Wednesday, April 27, 2005

Sonofusion In A Crystal

Via Slashdot, Seth Putterman at UCLA claims to have achieved successful sonofusion using a heated piezoelectric crystal immersed in deuterium gas. Putterman says the process remains energy negative, and is possibly of interest in applications that need a non-fission source of neutrons.

An article in New Scientist goes somewhat further in describing the mechanics of the system:

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.

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", writes Justin Mullins in New Scientist. I agree, but this makes an interesting first step.

Update 4/28: More on this in the New York Times, a (temporarily shut down due to the Slashdot effect) link to Seth Putterman's UCLA web page on the research, and Physics News. The latter adds

By using a larger tungsten tip, cooling the crystal to cryogenic temperatures, and constructing a target containing tritium, the researchers believe they can scale up the observed neutron production 1000 times, to more than 106 neutrons per second. (Naranjo, Gimzewski, Putterman, Nature, 28 April 2005).
Also, it appears Taleyarkin will have an article in the May 2005 issue of IEEE Spectrum. The contentious sonofusionist will have his day in print, it seems.