﻿the 
  7 
  Rays 
  of 
  the 
  Thorium 
  and 
  Actinium 
  Products. 
  941 
  

   Analysis 
  of 
  the 
  7 
  rays 
  from 
  Mesothorium 
  2. 
  

  

  The 
  mesothorium 
  2, 
  prepared 
  as 
  described, 
  was 
  used 
  for 
  

   this 
  experiment. 
  The 
  absorption 
  curves 
  obtained 
  are 
  shown 
  

   in 
  figs. 
  3 
  and 
  4. 
  Analysis 
  shows 
  that 
  the 
  rays 
  consist 
  of 
  two 
  

   types, 
  for 
  which 
  jul 
  = 
  26 
  and 
  /£= 
  0*116 
  respectively. 
  Fig. 
  3 
  

   shows 
  the 
  method 
  of 
  analysis 
  of 
  the 
  radiation 
  fj, 
  = 
  26 
  and 
  its 
  

   exponential 
  absorption 
  by 
  aluminium. 
  The 
  logarithm 
  curve 
  

   in 
  fig. 
  4 
  shows 
  the 
  absorption 
  for 
  the 
  penetrating 
  radiation 
  

   /i 
  = 
  0'116. 
  

  

  Analysis 
  of 
  the 
  7 
  rays 
  from 
  Actinium 
  (B 
  + 
  C 
  + 
  D). 
  

  

  The 
  7 
  rays 
  emitted 
  by 
  the 
  actinium 
  products 
  were 
  examined 
  

   by 
  the 
  same 
  method 
  as 
  that 
  adopted 
  in 
  the 
  case 
  of 
  thorium. 
  

   Owing 
  to 
  the 
  short 
  periods 
  of 
  actinium 
  C 
  (2*1 
  min.) 
  and 
  of 
  

   actinium 
  D 
  (4*71 
  min.) 
  it 
  was 
  impossible 
  to 
  complete 
  the 
  

   examination 
  of 
  the 
  separate 
  products 
  with 
  the 
  small 
  amount 
  

   of 
  material 
  at 
  our 
  disposal 
  *. 
  

  

  An 
  actinium 
  preparation 
  was 
  dissolved 
  in 
  hydrochloric 
  

   acid, 
  and 
  the 
  actinium 
  X 
  was 
  separated 
  by 
  the 
  ammonia 
  

   method. 
  In 
  this 
  manner 
  the 
  actinium 
  X 
  was 
  obtained 
  on 
  a 
  

   watch-glass 
  mixed 
  with 
  a 
  thin 
  layer 
  of 
  material. 
  The 
  

   preparation 
  was 
  covered 
  with 
  goldbeater's 
  skin 
  as 
  in 
  the 
  

   case 
  of 
  the 
  radiothorium 
  preparation 
  in 
  order 
  to 
  prevent 
  

   the 
  escape 
  of 
  the 
  emanation. 
  Shortly 
  after 
  the 
  separation 
  the 
  

   actinium 
  X 
  is 
  in 
  equilibrium 
  with 
  its 
  later 
  products 
  actinium 
  

   (B 
  + 
  C 
  + 
  D), 
  and 
  the 
  whole 
  then 
  decays 
  with 
  the 
  compara- 
  

   tively 
  long 
  period 
  of 
  actinium 
  X 
  (10*2 
  days). 
  The 
  7 
  rays 
  in 
  

   this 
  preparation 
  arise 
  from 
  the 
  active 
  deposit, 
  viz. 
  actinium 
  

   (B 
  + 
  C 
  + 
  D). 
  

  

  The 
  absorption 
  curve 
  in 
  aluminium 
  of 
  this 
  preparation 
  

   was 
  obtained 
  up 
  to 
  a 
  thickness 
  of 
  9 
  cm. 
  Beyond 
  6 
  cm. 
  the 
  

   absorption 
  is 
  exponential 
  with 
  an 
  absorption 
  coefficient 
  

   yu, 
  = 
  0'198. 
  The 
  curves 
  obtained 
  are 
  shown 
  in 
  figs. 
  5 
  and 
  6. 
  

   Analysis 
  as 
  in 
  previous 
  cases 
  shows 
  that 
  the 
  curves 
  can 
  be 
  

   separated 
  into 
  exponentials 
  with 
  absorption 
  coefficients 
  

   (j, 
  = 
  120, 
  ^=31,/x 
  = 
  0-46, 
  and/A 
  = 
  0198 
  respectively. 
  Fig. 
  5 
  

   shows 
  the 
  analysis 
  of 
  the 
  softer 
  portions 
  of 
  the 
  radiation, 
  and 
  

   fig. 
  6 
  the 
  separation 
  of 
  the 
  two 
  more 
  penetrating 
  groups. 
  

   From 
  analogy 
  with 
  the 
  thorium 
  series, 
  there 
  appears 
  to 
  be 
  

   little 
  doubt 
  that 
  the 
  radiations 
  fi=120, 
  /x 
  = 
  33, 
  and 
  yu, 
  = 
  0'46 
  

   belong 
  to 
  actinium 
  B, 
  and 
  that 
  for 
  which 
  ja 
  = 
  0*198 
  to 
  

   actinium 
  D. 
  

  

  * 
  The 
  actinium 
  preparation 
  used 
  in 
  these 
  experiments 
  was 
  separated 
  

   from 
  radioactive 
  residues 
  (see 
  Boltwood, 
  Proc. 
  Roy. 
  Soc. 
  A. 
  lxxxv. 
  

   1911, 
  p. 
  77) 
  loaned 
  to 
  one 
  of 
  us 
  by 
  the 
  Royal 
  Society. 
  

  

  