A frequent collaborator and customer of Sandia’s nuclear materials monitoring user facility has entered into a cooperative research and development agreement to make more sensitive room-temperature radiation monitors.
Digirad Corporation of San Diego will work with a Sandia team led by Ralph James of Materials Processing Dept. 8230 in the three-year, $3.6 million CRADA.
"The CRADA is primarily for the Department of Energy to improve the availability of large-volume detectors that operate at room temperature and have very good energy resolution," says Clinton Lingren, Digirad’s patent and regulatory officer. "It can be used any place portable gamma spectrometers or cameras would be used."
Adds Michael O’Connell, group leader of the Office of Research and Development in DOE’s Office of Nonproliferation and National Security, "The department seeks technical partnerships with industry to provide the solutions to our national security needs. This CRADA with Digirad will ‘fast track’ the commercialization of a new radiation detector that will provide one more tool to safeguard fissile material and to counter nuclear smuggling worldwide."
In addition to addressing nuclear material smuggling, Ralph says, the monitors have health care applications for detecting cancerous tumors, heart disease, and osteoporosis.
Can pinpoint radiation source
The monitors detect gamma rays with crystals of a compound semiconductor material, cadmium zinc telluride (CZT). Unlike existing scintillators used for the same purpose, CZT-based monitors have the advantage of compactness, field-portability, and high spatial resolution.
When a gamma ray strikes CZT, it creates an electrical signal that is channeled so that it is easy to locate the radiation source. Scintillators, on the other hand, cannot pinpoint a radiation source as easily because radiation causes a light signal to be emitted in all directions.
Being able to grow larger flawless CZT crystals will increase sensitivity, so that weaker radiation sources can be detected or sources can be spotted from a greater distance. In medicine, patients can thus be exposed to the lowest possible dose of radioactive tracers, Ralph says. In nonproliferation, he envisions that these improvements will foster creation of either hand-held or fixed detectors capable of offering more precise information than existing systems based on scintillators. Compared to arrays of smaller detectors, large-volume CZT detectors also have the advantage of much simpler electronic read-outs, he says.
The CRADA partners are bringing different capabilities to the project. Digirad has extensive crystal-growing facilities, while Sandia’s lab can characterize the properties of the material and performance of fabricated devices.
Other participants in the CRADA are the University of California, Los Angeles, Carnegie Mellon University, and the University of Minnesota. The first two universities will provide measurements of material properties; the latter will assist with computer simulations of the crystal growth process.
Besides Ralph, others working on the project at Sandia include Bruce Brunett, Eileen Cross, Haim Hermon, Ed Lee, Jim Lund, Richard Olsen, John Van Scyoc, Colin Hackett, and Ed Tarver.