Angular correlation measurements in Ne 21

Abstract

The 1.75 MeV, 2.80 MeV, 2.87 MeV and 3.67 MeV states in Ne 21 were studied using the F 19(He 3, pγ)Ne 21 reaction at He 3 energies of 4.70 MeV and 5.20 MeV. Angular correlations between protons and gamma rays were measured with the proton counter at 0°. The spin assignment for the 1.75 MeV second-excited state was found to be J = 7 2 . A weak direct branch of about 6% from the 1.75 MeV state to the J π = 3 2 + ground state and the measured quadrupole to dipole amplitude ratio σ = 0.11±0.04 for the gamma transition to the J π = 5 2 + first-excited state imply a positive parity for the 1.75 MeV state. The J π = 1 2 + excited state at 2.80 MeV decays with a branching ratio of 50 : 50 to the ground state and first-excited state, respectively. From the 2.87 MeV excited state there exist a strong 1.12 MeV transition to the J π = 7 2 + state at 1.75 MeV accounting for more than 50% of the total decay. The decay of the 3.67 MeV excited state via a 0.87 MeV transition to the J π = 1 2 + state at 2.80 MeV accounts for more than 20% of the total decay. The angular correlation of the 0.87 MeV transition limits the possible spin assignments for the 3.67 MeV state to J = 1 2 and J = 3 2 . It is suggested, that the 3.67 MeV state belongs to the first-excited K = 1 2 + rotational band and has the assignment J π = 3 2 + .