The slowing down spectra of neutrons were obtained for heavy water, light water, and mixtures of heavy water and light water. It was assumed that fission neutrons are produced uniformly throughout an infinite moderator and the only process considered was elastic scattering, spherically symmetric in the center-of-mass system. The (n,2n) reaction with the deuterium nucleus and absorption were assumed negligible. The average transfer cross section, fast diffusion coefficient, the slowing down area, and average velocity ratio were obtained for two-group calculations using the epithermal spectra. (auth).

Ceramic fuel element specimens consisting of a uranium oxide-thorium oxide solid solution dispersed in beryllium oxide were fabricated by hot pressing in graphite dies. Details of fabrication techniques are given. Tests for overall composition, homogeneity and size and shape of fuel grains made during and at the completion of the work indicate that the specimens are in general agreement with initial specifications.