Models, measurements and evaluation

A unified program of physical measurements and theoretical calculations for the provision of evaluated neutron data in the continuum region is outlined. The basic theoretical concepts are the optical, coupled-channel and statistical R-matrix models. The complementary measurement program provides the essential experimental foundation consisting primarily of neutron total and scattering cross sections. The integrated use of experiment and theory to provide evaluated data sets is discussed inclusive of: 1) average total and elastic scattering cross sections and the optical and coupled-channel models, 2) inelastic neutron scattering cross sections and the statistical and direct-reaction models, and 3) resonance statistics and fluctuations. The importance of physical concepts is emphasized throughout. (auth.)