﻿Investigation 
  of 
  the 
  Nature 
  of 
  y 
  Rays. 
  

  

  927 
  

  

  But 
  there 
  is 
  a 
  difference 
  in 
  the 
  case 
  of 
  Al 
  or 
  any 
  substance 
  

   o£ 
  small 
  atomic 
  weight. 
  The 
  soft 
  7 
  rays 
  give 
  rise 
  to 
  much 
  

   less 
  secondary 
  radiation, 
  and, 
  moreover, 
  they 
  are 
  not 
  used 
  

   up 
  so 
  fast. 
  Both 
  these 
  causes 
  operate 
  to 
  make 
  the 
  logarithmic 
  

   absorption 
  curve 
  o£ 
  Al 
  more 
  nearly 
  a 
  straight 
  line, 
  as 
  is 
  

   actually 
  the 
  case. 
  

  

  It 
  appears 
  that 
  a 
  screen 
  o£ 
  any 
  material 
  absorbs 
  the 
  soft 
  

   rays 
  faster 
  than 
  the 
  hard. 
  Consequently, 
  for 
  example, 
  a 
  zinc 
  

   screen 
  or 
  a 
  lead 
  screen 
  may 
  be 
  used 
  indifferently 
  in 
  order 
  to 
  

   reduce 
  the 
  ratio 
  of 
  the 
  emergence 
  radiation 
  of 
  lead 
  to 
  that 
  of 
  

   zinc. 
  But 
  a 
  screen 
  of 
  large 
  atomic 
  weight 
  acts 
  more 
  rapidly. 
  

   If 
  the 
  screens 
  of 
  lead 
  and 
  zinc 
  are 
  chosen 
  of 
  such 
  thicknesses 
  

   that 
  they 
  absorb 
  hard 
  rays 
  to 
  an 
  equal 
  extent, 
  then 
  the 
  former 
  

   absorbs 
  more 
  of 
  the 
  soft 
  rays 
  than 
  the 
  latter. 
  The 
  curve 
  CO 
  

   (fig. 
  2) 
  shows 
  the 
  results 
  which 
  were 
  obtained 
  when 
  a 
  zinc 
  

   plug 
  of 
  2'05 
  cm. 
  thickness 
  was 
  placed 
  in 
  the 
  conical 
  opening. 
  

   In 
  both 
  CC 
  and 
  AA 
  the 
  value 
  for 
  Sn 
  is 
  a 
  little 
  too 
  small 
  ; 
  we 
  

   were 
  not 
  aware 
  at 
  the 
  time 
  that 
  our 
  Sn 
  plate 
  was 
  rather 
  too 
  

  

  

  

  

  Fig. 
  

  

  3. 
  

  

  

  

  

  

  

  

  

  

  

  1600 
  

  

  t 
  

   | 
  

  

  \ 
  

  

  

  

  

  

  W 
  PLUG 
  

  

  A 
  

  

  

  

  / 
  

  

  

  

  

  ,% 
  

  

  

  

  

  / 
  / 
  

  

  /CM. 
  Zn 
  

  

  ■Z-fcM. 
  At 
  

  

  S^fflP 
  

  

  x 
  

  

  ife 
  

  

  

  ^/ 
  

  

  

  20SCM. 
  Zn 
  

   ■96 
  CM 
  P6 
  

   3-0 
  en. 
  Zn 
  

  

  

  

  

  <?ca 
  

  

  

  ^^^ 
  

  

  

  

  

  /■6/CAf. 
  Pt> 
  

  

  ■30 
  CM 
  Pb 
  

  

  

  

  

  

  

  

  

  

  

  90 
  

  

  thin. 
  In 
  fig. 
  3 
  are 
  drawn 
  several 
  curves, 
  each 
  showing 
  the 
  

   result 
  of 
  using 
  some 
  particular 
  plug. 
  In 
  order 
  to 
  avoid 
  

  

  