﻿«.'o 
  

  

  618 
  Dr. 
  J. 
  A. 
  Gray 
  on 
  the 
  Scattering 
  and 
  

  

  rays 
  do 
  not 
  differ 
  much 
  in 
  penetrating 
  power 
  from 
  the 
  

   primary. 
  A 
  certain 
  similarity 
  to 
  the 
  scattering 
  of 
  a 
  rays 
  

   may 
  here 
  be 
  noted. 
  When 
  an 
  a, 
  ray 
  is 
  scattered 
  through 
  a 
  

   large 
  angle 
  there 
  is 
  little 
  doubt 
  that 
  it 
  loses 
  velocity, 
  the 
  

   loss 
  being 
  Greater 
  the 
  greater 
  the 
  angle 
  of 
  scattering. 
  

  

  It 
  was 
  stated 
  above 
  that 
  Sadler 
  and 
  Mesham 
  found 
  that 
  

   X 
  rays 
  are 
  softened 
  by 
  scattering. 
  The 
  change 
  in 
  quality 
  

   appeared 
  to 
  be 
  greater 
  the 
  greater 
  the 
  penetrating 
  power 
  of 
  

   the 
  X 
  rays, 
  and 
  this 
  point 
  is 
  supported 
  by 
  the 
  present 
  expe- 
  

   riments, 
  the 
  7 
  rays 
  scattered 
  through 
  an 
  angle 
  of 
  110° 
  being 
  

   not 
  much 
  more 
  penetrating 
  than 
  the 
  rays 
  excited 
  in 
  lead 
  by 
  

   the 
  7 
  rays 
  of 
  radium 
  E. 
  It 
  seems 
  quite 
  probable 
  that 
  the 
  

   change 
  in 
  quality 
  is 
  small 
  for 
  very 
  soft 
  X 
  rays. 
  It 
  will 
  be 
  seen 
  

   that 
  the 
  rays 
  scattered 
  through 
  50° 
  are 
  still 
  much 
  softer 
  than 
  

   the 
  primary 
  rays 
  even 
  after 
  passing 
  through 
  a 
  centimetre 
  

   of 
  lead, 
  so 
  the 
  softening 
  must 
  happen 
  to 
  every 
  type 
  of 
  y 
  ray 
  

   scattered. 
  

  

  We 
  can 
  deduce 
  the 
  following 
  results 
  from 
  the 
  tables: 
  — 
  

  

  1. 
  The 
  quantity 
  of 
  radiation 
  scattered 
  per 
  unit 
  mass 
  is 
  

   approximately 
  independent 
  of 
  the 
  nature 
  of 
  the 
  radiator. 
  

  

  At 
  first 
  sight 
  it 
  would 
  appear 
  that 
  lead 
  scattered 
  much 
  

   less 
  7 
  radiation 
  per 
  unit 
  mass 
  than 
  either 
  carbon 
  or 
  iron. 
  

   This, 
  however, 
  is 
  mainly 
  due 
  to 
  the 
  fact 
  that 
  lead 
  absorbs 
  the 
  

   scattered 
  radiation 
  so 
  much 
  that 
  less 
  of 
  it 
  escapes 
  from 
  the 
  

   radiator. 
  

  

  Consider 
  Table 
  I. 
  (b). 
  The 
  primary 
  rays 
  pass 
  through 
  the 
  

   radiator 
  approximately 
  normally, 
  the 
  scattered 
  rays 
  at 
  an 
  

   angle 
  of 
  50° 
  with 
  the 
  normal. 
  If 
  fi 
  is 
  the 
  absorption 
  co- 
  

   efficient 
  of 
  the 
  primary, 
  X 
  thnt 
  of 
  the 
  scattered 
  rays, 
  p 
  the 
  

   density, 
  A 
  the 
  area, 
  d 
  the 
  depth 
  of 
  the 
  radiator, 
  the 
  amount 
  

   of 
  scattered 
  radiation 
  entering 
  the 
  electroscope 
  will 
  be 
  ap- 
  

   proximately 
  proportional 
  to 
  

  

  VA^-^- 
  x 
  ^- 
  x 
  ) 
  sec50 
  °^X, 
  i. 
  e. 
  Xgec 
  ^ 
  _ 
  -( 
  e 
  -^-e- 
  Xd 
  ^ 
  °), 
  

  

  or 
  S, 
  say, 
  

   For 
  carbon 
  p 
  =1*68, 
  A 
  = 
  94 
  sq. 
  cm., 
  <^ 
  = 
  5'84cm., 
  

   yu,=0-074, 
  \ 
  =0-118, 
  S 
  = 
  444. 
  

  

  „ 
  iron 
  p 
  = 
  7-7, 
  A 
  = 
  104 
  sq. 
  cm. 
  ; 
  d 
  = 
  T28 
  cm., 
  

  

  ^ 
  = 
  0-30, 
  A, 
  =0*62, 
  S 
  = 
  468, 
  

  

  „ 
  lead 
  /o 
  = 
  ll*4, 
  A 
  = 
  84 
  sq. 
  cm., 
  #"=G"88 
  cm., 
  

   ^=0-56, 
  X=l-83, 
  S 
  = 
  212. 
  

  

  These 
  numbers 
  (S) 
  agree 
  fairly 
  well 
  with 
  the 
  experimental 
  

   values. 
  Carbon 
  and 
  iron 
  give 
  about 
  the 
  same 
  value, 
  and 
  lead 
  

  

  