Seligmann, Age 14, Of Seattle, Wash., for his question:
What are gamma rays?
Radioactive substance pours out streams of penetrating energy. Some of its rays can be stopped by a few sheets of paper, and stronger rays can be stopped by metal foil. The most piercing rays given off by radioactivity are gamma rays. A shield of solid lead five or six inches thick is needed to stop these deadly streams of energy.
The 20th century opened with a flurry of scientific excitment. Radioactivity had been discovered, and every wide awake physicist was busy probing its mysteries. The penetrating energy given off by a radioactive substance was soon separated into three different types. Alpha rays were found to be streams of proton particles charged with positive electricity. Beta rays were streams of negatively charged electron particles.
The nature of the gamma rays given off by radioactivity was fathomed a little later. These amazing rays had much to tell us, and just few years ago they were used to test one of Einstein's complex theories of relativity. Unlike alpha and Beta rays, gamma rays are not streams of particles. They are penetrating streams of pure energy somewhat like Xrays. Both are forms of electromagnetic energy with shorter brave lengths than ordinary light.
Shorter wave lengths have more penetrating energy. X rays are a million Million times shorter than radio, and gamma rays are 100 times shorter than the wave lengths of x rays. Gamma rays given off by radioactive decay can pierce flesh, bone and wood. Six inches of lead is needed to stop them.
Uranium 238 decays step by step to the isotope lead 206. In the process, eight alpha particles and a number of beta particles are not forth. But the weight of the final lead plus the lost particles is a little less than the original uranium. This fraction of lost weight has been converted to pure energy and given off as searing Gamma rays.
In 1934, the positively charged positron was discovered. This tiny particle is equal in mass to the negative electron. In radioactivity, positron meets electron, and the two particles of matter convert each other to a gamma ray of energy. This energy can be converted back to matter as a pair of particles, a positron and an electron.
Einstein suggested that the path of light is bent by a field of gravity, and Gamma rays were used to test this theory. Wave lengths, it was argued, should be shortened by more intense gravity. A beam of gamma rays was sent 75 feet down into the earth where gravity is slightly stronger, and the short short gammma wave lengths were made slightly shorter.