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. In addition, there is very strong evidence that the radio-active lead obtained by Hofmann contains the three products radium D, E and F together.
The changes of radium as far as they are at present known, are shown diagrammatically in [Fig. 95]. It is possible that further investigation will show that the transformation does not end with radium F.
Fig. 95.
While we have shown that radium D is the parent of E, we have not given any conclusive evidence that E is the parent of F. This evidence is, however, supplied by the following experiment. A platinum plate, made active in the manner already described, was placed in an electric furnace and heated for four minutes at about 1000° C. Most of the products D and F were volatilized, but E was left behind. Since the parent matter D was removed, E at once commenced to lose its β ray activity. At the same time it was observed that the small α ray activity, left behind on the platinum plate, increased rapidly at first and then more slowly, as the activity of E became smaller and smaller. This experiment shows conclusively that E was the parent of F, the α ray product.
235. Rate of transformation of radium D. It has been observed experimentally that each of the products of radium, which emit α rays, supplies about an equal proportion of the activity of radium when in radio-active equilibrium. Since, when equilibrium is reached, the same number of particles of each of the successive products must break up per second, this is an expression of the fact that every atom of each product breaks up with the expulsion of an equal number (probably one) of α particles. Now radium D is directly derived from radium C, and, since the rate of change of D is very slow compared with that of C, the number of particles of D initially present must be very nearly equal to the number of particles of radium C which break up during the time that radium D is being formed. Now D does not itself give out rays, but the succeeding product E does. The products D and E are practically in radio-active equilibrium one month after D is set aside, and the variation of the β ray activity of E then serves as a measure of the variation of the parent product D. Suppose that a vessel is filled with a large quantity of radium emanation. After several hours, the product radium C, which emits β rays, reaches a maximum value, and then decreases at the same rate as the emanation loses its activity, i.e. it falls to half value in 3·8 days. If N1 is the number of β particles expelled from radium C at its maximum value, the total number Q1 of β particles expelled during the life of the emanation is given approximately by
where λ1 is the constant of change of the emanation.
After the emanation has disappeared, and the final products D + E are in radio-active equilibrium, suppose that the number of β particles N2 expelled per second by radium E is determined. If Q2 is the total number of particles expelled during the life of D + E, then Q2 as before is approximately given by Q2 = N2/λ2 where λ2 is the constant of change of radium D. Now we have seen that if each particle of C and of E gives rise to one β particle, it is to be expected that
Q1 = Q2,