Calculation of Thermalization of Pulsed Neutrons by Few-Pole Expansion Method

Abstract

The thermalization of pulsed neutrons has been numerically calculated with the application of the few-pole expansion method, which gives an approximate solution in the form of a superposition of pseudo modes (functions of energy) with pseudo decay constants (also functions of energy). The time dependent neutron flux, the Cd and Gd γ-activation responses, as well as the neutron temperature in a pulsed water assembly have been obtained as examples, and the results compared with experimental data, with calculations by direct time integration method, and with calculated time eigenvalues of the medium. These examples attest to the efficacy of the few-pole expansion method, the adoption of only three pseudo modes having yielded accurate numerical solutions, with only a small fraction of the computing time required by other methods such as direct time integration.