﻿Homogeneous 
  Secondary 
  Rontgen 
  Radiations. 
  563 
  

  

  is 
  a 
  more 
  penetrating 
  radiation. 
  The 
  most 
  penetrating 
  

   portion 
  of 
  this 
  is 
  about 
  twice 
  as 
  intense 
  as 
  the 
  corresponding 
  

   radiation 
  from 
  substances 
  o£ 
  the 
  H-S 
  group. 
  

  

  The 
  radiations 
  from 
  other 
  elements 
  of 
  the 
  Cr-Zn 
  group 
  

   have 
  not 
  been 
  examined 
  so 
  minutely 
  as 
  that 
  from 
  copper, 
  

   but 
  it 
  has 
  been 
  seen 
  that 
  these 
  also 
  contain 
  a 
  small 
  quantity 
  

   of 
  a 
  more 
  penetrating 
  radiation 
  which 
  is 
  probably 
  scattered 
  

   radiation. 
  This 
  more 
  penetrating 
  radiation 
  was 
  more 
  evident 
  

   in 
  the 
  radiation 
  from 
  thick 
  iron, 
  probably 
  because 
  the 
  homo- 
  

   geneous 
  iron 
  radiation 
  being 
  very 
  absorbable 
  emerges 
  from 
  

   a 
  thinner 
  surface 
  layer, 
  while 
  a 
  scattered 
  radiation 
  emerges 
  

   from 
  greater 
  depths 
  than 
  in 
  the 
  metals 
  of 
  higher 
  atomic 
  

   weight 
  owing 
  to 
  the 
  greater 
  transparency 
  of 
  iron 
  than 
  sub- 
  

   stances 
  of 
  higher 
  atomic 
  weight. 
  Consequently 
  the 
  scattered 
  

   rays 
  — 
  if 
  we 
  may 
  assume 
  them 
  to 
  be 
  such 
  — 
  are 
  in 
  reality 
  

   from 
  a 
  much 
  greater 
  mass 
  of 
  iron 
  than 
  the 
  homogeneous 
  

   rays, 
  and 
  produce 
  more 
  than 
  their 
  appropriate 
  portion 
  of 
  

   the 
  total 
  ionization. 
  

  

  It 
  may 
  be 
  objected 
  that 
  in 
  this 
  case 
  the 
  radiation 
  was 
  

   transmitted 
  through 
  a 
  second 
  substance 
  Al, 
  and 
  may 
  have 
  

   contained 
  a 
  considerable 
  quantity 
  of 
  secondary 
  radiation 
  

   from 
  Al 
  of 
  a 
  kind 
  not 
  existent 
  in 
  the 
  original 
  radiation 
  from 
  

   copper. 
  The 
  production 
  of 
  a 
  secondary 
  radiation 
  more 
  pene- 
  

   trating 
  than 
  the 
  primary 
  producing 
  it 
  is, 
  however, 
  contrary 
  

   to 
  all 
  experience. 
  

  

  Energy. 
  — 
  The 
  ionization 
  produced 
  by 
  the 
  secondary 
  rays 
  

   from 
  one 
  of 
  the 
  elements 
  of 
  this 
  group 
  has 
  been 
  shown 
  to 
  be 
  

   enormous 
  in 
  comparison 
  with 
  that 
  produced 
  by 
  the 
  secondary 
  

   scattered 
  rays 
  from 
  an 
  equal 
  mass 
  of 
  an 
  element 
  of 
  low 
  

   atomic 
  weight. 
  From 
  a 
  sheet 
  of 
  copper 
  '00067 
  cm. 
  thick, 
  

   absorbing 
  14 
  per 
  cent, 
  of 
  the 
  primary 
  radiation, 
  the 
  secondary 
  

   radiation 
  produced 
  an 
  ionization 
  in 
  the 
  detecting 
  electro- 
  

   scope 
  200 
  times 
  as 
  great 
  as 
  that 
  from 
  an 
  equal 
  mass 
  of 
  

   paper. 
  Correcting 
  for 
  absorption 
  of 
  primary 
  and 
  secondary 
  

   rays, 
  the 
  ratio 
  of 
  ionization 
  produced 
  by 
  the 
  rays 
  from 
  equal 
  

   masses 
  of 
  copper 
  and 
  paper 
  was 
  approximately 
  300 
  : 
  1. 
  This 
  

   is 
  considerably 
  greater 
  than 
  would 
  have 
  been 
  found 
  if 
  all 
  

   the 
  radiation 
  absorbed 
  had 
  been 
  simply 
  scattered 
  as 
  an 
  

   untransformed 
  radiation. 
  This, 
  how 
  7 
  ever, 
  by 
  no 
  means 
  gives 
  

   us 
  a 
  measure 
  of 
  the 
  energy 
  of 
  the 
  secondary 
  rays, 
  for 
  these 
  are 
  

   of 
  much 
  more 
  absorbable 
  type 
  than 
  the 
  primary. 
  The 
  per- 
  

   centage 
  absorption 
  by 
  a 
  thin 
  sheet 
  of 
  aluminium 
  is 
  about 
  

   five 
  times 
  as 
  great 
  for 
  these 
  secondary 
  rays 
  as 
  for 
  the 
  primary. 
  

   If 
  we 
  assumed 
  the 
  same 
  ratio 
  for 
  the 
  ionizations 
  produced 
  

   in 
  air 
  by 
  the 
  two 
  radiations 
  if 
  of 
  equal 
  intensity, 
  we 
  should 
  

   be 
  led 
  to 
  conclude 
  that 
  the 
  energy 
  of 
  this 
  homogeneous 
  

  

  2 
  P2 
  

  

  