When China native Zhong He arrived at the University of Michigan in Ann Arbor 16 years ago, he began work on a portable gamma ray device that could verify whether Russia, for example, had dismantled nuclear missiles as part of a weapons reduction treaty.
The assignment, initially funded by the Department of Energy, became more urgent after 9/11. Responding to multiple terrorist threats, the government tasked He and his team of Ph.D. graduate students with developing advanced nuclear detectors to determine the precise location and identity of nuclear materials that may be smuggled between countries or used to produce dirty bombs.
The research effort was especially challenging because conventional gamma ray detection devices (using high-purity germanium) are bulky and must be cooled to -200 degrees Celsius (-328 degrees Fahrenheit), often using liquid nitrogen.
“All nuclear materials emit gamma rays — as do many building materials like masonry and cinder blocks, due to minute amounts of radioactive material in the ground,” says He, professor of nuclear engineering and radiological sciences at U-M’s College of Engineering.
“We needed to find a way to detect very accurately, for example, the unique gamma-ray spectrum of uranium-235 or plutonium-239, which are unique signatures of special nuclear materials for weapons use.”
Due to technical advances — He says a good analogy is comparing the power of today’s cell phones with desktop computers from 10 years ago — the U-M team just delivered its first gamma-ray detection prototype to the Defense Department.
Called Polaris, U-M’s semiconductor-based gamma-ray imaging detector is roughly one square foot in size. The metal-encased device includes two optical imaging cameras, 18 advanced gamma-ray sensors, a small array of electronic circuitry, and two miniature cooling fans.
“Over the next two to three years, our goal is to develop Polaris into a hand-held device that military and security personnel could easily operate in the field to detect a dirty bomb or nuclear material that may be smuggled into other countries,” Wang says. “The device also would be connected to the Internet, which would allow the military to monitor the tests from a remote lab or location.”
Apart from nuclear detection activities, which include inspections of suspected nuclear facilities around the world, Kaye says future generations of Polaris could be used to locate cancer cells (even trace amounts) in the human body. In addition, astronauts or robots could use the device to detect water on the moon, Mars, Europa, and other planets.
Last summer, NASA officials reported that a gamma-ray spectrometer aboard the Spirit rover found rock formations containing carbonates, which are minerals that form readily in watery, carbon-rich environments. The discovery lends greater credence to speculation that Mars may once have had a wetter, warmer climate.
“We are actively working on our next prototype,” Kaye says. “The sensors can’t get much smaller, but the amount of space needed for the electronic circuitry can certainly be reduced as advances are made.”
Several patents have been approved for Polaris, and U-M is seeking commercial partners to assist in bringing the technology to market.
