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Jarrod Allred

Developing the next generation of room temperature radiation detectors

Sara Harrison

Jarrod Allred, a participant in the U.S. Domestic Nuclear Detection Office (DNDO) Summer Internship Program, is checking a thallium bromide radiation detector’s waveforms for unusual behavior as part of his research into increasing the equipment’s operating lifespan. (Photo courtesy of Barry Goldman from Lawrence Livermore National Laboratory)

Versatility and reliability are important attributes when developing radiation detection equipment that can be both effective and adaptable in field operations. This was the challenge Jarrod Allred, a master’s student in nuclear engineering from Texas A&M University, was tasked with as part of his recent internship at Lawrence Livermore National Laboratory.

As a participant in Domestic Nuclear Detection Office (DNDO) Summer Internship Program, Allred joined a program that provides undergraduate and graduate students opportunities to participate in projects at federal research facilities across the U.S. Their focus is to help DNDO meet its mission of “implementing domestic nuclear detection efforts for a managed and coordinated response to radiological and nuclear threats, as well as integration of federal nuclear forensics programs.”

His research opportunity was to help make thallium bromide a more reliable option for high energy resolution radiation detection. Current technology used in high performance semiconductor radiation detectors, like germanium, has to be cooled before operating. This limits the detector’s usefulness in the field. In recent years, thallium bromide has emerged as an attractive alternative because it can operate at room temperature, be manufactured into larger crystals than alternative room-temperature semiconductor materials, and still obtain a high energy resolution spectrum. Being able to operate radiation detectors at room temperature increases their versatility and usefulness, making them more adaptable to use as a portable system.

However, according to Allred, chemical stability issues still exist with the use of thallium bromide in detectors. The biggest challenge comes from the polarization of the crystal due to ionic conduction, which is the movement of an ion through defects in the crystal. This ionic migration can result in the material degradation of thallium bromide.
To determine where this degradation can occur, Allred developed a diagnostic tool that can measure the changes in the internal electric field of the detector.

“By developing diagnostic tools to identify and quantify the change in internal electric field, we can find the points of greatest degradation in the crystal,” Allred said. “From there, we can take necessary steps through chemical and physical processes to mitigate the degradation.”
The DNDO Summer Internship Program is funded by DNDO and administered through the U.S. Department of Energy’s Oak Ridge Institute for Science and Education (ORISE). ORISE is managed for DOE by ORAU.

Allred applied for this program because he wanted to increase his exposure to nuclear detector technology and to expand his professional network. In addition to broadening his knowledge base and professional network, Allred also learned to use multiple software programs he had minimal exposure to previously. “Through this experience I gained a greater understanding of semiconductor detectors, both in their operation and design. I also was able to develop better data analysis techniques and improve upon my programing skills,” stated Allred.

“My favorite part has been being involved in the development of new detector technology because it was exciting to see the benefits these new materials could bring,” he said. “I enjoyed being a part of a program that was developing new tools that could aid in detecting nuclear material and potentially keep the U.S. and the world safer.”

After completing his master’s degree, Allred plans to pursue further opportunities at a national laboratory, something he thought was a possibility before beginning his internship but has since become a greater reality.