. The Bell System technical journal . the mixture of radioactive bodies known as actiniumactive deposit, from which a-particles of a range of about 10 lately been observed in the Institut du Radium. Thus far I have written as though RaC and ThC were isolablesubstances, of which one may obtain pure samples and analyze atleisure the a-rays thereof. The truth, however, is far otherwise; forthe difficulties of making one radioactive substance practically freefrom others, serious in most cases, are utterly insuperable in RaC and ThC are so very ephemeral (their half-lives are too
. The Bell System technical journal . the mixture of radioactive bodies known as actiniumactive deposit, from which a-particles of a range of about 10 lately been observed in the Institut du Radium. Thus far I have written as though RaC and ThC were isolablesubstances, of which one may obtain pure samples and analyze atleisure the a-rays thereof. The truth, however, is far otherwise; forthe difficulties of making one radioactive substance practically freefrom others, serious in most cases, are utterly insuperable in RaC and ThC are so very ephemeral (their half-lives are toosmall to measure, and are guessed from the Geiger-Nuttall relation as10~^ and 10~^^ second respectively) that they can never be disseveredfrom their mother-elements RaC and ThC which are also one finds the long-range particles designated as belonging toRaC or ThC, and indeed I have nowhere found stated any compellingreason for attributing them to the C-elements rather than the C- 586 BELL SYSTEM TECHNICAL JOURNAL. Fig. 6—Annular magnet employed for analysis of alpha-ray spectra. (After Ruther-ford, Wynn-Williams, Lewis & Bowden; Proc. Roy. Soc).
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