﻿the 
  y 
  Rays 
  of 
  the 
  Thorium 
  and 
  Actinium 
  Products. 
  945 
  

  

  attention 
  to 
  the 
  fact 
  that 
  substances 
  which 
  emit 
  a 
  rays 
  also 
  

   emit 
  a 
  7 
  radiation 
  of 
  feeble 
  intensity. 
  This 
  has 
  been 
  shown 
  

   to 
  be 
  the 
  case 
  for 
  the 
  «-ray 
  substances 
  ionium, 
  radiothorium, 
  

   and 
  polonium. 
  

  

  They 
  have 
  also 
  examined 
  the 
  y 
  radiation 
  from 
  radium 
  

   itself, 
  which 
  is 
  also 
  known 
  to 
  emit 
  a 
  weak 
  /3 
  radiation. 
  

   "With 
  the 
  exception 
  possibly 
  of 
  radium, 
  this 
  y 
  radiation 
  

   observed 
  from 
  a-ray 
  products 
  has 
  probably 
  an 
  entirely 
  

   different 
  origin 
  from 
  the 
  intense 
  primary 
  y 
  radiation 
  from 
  

   the 
  /3-ray 
  products. 
  It 
  would 
  appear 
  to 
  be 
  excited 
  in 
  the 
  

   radioactive 
  atoms 
  by 
  the 
  escape 
  of 
  a 
  particles. 
  In 
  their 
  

   experiments 
  on 
  the 
  «-ray 
  product 
  ionium, 
  Chadwick 
  and 
  

   Russell 
  have 
  drawn 
  attention 
  to 
  the 
  fact 
  that 
  the 
  softer 
  types 
  

   of 
  radiation 
  predominate. 
  This 
  is 
  the 
  exact 
  opposite 
  of 
  the 
  

   primary 
  7-ray 
  products, 
  where 
  the 
  penetrating 
  typos 
  of 
  

   radiation 
  are 
  relatively 
  far 
  more 
  intense. 
  

  

  It 
  is 
  of 
  interest 
  to 
  compare 
  the 
  types 
  of 
  primary 
  7 
  rays 
  

   emitted 
  by 
  different 
  radioactive 
  products. 
  In 
  the 
  first 
  

   place, 
  it 
  is 
  clear 
  from 
  the 
  table 
  that 
  each 
  of 
  the 
  products 
  

   radium 
  B, 
  thorium 
  B, 
  and 
  probably 
  actinium 
  B, 
  which 
  

   occupy 
  the 
  same 
  relative 
  position 
  in 
  the 
  radioactive 
  series 
  

   and 
  have 
  very 
  similar 
  if 
  not 
  identical 
  chemical 
  properties, 
  

   emit 
  three 
  distinct 
  types 
  of 
  y 
  radiation 
  which 
  appear 
  to 
  be 
  

   closely 
  analogous 
  in 
  relative 
  penetrating 
  power. 
  Similar 
  

   results 
  appear 
  to 
  hold 
  for 
  radium 
  C, 
  thorium 
  D, 
  and 
  

   actinium 
  D, 
  each 
  of 
  which 
  emits 
  only 
  one 
  penetrating 
  type 
  

   of 
  7 
  radiation. 
  Xeither 
  of 
  the 
  two 
  products 
  radium 
  D 
  and 
  

   radium 
  E 
  corresponds 
  in 
  radioactive 
  or 
  chemical 
  properties 
  

   with 
  any 
  member 
  of 
  the 
  thorium 
  or 
  actinium 
  series 
  and 
  also 
  

   shows 
  no 
  close 
  analogy 
  in 
  their 
  types 
  of 
  radiation. 
  

  

  In 
  a 
  previous 
  paper 
  * 
  one 
  of 
  us 
  has 
  suggested 
  that 
  the 
  

   types 
  of 
  7 
  rays 
  emitted 
  by 
  radioactive 
  substances 
  should 
  

   correspond 
  to 
  one 
  or 
  more 
  of 
  the 
  types 
  of 
  characteristic 
  

   radiation 
  excited 
  in 
  the 
  atom 
  by 
  the 
  escape 
  of 
  /3 
  particles. 
  

   For 
  example, 
  the 
  single 
  type 
  of 
  7 
  radiation 
  from 
  radium 
  C 
  

   and 
  thorium 
  D 
  has 
  about 
  the 
  penetrating 
  power 
  to 
  be 
  

   expected 
  for 
  a 
  radiation 
  of 
  the 
  ;i 
  K 
  " 
  series 
  found 
  by 
  

   Barkla 
  J. 
  

  

  It 
  will 
  be 
  observed 
  from 
  the 
  table 
  that 
  all 
  the 
  B 
  products 
  

   emit 
  a 
  soft 
  type 
  of 
  radiation 
  which 
  is 
  on 
  an 
  average 
  much 
  

   less 
  penetrating 
  than 
  ordinary 
  X 
  rays. 
  From 
  a 
  comparison 
  

   of 
  the 
  results 
  given 
  by 
  Chapman 
  J 
  it 
  would 
  appear 
  that 
  the 
  

   radiations 
  from 
  radium 
  B, 
  /i 
  = 
  I0, 
  from 
  thorium 
  B, 
  fi 
  = 
  32, 
  

  

  * 
  Rutherford, 
  Phil. 
  Mag. 
  xxiv. 
  p. 
  453 
  (1912). 
  

  

  t 
  Barkla. 
  Phil. 
  Mag. 
  xxii. 
  p. 
  396 
  (1911). 
  

  

  % 
  Chapman, 
  Proc. 
  Eoy. 
  Soc. 
  ser. 
  A. 
  Ixxxvi. 
  p. 
  439 
  (1912). 
  

  

  