Fig. 84.

214. Products of Actinium. There is one very interesting point of distinction between the radio-active behaviour of thorium and actinium. The latter after removal of actinium X, shows only about 5 per cent. of the original activity, while thorium, after removal of Th X, always shows a residual activity of about 25 per cent. of the maximum value. This very small residual activity indicates that actinium, if completely freed from all its products, would not give out rays at all, in other words, the first change in actinium is a rayless one.

The radio-active products of actinium are shown graphically in [Fig. 84]. Some of their chemical and physical properties are tabulated below.

ProductsTime to be half transformedRaysSome Physical and Chemical properties
Actinium?No raysInsoluble in ammonia
Actinium X10·2 daysα, (β and γ)Soluble in ammonia
Emanation3·9 secs.α raysBehaves as a gas
Actinium A35·7 mins.No raysSoluble in ammonia and strong acids.
Actinium B2·15 mins.α, β and γVolatilized at 100°C. B can be separated from A by electrolysis

CHAPTER XI.
TRANSFORMATION PRODUCTS OF RADIUM.

215. Radio-activity of radium. Notwithstanding the enormous difference in their relative activities, the radio-activity of radium presents many close analogies to that of thorium and actinium. Both substances give rise to emanations which in turn produce “excited activity” on bodies in their neighbourhood. Radium, however, does not give rise to any intermediate product between the element itself and the emanation it produces, or in other words there is no product in radium corresponding to Th X in thorium.

Giesel first drew attention to the fact that a radium compound gradually increased in activity after preparation, and only reached a constant value after a month’s interval. If a radium compound is dissolved in water and boiled for some time, or a current of air drawn through the solution, on evaporation it is found that the activity has been diminished. The same result is observed if a solid radium compound is heated in the open air. This loss of activity is due to the removal of the emanation by the process of solution or heating. Consider the case of a radium compound which has been kept for some time in solution in a shallow vessel, exposed to the open air, and then evaporated to dryness. The emanation which, in the state of solution, was removed as fast as it was formed, is now occluded, and, together with the active deposit which it produces, adds its radiations to that of the original radium. The activity will increase to a maximum value when the rate of production of fresh emanation balances the rate of change of that already produced.

If now the compound is again dissolved or heated, the emanation escapes. Since the active deposit is not volatile and is insoluble in water, it is not removed by the process of solution or heating. Since, however, the parent matter is removed, the activity due to the active deposit will immediately begin to decay, and in the course of a few hours will have almost disappeared. The activity of the radium measured by the α rays is then found to be about 25 per cent. of its original value. This residual activity of radium, consisting entirely of α rays, is non-separable, and has not been further diminished by chemical or physical means. Rutherford and Soddy[[314]] examined the effect of aspiration for long intervals through a radium chloride solution. After the first few hours the activity was found to be reduced to 25 per cent., and further aspiration for three weeks did not produce any further diminution. The radium was then evaporated to dryness, and the rise of its activity with time determined. The results are shown in the following table. The final activity in the second column is taken as one hundred. In column 3 is given the percentage proportion of the activity recovered.

Time in daysActivityPercentage Activity recovered
025·00
0·7033·711·7
1·7742·723·7
4·7568·558·0
7·8383·578·0
16·096·095·0
21·0100·0100·0

The results are shown graphically in [Fig. 85].