Evaluation Of Thermal Neutron Scattering Cross Sections For Reactor Moderators PDF Download

Because of recent advances in experimental techniques, which improved the accuracies of thermal capture and scattering cross sections by an order of magnitude, a more stringent approach in the evaluation of the thermal constants is developed. In the present approach, the following aspects are introduced: (1) a consistency between thermal cross sections, coherent and incoherent scattering lengths, and neutron resonance parameters is achieved; (2) a consistency between the isotopic and element cross sections is sought; in addition, for each isotope, the requirement that the partial cross sections add up to the total is fulfilled; (3) where possible, charged particle data particularly derived from (d, p) reactions on light and medium weight isotopes are used in locating the positions and strengths of bound levels. Such a procedure is useful in the evaluation of the shape of the cross sections in the thermal region; and (4) the Lane-Lynn theory of direct capture is called upon to calculate thermal cross sections and check for consistencies for certain isotopes. Extensive examples to illustrate these procedures are presented.