Dirty Bombs Continued

We have received several questions about our analysis of the dirty bomb threat published in the March/April PIR, and trust that the following addresses most of them.

• What were the technical parameters for your simulations? The Cs-137 source in example one was 2 curies (Ci); the Co-60 source in example two was 10,000 Ci; and the Am-241 source in example three was 10 Ci.  We assumed light winds of 2 mph, and complete dispersal of the materials.  For the Am-241 case, we assume an inhalable fraction of 20%.
• Why didn’t you challenge the linear no-threshold assumption?  We were asked to estimate the areas that would need to be decontaminated under existing EPA and NRC standards.  These guidelines, developed through standard agency procedures, use the linear no-threshold assumption. Clearly, there has been some controversy over the agencies’ decisions, but our analysis was not designed to reopen debate on this issue.  We did point out that there may be a need to rethink EPA safety guidelines in the event of a radiological attack.