of ol particles from various Radioactive Substam 



619 



Substance. 



Range 

 atO°. 



Initial 

 Velocity. 



Transformation 

 Constant. 



Half-value 

 Period. 



Uranium 



2*58 cms 



l-51 X 10 9Cm ^ 



sec. 



-18 



4-6 xlO 



5 X 10 9 years 





2-84 „ 

 313 „ 



1-56 ., „ 

 1-61 „ „ 







Radium 



—li 

 1-1 XlO 



2000 years 



Ra Emanation ... 



3-94 „ 



1-74 „ „ 



2-085xl0~ 



3-85 days 



Radium A 



4-o0 „ 

 6-57 „ 

 3-58 „ 



1-81 „ ,., 

 2-06 „ „ 

 1-68 „ „ 



385 XlO 

 5-fiO XlO" 8 



30 minutes 





Polonium 



143 days 





Radioactinium ... 



4-55 „ 



1-82 „ „ 



41 XlO"' 



195 days 



Actinium X 



417 „ 



1-77 „ „ 



7-6 XlO"' 



10 5 days 



Act Emanation ... 



540 „ 



1-93 „ „ 



18 xlO" 1 



3'9 seconds 



Actinium A 



616 „ 



2-02 „ „ 



350 



5 J^ second 



Actinium C 



5-12 „ 



1-90 „ „ 



5*4 xlO -3 



215 minutes 



All the products in the uranium -radium series are marked 

 on the curve except ionium and radium 0. In the case of 

 ionium the period has not yet been determined, but according 

 to Soddy* it is between 5 x 10* and 10 6 years. It will be 

 seen that the numbers of the uranium-radium series lie very 

 closely on a straight line. Assuming that ionium is no ex- 

 ception to the rule, and taking the range of its a. particles to 

 be 2'84 cm., an inspection of the curve shows that its half- 

 value period should be nearly as high as one million years. 



The discussion of radium C presents some difficulties, for 

 from its range the half-value period of the product should be 

 exceedingly short, about 10 -6 second. The recent work of 

 Hahn and Meitnerf and of FajansJ has shown that the sub- 

 stance ordinarily called radium C is undoubtedly complex, and 

 that the changes occurring in these substances are perhaps 

 irregular. There is certainly no definite evidence yet 

 available which would contradict the possibility that the 

 period of transformation of the product which gives rise to 

 the long-range a particles is very short. 



It should be pointed out that a certain difficulty exists 

 with regard to uranium. Boltwood § has shown that the 

 change in uranium gives rise to two a particles for one in 

 each of the successive products, and this has been confirmed 



* F. Soddv, Le Radium, vii. p. 295 (1910). 



t O. Hahii and L. Meitner, Phys. ZeiUchr. x. p. 697 (1909). 



t K. Fajans, Phys. Zeitsc.hr. xii. p. 369 (1911). 



§ B. B. Boltwood, Amer. Journ. of Sci. xxv. p. 269 (1908). 



