Thursday, June 30, 2005

Not-Fake Cold Fusion

I regret my failure to post on this news sooner, but thought an item this important worthwhile even a delayed. I discovered via Slashdot Science that Christian Science Monitor reported earlier this month that scientists at UCLA have achieved cold fusion...really. The result was published in Nature, the top-ranking scientific research journal. (If you need some background, LBL has a basic explanation of fusion in general)

The Nature's popular summary describes the experiment:

Now Putterman, a physicist at the University of California, Los Angeles, has turned a tiny crystal into a particle accelerator. When its electric field is focused by a tungsten needle, it fires deuterium ions into a target so fast that the colliding nuclei fuse to create a stream of neutrons.

Putterman is not claiming to have created a source of virtually unlimited energy, because the reaction isn't self-sustaining. But until now, achieving any kind of fusion in the lab has required bulky accelerators with large electricity supplies. Replacing that with a small crystal is revolutionary. "The amazing thing is that the crystal can be used as an accelerator without plugging it in to a power station," says Putterman.

The scientific article's abstract downplays the power genering possibilities:

Although the reported fusion is not useful in the power-producing sense, we anticipate that the system will find application as a simple palm-sized neutron generator.

(I know you were pining for a portable neutron source just the other day...)

I wonder if the pessimism about power generation is technically warranted. A quick look over the scientific article doesn't explain why the authors conclude so. Certainly it would be surprising if the reacion itself were self-sustaining, since each trigger particle is injected separately, but I wonder if energy drawn from ejected particles could be channeled back into trigger-particle acceleration to make it effectively self-sustaining. (There are political reasons to cool expectations of energy generation.)


The New York Times article explains why the new process is unlikely to generate energy:
...because only one in a million of the collisions actually produce fusion, the device is an inefficient generator of energy.

Michelle Thaller, "Coming in out of the cold: Cold fusion, for real," Christian Science Monitor (June 06, 2005).

Brian Naranjo, James K. Gimzewski and Seth Putterman, "Observation of nuclear fusion driven by a pyroelectric crystal," Nature 434:7037 (28 April 2005), 1115-1118. [Abstract]

Mark Peplow, "Physicists look to crystal device for future of fusion: Desktop apparatus yields stream of neutrons," Nature 434:7037 (28 April 2005), 1057.

Kenneth Chang, "Itty-Bitty and Shrinking, Fusion Device Has Big Ideas," New York Times (April 28, 2005), A18.


Anonymous said...

I'm almost certain the hedging is based on history, not science. The term cold fusion is a dirty word. Its replacement, table-top fusion, is never invoked without plenty of caveats.

rcjhawk said...

Whether or not this result holds up to experimental scrutiny, it's not a claim of "cold fusion." The experiment fires high-speed deuterium nuclei at a target. That's the same mechanism as in an H-bomb, it's just that here the acceleration of the ions isn't set off by a U-235 explosion.

The question about this experiment isn't "Can you cause fusion by crashing D ions into things?" (Yes, you can.) The question is "Can the electric field at a tungsten tip accelerate D ions enough to cause fusion?"

"Cold fusion," at least the version that I've been exposed to, involves fusion of two D ions that somehow occurs without a high-speed collision. That's not what is happening here (if it, indeed, happened).