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Date:
2004-03-03
URL:
http://www.sciencedaily.com/releases/2004/03/040303080222.htm

Evidence Bubbles Over To Support Tabletop Nuclear Fusion Device

WEST LAFAYETTE, Ind. - Researchers are reporting new evidence supporting their 
earlier discovery of an inexpensive "tabletop" device that uses sound waves 
to produce nuclear fusion reactions. 

The researchers believe the new evidence shows that "sonofusion" generates 
nuclear reactions by creating tiny bubbles that implode with tremendous 
force. Nuclear fusion reactors have historically required large, 
multibillion-dollar machines, but sonofusion devices might be built for a 
fraction of that cost. 

"What we are doing, in effect, is producing nuclear emissions in a simple 
desktop apparatus," said Rusi Taleyarkhan, the principal investigator and a 
professor of nuclear engineer at Purdue University. "That really is the 
magnitude of the discovery - the ability to use simple mechanical force for 
the first time in history to initiate conditions comparable to the interior 
of stars." 

The technology might one day result in a new class of low-cost, compact 
detectors for security applications that use neutrons to probe the contents 
of suitcases; devices for research that use neutrons to analyze the molecular 
structures of materials; machines that cheaply manufacture new synthetic 
materials and efficiently produce tritium, which is used for numerous 
applications ranging from medical imaging to watch dials; and a new technique 
to study various phenomena in cosmology, including the workings of neutron 
stars and black holes. 

Taleyarkhan led the research team while he was a full-time scientist at the 
Oak Ridge National Laboratory, and he is now the Arden L. Bement Jr. 
Professor of Nuclear Engineering at Purdue. 

The new findings are being reported in a paper that will appear this month in 
the journal Physical Review E, published by the American Physical Society. 
The paper was written by Taleyarkhan; postdoctoral fellow J.S Cho at Oak 
Ridge Associated Universities; Colin West, a retired scientist from Oak 
Ridge; Richard T. Lahey Jr., the Edward E. Hood Professor of Engineering at 
Rensselaer Polytechnic Institute (RPI); R.C. Nigmatulin, a visiting scholar 
at RPI and president of the Russian Academy of Sciences' Bashkortonstan 
branch; and Robert C. Block, active professor emeritus in the School of 
Engineering at RPI and director of RPI's Gaerttner Linear Accelerator 
Laboratory. 

The discovery was first reported in March 2002 in the journal Science. 

Since then the researchers have acquired additional funding from the U.S. 
Defense Advanced Research Projects Agency, purchased more precise instruments 
and equipment to collect more accurate data, and successfully reproduced and 
improved upon the original experiment, Taleyarkhan said. 

"A fair amount of very substantial new work was conducted, " Taleyarkhan said. 
"And also, this time around I made a conscious decision to involve as many 
individuals as possible - top scientists and physicists from around the world 
and experts in neutron science - to come to the lab and review our procedures 
and findings before we even submitted the manuscript to a journal for its own 
independent peer review." 

The device is a clear glass canister about the height of two coffee mugs 
stacked on top of one another. Inside the canister is a liquid called 
deuterated acetone. The acetone contains a form of hydrogen called deuterium, 
or heavy hydrogen, which contains one proton and one neutron in its nucleus. 
Normal hydrogen contains only one proton in its nucleus. 

The researchers expose the clear canister of liquid to pulses of neutrons 
every five milliseconds, or thousandths of a second, causing tiny cavities to 
form. At the same time, the liquid is bombarded with a specific frequency of 
ultrasound, which causes the cavities to form into bubbles that are about 60 
nanometers - or billionths of a meter - in diameter. The bubbles then expand 
to a much larger size, about 6,000 microns, or millionths of a meter - large 
enough to be seen with the unaided eye. 

"The process is analogous to stretching a slingshot from Earth to the nearest 
star, our sun, thereby building up a huge amount of energy when released," 
Taleyarkhan said. 

Within nanoseconds these large bubbles contract with tremendous force, 
returning to roughly their original size, and release flashes of light in a 
well-known phenomenon known as sonoluminescence. Because the bubbles grow to 
such a relatively large size before they implode, their contraction causes 
extreme temperatures and pressures comparable to those found in the interiors 
of stars. Researches estimate that temperatures inside the imploding bubbles 
reach 10 million degrees Celsius and pressures comparable to 1,000 million 
earth atmospheres at sea level. 

