﻿942 
  Prof. 
  Rutherford 
  and 
  Mr. 
  Richardson 
  : 
  Analysis 
  of 
  

  

  Analysis 
  of 
  the 
  7 
  rays 
  from 
  Radioactinium. 
  

  

  Dr. 
  Russell 
  and 
  Mr. 
  Chadwick 
  recently 
  examined 
  in 
  this 
  

   Laboratory 
  the 
  7 
  rays 
  from 
  radioactinium, 
  which 
  they 
  found 
  

   to 
  be 
  far 
  greater 
  in 
  intensity 
  than 
  could 
  be 
  ascribed 
  to 
  

   excitation 
  by 
  a. 
  rays. 
  An 
  approximate 
  analysis 
  was 
  made 
  by 
  

   them 
  of 
  the 
  types 
  of 
  radiation 
  present. 
  In 
  the 
  course 
  of 
  

   our 
  later 
  experiments 
  with 
  actinium, 
  the 
  emission 
  of 
  an 
  

   intense 
  7 
  radiation 
  from 
  radioactinium 
  was 
  evident. 
  The 
  

   actinium 
  X 
  was 
  successively 
  separated 
  from 
  the 
  radio- 
  

   actinium 
  preparation, 
  and 
  after 
  the 
  second 
  operation 
  it 
  

   was 
  found 
  that 
  the 
  7 
  radiation 
  from 
  the 
  precipitate, 
  viz. 
  

   actinium 
  and 
  radioactinium, 
  reached 
  a 
  definite 
  minimum 
  

   of 
  activity. 
  Measured 
  in 
  the 
  ordinary 
  electroscope, 
  the 
  

   7-ray 
  effect 
  of 
  the 
  actinium 
  and 
  radioactinium 
  was 
  about 
  

   25 
  per 
  cent, 
  of 
  the 
  activity 
  of 
  the 
  actinium 
  in 
  equilibrium 
  

   with 
  all 
  its 
  products. 
  The 
  actinium 
  and 
  radioactinium 
  

   precipitate 
  formed 
  a 
  comparatively 
  thick 
  deposit 
  of 
  several 
  

   grams 
  (about 
  10 
  grms.) 
  in 
  weight. 
  Notwithstanding 
  this 
  

   comparatively 
  thick 
  layer, 
  the 
  presence 
  of 
  a 
  considerable 
  

   amount 
  of 
  soft 
  radiation 
  was 
  evident. 
  Analysis 
  showed 
  that 
  

   the 
  radiation 
  from 
  this 
  material, 
  which 
  is 
  to 
  be 
  ascribed 
  to 
  

   radioactinium, 
  consists 
  of 
  two 
  distinct 
  types 
  for 
  which 
  fi 
  = 
  25 
  

   and 
  /n 
  = 
  *190. 
  The 
  absorption 
  curves 
  obtained 
  are 
  shown 
  in 
  

   figs. 
  7 
  and 
  8. 
  The 
  7-ray 
  effect 
  due 
  to 
  the 
  more 
  penetrating 
  

   type 
  was 
  less 
  than 
  2 
  divs. 
  per 
  min. 
  under 
  the 
  experimental 
  

   conditions, 
  and 
  it 
  was 
  consequently 
  difficult 
  to 
  determine 
  its 
  

   absorption 
  coefficient 
  with 
  as 
  great 
  an 
  accuracy 
  as 
  was 
  

   desired. 
  An 
  examination 
  of 
  the 
  rise 
  curve 
  of 
  the 
  actinium 
  

   and 
  radioactinium 
  preparation 
  showed 
  that 
  the 
  radiation 
  

   could 
  not 
  be 
  ascribed 
  to 
  some 
  actinium 
  X 
  which 
  had 
  not 
  

   been 
  separated. 
  In 
  addition 
  it 
  is 
  seen 
  that 
  the 
  soft 
  type 
  

   /Lt 
  = 
  25 
  is 
  quite 
  distinct 
  from 
  the 
  corresponding 
  radiation 
  

   from 
  actinium 
  B, 
  viz. 
  yu, 
  = 
  31. 
  It 
  is 
  of 
  interest 
  to 
  observe 
  

   that 
  the 
  hard 
  type 
  of 
  radiation 
  from 
  radioactinium 
  appears 
  

   to 
  be 
  slightly 
  more 
  penetrating 
  than 
  that 
  emitted 
  from 
  

   actinium 
  D. 
  

  

  Summary. 
  

  

  For 
  convenience, 
  ihe 
  types 
  of 
  7 
  rays 
  emitted 
  from 
  all 
  the 
  

   products 
  so 
  far 
  examined 
  are 
  included 
  in 
  the 
  following 
  table. 
  

   In 
  order 
  to 
  complete 
  the 
  series 
  it 
  will 
  be 
  necessary 
  to 
  examine 
  

   the 
  types 
  of 
  7 
  rays 
  emitted 
  by 
  uranium 
  X. 
  It 
  is 
  intended 
  

   to 
  continue 
  the 
  experiments 
  in 
  this 
  direction. 
  

  

  