Evidence bubbles over to support tabletop nuclear fusion device...
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March 2, 2004
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 engineering 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
The technology might one day, in theory, lead to a new source of clean
energy. It may 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
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
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
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
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
"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
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
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
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
"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."
Writer: Emil Venere, (765) 494-4709, [Only registered users see links. ]
Sources: Rusi P. Taleyarkhan, (765) 494-0198, [Only registered users see links. ]
James Riordon, (301) 209-3238, [Only registered users see links. ]
Theresa Bourgeois, RPI director of media relations, (518) 276-2840, [Only registered users see links. ]
Additional Evidence of nuclear emissions during acoustic cavitation
R.P. Taleyarkhan1, J.S. Cho2, C.D. West3, R. T. Lahey3, Jr., R.I.
Nigmatulin4, and R.C. Block3
1Purdue University, West Lafayette, Indiana 47907, 2Oak Ridge Associated
Universities, Oak Ridge, Tennessee 37830, 3Rensselaer Polytechnic Institute,
Troy, New York 12180,
4Russian Academy of Sciences,
6 Karl Marx Street, Ufa 450000, Russia
Time spectra of neutron and sonoluminescence emissions were measured in
cavitation experiments with chilled deuterated acetone. Statistically
significant neutron and gamma ray emissions were measured with a calibrated
liquid-scintillation detector, and sonoluminescence emissions were measured
with a photomultiplier tube. The neutron emission energy corresponded to
<2.5 MeV and had an emission rate of up to ~4X105 n/s. Measurements of
tritium production were also performed and these data implied a neutron
emission rate due to D-D fusion which agreed with what was measured. In
contrast, control experiments using normal acetone did not result in
statistically significant tritium activity, or neutron or gamma ray
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