Since the invention of nuclear power, there have been numerous “accidents.” From Three Mile Island and Chernobyl to the more recent problems in Fukushima, it would seem nuclear power is not fully under our control. Recently a Chinese scientist has warned that the single mountain under which North Korea most likely conducted its five most recent nuclear bomb tests, including the latest and most powerful could be at risk of collapsing. Wang Naiyan, the former chairman of the China Nuclear Society and senior researcher on China’s nuclear weapons program, said that if Wen’s findings were reliable, there was a risk of a major environmental disaster. Another test might cause the whole mountain to cave in on itself, leaving only a hole from which radiation could escape and drift across the region, including China, he said. Terrorist attacks involving the use of radiological and nuclear materials also pose a potential threat to U.S. citizens and service members.
Early detection of these materials and devices made from them is a critical part of the U.S. strategy to prevent attacks. Sensitive, compact, real-time, and low-cost detectors, along with innovative deployment and networking strategies, would significantly enhance detection
and deterrence of such an attack. One of thrust areas of DARPA is to counter CBRNE threats by developing and testing networked, mobile and cost-effective nuclear- and radiological-weapons detectors that can easily be deployed to provide real-time surveillance over city-scale areas.
Current handheld radiological detectors are expensive and lack networking capability. In addition, existing neutron detectors used
for nuclear materials detection at, for example, ports of entry, are large, expensive, and rely on exotic materials, such as helium-3, a rare isotope of helium that can capture a neutron from radiating nuclear sources. These limitations have prohibited widescale and continuous deployment of radiation detection systems. Adding further complexity to the situation, abundant sources of non-threatening radiation
in hospitals, on sites, and in industry settings can trick existing detectors, causing false alarms.
The SIGMA program began in 2014 with the challenge to the technology community of transforming nuclear and radiological threat detection for city-scale monitoring. It was designed to investigate new technologies that have the potential to protect city-and metropolitan-sized areas from radiological and nuclear-based terror threats through large-scale deployment of low-cost, high-capability radiation sensors and automated detection algorithms to provide real-time alerts of potential threats.
Key components of the SIGMA system include small and large form-factor mobile and static radiation sensors intended to support agile deployment strategies; the network infrastructure to connect thousands (up to ten thousand) of these sensors; the cloud-computing infrastructure to automatically analyze streaming spectroscopic data from these sensors in real-time as well as store—in an easily retrievable manner—many billions of these spectra for spatiotemporal and forensic analyses.
The task required fundamental advances in a range of fields including sensing, data fusion, analytics, and social and behavioral modeling. Realizing this capability required significant advances in:
• low-cost, high-capability detectors that can be networked together;
• scalable network architecture using commercial cellular communications and open-source network infrastructure that can handle tens of thousands of realtime sensor feeds; and
• efficient algorithms that maximize detection and source-tracking capabilities while minimizing false alarms and system latency that can
prolong detection times.
Even so, within just a few years, innovative performers contracted to work in the program had developed and demonstrated an automated, low-cost, networked radiation detection capability for counter-terrorism and continuous cityto-region scale radiation monitoring. SIGMA program has successfully created high quality, handheld radiological sensors—the size of an average smart phone—at a fraction the cost of today’s devices. SIGMA developed not only that hardware but also the software to monitor thousands of those mobile detectors in real time—an essential capability to discern the movement of nuclear materials before they can be incorporated into a terrorist’s weapon. In addition, the sensors retain local detection capabilities in the event of a network outage. Lastly, these sensors are inventoried, managed, and displayed to analysts to reveal individual and collective device status and sensor output. DARPA has achieved these core components and their integration into the SIGMA system. SIGMA has succeeded in making large-scale radiation sensor networks technically feasible and operationally practical , and it is now being operationally deployed.
In April 2018, DARPA’s performer teams partnered with the Indianapolis Metropolitan Police Department, Indianapolis Motor Speedway, and the Marion County Health Department to deploy the network on-site at the Indianapolis Motor Speedway. “With this network, we’re able to use just the chemical sensor outputs and wind measurements to look at chemical threat dynamics in real time, how those chemical threats evolve over time, and threat concentration as it might move throughout an area.”
The December 2019 exercise marked the capstone for DARPA’s SIGMA program, culminating a five-year effort to develop and deploy an automated, high-performance, networked radiation detection capability for counterterrorism and continuous city-to-region scale radiological and nuclear threat monitoring. On a blustery winter day last December, a car carrying radioactive material approached one of the Port Authority of New York and New Jersey’s major transportation hubs. As the car got closer, an alarm flashed and sounded on a large monitor in the police operations center, identifying on a digital map the exact location of the vehicle and the specific radioactive isotope radiating from the car – Cesium-137. Within minutes, officers in the Port Authority Police Department – equipped with vehicle-mounted and pocket-sized radiation sensors displaying the same real-time digital map – tracked the vehicle and apprehended the suspects in a parking lot. “We want to thank the Port Authority for their outstanding support throughout the SIGMA program and their continued support as we test SIGMA+ sensors,” said Mark Wrobel, DARPA program manager in the Defense Sciences Office. “Being able to test and refine the system in the country’s largest metropolitan region was invaluable in taking SIGMA from a research project to an operationally deployed system in just five years.”
The transition of the radiation-detection system took place prior to the coronavirus disease (COVID-19) pandemic. In the eight months since the SIGMA transition, DARPA has been developing and testing additional sensors under its SIGMA+ effort to detect chemical, biological and explosive threats as well. In its five years, the now-completed SIGMA program progressed from a basic and applied research program to a deployed operational system, providing revolutionary radiationdetection capability at multiple locations in the United States and overseas. Arktis, Silverside, Kromek, and Two Six Labs now all offer SIGMA sensors and networking capabilities as commercial products, which will drive down the cost or radiological detection and monitoring for the Department of Defense and other U.S. Government users.
DARPA has greenlit an automated, networked radiation detection system known as SIGMA for use by the Port Authority of New York and New Jersey, promising new protections for the region. “New York City and Northern New Jersey have some of the nation’s most critical transportation infrastructure – heavily trafficked tunnels, bridges, airports, train and bus stations, and ferry terminals,” Dave Warrington, senior manager for strategic preparedness in the Port Authority’s Office of Emergency Management, said. “This unique partnership with DARPA was mutually beneficial – DARPA had access to our transportation nodes to collect real background radiological data for developing the system, and the Port Authority now has a network of high-performance stationary, vehicle-mounted, and wearable sensors providing enhanced, 24-hour nuclear and radiological threat detection.”
According to users of the system, it’s user friendly, based on an app-like Android interface. Officials and first responders can use it to track alerts and threats in real-time, allowing for enhanced coordination. The system also doesn’t sacrifice power for portability. It’s versatile, based in worn, portable sensors, vehicular mounted sensors, and stationary sensors at key transportation nodes. It can also be constantly improved through regular software updates.
DARPA is currently extending the capabilities for networked chemical detection by investigating additional sensor modalities, including short-range point sensors based on, for example, mass spectrometry, and long-range spectroscopic systems. As these systems are further developed, they will be integrated into the SIGMA+ network architecture to increase the system’s capabilities for city-scale monitoring of
chemical and explosive threats as well as threat precursors. In 2020, DARPA directed some of the SIGMA effort directly to the challenge of detecting SARS-CoV-2, the virus at the heart of the COVID-19 pandemic, in buildings and other environmental settings.
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