138 
Mr.  K,  K.  McCkmg  on  the 
5,  and  6.     As  will  be  observed,  they  are  all  exactly  similar  in 
character  to  the  one  for  air. 
Fig.  4. 
70 
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V/C/Af. 
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40 
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30 
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20 
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J 
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10 
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10     ZQ     JO 
50      60      70      80     90      100     110     120     150     140 
/o/v/z/l  t/on 
In  each  of  these  curves,  as  in  the  case  of  air,  there  are  two 
characteristic  points,  namely,  that  at  which  the  maximum 
ionization  occurs  and  that  at  which  the  a  particles  cease  to 
ionize.  The  range  for  each  of  these  points  is,  of  course,  less 
than  for  the  corresponding  points  for  air,  and  the  range 
naturally  decreases  the  greater  the  absorbing  thickness  of 
aluminium.     The  distances  at  which  the  maximum  ionization 
