256 Analysis of y Rays from Uranium Products. 



by radium B, thorium B, and actinium B. The single pene- 

 trating type of radiation for which \x = 0*140 would then be 

 due to uranium X 2 . Under these conditions the <y rays 

 emitted by uranium X x and uranium X 2 would appear to 

 be quite analogous to those emitted by the other members of 

 the radioactive series. 



Attention has already been drawn to the fact * that those 

 radiations which correspond to the " L " series of Bark la 

 seem to persist throughout the whole series of radioactive 

 substances, with the exception of the D products. The 

 ratiation for which fi = 24 and which appears to be emitted 

 by uranium 1L 1 evidently belongs to the " L " series. This 

 result gives additional evidence that the atomic weight of 

 actinium is about 230 and that actinium is probably a branch 

 product of the uranium series. Fleck f has already pointed 

 out that the branch cannot come from uranium X 2 . Now 

 previous work has shown that in the case of radium C and 

 thorium B, branch products occur either immediately before 

 or after the emission of a single penetrating type of j 

 radiation. If we assume that the actinium branch comes 

 from uranium X 1? then the analogy with the other radio- 

 active bodies would be complete. 



Summary. 



It has been shown that uranium X, by which are denoted 

 the products uranium X x and uranium X 2 in equilibrium, 

 emits three types of: y rays having absorption coefficients in 

 aluminium />& = 24, fi = 0*70, and /jl = 0'140 (cm.) -1 . 

 Evidence has been given that the first two types are 

 probably emitted by uranium X x whilst the third penetrating 

 type is due to uranium X 2 . 



The results obtained support also the view that the atomic 

 weight of actinium is about 230 and that actinium is pro- 

 bably a branch product from uranium X t . 



My best thanks are due to Professor Rutherford for his 

 kind interest and constant help throughout the course of 

 these experiments. 



University of Manchester, 

 December, 1913. 



* Rutherford and Richardson, Phil, Mao-, xxvi, p. 937 (1913). 

 t Fleck, Phil. Mag. xxvi. p. 528 (1913), 



