FOLDING ANGLE AND EXCITATION-ENERGY OF FRAGMENTS FROM U-235(N(TH),F) AND CF-252(SF) REACTIONS

Coincident fragments from U-235(n(th),f) and Cf-252(sf) reactions were investigated with a double-arm fission-fragment spectrometer and PIN- diode arrays. Based on the measurement of kinetic energy, velocity and direction of complementary fragments the total kinetic energy, the to tal mass, the individual fragment masses, the total number of emitted neutrons as well as the folding angle were deduced event by event. A n early linear correlation between average folding angle and average tot al excitation energy of the fragments (and, consequently, the average number of neutrons) was found. Fragment deflection by prompt neutron e mission is accordingly described by a complex statistical evaporation model in connection with a semi-empirical calculation of energy partit ion in nuclear fission. In addition, the folding-angle distribution du e to ternary fission is estimated. All experimental fragment distribut ions and correlations are well reproduced by the model calculations.