The moments method is applied to the problem of calculating the neutron dose and fluence distributions in an infinite medium of air. These calculations are compared with Monte Carlo and Discrete Ordinates (S[subscript lower case]n) results. Simple parametric representations for the distributions are given which facilitate the calculation of dose and flux distributions in air with a different density.

The spatial and angular distributions of the fast-neutron dose rate in air as calculated by Monte Carlo methods are used to predict the results of fast-neutron dose rate measurements taken in unshielded vertical concrete-lined cylindrical holes at the ORNL-TSF. The agreement of the predictions with the measured data demonstrate that: 1) the air-scattered fast-neutron dose rate entering the holes is not appreciably affected by the presence of the air-ground interface, 2) the angular distribution of the air-scattered fast-neutron dose rate entering the holes for a given reactor angle does not vary significantly with distance for source detector separation distances between 100 and 450 ft., and 3) simplified calculational techniques based on the use of infinite-medium air-transport data for fast neutron radiation environment incident upon and in the holes.

The experiment provided confirmation, both qualitative and quantitative, of the "first-last collision model" of the air-ground interface effect.

The general description of the radiation field was determined for several neutron source energies in infinite air and in an air-over-ground geometry for source heights of 50 and 1125 feet. The effect on dose of source height and detector height and the effect of the ground on energy, angular, and time dependence is discussed for both fission and 12.2- to 15-MeV neutron sources. The satisfactory agreement of calculations with experimental results from operations BREN and HENRE and the agreement between Monte Carlo and discrete ordinates results lend confidence to the cross sections used and the computational techniques. (Author).