Cheap detectors keep the peace

Associate Professor Abi Farsoni and graduate student Steven Czyz discuss a prototype device.

Associate professor Abi Farsoni, left, and graduate student Steven Czyz discuss a prototype device for detecting radioxenon signals that can indicate the occurrence of a nuclear weapon test.

In September 2017, a series of earth-rippling shivers caught the attention of scientists around the globe. At first blush, the seismic activity suggested an earthquake with an approximate magnitude of 6.0. Then, as the source of the vibrations became clear, government agencies and heads of state began to take close notice.

Eventually, it was discovered that North Korea had detonated a nuclear weapon several hundred feet below ground. The weapon was the largest the country had tested, with several times the explosive power of the bombs dropped on Hiroshima and Nagasaki.

Although seismic activity is one indicator of a nuclear blast, it is not foolproof. A more accurate way of confirming that a nuclear weapon has been tested is by capturing and analyzing trace amounts of telltale radionuclides, including radioactive isotopes of the noble gas xenon (also known as radioxenon), that leak out of the test site and drift into the atmosphere.

The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), based in Vienna, uses highly sensitive radionuclide detectors to verify incidents of nuclear testing, and then alerts member governments. While there are 80 radionuclide monitoring stations and 16 radionuclide laboratories within the global network of 321 monitoring stations of the International Monitoring System (IMS), the verification arm of the CTBTO, there is a pressing need to develop less expensive detectors to replace aging units and increase overall global detection capacity.

Abi Farsoni, associate professor of nuclear science and engineering, and his colleagues at Oregon State’s Radiation Detection Group (RDG) are collaborating with the Consortium for Verification Technology, a group of 12 universities and nine national laboratories in the United States working together to develop new technologies for nuclear treaty verification. The RDG is the only group in the consortium working on radioxenon detectors.

Current detectors deployed by the CTBTO run about $500,000. Farsoni projects the cost for the detectors he and others are designing will be between $20,000 and $50,000. To achieve this enormous cost reduction, the researchers plan to optimize two aspects of radioxenon detectors: the device’s electronic processing unit and the materials used to analyze the radioactive xenon signals.

“I would say 99 percent of the research groups working on radiation detection are using off-the-shelf digital systems and electronics,” Farsoni said. One problem with these systems is that they are not cheap. Another problem is that manufacturers do not provide the source code, meaning adjustments to the analysis algorithms are impossible. “That’s why we are developing and building our own, so we can change the source code,” he said.

In addition to custom building the electronics, RDG researchers have made a number of important changes to the materials used inside the detectors that will further drive down costs and enhance their capabilities. Lily Ranjbar, teaching faculty in nuclear science and engineering at Oregon State, pioneered the use of cadmium zinc telluride (CZT) materials to replace the high-purity germanium most detectors are built with. Using CZT allows detectors to operate at room temperature, eliminating the costly coolant systems required for germanium-based detectors.

Steven Czyz, a doctoral student in Farsoni’s lab, and Salam Alhawsawi, a former doctoral student of Farsoni’s and co-founder of GenX Detectors, have taken Ranjbar’s CZT design and coupled it with silicon detectors that sense radioxenons in a slightly different way. Because airborne radioxenon exists in such small amounts, traditional detectors have to sample the air for up to 24 hours before definitively determining the presence of the radionuclide. Using silicon and CZT detectors in parallel can bring the sampling cycle down to eight hours, which has been a long-time goal of the IMS.

Farsoni believes the cost-saving innovations and other improvements developed at Oregon State may soon be incorporated into the next generation of detector units that the IMS could plug into its ever-expanding radionuclide detection network.

“The mission of the CTBTO and the work we are doing is helping reduce the nuclear competition around the world,” Ranjbar said. “It is also helping prevent new nuclear weapons from emerging.”

“I grew up in Iran. I spent most of my childhood living in war, and I still remember, clearly, how tough those days were,” Ranjbar added. “I don’t want any other children around the world to see the kind of things that I’ve seen — those things I felt. That’s why I entered this field. I want to help people have a better life, to feel safer, and to promote peace all around the globe.”

Jan. 14, 2019