I. INTRODUCTION A knowledge of the radiation field in air due to y-ray emitters distributed in the soil is important for estimating exposure rates from a given source concentration, evaluating hazards to the population, and properly interpreting and relating radiation measurements made at ground level and at airplane altitudes. The sources of this radiation are the naturally occurring radioisotopes, fallout from nuclear weapons tests, or unanticipated releases into the environment from a nuclear reactor installation. The calculation of the exposure rate in air due to these sources in the soil has usually been based on infinite medium buildup factors. The exposure rate from a distributed source in the soil was usually calculated by assuming a single medium composition, either all air if the sources were distributed close to the interface or all soil (aluminum was usually substituted for soil) if the sources were distributed throughout the soil half space. The easily computed direct beam exposure rate for each point source element in the chosen medium was multiplied by the appropriate buildup factor and an integration performed numerically (or analytically by substituting a functional fit to the buildup factor data) to obtain the total exposure rate‘), This rough solution was necessary because of the lack of analytical transport methods for solving the one-dimensional two-media Y-ray transport problem. The infinite medium buildup factor approach, besides failing to account for the differences in the transport properties of soil and air at low energies, provided no information on the energy and angle distribution of the y-rays entering the detector; information important for interpreting field measurements. In this report, we present accurate calculations of y-ray exposure rates in air (better than +5% S.D.) for source distributions characteristic of natural and fallout y-ray emitters in the soil as well as differential energy spectra,