New Radiation Detector Technology Will Help Secure U.S. Cities
You won’t see any Geiger counters trained on trucks entering the Midtown Tunnel into Manhattan. Brookhaven scientists are pioneering research to detect radiological threats at transportation choke-points in many urban areas.
by Kay Cordtz
In the post-9/11 environment, security personnel at bridges and tunnels leading into New York and other large cities have a daunting task to perform: to screen vehicles and their passengers for radiation, which might be evidence of a so-called “dirty bomb” or other radiological device. Unfortunately, much of the existing technology does not discriminate between such threats and the gamma rays that might be given off by a person who recently received a heart stress test, a truck loaded with granite or a crate of bananas. And while the presence of neutrons will more clearly indicate a potential threat, their source can be difficult to locate.
Brookhaven scientists are in the forefront of technological advances that may bring solutions to some of these problems. Working for the Department of Energy (DOE), the National Nuclear Security Administration (NNSA) and the Defense Department’s Defense Threat Reduction Agency (DTRA), Brookhaven is developing gamma ray spectroscopy to identify specific radioactive isotopes and imaging systems to locate the source of neutrons. Precise isotope identification will help law enforcement differentiate between potentially dangerous radioactive materials and otherwise harmless radiation sources.
Characterizing gamma rays
A team of Brookhaven researchers works on a directional detection system for “fast” neutrons. Checking the calibrations are, left to right, Cynthia Salwen, Leon Forman, and Istvan Dioszegi.
Community Outreach Programs Stress Training And Vigilance
Brookhaven Lab is the key to the federal government’s response to possible radiological emergencies in the Northeast United States, responsible for training first responders, monitoring high-risk events, and coordinating response as situations develop. As the Regional Coordinating Office for the DOE/NNSA Radiological Assistance Program, known as RAP, the Laboratory provides first-responder radiological assistance to local, state, tribal and federal agencies in the detection, identification and analysis, and response to events involving the use of radiological/nuclear material. More...
“We live in a world awash with gamma radiation coming from walls, from the ground, from space, and even from our own bodies,” said Ralph James of the Nonproliferation and National Security Department, who conducts research in gamma spectroscopy. “A useful detector must be able to discern a material of potential threat from these naturally occurring sources.”
Existing germanium crystal detectors are large and bulky and must be cryogenically cooled to operate, making them impractical in many field operations. Detectors based on scintillators, which convert x-ray energy into visible light, operate at room temperature, but they have poor ability to identify isotopes. Brookhaven is working to combine the advantages of both minus their drawbacks by developing detectors based on cadmium zinc telluride (CZT) crystals.
When a gamma ray strikes a CZT detector, it creates electron-hole pairs. These drift under the influence of an applied electric field, creating a signal that reveals a unique signature of the isotope. Brookhaven scientists grow and characterize the crystals, fabricate them into detectors, test them for performance, design the electronics to read the signals, and integrate the components into working field instruments.
“It’s very unusual to have research that spans fields ranging from crystal growth to prototype instrumentation,” James said. “This work reaches across the Lab, connecting basic and applied programs. It also takes advantage of the unique tools at the National Synchrotron Light Source to identify the material properties limiting detector performance.” He added that “the higher resolutions and precise energies that will be offered by the soon-to-be-built NSLS-II are expected to provide an added boost.”
The CZT detectors meet the need for portable devices that can detect and image radiation without the false alarms characteristic of many conventional systems. They are now being deployed in niche applications. For use at greater standoff distances, however, they begin to lose performance ability.
