Abstract
Photoneutron cross sections involving the emission of one and two neutrons from have been measured over the energy interval 8.5 to 39.7 MeV using monoenergetic photons from positron in-flight annihilation. The 6-MeV wide giant dipole resonance is observed to be centered at 23 MeV and a pygmy resonance is seen at about 13 MeV. Such structure as is apparent in the cross sections is not as pronounced as for the cases of and . Comparison of the total photoneutron cross section with recent ground-state data indicates that much of the pygmy resonance decays to the ground or first excited state of , but that the giant dipole resonance decays mainly to highly excited states in the daughter. Excellent agreement is observed between the present results and a recent two-particle, one-hole shell-model calculation of the isospin-split giant dipole resonance states for this nucleus. New photoneutron cross-section results for up to 39.7 MeV are reported as well.
NUCLEAR REACTIONS , MeV and , MeV; measured neutron yield for monenergetic photons; , , integrated cross sections, isospin splitting of the giant resonance for .
- Received 20 August 1979
DOI:https://doi.org/10.1103/PhysRevC.21.503
©1980 American Physical Society