﻿944 
  Prof. 
  Rutherford 
  and 
  Mr. 
  Richardson 
  : 
  Analysis 
  of 
  

  

  (100,000 
  volts), 
  S. 
  J. 
  Allen 
  * 
  showed 
  that 
  X 
  rays 
  could 
  be 
  

   produced 
  of 
  penetrating 
  power 
  about 
  corresponding 
  to 
  

   type 
  (3). 
  Type 
  (4) 
  is 
  more 
  penetrating 
  than 
  any 
  X 
  rays 
  

   produced 
  or 
  likely 
  to 
  be 
  produced 
  in 
  X-ray 
  tubes. 
  

  

  Thorium 
  D 
  emits 
  the 
  most 
  penetrating 
  type 
  of 
  7 
  rays 
  

   known, 
  while 
  radium 
  C 
  and 
  mesothorium 
  2 
  come 
  next 
  with 
  

   radiations 
  of 
  nearly 
  equal 
  penetrating 
  power. 
  Actinium 
  

   products, 
  as 
  has 
  long 
  been 
  known, 
  emit 
  less 
  penetrating 
  

   types 
  of 
  radiation 
  than 
  radium 
  or 
  thorium 
  products. 
  The 
  

   penetrating 
  radiation 
  from 
  radium 
  D 
  has 
  no 
  apparent 
  analogy 
  

   with 
  that 
  emitted 
  by 
  any 
  other 
  product. 
  

  

  General 
  Considerations. 
  

  

  In 
  the 
  above 
  table 
  we 
  have 
  included 
  the 
  types 
  of 
  primary 
  

   7 
  rays 
  emitted 
  by 
  radioactive 
  substances. 
  In 
  every 
  case 
  the 
  

   emission 
  of 
  the 
  7 
  rays 
  observed 
  is 
  accompanied 
  by 
  a 
  well- 
  

   marked 
  primary 
  /3 
  radiation. 
  As 
  we 
  have 
  already 
  pointed 
  

   out 
  in 
  our 
  experiments 
  on 
  radium 
  D 
  and 
  radium 
  E 
  f 
  , 
  there 
  

   does 
  not 
  appear 
  to 
  be 
  any 
  obvious 
  connexion 
  between 
  the 
  

   relative 
  intensity 
  of 
  the 
  (3 
  and 
  7 
  rays. 
  For 
  example, 
  con- 
  

   sider 
  the 
  case 
  of 
  radium 
  D 
  and 
  radium 
  E. 
  On 
  the 
  one 
  hand, 
  

   radium 
  D 
  emits 
  a 
  comparatively 
  feeble 
  (3 
  radiation, 
  shown 
  

   by 
  Hahn 
  J 
  to 
  consist 
  of 
  two 
  groups 
  of 
  low 
  velocity 
  but 
  a 
  

   well-marked 
  7 
  radiation 
  ; 
  and 
  on 
  the 
  other, 
  radium 
  E 
  emits 
  

   an 
  intense 
  /3 
  radiation 
  comprising 
  particles 
  projected 
  with 
  

   nearly 
  the 
  velocity 
  of 
  light, 
  but 
  gives 
  a 
  7 
  radiation 
  ex- 
  

   ceedingly 
  feeble 
  in 
  quantity 
  compared 
  with 
  that 
  from 
  

   radium 
  D. 
  

  

  The 
  experiments 
  of 
  Hahn, 
  v. 
  Baeyer 
  and 
  Meitner 
  have 
  

   shown 
  that 
  practically 
  all 
  the 
  /3-ray 
  products 
  emit 
  a 
  number 
  

   of 
  distinct 
  groups 
  of 
  /3 
  rays 
  of 
  definite 
  speed. 
  The 
  only 
  

   exception 
  to 
  this 
  is 
  radium 
  E 
  which 
  gives 
  a 
  continuous 
  

   spectrum 
  of 
  ft 
  rays 
  in 
  which 
  no 
  evidence 
  of 
  groups 
  has 
  yet 
  

   been 
  observed. 
  It 
  should 
  be 
  mentioned 
  also 
  that 
  no 
  evidence 
  

   of 
  groups 
  has 
  so 
  far 
  been 
  observed 
  in 
  the 
  ft 
  rays 
  of 
  uranium 
  

   X, 
  but 
  more 
  experiments 
  are 
  required 
  on 
  this 
  point. 
  It 
  may 
  

   prove 
  significant 
  that 
  radium 
  E, 
  which 
  shows 
  no 
  sign 
  of 
  

   definite 
  groups 
  of 
  /3 
  rays, 
  should 
  be 
  the 
  only 
  /3-ray 
  product 
  

   which 
  emits 
  y 
  rays 
  exceedingly 
  feeble 
  in 
  intensity. 
  

  

  In 
  addition 
  to 
  these 
  primary 
  7 
  rays 
  of 
  marked 
  intensity, 
  

   Mr. 
  Chadwick 
  and 
  Dr. 
  Russell 
  § 
  have 
  recently 
  drawn 
  

  

  * 
  S. 
  J. 
  Allen 
  & 
  E. 
  J. 
  Lorentz, 
  Phys. 
  Rev. 
  i. 
  ser. 
  2, 
  p. 
  35 
  (1913). 
  

   t 
  Rutherford 
  & 
  Richardson, 
  Phil. 
  Mag. 
  xxvi. 
  p. 
  324 
  (1913). 
  

   X 
  Hahn, 
  Baeyer 
  & 
  Meitner, 
  Phys. 
  Zeit. 
  xii. 
  p. 
  378 
  (1911). 
  

   § 
  Chadwick 
  & 
  Russell, 
  Proc. 
  Roy. 
  Soc. 
  A. 
  lxxxyiii. 
  p. 
  217 
  (1913). 
  

  

  