PDA

View Full Version : {news} Nuclear flash in a pan..?


gypseyman
7th March 2002, 09:46 AM
5 March 2002
PHILIP BALL

To physicists, it sounds like the discovery of the Holy Grail. Researchers in the United States and Russia are tentatively claiming to have seen nuclear fusion in a simple bench-top experiment with nothing more than a beaker of liquid and some sound waves1.

The findings cock a snook at decades of efforts to harness nuclear fusion for energy generation in hugely expensive reactors that create extreme conditions of temperature and pressure. If the claims are verified, the team will have achieved the same processes at a tiny fraction of the cost, using equipment available to almost anyone.

But that does not in itself guarantee that this new process would be useful for power generation. It's one thing to produce a tiny amount of nuclear fusion, as the results seem to imply. Turning it into a viable industrial process is another matter entirely.

"Scientists will - and should - remain sceptical until the experiments are reproduced by others," says nuclear physicist Fred Becchetti of the University of Michigan. Past claims for 'table-top fusion' have, he warns, been irreproducible.

Indeed, the new findings are already exciting controversy2. The problem is that to some they evoke the notorious and now discredited 1989 'cold fusion' claim, which involved a chemical process in a test-tube. But the two processes have nothing in common - the new method isn't 'cold' at all.

Bursting the bubble

At the centre of all the excitement is a process called cavitation. This is the rapid collapse of bubbles in a liquid that high-frequency acoustic vibrations induce.

The bubbles' implosions may create temperatures of over a million degrees centigrade and phenomenally high pressures, claim Rusi Taleyarkhan of Oak Ridge National Laboratory in Tennessee, and his co-workers. Such conditions can fuse two atomic nuclei.

Nuclei coalesce constantly inside the Sun. Here temperatures top 10 million degrees centigrade and hydrogen-rich matter is squeezed to high densities in a form of matter called a plasma. When two hydrogen nuclei fuse, it's really their subatomic particles called protons that combine. This produces a particle called a deuteron, the nucleus of 'heavy hydrogen' or deuterium. The reaction releases an immense amount of energy.

Physicists can't hope to fuse protons in a nuclear reactor, because the conditions needed are just too extreme. Instead they are trying to fuse deuterons, or a deuteron and the nucleus of an even heavier form of hydrogen, called tritium. These fusion reactions also release lots of energy, but at slightly lower temperatures and pressures.

So far, though, despite millions of dollars of research funding, no one has kept a plasma of fusing particles stable enough to extract energy continuously and reliably.

Sound and light show

Taleyarkhan's team is working with one of the most enticing of the many schemes for low-cost table-top nuclear fusion so-far proposed. It builds on the phenomenon of sonoluminescence - the light flashes emitted by the imploding bubbles that sound or ultrasound waves form in liquids.

The tremendous concentration of energy during cavitation is thought to cause these flashes. The diffuse energy of the acoustic waves is focused into a very small region of the liquid, causing its molecules to emit light.

Some estimates suggest that the energy focusing might be great enough to induce nuclear fusion. Taleyarkhan's team has seen hints of that. The researchers induced sonoluminescence in the organic liquid acetone, in which they had replaced all the hydrogen atoms with deuterium.

As well as light flashes, the team saw neutrons emitted from the acetone. Such neutrons are an expected by-product of the fusion of two deuterons. And the researchers detected tiny quantities of tritium - another product of the fusion reaction - after several hours of cavitation.

Both findings would be hard to explain unless one assumes that fusion had occurred. The group saw neither tritium nor neutrons (above the low background level) in normal, deuterium-free acetone exhibiting sonoluminescence. That also supports the case for fusion, as cavitation doesn't create conditions extreme enough to fuse normal hydrogen protons.


References
Taleyarkhan, R. P. et al Evidence for nuclear emissions during acoustic cavitation. Science, 295, 1868 - 1873, (2002).
For more on this story see Nature's News and Features Section tomorrow, 7 March 2002

jema
7th March 2002, 10:00 AM
Fascinating, though until it is reputably reproduced I will tend to be sceptical, load of people who should have know better jumped on the "cold fusion" bandwagon...

jema

GITster
7th March 2002, 02:39 PM
Originally posted by jema
Fascinating, though until it is reputably reproduced I will tend to be sceptical, load of people who should have know better jumped on the "cold fusion" bandwagon...

jema

Why, i did it just the other day....

dicki
7th March 2002, 07:36 PM
hummm i'm very sceptical.... temperatures of over a million degrees in a liquid? that would vaporise anything and make it explode, i have heard of cavitation and it may be an interesting way of releasing the trapped energy in a bubble but temps of a million degrees? no way.

i also don't think you can trigger such a fundamental nuclear reaction by chemical means the forces your playing with are too powerful they need the high temperatures to operate at all

dicki

Gibbon
7th March 2002, 09:13 PM
Good stuff Gypseyman, sounds promising but as Jema says have yet to be convinced...

speculative
8th March 2002, 07:13 PM
That's pretty interesting, as one of the "time travel" theories I read in Discover, Omni, or maybe it was Scientific American dealt with the rapid expansion/collapse of bubbles/balloons... Don't remember too much about the explanation behind it though, but had to do with the creation of tremendous gravitational forces, so this "cavitation" thing is interesting, thanks for the post.

nitan
8th March 2002, 09:59 PM
interesting stuff, would be gr8 if something were to come of it but i doubt it...

cavitation?!?...wasnt that the principle behind that dodgy Keanu Reeves movie with Morgan Freeman in it?...i think it was called chain reaction....:confused:

nitan:)