8He Spectroscopy with Stopped-Pion Absorption by 12C and 14C
The structure of the levels of heavy helium isotope 8He is investigated using the reactions of stopped-pion absorption by carbon isotopes 12С(π−, p3He)X, 14С(π−, d4He)X, and 14С(π−, t3He)X. Measurements are made with the two-arm multilayer semiconductor spectrometer at the LANL accelerator. Excited states of the 8He nucleus with energies of excitation of up to ~ 20 MeV are sought using the measured missing-mass spectra for these reactions. An excited state with Ex ≈ 6.4 MeV and Г ≤ 1 MeV is observed for the first time. Its structure is probably due to two valence nucleons on the (1p1/2)2 shell.