Page:Radio-activity.djvu/425

 This parent product must be transformed very slowly since the β ray product, which arises from it, soon reaches an equilibrium value, which does not change appreciably over a period of more than one year. The experimental evidence points to the conclusion that the parent product does not give rise to β rays, but that the β rays arise entirely from the next product. This parent product cannot give rise to α rays, for we have seen that the initial α ray activity is at first extremely small, but increases steadily with the time for a period of at least eighteen months. Thus the parent product does not give rise to either α or β rays, and must be a "rayless" product.

The first three transition products of the radium emanation, viz. radium A, B and C, have already been analysed, and shown to be consecutive. It thus seems probable that the active deposit of slow change must arise from the successive transformations of the last product radium C. The results already obtained can be completely explained if it is supposed that three transition products, viz. radium D, E and F, are present in the active deposit of slow rate of change. The properties of these products are summarized below.

Radium D is a rayless product of very slow rate of change. It will be shown later that it is half transformed in about 40 years. It is volatile below 1000° C. and is soluble in strong acids.

Radium E is produced from radium D. In breaking up, it emits β (and probably γ) rays but no α rays. It is half transformed in about 6 days and is not so volatile as radium D and F.

Radium F is produced from radium E. It emits only α rays and is half transformed in 143 days. This substance in solution attaches itself to bismuth. It is volatile at about 1000° C.

Apart from their value and interest in showing the stages of transformation of the radium atom, the results of this analysis have an important bearing upon the origin of some of the well-known radio-active substances separated from pitchblende; for it will be shown later that the product radium F is the radio-active substance present in radio-tellurium and probably also in polonium.