At that point, deuterium atoms fuse together, the same way hydrogen atoms fuse 
in stars, releasing neutrons and energy in the process. The process also 
releases a type of radiation called gamma rays and a radioactive material 
called tritium, all of which have been recorded and measured by the team. In 
future versions of the experiment, the tritium produced might then be used as 
a fuel to drive energy-producing reactions in which it fuses with deuterium. 

Whereas conventional nuclear fission reactors produce waste products that take 
thousands of years to decay, the waste products from fusion plants are 
short-lived, decaying to non-dangerous levels in a decade or two. The desktop 
experiment is safe because, although the reactions generate extremely high 
pressures and temperatures, those extreme conditions exist only in small 
regions of the liquid in the container - within the collapsing bubbles. 

One key to the process is the large difference between the original size of 
the bubbles and their expanded size. Going from 60 nanometers to 6,000 
microns is about 100,000 times larger, compared to the bubbles usually formed 
in sonoluminescence, which grow only about 10 times larger before they 
implode. 

"This means you've got about a trillion times more energy potentially 
available for compression of the bubbles than you do with conventional 
sonoluminescence," Taleyarkhan said. "When the light flashes are emitted, 
it's getting extremely hot, and if your liquid has deuterium atoms compared 
to ordinary hydrogen atoms, the conditions are hot enough to produce nuclear 
fusion." 

The ultrasound switches on and off about 20,000 times a second as the liquid 
is being bombarded by neutrons. 

The researchers compared their results using normal acetone and deuterated 
acetone, showing no evidence of fusion in the former. 

Each five-millisecond pulse of neutrons is followed by a five-millisecond gap, 
during which time the bubbles implode, release light and emit a surge of 
about 1 million neutrons per second. 

In the first experiments, with the less sophisticated equipment, the team was 
only able to collect data during a small portion of the five-millisecond 
intervals between neutron pulses. The new equipment enabled the researchers 
to see what was happening over the entire course of the experiment. 

The data clearly show surges in neutrons emitted in precise timing with the 
light flashes, meaning the neutron emissions are produced by the collapsing 
bubbles responsible for the flashes of light, Taleyarkhan said. 

"We see neutrons being emitted each time the bubble is imploding with 
sufficient violence," Taleyarkhan said. 

Fusion of deuterium atoms emits neutrons that fall within a specific energy 
range of 2.5 mega-electron volts or below, which was the level of energy seen 
in neutrons produced in the experiment. The production of tritium also can 
only be attributed to fusion, and it was never observed in any of the control 
experiments in which normal acetone was used, he said. 

Whereas data from the previous experiment had roughly a one in 100 chance of 
being attributed to some phenomena other than nuclear fusion, the new, more 
precise results represent more like a one in a trillion chance of being 
wrong, Taleyarkhan said. 

"There is only one way to produce tritium - through nuclear processes," he 
said. 

The results also agree with mathematical theory and modeling. 

Future work will focus on studying ways to scale up the device, which is 
needed before it could be used in practical applications, and creating 
portable devices that operate without the need for the expensive equipment 
now used to bombard the canister with pulses of neutrons. 

"That takes it to the next level because then it's a standalone generator," 
Taleyarkhan said. "These will be little nuclear reactors by themselves that 
are producing neutrons and energy." 

Such an advance could lead to the development of extremely accurate portable 
detectors that use neutrons for a wide variety of applications. 

"If you have a neutron source you can detect virtually anything because 
neutrons interact with atomic nuclei in such a way that each material shows a 
clear-cut signature," Taleyarkhan said. 

The technique also might be used to synthesize materials inexpensively. 

"For example, carbon is turned into diamond using extreme heat and temperature 
over many years," Taleyarkhan said. "You wouldn't have to wait years to 
convert carbon to diamond. In chemistry, most reactions grow exponentially 
with temperature. Now we might have a way to synthesize certain chemicals 
that were otherwise difficult to do economically. 

"Several applications in the field of medicine also appear feasible, such as 
tumor treatment." 

Before such a system could be used as a new energy source, however, 
researchers must reach beyond the "break-even" point, in which more energy is 
released from the reaction than the amount of energy it takes to drive the 
reaction. 

"We are not yet at break-even," Taleyarkhan said. "That would be the ultimate. 
I don't know if it will ever happen, but we are hopeful that it will and 
don't see any clear reason why not. In the future we will attempt to scale up 
this system and see how far we can go."



-- 
Stephen Carville http://www.heronforge.net/~stephen/gnupgkey.txt
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Right wing socialists hate privacy as much as left wing socialists hate guns.