http://www.everything2.com/index.pl?node_id=1848494
The term cold fusion was first coined in 1983 in relation to work on
muon catalysed fusion, but entered the public consciousness six years
later during the storm of publicity that surrounded Fleischmann and
Pons' claim of excess heat production during an electrolysis experiment.
Those results are now generally discredited by the scientific community,
but retain popularity with those on the fringe, where even more
outlandish claims are advanced. The announcement is also derided for
being 'press conference science'- attempting to get the jump on a rival
team at Brigham Young University, the University of Utah scientists
leaked their findings to the press before going through a thorough
process of peer review. But amidst all the backlash and accusations of
pseudoscience, it's worth recalling that both groups had been accepted
for publication by Nature and all involved were, at the time, respected
scientists. So what went wrong?
Fleischmann, Pons and cold nuclear fusion in condensed matter
The original experiment consisted of performing electrolysis in heavy
water with Palladium electrodes. The supply of electricity allows the
water molecules to be broken into ions, and thus for a current to flow
from one electrode to the other. This process is not completely
efficient, so heat is generated as a by-product; surrounding the
experimental apparatus with a calorimeter, this heat generation can be
measured. So far, nothing controversial- the movement of heat, charge
and associated chemical changes are readily explained and balanced by
conventional theories. But in Fleischmann and Pons' experiment, the
heating rate exceeded, by around 10W, that which would be expected in
line with those theories. The inability to explain this through
thermodynamics, electrical theory or chemistry therefore led the
researchers to a controversial conclusion- that the explanation must be
nuclear, with fusion in the heavy water being responsible for the
additional power output.
How realistic, then, is such a claim? There are two major reaction paths
for deuterium fusion, of roughly equal probability. They are as follows.
d + d --> t + n +4.0MeV
d + d --> 3He + p + 3.3MeV
Where are the neutrons?
Thus, if energy is being produced, then the same should be true of
neutrons, tritium, helium, and preferably all three. The neutron output
that would correspond to a 10W heating effect would be staggering,
implying a production rate of over 1013 neutrons per second. To place
that in context, a typical university Physics facility for students
would not allow the use of sources churning out more than about 109
neutrons per second. The 'cold fusion' device would therefore have to be
10,000 times more potent- running un****elded, this would probably have
offed the researchers long before they could announce any results.
Moreover, such a rate simply wasn't observed, with the measured yield
being around 104/s.
Where's the Helium?
Perhaps, however, the 50/50 distribution between reaction paths was
inappropriate in this situation, and there was a dispro****tionate
tendency (for some unexplained reason) to follow the Helium generating
path instead. Moreover, unlike the sub-expectation neutron production,
several research groups claimed to observe Helium formation. There's
also a third possible reaction path, with a greater energy yield and
also giving rise to Helium, but that is eight orders of magnitude less
probable than the two main reactions. Ultimately though it's irrelevant-
careful checks revealed that any observed Helium was the result of air
leakage into the experimental setup.
The demise of a theory
With time, the evidence against cold nuclear fusion piled up: Neutron
and Tritium production being ruled out by the BYU team, and erratic
observations of excess heat ultimately being attributed to poor
calorimetric techniques. Fleischmann and Pons both lost their jobs, yet
somehow managed to secure (and spend) $30million from Toyota to continue
their research in France. When that ran out, Pons admitted defeat, but
Fleischmann returned to the UK and continues to work on cold fusion
theory.
Muon catalysed fusion
But what of the original claimant to the cold fusion name, the technique
now (presumably to maintain some distance) known as Muon catalysed
fusion? Simply put, it works, and at room temperature, but, much like
the Farnsworth Fusor, requires more energy to sustain than is produced,
making it worthless as an energy source (although it makes a fine
Neutron source if you have a use for such a thing). In essence, a muon
behaves exactly like an electron, except it is around 200 times more
massive. Thus Hydrogen with muons in place of electrons allows the
nuclei to get around 200 times closer to each other, which drastically
increases the probability of fusion: as this decreases exponentially
with distance, so a 200-fold reduction in distance equates to a
probability some 75 orders of magnitude higher than for regular Hydrogen.
This fusion process takes around 10-8 seconds, which seems blisteringly
fast, until you take into account the lifespan of a muon- an average of
2.2 microseconds. Assuming no other limiting factors, this means that
any given muon is only good for a couple of hundred fusions, or an
energy output of around 4GeV. Sadly, there are limiting factors -
although experimental rates of around 150 fusions per muon have been
achieved - but more to the point, Muons aren't cheap. Producing them
through Proton bombardment of Lithium or Carbon checks in at around
10GeV each, more than double the energy that can then be reclaimed.
So, despite more than its share of crackpots and controversies, cold
fusion is not purely in the domain of sci-fi or pseudoscience. But if
you're after a revolution in our energy supply, you'd be better looking
elsewhere.
Reference
"How Cold is Cold Fusion?"- Janne Wallenius, Royal Institute of
Technology (KTH),Sweden: Seminar at the University of Edinburgh Physics
Department, 23/11/06.
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