﻿622 
  Scattering 
  and 
  Absorption 
  of 
  the 
  7 
  Rays 
  of 
  Radium. 
  

  

  the 
  7 
  rays 
  of 
  radium 
  could 
  not 
  penetrate 
  more 
  than 
  26 
  cm. 
  

   of 
  mercury. 
  

  

  The 
  tables 
  show 
  that 
  much 
  less 
  scattered 
  radiation 
  escapes 
  

   from 
  a 
  lead 
  radiator 
  than 
  from 
  a 
  carbon 
  radiator; 
  consequently 
  

   when 
  the 
  rays 
  are 
  exponentially 
  absorbed 
  by 
  the 
  two 
  mate- 
  

   rials, 
  the 
  rays 
  coming 
  through 
  carbon 
  will 
  be 
  more 
  hetero- 
  

   geneous 
  than 
  those 
  coming 
  through 
  lead. 
  If 
  <y 
  rays 
  are 
  

   being 
  exponentially 
  absorbed 
  by 
  carbon 
  and 
  aluminium, 
  the 
  

   issuing 
  rays 
  will 
  not 
  be 
  exponentially 
  absorbed 
  by 
  the 
  lead, 
  

   as 
  they 
  contain 
  too 
  great 
  a 
  proportion 
  of 
  soft 
  rays. 
  When 
  

   examined 
  by 
  lead 
  these 
  softer 
  rays 
  will 
  be 
  cut 
  out 
  until 
  the 
  

   7 
  rays 
  are 
  exponentially 
  absorbed 
  by 
  lead, 
  i. 
  e. 
  lead 
  will 
  

   harden 
  the 
  rays. 
  Evidence 
  for 
  this 
  is 
  found 
  in 
  recent 
  expe- 
  

   riments 
  of 
  Rutherford 
  and 
  Richardson 
  *, 
  who 
  found 
  that 
  

   7 
  rays 
  exponentially 
  absorbed 
  by 
  aluminium 
  are 
  " 
  hardened 
  " 
  

   by 
  lead. 
  We 
  may 
  generalize 
  this 
  result 
  by 
  saying 
  that 
  rays 
  

   which 
  are 
  absorbed 
  exponentially 
  by 
  any 
  material 
  are 
  hardened 
  

   by 
  substances 
  of 
  higher 
  atomic 
  weight. 
  On 
  the 
  other 
  hand, 
  

   rays 
  which 
  are 
  exponentially 
  absorbed 
  by 
  lead 
  would 
  probably 
  

   be 
  softened 
  when 
  passed 
  through 
  carbon, 
  or 
  7 
  rays 
  which 
  are 
  

   absorbed 
  exponentially 
  by 
  any 
  substance 
  are 
  " 
  softened 
  " 
  by 
  

   substances 
  of 
  lower 
  atomic 
  weight. 
  Here 
  the 
  terms 
  softened 
  

   and 
  hardened 
  are 
  used 
  to 
  indicate 
  a 
  greater 
  or 
  smaller 
  pro- 
  

   portion 
  of 
  softer 
  rays. 
  These 
  results 
  only 
  apply 
  to 
  the 
  cases 
  

   where 
  it 
  is 
  safe 
  to 
  say 
  that 
  as 
  the 
  7 
  rays 
  become 
  softer 
  the 
  

   absorption 
  per 
  unit 
  mass 
  increases 
  with 
  the 
  atomic 
  weight 
  of 
  

   the 
  absorber. 
  

  

  The 
  experiments 
  are 
  being 
  continued, 
  and 
  the 
  writer 
  hopes 
  

   to 
  give, 
  in 
  a 
  later 
  paper, 
  a 
  fuller 
  discussion 
  of 
  the 
  points 
  

   considered. 
  

  

  Summary. 
  

  

  1. 
  When 
  7 
  rays 
  are 
  scattered, 
  there 
  is 
  a 
  change 
  in 
  quality, 
  

   the 
  scattered 
  rays 
  being 
  less 
  penetrating 
  the 
  greater 
  the 
  angle 
  

   of 
  scattering. 
  The 
  change 
  is 
  gradual 
  and 
  small 
  when 
  the 
  

   angle 
  of 
  scattering 
  is 
  small. 
  

  

  2. 
  A 
  similar 
  explanation 
  must 
  be 
  given 
  of 
  the 
  scattering 
  of 
  

   X 
  and 
  7 
  rays. 
  There 
  is 
  probably 
  very 
  little 
  direct 
  scattering 
  

   of 
  X 
  and 
  7 
  rays. 
  

  

  3. 
  The 
  quality 
  and 
  quantity 
  of 
  the 
  scattered 
  radiation 
  is 
  

   approximately 
  independent 
  of 
  the 
  nature 
  of 
  the 
  radiator. 
  

  

  4. 
  The 
  softer 
  the 
  type 
  of 
  7 
  rays, 
  the 
  greater 
  the 
  percentage 
  

   scattered 
  per 
  unit 
  mass. 
  

  

  5. 
  A 
  discussion 
  is 
  given 
  of 
  the 
  bearing 
  of 
  the 
  results 
  on 
  

  

  * 
  Rutherford 
  and 
  Richardson, 
  Phil. 
  Mag. 
  xxv. 
  p. 
  722,(1918). 
  

  

  