The Effect of Chemical Binding and Thermal Motion on a Pulse of Slowing Down Neutrons

By associating the absorption cross section with the Laplace transform variable in the time domain, it is shown how Corngold's asymptotic solution for slowing down can be applied directly to the problem of a pulse of neutrons slowing down in an infinite medium. In this way, the effect of chemical binding and thermal motion on the slowing-down time, dispersion and spectrum shape have been determined. Some new results for these quantities have been obtained, and the limitations of the asymptotic method have been pointed out. A first-order correction to the slowing-down time has been deduced for a finite medium large enough to be characterized by a DB² term.