continuum (soft dipole excitation) was considered. The lowest-energy group of events in the 10 He spectrum was observed at ∼ 3 MeV with a cross-section of ∼ 140 μb/sr. This result is consistent with the previously reported observation of 10 He providing a new g.s. position for 10 He at about 3MeV.