﻿648 
  Tlie 
  fy-Rays 
  of 
  Uranium 
  and 
  Radium, 
  

  

  Lead 
  is 
  entirely 
  anomalous 
  with 
  the 
  value 
  of 
  the 
  ratio 
  

   1*4:65, 
  and 
  this 
  no 
  doubt, 
  as 
  explained^ 
  is 
  to 
  he 
  attributed 
  

   partly 
  to 
  the 
  disposition 
  employed, 
  and 
  possibly 
  also 
  to 
  the 
  

   fact 
  that 
  the 
  measurements 
  were 
  done 
  in 
  a 
  lead 
  electroscope. 
  

   It 
  is 
  rather 
  curious 
  that 
  lead, 
  of 
  all 
  metals, 
  seems 
  in 
  many 
  

   ways 
  to 
  be 
  the 
  most 
  unsuited 
  for 
  accurate 
  measurements 
  of 
  

   the 
  absorption 
  of 
  7-rays, 
  and 
  yet 
  it 
  is 
  the 
  one 
  which 
  we, 
  in 
  

   common 
  with 
  previous 
  investigators, 
  have 
  worked 
  with 
  most. 
  

   We 
  have 
  noticed 
  repeatedly 
  that 
  it 
  is 
  more 
  difficult 
  to 
  obtain 
  

   consistent 
  results 
  with 
  lead 
  as 
  the 
  absorber 
  than 
  with 
  any 
  

   other 
  material. 
  This 
  is 
  partially 
  perhaps, 
  but 
  not 
  wholly, 
  

   due 
  to 
  its 
  own 
  high 
  natural 
  radioactivity, 
  necessitating 
  

   frequent 
  redetermination 
  of 
  the 
  natural 
  leak. 
  If 
  we 
  were 
  

   repeating 
  the 
  work 
  we 
  should 
  use 
  by 
  preference 
  another 
  

   metal 
  in 
  many 
  of 
  the 
  measurements 
  described 
  in 
  the 
  first 
  part 
  

   of 
  the 
  paper. 
  

  

  Summary 
  of 
  Results, 
  

  

  1. 
  The 
  7-radiatiou 
  of 
  uranium 
  X, 
  separated 
  from 
  50 
  

   kilograms 
  of 
  uranyl 
  nitrate, 
  has 
  been 
  compared 
  with 
  the 
  

   7-radiation 
  of 
  radium, 
  and 
  it 
  is 
  concluded 
  that 
  the 
  yS- 
  and 
  

   7-radiations 
  are 
  probably 
  not, 
  as 
  hitherto 
  assumed, 
  inter- 
  

   dependent. 
  

  

  2. 
  The 
  initial 
  7-radiation 
  of 
  the 
  uranium 
  X 
  in 
  equilibrium 
  

   with 
  1 
  kilogram 
  of 
  uranium 
  (elementj 
  is 
  equal 
  to 
  that 
  of 
  

   0'015 
  milligram 
  of 
  a 
  particular 
  sample 
  of 
  a 
  radium 
  compound, 
  

   which 
  may 
  be 
  provisionally 
  regarded 
  as 
  containing 
  66' 
  6 
  

   per 
  cent, 
  of 
  radium. 
  

  

  3. 
  The 
  ratio 
  of 
  the 
  /3- 
  to 
  the 
  7-rays 
  of 
  uranium 
  X 
  is 
  62 
  

   when 
  the 
  same 
  ratio 
  for 
  radium 
  C 
  is 
  taken 
  as 
  unity, 
  the 
  

   7-rays 
  being 
  measured 
  through 
  1 
  cm. 
  of 
  lead. 
  Correcting 
  

   for 
  the 
  absorption 
  in 
  the 
  lead, 
  and 
  assuming 
  the 
  rays 
  to 
  be 
  

   homogeneous 
  in 
  each 
  case, 
  the 
  value 
  of 
  the 
  ratio 
  for 
  uranium 
  

   is 
  50. 
  When 
  the 
  y-rays 
  are 
  measured 
  through 
  0*6 
  cm. 
  of 
  

   aluminium, 
  so 
  as 
  to 
  admit 
  any 
  soft 
  7-radiation 
  if 
  present, 
  the 
  

   ratio 
  for 
  uranium 
  is 
  18, 
  not 
  correcting 
  for 
  absorption. 
  It 
  is 
  

   not 
  yet 
  decided 
  whether 
  a 
  soft 
  primary 
  7-radiation 
  of 
  uranium 
  

   exists. 
  

  

  4. 
  The 
  7-radiation 
  accompanies 
  the 
  /S-radiation 
  of 
  ura- 
  

   nium 
  X, 
  and 
  decays 
  at 
  approximately 
  the 
  same 
  rate. 
  

  

  [4(2. 
  Later 
  results 
  give 
  0-028 
  (day)-^ 
  for 
  the 
  value 
  of 
  X 
  

   'determined 
  from 
  the 
  decay 
  of 
  the 
  7-rays. 
  This 
  is 
  about 
  

   10 
  per 
  cent, 
  less 
  than 
  the 
  known 
  value 
  derived 
  from 
  the 
  

   decay 
  of 
  the 
  /3-rays.] 
  

  

  5. 
  For 
  thicknesses 
  less 
  than 
  1 
  cm. 
  of 
  lead, 
  or 
  its 
  equivalent, 
  

   the 
  absorption 
  of 
  the 
  uranium 
  y-rays 
  does 
  not 
  follow 
  any 
  

  

  