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 in emanating power, reaching its original value after about 60 days. The behaviour of actinium and thorium is thus quite analogous, and the explanation advanced to explain the decay and recovery curves of thorium applies equally well to the corresponding curves of actinium.

Fig. 82.

The actinium X is produced at a constant rate from the parent matter actinium, and is transformed according to an exponential law with the time. The constant of change λ = ·068 (day)^{-1}, and this value is characteristic of the product actinium X. As in the case of thorium, the above experiments show that the emanation does not arise from actinium itself but from actinium X. The emanation in turn breaks up and gives rise to an active deposit on the surface of bodies.

212. Analysis of the active deposit from the emanation. Debierne observed that the excited activity produced by actinium decayed to half value in about 41 minutes. Miss Brooks showed