Resonance absorption for heavy moderators in homogeneous media

Abstract

Resonance absorption is investigated in homogeneous media with heavy moderators. An intermediate resonance approximation is developed in which intermediate parameters are introduced for both the absorber and the moderator scattering, and a method for calculating these intermediate parameters is developed. Monte Carlo calculations of resonance capture are done for some 238U resonances and for a set of moderator masses. The second-order methods of Chernick and Vernon and of Spinney, the intermediate resonance method of Forti and the intermediate resonance approximation developed in this paper are compared against Monte Carlo calculations. It is found that the intermediate resonance method developed in this paper compares best with the Monte Carlo results. Doppler coefficients calculated by the intermediate resonance approximation method of this paper are generally in agreement with the Monte Carlo calculations. An equivalence among homogeneous systems is established which states that homogeneous media with moderators of different mass but having the same effective moderator scattering cross section per absorber atom have the same resonance absorption for an individual resonance.