Gamma-Ray Dose From an Overhead Plume

Abstract

Standard plume models can underestimate the gamma-ray dose when most of the radioactive material is above the heads of the receptors. Typically, a model is used to calculate the air concentration at the height of the receptor, and the dose is calculated by multiplying the air concentration by a concentration-to-dose conversion factor. Models indicate that if the plume is emitted from a stack during stable atmospheric conditions, the lower edges of the plume may not reach the ground, in which case both the ground-level concentration and the dose are usually reported as zero. However, in such cases, the dose from overhead gamma-emitting radionuclides may be substantial. Such underestimates could impact decision making in emergency situations. The Monte Carlo N-Particle code, MCNP, was used to calculate the overhead shine dose and to compare with standard plume models. At long distances and during unstable atmospheric conditions, the MCNP results agree with the standard models. At short distances, where many models calculate zero, the true dose (as modeled by MCNP) can be estimated with simple equations.

Atmospheric dispersion of chemical, biological, and radiological hazardous pollutants: Informing risk assessment for public safety

“…Radiation exposure can be evaluated using Monte Carlo codes, e.g., the Monte Carlo N-Particle Transport Code (MCNP) [ 237 , 238 ], FLUktuierende KAskade (FLUKA) [239] , and GEometry and Tracking (GEANT4) [240] . The MCNP code has been utilized with Gaussian plume models to estimate the gamma radiation from the overhead plume [241] and the photon count rate from the plume of 41 Ar emitted from a training reactor [242] . Monte Carlo codes are currently the most sophisticated and reliable method to evaluate the gamma dose, but the method requires detailed information on the properties of the medium and is timeconsuming, making it impractical to couple with atmospheric transport models, especially during an emergency.…”

Effective dose conversion coefficient for gamma ray exposure from an overhead plume

“…In the case of an overhead plume exposure scenario, particularly during the stable weather and elevated release conditions, the ground level concentration is zero and hence, the standard submersion model can significantly underestimate the external gamma dose (McNaughton et al 2017). In this situation, direct gamma exposure to the ground receptor must be evaluated using a finite plume model for the realistic estimation of Effective dose conversion coefficient for gamma ray exposure from an overhead plume the external dose rate (Lahti et al 1981, 1982, Wang et al 2004, Pecha Petr and Pechova 2014, McNaughton et al 2017, Krishan et al 2018. Although many point kernel-based studies are available for this overhead finite plume exposure computation, Monte Carlo based simulations are rare and only one study is available at this point of time (McNaughton et al 2017).…”

“…In this situation, direct gamma exposure to the ground receptor must be evaluated using a finite plume model for the realistic estimation of Effective dose conversion coefficient for gamma ray exposure from an overhead plume the external dose rate (Lahti et al 1981, 1982, Wang et al 2004, Pecha Petr and Pechova 2014, McNaughton et al 2017, Krishan et al 2018. Although many point kernel-based studies are available for this overhead finite plume exposure computation, Monte Carlo based simulations are rare and only one study is available at this point of time (McNaughton et al 2017). This is due to the complexities involved in the geometry modelling and computational time.…”