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Fusion reactor could detect explosives

Cathode geometry

Cathode geometry: 10-cm symmetric inner cathode grid (large image)

Although the primary goal of UW-Madison's inertial electrostatic containment (IEC) fusion experiment is to produce more energy than it expends, airport and port security personnel may someday use the concept to detect the military high explosive composition 4, or C-4.

"Typical explosives are composed of carbon, hydrogen, nitrogen and oxygen," says Alex Wehmeyer, the master's student who determined the IEC could detect C-4. "The large quantities of nitrogen and oxygen in explosives in comparison to other materials is what makes explosives unique."

Wehmeyer used a general Monte Carlo N-particle transport code to model the IEC. In the model, he altered the device's cathode size, geometry and material composition to increase neutron-production rates from the fusion reaction. With 95-percent accuracy in repeated simulations, he was able to detect the nitrogen in C-4 using prompt gamma neutron activation analysis techniques. "Essentially, I wanted to maximize the number of thermal neutrons that would interact with the explosive material," he says.

The thermal neutrons interact with the nuclei — primarily nitrogen and hydrogen — of the C-4. As a result, the nuclei capture thermal neutrons and emit a characteristic gamma ray. From the nitrogen, that gamma ray is 10.83 megavolts; from the hydrogen, it is 2.22 megavolts. "The detection of these characteristic gamma rays is the key to explosive detection by thermal neutron activation analysis," says Wehmeyer.

Cathode geometry

Cathode geometry: 10-cm latitude/longitude inner cathode grid (large image)

Now an instructor in the Department of Physics at the United States Military Academy, Wehmeyer conducted the research during the past two years. Student Ryan Giar will continue the work, developing an improved system that will include additional detectors and an alternate configuration to increase the number of 10.83 megavolt gamma rays it can detect.

Cathode size

Cathode size: Left — 10-cm inner cathode grid diameter, right — 20-cm inner cathode grid diameter (large image)