Applied theory of resolved and unresolved neutron resonances

This paper reviews utilization of resonance theory in basic and applications-oriented neutron cross section work. The basic resonance representations and the practically important resonance approximations are presented, with account of resonance parameter conversion, distant-level contributions, bound levels and Doppler broadening. Principal concepts and methods for reduction and analysis of resonance data are discussed, including flux and detector efficiency determination, instrumental resolution, multiple-scattering corrections as well as resonance parameter extraction by generalized (Bayesian) and conventional (maximum-likelihood) least-squares fitting. Level-statistical theory as used in the unresolved resonance region is reviewed, with emphasis on recent progress concerning calculation of resonance-averaged partial cross sections including width fluctuations and elastic enhancement, and on problems concerning the treatment of self-shielding. The review is illustrated with examples from recent evaluation work involving modern fitting and cross section generating codes