﻿Ionization 
  of 
  the 
  Alpha 
  Particle 
  in 
  Simple 
  Gases. 
  405 
  

  

  wire. 
  The 
  pressure 
  was 
  also 
  decreased 
  slowly 
  by 
  steps, 
  

   the 
  scintillations 
  counted, 
  and 
  the 
  equivalent 
  range 
  cal- 
  

   culated 
  for 
  each 
  pressure 
  until 
  the 
  number 
  of 
  scintillations 
  

   became 
  constant. 
  This 
  occurred 
  for 
  an 
  equivalent 
  range 
  of 
  

   about 
  5*8 
  cm. 
  The 
  source 
  was 
  then 
  moved 
  to 
  slightly 
  

   different 
  positions 
  and 
  the 
  above 
  observations 
  repeated 
  for 
  

   each 
  position. 
  Account 
  was 
  taken 
  of 
  the 
  decay 
  of 
  the 
  source 
  

   while 
  the 
  observations 
  were 
  being 
  made, 
  and 
  the 
  results 
  

   corrected 
  accordingly. 
  The 
  experiment 
  was 
  repeated 
  several 
  

   times 
  for 
  each 
  gas, 
  and 
  the 
  mean 
  values 
  of 
  all 
  observations 
  

   taken 
  for 
  final 
  results. 
  Curve 
  II. 
  fig. 
  2 
  represents 
  the 
  mean 
  

   results 
  for 
  air. 
  The 
  ordinates 
  are 
  the 
  observed 
  scintillations 
  

   per 
  minute, 
  and 
  the 
  abscissae 
  are 
  the 
  corresponding 
  ranges 
  at 
  

   15° 
  C. 
  and 
  760 
  mm. 
  It 
  is 
  seen 
  from 
  Curve 
  II. 
  that 
  there 
  is 
  

   a 
  rather 
  slow 
  decrease 
  in 
  the 
  number 
  of 
  particles 
  from 
  

   5'9 
  cm. 
  to 
  about 
  6*3 
  cm. 
  range, 
  and 
  then 
  the 
  number 
  

   decreases 
  quite 
  rapidly, 
  but 
  almost 
  uniformly, 
  to 
  the 
  end 
  of 
  

   the 
  range. 
  The 
  intersection 
  of 
  this 
  curve 
  with 
  the 
  axis 
  

   gives 
  the 
  range 
  in 
  air. 
  

  

  Fig. 
  2. 
  

  

  ,1 
  

  

  4-5 
  5-0 
  5-5 
  6-0 
  6-5 
  70 
  29-5 
  30 
  30-5 
  31 
  31-5 
  32 
  32-5 
  

  

  The 
  ordinates 
  for 
  all 
  curves 
  are 
  the 
  scintillations 
  per 
  minute. 
  The 
  

   abscissae 
  for 
  I., 
  II., 
  III., 
  and 
  IV. 
  are 
  the 
  ranges 
  in 
  centimetres 
  of 
  the 
  

   alpha 
  particles 
  from 
  radium 
  C 
  in 
  oxygen, 
  air, 
  hydrogen, 
  and 
  helium, 
  

   respectively. 
  

  

  Experiments 
  were 
  performed 
  in 
  the 
  above 
  manner 
  for 
  each 
  

   of 
  the 
  gases 
  oxygen, 
  hydrogen, 
  and 
  helium. 
  The 
  mean 
  

   results 
  obtained 
  are 
  represented 
  by 
  the 
  Curves 
  I., 
  III., 
  and 
  

   IV., 
  respectively, 
  in 
  fig. 
  2. 
  There 
  is 
  but 
  little 
  difference 
  

   between 
  the 
  rates 
  of 
  decrease 
  of 
  the 
  number 
  of 
  particles 
  near 
  

   the 
  end 
  of 
  the 
  range 
  in 
  oxygen 
  and 
  air. 
  The 
  small 
  difference 
  

  

  