Rickey Page, age 14, of Peterborough, Ont., for the question:

Ordinary water, as w© all know, is composed of hydrogen and oxygen. The basic recipe calls for two atoms of oxygen to four atoms of hydrogen. In heavy water, many of the hydrogen atoms are replaced with atoms of heavy hydrogen. The scientific name for heavy hydrogen is deuterium. It is an isotope of ordinary hydrogen. And isotope is one of these glamour words of the Atomic age. In feet, the entire Atomic Age would be impossible without isotopes:

The hydrogen atom is the simplest of all atoms. Normally it contains but two electrically charged particles. The nucleus is one positive . proton. Orbiting the nucleus is one lone negative electron. In bulk, the element hydrogen should weigh just so much and no more. But careful weighing proved that hydrogen weighed a little more than it should. A few of the atoms, it seemed, ware overweight.

Much work was done before these rare overweight atoms could be separated. from normal hydrogen. The result was a small quantity of heavy hydrogen, or deuterium. The atoms of this substance ware isotopes. They were just like ordinary hydrogen except for weight. They weighed almost twice as much as ordinary hydrogen. Each contained an extra neutron, an electrically neutral particle, in the nucleus.

Later tritium, another isotope of hydrogen, was discovered. There era two extra neutrons in the tritium atom. This makes for a rather top heavy atom. Tritium is a radioactive isotope with a half life of 12.5 years. In this period of time half of any quantity of tritium will decay by radioactivity.

Rare isotope !toms occur wherever hydrogen is present. The air in the air we breathe, the food we eat end the water we drink. Modern science sifts out those rare overweight atoms to make deuterium and, tritium in bulk.

Like ordinary hydrogen deuterium combines with oxygen to form water.  This water, however, is heavy water. Its scientific name is deuterium oxide. Its extra weight gives it away. When  fed to a plant it can be traced through the living tissues. For this reason it is valuable as a tracer material.

Both deuterium and tritium do valuable work as tracers in the field of biochemistry. By tracing them through living tissue scientists can study the processes by which plants and animals make use of hydrogen.

Heavy water, however, has a still more dramatic fob to do in this Atomic Age. Loaded with extra neutrons, it tends to pick up fewer stray neutrons than does ordinary water. And in an atomic reactor, we do not want neutrons picked up by nearby materials. This is where heavy water, deuterium oxide, is useful: It is fed to the atomic reactor where it acts as a moderator.