Abstract
A series of experiments has been performed to measure prompt neutron angular and energy distributions from thermal neutron-induced fission of 235,233U in correlation with the fission fragments. These distributions have been analyzed with the assumption of neutron isotropic emission from accelerated fission fragments. The performed analysis demonstrates that all obtained results can be described within 5% accuracy using this assumption. This discrepancy is approximately constant and doesn’t depend on fragment mass and the total kinetic energy (TKE). Some minor peculiarities of angular distribution may be interpreted as a result of anisotropy of the fission neutron angular distribution in the fragment center-of-mass system.
Highlights
It is well known that the main part of prompt fission neutrons are emitted from the excited fragments accelerated in the Coulomb field of nuclei
The direct answer to the question on properties of these additional neutrons could be obtained from the measurements of angular and energy distributions of prompt fission neutrons in the laboratory system in the correlation with the fission fragment characteristics
The total prompt neutron spectrum, PFNS, for all investigated isotopes agrees within experimental errors with one calculated in the assumption of anisotropy (A2 = 0.04) of the fission neutron angular distribution in the center-of-mass system of fragments (Fig. 4, right)
Summary
It is well known that the main part of prompt fission neutrons are emitted from the excited fragments accelerated in the Coulomb field of nuclei. Using the data of these works, it was ascertained [2] that about 0.4 neutrons per fission can not be described within the framework of a simple evaporation model. The direct answer to the question on properties of these additional neutrons could be obtained from the measurements of angular and energy distributions of prompt fission neutrons in the laboratory system in the correlation with the fission fragment characteristics. The measurements of this type were performed recently at the PNPI RAS. In the present paper we present first results of these measurements
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