| 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 Brooks13 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 actinium14. Recent work has verified this supposition. Giesel15 and Godlewski16 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.
After separation of actinium X, the activity, whether measured by the α or β rays, increases about 15 per cent. during the first day, and afterwards decays exponentially with the time, falling to half value in 10·2 days. The activity of the separated actinium was small at first but steadily increased with the time, reaching a practical maximum after an interval of sixty days. After the first day, the decay and recovery curves of activity are complementary to one another. The curves of rise and decay are shown graphically in Fig. 82, curves I and II respectively.