Existence of Uranium Y. 221 



electroscope filled with hydrogen, measurements being taken 

 in the magnetic field with the preparation alternately bare 

 and covered with a mica strip. In the former work, with 

 large quantities of uranium y a quickly decaying a-radiation 

 would not have been detected. In the present experiments, 

 only 200 grams of the purest uranyl nitrate were employed, 

 and the uranium X was separated from it, as described, with 

 as little loss of time as possible. In one experiment only 

 30 minutes elapsed between the end of the separation and 

 the first measurement. Measurements were continued for 

 several days, but no evidence of a rapidly decaying a-radia- 

 tion was observed. The actual a-ray leak amounted to less 

 than a division a minute and remained sensibly constant. It 

 may well have been due to a trace of uranium. 



If uranium Y is the parent of actinium it is to be expected, 

 since it appears to be isotopic with uranium Xj, that one st- 

 and one /3-purticle must be expelled from it before actinium 

 is produced. So far, there is no evidence of the a-ray 

 change. 



Summary. 



(1) AntonofFs main result regarding the abnormal decay 

 of the soft /3-rays of uranium X has been confirmed, but the 

 abnormal decay was obtained for all uranium X prepara- 

 tions, however separated, for which the time of reaccumula- 

 tion was short. 



(2) If uranium Y has a separate existence it appears to be 

 isotopic with uranium Xj. This makes it unusually difficult 

 to obtain further evidence as to whether it has a separate 

 existence. 



(3) The recovery curves of the /3-rays of uranium after 

 separation of uranium X reveal some slight evidence of the 

 existence of uranium Y, which though scarcely beyond the 

 limit of possible error is shown to be of the right order to be 

 expected. 



(4) The ionization contributed by uranium Y is about of 

 the order to be expected if it is the parent of actinium in a 

 branch claiming 8 per cent, of the atoms, and if the atoms of 

 uranium X x and Y produce equal ionizations on disintegration. 



(5) No evidence was obtained of an a-radiation from 

 uranium X + Y separated as rapidly as possible from uranium. 



I desire to acknowledge the assistance rendered by Mrs. 

 Soddy, who carried out most of the large number of 

 measurements involved in the work. 



Physical Chemistry Laboratory, 

 Glasgow University. 

 Dec. 10, 1013. 



