550 



Sir E. Rutherford on Collision of 



This peculiarity of the absorption curve is only marked 

 for long-range a. particles. In fig. 5 the absorption curves 

 for initial ranges of the a particles 7 cm., 6' 6, (M, 5*7, 4*8, 

 3*9 cm. are shown. The range was reduced by interposing 



ig. 



10 



? 6 









Observed curves of absorption ofH atoms 







A 







A. range of incident 



ct particles 7 cms 













B 



1, 



6-6 »» 



r~" 





^e 







C 



„ 



61 ». 



V\^ 









D 



E 



,, 



5-7 » 

 48- •» 

 3-9 m 



^\\ 











0" 



" 







^ 

















\o 



K 



\ 





\ 









nT 



\^ 















./> N. 





















^^^. 







10 



13 16 19 22 



Range of H atoms in cms. of air 



25 



23 



gold or aluminium screens of known stopping power for the 

 a particles close to the source. Even when the range of 

 the ol particles is reduced from 7 to G cm., the absorption 

 curve already shows an evident decrease of number with 

 thickness of absorber, and this decrease becomes much more 

 marked for decreasing ranges between 6 and 3 cm. 



The absorption curves for ranges between 5*7 and 3*9 cm, 

 are very similar in shape to the theoretical curves. For 

 example, in curve F for an initial range of a particles of 

 3*9 cm. the number of H particles is reduced to \, 5, \ for 

 increase of absorption of 2*4, 4'0, 5 - 5 cm. respectively. The 

 numbers are in good agreement with the calculated values, 

 viz. 2'8, 5*0, 6*4 cm. respectively. The numbers are in still 

 closer agreement if we take the average range of the a parti- 

 cles acting on the hydrogen column, viz. 3*9 — *4 = 3"5 cm. 

 The corresponding numbers are then 2'3, 4'2, 5*0 cm. 

 respectively. 



