APS News

Physics Helps Bolster Homeland Security

Many physicists are applying basic physics in unexpected ways to homeland security problems, and several groups reported their progress at the April Meeting.

For instance, a group of researchers from Sandia National Laboratory and Lawrence Livermore National Laboratory has proposed building small neutrino detectors for monitoring nuclear reactors.

Nuclear reactors that produce electric power must be monitored to make sure that fissile materials are not diverted for weapons purposes. Currently, the International Atomic Energy Agency monitors nuclear reactors with regular detailed inspections, which are time-consuming and costly.

Now, Nathaniel Bowden of Sandia National Laboratory and his colleagues have proposed a new method for real-time monitoring of nuclear reactors. A smaller version of the same type of detector that scientists use to study solar or atmospheric neutrinos could detect the antineutrinos produced by nuclear power reactors and give a measure of the amount of plutonium in the reactor core, Bowden and colleagues suggest.

Neutrinos interact infrequently and are hard to detect, Bowden points out, but they are also impossible to shield, so it would be impossible to hide the antineutrinos produced in a nuclear reactor.

Bowden and colleagues have already built a prototype detector, which they have installed about 25 meters from the San Onofre nuclear generating station in San Clemente, Calif. The prototype detector is about 3 m by 3 m by 3 m, and the researchers believe it could be made even smaller.

About 1026 antineutrinos are emitted by the reactor each day, and several thousand interact with a proton in the detector.

With the prototype, the researchers can clearly see the reactor turning on and off, and they have preliminary indications of sensitivity to production of plutonium.

If the IAEA could adopt this system, it would allow real-time monitoring of plutonium production that could greatly reduce the need for inspections, Bowden says. He and colleagues plan to carry out a cost-benefit analysis to determine whether this method of monitoring reactors would be practical.

In another example of basic science being applied to security problems, seismologist Paul Richards of Columbia University discussed using earthquake detectors to sense nuclear explosions.

To a non-specialist, an earthquake looks very similar to a nuclear explosion, but scientists can tell them apart because of the different patterns of shear and compression waves. Even if a country attempts to evade detection, tests above 1 or 2 kilotons cannot be confidently hidden, said Richards. There is already a large seismic monitoring infrastructure already in place that can detect explosions from a distance, and seismologists can distinguish a nuclear explosion from the 200 earthquakes that occur every day. In fact, seismology has turned out to be the most important way of monitoring nuclear explosions, said Richards.

However, locating an explosion precisely enough is still challenging. Richards and others are working on techniques for solving that problem. In addition to improving the monitoring of nuclear testing, the research is also leading to improvements in seismologists’ ability to precisely locate earthquakes, he said. Richards received the Szilard Award for his work in this area.

Edward Hartouni of Lawrence Livermore National Laboratory talked about how scientists are working the problem of monitoring cargo entering the country to keep out illicit nuclear material. Millions of cargo containers enter the country each year, and at some ports as many as ten containers per minute must be processed. Opening and searching each one would be impossible. Radiation detectors would detect non-threatening radioactive materials, such as fiestaware. All solutions proposed so far have problems, but physicists are continuing to work on better methods of monitoring cargo, said Hartouni.

These are all examples of how scientists working on basic research can apply their knowledge to problems in homeland security, said Hartouni. By supporting scientists to do basic research, “we produce a large reservoir of knowledge which we can draw from,” he said.



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