﻿Recoil 
  Atoms 
  from 
  Thorium 
  C 
  and 
  Actinium 
  C. 
  591 
  

  

  II. 
  Second 
  Method 
  — 
  Ionization 
  hy 
  Recoil. 
  

  

  Wertenstein 
  * 
  has 
  shown 
  clearly 
  that 
  recoiling 
  atoms 
  

   produce 
  an 
  intense 
  ionization 
  over 
  their 
  path. 
  He 
  adopted 
  

   this 
  property 
  of 
  the 
  recoil 
  atoms 
  as 
  a 
  method 
  of 
  determining 
  

   the 
  range 
  of 
  recoil 
  of 
  radium 
  D 
  from 
  radium 
  C, 
  his 
  experi- 
  

   mental 
  arrangement 
  being 
  similar 
  in 
  principle 
  to 
  that 
  of 
  

   Bragg 
  for 
  determining 
  the 
  range 
  of 
  the 
  a-particles. 
  In 
  this 
  

   way 
  a 
  value 
  of 
  about 
  0*15 
  mm. 
  was 
  obtained 
  for 
  the 
  range 
  

   in 
  air 
  at 
  atmospheric 
  pressure. 
  Recently 
  he 
  has 
  shown 
  t 
  

   that 
  the 
  range 
  of 
  atoms 
  recoiling 
  from 
  polonium 
  is 
  about 
  

   O09 
  mm. 
  Thus 
  he 
  concludes 
  that 
  the 
  ranges 
  of 
  the 
  recoiling 
  

   atoms 
  are 
  roughly 
  proportional 
  to 
  the 
  ranges 
  of 
  the 
  a-particles 
  

   emitted 
  by 
  the 
  parent 
  products. 
  

  

  Fig. 
  

  

  -£/IRTh 
  

  

  

  -wo 
  Volts 
  

  

  - 
  -4-Ol/oLTS 
  

  

  ~ 
  Earth 
  

  

  In 
  the 
  experiments 
  described 
  in 
  this 
  paper, 
  the 
  apparatus 
  

   employed 
  was 
  a 
  modification 
  of 
  that 
  used 
  above 
  (see 
  fig. 
  1). 
  

   The 
  arrangement 
  is 
  shown 
  in 
  fig. 
  3. 
  A 
  hemispherical 
  

   ionization 
  chamber 
  is 
  formed 
  by 
  means 
  of 
  two 
  concentric 
  

  

  * 
  Loc. 
  cit. 
  

  

  t 
  Bianu 
  and 
  Wertenstein, 
  Co?nptes 
  Rendus, 
  Aug. 
  19] 
  2. 
  

  

  