Measurement of a highly retarded α-particle decay in 20Ne

The partial widths for α-particle and γ-ray decay of the second 2+ T = 1 level in 20Ne at 12.22 MeV have been measured. The reaction 19F(3He, d)20Ne was employed, with deuterons detected in singles and in coincidence with γ-rays from the decay of the 12.22 MeV level. The coincidence efficiency was determined using the 100% γ-decay of the 10.89 MeV 3+ T = 1 level. The ratio of the γ-decay width to the total width of the 12.22 MeV level was measured to be 0.88 ±0.05, which combined with a recent 16O(α, γ)20Ne measurement yields a very small α-particle width of 0.32±0.06 eV. This result is also of relevance to the radiative decay of the 18.43 MeV 2+ T = 2 level in 20Ne, and confirms a large discrepancy between the measured γ-decay width of the 2+ T = 2 level and the predictions of the shell model. © 1984.