Gamma-Ray Scattering Near an Air-Ground Interface

This paper reviews the status of experimental and theoretical gamma-radiation intensity at or near an air-ground interface. Various measurements of radiation scattered to a detector 3 ft above an air-ground interface containing a point source of ⁶⁰Co or ¹³⁷Cs at various distances are compared with Monte Carlo data and moments method calculations for an infinite homogeneous air medium. Other measurements and calculations of skyshine radiation backscattered by the air under similar circumstances are also analyzed. It is shown that the three approaches - experimental, Monte Carlo, and moments method - produce consistent results for ⁶⁰Co. For an infinite plane source of ¹³⁷Cs, however, experimental measurements over ice and over concrete indicate about 20% less scattered radiation over concrete than would be received from the same source in an infinite homogeneous air medium.