This program evaluates the gamma-ray skyshine dose from an isotropic, monoenergetic, point gamma-photon source collimated into either a vertical cone (i.e., silo geometry) or into a vertically oriented structure with an N-sided polygon cross section. An overhead laminate shield composed of two different materials is assumed, although shield thicknesses of zero may be specified to model an unshielded skyshine source.

The skyshine dose calculation is based on a Monte Carlo algorithm to evaluate the gamma-ray transport through the source shields and the integral line-beam method, using an improved 3-parameter approximation for the line-beam response function, to describe the subsequent transport of gamma photons through the atmosphere. The source energy may be any energy between 0.02 and 100 MeV. In the Monte Carlo shield calculation, positron transport and bremsstrahlung production are neglected, although the air transport calculation using the line-beam response function does include these components. Consequently, for heavily shielded sources with energies above about 20 MeV, McSKY results must be used cautiously especially at detector locations near the source where shield-generated bremsstrahlung may be significant.

For a user's manual, see J.K. Shultis, R.E. Faw and M.H. Stedry, McSKY: A Hybrid Monte-Carlo Line-Beam Code for Shielded Gamma Skyshine Calculations, Report 9501, Institute for Computational Research in Engineering and Scinece, Kansas State University, Manhattan, KS, January 1995; also published as Report SAND95-1747, Sandia National Laboratory, Albuquerque, NM, August 1995. This report, in PostScript and Adobe PDF formats, is provided in the code distribution package available from this site.

For additonal details, see also M.H. Stedry, J.K. Shultis, and R.E. Faw, "Effect of an Overhead Shield on Gamma-Ray Skyshine," Nuclear Science & Engineering, 123, 289-294 (1996). Click for Abstract