From: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> Date: 27 April 2005 5:07:40 PM PDT Subject: Desktop nuclear fusion demonstrated
http://www.newscientist.com/article.ns?id=dn7315
An astonishingly simple demonstration of nuclear fusion in a tabletop
device has been performed, involving heating an ordinary crystal soaked in
deuterium gas.
While the technique is unlikely to lead to power generation, such a device
could act as a portable source of neutrons for analysing materials and
medical imaging, and perhaps even spacecraft propulsion.
The key to the system is a crystal made of lithium tantalate. The crystal
is asymmetric and, as a result, heating the material causes positive and
negative charges to migrate to opposite ends of the crystal, setting up an
electric field. The phenomenon is known as the pyroelectric effect.
In 1992, James Brownridge at the State University of New York in
Binghamton, US, used crystals of lithium tantalate to generate X-rays by
heating the crystals to about 100ºC in a dilute gas. The resultant electric
field strips electrons from the gas molecules and accelerates them to huge
energies. The electrons then collide with stationary nuclei in the crystal
and generate X-rays.
When Seth Putterman at the University of California, Los Angeles, US, heard
of the phenomenon a few years ago, he immediately realised that the
electric fields were powerful enough for nuclear fusion to occur,
specifically to fuse nuclei of an isotope of hydrogen called deuterium. The
fields inside the crystals can reach a “mind boggling” 107 electronvolts,
he says.
Strong case
To test whether these fields could indeed cause nuclear fusion, Putterman
and UCLA colleagues Brian Naranjo and James Gimzewski first bathed a
crystal of lithium tantalate in deuterium gas. The setup was then cooled to
-33ºC and then heated to about 7 ºC over three and a half minutes.
The resultant electric field accelerated deuterium nuclei over a distance
of 1 centimetre to energies in excess of 100 kiloelectronvolts. The
accelerated nuclei then collided and fused with deuterium nuclei that had
permeated the surface of the crystal lattice. The fusion produced 400 times
more neutrons than found in background measurements.
Fusion science is littered with hype and over-optimistic claims, but
Putterman has convinced his peers that something interesting is going on.
“They make a very strong case for having seen fusion,” says Nigel Hawkes, a
nuclear physicist at the National Physical Laboratory in Teddington, UK.
But he is cautious about the potential for desktop neutron machines: “It’s
too early to say where this might lead.”
Microthrusters
One problem is the small number of neutrons the experiment produces - a few
hundred per second. A commercial neutron generator would need to produce at
least tens of millions of neutrons per second.
Today, neutrons are created in nuclear reactors or particle accelerators
which can cost millions of dollars to build and maintain. The prospect of a
desktop alternative is a powerful incentive to continue the research and
Putterman’s team hopes to increase the yield by operating at lower
temperatures and by using an array of crystals.
Putterman also suggests the crystals could be used as microthrusters for
tiny spacecraft. By accelerating deuterium in one direction, the spacecraft
would be propelled in the opposite direction.
Journal reference: Nature (vol 434, p 1115)
