What is the difference between nuclear fusion and cold fusion?
Asked by: Robert Hernandez
Nuclear fusion can produce energy when the nuclei of lighter elements come together
(fuse), creating larger nuclei. Energy is liberated when the total mass of the end
is slightly less than the mass of the lighter nuclei going into the process, with that
difference in mass being converted to energy via Einstein's famous E=mc2 relationship.
Because the protons in nuclei are all positively charged, and like charges repel, nuclei
need some convincing to get them to fuse. That convincing ordinarily involves high
temperature and pressure, such as exists at the core of a star or under conditions
created by a fission bomb.
Cold fusion is an attempt to get fusion to occur under less extreme conditions, possibly
as a result of chemical reactions. Despite the flurry of publicity several years ago,
cold fusion remains unrealized speculation for now.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor
Cold fusion, if it worked, would be a form of
Although many nuclei can be fused, this subject
normally refers to fusion of hydrogen isotopes
deuterium or tritium to form helium. When this
happens energy is released. Unfortunately, the
hydrogen nuclei are positively charged and
repel one another -- very strongly so at short
distances. This makes fusion difficult to
achieve. In the Sun very high levels of heat and
pressure overcome the repulsion. On Earth fusion
can also be forced this way, but so far not with
more energy being released than what went into
building the neccessary heat and pressure.
Early in 1989 two chemists, Prof. G. Stanley Pons
and Prof. Martin Fleischmann were experimenting
with electrolyzing heavy water, (which contains
tritium), using palladium electrodes. Hydrogen in
all its forms has a very strong affinity for
palladium. From their measurements, Pons and
Fleischmann calculated that more energy was being
released from the process, as heat, than was
being put into it as electricity. They speculated
that somehow tritium nuclei were being forced
close together enough to cause fusion. This would
account for the apparent excess heat being
released. The process was called cold fusion
because the temperatures involved were far lower
than any at which fusion had been known to occur.
Today it is believed by most scientists familiar
with the facts of the case that the procedures
of Pons and Fleischmann were flawed and their
Answered by: Craig Busse, B.S., Process Engineer, Lucent Technologies, Whippany NJ