Skyshine Line-Beam Response Functions for 20- to 100-MeV Photons

The line-beam response function, needed for skyshine analyses based on the integral linebeam method, was evaluated with the MCNP Monte Carlo code for photon energies from 20 to 100 MeV and for source-to-detector distances out to 1000 m. These results are compared with pointkernel results, and the effects of bremsstrahlung and positron transport in the air are found to be important in this energy range. The three-parameter empirical formula used in the integral line-beam skyshine method was fit to the MCNP results, and values of these parameters are reported for various source energies and angles.