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  LXV. 
  The 
  y-Rai/s 
  of 
  Uranium 
  and 
  Radium 
  *. 
  Bi/ 
  Frederick 
  

   SoDDY, 
  M.A., 
  and 
  Alexander 
  S. 
  Russell, 
  1/. 
  J.., 
  jB.^c.f 
  

  

  1. 
  Introduction. 
  

  

  HAYING- 
  at 
  our 
  disposal 
  50 
  kilograms 
  of 
  the 
  purest 
  

   commercial 
  uranyl 
  nitrate, 
  provided 
  by 
  the 
  generosity 
  

   o£ 
  a 
  friend, 
  we 
  have 
  been 
  enabled 
  to 
  study 
  the 
  radioactivity 
  

   of 
  uranium 
  X 
  on 
  a 
  considerably 
  larger 
  scale 
  than 
  previously 
  

   attempted. 
  This 
  body, 
  which 
  was 
  discovered 
  by 
  Sir 
  William 
  

   Crookes 
  (Proc. 
  Roy. 
  Soc. 
  1900, 
  Ixvi. 
  p. 
  409), 
  was 
  early 
  re- 
  

   cognized 
  (Rutherford 
  and 
  Soddy, 
  Phil. 
  Mag. 
  1903, 
  v. 
  p. 
  441) 
  

   as 
  a 
  disintegration 
  product 
  of 
  uranium 
  producing 
  the 
  whole 
  

   of 
  the 
  /3-rays 
  but 
  none 
  of 
  the 
  a-rays 
  of 
  that 
  element. 
  It 
  has 
  a 
  

   period 
  of 
  average 
  life 
  of 
  about 
  31 
  days. 
  The 
  period 
  is 
  long- 
  

   enough 
  to 
  allow 
  of 
  the 
  separation 
  of 
  the 
  greater 
  part 
  of 
  the 
  

   substance, 
  even 
  from 
  a 
  large 
  quantity 
  of 
  uranium. 
  When 
  

   the 
  activity 
  of 
  one 
  product 
  has 
  decayed 
  too 
  far 
  to 
  work 
  with, 
  

   a 
  fresh 
  crop 
  can 
  be 
  obtained 
  by 
  repeating 
  the 
  process. 
  At 
  

   each 
  separation 
  the 
  uranyl 
  nitrate 
  is 
  rendered 
  purer, 
  any 
  

   fortuitous 
  impurities 
  present 
  being 
  eliminated, 
  and 
  as 
  it 
  is 
  

   necessary 
  in 
  certain 
  problems 
  to 
  be 
  sure 
  that 
  no 
  radioactive 
  

   impurities 
  are 
  present 
  initially, 
  it 
  is 
  intended 
  to 
  carry 
  out 
  

   periodically 
  a 
  long 
  series 
  of 
  such 
  separations. 
  The 
  present 
  

   work 
  is 
  concerned 
  with 
  the 
  first 
  three 
  separations, 
  carried 
  

   out 
  at 
  intervals 
  of 
  about 
  three 
  months, 
  and 
  is 
  devoted 
  to 
  a 
  

   comparison 
  of 
  the 
  7-radiation 
  of 
  the 
  active 
  preparations 
  

   separated, 
  with 
  the 
  7-rays 
  of 
  radium. 
  We 
  have 
  found 
  that, 
  

   as 
  in 
  all 
  other 
  known 
  cases, 
  the 
  7-rays 
  of 
  uranium 
  accompany 
  

   the 
  /8-rays, 
  both 
  resulting 
  entirely 
  in 
  the 
  disintegration 
  of 
  

   uranium 
  X. 
  The 
  results 
  here 
  recorded 
  do 
  not, 
  however, 
  

   bear 
  out 
  either 
  of 
  the 
  rival 
  views 
  of 
  the 
  origin 
  of 
  the 
  7-rays, 
  

   but 
  rather 
  indicate 
  that 
  the 
  y^-rays 
  and 
  7-rays 
  may 
  be 
  entirely 
  

   distinct 
  in 
  origin. 
  

  

  Our 
  knowledge 
  of 
  the 
  7-rays 
  of 
  uranium 
  has 
  previously 
  

   been 
  practically 
  confined 
  to 
  the 
  work 
  of 
  Eve, 
  who 
  examined 
  

   the 
  7-rays 
  of 
  uranyl 
  nitrate. 
  Eve 
  found 
  in 
  the 
  first 
  place 
  

   that 
  uranium 
  only 
  gave 
  out 
  about 
  -^ 
  as 
  much 
  7-radiation 
  

   as 
  thorium, 
  though 
  its 
  /3-radiation 
  is, 
  as 
  is 
  well 
  known, 
  very 
  

   much 
  more 
  intense. 
  Eve 
  states 
  that 
  while 
  the 
  7-rays 
  of 
  

   radium 
  and 
  thorium 
  are 
  of 
  similar 
  penetrating 
  power, 
  the 
  

   7-rays 
  of 
  uranium 
  are 
  much 
  less 
  penetrating^ 
  and 
  are 
  prac- 
  

   tically 
  completely 
  absorbed 
  by 
  1 
  cm. 
  of 
  lead. 
  Over 
  a 
  range 
  

  

  * 
  A 
  preliminary 
  account 
  of 
  part 
  of 
  this 
  work 
  was 
  published 
  in 
  'Nature/ 
  

   3Iarch 
  4th, 
  1909, 
  p. 
  7, 
  and 
  Phys. 
  Zeit. 
  1909, 
  x. 
  p. 
  249. 
  

   t 
  Communicated 
  by 
  the 
  Authors. 
  

  

  