MULTI-PARAMETRIC MEASUREMENT OF PROMPT NEUTRONS AND FISSION FRAGMENTSFOR U-233(N(TH),F)

The multiplicity and the energy of prompt neutrons from the fragments for U-233(n(th), f) were measured as functions of fragment mass and to tal kinetic energy. Average neutron energy against the fragment mass s howed a nearly symmetric distribution about the half mass division wit h two valleys at 98 and 145 u. This shape formed a contrast with a saw -tooth distribution of the average neutron multiplicity. It indicates that the shell-effects, which are pronounced for the fragments having the proton number or neutron number close to the magic-number of 50 or 82, affected the neutron emission process. The slope of the neutron m ultiplicity with total kinetic energy depended on the fragment mass an d showed the minimum at about 130 u. The obtained neutron data were ap plied to determine the total excitation energy of the system, and the resulting value in the typical asymmetric fission lied between 22 and 25 MeV. The excitation energy agreed with that determined by subtracti ng the total kinetic energy from the Q-value within 1MeV: thus satisfi ed the energy conservation. In the symmetric fission, where the mass y ield was drastically suppressed, the total excitation energy is si,sig nificantly large and reaches to about 40 MeV, suggesting that fragment pairs are preferentially formed in a compact configuration at the sci ssion point.