﻿Analysis 
  of 
  ft 
  Rays 
  from 
  Radium 
  B 
  and 
  Radium 
  C. 
  719 
  

  

  from 
  several 
  radioactive 
  substances. 
  They 
  have 
  shown 
  that 
  

   radium 
  B 
  emits 
  three 
  distinct 
  types 
  of 
  y 
  rays, 
  radium 
  C 
  

   one 
  penetrating 
  type, 
  radium 
  D 
  two 
  distinct 
  types, 
  while 
  

   radium 
  E, 
  which 
  gives 
  a 
  continuous 
  spectrum 
  of 
  ft 
  rays, 
  

   emits 
  only 
  a 
  minute 
  amount 
  of 
  y 
  radiation. 
  

  

  Before 
  any 
  theory 
  of 
  the 
  origin 
  of 
  ft 
  and 
  y 
  rays 
  can 
  be 
  

   adequately 
  tested, 
  it 
  is 
  necessary 
  to 
  determine 
  with 
  the 
  

   greatest 
  possible 
  precision 
  the 
  velocity 
  of 
  each 
  of 
  the 
  com- 
  

   ponent 
  groups 
  of 
  ft 
  rays. 
  We 
  have 
  consequently 
  made 
  a 
  

   large 
  number 
  of 
  experiments 
  to 
  determine 
  the 
  groups 
  of 
  

   ft 
  rays 
  emitted 
  by 
  radium 
  B 
  and 
  by 
  radium 
  C 
  separately. 
  

   A 
  strong 
  source 
  of 
  radium 
  emanation 
  enclosed 
  in 
  a 
  thin- 
  

   walled 
  a-ray 
  tube 
  affords 
  a 
  most 
  convenient 
  source 
  for 
  

   determining 
  the 
  velocity 
  of 
  the 
  swifter 
  groups 
  of 
  ft 
  rays 
  from 
  

   radium 
  B 
  and 
  C 
  together. 
  An 
  intense 
  source 
  of 
  radium 
  C 
  

   deposited 
  on 
  a 
  nickel 
  wire 
  has 
  allowed 
  us 
  to 
  distinguish 
  

   between 
  the 
  groups 
  to 
  be 
  ascribed 
  to 
  radium 
  B 
  and 
  radium 
  G 
  

   separately. 
  Since 
  it 
  is 
  important 
  to 
  determine 
  the 
  velocity 
  

   of 
  groups 
  of 
  ft 
  rays 
  which 
  are 
  photographically 
  very 
  weak, 
  

   it 
  was 
  necessary 
  to 
  devise 
  a 
  method 
  of 
  bringing 
  out 
  the 
  

   presence 
  of 
  groups 
  of 
  ft 
  rays, 
  the 
  total 
  energy 
  of 
  which 
  

   might 
  be 
  only 
  a 
  small 
  fraction 
  of 
  that 
  distributed 
  in 
  the 
  

   more 
  intense 
  groups. 
  For 
  this 
  purpose, 
  we 
  have 
  used 
  a 
  

   special 
  method 
  which 
  appears 
  to 
  be 
  very 
  similar 
  in 
  principle 
  

   to 
  that 
  employed 
  by 
  Danysz 
  in 
  his 
  later 
  investigation 
  (loc. 
  

   cit.) 
  . 
  The 
  great 
  theoretical 
  and 
  practical 
  advantages 
  of 
  this 
  

   arrangement 
  lie 
  in 
  the 
  fact 
  that 
  the 
  ft 
  rays 
  of 
  a 
  definite 
  

   velocity 
  comprised 
  in 
  a 
  comparatively 
  wide 
  cone 
  of 
  rays 
  can 
  

   be 
  concentrated 
  in 
  a 
  line 
  of 
  very 
  narrow 
  width 
  on 
  the 
  photo- 
  

   graphic 
  plate. 
  In 
  this 
  way 
  a 
  group 
  of 
  ft 
  rays 
  of 
  very 
  small 
  

   energy 
  can 
  be 
  detected 
  even 
  when 
  there 
  is 
  a 
  marked 
  

   darkening 
  of 
  the 
  photographic 
  plate 
  due 
  to 
  the 
  7 
  rays 
  and 
  

   the 
  scattered 
  ft 
  rays 
  which 
  must 
  always 
  be 
  present. 
  

  

  The 
  method 
  employed 
  is 
  shown 
  in 
  fig. 
  1. 
  The 
  source 
  S 
  is 
  

   attached 
  about 
  1 
  cm. 
  from 
  the 
  end 
  of 
  a 
  lead 
  block 
  L 
  

   (9x4x3*2 
  cm.)- 
  A 
  comparatively 
  wide 
  slit 
  V 
  is 
  arranged 
  

   vertically 
  above 
  the 
  source,, 
  and 
  the 
  latter 
  was 
  usually 
  

   1-2 
  cm. 
  below 
  the 
  slit. 
  The 
  photographic 
  plate 
  PP 
  is 
  laid 
  

   on 
  the 
  top 
  of 
  the 
  lead 
  block. 
  It 
  rested 
  against 
  one 
  end 
  of 
  

   a 
  plate 
  about 
  1*5 
  cm. 
  from 
  the 
  edge 
  of 
  the 
  slit. 
  The 
  photo- 
  

   graphic 
  plate 
  was 
  kept 
  in 
  position 
  by 
  means 
  of 
  a 
  small 
  

   screw 
  attached 
  to 
  the 
  lead 
  block. 
  When 
  the 
  source 
  and 
  

   photographic 
  plate 
  were 
  placed 
  in 
  position, 
  the 
  whole 
  

   apparatus 
  was 
  lowered 
  into 
  a 
  brass 
  vessel 
  B 
  B, 
  which 
  was 
  

   closed 
  by 
  an 
  upper 
  plate 
  by 
  means 
  of 
  screws. 
  The 
  vessel 
  

   was 
  then 
  exhausted 
  to 
  a 
  low 
  vacuum 
  in 
  a 
  few 
  minutes. 
  The 
  

  

  