Angular correlation studies using the 13C( 3He,pγ) 15N reaction

Abstract

Levels in 15N up to 8.57 MeV excitation energy were studied using the 13C( 3He, pγ) 15N reaction at 3He energies of 4.95 and 5.25 MeV. Angular correlations between protons and gamma rays were measured with the proton counter either at 0° or 180°. The spin assignments for the 7.16, 7.57 and 8.57 MeV states were found to be J = 5 2 , J = 7 2 and J = 3 2 , respectively. The possible spin assignments for the 8.31 MeV state are J = 1 2 or J = 3 2 . Branching ratios were measured for all states. The 6.33 MeV J π = 3 2 − and the 7.31 MeV J π = 3 2 + states decay to the ground state only. The 7.16 and the 7.57 MeV state decay to the 5.28 MeV state only with quadrupole to dipole amplitude ratios δ = −0.04±0.05 and δ = −0.04±0.01, respectively. The octupole to quadrupole amplitude ratio for the transition from the 5.28 MeV J π = 5 2 + state to the ground state is ϱ = −0.09±0.02 or 4.5±0.3. The 8.31 MeV state decays to the ground state, the 5.3 MeV doublet, the 6.33 MeV state and the 7.31 MeV state with branching ratios of 70 : 12 : 12 : ≦ 6. The 8.57 MeV state decays to the ground state, the 5.28 MeV state and the 6.33 MeV state with branching ratios of 27 : 66 : ≦ 7. For the quadrupole to dipole amplitude ratio of the transition from the 8.57 MeV state to the 5.28 MeV state we get δ = 0.03±0.05. The results are discussed in the framework of Lane's weak-coupling model and compared with shell model predictions.