Investigation of a Gaussian Plume in the Vicinity of an Urban Cyclotron Using Helium as a Tracer Gas

Abstract

Studies focusing on the radiological impact of fluorine 18 on populations living near to cyclotrons (<200 m) frequently assume normal distribution of atmospheric concentration for simplification purposes. On this basis, Gaussian models are used, despite their limits, as deployment requires little input data and computing resources. To estimate the ability of a Gaussian model to predict atmospheric dispersion in an urban environment, we used helium as a new passive tracer of atmospheric dispersion in the near-field range (<500 m) of the Beuvry hospital cyclotron (France). The atmospheric transfer coefficients (Formula presented.) measured in the field were compared with those modeled using a Gaussian equation. According to the results, helium is an effective tracer of atmospheric dispersion when attempting to determine atmospheric transfer coefficients ((Formula presented.) downwind of a discharge point. The Briggs-rural, Briggs-urban and Doury Gaussian models underestimate (Formula presented.) and sometimes maximum (Formula presented.) in the prevailing weather conditions during the experiments. By compiling the results of this study with data from the literature, it appears that the maximum (Formula presented.) observed obey a power law as a function of the distance from the discharge point, for distances from the discharge point in excess of 20 m.