﻿the 
  y 
  Rays 
  of 
  the 
  Thorium 
  and 
  Actinium 
  Products. 
  939 
  

  

  expelled. 
  The 
  residue 
  was 
  obtained 
  on 
  a 
  watch-glass 
  and 
  

   consisted 
  of 
  a 
  thin 
  layer 
  of 
  solid 
  matter. 
  This 
  residue 
  

   contained 
  all 
  the 
  radiothorium 
  and 
  mesothorium 
  2. 
  Since 
  

   radiothorium 
  itself 
  does 
  not 
  emit 
  y 
  rays, 
  the 
  examination 
  of 
  

   this 
  source 
  immediately 
  after 
  its 
  preparation 
  gave 
  the 
  y 
  rays 
  

   belonging 
  to 
  mesothorium 
  2. 
  The 
  latter 
  decays 
  to 
  half 
  value 
  

   in 
  6'2 
  hours, 
  and 
  has 
  practically 
  disappeared 
  in 
  the 
  course 
  

   of 
  two 
  days, 
  In 
  the 
  meantime 
  the 
  radiothorium 
  had 
  pro- 
  

   duced 
  thorium 
  X 
  and 
  its 
  subsequent 
  products, 
  viz. 
  thorium 
  

   emanation 
  and 
  the 
  active 
  deposit, 
  and 
  this 
  source 
  was 
  used 
  

   to 
  test 
  again 
  the 
  y 
  radiation 
  from 
  thorium 
  (B 
  + 
  C-fD). 
  

   We 
  obtained 
  no 
  definite 
  evidence 
  that 
  thorium 
  X 
  emits 
  a 
  

   quantity 
  of 
  y 
  rays 
  which 
  could 
  be 
  detected 
  in 
  our 
  expe- 
  

   riments 
  *. 
  

  

  Analysis 
  of 
  the 
  y 
  rays 
  from 
  Thorium 
  (C+D). 
  

  

  The 
  7 
  radiation 
  was 
  examined 
  in 
  the 
  electroscope 
  con- 
  

   taining 
  methyl 
  iodide, 
  using, 
  as 
  before, 
  a 
  strong 
  magnetic 
  

   field 
  to 
  remove 
  the 
  /3 
  rays. 
  The 
  source 
  used 
  in 
  these 
  

   experiments 
  consisted 
  of 
  the 
  deposit 
  of 
  thorium 
  (C 
  + 
  D) 
  on 
  

   the 
  nickel 
  wire 
  mentioned 
  above. 
  The 
  absorption 
  curve 
  

   shoved 
  that 
  two 
  types 
  of 
  radiation 
  were 
  present. 
  About 
  

   80 
  per 
  cent, 
  of 
  the 
  total 
  radiation 
  consisted 
  of 
  a 
  very 
  hard 
  

   type, 
  which 
  was 
  exponentially 
  absorbed 
  in 
  aluminium 
  

   and 
  had 
  an 
  absorption 
  coefficient 
  in 
  that 
  substance 
  of 
  

   yL6=0*096 
  (cm.) 
  -1 
  . 
  The 
  other 
  radiation 
  present 
  was 
  much 
  

   less 
  penetrating 
  and 
  was 
  completely 
  stopped 
  by 
  2 
  mm. 
  of 
  

   aluminium. 
  This 
  soft 
  radiation, 
  however, 
  was 
  not 
  absorbed 
  

   exponentially 
  by 
  aluminium, 
  and 
  would 
  thus 
  appear 
  to 
  be 
  

   complex 
  in 
  character. 
  The 
  general 
  evidence 
  indicates 
  that 
  

   th's 
  soft 
  radiation 
  is 
  not 
  emitted 
  by 
  thorium 
  C 
  or 
  thorium 
  D, 
  

   but 
  is 
  excited 
  in 
  the 
  nickel 
  by 
  the 
  a 
  or 
  /3 
  rays. 
  It 
  will 
  be 
  

   remembered 
  that 
  a 
  radiation 
  of 
  almost 
  identical 
  type 
  was 
  

   found 
  when 
  radium 
  C 
  was 
  deposited 
  on 
  nickel 
  f 
  . 
  It 
  is 
  

   intended 
  to 
  make 
  a 
  more 
  detailed 
  examination 
  as 
  to 
  whether 
  

   radiations 
  of 
  this 
  kind 
  are 
  to 
  be 
  attributed 
  to 
  the 
  excitation 
  

   of 
  one 
  or 
  more 
  types 
  of 
  characteristic 
  radiation 
  by 
  the 
  

  

  * 
  L. 
  Meitner 
  and 
  Halm 
  {Phys. 
  Zeit. 
  xiv. 
  p. 
  873, 
  1913) 
  have 
  recently 
  

   examined 
  the 
  products 
  thorium 
  X 
  and 
  thorium 
  C 
  for 
  y 
  rays. 
  Both 
  of 
  

   these 
  products 
  have 
  been 
  found 
  to 
  emit 
  y 
  rays 
  in 
  small 
  quantity. 
  The 
  

   presence 
  of 
  a 
  small 
  amount 
  of 
  y 
  radiation 
  from 
  these 
  substances 
  would, 
  

   however, 
  have 
  no 
  appreciable 
  effect 
  on 
  the 
  absorption 
  curves 
  obtained 
  by 
  

   the 
  methods 
  used 
  in 
  our 
  experiments. 
  

  

  t 
  Rutherford 
  & 
  Richardson, 
  Phil. 
  Ma<r. 
  xxv. 
  p. 
  730 
  (1913). 
  

  

  3 
  S 
  2 
  

  

  