Coherent Scattering

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Physics 108 Lecture 33 X-ray Interactions
with Matter
Most Common X-ray Interactions

• Coherent Scattering
• The X-ray is absorbed and re-emitted at the same
  ____________, but in a different direction.
• Compton Scattering
• the X-ray collides with an electron in an atom
  and bounces off at some _________________, thus
  being scattered away from its original path.
• Photoelectric Effect
• the X-ray collides with an electron in an atom
  and _____________ the atom by knocking the
  electron completely out of the atom.
• Pair Production
• an X-ray with energy of _____________ or more
  disappears due to a complex electromagnetic
  interaction with the material and creates an
  ___________________________________, each with
  mass equivalent to an energy of
  _________________(from Einsteins Emc2).

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Coherent Scattering
Diagram
Equations
Relative Likelihood
Medium for low energy X-rays Low for medium to
high energy X-rays
Compton probability
X-ray energy (MeV)
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Compton Scattering
Diagram
Equations (can be derived by combining energy
and momentum conservation)
Relative Likelihood
High for low energy X-rays Medium for high
energy X-rays
Compton probability
X-ray energy (MeV)
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Photoelectric Effect
Diagram
Equation
K, L, M edge explanation
Ebinding - Specific values for each material K
shell (most energy loss) L shell (less energy
loss) M shell (not much energy loss)
Relative Likelihood
High for low energy X-rays Low for high energy
X-rays
Photoelectric probability
X-ray energy (MeV)
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Pair Production
Diagram
Equation
Explanation of equation
E1 Total incident photon energy 1.022 MeV
energy lost to make e-/e pair Energy loss is
divided equally among e-/e pair
Relative Likelihood
Zero below 1.022 MeV Low to medium for
low-medium energy X-rays High for high energy
X-rays
Pair Prod. probability
X-ray energy (MeV)
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Example (X-ray interactions with matter) Three
identical X-rays of energy 1.5MeV enter a
patient. One undergoes Compton scattering at
25?, one undergoes the photoelectric effect with
a K-shell electron in a Calcium atom, and one
undergoes pair production. Find the final energy
of all the particles after the interaction.
Given                     Path              
Want     Conversions/Equations
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Example (X-ray interactions with matter)
CONTINUED
Given                     Path              
Want     Conversions/Equations