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  XVII. 
  The 
  Secondary 
  y 
  Rays 
  due 
  to 
  the 
  y 
  Rays 
  of 
  Radium 
  0. 
  

   By 
  A. 
  S. 
  Eve, 
  D.Sc, 
  Associate 
  Professor 
  of 
  Mathematics, 
  

   Lecturer 
  in 
  Radioactivity, 
  McGiU 
  University, 
  Montreal 
  *. 
  

  

  THE 
  Rontgen 
  rays 
  and 
  the 
  y 
  rays 
  from 
  radioactive 
  sub- 
  

   stances 
  have 
  so 
  many 
  properties 
  in 
  common 
  that 
  they 
  

   are 
  generally 
  believed 
  to 
  be 
  fundamentally 
  o£ 
  the 
  same 
  nature. 
  

   But 
  the 
  secondary 
  radiations 
  caused 
  by 
  X 
  rays 
  and 
  by 
  y 
  rays, 
  

   respectively, 
  appear 
  at 
  first 
  to 
  be 
  widely 
  different. 
  Whilst 
  

   the 
  y 
  rays 
  give 
  rise 
  to 
  secondary 
  radiations 
  following 
  the 
  

   order 
  of 
  the 
  densities 
  of 
  the 
  radiators, 
  the 
  X 
  rays 
  cause 
  

   secondary 
  radiations 
  strongly 
  diverging 
  from 
  that 
  order. 
  

   Thus 
  Townsendt 
  found 
  actually 
  more 
  secondary 
  radiation 
  from 
  

   solid 
  paraffin 
  than 
  from 
  lead. 
  The 
  values 
  he 
  obtained 
  were 
  : 
  — 
  

  

  Table 
  I. 
  

   X 
  Rays, 
  Secondary 
  Radiation. 
  

  

  Radiator. 
  

  

  Rays 
  through 
  Air. 
  

  

  Rays 
  through 
  *25 
  nam. 
  

   of 
  Aluminium. 
  

  

  Air 
  

  

  o 
  

  

  6-0 
  

  

  7'5 
  

  

  24 
  

   30 
  

   06 
  

  

  68 
  

   70 
  

  

  1 
  

   35 
  

  

  3-0 
  

   60 
  

   155 
  

   25 
  

   30 
  

   2-5 
  

  

  

  Glass 
  

  

  Lead 
  

  

  Solid 
  Paraffin 
  

  

  Zinc 
  

  

  

  

  Let 
  us 
  compare 
  the 
  secondary 
  radiations 
  from 
  the 
  y 
  rays 
  

   of 
  radium 
  inclosed 
  in 
  lead. 
  

  

  Table 
  II. 
  

   7 
  Rays, 
  Secondary 
  Radiation 
  {. 
  

  

  Radiator. 
  

  

  

  

  100 
  

   61 
  

   59 
  

   30 
  

   35 
  

   20 
  

  

  Copper 
  

  

  Brass 
  

  

  Aluminium 
  

  

  Glass 
  

  

  Solid 
  Paraffin 
  

  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

   t 
  Proc, 
  ( 
  iamb. 
  Phil. 
  Soc. 
  vol 
  x., 
  p, 
  

   | 
  Phil. 
  Mag. 
  Dec. 
  L904, 
  

  

  117 
  (1€ 
  

  

  