a. Particles with Light Atoms. 

 that for a particles of range r 



547 



>/Q 



•46xlO-«(r /r)^^/ R ^-l), 



where r is range of a. particle from radium 0, viz. 70 cm., 

 and R max . is the maximum range of the H atom for a range r. 

 viz. 4r. 



The values of n/Q for different values of R are given in 

 Table I. for a particles of range 7, 5, and 3 cm. in air 

 respectively. It should he noted that Q/n represents the 

 number of a. particles required to produce on the average in 

 traversing one centimetre of the gas one H atom, which has 

 a range equal to or greater than R cms. of air. 



Table I. 



Range of a particles Range of a particles Range of a particles 



= 7 nms. =5 r»ms — 3 p.ms 



5 cms. 



= 3 cms. 



Range R 



n/Q 



1 



of H atoms. 





1 cm. 



6-3x10-6 



2 



40 „ 



4 „ 



2-8 . 





7 ,3 



1-46 , 





10 „ 



•98 , 





14 „ 



•60 , 





18 „ 



•34 , 





22 „ 



•19 . 





24 „ 



•12 , 





26 „ 



•05 , 





28 „ 



, 





Range R 



n/Q. 



of H atoms. 



1 cm. 



7-9XJ0-6 1 



2 „ 



4-9 „ 



4 „ 



2-8 „ 



• 7 „ 



1-53 „ 



10 „ 



•95 „ 



14 „ 



•45 „ 



16 „ 



•27 „ 



18 „ 



'12 „ 



20 „ 



„ 



Range R 

 of H atoms. 



»/Q. 



1 cm. 



H-lXlO-6 



2 „ 



6-5 „ 



3 „ 



4-5 „ 



4 „ 



3-3 „ 



5 „ 



2-5 „ 



6 ,. 



1-9 „ 



8 „ 



1-0 ,, 



10 „ 



•4 „ 



12 ., 



„ 



These results are shown graphically in fig. 3, curves A,B, 

 and C respectively, for ranges of the H atoms from 5 to 

 28 cm. It is seen that the curve A is approximately 

 exponential between 8 and 18 cm., falling to half value in 

 about 5' 3 cm. This holds equally for curves B and C over 

 corresponding ranges. These curves give the theoretical 

 variation in number of the H atoms with range such as 

 would be observed if the numbers of H atoms were counted 

 for different thicknesses of absorber. 



As the value of n/Q is less than 1/100000, it is not feasible 

 with the present arrangement to detect H atoms within the 

 range of the much more numerous a particles. For this 

 reason, it is not possible to compare theory with experiment 



