Researchers at the Oak Ridge National Laboratory have found what atomic theorists said shouldn't exist: a stable ion of calcium.

"This was a surprise," University of Tennessee physicist David J. Pegg, one of the researchers, said Tuesday."There is no immediate direct application, but the information may be used as a building block," Pegg said. "If nobody cared . . . about the structure of atoms we wouldn't have lasers or transistors or anything like that."

The findings were included in a four-page report in Physics Today, a journal of the American Physical Society, and in Physical Review Letters, Science News and a British publication called The New Scientist.

Atoms are usually electrically neutral because they have the same number of positively charged protons and negatively charged electrons. An ion is an atom or group of atoms with an electrical charge.

Theory held that calcium, along with barium, strontium and other elements in a series known as alkaline earths, should not be able to hold a negative charge, Pegg said. The theory was that the atoms would automatically discharge any extra electron they picked up, ridding themselves of the negative charge.

Pegg and his assistant, UT graduate student Jeffrey Thompson, along with Oak Ridge scientists Robert Compton and Gerald Alton, decided to test the theory.

To their surprise they found that when they added an electron to a calcium atom, the electron stayed there, giving the atom a negative charge.

"So we then said, `Perhaps the theorists are wrong,' " Pegg said.

The next step was to see if they could knock the electron off the atom, since it wouldn't leave of its own accord.

Using a laser beam, the researchers found that they could knock the electron off, and concluded the ion was stable, Pegg said.

Studying the stability of negative calcium ions is something that required the most modern equipment, Pegg said, particularly the Cray supercomputer at Vanderbilt University.

"Somebody may have tried to do this in the 1960s, for instance, and couldn't," he said.