﻿y-Rai/s 
  of 
  Uranium 
  and 
  Radium, 
  629 
  

  

  7-activitv 
  of 
  1 
  kilogram 
  of 
  uranium 
  is 
  equal 
  to 
  that 
  of 
  

   •009 
  mg. 
  of 
  radium, 
  or 
  radium 
  gives 
  about 
  10^ 
  times 
  more 
  

   7-raYS 
  than 
  uranium. 
  

  

  4. 
  The 
  Relative 
  Value 
  of 
  the 
  Ratio 
  of 
  j- 
  to 
  ^-Rays 
  

   for 
  Uranium 
  J 
  and 
  Radium 
  C. 
  

  

  It 
  appeared 
  very 
  desirable 
  to 
  carry 
  out 
  an 
  accurate 
  deter- 
  

   mination 
  of 
  the 
  relative 
  value 
  of 
  the 
  ratio 
  of 
  7- 
  to 
  y8-rays 
  for 
  

   uranium 
  and 
  radium 
  under 
  strictly 
  comparable 
  conditions. 
  

   Two 
  electroscopes 
  were 
  used, 
  one 
  for 
  the 
  measurement 
  of 
  

   /3-rays 
  and 
  the 
  other 
  for 
  the 
  7-rays. 
  The 
  former 
  had 
  a 
  base 
  

   of 
  very 
  thin 
  aluminium 
  foil. 
  0*095 
  mm. 
  thick, 
  and 
  was 
  set 
  

   up 
  so 
  that 
  the 
  active 
  preparations 
  could 
  be 
  placed 
  on 
  the 
  

   floor 
  119*5 
  cm, 
  below 
  the 
  base. 
  The 
  y-ray 
  electroscope 
  

   was 
  the 
  lead 
  cylindrical 
  electroscope 
  with 
  a 
  base 
  of 
  lead 
  

   •975 
  cm. 
  thick 
  described 
  under 
  section 
  10, 
  and 
  the 
  prepara- 
  

   tions 
  were 
  placed 
  13*1 
  cm. 
  beneath 
  the 
  base. 
  As 
  the 
  source 
  

   of 
  the 
  /5- 
  and 
  7-rays 
  of 
  radium 
  was 
  employed 
  a 
  film 
  of 
  

   radium 
  C^ 
  prepared 
  by 
  exposing 
  one 
  side 
  of 
  a 
  negatively 
  

   charged 
  copper 
  disk 
  to 
  the 
  radium 
  emanation 
  for 
  12*5 
  hours. 
  

   After 
  the 
  exposure 
  the 
  disk 
  was 
  placed 
  in 
  a 
  brass 
  cell 
  and 
  a 
  

   piece 
  of 
  0*095 
  mm. 
  thick 
  aluminium 
  foil 
  was 
  cemented 
  over 
  

   the 
  cell 
  to 
  prevent 
  any 
  possible 
  escape 
  of 
  adhering 
  emanation. 
  

   A 
  similar 
  sheet 
  of 
  aluminium 
  covered 
  the 
  uranium 
  X 
  pre- 
  

   paration. 
  This 
  consisted 
  of 
  one 
  of 
  the 
  three 
  preparations 
  of 
  

   the 
  third 
  separation, 
  possessing 
  0*108 
  of 
  the 
  total 
  activity. 
  

   The 
  date 
  of 
  these 
  measurements 
  was 
  one 
  week 
  after 
  those 
  

   described 
  in 
  the 
  last 
  section. 
  

  

  Half 
  an 
  hour 
  after 
  the 
  preparation 
  of 
  the 
  film 
  of 
  radium 
  C 
  

   alternative 
  measurements 
  of 
  the 
  y8- 
  and 
  7-rays 
  were 
  taken 
  

   over 
  several 
  hours, 
  and 
  from 
  the 
  decay 
  curve 
  obtained 
  from 
  

   the 
  measurements 
  the 
  /3- 
  and 
  7-activity 
  at 
  any 
  time 
  could 
  

   be 
  readily 
  deduced. 
  Other 
  similar 
  measurements 
  were 
  also 
  

   made 
  of 
  the 
  /3-rays 
  when 
  the 
  base 
  of 
  the 
  electroscope 
  con- 
  

   sisted 
  of 
  a 
  sheet 
  of 
  aluminium 
  foil 
  0*9 
  mm. 
  thick, 
  and 
  of 
  the 
  

   7-rays 
  when 
  the 
  base 
  of 
  the 
  electroscope 
  consisted 
  of 
  plates 
  

   of 
  aluminium 
  1 
  and 
  6 
  mm. 
  thick. 
  The 
  latter 
  thickness 
  is 
  

   sufficient 
  to 
  reduce 
  the 
  /3-radiation 
  of 
  both 
  elements 
  to 
  an 
  

   inappreciable 
  amount. 
  The 
  former, 
  however, 
  was 
  found 
  to 
  

   allow 
  a 
  little 
  of 
  the 
  /3-radiation 
  of 
  radium 
  only 
  to 
  get 
  through. 
  

   For 
  all 
  dispositions 
  measurements 
  were 
  also 
  taken 
  with 
  the 
  

   uranium 
  X. 
  In 
  this 
  way 
  the 
  relative 
  ratio 
  of 
  the 
  7- 
  to 
  yS- 
  

   activity 
  of 
  uranium 
  and 
  radium 
  under 
  comparable 
  conditions 
  

   was 
  ascertained. 
  It 
  may 
  be 
  assumed 
  that 
  0*195 
  mm. 
  of 
  

   aluminium 
  cuts 
  down 
  the 
  /3-rays 
  of 
  uranium 
  and 
  radium 
  to 
  

   practically 
  the 
  same 
  extent, 
  since 
  the 
  absorption 
  is 
  but 
  small. 
  

  

  