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  XXI 
  Y. 
  Some 
  Experiments 
  with 
  the 
  Active 
  Deposit 
  of 
  Thorium. 
  

   By 
  E. 
  Marsden, 
  M.Sc, 
  Lecturer 
  in 
  Physics, 
  and 
  R. 
  H. 
  

   Wilson, 
  B.Sc, 
  University 
  of 
  Manchester 
  *. 
  

  

  IN 
  a 
  recent 
  paper 
  Darwin 
  and 
  one 
  of 
  us 
  f 
  suggested 
  the 
  

   following 
  scheme 
  for 
  the 
  transformations 
  in 
  the 
  active 
  

   deposit 
  of 
  thorium 
  : 
  — 
  

  

  /3 
  

  

  / 
  

  

  o 
  / 
  // 
  

  

  ^rThC^r— 
  -ThD 
  — 
  

  

  60-51T1 
  3 
  '07 
  m 
  

  

  -ThB- 
  

  

  53 
  sees. 
  o-!4secs. 
  io-6hrs. 
  

  

  /3 
  a 
  (8-6) 
  

  

  / 
  / 
  

  

  -VThC* 
  ThC, 
  — 
  > 
  ? 
  

  

  60-5T11 
  lOS^CS. 
  

  

  In 
  this 
  scheme 
  C 
  a 
  J 
  and 
  CL 
  were 
  presumed 
  to 
  denote 
  the 
  

   same 
  substance 
  thorium 
  C 
  breaking 
  down 
  in 
  different 
  ways, 
  

   i. 
  e. 
  with 
  the 
  expulsion 
  of 
  an 
  a 
  or 
  a 
  /3 
  particle. 
  Miss 
  Meitner 
  §, 
  

   however, 
  has 
  obtained 
  results 
  which 
  apparently 
  show 
  that 
  the 
  

   fraction 
  of 
  thorium 
  G 
  (i. 
  e. 
  C 
  a 
  ) 
  which 
  gives 
  rise 
  to 
  the 
  7-ray 
  

   product 
  D 
  can 
  be 
  isolated 
  and 
  separated 
  from 
  the 
  rest 
  of 
  the 
  

   products. 
  In 
  her 
  experiments 
  a 
  hydrochloric 
  acid 
  solution 
  

   of 
  the 
  active 
  deposit, 
  B-f 
  C 
  + 
  D, 
  w 
  T 
  as 
  taken, 
  a 
  few 
  drops 
  

   of 
  stannous 
  chloride 
  added, 
  and 
  successive 
  nickel 
  plates 
  

   immersed 
  for 
  twenty 
  minutes. 
  The 
  solution 
  was 
  then 
  

   divided 
  into 
  two 
  portions 
  which 
  were 
  boiled 
  to 
  dryness 
  on 
  

   watch-glasses, 
  and 
  the 
  variation 
  of 
  activity 
  observed 
  by 
  a 
  and 
  

   by 
  7 
  rays, 
  respectively, 
  for 
  the 
  ensuing 
  five 
  hours. 
  The 
  

   results 
  are 
  shown 
  in 
  fig. 
  1, 
  where 
  the 
  curve 
  marked 
  a 
  gives 
  

   the 
  variation 
  of 
  the 
  a-ray 
  activity, 
  and 
  that 
  marked 
  7 
  the 
  

   variation 
  of 
  the 
  7-ray 
  activity. 
  With 
  no 
  stannous 
  chloride 
  

   added, 
  both 
  the 
  a- 
  and 
  the 
  7-ray 
  curves 
  rose 
  together 
  from 
  

   the 
  same 
  small 
  initial 
  percentage 
  of 
  the 
  maximum. 
  

  

  Since 
  the 
  7 
  rays 
  all 
  come 
  from 
  thorium 
  D 
  ||, 
  which 
  in 
  con- 
  

   sequence 
  of 
  its 
  short 
  period 
  practically 
  accompanies 
  C 
  a 
  in 
  

   proportional 
  amount, 
  these 
  results 
  were 
  interpreted 
  by 
  

  

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

  

  t 
  Marsden 
  & 
  Darwin, 
  Proc. 
  Roy. 
  Soc. 
  A. 
  lxxxvii. 
  p. 
  17(1912). 
  

  

  X 
  As 
  we 
  are 
  only 
  dealing 
  with 
  the 
  thorium 
  products 
  they 
  will 
  in 
  this 
  

   paper 
  be 
  simply 
  denoted 
  by 
  A, 
  B, 
  &c. 
  When 
  C 
  is 
  mentioned 
  it 
  will 
  be 
  

   taken 
  to 
  signify 
  (Ca+C^+C,,). 
  

  

  § 
  Lise 
  Meitner, 
  Phys. 
  Zcitschr. 
  xiii. 
  p. 
  623 
  (1912). 
  

  

  || 
  Except 
  some 
  soft 
  7 
  rays 
  from 
  B 
  (see 
  later). 
  

  

  