Estimation of radioactivity levels associated with a 90Sr dirty bomb event

This paper reports the results of using a Gaussian model to estimate the maximum inhalation doses (mSv), the spatial extent (km2) and radioactivity (Bq) of contamination within an urban area after the initial dispersion of 90Sr radiological dispersion device (dirty bomb) in a terrorist event. For modeling purposes, aerosol dispersion of approximately 7 g of 90Sr equaling 3.7×1013 Bq (1000 Ci) with effective release heights of 50 and 100 m above street level is estimated under varying local-scale atmospheric conditions. Maximum inhalation doses at the level of 1, 5, 10, 50 mSv are used as evaluative criteria to assess probable consequences. The intentional release of a relatively small amount of 90Sr using a conventional explosive has the potential to cause internal exposure to beta-radiation with relatively high maximum inhalation doses achieving hundreds of mSv, but the spatial extent of the area within which high exposures might occur is very small with most of the population receiving maximum inhalation doses between 1 and 10 mSv. The extent of radiation contamination (area and activity) is dependent on 90Sr particle size, the height of release, and local weather conditions.