By Keith Hautala
Small, efficient radiation detector could find its way into mammogram machines
In 2015, a team of Oregon State University researchers devised a new solid-state, scintillator-type radiation detector that offers several key advantages over existing designs: It’s more compact, less expensive to produce, and, critically, does not require lots of high-voltage current to operate.
The invention grew out of research by Kendon Shirley (’13 B.S., Radiation Health Physics) and Salam Alhawsawi (’18 Ph.D., Radiation Health Physics), working with Steven R. Reese, associate professor of nuclear science and engineering, and director of the Radiation Center.
The mechanism is small enough that it could be incorporated into a handheld device, such as a smartphone. A variety of applications exist for cheap, portable, low-power radiation detectors in fields such as environmental safety and health care. For example, a pocket-sized detector could alert individual users when radiation levels become abnormally high. And many such detectors networked together could be used to generate a map identifying the size and location of a radiation public health emergency.
“Thousands of phones could send signals to a central location that analyzes the data,” Alhawsawi said, discussing the invention’s potential in a 2016 interview. “After Fukushima in Japan, people started using radiation detectors that plug into phones through the headphone jack. It’s one way to monitor background radiation levels to see if there’s something to be concerned about.”
Alhawsawi, Shirley, and Reese formed a company, GenX Detectors LLC, to further develop and market the mechanism. A patent (U.S. Patent No. 10,705,228) was awarded in July 2020, and the technology is currently available for licensing. Reese says the detector was an entrepreneurial project from the start.
“We basically bootstrapped it, just the three of us,” Reese said. “There was no external funding, although we did receive a small but vital award from the university’s Office for Commercialization and Corporate Development. We’re eminently grateful for that support. It allowed us to perform experiments on some prototypes of the sensor.”
Scintillator-type radiation detection instruments typically rely on two key components: a scintillation crystal and a photomultiplier tube.
The scintillation crystal is a special type of material that converts high-energy radiation, such as X-rays or gamma rays, into visible or near-visible light. When the crystal is struck by radiation, it absorbs energy, causing electrons to move from a stable state to an excited state. When those electrons return to their stable state, they release their energy in the form of light emission, or fluorescence.
However, the photons generated by the scintillation crystal are very low in energy and require amplification to provide a useful signal. That’s where the photomultiplier tube comes in. Inside the photomultiplier is a photocathode designed to absorb the low-energy photons and, in turn, generate electrons. The electron multiplication structure within the photomultiplier tube consists of multiple stages of dynodes (basically, an electrode inside a vacuum tube) that amplify the number of photoelectrons.
Shirley and Alhawsawi, now an assistant professor at King Abdulaziz University in Jeddah, Saudi Arabia, found that thin-film materials could take the place of the bulky, power-hungry photomultiplier. The photovoltaic and photo-thermoelectric properties of these materials allow them to generate photoelectrons upon absorbing photons emitted from the scintillation crystal.
The team coupled a film of graphene — a single atom’s thickness of graphite — with the crystal. The result was a light-harvesting device that is more robust, smaller, and less expensive, without need for a photomultiplier. The innovation took advantage of mechanical, electrical, and optical properties of graphene that had been studied extensively, albeit separately, in the physics world.
“We combined all three in our work, and we also took the use of graphene from a nanoscale to a scale of millimeters and centimeters, which is more than 10 orders of magnitude larger,” Alhawsawi said.
GenX has proposals in the works to bring the technology to market with assistance from the federal government’s Small Business Innovation Research and Small Business Technology Transfer programs. Reese says the company is focusing on one specific application in the health care field, mammography, as the most likely target for commercialization.
“This could have a dramatic impact on the way mammography images and tomographs are taken,” Reese said. “By substantially improving the X-ray sensitivity of the sensor, we can dramatically reduce the radiation dose the patient receives. The idea is to take this technology and develop ways to place it in existing imaging and tomography units.”