NEUTRON SPECTRA FROM MONOENERGETIC PHOTONS ON BISMUTH.
ILLINOIS UNIV URBANA DEPT OF PHYSICS
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Spectra of photoneutrons from a Bi209 target were obtained in the electric dipole giant resonance region 12 MeV - 16 MeV. Gamma-ray energy resolution of 1.5 was attained using a bremsstrahlung monochromator the neutron energies were measured with a time-of-flight technique with resolution which varied from 10 at 2 MeV to 15 at 6 MeV. About 88 of the neutrons emitted by 14-MeV gamma rays are statistical. The inferred level density of Bi208 near its ground state is not a simple function of excitation energy, but from 4 to 7 MeV it increases exponentially with energy in that energy range the temperature is about 1 MeV. The non-statistical high-energy neutrons leave the Bi208 nucleus at the excitation energies at which the states are well represented as single-neutron holes in Bi209. These high-energy neutrons are intimately connected with the giant resonance. If the giant resonance is dominated by a single dipole state, the absolute width which characterizes the decay of the dipole state into the compound nucleus must increase by a factor of about 3 between 12 and 16 MeV. Author
- Nuclear Physics and Elementary Particle Physics