Differential neutron albedos for cylindrical water surfaces

Total albedos, as well as albedos differentiated in terms of both energy and direction, were calculated by means of a Monte Carlo program for cylindrical water surfaces of different radii of curvature. It is shown that a cylindrical coordinate system in which the polar angle is measured relative to the normal on the scattering surface is preferable to one in which this angle is measured relative to the axial direction of the surface. For small polar angles in the preferred system, even when the surface radius approaches the mean free path of the incident neutrons, the effect of this radius remains small. With increasing polar angles the effect of the surface radius becomes more important, especially for those neutrons moving more or less perpendicular to the axial direction of the surface. In the latter case, even at radii as large as 10 n mean free paths, the radial effect at a large polar angles is significant.