On the energy balance and on dynamical aspects of proton induced fission of 235,236,238U by coincident spectroscopy of neutrons and fragments

An improved experimental set up has been developed and applied to the measurement of neutrons in coincidence with fragments originating in proton induced fission of heavy nuclei. The reaction systems studied were p+235,236,238U for Ep = 12.84 MeV and Ep = 20.4 MeV. Data interpretation focuses on the following aspects: 1. Neutron multiplicities and average kinetic energies were studied as a function of fragment mass and total kinetic energies of these fragments. 2. The isotropic (i.e. the prefission plus scission) neutrons reveal a dependence of their multiplicities on the primary excitation energy E*CN that indicates a preference of the neutron over the fission exit channel with increasing E*CN not found in statistical model calculations. 3. A consistent analysis of all existing data for p+235,236,238U covering the interval 18 MeV ≤ E*CN ≤ 30 MeV in terms of neutron multiplicities and nuclear temperatures yields that pre- and postfission neutrons carry away comparable fractions of the additional energy ΔE*CN. 4. The total energy released in neutron and fragment emission is shown for p+238U (Ep = 20.4 MeV) to compare with the energy expected from mass tables for the fragmentations selected to within 2-3%. (orig.)