Tiny Wafer Developed By K-State Professor; Detects Neutron Signals From Hidden Nuclear Weapons, Materials

The essence of the small, portable detectors is a small wafer developed by Douglas McGregor, a K-State associate professor of mechanical and nuclear engineering. McGregor, who has been working on producing semiconductor neutron detectors for approximately nine years, has been at K-State since April, when he moved his entire detector fabrication laboratory here from the University of Michigan.

The working part of the wafer, which is about the size of a collar button, operates by fabricating a diode out of semiconductor material such as gallium arsenide, a semiconductor material similar to silicon. McGregor said gallium arsenide was selected because of its low-noise characteristics at room temperature. The devices are coated with combinations boron 10 or lithium to make the neutron sensitive. When neutrons strike and are absorbed by the coatings, McGregor said they undergo an immediate reaction, ejecting charged particles and leaving a trail of ionization within the detector, a signature easily discernable by the detector as a neutron-induced event. Several patents on the device structures are pending.

According to McGregor, the wafers can be tailored according to the need of the user. The detector designs utilize a minimal amount of voltage, with some designs actually operating on their own internally generated voltage, without the need for an external power supply.

"We can batch produce these and make hundreds at a time with one process run, whereas some alternative methods of applying boron, as used by other research laboratories, allow for fabrication of only one or two detectors at a time, McGregor said. "We can actually make these detectors for a cost of no more than $10 to $20 apiece, so that's pretty low.

McGregor said the process of detecting weapons is a two-fold problem: Weapons monitoring in other countries and weapons monitoring in the United States.

"We have stockpiles of weapons that we don't want anyone tampering with," McGregor said. "These detectors can be placed within the vicinity of these stockpiles and can monitor any change in the amount of neutrons that are being emitted by those weapons. Any alteration in the expected signal would set off an alarm and draw attention towards that facility."

McGregor said that although the tiny neutron detectors are still in the research phase and there are other neutron detectors that are more efficient, McGregor said those other detectors are larger and require far more voltage to operate. Previous neutron detectors have been made of large tubes of gas. The gas in the tubes is ionized when neutrons pass through the tube. McGregor said that not only are the tubes bulky in size, but also require more power to operate.

"Feasibly we could make our devices so that they could compete with what is out there right now," McGregor said. "The advantage is that our devices are thinner, smaller, and far more rugged than what is produced now."

McGregor said that although he has been conducting his detector research for over nine years, it has generated a lot more interest since the 9/11 attacks.

"The increased interest in this research has a lot to do with the fear of weapons of mass destruction being moved into this country," McGregor said. "These detectors would add to our ability to detect neutron radiation and nuclear weapons."

The U.S. Department of Energy's Argonne National Laboratory, where McGregor has developed a long-standing collaboration with co-inventor Raymond Klann, funds much the detector research. Lawrence Livermore National Laboratory and other DOE programs contracts have contributed additional funding to the detector research.