THE ANGULAR DISTRIBUTION OF FISSION FRAGMENTS FROM THE FAST NEUTRON-INDUCED FISSION OF U-234 (thesis)
Submitted to Univ. of Tennessee, Knoxville. The fast neutron-induced fission cross section of U/sup 234/ was measured from threshold to 4-Mev neutron energy. A maximum of 1.26 barns was found at 850 kev followed by a minimum of 1.10 barns at 8050 kev. The angular ani-sotropy of the fragment distribution was measured for neutron energies from 400 kev to 4 Mev. Extrema in the ratio sigma /sub f//( sigma /sub f(90 deg ) were found at 500, 850, and 1050 kev; the distribution at 500 kev showing a maximum in the direction normal to the beam (side-wise peaking) while that at 850 kev showed a maximum along the beam direction. The distribution at 8050 kev showed forward peaking but to a lesser extent than for energies immediately higher or lower. The behavior was analyzed according to the theories of Bohr and Wheeler. The dip in cross section between 850 and 1050 kev is consistent with the suggestion of Wheeler that neutron competition in the decay of the compound nucleus enters with increased strength in this area. Vibration-rotational levels in U/sup 234/ beginning at 790 kev are known to exist and inelastic neutron scattering to these levels serves to depress the fission cross section. The changes in fragment angular distribution are shown to be explainable in terms of the theory of Bohr which states that fission occurs through distinct channels composed of a K-band structure analogous to that observed at low excitations in heavy deformed nuclei. More detailed angular distribution measurements were carried out at 850 and 1050 kev. The overall picture is consistent with a K-band structure in U/sup 235/* near the saddle point deformation of K equals 1/2+, 3/2--, 1/2-- in that order, the bands being separated from each other by a few hundred kilovolts. (auth)
- Research Organization:
- Oak Ridge National Lab., Tenn.
- DOE Contract Number:
- W-7405-ENG-26
- NSA Number:
- NSA-16-029785
- OSTI ID:
- 4801173
- Report Number(s):
- ORNL-3306
- Country of Publication:
- United States
- Language:
- English
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