The Los Alamos model of neutron emission in fission

Theoretical representations of two of the observables in prompt neutron emi ssion in fission are given, namely, the prompt fission neutron spectrum N(E ) and the average prompt neutron multiplicity <(nu)over bar>(p). Early repr esentations of these observables are presented and their deficiencies are d iscussed. This is followed by a description of the Los Alamos model for the calculation of the two quantities. Emphasis is placed upon predicitability and accuracy. In particular, the dependencies of N(E) and <(nu)over bar>(p ) upon the fissioning nucleus and its excitation energy are treated in deta il. Recent work in the calculation of the prompt fission neutron spectrum m atrix N(E, E-n), where E-n is the energy of the neutron inducing fission, i s then discussed. Concluding remarks address the current status of our abil ity to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches.