A team of researchers from North Carolina State University, the University of Michigan and Oak Ridge National Laboratory have constructed a low-energy positron beam at NC State’s PULSTAR nuclear reactor with the highest positron rate of any such facility worldwide. Positrons, the antiparticle of electrons, are generated using the intense radiation in the vicinity of the reactor core.
Dr. Ayman Hawari, associate professor of nuclear engineering and director of the Nuclear Reactor Program at NC State, reports that the measurements of the beam rate are 5-6x108 positrons per second.
“These numbers are two orders of magnitude higher than those available using regular lab sources and exceed intensities currently reported by other international facilities,” says Hawari.
Once the stuff of science fiction, these anti-matter, or positron, beams have a multitude of uses in nanoscience and materials engineering because of the positron’s ability to gravitate toward and trap in defects or pores in a material at sizes as small as a single atom. Positrons are used to detect damage from radiation in nuclear reactors and are impacting the emerging field of nanoengineered materials where nanometer-sized voids control properties such as dielectric constant in microelectronic devices and hydrogen storage in fuel cells.
An intense positron beam means that researchers will have better measurements of a material’s porosity, especially in high-tech thin film applications where traditional techniques falter. This beam will be used in Positron Annihilation Lifetime Spectrometry (PALS) and Doppler Broadening Spectrometry (DBS). Hawari also believes that other positron analysis techniques will become possible. While the spectrometers are not yet built, they are on the books for completion next year.
NC State has a pioneering history in the field of Nuclear Engineering. Its first nuclear reactor, which began operation in 1953, was the first public research nuclear reactor ever constructed. The PULSTAR Nuclear Reactor, in operation since 1972, is a 1-MW pool-type research reactor using 4% enriched, pin-type fuel of uranium dioxide with a zircaloy cladding. These characteristics make it similar to some commercial reactors and make it possible for an array of research and teaching opportunities.
In 2002 the PULSTAR reactor program received U.S. Department of Energy (DOE) funding from the Innovations in Nuclear Infrastructure and Education (INIE) program. NC State led the Multi-University South East INIE Consortium (MUSIC) and used that funding to start several projects, including the Intense Positron Beam collaboration with Michigan and Oak Ridge. This team received a major boost when the National Science Foundation awarded a $1 million Major Research Instrumentation grant to build the intense positron beam at NC State, now complete, and the auxiliary spectrometers.
For more information, see David Pond's story "NC State Nuclear Reactor Program Celebrates Scientific Breakthrough" at http://www.ncsu.edu/featured-stories/
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