Philip Krasicly, age 3 i., of Bridgeport, Conn.., for his question:

What are mesons?

Not so long ago We knew of only three different atomic particles    the proton, the electron and the neutron. These three are indeed the basic building blocks of all the assorted atoms. But now we know of at least 30 atomic particles, are some of these newcomers are mesons.

Andy's readers often ask what stinks the particles of an atom together. Scientists asked themselves the same question. The central nucleus and its orbiting electrons are attracted together by opposite charges of electricity. The nucleus is positive and the electrons are negative. But the particles in the tight nucleus are not opposites. These nucleons cannot be locked together by electrical energy.

The nucleus of the atom must be held together with a much stronger cement. Scientists searched for this mighty binding force    and found the mesons. They used math, super duper math, to tackle the problem, and in i935 Hideki Yukawa of Japan had a theory.

There is another particle, he figured. It must shift from one nucleon to another, and this is the energy that locks the nucleus together. This particle, he predicted, is heavier than the light electron, but less heavy than the bury proton. Later, two of Yukawa's particles were found in atomic fragments caused by cosmic rays. They were named mesons because, as Yukawa predicted, they are middleweight particles.

The mu meson, or moon, did not act as a nucleon cement as expected. But the pi meson, the pion, did. Later the K meson, the kayon, was founds and all this searching led to the discovery of still more particles. Mesons live and die in a flash, and the specks of energy are too small to be shown by the best microscopes, but We know they exist.

Some high speed mesons leave trails on film or in misty cloud chambers. Some can be coaxed to click an electronic counter. We know they Can change nucleons, and perhaps many of them work in a nucleus. The big atom smashers are used to reveal more of their secrets, for we need to know more, far more, about the busy mesons.

We do not know all about the nucleus of the little atom  far from it. Our knowledge is somewhat like a half finished jigsaw puzzle. We have lots of particles. Hut We are Still trying to figure how to fit the pieces together  their different roles and how they interact with each other. But one thing is surf. The little nucleus is a mighty powerhause of busy activity.