The Neutron Velocity Spectrum in a Heavy Moderator¹

The differential equation developed by Wilkins to represent the velocity spectrum of neutrons in a heavy moderator is investigated for the case of 1/υ absorption. An exact solution to terms of second order in the absorption parameter allows an accurate determination of the asymptotic neutron density. For large absorption parameters a numerical integration can yield higher accuracy. The analytic solution is applied to the calculation of the total migration area of neutrons from a monoenergetic source.