﻿Investigation 
  of 
  the 
  Nature 
  of 
  <y 
  Rays. 
  931 
  

  

  I. 
  

  

  Substance. 
  

   Lead 
  . 
  . 
  . 
  

  

  II. 
  

  

  Thickness 
  of 
  screen 
  

  

  to 
  give 
  half-value 
  

  

  in 
  mm. 
  

  

  . 
  -083 
  

  

  in. 
  

  

  X 
  calculated 
  

  

  from 
  II., 
  in 
  

  

  cni.-l. 
  

  

  84 
  

  

  IY. 
  

  

  X 
  for 
  /3 
  rays. 
  

  

  (McClelland 
  and 
  

  

  Hackett.) 
  

  

  93 
  

  

  Tin 
  . 
  . 
  . 
  

  

  . 
  -141 
  

  

  50 
  

  

  52 
  

  

  Copper 
  . 
  . 
  

   Aluminium 
  . 
  

  

  . 
  -137 
  

   . 
  -50 
  

  

  51 
  

   14 
  

  

  55 
  

   14 
  

  

  Celluloid 
  . 
  

  

  . 
  -98 
  

  

  — 
  

  

  — 
  

  

  The 
  third 
  column 
  shows 
  the 
  values 
  o£ 
  X 
  calculated 
  from 
  

   the 
  results 
  in 
  the 
  second 
  column. 
  The 
  fourth 
  column 
  shows 
  

   the 
  values 
  of 
  \ 
  for 
  the 
  primary 
  /3 
  rajs 
  of 
  radium, 
  as 
  given 
  

   by 
  McClelland 
  and 
  Hackett 
  (Trans. 
  Roy. 
  Soc. 
  Dublin, 
  

   March 
  22, 
  1907, 
  p. 
  49). 
  A 
  comparison 
  of 
  the 
  last 
  two 
  

   columns 
  shows 
  clearly 
  that 
  the 
  secondary 
  /3 
  rays 
  excited 
  by 
  

   the 
  y 
  rays 
  possess 
  nearly 
  the 
  same 
  velocity, 
  no 
  matter 
  in 
  

   what 
  substance 
  they 
  are 
  excited, 
  and 
  that 
  this 
  velocity 
  is 
  the 
  

   same 
  as 
  that 
  of 
  the 
  primary 
  j3 
  rays. 
  Only 
  hard 
  y 
  rays 
  have 
  

   been 
  used 
  to 
  excite 
  the 
  /5 
  rays 
  in 
  these 
  experiments, 
  while 
  

   the 
  values 
  of 
  McClelland 
  and 
  Hackett 
  refer 
  to 
  /3 
  rays 
  of 
  

   ordinary 
  heterogeneity. 
  It 
  is 
  scarcely 
  possible 
  in 
  the 
  present 
  

   state 
  of 
  knowledge 
  to 
  estimate 
  what 
  allowance 
  should 
  be 
  

   made 
  for 
  this 
  difference, 
  but 
  it 
  is 
  clear 
  that 
  the 
  main 
  con- 
  

   clusion 
  cannot 
  be 
  affected 
  by 
  it. 
  The 
  value 
  of 
  X 
  varies 
  

   rapidly 
  with 
  the 
  speed 
  of 
  the 
  /3 
  particle, 
  and 
  there 
  is 
  room 
  

   for 
  considerable 
  alteration 
  of 
  the 
  values 
  in 
  the 
  table 
  without 
  

   any 
  important 
  alteration 
  in 
  the 
  associated 
  speed. 
  Nor 
  does 
  

   much 
  error 
  arise 
  from 
  neglect 
  of 
  the 
  correction 
  discussed 
  

   above, 
  which 
  makes 
  the 
  emergence 
  radiations 
  too 
  small. 
  

   The 
  various 
  curves 
  of 
  figs. 
  4 
  to 
  8 
  should 
  really 
  run 
  a 
  little 
  

   way 
  past 
  the 
  point 
  taken 
  as 
  origin 
  of 
  co-ordinates. 
  

  

  If 
  we 
  consider 
  the 
  corresponding 
  values 
  for 
  the 
  soft 
  rays, 
  

   or, 
  rather, 
  soft 
  together 
  with 
  hard 
  rays, 
  we 
  find, 
  as 
  expected, 
  

   that 
  the 
  /3 
  rays 
  which 
  they 
  produce 
  are 
  of 
  a 
  much 
  less 
  

   penetrating 
  character. 
  Also, 
  the 
  difference 
  between 
  the 
  

   curves 
  A 
  and 
  B 
  is 
  most 
  marked 
  in 
  the 
  case 
  of 
  lead 
  and 
  tin, 
  

   a 
  result 
  which 
  is 
  in 
  agreement 
  with 
  what 
  has 
  gone 
  before. 
  

   For 
  these 
  metals 
  the 
  thicknesses 
  of 
  screen 
  required 
  to 
  give 
  

   half 
  the 
  full 
  emergence 
  radiation 
  are 
  '030 
  mm. 
  and 
  '048 
  mm. 
  

   respectively, 
  which 
  may 
  be 
  compared 
  with 
  the 
  values 
  '083 
  

   and 
  *141 
  obtained 
  when 
  hard 
  rays 
  were 
  used. 
  The 
  amount 
  

   of 
  soft 
  radiation 
  is 
  so 
  large 
  that 
  we 
  may 
  consider 
  the 
  effect 
  

   of 
  the 
  hard 
  radiation 
  mixed 
  with 
  it 
  as 
  a 
  correction 
  to 
  be 
  

   allowed 
  for. 
  The 
  effect 
  of 
  the 
  hard 
  radiation 
  which 
  has 
  been 
  

  

  3 
  P2 
  

  

  