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LXXXVIII. The Constant of Uranium X. By Frederick 

 Soddy, M.A., and Alexander S. Russell, M.A., B.Sc, 

 1651 Exhibition Scholar, late Carnegie Research Scholar*. 



THE value of the coefficient of decay (X) of the /3-rays of 

 uranium X was originally found to be 0*031 (day) -1 ")"- 

 This result gives a period of half-change of about 22 days. 

 Subsequent investigators of this body have not made special 

 measurements of its decay, but have simply stated that such 

 measurements as have been made point to a similar result. 

 Moore and Schlundt %. however, examined over a period of 

 about 50 days, a number of preparations of uranium X 

 separated in various ways from the parent body, and found 

 that the rays decayed to half-value in 21 or 22 days. With 

 the intensely active preparations of uranium X, separated 

 by us from 45 kilograms of uranyl nitrate, we have been able 

 to examine the decay of both ft- and y-rays, over periods of 

 time up to 230 days in the case of the latter, and for con- 

 siderably longer in the case of the former. In 230 days 

 the activity decays to 0*15 per cent, of the initial value. 



The investigation proves that the ft- and 7-rays decay at 

 exactly the same rate, the value of the constant X being 

 0*0282 (day) -1 . The period of average life of the body is 

 therefore 35*5 days and its period of half-change 24*6 days. 

 This value of the constant A, is about 10 per cent, less than 

 the value obtained originally. 



Ten preparations of uranium X, prepared in different ways, 

 at different times, and of intensity varying over a wide range, 

 have been examined. The ft-niy measurements were carried 

 out in a brass electroscope having a zinc base 0'OJO cm. in 

 thickness. The preparations were placed generally either at 

 a distance of 115 cm. or of 13*5 cm., covered with thicknesses 

 of sheet zinc or not, according to their intensity. By altering 

 the distance of the preparation from the electroscope, and the 

 amount of zinc covering the active body, measurements 

 could be made with one preparation over considerable periods 

 of time, and yet with the rate of leak of the electroscope 

 always within accurately measurable limits. The 7-ray 

 measurements were carried out in a thick lead electroscope 

 with base 0*975 cm. thick. The distances from the pre- 

 paration to the base of the electroscope varied from 10 to 

 2 cm. Two standards were employed in each of the two sets 

 of measurements, so that, in the event of an accident to one 

 of them, the measurements of decay might still be continued. 



* Communicated by the Authors. 



f Rutherford and Soddv, Phil. Mag. [6] v. p. 444 (1008). 



I Phil. Mag. u 6j xii. p. 393 (1906). 



