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Accuracy of Cloudshine Gamma Dose Calculations in the CAP-88 Dispersion Model

McNaughton, Michael W.; Gillis, Jessica M.; Ruedig, Elizabeth; Whicker, Jeffrey J.; Fuehne, David P.

doi: 10.1097/HP.0000000000000653
Operational Topics

The U.S. Environmental Protection Agency dispersion model, CAP‐88, calculates ground-level dose using the ground-level concentration and the semi-infinite cloud approximation. Doses can be underestimated for elevated plumes during stable atmospheric conditions at receptor locations within a kilometer downwind of a stack. The purpose of this paper is to identify when CAP‐88 calculations of gamma dose from cloudshine are inaccurate and provide estimates of the inaccuracy. The method used compares CAP‐88 estimates with Monte Carlo N-Particle (MCNP) estimates. Comparisons were made at distances of 800 m and 3,000 m downwind of the stack and for plume heights from 0 to 50 m. For these conditions, the annual dose calculated by CAP‐88 is greater than or equal to that calculated by MCNP.

*MS J978, Los Alamos National Laboratory, Los Alamos, NM 87545.

The authors declare no conflicts of interest.

Michael McNaughton is a Certified Health Physicist at Los Alamos National Laboratory. He studied mathematics at the University of Oxford and nuclear physics at the University of London and the University of California. Since then, he has worked for forty years in nuclear physics and health physics at Los Alamos National Laboratory. His email is

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