8He Spectroscopy with Stopped-Pion Absorption by 12C and 14C

Abstract

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 E_x ≈ 6.4 MeV and Г ≤ 1 MeV is observed for the first time. Its structure is probably due to two valence nucleons on the (1p_1/2)² shell.