Posted on 01/10/2006 6:15:20 PM PST by PatrickHenry
Can the popping of tiny bubbles trigger nuclear fusion, a potential source of almost unlimited energy? This controversial idea is back on the table, because its main proponent has new results that, he claims, will silence critics. But others say that the latest experiment simply comes with its own set of problems.
The idea is simple enough. Blast a liquid with waves of ultrasound and tiny bubbles of gas are created, which release a burst of heat and light when they implode. The core of the bubble reaches 15,000° C, hot enough to wrench molecules apart. Physicists have even suggested that the intense conditions of this sonoluminescence could fuse atomic nuclei together, in the same process that keeps our Sun running.
Physicist Rusi Taleyarkhan of Purdue University in West Lafayette, Indiana, published the first evidence1 of this 'sonofusion' in 2002; he has been dogged by sceptics ever since.
The underlying physics behind the idea is valid, says Ken Suslick. An expert in sonoluminescence at the University of Illinois in Urbana-Champaign, Suslick tried and failed to replicate Taleyarkhan's first results. If the bubbles' collapse is sufficiently intense, it should indeed be able to crush atoms together. Taleyarkhan just hasn't done enough to prove it, says Suslick.
Needle in a haystack
Taleyarkhan's first experiments were conducted while he was based at Oak Ridge National Laboratory in Tennessee. His idea was to use liquid acetone in which hydrogen atoms had been replaced by their heavier brethren, deuterium. When deuterium nuclei fuse together, they emit a characteristic burst of neutrons. But critics pointed out that Taleyarkhan was using an external source of neutrons to 'seed' the bubbles, and that these were swamping his measurements of neutrons produced by the fusion reaction itself.
"This time round there are no external neutrons," he explains. Instead, his team loaded a mixture of deuterated acetone and benzene with a uranium salt. As the uranium undergoes radioactive decay it releases alpha particles, which can also seed bubble formation, says Taleyarkhan.
"In this experiment we use three independent neutron detectors and a gamma-ray detector," he adds. The results from the four instruments prove that fusion is happening inside his experiment, asserts Taleyarkhan.
Although uranium can release neutrons during fission reactions, Taleyarkhan rules them out because the neutrons he finds bear the energetic hallmark of having come from the fusion of two deuterium nuclei2.
Taleyarkhan's test reactor still puts out a lot less energy than it takes in, making it impractical for generating power. "We have a way to go before we break even," he admits. But in the meantime, he adds, it could be a cheap source of neutrons for analysing the structure of materials. The results are to be published in Physical Review Letters in a few weeks' time.
Unreliable sources
There is one big problem, however: the experiment doesn't always work, and the group is not sure why. Seth Putterman, a physicist at the University of California, Los Angeles, who has also tried to verify some of Taleyarkhan's experiments, notes that the paper does not reveal how many failed runs were required before the team saw a trace of fusion neutrons. "As a paper it doesn't convince me," says Putterman.
Putterman notes that the team did not continuously monitor background neutron levels. Although the neutron count doubles at some points in the experiments, Putterman says that neutrons produced in random showers of cosmic rays, rather than fusion events, could be responsible. But Taleyarkhan points out that the neutron count was smaller in detectors further from the reaction chamber.
To prove that the neutrons are coming from fusion as bubbles burst, Putterman and Suslick suggest that the team closely monitor exactly when the neutrons appear. The current experiment simply counts up the number of neutrons detected over minutes, so correlations with bubble bursts cannot be seen. "The key to improving the signal is timing," says Putterman.
Finding proof
Another obvious way to confirm that fusion is happening would be to look for tritium, a heavier isotope of hydrogen produced by fusion reactions. Tritium leaves a telltale signature of high-energy electrons when it decays and Taleyarkhan claimed to see this in similar previous experiments1,3. But in the current tests, tritium's signature is overwhelmed by ?-decay from the uranium, making it impossible to spot.
Given that Suslick and Putterman have both investigated Taleyarkhan's past claims, they think it odd that they were not consulted by the editors of Physical Review Letters about the paper. "There are other people who are very knowledgeable about this," comments Martin Blume, editor-in-chief of the American Physical Society.
Taleyarkhan says that Suslick and Putterman are welcome to visit his lab to see the results for themselves. Both are eager to go as soon as possible. "We look forward to seeing the experiment run," says Putterman.
[Footnotes are at the end of the original article.]
Perhaps the most amusing, and telling aspect of the heady
Pons-Fleishman days was that the proponents were reportedly
running their tests with no provision for shielding from any
likely radiation from the supposed reactions, whereas the
skeptics trying to duplicate were using shielding just in
case they were mistaken.
Had P-F been correct, we'd likely now have "too cheap to
meter" energy, and a bunch of dead champions of same.
Mme Curie was severely radiated before the danger was known. They don't even let shoe stores have those foot x-ray machines anymore; it's too bad, that was great fun.
[Blast a liquid with waves of ultrasound and tiny bubbles of gas are created, which release a burst of heat and light when they implode. The core of the bubble reaches 15,000° C]
This is not a rehash of that cold fusion baloney.
But creating localized very high temperatures is relatively easy to do if you only want to create microscopic amounts of fusion reactions. The difficult part is using the fusion to make significant amounts of heat in a controlled process that can be used to generate electricity.
From what I can tell, peer review was done but some people who figured themselves as naturals to be in the loop weren't.
On the extreme edge of my memories as a yoot. When those shoes fit, they really fit.
This means there results produce fusion at a rate somewhere less than double, but on average closer to what happens when the beaker just sits on the desk.
They used to make wristwatches with radium dials. Glow in the dark all night. The watches weren't particularly dangerous, but they aren't available generally anymore. Something about the people that painted the radium on there.
While I still have my attention; Those flouroscopes were continously on. You could see your own toes wiggle. Even so, I'd end up with second hand as long as they'd fit; as my deformed toes to this day can attest. Kids these days think they have it tough?
If they do achieve fusion, an expected result would be an intense neutron radiation field (as well as gamma radiation).
The fusion reaction between two deuterium atoms is:
D + D yields Helium-3 plus a neutron and gamma radiation
I love it - a physicist named Putterman.
NCSU used to have a physicist in Materials Science named Scattergood and a plant patholigist named Weed.
You can get watches with tiny tritium gas lamps. They use those on night sights and emergency exit signs.
The physicist involved believes this will not be a power source. But it could be an inexpensive source for neutrons that can be used in other applications. It's morew about the science of fusion than about energy production.
"On the extreme edge of my memories as a yoot. When those shoes fit, they really fit."
Sure, but were they matching the shoes to the feet or trimming the feet to match the shoes?
They're fairly regular. Here's another one from 2 months ago.
If I can thread poach a little...There is a major project by FReepers and others regarding protein folding and distributed computing. The effort is dedicated to Ronald Reagan.
http://vspx27.stanford.edu/cgi-bin/main.py?qtype=teampage&teamnum=36120
FReepers are ranked nationally (top 566 and growing) in our efforts to help this massive science project. Please join us if you would like to contribute. Here is one of several threads that can help point you to start donating your unused CPUs if you are interested.
http://www.freerepublic.com/focus/f-bloggers/1554097/posts
Seems very questionable if it is non-replicable and there was a selective peer review.
Thanks for the ping.
I thought this thread was going to have something to do with intel chips inside Macs now.
Thanks for the ping!
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