3. By exposure to magnetic and electric fields, noting extent and direction of deflection.
4. By their relative absorption by solids and gases.
5. By the scintillations on a zinc sulphide screen.
Identification of the Rays
The alpha rays have been identified as similar to the so-called canal rays. These were first observed in the study of the X rays. When an electrical discharge is passed through a vacuum tube with a cathode having holes in it, luminous streams pass through the holes toward the side away from the anode and the general direction of the stream. They travel in straight lines and render certain substances phosphorescent. These rays are slightly deflected by a magnetic field and in an opposite direction from that taken by the cathode rays in their deflection. The rays seem to be positive ions with masses never less than that of the hydrogen atom. Their source is uncertain, but they may be derived from the electrodes.
The beta rays are identical in type with the cathode rays and are negative electrons.
The gamma rays are analogous to the X rays and are of the order of light. They are in general considerably more penetrating than X rays. For example, the gamma rays sent out by 30 milligrams of radium can be detected by an electroscope after passing through 30 centimeters of iron, a much greater thickness than can be penetrated by the ordinary X rays.