Scattering by an atom

1
Scattering by an atom
Atomic Scattering Factor
dEa
S-So
S
dV
2q
r
So
charge in dV
Scattering by dV
spherical cloud of electrons (assumed)
Notes 11/2/99 pg. 1 pg. 2
Notes 10/28/99 pg. 1 pg. 2
2
Scattering by an atom
Atomic Scattering Factor
3
Atomic scattering factor

• 6 ions and one neutral atom - each with 10
  electrons
• As nuclear charge increases, electrons are drawn
  closer to the nucleus, pathlength differences are
  decreased, and scattering curves deviate less and
  less from the point atom (zero path
  differences)
• The outermost (weakly bound) electrons make
  appreciable contributions to the total scattering
  only at small angles
• Innermost electrons (K shell) contribute to
  scattering at all angles, contributions from L
  shell electrons falls off more rapidly, and
  valence electrons make small total contributions
  limited to small angles

Notes 11/4/99 pg. 1 pg. 2 pg. 3 pg. 4 pg. 5
4
Atomic scattering factor
Lithium (Z 3)
Hydrogen (Z 1)
5
Scattering Summarized
6
Structure Factor
Let B be located at x y z or fractional
coordinates
7
Structure Factor
Vector summation of E1 and E2
8
Structure Factor
Notes 11/11/99 pg. 1 pg. 2 pg. 3
Notes 11/9/99 pg. 1 pg. 2