Beta Rays and by Gamma Rays from Radium C. 559 



namely *008, I found from several experiments K/K' = 117, 

 whence K = 4'35 x 10 11 , and 



N = 4tt x 4-35 x 10 n /-008 = 6Sx 10 u 



including the rays from radium B. 



It is quite clear that the total number of ions due to the 

 ft rays from a curie of radium C cannot be easily determined 

 with any great precision, but the number lies between 4 and 

 6 times "lO 14 . 



The difficulties are : — 



(1) The presence of radium B. 



(2) The complex character of the ft rays from radium 0. 



(3) The uncertainty as to the entire removal of the 



ft rays when measuring the y-ray effect. The work 

 requires repetition by those who are fortunate 

 enough to be able to obtain a large amount of the 

 active deposit of radium. 



Average total ions for one ft particle, and ions 

 per unit path. 



It has been found by Makower * that a gramme of radium 

 emits about 5 X 1 1U ft particles per second, and theory 

 suggests that radium B and radium C both emit 3*4 x 10 10 

 ft particles per second, corresponding to the known number 

 of a particles. 



If that is so, 3'4 x 10 10 ft particles from one curie of 

 radium C are producing about 4 x 10 14 ions, and therefore 

 one particle produces in an average path 1*2 x 10 4 ions. As 

 the average path is 1/-004, or 250 cm., it follows that a 

 ft particle produces about 48 ions per centimetre f. If the 

 radius of a molecule is taken as 10~ 8 cm., and the number 

 of molecules in a cm. 3 of the atmosphere as N = 2*7 x 10 19 , it 

 follows, from the formula of Clausius, that the mean path 

 between collisions by a ft particle with air molecules, at 

 atmospheric pressure, is 



L = l/N7r<r 2 = 3/8500 cm., 



so a ft particle ionizes only about 48 ions cut of every 8500 

 molecules which it directly encounters. Unless the ft particle 

 is an adept at swerving, it must pass right through 180 

 molecules for every one which it succeeds in ionizing. Or, 

 on the other hand, if every collision were supposed successful 



* Phil. Mag. Jan. 1909. 



t Cf. Durack, Phil. Mag-. May 1903, who found a mean path of 6 cm. 

 for a ft panicle in air at 2 nun. pressure. 



