456 



without absorption and practically all, at least 99%, of the ionization is pro- 

 duced by the a rays. In the § ray electroscope the radiation must pass 

 through .05 mm. aluminum, which absorbs all the alpha rays and the ioniza- 

 tion is produced by the ^ rays. In thej ray electroscope the radiation must 

 pass through 2 mm. of lead, which completely absorbs the a and p radiation 

 leaving thej' rays to produce the ionization. Thus for very weak radioactive 

 bodies the a rays are used, to produce the ionization. 



TABLE 2. 

 Uranium Radium Series. 





Radiation. 



Half- 

 value 

 Period. 



Transforma- 

 tion Con- 

 stant sec -1 . 



Range of a 



rays in cms. 



(15° C). 



Absorption Coefficients. 



Substance. 



(3 rays 

 Alum. cm" 1 . 



y rays 

 Lead cm" 1 . 



Uranium 1 



a 

 a. 



$.y 

 P 



a 



«,P 



a 

 a 



^y 

 «. P. y 



p 

 p 



a 



5X10 9 years. 

 2 X 10 s years. 

 24 ' 6 days . 

 1 5 days. 

 2X10= years. 

 2000 v ears. 

 3 85 days. 

 3'0min. 

 26 7 min. 

 19 '5 min. 

 1 4 min. 

 16 '5 years. 

 5 days. 

 136 days. 



4 '6X10-" 

 11X10-" 



3'26X10" 7 



5'34X10- 6 



11X10-" 



1 ixio-» 



2'085X10- f > 

 3 85X10"= 

 4" 33X10-" 

 5'93X10-< 

 8'25X10"= 

 l'33Xl0-= 

 1 60X10"' 

 5'90X10" 8 



2 '50 



3 00 



3 30 

 416 



4 75 



6 94 

 3'77 



14'4 and 510 

 360 



200 



13 and 91 

 13 and 53 



13 

 very soft. 



43 





Uranium X 



(Uranium Y) 



Ionium 



Radium 



Radium Emanation. . . . 



Radium A 



Radium B 



72 



4-6 

 50 













very soft. 



Radium F (Polonium). . 





The substances in parentheses are products not in the direct line of transformation. 

 Makower & Geiger's Practical Measurements in Radioactivity. 



One notes in the radioactive series (Table 2), that the disintegration 

 product of radium is emanation, a gas, which gives off an a particle and 

 changes into Had. A. This emanation is a gas and obeys all the gas laws. 

 Rad. A has a half value period of three minutes and gives off an a particle 

 and changes into Rad. B. Rad. B has a half value period of 26.8 minutes and 

 gives off £ andj radiation and changes into Rad. C. Rad. C has a half value 

 period of 19.5 minutes, gives off a, p andj particles and changes into Rad. 

 C 2 and Rad. D. Rad. D has a slow half value period of 16.5 years. This is 

 so slow that the ionization produced by this change can be neglected in com- 



