The nuclear reaction that powers the Sun has been reproduced in a pocket-sized device, scientists announced today.

Researchers have for years tried to harness nuclear fusion to power the world. But its cousin, nuclear fission -- the breaking apart of atoms -- is the only method so far commercially viable.

The latest invention is not in the same league as efforts to build complex commercial reactors. The new device creates a relatively small number of reactions, and requires more energy to operate than it produces.

But the configuration is so small and simple that its creators think it may inspire unforeseen applications.

"I certainly find it interesting that you can heat a cubic centimeter crystal in your hand, then plunge it in cold water and it will cause nuclear fusion," Seth Putterman from the University of California Los Angeles told LiveScience.

Putterman's lay description greatly oversimplifies how the compact apparatus works.

Specifically, Putterman and collaborators heat a pyroelectric crystal, lithium tantalate, from minus 30 degrees Fahrenheit to plus 45 in a matter of minutes. This generates an electrical charge -- 100,000 volts -- across the tiny crystal, which is housed in a chamber filled with deuterium gas, a heavy form of hydrogen.

The high voltage is focused onto a needle-thin tip, which strips electrons from nearby deuterium nuclei and then accelerates them at a solid target containing deuterium. When two deuterium nuclei collide together at high speed, they fuse to form helium.

The Sun also fuses atoms in nuclear reactions that create light and heat.

The byproduct of the newly discovered lab reaction is a particle called the neutron. The scientists detect about 1,000 neutrons per second. Because neutrons are so penetrating, Putterman said that a hand-held neutron source might one-day be used to do geologic surveys or to look into cargo containers for nuclear devices.

"Current neutron generators are extremely cumbersome," Putterman said. "They are about as big as a dentist's X-ray machine, so you can't carry them into the field."

Pyroelectric crystals could also provide a beam of ions for use as a microthruster in a miniature spacecraft. The research is described in the April 28 issue of the journal Nature.

The Real Deal

(AP) - Previous claims of tabletop fusion have been met with skepticism and even derision by physicists.

In one of the most notable cases, Dr. B. Stanley Pons of the University of Utah and Martin Fleischmann of Southampton University in England shocked the world in 1989 when they announced that they had achieved so-called cold fusion at room temperature. Their work was discredited after repeated attempts to reproduce it failed.

Fusion experts noted that the new UCLA experiment is credible because, unlike the 1989 work, it did not violate basic principles of physics.

"This doesn't have any controversy in it because they're using a tried and true method,'' said David Ruzic, professor of nuclear and plasma engineering at the University of Illinois at Urbana-Champaign. "There's no mystery in terms of the physics.''

-- Associated Press