Relative Activity of Radium and Uranium. 65 



uranium to be transformed in the mode leading to the 

 production of actinium. Nor is there any apparent advan- 

 tage gained by assuming that the transformation of either 

 U I. or U II. into the first member of the side series is 

 accompanied by the expulsion of a /3-particle instead of an 

 a-particle. 



It might, however, be assumed that the branching of the 

 series takes place at some other point, as at radium, for 

 example, and that 86 per cent, of the radium atoms disin- 

 tegrate with the emission of a-rays to form the emanation, 

 etc., while 14 per cent, disintegrate (emitting /3-rays) to 

 form actinium. Direct evidence of the emission of /3-rays 

 by a specimen of radium has been obtained by Hahn and 

 Meitner*. Under these conditions the a-ray activity of 

 ionium would be proportional to the uranium radiation and 

 would equal 0*53. The activity of the actinium series would 

 equal 0*56 and the activity of the radium + emanation 4- 

 radium A, C, and F would be 3'01 (the sum of the values 

 given in Table V.). The sum of all of these together with 

 uranium is 5*10 for the total activity of the uranium series 

 (as in uraninite). There are, however, serious objections to 

 the assumption that the side branch arises at radium, aside 

 from the fact that the values mentioned are widely different 

 from those found in Boltwood's experiments and the value 

 found in the present experiments for the total activity of the 

 uranium products. 



The most significant objection is presented by the agree- 

 ment of the value found for the disintegration constant or 

 radium by Rutherford and Greigerf and the value of this 

 constant found by Miss GleditschJ. The Rutherford and 

 Geiger estimate was based on the number of a-particles 

 emitted per second by the radium C in equilibrium with one 

 gram of radium. If only eighty-six out of every hundred of 

 the radium atoms disintegrate to form radium C, then this 

 estimate would be 14 per cent, too low. The method 

 employed by Miss Gleditsch depended on the production of 

 radium from the ionium in equilibrium with a known amount 

 of radium, and was measured in terms of the fraction of the 

 total equilibrium amount which was produced in a known 

 period of time. This would have given the true value for 

 the disintegration constant irrespective of the mode of 



* Physih. Zeitschr. x. p. 741 (1909). 



t Rutherford, Phil. Mag. xxviii. p. 326 (1914). 



% Am. Journ. Sci. xli. p. 112 (1916). 



Phil. Mag. S. 6. Vol. 40. No. 235. July 1920. F 



