﻿[ 
  ^^75 
  ] 
  

  

  XXXY. 
  Primary 
  and 
  Secondary 
  Gamma 
  Rays. 
  

   By 
  A. 
  S. 
  Eve, 
  Ji.JL., 
  D.Sc, 
  McGUl 
  University^ 
  Montreal 
  *. 
  

  

  WHATEVER 
  may 
  be 
  the 
  views 
  held 
  about 
  Bragg's 
  

   theory 
  o£ 
  the 
  nature 
  of 
  the 
  Rontgen 
  and 
  gamma 
  

   rays, 
  it 
  is 
  certain 
  that 
  his 
  able 
  advocacy 
  had 
  led 
  to 
  a 
  notable 
  

   increase 
  of 
  our 
  knowledge 
  of 
  the 
  properties 
  of 
  both 
  types 
  of 
  

   radiation. 
  The 
  gamma 
  rays 
  in 
  particular 
  are 
  so 
  little 
  affected 
  

   by 
  physical 
  conditions 
  that 
  new 
  methods 
  of 
  investigation 
  are 
  

   essentially 
  valuable. 
  Therefore, 
  the 
  plan 
  adopted 
  by 
  Bragg 
  

   of 
  examining 
  the 
  incident 
  and 
  emergent 
  secondary 
  radiations, 
  

   consisting 
  of 
  electrons 
  or 
  corpuscles, 
  from 
  a 
  reversible 
  pair 
  

   of 
  dissimilar 
  metals 
  traversed 
  by 
  the 
  gamma 
  rays, 
  appears 
  to 
  

   be 
  a 
  promising 
  line 
  of 
  attack. 
  He 
  has 
  himself 
  published 
  f 
  a 
  

   few 
  results 
  showing 
  the 
  changes 
  produced 
  in 
  the 
  ionization 
  

   current 
  of 
  an 
  electroscope, 
  when 
  four 
  plates, 
  two 
  above 
  and 
  

   two 
  below, 
  of 
  dissimilar 
  substances, 
  are 
  traversed 
  by 
  a 
  

   pencil 
  of 
  7 
  rays, 
  and 
  are 
  interchanged 
  in 
  the 
  four 
  possible 
  

   arrangements. 
  In 
  this 
  manner 
  he 
  has 
  proved 
  the 
  asvmmetry 
  

   of 
  the 
  incident 
  and 
  emergent 
  secondary 
  radiations. 
  

  

  The 
  writer 
  has 
  for 
  some 
  months 
  made 
  an 
  experimental 
  

   study 
  of 
  effects 
  produced 
  in 
  a 
  similar 
  way 
  with 
  primary 
  and 
  

   secondary 
  7 
  rays 
  from 
  radium 
  C. 
  and 
  with 
  the 
  primary 
  7 
  rays 
  

   from 
  uranium 
  X. 
  The 
  main 
  results 
  are 
  capable 
  of 
  con- 
  

   siderable 
  simplification, 
  although 
  the 
  underlying 
  ultimate 
  

   processes 
  remain 
  obscure. 
  

  

  The 
  first 
  paper 
  on 
  JSecondary 
  Radiation 
  due 
  to 
  the 
  /5 
  and 
  

   7 
  rays 
  of 
  radium 
  was 
  published 
  % 
  in 
  December 
  1904, 
  and 
  the 
  

   results 
  then 
  obtained 
  have 
  been 
  on 
  the 
  whole 
  well 
  substan- 
  

   tiated 
  b}' 
  later 
  observers. 
  The 
  work 
  of 
  McClelland 
  § 
  , 
  how^ever, 
  

   placed 
  the 
  theory 
  of 
  absorption 
  of 
  the 
  ^ 
  rays 
  and 
  the 
  laws 
  of 
  

   reflected 
  or 
  incident 
  secondary 
  radiation 
  on 
  a 
  sound 
  basis, 
  and 
  

   a 
  host 
  of 
  other 
  workers 
  in 
  the 
  field 
  have 
  contributed 
  to 
  steady 
  

   advance 
  in 
  various 
  directions. 
  In 
  particular 
  McClelland 
  

   found 
  that 
  the 
  amount 
  of 
  incident 
  secondary 
  radiations 
  from 
  

   various 
  elements 
  followed 
  the 
  order 
  of 
  atomic 
  weights. 
  Such 
  

   radiations 
  ha\e 
  been 
  proved 
  to 
  come 
  from 
  a 
  very 
  slight 
  depth, 
  

   and 
  to 
  consist 
  of 
  high 
  velocity 
  negatively 
  charged 
  particles.. 
  

   Using 
  relatively 
  large 
  masses, 
  Kleeman 
  || 
  and 
  the 
  writer 
  \ 
  

  

  * 
  Commimicated 
  bv 
  the 
  Author. 
  

  

  t 
  Phil. 
  Mair. 
  May 
  1908. 
  

  

  X 
  Phil. 
  Mug. 
  Dec. 
  1904. 
  

  

  § 
  Traus. 
  Rov. 
  Dublin 
  >;oc. 
  xxvii. 
  p. 
  9 
  (IGOo). 
  

  

  [• 
  Phil. 
  Magi 
  3Iay 
  1908. 
  

  

  C 
  Phil. 
  Matr. 
  Aug. 
  1908. 
  

  

  