Abstract
Photoneutron angular distributions were measured by time-of-flight techniques for the reaction over the region of excitation energy from 15 to 25 MeV. Ground state cross sections were obtained by stepping the bremsstrahlung end point over the energy region of interest in 2 MeV intervals. By fitting the spectral data to a series of Legendre polynomials, angular distribution coefficients were extracted and interpreted on the basis of a simple single particle model. It appears that a large fraction of the photoabsorption strength leading to decays via the ground state channel is due to the formation of , states in which decay by -wave neutron emission. The data support an approximation of purely electric dipole absorption in the region measured. Some small amount of -wave neutron emission interfering with the dominant transition is consistent with an observed value for the coefficient of -0.7±0.2. The () cross section integrated between threshold and 30 MeV is estimated to represent about one-third of the total strength in the neutron channel. A state identified at 17.3 MeV is consistent in energy and composition with a theoretical prediction based on a shell model calculation using a residual interaction with a Soper mixture of exchange forces.
NUCLEAR REACTIONS , MeV; measured differential cross sections as function of angle; extracted Legendre coefficients; estimated matrix-element ratio in dipole approximation.
- Received 8 October 1982
DOI:https://doi.org/10.1103/PhysRevC.27.506
©1983 American Physical Society