H. 31. Dadourian — Atmospheric Radio-activity . 311 



So far as the writer is aware no evidence has been put for- 

 ward to show that the positively charged particles of the active- 

 deposit of radium are attracted toward the negatively charged 

 wire with either greater or less force than those experienced 

 by the particles of the active-deposit of thorium. Hence 

 we will assume the force experienced in an electric field by 

 the particles of both groups to be the same. This amounts to 

 setting K = K' 



n = A N = K A, M, = K A 2 M 2 = K A 3 M 8 (7) 



n! '= A'N' = K A', M\ = K A' 2 M' 2 = K A' 3 M' s (8) 



Now let us consider the activity of the wire shortly after the 

 removal of the potential difference from it. The amount of 

 Ra A becomes negligible after the first few minutes of the 

 process of disintegration. Therefore its direct contribution to 

 the activity of the wire may be neglected. Since Ra B is 

 ra.yless. we may assume the component of the activity which is 

 due to the radium group to be proportional to the number of 

 Ra C particles present. Supposing the ionizing power of an 

 a-particle to be proportional to its range, we can write 



I = AR,M. ' ( 9 ) 



where R 3 is the range and M 3 the number of the a-particles of 

 Ra C. k is the number of ions produced by an a-particle 

 while moving through a distance of l cm . 



The component of the ionization produced by the thorium 

 group is due to Th B and Th C ; Th A does not emit a-parti- 

 cles, therefore its effect may be neglected. On account of the 

 absence of any evidence to the contrary, we will assume that 

 the a-particles of the thorium group produce the same number of 

 ions as those of the radium group in traversing a distance of 

 one centimeter. Then v-e may write for the component 

 of the ionization of the wire which is due to the thorium group, 

 I'=*(R',M', + R',M',) (10) ' 



where h is the same constant as that in the last equation. 

 R',, and R' 3 are the ranges and M r 2 and M' a the numbers of the 

 a-particles of Th B and Th C respectively. Dividing equa- 

 tion (10) by equation (9) 



I'_ R',M', + R',M' , (u) 



I ~ R,M, l ^ 



substituting for M 2 , M^ and M r 3 expressions obtained from 

 equation (7) and (8) and simplifying 



r_ N'VA t (A , ,R',+X',R' 1 ) , . 



I " NAA' 2 A' 3 ll 3 l ~ ] 



N'_I' AA' 2 A' 3 R 3 . s 



■■N-I A'A 3 (A' 3 K' 2 + A' 2 R 3 ) l } 



