﻿of 
  the 
  y 
  Rays 
  from 
  Radium 
  D 
  and 
  Radium 
  E. 
  329 
  

  

  by 
  about 
  1 
  mm. 
  of 
  aluminium. 
  A 
  small 
  amount 
  of 
  a 
  more 
  

   penetrating 
  type 
  of 
  radiation 
  is 
  also 
  present. 
  The 
  curve 
  was 
  

   analysed 
  as 
  in 
  previous 
  experiments. 
  The 
  soft 
  part 
  of 
  the 
  

   radiation 
  was 
  found 
  to 
  be 
  absorbed 
  exponentially 
  in 
  aluminium 
  

   (see 
  logarithmic 
  curve 
  fig. 
  2), 
  the 
  value 
  of 
  the 
  absorption 
  

   coefficient 
  //, 
  being 
  45, 
  45. 
  46, 
  44, 
  44 
  in 
  the 
  five 
  distinct 
  

   experiments, 
  giving 
  a 
  mean 
  value 
  /u 
  = 
  45 
  (cm.) 
  -1 
  . 
  

  

  The 
  absorption 
  curve 
  for 
  the 
  penetrating 
  radiation 
  is 
  shown 
  

   in 
  fig. 
  3, 
  the 
  logarithm 
  of 
  the 
  ionization 
  being 
  plotted 
  as 
  

   ordinate. 
  It 
  will 
  be 
  seen 
  that 
  the 
  points 
  lie 
  nearly 
  on 
  a 
  

  

  Fig. 
  3. 
  

  

  No 
  

  

  

  

  

  i 
  

  

  \ 
  

  

  \ 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  \ 
  

  

  0-5 
  1-0 
  

  

  TH/CH/V£SS 
  /n/ 
  CMS. 
  OF/lLl/MINIUi\ 
  

  

  1-5 
  2-0 
  2-5 
  3-0 
  

  

  straight 
  line, 
  showing 
  that 
  the 
  y 
  rays 
  are 
  absorbed 
  according 
  

   to 
  an 
  exponential 
  law. 
  The 
  meau 
  value 
  of 
  the 
  absorption 
  co- 
  

   efficient 
  for 
  several 
  experiments 
  was 
  found 
  to 
  be 
  0"99 
  (cm.) 
  -1 
  

   in 
  aluminium. 
  It 
  will 
  be 
  seen 
  from 
  the 
  figure 
  that 
  only 
  

   about 
  7 
  per 
  cent, 
  of 
  the 
  total 
  y-ray 
  ionization 
  is 
  due 
  to 
  the 
  

   more 
  penetrating 
  type 
  of 
  radiation. 
  As 
  the 
  maximum 
  ioni- 
  

   zation 
  obtainable 
  under 
  the 
  experimental 
  conditions 
  was 
  

   about 
  19 
  divisions 
  per 
  minute 
  in 
  the 
  electroscope, 
  the 
  amount 
  

   due 
  to 
  the 
  penetrating 
  rays 
  was 
  only 
  between 
  1 
  and 
  2 
  divisions 
  

   a 
  minute. 
  It 
  is 
  consequently 
  difficult, 
  when 
  dealing 
  with 
  

   such 
  small 
  effects, 
  to 
  obtain 
  a 
  very 
  accurate 
  value 
  of 
  the 
  absorp- 
  

   tion 
  coefficient 
  of 
  this 
  radiation. 
  Several 
  experiments 
  were 
  

   made, 
  the 
  values 
  of 
  jjl 
  varying 
  between 
  0'97 
  and 
  1*02. 
  The 
  

   radiation 
  was 
  in 
  all 
  cases 
  absorbed 
  according 
  to 
  an 
  exponential 
  

   law, 
  indicating 
  that 
  the 
  rays 
  consisted 
  of 
  one 
  homogeneous 
  

   type. 
  The 
  absorption 
  curves 
  of 
  both 
  types 
  of 
  radiation 
  were 
  

   also 
  determined 
  in 
  carbon 
  as 
  well 
  as 
  in 
  aluminium. 
  Allowing 
  

   for 
  the 
  difference 
  in 
  the 
  absorption 
  coefficients, 
  the 
  curves 
  

   Phil. 
  Mao. 
  S. 
  6. 
  Vol. 
  26. 
  No. 
  152. 
  Aug. 
  1913. 
  Z 
  

  

  