Science: Atomic Glue

The mysteries of matter are arranged in tiers, like a series of dark basements, one below the other, leading down into the earth. When the physicists first discovered nuclear particles (protons and neutrons), they felt that they were close to understanding how atoms are put together. Now they are not so sure. The more they learn about atoms, the more they know they do not know.

Last week Columbia University told about its meson beams, a powerful new tool that the physicists are using to explore the atom’s sub-basement of mystery. Columbia’s monster cyclotron starts with protons (positively charged nuclear particles), and whirls them around in a spiral path in a vacuum chamber 14 ft. in diameter. When they reach the outside spiral, they are moving at 140,000 miles per second (more than, seven-tenths of the speed of light), and carry 385 million electron volts of energy. At the peak of their speed and power, the protons hit a block of beryllium. Out of it sprays a swarm of “pi mesons”—elusive, still-mysterious particles first found in cosmic rays.

Meson Cloud. Physicists say that mesons are matter, but certainly they are matter of a very special kind. Pi mesons, whose mass is 276 times that of an electron, “live” on the average only three 100-millionths of a second. Then they change into lighter “mu mesons” (210 electron masses), which live somewhat longer, eventually decaying into ordinary electrons. The mass that mesons lose in these transformations turns principally into energy, a striking example of Einstein’s principle: that mass is equivalent to energy.

A large part of physical research now centers on mesons. Physicists believe that they are the “glue” that holds atoms together. According to the best-established theory, the nucleons (protons and neutrons that form the nuclei of atoms) have some sort of core surrounded by a cloud of rapidly moving mesons. Each shares its meson cloud with neighboring nucleons. If it were not for this sharing of mesons, the physicists believe, most atoms would fly apart, their protons repelling one another with enormous force.

The theoretical physicists have known about mesons for years, and Nobel Prizewinner Hideki Yukawa predicted their discovery before any were found. But until recently the only way to study mesons was to wait patiently until the proper kind of cosmic ray from space blundered into the physicists’ apparatus. Now the big new cyclotrons supply dense beams of mesons, which can be turned on at will.

Unseen Searchlight. Columbia’s cyclotron yielded its first meson beam about a year ago, when Dr. Eugene T. Booth (now working on a secret Government project) was in charge of the great machine. Since then, the meson beam has played like an unseen searchlight around the flank of the cyclotron, lighting up dark corners of atomic physics. The mass of the quick-vanishing pi meson has been measured accurately, as well as its “spin,” which is something like rotation. Dr. James Rainwater, the present boss of the cyclotron, is finding out what happens when mesons hit protons, neutrons, or other atomic particles. He hopes that a slight improvement in the cyclotron’s internal apparatus will increase its meson yield 1,000 times.

Meson research has not yet produced results that mean much to laymen. But all the world’s physicists are watching over the shoulders of the meson men, sure that a moment of great discovery cannot be far away. The present work with the meson beam, meaningless except to experts, is like the dusty digging above an Egyptian tomb, with the burial chamber packed full of fantastic gold only just out of reach.