SEMIEMPIRICAL FORMULA FOR DIFFERENTIAL DOSE ALBEDO FOR FAST NEUTRONS ON IRON, ALUMINUM, SOIL AND CONCRETE.

Presented in this paper is a four-parameter formula for differential dose albedo which is based on the current of fast neutrons reflecting from iron, aluminum, soil and concrete. The fast neutrons have energy ranging from 0.1 to 14 Mev. The types of soil considered are dry, 50 saturated, and 100 saturated. In the derivation of this formula, it is assumed that the reflected neutrons are either singly scattered or scattered many times prior to their emergence from the scattering material. The group of neutrons between these two extremes are treated as a linear combination of the two extremes. The scattering cross section of the neutron is approximated by the first-order Legendre polynomial expansion in terms of the scattering angle. Four empirical parameters for the formula are obtained by a nonlinear regression method and are the best fit to the values of differential dose albedo obtained from Monte Carlo data for dose-reflection factors by Allen et al. The agreement between values of differential dose albedo obtained by the four-parameter formula and values obtained from the dose-reflection factors by Allen et al averages about 30. Further, there is even better agreement in the total dose albedo, which is the integrated values of the differential dose albedo over the entire hemisphere of the reflecting surface. Author