﻿Recoil 
  Atoms 
  from 
  Thorium 
  C 
  and 
  Actinium 
  C. 
  597 
  

   Summary. 
  

  

  1. 
  The 
  ranges 
  of" 
  recoil 
  from 
  thorium 
  C 
  and 
  actinium 
  G 
  

   have 
  been 
  determined 
  in 
  air 
  and 
  hydrogen 
  by 
  two 
  different 
  

   methods, 
  (a) 
  by 
  collecting 
  the 
  recoiling 
  products 
  at 
  different 
  

  

  pressures 
  and 
  measuring 
  the 
  

   ionization 
  produced 
  by 
  the 
  

   pressures. 
  

  

  The 
  results 
  are 
  as 
  follows 
  :- 
  

  

  activity, 
  (b) 
  by 
  measuring 
  the 
  

   recoiling 
  atoms 
  at 
  different 
  

  

  Parent 
  Product. 
  

  

  Recoil 
  Product. 
  

  

  Eange 
  of 
  Recoil 
  in 
  Air. 
  

  

  Range 
  in 
  Hydrogen. 
  

  

  1st 
  Method. 
  

  

  2nd 
  Method. 
  

  

  1st 
  Method. 
  

  

  2nd 
  Method. 
  

  

  Actinium 
  0. 
  

   Thorium 
  C 
  r 
  

   Thorium 
  C 
  2 
  . 
  

  

  Actinium 
  D. 
  

  

  Thorium 
  D. 
  

  

  ? 
  

  

  0-12 
  mm. 
  

   012 
  mm. 
  

  

  0-126 
  mm. 
  

   0*175 
  mm. 
  

  

  0*52 
  mm. 
  

   055 
  mm. 
  

  

  055 
  mm. 
  

   074 
  mm. 
  

  

  2. 
  The 
  range 
  of 
  the 
  recoil 
  atom 
  from 
  actinium 
  C 
  is 
  found 
  

   to 
  be 
  the 
  same 
  both 
  by 
  the 
  activity 
  and 
  ionization 
  methods 
  ; 
  

   on 
  the 
  other 
  hand, 
  the 
  apparent 
  range 
  of 
  recoil 
  atoms 
  from 
  

   thorium 
  C 
  is 
  markedly 
  longer 
  by 
  the 
  ionization 
  method. 
  

  

  3. 
  These 
  differences 
  receive 
  a 
  satisfactory 
  explanation 
  by 
  

   supposing 
  that 
  two 
  distinct 
  groups 
  of 
  recoil 
  atoms 
  are 
  

   emitted 
  during 
  the 
  transformation 
  of 
  thorium 
  C 
  ; 
  the 
  shorter 
  

   range 
  group 
  is 
  radioactive, 
  the 
  other 
  rayless. 
  

  

  4. 
  The 
  order 
  of 
  disintegration 
  of 
  the 
  thorium 
  series 
  has 
  

   been 
  shown 
  to 
  agree 
  with 
  that 
  suggested 
  by 
  Marsden 
  and 
  

   Darwin 
  (by 
  an 
  entirely 
  different 
  method), 
  viz., 
  thorium 
  D 
  is 
  

   the 
  product 
  resulting 
  from 
  the 
  disintegration 
  of 
  thorium 
  G 
  x 
  

   (emitting 
  a-particles 
  of 
  4*8 
  cm. 
  range). 
  The 
  product 
  result 
  

   recoiling 
  from 
  thorium 
  C 
  2 
  (emitting 
  a-particles 
  of 
  8'6 
  cm. 
  

   range) 
  is 
  probably 
  rayless. 
  

  

  In 
  conclusion 
  I 
  should 
  like 
  to 
  express 
  my 
  sincere 
  thanks 
  

   to 
  Prof. 
  Rutherford 
  and 
  to 
  Dr. 
  Hans 
  Geiger 
  for 
  suggesting 
  

   this 
  research, 
  and 
  for 
  much 
  helpful 
  advice 
  during 
  its 
  progress. 
  

  

  Physical 
  Laboratories, 
  

  

  The 
  University, 
  Manchester, 
  

   July 
  1913. 
  

  

  Phil. 
  Mag. 
  S. 
  6. 
  Vol. 
  26. 
  No. 
  154. 
  Oct. 
  1913. 
  2 
  S 
  

  

  