The wonders of radium

by Maynard Shipley

THE RADIOACTIVE DISINTEGRATION SERIES

In order to show the decomposition products of the two parent radioactive elements—Uranium and Thorium—and their chief characteristics, together with their relations to one another, and the time required for the product (element) to be half transformed, it is customary to arrange them in a disintegration series. There are three series, Uranium I, Uranium Y, and Thorium.

In the first table given below is shown how the series known as Uranium I is transformed into the end-product, uranium lead. This is followed by the Uranium Y (or Actinium) series, and by the Thorium series; the end-product of all three being a characteristic type of lead. In the tables T is the “time-period” of a product, or the time required for the product to be half transformed. In the column “Rays” is shown what type of ray, or rays, is, or are, emitted during the disintegration process—A=Alpha rays (or particles), B=Beta rays (negative electrons), and G=Gamma rays (or X-rays of very high “frequency”).

“In the great majority of cases,” says Sir Ernest Rutherford, “each of the radioactive elements breaks up in a definite way, giving rise to one Alpha or Beta particle and to one atom of the new product. Undoubted evidence, however, has been obtained that in a few cases the atoms break up in two or more distinct ways, giving rise to two or more products characterized by different radioactive properties. A branching of the uranium series was early demanded in order to account for the origin of Actinium.”

In the first column is given the “atomic weight” of each radioactive element, the weight decreasing with (almost) every “disintegration period.” The figures followed by an interrogation point are Rutherford’s, and indicate that slightly different figures are given by other authorities.