The National Nuclear Security Administration (NNSA) will spend the four days leading up to the Boston Marathon conducting a helicopter-based survey to measure naturally occurring background radiation in a ten square mile area west of downtown Boston. The measurements are being taken to “establish baseline levels [which] is a normal part of security and emergency preparedness”, especially before large public events such as the marathon.
A Government Accountability Office (GAO) report in 2006 reported “significant benefits” to such surveys in the event of nuclear terrorism:
There are significant benefits to conducting aerial background radiation surveys of U.S. cities. Specifically, the surveys can be used to compare changes in radiation levels to (1) help detect radiological threats in U.S. cities more quickly and (2) measure contamination levels after a radiological attack to assist in and reduce the costs of cleanup efforts.