Generalized Nelkin's expansion in plane lattices by perturbation calculus

Abstract

The decay of a neutron burst in a plane lattice with symmetric cells is computed by perturbation calculus up to the second order. The perturbation is shown to be negative when the unperturbed system is the homogeneous system obtained by volume averaging of the cross-section in the cell. As an illustration, generalized Nelkin's expansion is computed for plane water-beryllium lattices.