Evaluation of ln E₁/E₂ for Resonance Neutrons in Uranium Lattices

The calculation of the resonance escape probability in a lattice by means of a diffusion theory model requires a knowledge of the logarithmic energy width, ln E₁/E₂, of the resonance absorption region. This quantity is evaluated by fitting the results of a diffusion theory analysis which is averaged over neutron energy to an experimental value of the effective resonance integral. The result is In E₁/E₂ ≃ 2.6, which is much less than the value 5.6 which is ordinarily used in these calculations.