Exam Review 9/4 PPT3 Flashcards
Bremss or Characteristic? Electrons interact with a nucleus
Bremss
Bremss or Characteristic? Electrons interact with orbital e-
Characteristic
A high speed electron passes near a nucleus and is deflected from its pass after being acted upon by Coulomb forces. They lose energy, slow down and propagates the energy through space.
Bremss
T or F?
Electron can engage in multiple Bremsstrahlung interactions
T
What determines the energy for Brem?
How close it gets to nucleus and how much it makes it change its path.
Probability of bremms production varies with __ of the target
Z^2
Bremms produces a ___energetic beam
Poly
Average energy for bremss?
E avg = 1/3 max photon energy
Explain this graph
…
Why doesn’t graph start at 0?
Bc the beam is filtered
Explain the peaks in this graph
Sharp peaks on graph occur when vacancies are produced and electrons drop down to fill the gap. They occur at specific energies for each element.
What is the avg energy ?
1/3 of 150 = 50keV
An electron interacts with an atom by ejecting an orbital electron, which leaves the atom ionized. A vacancy is created and an outer
orbital electron will fall down to a closer orbital. When an electron moves down there is an energy potential, which results in x-rays.
Characteristic
Characteristic produces a ___energetic beam
mono
mA and mAs: If you double mA, how does it affect output?
Output is doubled
kVp.. slide 17
..
What happens if you increase energy? Does it affect characteristic and bremss?
It does not affect characteristic.
It will only affect the Bremss.
For characteristic x-rays, would you see the same energies produced for different targets?
No, they have diff binding energies
Atomic # of tungsten
74
What doe this graph show?
The higher the energy of the beam, the more forward the angular dependence is (the more forward the beam is)
What does a voltage rectifier do?
allows current flow in only one direction
Explain what is happening here and why?
HVL thickness will increase for each succeeding HVL in a polyenergetic beam due to the first one hardening the beam (filtering out the lower energy photons) and the resulting energy of the beam being higher.
In monoenergetic beams, the same HVL will be used.
low E photons are filtered out and the beam therefore acquires a higher average energy than before
beam hardening
What is meant by: To measure a beam’s transmission through an absorber, the
measurement must be done under “good geometry”?
Beam must be measured where there isn’t scatter - don’t want to measure scattered photons.
Anode-heel effect
..
Inherent filtration
..
___ filtration attenuates both low & high-energy photons, but a larger fraction of low energy photons are attenuated
Added filtration
___ filtration includes the glass or metal enclosure of an x-ray tube
Inherent
