﻿Active 
  Deposit 
  of 
  Actinium 
  in 
  Electric 
  Fields. 
  385 
  

  

  No 
  matter 
  whether 
  the 
  wire 
  was 
  charged 
  positively 
  or 
  

   negatively, 
  or 
  not 
  charged 
  at 
  all, 
  the 
  distribution 
  of 
  the 
  

   active 
  deposit 
  along 
  the 
  wire, 
  if 
  measurable, 
  was 
  always 
  the 
  

   same. 
  It 
  decreased 
  exponentially 
  with 
  the 
  distance 
  from 
  

   the 
  centre 
  of 
  the 
  tube. 
  If 
  we 
  assume 
  that 
  the 
  density 
  of 
  the 
  

   emanation 
  at 
  the 
  centre 
  of 
  the 
  tube 
  is 
  unity, 
  then 
  at 
  any 
  

   other 
  point 
  distance 
  sc 
  from 
  there, 
  the 
  density 
  is 
  e~ 
  Kt 
  , 
  where 
  X 
  

   is 
  the 
  decay 
  constant 
  of 
  the 
  emanation 
  and 
  t 
  is 
  the 
  time 
  taken 
  

   for 
  the 
  air 
  to 
  traverse 
  the 
  distance 
  x. 
  If 
  v 
  be 
  the 
  velocity 
  of 
  

   the 
  air-current 
  w=vt, 
  hence 
  the 
  distribution 
  of 
  the 
  emanation 
  

  

  may 
  be 
  written 
  e 
  v 
  . 
  Since 
  this 
  is 
  the 
  law 
  of 
  distribution 
  

   of 
  the 
  active 
  deposit 
  under 
  steady 
  conditions, 
  the 
  ratio 
  of 
  the 
  

   anode 
  to 
  the 
  cathode 
  activity 
  is 
  independent 
  of 
  the 
  amount 
  of 
  

   emanation 
  employed 
  — 
  a 
  point 
  of 
  some 
  importance 
  in 
  any 
  

   theory 
  of 
  the 
  changes 
  occurring. 
  

  

  II. 
  

  

  By 
  means 
  of 
  the 
  apparatus 
  just 
  described 
  we 
  introduce 
  

   immediately 
  into 
  a 
  uniform 
  electric 
  field 
  a 
  quantity 
  of 
  

   emanation 
  free 
  from 
  active 
  deposit 
  and 
  dust 
  nuclei. 
  When 
  

   an 
  emanation 
  atom 
  disintegrates, 
  the 
  motion 
  of 
  the 
  resulting 
  

   deposit 
  atom 
  is 
  therefore 
  determined 
  by 
  the 
  momentum 
  due 
  

   to 
  recoil, 
  the 
  velocity 
  of 
  the 
  air 
  current, 
  the 
  motion 
  due 
  to 
  

   diffusion 
  and 
  the 
  action 
  of 
  the 
  electric 
  field. 
  We 
  know 
  that 
  

   the 
  a 
  particles 
  projected 
  from 
  radioactive 
  substances 
  are 
  

   emitted 
  equally 
  in 
  all 
  directions. 
  Hence 
  it 
  follows 
  that 
  the 
  

   motion 
  of 
  the 
  deposit 
  atoms 
  due 
  to 
  recoil 
  must 
  be 
  distributed 
  

   in 
  the 
  same 
  way, 
  so 
  the 
  distribution 
  of 
  active 
  matter 
  in 
  the 
  

   gas 
  is 
  unaffected 
  by 
  recoil. 
  If 
  the 
  wire 
  and 
  tube 
  were 
  

   earthed, 
  the 
  activities 
  on 
  them 
  due 
  to 
  the 
  diffusion 
  of 
  the 
  

   active 
  matter 
  would 
  be 
  proportional 
  to 
  their 
  areas. 
  This 
  

   result 
  in 
  our 
  case 
  may 
  be 
  modified 
  by 
  the 
  action 
  of 
  the 
  air 
  

   current, 
  for 
  near 
  the 
  central 
  portions 
  of 
  the 
  wire 
  the 
  stream- 
  

   lines 
  are 
  not 
  parallel 
  to 
  the 
  axis 
  of 
  the 
  tube. 
  The 
  electric 
  

   field 
  will 
  drag 
  the 
  charged 
  deposit 
  atoms 
  to 
  the 
  electrodes. 
  

   Suppose 
  we 
  obtain 
  a 
  certain 
  amount 
  of 
  activity 
  on 
  the 
  wire 
  

   when 
  no 
  field 
  is 
  present, 
  and 
  that 
  we 
  have 
  charged 
  deposit 
  

   atoms 
  in 
  the 
  gas. 
  If 
  now 
  we 
  apply 
  a 
  very 
  weak 
  electric 
  

   field, 
  charging 
  the 
  wire 
  positively, 
  the 
  activity 
  collected 
  by 
  

   it 
  will 
  increase 
  if 
  we 
  have 
  negatively 
  charged 
  deposit 
  atoms 
  

   present. 
  Similarly, 
  if 
  it 
  be 
  charged 
  negatively, 
  the 
  activity 
  

   collected 
  by 
  it 
  will 
  again 
  increase, 
  if 
  positively 
  charged 
  

   deposit 
  atoms 
  are 
  present. 
  Hence, 
  if 
  deposit 
  atoms 
  carrying 
  

   both 
  negative 
  and 
  positive 
  charges 
  are 
  present, 
  we 
  shall 
  

   obtain 
  a 
  minimum 
  activity 
  on 
  the 
  wire 
  when 
  it 
  is 
  uncharged. 
  

  

  