Photoneutron angular distribution of 19F

Photoneutron time-of-flight spectra from the reaction 19F(γ,n0)18F were measured between 480 and 1390 using 10 m flight paths over the excitation energy range from 15-25 MeV. The measured values of the normalized Legendre a1 and a3 coefficients are very small or close to zero over the energy region studied, indicating dominance of E1 absorption in this region. A simple model-dependent analysis of the a2 coefficient showed that the likely reaction mechanisms are mainly s→p and d→p single-particle transitions of channel spin 1/2. A comparison of the present angle-integrated ground-state cross section with the (γ,ntot) work of Veyssiere et al. indicates that decays to excited states in 18F are much preferred (typically by a factor of 5) over the ground-state channel. The 19F(γ,n0) cross section shows reasonable agreement in structure and magnitude with the 19F(γ,p0) cross section of Kerkhove et al. as well as with the 18O(γ,n0) data of Jury et al. (although some discrepancies are seen at 16 MeV and above 23 MeV). (orig.)