Cold traps for 'hot' atoms.

Handling radioactive atoms is always a tricky business. But creating radioactive particles by slamming atoms or protons into a target, slowing down -- and thus cooling -- the products, and capturing the chilled atoms in a trap before they decay into other elements offers even greater challenges than usual. Several research groups have now succeeded in using lasers and magnetic fields to accomplish this feat.

Luis A. Orozco and his collaborators at the State University of New York at Stony Brook worked with the radioactive isotope rubidium-79. To slow down the atoms, the researchers introduced them into a specially coated glass cell. As the atoms bounced around, their speeds changed and the slowest ones were caught in a web of laser light and magnetic fields within the cell.

To study subtle nuclear effects, the researchers hope to use the same method to trap francium atoms, which exist only as short-lived, intensely radioactive isotopes. "This would open an avenue to really exciting, new physics," Orozco says. Researchers could make extremely sensitive measurements of light emitted and absorbed by trapped atoms to obtain insights into nuclear and particle physics.

Stuart Freedman and his team at the University of California, Berkeley, used a somewhat different technique to capture radioactive sodium-21 atoms. In this case, a laser beam slowed down sodium atoms before they entered the trap's magnetic and optical fields. "We were the first to demonstrate this [particular method]," says team member Song-Quan Shang of Lawrence Berkeley Laboratory in Berkeley, Calif.

The availability of cold, trapped radioactive atoms makes possible the detailed study of such nuclear processes as alpha and beta decay. Because the laser wavelengths necessary for capturing atoms are unique to each isotope, such schemes can also serve as isotope analyzers, which aid in determining the age of rocks and other materials.