﻿Homogeneous 
  Secondary 
  Rontgen 
  Radiations. 
  565 
  

  

  the 
  intensity 
  of 
  secondary 
  radiation 
  from 
  members 
  of 
  this 
  

   group 
  is 
  independent 
  of 
  the 
  direction 
  of 
  electric 
  force 
  in 
  the 
  

   primary 
  radiation. 
  Again, 
  this 
  result 
  may 
  be 
  taken 
  as 
  

   applicable 
  to 
  the 
  homogeneous 
  rays, 
  as 
  these 
  constitute 
  the 
  

   bulk 
  of 
  the 
  radiation 
  from 
  these 
  metals. 
  

  

  Efficiency 
  of 
  Primary 
  Rays 
  as 
  Secondary 
  Ray 
  Producers. 
  — 
  

   Although 
  in 
  addition 
  to 
  the 
  relatively 
  small 
  amount 
  of 
  

   scattered 
  radiation, 
  rays 
  of 
  only 
  one 
  penetrating 
  power 
  were 
  

   emitted 
  by 
  an 
  elementary 
  substance 
  upon 
  which 
  a 
  hetero- 
  

   geneous 
  primary 
  beam 
  fell, 
  it 
  was 
  still 
  possible 
  that 
  only 
  one 
  

   constituent 
  (rays 
  of 
  one 
  penetrating 
  power) 
  in 
  each 
  hetero- 
  

   geneous 
  primary 
  beam 
  was 
  producing 
  this 
  radiation. 
  It 
  

   was 
  therefore 
  important 
  to 
  determine 
  to 
  what 
  extent 
  each 
  

   constituent 
  of 
  the 
  primary 
  beam 
  was 
  effective 
  in 
  producing 
  

   these 
  secondary 
  rays. 
  

  

  To 
  do 
  this, 
  a 
  portion 
  of 
  the 
  primary 
  beam 
  direct 
  from 
  the 
  

   X-ray 
  tube 
  was 
  sent 
  through 
  one 
  electroscope 
  while 
  another 
  

   portion 
  was 
  incident 
  on 
  a 
  secondary 
  radiator, 
  some 
  of 
  the 
  

   rays 
  from 
  which 
  passed 
  through 
  a 
  second 
  electroscope. 
  The 
  

   method 
  was 
  then 
  simply 
  to 
  place 
  absorbing 
  plates 
  in 
  the 
  

   primary 
  beam 
  before 
  falling 
  on 
  the 
  radiator, 
  and 
  to 
  observe 
  

   the 
  extent 
  by 
  which 
  the 
  primary 
  and 
  the 
  secondary 
  radiations 
  

   were 
  reduced. 
  It 
  is 
  obvious 
  that 
  the 
  more 
  penetrating 
  con- 
  

   stituents 
  of 
  the 
  primary 
  beam 
  penetrate 
  to 
  greater 
  depths 
  

   than 
  the 
  absorbable 
  constituents, 
  and 
  so 
  are 
  really 
  trans- 
  

   mitted 
  through 
  a 
  greater 
  mass 
  than 
  these. 
  Hence, 
  if 
  two 
  

   homogeneous 
  constituents 
  of 
  primary 
  radiation 
  in 
  passing 
  

   through 
  equal 
  masses 
  of 
  radiating 
  substance 
  were 
  equally 
  

   efficient 
  as 
  secondary-ray 
  producers, 
  the 
  radiation 
  emitted 
  

   by 
  a 
  thick 
  plate 
  would 
  be 
  produced 
  principally 
  by 
  the 
  more 
  

   penetrating 
  constituents 
  ; 
  consequently 
  an 
  absorbing 
  plate 
  

   placed 
  in 
  the 
  position 
  indicated, 
  would, 
  by 
  cutting 
  off 
  the 
  

   more 
  easily 
  absorbed 
  constituents, 
  produce 
  less 
  diminution 
  

   of 
  the 
  ionization 
  in 
  electroscope 
  E 
  2 
  than 
  of 
  that 
  in 
  E 
  x 
  . 
  It 
  

   was 
  therefore 
  necessary 
  to 
  use 
  as 
  the 
  radiator 
  a 
  sheet 
  of 
  

   metal 
  which 
  would 
  absorb 
  very 
  little 
  of 
  the 
  primary 
  radia- 
  

   tion, 
  so 
  that 
  even 
  the 
  deepest 
  layers 
  would 
  transmit 
  different 
  

   constituents 
  in 
  proportions 
  approximately 
  the 
  same 
  as 
  those 
  

   transmitted 
  through 
  the 
  first 
  surface-layer. 
  

  

  It 
  was 
  found 
  that 
  a 
  sheet 
  of 
  Cu 
  '00067 
  cm. 
  in 
  thickness 
  

   when 
  placed 
  in 
  the 
  primary 
  beam 
  produced 
  an 
  absorption 
  of 
  

   only 
  14*5 
  per 
  cent., 
  as 
  measured 
  by 
  the 
  ionization 
  produced 
  

   in 
  an 
  electroscope. 
  This 
  was 
  considered 
  sufficiently 
  thin 
  for 
  

   use 
  as 
  a 
  radiator. 
  The 
  deflexions 
  of 
  the 
  electroscopes 
  were 
  

   first 
  observed 
  when 
  no 
  absorbing 
  plate 
  was 
  used. 
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