﻿of 
  tlie 
  7 
  Rays 
  from 
  Radium 
  D 
  and 
  Radium 
  E. 
  325 
  

  

  (5 
  days) 
  of 
  radium 
  E, 
  it 
  has 
  been 
  usual 
  to 
  employ 
  radium 
  

   D-f-E 
  in 
  equilibrium 
  as 
  a 
  source 
  of 
  radiation. 
  It 
  has 
  long 
  

   been 
  known 
  that 
  most 
  of 
  the 
  ft 
  radiation 
  emitted 
  from 
  such 
  a 
  

   source 
  arises 
  from 
  radium 
  E. 
  J. 
  A. 
  Gray* 
  examined 
  the 
  

   ft 
  rays 
  from 
  radium 
  E 
  in 
  a 
  magnetic 
  field 
  and 
  found 
  them 
  to 
  

   be 
  very 
  complex, 
  giving 
  a 
  continuous 
  spectrum 
  which 
  showed 
  

   the 
  presence 
  of 
  some 
  rays 
  of 
  velocity 
  close 
  to 
  that 
  of 
  light. 
  

   This 
  was 
  confirmed 
  by 
  Gray 
  and 
  W. 
  Wilson 
  f 
  using 
  the 
  electric 
  

   method. 
  Hahn, 
  Baeyer, 
  and 
  Meitner 
  J 
  have 
  found 
  that 
  the 
  

   weak 
  ft 
  radiation 
  from 
  radium 
  D 
  consists 
  essentially 
  of 
  two 
  

   groups 
  oi: 
  homogeneous 
  rays 
  of 
  velocity 
  *33 
  and 
  '39 
  compared 
  

   with 
  that 
  of 
  light. 
  The 
  question 
  of 
  the 
  ft 
  radiation 
  from 
  

   radium 
  D 
  + 
  E 
  together 
  has 
  been 
  re-examined 
  by 
  Danysz 
  §. 
  

   While 
  radium 
  D 
  emits 
  groups 
  of 
  ft 
  rays 
  of 
  definite 
  velocity, 
  

   radium 
  E 
  is 
  anomalous 
  in 
  giving 
  a 
  continuous 
  spectrum 
  of 
  

   ft 
  rays 
  in 
  which 
  no 
  definite 
  evidence 
  of 
  groups 
  of 
  homogeneous 
  

   rays 
  has 
  so 
  far 
  been 
  obtained. 
  

  

  The 
  only 
  definite 
  study 
  of 
  the 
  7 
  radiation 
  from 
  radium 
  D 
  + 
  E 
  

   has 
  been 
  made 
  by 
  J. 
  A. 
  Gray||. 
  He 
  found 
  that 
  a 
  compa- 
  

   ratively 
  soft 
  type 
  of 
  7 
  radiation 
  was 
  present, 
  and 
  also 
  a 
  

   harder 
  type 
  whose 
  mass 
  absorption 
  coefficient 
  in 
  aluminium 
  

   was 
  0*4. 
  Gray 
  showed 
  that 
  radium 
  D 
  + 
  E, 
  in 
  consequence 
  

   of 
  its 
  poverty 
  in 
  7 
  rays, 
  was 
  an 
  ideal 
  source 
  for 
  studying 
  the 
  

   production 
  in 
  ordinary 
  matter 
  of 
  7 
  rays 
  by 
  ft 
  rays. 
  The 
  

   properties 
  of 
  the 
  7 
  radiation 
  excited 
  in 
  different 
  materials 
  

   have 
  been 
  studied 
  by 
  him 
  in 
  some 
  detail. 
  Gray 
  had 
  intended 
  

   to 
  examine 
  the 
  types 
  of 
  7 
  radiation 
  emitted 
  by 
  radium 
  D 
  and 
  

   radium 
  E 
  separately, 
  but 
  was 
  unable 
  to 
  complete 
  the 
  expe- 
  

   riments 
  before 
  leaving 
  Manchester 
  in 
  1912. 
  

  

  Preparation 
  of 
  Material. 
  

  

  In 
  order 
  to 
  analyse 
  the 
  7 
  radiation 
  in 
  detail, 
  it 
  was 
  

   necessary 
  to 
  obtain 
  very 
  active 
  preparations 
  of 
  radium 
  D-f-E 
  

   and 
  to 
  isolate 
  the 
  two 
  components. 
  From 
  the 
  experiments 
  

   of 
  Gray, 
  it 
  is 
  known 
  that 
  the 
  7 
  radiation 
  excited 
  in 
  heavy 
  

   elements 
  by 
  the 
  ft 
  rays 
  from 
  radium 
  D-fE 
  is 
  greater 
  in 
  

   amount 
  than 
  the 
  primary 
  7 
  radiation. 
  It 
  is 
  consequently 
  

   of 
  importance 
  that 
  the 
  preparation 
  of 
  radium 
  D 
  and 
  of 
  

   radium 
  E 
  should 
  contain 
  a 
  minimum 
  amount 
  of 
  impurity, 
  

   and 
  should 
  be 
  tested 
  either 
  on 
  filter-paper 
  or 
  a 
  glass 
  or 
  

  

  * 
  J. 
  A. 
  Gray, 
  Proc. 
  Koy. 
  Soc. 
  A. 
  Ixxxiv. 
  p. 
  136 
  (1910). 
  

  

  t 
  Gray 
  and 
  Wilson, 
  Phil. 
  Mag. 
  xx. 
  p. 
  870 
  (1910). 
  

  

  t 
  Hahn, 
  Baeyer, 
  and 
  Meitner, 
  Phys. 
  Zeit. 
  xii. 
  p. 
  378 
  (1911). 
  

  

  § 
  Danysz, 
  Le 
  Radium, 
  x. 
  (1913). 
  

  

  || 
  J. 
  A. 
  Gray, 
  Proc. 
  Roy. 
  Soc. 
  A. 
  lxxxvii. 
  p. 
  489 
  (1912). 
  

  

  