produced by Particles from Radioactive Substances. 609 



Some experiments were done with films of uranium of 

 55 cm. diameter and '0088 grm. and *0036 grm. respectively 

 o£ U 3 8 per sq. cm. In other experiments UX was par- 

 tially separated by means of a very small quantity of iron 

 from several grams of uranium nitrate. The exact fraction 

 separated was determined by measuring the /3-ray activity 

 of the uranium nitrate solutions both before and after the 

 separations of the U X. The nitrate was then converted into 

 U 3 8 in order to determine accurately the number of a. 

 particles. The advantage of the second method is the fact 

 that a very thin film of comparatively very active preparation 

 of UX was obtained. The results by the two methods were 

 in agreement. 



Soft /3 radiations from ThA, Act A, RaD, Radioactinium. 

 — The activity of the soft /3 radiation cannot be obtained 

 very accurately owing to the fact that the extrapolations are 

 necessarily great, and that the values of the absorption co- 

 efficients are rather doubtful. In addition there is also 

 another difficulty due to the presence of hard ft rays, and 

 the value of the soft radiations had to be obtained by the 

 differential method. We may mention that in comparing 

 the hard radiations with the soft radiations from preparations 

 of actinium X and radioactinium we observe that actinium X 

 also emits soft /3 rays. 



Results. 



In order to illustrate the method of calculation the actual 

 figures of one experiment are given below for a preparation 

 of actinium C. 



Ionization current in the bulb (P = 5*4G cm. of Hg) 



8-69 xlO- 1 E.S.U. 

 Number of a particles calculated, 



1-44 x 10 5 per sec. 

 /3-ray current corrected for absorption in the aluminium 



1-72 xlO" 1 E.S.U. 



Corrected for absorption by the air in the electroscope, 

 namel}', for one-half of 15 cm, air, 



1-90 xlO" 1 E.S.U. 

 Corrected for reflexion in the electroscope (27 per cent.), 



J -39 xlO" 1 E.S.U. 



Therefore the current produced per centimetre of path at 



