Properties of bound states of 18O above the 4.45 MeV state

Abstract

The decay modes, spins and the mixing ratios of some of the de-excitation gamma rays of the 18O states located at 5.09, 5.25, 5.33, 5.37 and 5.52 MeV have been determined by p- γ angular correlation measurements using the 18O(p, p′ γ) 18O reaction. The 5.09 MeV level ( J π = 3 −) decays to the 3.92 MeV (14%), 3.55 MeV (5%) and 1.98 MeV (81%) levels; the mixing ratio of the 5.09 → 1.98 MeV transition is δ(5.09 → 1.98) = 0±0.02. The 5.25 MeV level ( J π = 2 +) decays to the 1.98 MeV (60%) and to the ground state (40%); δ(5.25 → 1.98) = 0.2±0.1. The 5.33 MeV level ( J π = 0 +) decays to the 4.45 MeV (27%), 3.92 MeV (10%) and 1.98 MeV (63%) levels. The 5.37 MeV level ( J π = 3 +) decays to the 3.92 MeV (15%) and 1.98 MeV (85%) levels; δ(5.37 → 1.98) = 0±0.05. The 5.52 MeV level ( J = 1, 2; the value J π = 2 − is suggested) decays to the 4.45 MeV (25%), 3.92 MeV (10%) and 1.98 MeV (65%) levels; if J = 2 then δ(5.52 → 4.45) = 0±0.04 and δ(5.52 → 1.98) = 0±0.02. A tentative interpretation of these results in the light of available theoretical calculations is presented. In particular, special reference is made to Harvey's model for the negative parity states and Engeland's core excitation model for the positive parity states.