﻿Ionization 
  of 
  the 
  Alpha 
  Particle 
  in 
  Simple 
  Gases. 
  409 
  

  

  Since 
  the 
  source 
  could 
  not 
  be 
  moved 
  closer 
  than 
  4 
  centi- 
  

   metres 
  to 
  the 
  ionization 
  vessel, 
  the 
  form 
  of 
  the 
  curve 
  from 
  

   to 
  4 
  centimetres 
  was 
  assumed 
  to 
  be 
  the 
  same 
  as 
  the 
  pro- 
  

   longation 
  of 
  the 
  part 
  of 
  the 
  curve 
  above 
  4 
  centimetres. 
  

   Such 
  an 
  assumed 
  form 
  of 
  the 
  curve 
  cannot 
  be 
  far 
  from 
  

   correct. 
  

  

  Fiff. 
  4. 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  vim 
  

  

  

  

  

  

  

  

  

  

  | 
  

  

  

  

  

  

  

  

  

  

  \ 
  

  

  

  

  

  

  

  

  

  

  1 
  

  

  

  

  

  

  

  

  

  

  \ 
  

  

  The 
  ordinates 
  are 
  tlie 
  relative 
  ionizations. 
  The 
  abscissae 
  are 
  the 
  

   distances 
  in 
  centimetres 
  of 
  the 
  polonium 
  from 
  the 
  ionization 
  chamber. 
  

   Curves 
  L, 
  II., 
  and 
  III. 
  were 
  obtained 
  when 
  the 
  maximum 
  range 
  of 
  the 
  

   alpha 
  particle 
  was 
  17'62 
  centimetres 
  in 
  hydrogen, 
  helium, 
  and 
  air 
  

   respectively. 
  

  

  Using 
  the 
  above 
  described 
  method, 
  ionization 
  curves 
  were 
  

   obtained 
  in 
  helium 
  at 
  normal 
  pressure, 
  hydrogen 
  at 
  a 
  slightly 
  

   reduced 
  pressure, 
  and 
  air 
  at 
  a 
  pressure 
  of 
  about 
  16'3 
  centi- 
  

   metres. 
  Under 
  these 
  conditions 
  the 
  range 
  of 
  the 
  alpha 
  

   particle 
  was 
  the 
  same 
  for 
  each 
  gas. 
  The 
  curves 
  obtained 
  

   are 
  shown 
  in 
  fig. 
  4. 
  Curve 
  I. 
  was 
  obtained 
  in 
  hydrogen, 
  

   Curve 
  II. 
  in 
  helium, 
  and 
  Curve 
  III. 
  in 
  air. 
  The 
  area 
  under 
  

   the 
  air 
  curve 
  is 
  practically 
  the 
  same 
  as 
  that 
  under 
  the 
  

   hydrogen 
  curve. 
  The 
  area 
  under 
  the 
  helium 
  curve 
  is 
  about 
  

   5 
  per 
  cent, 
  greater 
  than 
  that 
  under 
  the 
  hydrogen 
  or 
  air 
  

   curve. 
  Bence 
  the 
  ionization 
  produced 
  by 
  an 
  alpha 
  particle 
  

   is 
  5 
  per 
  cent, 
  more 
  in 
  helium 
  than 
  it 
  is 
  in 
  hydrogen 
  or 
  air, 
  arid 
  

   consequently 
  the 
  helium 
  molecule 
  is 
  more 
  readily 
  ionized. 
  

  

  There 
  is 
  but 
  little 
  difference 
  in 
  the 
  shape 
  of 
  the 
  curves. 
  

   The 
  helium 
  curve 
  has 
  a 
  slightly 
  more 
  pronounced 
  peak 
  than 
  

   the 
  others, 
  and 
  this 
  peak 
  occurs 
  a 
  little 
  nearer 
  the 
  end 
  of 
  the 
  

  

  