X-Ray Interactions Flashcards
What is Rayleigh scattering?
Incident photon interacts with whole atom, which it
excites
Scattered photon is emitted with no loss of energy
What energy x-rays does Rayleigh scatter usually occur at?
low energy x-rays (15-30keV)
What is Compton Scatter?
Incident photon interacts with loosely bound (“free”) or valence shell electrons
The incident photon energy must greatly exceed the binding energy of the “free” electron
Results in scattered X-Ray photon and an ejected Compton electron
In compton scatter, what must the incident photon exceed?
the incident photon’s energy must greatly exceed the binding energy of the valent electron
How is the incoming photon changed when it comes out the other side?
It comes out slightly lower in energy, this is because the Compton electron has absorbed some of the energy
The probability of Compton scatter is proportional to…
the density of the material
what is the range of angle that the scattered photon can be scattered at?
Anywhere between 0-180 degrees
Forward scatter photons are of _____ energy
higher
what other interactions can occur after Compton scatter?
Scattered photons can further interact with other atoms, leading to further Compton scatter and reach the image receptor
Is the probability of Compton scatter dependent on atomic number?
NO it is independent of the atomic number
What is the photoelectric effect?
Incident X-Ray photon interacts with a tightly bound
electron
Usually from the K or L shell
Photon energy must be at least equal to or greater than
the binding energy of the ejected electron
The photoelectric effect is dependent on..
atomic number
the higher the number the more likely it is to have an interaction
The photoelectric effect is important to consider in…
Area using energies below 50 keV e.g., Mammography
This is because characteristic radiation produced by PE in soft tissues is of low energy and does not exit the patient
What are auger electrons?
the difference in binding energy between the shells
