Reflexion of the ^-Particles by Matter. 

 Ksr. 3. 



857 



•010 -(tfO -030 -040 -050 --060 -07Q 

 Aluminium //v cms. 



090 -100 -110 -IPO 



Table IV. 

 Coefficients of Absorption in cms. of Al. 



Ea T) (?). 



ThA. 



EaB. 



EaE. 



ActO. 



ThD. 



EaC. 



130 



1110 



75*0 



43-3 



28-5 



16-3 



13-5 



The coefficient of absorption of the /3-particles from RaB 

 was determined by using RaB obtained initially pure by 

 recoil from radium A, as well as by difference method, while 

 in the case of ThA and RaD(?) the difference method 

 alone was used. Act C was also obtained by the recoil 

 method, but in some determinations the actinium active 

 deposit was used. 



When the logarithm of the ionization given in column a, 

 Table III. is plotted against the thickness of aluminium we 

 still observe an initial drop. This must be attributed to weak 

 radiations possibly belonging to Ra D. 



In the case of Ra E, Act C, and Th D absorption curves, 

 it is found that down to about 5 per cent, of the initial 



Phil. Mag. S. 6. Vol. 20. No. 119. Nov. 1910. 3 L 



