Distribution of Prompt-Neutron Emission Probability for the Fission Fragments of U233

The kinetic energies of both members of coincident fragment pairs were measured in a double back-to-back grid ionization chamber. The pulse heights were recorded only when coincident with a prompt fast neutron detected in either one of two neutron counters placed on opposite sides of the fission chamber. The strong angular correlation of the direction of motion of the prompt fission neutrons with the direction of motion of the emitting fragment permitted the identification of the latter as the emitting fragment. The frequency distributions of modes obtained by gating with a neutron from the light or from the heavy fragment were compared with the distribution recorded without a neutron coincidence. Comparison of the three sets of data show (1) that neutron emission from the light fragment predominates at low mass ratios, whereas at high mass ratios neutron emission from the heavy fragment is more probable; (2) that a broad maximum in the total neutron yield exists in the region of the most probable fission mode; and (3) that the average total kinetic energy curve is essentially the same for the three conditions of measurement.