﻿410 
  Range 
  of 
  Alpha 
  Particle 
  in 
  Simjrte 
  Gases. 
  

  

  range. 
  The 
  peak 
  of 
  the 
  hydrogen 
  curve 
  is 
  also 
  nearer 
  the 
  

   end 
  of 
  the 
  range 
  than 
  it 
  is 
  for 
  the 
  air 
  curve, 
  and 
  it 
  is 
  also 
  

   more 
  pronounced. 
  The 
  formula 
  given 
  by 
  Geiger* 
  

  

  1 
  = 
  

  

  for 
  the 
  ionization 
  curve 
  can 
  be 
  made 
  to 
  coincide 
  very 
  well 
  

   with 
  the 
  curves 
  by 
  assuming 
  17 
  centimetres 
  as 
  the 
  value 
  of 
  

   r, 
  the 
  average 
  range 
  of 
  the 
  particle. 
  This 
  theoretical 
  curve 
  

   varies 
  more 
  from 
  the 
  air 
  curve 
  than 
  it 
  does 
  from 
  either 
  the 
  

   hydrogen 
  or 
  helium 
  curve. 
  

  

  From 
  the 
  results 
  on 
  the 
  decrease 
  in 
  the 
  number 
  of 
  particles 
  

   from 
  radium 
  C 
  near 
  the 
  end 
  of 
  the 
  range 
  in 
  air 
  or 
  oxygen 
  

   as 
  compared 
  with 
  those 
  for 
  hydrogen 
  or 
  helium, 
  it 
  would 
  

   seem 
  probable 
  that 
  a 
  greater 
  difference 
  should 
  exist 
  between 
  

   the 
  points 
  at 
  which 
  the 
  peaks 
  of 
  the 
  curves 
  occur 
  than 
  that 
  

   shown 
  by 
  the 
  curves 
  in 
  fig. 
  4. 
  

  

  Conclusions* 
  

  

  The 
  ranges 
  of 
  the 
  alpha 
  particles 
  from 
  radium 
  C 
  and 
  

   polonium 
  have 
  been 
  determined 
  by 
  the 
  scintillation 
  method 
  

   in 
  helium, 
  hydrogen, 
  oxygen, 
  and 
  air. 
  

  

  The 
  rate 
  at 
  which 
  the 
  number 
  of 
  alpha 
  particles 
  from 
  

   radium 
  C 
  diminishes 
  near 
  the 
  end 
  of 
  the 
  range 
  has 
  been 
  

   determined 
  by 
  the 
  scintillation 
  method 
  in 
  air, 
  oxygen, 
  

   hydrogen, 
  and 
  helium. 
  

  

  The 
  Bragg 
  ionization 
  curve 
  has 
  been 
  determined 
  in 
  helium 
  

   and 
  compared 
  with 
  the 
  air 
  and 
  hydrogen 
  curves 
  obtained 
  

   when 
  the 
  range 
  of 
  the 
  particle 
  was 
  the 
  same 
  as 
  that 
  in 
  

   helium. 
  The 
  ionization 
  curve 
  is 
  of 
  the 
  general 
  form 
  

  

  1 
  = 
  

  

  where 
  I 
  is 
  the 
  ionization 
  ; 
  c 
  a 
  constant 
  depending 
  upon 
  the 
  

   energy 
  required 
  to 
  produce 
  an 
  ion; 
  r 
  is 
  the 
  average 
  range; 
  

   and 
  x 
  the 
  distance 
  from 
  the 
  source 
  of 
  rays. 
  The 
  ratio 
  of 
  

   the 
  total 
  ionization 
  in 
  helium 
  to 
  that 
  in 
  air 
  or 
  hydrogen 
  is 
  

   1-05. 
  

  

  I 
  wish 
  to 
  express 
  my 
  thanks 
  to 
  Professor 
  Rutherford 
  for 
  

   furnishing 
  me 
  the 
  facilities 
  for 
  carrying 
  out 
  this 
  research, 
  

   and 
  for 
  his 
  unfailing 
  interest 
  throughout 
  the 
  course 
  of 
  the 
  

   work. 
  

  

  Physical 
  Laboratories, 
  

  

  The 
  University, 
  Manchester, 
  

   May 
  10, 
  1913. 
  

  

  * 
  Geiger, 
  Proc. 
  Hoy. 
  Soc. 
  A. 
  vol. 
  Ixxxiii. 
  n. 
  565, 
  p. 
  505. 
  

  

  