news.uns.purdue.edu/UNS/html4ever/2005/050712.Xu.fusion.html
July 12, 2005 Purdue findings support earlier nuclear fusion experiments WEST LAFAYETTE, Ind. Researchers at Purdue University have new evidence supporting earlier findings by other scientists who designed an inexpen sive "tabletop" device that uses sound waves to produce nuclear fusion r eactions.
The technology, in theory, could lead to a new source of clean energy and a host of portable detectors and other applications. The new findings were detailed in a peer-reviewed paper appearing in the May issue of the journal Nuclear Engineering and Design. The paper was w ritten by Yiban Xu, a post-doctoral research associate in the School of Nuclear Engineering, and Adam Butt, a graduate research assistant in bot h nuclear engineering and the School of Aeronautics and Astronautics. A key component of the experiment was a glass test chamber about the size of two coffee mugs filled with a liquid called deuterated acetone, whic h contains a form of hydrogen known as deuterium, or heavy hydrogen. The researchers exposed the test chamber to subatomic particles called neut rons and then bombarded the liquid with a specific frequency of ultrasou nd, which caused cavities to form into tiny bubbles. The bubbles then ex panded to a much larger size before imploding, apparently with enough fo rce to cause thermonuclear fusion reactions. Fusion reactions emit neutrons that fall within a specific energy range o f 25 mega-electron volts, which was the level of energy seen in neutron s produced in the experiment. The experiments also yielded a radioactive material called tritium, which is another product of fusion, Xu and But t said. The Purdue research began two years ago, and the findings represent the f irst confirmation of findings reported earlier by Rusi Taleyarkhan. Professor of Nuclear Eng ineering, discovered the fusion phenomenon while he was a scientist work ing at the Oak Ridge National Laboratory. "The two key signatures for a fusion reaction are emission of neutrons in the range of 25 MeV and production of tritium, both of which were seen in these experiments," Xu said. The same results were not seen when the researchers ran control experimen ts with normal acetone, providing statistically significant evidence for the existence of fusion reactions. "The control experiments didn't show anything," Xu said. "We changed just one parameter, substituting the deuterated acetone with normal acetone. " Deuterium contains one proton and one neutron in its nucleus. Normal hydr ogen contains only one proton in its nucleus. Taleyarkhan led a research team that first reported the phenomenon in a 2 002 paper published in the journal Science. Those researchers later cond ucted additional research at the Oak Ridge National Laboratory, Renssela er Polytechnic Institute and the Russian Academy of Sciences and wrote a follow-up paper that appeared in the journal Physical Review E in 2004, just after Taleyarkhan had come to Purdue. Scientists have long known that high-frequency sound waves cause the form ation of cavities and bubbles in liquid, a process known as "acoustic ca vitation," and that those cavities then implode, producing high temperat ures and light in a phenomenon called "sonoluminescence." In the Purdue research, however, the liquid was "seeded" with neutrons be fore it was bombarded with sound waves. Some of the bubbles created in t he process were perfectly spherical, and they imploded with greater forc e than irregular bubbles. The research yielded evidence that only spheri cal bubbles implode with a force great enough to cause deuterium atoms t o fuse together, similar to the way in which hydrogen atoms fuse in star s to create the thermonuclear furnaces that make stars shine. Nuclear fusion reactors have historically required large, expensive machi nes, but acoustic cavitation devices might be built for a fraction of th e cost. Researchers have estimated that temperatures inside the implodin g bubbles reach 10 million degrees Celsius and pressures comparable to 1 ,000 million earth atmospheres at sea level. Xu and Butt now work in Taleyarkhan's lab, but all of the research on whi ch the new paper is based was conducted before they joined the lab, and the research began at Purdue before Taleyarkhan had become a Purdue facu lty member. The two researchers used an identical "carbon copy" of the o riginal test chamber designed by Taleyarkhan, and they worked under the sponsorship and direction of Lefteri Tsoukalas, head of the School of Nu clear Engineering. Although the test chamber was identical to Taleyarkhan's original experim ent, and the Purdue researchers were careful to use deuterated acetone, they derived the neutrons from a less-expensive source than the Oak Ridg e researchers. The scientists working at Oak Ridge seeded the cavities w ith a "pulse neutron generator," an apparatus that emits rapid pulses of neutrons. Xu and Butt derived neutrons from a radioactive material that constantly emits neutrons, and they simply exposed the test chamber to the material. Development of a low-cost thermonuclear fusion generator would offer the potential for a new, relatively safe and low-polluting energy source. Wh ereas conventional nuclear fission reactors make waste products that tak e thousands of years to decay, the waste products from fusion plants wou ld be short-lived, decaying to non-dangerous levels in a decade or two. For the same unit mass of fuel, a fusion power plant would produce 10 ti mes more energy than a fission reactor, and because deuterium is contain ed in seawater, a fusion reactor's fuel supply would be virtually infini te. A cubic kilometer of seawater would contain enough heavy hydrogen to provide a thousand years' worth of power for the United States. Such a technology also could result in a new class of low-cost, compact d etectors for security applications that use neutrons to probe the conten ts of suitcases; devices for research that use neutrons to analyze the m olecular structures of materials; machines that cheaply manufacture new synthetic materials and efficiently produce tritium, which is used for n umerous applications ranging from medical imaging to watch dials; and a new technique to study various phenomena in cosmology, including the wor kings of neutron stars and black holes. The desktop experiment is safe because, although the reactions generate e xtremely high pressures and temperatures, those extreme conditions exist only in small regions of the liquid in the container within the colla psing bubbles, Xu said. Purdue researchers plan to release additional data from related experimen ts in October during the Nuclear Reactor Thermal Hydraulics conference i n Avignon, France. The 2004 paper was written by Taleyarkhan while a distinguished scientist at Oak Ridge National Laboratory, postdoctoral fellow JS Cho at Oak Ri dge Associated Universities;
PHOTO CAPTION: Purdue University researchers Yiban Xu, standing, and Adam Butt, in the f oreground, look at a monitor connected to a camera trained on a nearby e xperiment. The research has yielded evidence supporting earlier findings by other scientists who designed an inexpensive "tabletop" device that uses sound waves to produce nuclear fusion reactions. Xu is a post-docto ral research associate in the Purdue's School of Nuclear Engineering, an d Butt is a graduate research assistant in both nuclear engineering and the School of Aeronautics and Astronautics. The technology might one day , in theory, lead to a new source of clean energy and a host of portable detectors and other applications.
jpg ABSTRACT Confirmatory experiments for nuclear emissions during acoustic cavitation Yiban Xu^a,*, Adam Butt^a,b a School of Nuclear Engineering b School of Aeronautics and Astronautics Purdue University Confirmatory experiments were conducted to assess the potential for nucle ar fusion related emissions of neutrons and tritium during neutron-seede d acoustic cavitation of deuterated acetone. Corresponding control exper iments were conducted with normal acetone. Statistically significant (5- 11 SD increased) emissions of 245 MeV neutrons and tritium were measu red during ...
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