Heart of matter.

When Brad Filippone and a team of physicists first tried to slow down neutrons six years ago, their initial experiment was pretty much a bomb.

"The first time, we got zero, none," said Filippone, a physics professor at the California Institute of Technology. "It was really disappointing."

But their latest attempt was a success. Filippone and a group of Caltech colleagues and scientists from universities around the nation were recently' able to slow down neutrons (which usually travel at 10 percent of the speed of light) to about 15 miles per hour. The scientists collected about 140 neutrons per cubic centimeter, the most significant number since the efforts in 1970s.

"We were really excited about the measurements," Filippone said. "We went out and had several big collaboration dinners."

The researchers honed the technique of trapping slowed, ultracold neutrons at the Los Alamos National Laboratory. There, they smashed protons from a nuclear accelerator into a material like tungsten; this knocks the neutrons out of their nuclei. Passing through plastic material and heavy hydrogen further slows the neutrons until they eventually emerge at the desired speeds.