326 Prof. Rutherford and Mr. Grier on Deviable 



illustrates the quantitative connexions between the ionizing 

 action of a- and /3-rays for the conditions of the experiment : — 



Total ionization. Ionization. Ratio ionization. 



o-rays. /3-rays. 



/3 



a 



Uranium ... 1 1 *0074 



Thorium ... 1 "27 '0020 



Radium ... 2000 1350 -0033 



In the above table the total number of ions produced by 

 a- and /3-rays of uranium is, in each case, taken as unity for 

 purposes of comparison. The third column gives the actual 

 ratio of ft to a observed for equal weights of substance. 



The results are only approximate, for the ionizing action 

 of the rays from a given weight of substance depends on its 

 fineness of division. 



It will be observed that the ratio ionization of /3 to a. is 

 greatest for uranium and least for thorium. The intensity 

 of a- and /3-rays of radium of course depends on the purity of 

 radium. In this experiment radium obtained from Paris 

 was used. The radium from P. de Haen, Hannover, gave 

 similar results. 



For increasing thicknesses of the radioactive substance 



the ratio of ionization 3 steadily decreases to a constant 



value, since the a-rays are more readily absorbed than the /3 

 in the radioactive substance itself. 



§ 10. Comparison of energy radiated by a- and /3-rays. 



On the assumptions that 



(1) The same energy is required to produce an ion for 

 both a- and /3-rays ; 



(2) That all the energy emitted into the air from a radio- 

 active substance is used up in producing ions ; 



we can form an approximate estimate of the ratio of 

 the energy radiated by the a- and /3-rays. 



If \ is the coefficient of absorption of the deviable rays in 

 air, the rate of production of ions per unit volume at a dis- 

 tance * from the source is qe~ Kx , where q is the rate of 

 ionization at the source. 



The total number of ions produced by complete absorption 

 of the rays is 



I qe~ Xx dx< 

 Jo K 



-I 



