Table 506 (concluded). 

 RADIOACTIVITY. 



397 



'*/3Al '^ ^^^ absorption coefficient of the /3-rays in Al, thickness measured in cm.; /* .| and /".^pu ditto for y-rays in AI 



and Pb, unit the cm; the latter is given only for the most penetrating type of 7-rays. If lo is the initial intensity and 



I the intensity after the rays have traversed x cm of the absorbent then, I = loe ~^^; logioTo/I = 0.4343 MX. If D is 

 the thickness corresponding to the absorption of V2 the rays then D/n = 0.693. (Adapted from report of International 

 Committee on Chemical Elements, 1923; J. Am. Ch. See. 45, p. 867, 1923. Col. 4 is from Geiger, Z. fur Physik, 1921.) 



Notes: (38) ThC has double disintegration; 65% of atoms emit ^-rays and produce ThC having a-iays; 35% emit 

 a-rays and give ThC" having /3 rays; (41 ) 469 corresponds to V 0.0572 directly measured; (42) also called ThD. Paren- 

 theses indicate relatively feeble radiation. 



Smithsonian Tables. 



