The Defense Advanced Research Projects Agency (DARPA) of the U.S. Department of Defense concluded its biggest and longest test deployment of vehicle-mounted radiation detectors in Washington, D.C. This test was part of the SIGMA program, which aims to prevent attacks involving radiological “dirty bombs” and other nuclear threats.

Between July 2016 and February 2017, D.C. Fire and Emergency Medical Services ambulances were outfitted with DARPA-developed nuclear and radiological detectors, providing the first city-scale, dynamic, real-time map of background radiation levels throughout the capital as well as identifying any unusual spikes that could indicate a threat.

According to a press release, DARPA chose emergency vehicles for the test because they travel to every corner of the district, providing a large-scale scan for radiological risks.

Up to 73 large detectors were deployed, logging over 100,000 hours of detector operation and covering more than 150,000 miles. The detectors were able to distinguish benign sources — such as the natural granite used in construction and lingering radiation from medical services — from threatening ones in real time. This offered DARPA the opportunity to test and refine the wireless data fusion aspects of the system, which constantly fed information about vehicle location and radiation readings to a central command post.

In addition, the detectors provided detailed background radiation maps of the district against which future sources may be more easily detected. The deployment also offered an opportunity to test and refine the wireless data fusion aspects of the system, which constantly fed information about vehicle location and radiation readings to a central command post.

The devices run on advanced software that can detect the tiniest traces of radioactive materials. Those devices, networked with detectors along major roadways, bridges, and other fixed infrastructure, promise significantly enhanced awareness of radiation sources and greater advance warning of possible threats. The SIGMA detectors themselves do not emit radiation but detect gamma and neutron radiation emanating from sources.

In addition to vehicle-mounted detectors, the SIGMA project has also developed inexpensive, smartphone-sized mobile devices that can be worn on a belt by police officers or others. DARPA plans to further test SIGMA’s wide-area monitoring capability and transition the operational system to local, state, and federal entities in 2017 and 2018.