Joe Stothart, age 14, of Bowling Green, Ohio, for his question:
WHAT IS A GAMMA RAY?
A gamma ray is electromagnetic radiation of the same character as an X ray, but it has a much shorter wave length. Members of the uranium radium series of radioactivity elements give off gamma rays when they disintegrate to form new elements.
Although gamma rays in large amounts may be harmful to the body, they can also be of great benefit. They may be used to treat some cancers, tumors and skin afflictions.
With X ray machines, medical experts can use gamma rays to examine the body for broken bones or foreign objects, and for signs of disease such as tuberculosis.
Sources of strong gamma rays, such as radium and radiocobalt, may be used to X ray iron castings for flaws. Penetrating gamma rays from a betatron may be used to inspect thick metal for flaws or cracks.
Scientists have also used gamma rays experimentally to preserve food and to vulcanize rubber.
When a nucleus emits a gamma ray, it remains unchanged. All that happens is that it loses a certain amount of energy. But it gives off a very penetrating ray if it loses a very large amount of energy, say, 5 million electron volts.
Gamma rays lose energy by colliding with atoms in passing through water, air, lead, iron or any other material. In these collisions, gamma rays may knock electrons loose from their parent atoms. This process is called ionization, because it changes the previously neutral atom or group of atoms into a charged particle called an ion.
High energy gamma rays may create matter by completely disappearing and forming a pair of electrons, one a positively charged positron and one a negatively charged ordinary electron, or negatron.
This creative process is the opposite of what happens when a positron unites with an ordinary electron. When these two particles unite, they are destroyed and two gamma rays are formed.
When a gamma ray passes through the body, it produces ionization in tissue. If too many bombard the tissue, it may be harmful to the cells.
Extremely small amounts of gamma rays bombard us from the neutral radioactivity of the chairs we sit on, the water we drink and the air we breathe. Only large amounts of gamma radiation are dangerous.
A gamma ray will give off a very penetrating ray if it has a large amount of energy. But a sheet of iron about one inch thick will stop 50 percent of gamma rays. It takes about nine inches of water to equal this absorbing ability.
A heavy element such as lead is good for stopping gamma rays. About one half inch of lead equals one inch of iron in absorbing power.
In 1895, X rays were first produced by a famous German physicist, Wilhelm Roentgen, but scientists did not discover until some years later that radioactive elements gave off penetrating gamma rays.