Prompt Fission Neutron Spectra and Fragment Characteristics for Spontaneous Fission of Even-Numbered Plutonium Isotopes

A phenomenological scission point model including temperature-dependent shell effects is used to solve the energy partition problem as a function of mass asymmetry (A₁/A₂) for plutonium fission. Relevant fragment data such as average excitation energy and total kinetic energy are used as the basis for applying a temperature distribution model based on the Madland-Nix theory that includes the full mass number dependence of spectra, a realistic temperature distribution of fragments, a modified center-of-mass (CMS) spectrum ansatz, CMS anisotropy of neutron emission, and competition of neutron and gamma-ray emission. This new model describes neutron multiplicity, energy, and angular distribution of prompt fission neutrons. Calculated data for ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu spontaneous fission are presented and discussed in comparison with experimental data.