Photoneutron time-of-flight spectra from the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$(γ,${\mathrm{n}}_0$${)}^{13}$C reaction were measured as functions of laboratory angle over the excitation energy region from 10 to 28 MeV. Angular distribution coefficients and differential cross sections were extracted as functions of excitation energy between 10 and 23 MeV. The angle-integrated ground-state cross section indicates that ground state transitions dominate the $T_{<}$ giant dipole resonance region below 13 MeV, but only contribute about 50% of the strength in the neutron channel in the rest of the giant dipole resonance region. The results support a mechanism of dominant E1 absorption in the energy region from 13 to 23 MeV where an average value of $a_2$=-0.5 indicates $p_{1/2}$→$d_{3/2}$ single-particle neutron transitions. Angular distribution information suggests that much of a prominent resonance at 11.3 MeV (with an integrated cross section of about 1.03 MeV mb) is due to an M1 transition from the ground state of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$. If this is the case, there is little fragmentation of the M1 strength in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ brought about by the presence of valence neutrons. When combined with the observation of the lack of a pygmy E1 resonance below the giant dipole resonance region, these results suggest that a model of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ as a ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ‘‘core’’ with two valence, weakly coupled, neutrons is inappropriate. Below an excitation energy of about 19 MeV, there is reasonably good quantitative and qualitative agreement between the present data and the results of a recent shell model calculation.

• Received 27 August 1984

DOI:https://doi.org/10.1103/PhysRevC.31.318