The similarity in nature of X- and primary γ-rays

It has generally been supposed that X- and primary γ-rays are of the same nature. Both radiations are not deflected by electric and magnetic fields, and both excite cathode orβ -rays in materials in which they are being absorbed, the velocities of these cathode orβ -rays being independent of the material in which they are excited, and increasing with the penetrating power of the X- and γ-rays. These mutual properties, combined with the facts thatβ -rays can excite y-rays, and that primary γ-rays are emitted byβ -ray products, leave little doubt of the identity in nature of X- and primaryγ -rays, although penetrating γ-rays, like those of radium, possess many properties apparently different from those of X-rays. Further and practically conclusive proof, however, of the similarity in nature of X and γ-rays has been found by the writer in the course of some experiments on two types of very “soft” γ-radiation, viz., the primary γ-rays of radium E, and the γ-rays excited by theβ -rays of radium E in lead. The experiments show, for example, that the “softer” the γ-rays, the more nearly do their properties, with respect to absorption and scattering, approach those of X-rays. Further, the primary γ-rays of radium E excite the characteristic X-radiations of silver, tin, and other metals.