Ground state gamma transitions from states at 10.09 and 10.24 MeV in N 14 and reinvestigation of the 9.17- and 10.43-MeV gamma ray distributions

Abstract

The angular distributions of the ground state transitions from the N 14 9.17- and 10.43-MeV levels have been reinvestigated using the reaction C 13(p, γ)N 14 at the 1.75- and 3.11-MeV resonances. From the value obtained for the anisotropy of the 9.17( J π = 2 +) →→0( J π = 1 +) transition limits on the quadrupole-dipole mixture are obtained. The 10.43-MeV state is assigned J = 2 using the results of previous investigations. From a distribution measurement limits are set on the quadrupole-dipole mixture in the 10.43 → 0 transition. A strong, energy dependent cos θ term was observed in the angular distribution of the ground state gamma rays for proton bombarding energies between 2.7 and 3.2 MeV. For this energy range the (p, γ) excitation functions have been determined at angles of 0°, 90° and 140° with respect to the proton beam and additional distribution measurements have been made in the neighbourhood of the 3.11-MeV resonance. The theoretical fits of these data present evidence that the cos θ term mainly arises from interference between the 10.43-MeV level and “non-resonant background” caused by the “long tailed” 0.55-MeV resonance corresponding to the 8.06-MeV, J π = 1 −, T = 1 state. In as much as this explanation of the cos θ term is likely the 10.43-MeV level must have even parity. Rather marked variations of the strength of the cos θ term at proton bombarding energies of 2.75 and 2.90 MeV show the presence of levels at 10.09- and 10.24-MeV excitation energy in N 14 which decay extremely weakly to the ground state. The 10.09-MeV state is also clearly observed in the excitation functions. Estimates of the total widths and gamma widths of both these states are obtained from the excitation functions. Gamma rays from states at 10.09 and 10.24 MeV have not been reported previously.