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03/21/2002
Frisky Fusing Bubbles?
It occurred to me yesterday that I had not seen a single dolphin
either last year or this year during my predawn walks on the
beach here on Marco Island. However, this morning there they
were - three of them popping in and out of the water about a 7-
iron shot out on the Gulf. It also seemed about a year or two
since I last saw an article reporting the achievement of "tabletop
fusion". Sure enough, like the dolphins, one popped up a couple
weeks ago. You''ve probably seen news reports of what we
could term "bubble fusion".
Over the years, a number of studies have been reported in which
it was claimed that nuclear fusion had been achieved in simple
experiments on a bench top. The work garnering the most
publicity and heated controversy was, of course, "cold fusion".
Cold fusion has been thoroughly discredited since it was reported
some years ago by Stanley Pons and Martin Fleischmann in
Utah. Far from being the solution to all our energy problems,
cold fusion proved to be a case of otherwise very capable
scientists working beyond their field of expertise. Both cold
fusion and bubble fusion involve the purported achievement of
the long-sought goal of harnessing the energy released by nuclear
fusion in the hydrogen bomb and in our sun. In each case, the
apparatus is ridiculously simple when compared to the huge
multibillion-dollar machines that are used by physicists seeking
to make nuclear fusion into a commercial power source.
The bubble fusion work was published in a paper in the March
8th issue of Science. Science is one of the most prestigious
scientific journals, but already it is under fire in some quarters
for even publishing the paper. The work was performed in a
joint effort at Oak Ridge National Laboratory (ORNL) and
Rensselaer Polytechnic Institute (RPI), with the lead author being
Rusi Taleyarkhan of Oak Ridge. Before delving into the paper, I
think a refresher short course on nuclear fusion will be helpful,
both for you and for me. It won''t take long.
The classic fusion reaction that you see in textbooks is 4
hydrogens fusing to form helium. The difference in mass
between the helium and the four hydrogens is what produces the
sun''s energy, thanks to Einstein''s famous equation. Actually,
it''s not that simple and various steps are involved. The
"hydrogens" are actually protons, hydrogen atoms stripped of
their electrons by the 15 million degree temperature in the sun.
These protons have positive charges and, while opposites attract,
like charges repel each other. To get things going, you have to
overcome this proton''s dislike of another proton and get them
extremely close together. Fortunately for us, the sun''s high
temperature gooses up the speed of the protons enough so that
when they bang into each other they''re close enough to fuse.
When they do fuse, a heavy form of hydrogen called deuterium
is formed. Deuterium has a nucleus with a neutron in addition to
a proton. This makes it twice as heavy as regular hydrogen.
Even in the sun, the fusion of two protons is a relatively rare
event. Again, fortunately for us, this means that the sun is
burning up relatively slowly but just enough to provide the
energy we need to flourish here on earth. On earth, in the quest
for an alternative source of energy, workers have been laboring
with those hugely expensive machines to try to achieve fusion
with deuterium. It turns out it''s easier to get two deuteriums to
fuse than two hydrogens. Those porpoises are swimming in H2O
that contains a bit of so-called heavy water, D2O, with deuterium
instead of normal hydrogen. Seawater also contains a smaller bit
of heavier water, T2O, the T standing for tritium. Tritium is a
form of hydrogen with two neutrons and a proton in its nucleus.
If you''re confused, just remember that it''s virtually impossible to
fuse hydrogen but it''s less difficult to fuse deuterium. I''ve left
out a lot of details here but there''s another important point - if
two deuteriums fuse either a neutron or tritium are formed.
Now to the paper. In their work, Taleyarkhan et al. used acetone,
a common solvent. Acetone is a pretty simple compound, with
three carbons, 6 hydrogens and an oxygen in its formula. If you
want to get fusion in acetone what do you do? The ONRL/RPI
workers replaced the hydrogen atoms with deuterium atoms.
They put this "deuterated" acetone in a container and bombarded
it with high power ultrasound. In addition, they hit the acetone
with pulses of neutrons. Why the pulses of neutrons? They
initiated the formation of bunches of tiny bubbles.
These bubbles, under the influence of the changing pressures of
the sound waves, expand and contract until they eventually
collapse. The collapsing bubbles and the resulting shock waves
generate very high local temperatures and pressures. In fact,
light is given off, a feature known as sonoluminescence. In
earlier columns we discussed this so-called cavitation of bubbles
and work in which high temperatures were actually measured.
We also mentioned that some researchers thought that fusion
might occur in collapsing bubbles if the pressures and
temperatures could be made high enough.
This was precisely the goal of the work of the ORNL/RPI
workers. The situation is in some respects like that in cold
fusion. Pons and Fleischmann and others claimed to have
detected neutrons of the right energy as well as tritium in their
cold fusion. The tritium was in all likelihood background tritium
that is normally present. Also, there were apparently problems
with the neutron detectors that were either not properly calibrated
or the interpretation of the data was faulty.
The ORNL/RPI team believes they have detected both tritium
and neutrons of the correct energy (not the energy of the pulsed
neutrons). However, the authors of this paper are much more
circumspect in their claims than were Pons and Fleischmann.
Taleyarkhan and coworkers state up front that, while they believe
their work shows the presence of fusion, they emphasize the need
for others to reproduce their work.
And the hunt is now on to do just that. But, whoa! They have
unbelievers right in Oak Ridge itself. A couple workers named
Saltmarsh and Shapira have tried to repeat the work using the
same detectors and have failed to detect the neutrons, claiming
essentially that Taleyarkhan et al. goofed. The latter respond that
their critics have not properly calibrated their instruments.
Taleyarkhan also points to experiments where they did not use
the deuterated acetone, but plain acetone with ordinary hydrogen
atoms in it. Remember, we said that conditions had to be really
extreme to get ordinary hydrogen to fuse? Well, sure enough,
Taleyarkhan et al. say they found no neutrons or tritium in this
control experiment. On the face of it, this is a strong argument
that tritium and neutrons were detected with the deuterated
acetone. If so, does this mean that an unlimited supply of energy
is in our future? Nobody in this case is claiming any such thing.
So, what do we conclude? Is this another tempest in a teapot or
have these workers come up with real tabletop fusion? An
editorial in Science suggest to both the critics and supporters of
this work, "cool it" and let the normal process of scientific
verification or debunking proceed until the answer is found. Old
Bortrum is certainly not going to stick his neck out either way in
this case! I think we''ll know the answer soon. Keep tuned.
Allen F. Bortrum
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