Gamma rays are streams of electromagnetic waves. They are given off from elements such as radium, when they undergo a process known as radioactive decay.
In 1899 the British physicist Ernest Rutherford began a study of radioactivity. He found three types of radiation which he called alpha, Beta and gamma rays. Alpha rays were stopped by a thin sheet of paper, beta rays could get through several millimeters of aluminum, and gamma rays could pierce quite thick pieces of lead.
Alpha rays travel at up to 12,000 miles a second, beta rays from 80,000 to 180,000miles a second, and gamma rays at 186,000 miles a second, the speed of light.
Gamma rays have proved very helpful in medicine and industry. These rays are also given off by radioactive isotopes obtained as by-products in production processes. They can produce radio graphs of forgings and the seams of boilers and other pressure vessels, where freedom from flaws is vital.
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