The potential for a radiological or nuclear attack has been widely acknowledged in the last two decades. The use of a dirty bomb by terrorist organizations is considered to be a credible threat for which policymakers and relevant security agencies must prepare. Radioactive materials are stored in thousands of facilities around the world and may not be adequately protected against theft. This article analyzes a hypothetical dirty bomb attack in a large metropolitan area, evaluating the radiation dose to the involved population. The dispersion of radioactive materials is simulated using HOTSPOT code, considering a number of possible radionuclides (alpha, beta and gamma emitters) and scenarios. The findings of the present study corroborate and extend previous research demonstrating that it is unlikely that the atmospheric dispersion of radioactive material contained in a dirty bomb would produce deterministic effects in the exposed population. The radioactive material would be dispersed into the air resulting in relatively low doses. However, depending on the situation, the explosion of a dirty bomb is likely to contaminate properties (rendering them temporarily uninhabitable), thereby requiring potentially costly cleanup. Furthermore, due to the general fear of radiation, pervasive psychological effects are expected.

The malevolent dispersion of radioactive material, with the aim of contaminating people and the environment, is considered a credible terroristic threat. This article analyzes a hypothetical Dirty Bomb detonation in an urban area, estimating the radiological consequences to the involved population and to first responders. The dispersion of radioactive material is simulated using the HOTSPOT code, considering the explosion of devices containing (alternatively) 60Co, 137Cs, 192Ir, 238Pu or 241Am sources, frequently used in medical or industrial settings. Each source is evaluated separately. The resulting ground deposition is used to calculate the effective dose received by first responders in two different scenarios. Based on the dispersed radionuclide, the influence of the use of personal protective respirators is analyzed. Confirming previous published results, this article illustrates that the radioactive material is diluted by the detonation, resulting in relatively low doses to the general public. However, the emergency workers’ stay time in the most contaminated area must be carefully planned, in order to limit the received dose. Due to the general fear of radiation, extensive psychological effects are expected in the public, irrespective of the evaluated radiation dose.

Conventional and non-conventional emergencies are among the most important safety and security concerns of the new millennium. Nuclear power and research plants, high-energy particle accelerators, radioactive substances for industrial and medical uses are all considered credible sources of threats both in warfare and in terror scenarios. Estimates of potential radiation releases of radioactive contamination related to these threats are therefore essential in order to prepare and respond to such scenarios. The goal of this paper is to demonstrate that computational modeling codes to simulate transport of radioactivity are extremely valuable to assess expected radiation levels and to improve risk analysis during emergencies helping the emergency planner and the first responders in the first hours of an occurring emergency.