209. Radiations from Thorium products. It has been shown in the last section that the activity of thorium, by successive precipitations with ammonia, is reduced to a limiting value of almost 25 per cent. of the initial activity. This “non-separable activity” consists of α rays, the β and γ rays being altogether absent. According to the disintegration theory, this is an expression of the fact that the initial break-up of the thorium atom is accompanied only by the expulsion of α particles. We have seen in [section 156] that the thorium emanation also gives out only α rays. In the active deposit, thorium A gives out no rays, while thorium B emits all three types of rays.
Some hours after separation, Th X gives out α, β, and γ rays, but the appearance of β and γ rays is probably due to the thorium B associated with it. The β and γ ray activity of Th X is much reduced if a current of air is continuously aspirated through a solution of Th X to remove the emanation. It seems likely that if the emanation could be removed as fast as it was formed, so as to prevent the formation of thorium B in its mass, Th X itself would give out only α rays: but, on account of the rapid rate of change of the thorium emanation, it is difficult to realize this experimentally.
210. Transformation products of Thorium. The transformation products of thorium and the rays emitted by them are graphically shown below ([Fig. 81]).
Fig. 81.
A table of the transformation products of thorium is shown below, with some of their physical and chemical properties.
| Product | Time to be half transformed | λ (sec)-1 | Radiations | Physical and chemical properties |
|---|---|---|---|---|
| Thorium | α rays | Insoluble in ammonia | ||
| Th. X | 4 days | 2·00 × 10-6 | α rays | Soluble in ammonia |
| Emanation | 54 secs. | 1·28 × 10-2 | α rays | Inert gas, condenses -120° C. |
| Thorium A | 11 hours | 1·75 × 10-5 | no rays | Soluble in strong acids. Volatile at a white heat. B can be separated from A by electrolysis and by difference of volatility. |
| Thorium B | 55 mins. | 2·1 × 10-4 | α, β, γ rays | Same |
| ? | — | — | — | - |
211. Transformation products of Actinium. It has previously been pointed out (sections [17] and [18]) that the actinium of Debierne and the emanium of Giesel contain the same radio-active constituent. Both give out a short-lived emanation which imparts activity to the surface of bodies. Recently, thanks to Dr Giesel of Braunschweig, preparations of “emanium” have been placed on the market, and most of the investigations that are described later have been made with this substance.
Actinium X. Actinium and thorium are very closely allied in radio-active properties. Both emit an emanation which is rapidly transformed, but the rate of change of the actinium emanation is still more rapid than that of thorium, the activity decreasing to half value in 3·7 seconds. Miss Brooks[[308]] has analysed the active deposit from the emanation of actinium, and has shown that two successive changes occur in it, very similar in character to those observed in the active deposit of thorium. It thus seemed probable, from analogy, that an intermediate product, corresponding to Th X in thorium, would be found in actinium[[309]]. Recent work has verified this supposition. Giesel[[310]] and Godlewski[[311]] independently observed that a very active substance could be separated from “emanium,” very similar in chemical and physical properties to Th X in thorium. This product will, from analogy, be called “actinium X.” The same method, which was used by Rutherford and Soddy to separate Th X from thorium, is also effective in separating actinium X from actinium. After precipitation of the active solution with ammonia, actinium X is left behind in the filtrate. After evaporation and ignition, a very active residue remains. At the same time, the precipitated actinium loses a large proportion of its activity.
Giesel observed the separation of an active product, using a fluorescent screen to detect the radiations. A very complete examination of the product actinium X has been made by Godlewski in the laboratory of the writer.