Measurements have been made of the neutron-neutron energy correlations for coincident neutrons emitted in the spontaneous fission of ²⁵²Cf. The hypothesis that cooling of the fission fragments during the cascade evaporation of prompt neutrons affects the energies of successive neutrons in a cascade has been investigated by a comparison of the energy correlations of coincident neutrons from the same fragment with those of coincident neutrons from opposite fragments in the same fission. It is found that the energies of coincident neutrons are posftively correlated and that the correlation coefficient is greater for neutrons from opposite fragments than for neutrons from the same fragment. This provides a sensitive test of the nature of neutron emission in an evaporation cascade. The energy correlations of random (noncoincidental) neutrons have also been investigated and are found to show similar but smaller correlation trends. It is concluded that there is some evidence for the cascade cooling effect on the energies of prompt fission neutrons.

No description available.

No description available.

No description available.

Note:

Simultaneous measurements of the angular distribution, mass distribution and average total kinetic energy of fission fragments produced by the neutron-induced fission of 235U and 232Th have been made using a gridded ionisation chamber. The neutron energy range used was thermal to 1.9 MeV for 235U and 1.4 to 1.7 MeV for 232Th. The following topics were investigated: the interdependence of the fission fragment angular and mass distribution; the anomalous behaviour of fragment anisotropy for 235U(n,f) at neutron energies En below 150 keV; the possible existence of a third symmetric mass peak for 232Th(n,f); the mass fine structure in 235U(n,f) and 232Th(n,f); and the dependence of the fission fragment average total kinetic energy on the excitation energy of the fissioning nucleus. For this study, mono-energetic neutrons were produced by the and reactions. Four signals produced by the fission chamber were fed into a data acquisition system and processed by a specially modified comprehensive computer program. The results indicate that there is no interdependence between the angular and mass distributions of fragments for 235U(n,f) and for 232Th(n,f). The angular distribution of 235U fission fragments showed an anisotropy of less than one for En below 150 keV. For 232Th, the expected minimum in the anisotropy near En = 1.6 MeV was confirmed. No evidence for a third peak in the mass symmetry region of 232Th(n,f) was observed, within the yield sensitivity limitation of the chamber. Fine structure was observed in the mass yield distributions for 235U(n,f) and 232Th(n,f) at mass locations predicted by theory. The fission fragment average total kinetic energy for 235U(n,f) and 232Th(n,f) showed no significant dependence on the excitation energy of the fissioning nucleus. Possible reasons for some of these results are advanced.

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Thesis (Ph. D. in Chemistry)--University of California, Berkeley, June 1958. / Includes bibliographies : p. 101-105.

Thesis--University of California, Berkeley, 1962. / Includes bibliographical references (p. 50-53).