Estimating Total Effective Dose Equivalents from Terrorist Use of Radiological Dispersion Devices

Abstract

ABSTRACT Radiological dispersion devices (RDDs), commonly called “dirty bombs,” utilize a conventional explosive to deliberately disperse non-fissile material as an aerosol. This analysis models total effective dose equivalent (Sv) at various locations down-wind from the detonation site subsequent to terrorists detonating a 241Am, 137Cs, 60Co, 192Ir, or90Sr RDD. A source term for each isotope equaling 3.7 × 1013 Bq with an instantaneous release by either high explosives or low explosives at street level is assumed in order to evaluate total effective dose equivalent (TEDE) under various meteorological scenarios for intentional releases of non-fissile materials by terrorists. The inhalation pathway on average contributes most to TEDE. The inhalation pathway accounts for 96% (0.22 Sv) of the mean exposure estimate of 0.2321 Sv and occurs over an extremely short time frame (i.e., a few minutes). Ground shine, on average, contributes the second most to TEDE estimates accounting for approximately 4% (0.009 Sv) of the estimate. A cautionary note with regard to ground shine is warranted, however, because Hotspot estimates for this pathway are based on the assumption that a person is exposed for 4 days (96 hours). The TEDE for submersion (i.e., passing through the plume without inhaling particles) is negligible for the scenarios evaluated contributing less than 1% (5.2 × 10−6 Sv) to the TEDE estimate averaged across all 140 model runs (5 nuclides × 2 rainfall scenarios × 2 explosive scenarios × 7wind and atmospheric stability scenarios). The TEDE value for 241Am from inhalation is much greater, on average, than the inhalation TEDE value for 60Co, 137Cs, 192Ir, or 90Sr. This underscores the potentially high risk to human health posed by exposure to 241Am. Ground shine is the primary exposure pathway for 60Co and 137Cs due to the energetic and penetrating gamma rays those radionuclides emit. 192Ir and 90Sr have relatively low mean TEDE values for all of the pathways examined.