The chemistry of the radio-elements / by Frederick Soddy.

  • Frederick Soddy
Date:
1914
Catalogue details

Licence: In copyright

Credit: The chemistry of the radio-elements / by Frederick Soddy. Source: Wellcome Collection.

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    V THE BRANCHING OF THE DISINTEGRA- TION SERIES Before we can consider the disintegration series beyond the emanation group, some considerable changes that have recently been made must first be dealt with. It has long been recognised (I, pp. 57 and 79) that the transformations of the active deposits were not completely understood. The first step was the discovery of the evanescent A members of the thorium and actinium series corresponding with radium A. Their separate recognition, since previously their a-rays had been attributed to the emanations, removed one of the grounds for supposing (I, p. 37) that in these series the different a-ray changes did not all produce one a-particle per atom disintegrating, as in the case of the uranium series.^^ The numbers of a-particles expelled in the thorium series were directly counted by Barratt, who showed that, in equilibrium, per 100 a-particles of thorium emanation of range 5.0 cm. (at N.T.P.), 100 of range 5.4 cm. are given by the A member, whereas 35 of range 4.8 cm. and 65 of range 8.6 cm. are given by thorium C.^® This shows directly and beyond doubt that the series branches at or before the C member, 35 % of the atoms going by one route and 65 by another. The numbers of the atoms going along the two branches being of the same order makes the series comparatively simple to unravel experimentally. As a matter of fact, however, the far more difficult case of radium C, investigated by Fajans, was the first example of branching to be definitely established.^’^ It is clear (I, p. 58) that radium D must be the direct product of radium C in its a-ray change, becanse it is obtained from it in relatively large amount by recoil methods. Hence radium Cg, which gives ^-rays and no a-rays, cannot be intermediate as repre- sented on I, p. 55. Moreover, the small relative quantity of radium C2 obtained by recoil, the j8-activity of which is only of that of the source, cannot be explained, as it
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