ABSTRACT
The permanent radio-active substances uranium, thorium and radium all give out two types of rays, one easily absorbed and non-deviable by a magnetic field and the other more penetrating in character and deviated by a magnetic field. These rays are extraordinarily penetrating in character, and pass readily through great thicknesses of matter. The amount of ionisation produced by them is only a very small fraction of that produced by the other two types of radiation. Using testing vessels of ordinary size, the ionisation due to the penetrating rays is of the order of 1 part in 100 of that due to the deviable rays and 1 part in 10,000 of that due to the easily absorbed rays. Experiments were also made to see if the excited radio-activity, due to thorium and radium, which gives out deviable and non-deviable rays, also emits these penetrating rays.
