The 5/2− Resonance at 850 keV in 15N(α,γ)19F

Abstract

A weak resonance at 850 keV in 15N(α,γ)19F corresponding to a level at 4681 ± 1 keV in 19F has been found. Angular distributions and Doppler shifts have been measured for the primary decays to the 5/2− level at 1.35 MeV (63%), 3/2− level at 1.46 MeV (31%), and the 5/2+ level at 197 keV (6%). A spin of 5/2 has been assigned to the resonance level and negative parity is shown to be very likely. The lifetime of the resonance was measured by the Doppler shift attenuation method to be τ = (15.4 ± 3.0) × 10−15 s or Γ = 42.8 ± 8.5 meV. The measured value of ωγ was 6.0 ± 1.0 meV. These measurements together with previous information on Γγ/Γ imply the observed M1 transition strengths are a factor of 20 weaker than predicted for the 5/2 member of the K = 3/2− band in 19F which has previously been associated with this level.