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  XXX. 
  The 
  Range 
  and 
  Ionization 
  of 
  the 
  Alpha 
  Particle 
  in 
  

   Simple 
  Gases. 
  By 
  T. 
  S. 
  Taylor, 
  Ph.D., 
  John 
  Barling 
  

   Fellow, 
  University 
  of 
  Manchester 
  *. 
  

  

  Introduction. 
  

  

  T|^HE 
  problem 
  of 
  the 
  absorption 
  of 
  the 
  alpha 
  particles 
  by 
  

   -L 
  matter 
  has 
  been 
  considered 
  theoretically 
  by 
  Sir 
  J. 
  J. 
  

   Thomson 
  t, 
  Darwin 
  % 
  f 
  and 
  Bohr 
  §. 
  In 
  any 
  treatment 
  of 
  this 
  

   problem 
  the 
  exact 
  range 
  of 
  the 
  alpha 
  particle 
  in 
  the 
  substances 
  

   considered 
  is 
  an 
  important 
  constant. 
  The 
  rate 
  at 
  which 
  the 
  

   number 
  of 
  particles 
  near 
  the 
  end 
  of 
  the 
  range 
  decreases, 
  

   and 
  also 
  the 
  form 
  of^the 
  ionization 
  curve 
  for 
  different 
  sub- 
  

   stances, 
  are 
  helpful 
  in 
  the 
  consideration 
  of 
  the 
  laws 
  of 
  absorp- 
  

   tion 
  of 
  the 
  alpha 
  particles. 
  The 
  range 
  of 
  the 
  alpha 
  particles 
  

   and 
  the 
  ionization 
  produced 
  by 
  them 
  have 
  received 
  consi- 
  

   derable 
  attention 
  by 
  various 
  investigators. 
  The 
  results 
  ob- 
  

   tained 
  from 
  the 
  investigations 
  on 
  the 
  elementary 
  gases 
  are 
  of 
  

   especial 
  theoretical 
  interest. 
  As 
  yet 
  the 
  absorption 
  of 
  the 
  

   alpha 
  particle 
  in 
  the 
  simplest 
  gas, 
  helium, 
  has 
  received 
  but 
  little 
  

   attention. 
  The 
  range 
  of 
  the 
  alpha 
  particles 
  from 
  polonium 
  

   has 
  been 
  determined 
  by 
  Adams 
  ||, 
  but 
  the 
  range 
  of 
  the 
  

   alpha 
  particle 
  from 
  radium 
  and 
  the 
  ionization 
  curve 
  for 
  

   the 
  alpha 
  particle 
  in 
  helium 
  have 
  not 
  been 
  investigated. 
  It 
  

   was 
  for 
  the 
  purpose 
  of 
  investigating 
  the 
  latter 
  and 
  allied 
  

   problems, 
  as 
  well 
  as 
  redetermining 
  some 
  of 
  the 
  above-cited 
  

   values, 
  that 
  the 
  present 
  investigation 
  was 
  begun. 
  

  

  The 
  Ranges 
  of 
  the 
  Alpha 
  Particles 
  from 
  Radium 
  C 
  and 
  

   Polonium 
  in 
  Hydrogen, 
  Helium, 
  Oxygen, 
  and 
  Air. 
  

  

  In 
  this 
  determination 
  of 
  the 
  ranges 
  of 
  the 
  alpha 
  particles, 
  

   the 
  scintillation 
  method 
  was 
  used. 
  The 
  apparatus 
  (fig. 
  1) 
  

   consisted 
  essentially 
  of 
  a 
  long 
  glass 
  tube 
  closed 
  at 
  each 
  end 
  

   by 
  means 
  of 
  a 
  piece 
  of 
  sheet-glass 
  fastened 
  down 
  with 
  wax. 
  

   Upon 
  the 
  inner 
  surface 
  of 
  one 
  of 
  these 
  plates 
  over 
  the 
  ends 
  

   of 
  the 
  tube 
  was 
  a 
  zinc-sulphide 
  screen. 
  The 
  scintillations 
  

   were 
  observed 
  by 
  means 
  of 
  a 
  microscope 
  E. 
  A 
  side 
  tube 
  as 
  

   shown 
  in 
  the 
  figure 
  leads 
  to 
  the 
  pump, 
  charcoal 
  bulbs, 
  mano- 
  

   meter, 
  and 
  pressure 
  chamber. 
  The 
  pressure 
  in 
  the 
  chamber 
  

   as 
  well 
  as 
  that 
  in 
  the 
  apparatus 
  could 
  be 
  varied 
  at 
  will 
  by 
  

  

  * 
  Communicated 
  by 
  Prof. 
  E. 
  Rutherford, 
  F.R.S. 
  

  

  t 
  J. 
  J. 
  Thomson, 
  ' 
  Conduction 
  of 
  Electricity 
  through 
  Gases,' 
  pp. 
  370- 
  

   382. 
  

  

  % 
  C. 
  G. 
  Darwin, 
  Phil. 
  Mag. 
  xxiii. 
  p. 
  907 
  (1912). 
  

  

  § 
  N. 
  Bohr, 
  Phil. 
  Mag. 
  xxiv. 
  p. 
  10 
  (1913). 
  

  

  j| 
  E. 
  P. 
  Adams, 
  Physical 
  Review, 
  xxiv. 
  p. 
  113 
  (1907). 
  

  

  