PHYSICISTS PRODUCE FIRST COMPLETE ATOMS OF ANTIMATTER.

Byline: Malcolm W. Browne The New York Times

Physicists at the European Laboratory for Particle Physics announced Thursday that they had created, for 40 billionths of a second, the first complete atoms of antimatter ever made by human beings or seen in nature.

In an anti-atom, the antimatter equivalent of an ordinary atom, the electrical charges of all the component particles are reversed; while an ordinary atom has a positively charged nucleus with one or more negatively charged electrons orbiting it, the antimatter atom has a negatively charged nucleus with positively charged orbiting electrons. An ordinary atomic nucleus contains positively charged protons, while its antimatter counterpart contains negatively charged antiprotons.

Unless an antimatter atom is kept from coming into contact with an ordinary atom, the two atoms annihilate each other in a violent flash of energy - a fact that may explain the apparent absence of antimatter in the natural universe. Anti-protons are routinely made in physics laboratories, as are anti-electrons, which are also called positrons. But no one had heretofore succeeded in nudging a positron into orbit around an anti-proton, making an atom of antimatter. The announcement on Thursday by the European laboratory near Geneva, known by its former acronym, CERN, establishes that this bizarre kind of atom can actually exist.

Physicists hope one day to make comparative measurements of the properties of atoms and anti-atoms in terms of their gravitational attraction, their interactions with light, and other features. Subtle differences between atoms and their antimatter counterparts may shed light on the origin and evolution of the universe and help solve the puzzle as to why we are made of matter instead of antimatter.

Although most physicists discount the idea that anti-hydrogen might one day be developed as a very high potency fuel for interstellar rockets or superbombs, some scientists have not abandoned the dream of exploiting antimatter as a propellant. When combined with ordinary matter it annihilates, converting mass to energy far more efficiently than does a nuclear bomb.

Dr. Walter Oelert of the Juelich Institute for Nuclear Physics Research in Germany and his German and Italian colleagues reported that they created the 11 atoms of anti-hydrogen during a three-week experiment at CERN last September, but withheld the news until they and independent experts had thoroughly checked their results, which will be published in a forthcoming issue of the journal Physical Review B.

"We're absolutely sure now," he said in an interview, "and the experiment shows without doubt that anti-hydrogen can exist. No one really doubted it, but it's nice to have the experimental proof."

The anti-hydrogen atoms created in the experiment were moving at nearly the speed of light and survived only some 40 billionths of a second before colliding with atoms of ordinary matter and annihilating themselves. But from the pattern and types of debris created by these collisions, the scientists were able to establish the identity of the projectiles as anti-hydrogen atoms.