Chapters 6-7 Flashcards
what are 2 interactions that create x-rays?
- bremsstrahlung and characteristic
How much of electrons turn into x-ray photons?
1%
how much of electrons turn into heat?
99% (infrared radiation)
what part of the atom do the electrons collide with once they reach the Anode?
- they hit the outer shell of an atom
define exitation
- raise the atom to a higher energy level
How are characteristics released?
- ionization of target atoms
how is bremsstrahlung released?
- interactions with target nuclei
what’s involved in characteristics?
- filament electrons
- orbital electron of a target atom
define cascade reaction
- process of outer-shell electrons filling inner-shell vacancies continues down the line, creating a cascading effect
- happens with characteristic and photoelectric
define characteristic interactions
- when orbital electrons of target atoms are removed from their shell
- outer-shell electrons fill inner-shell vacancies
Why are characteristics given the term “characteristic”?
- difference in binding energy between the shells involved
define binding energy
- how strong the fore holds the nucleus of an atom
What shell holds the most energy?
- k shell
- since its closer to the nucleus, it has a stronger force
define k-shell
- innermost shell in an atom
- highest energy
- useful for imaging purposes
what is the binding energy of the k-shell in Tungsten?
69-69.5
What happens if the technique is lower than 70kVp?
- no photons will be produced in the k-shell interaction
in the k shell, what is the binding energy in the tungsten?
69.5 keV
in the L shell, what is the binding energy in the tungsten?
12.1 keV
in the M shell, what is the binding energy in the tungsten?
2.82 keV
in the N shell, what is the binding energy in the tungsten?
0.6 keV
in the O shell, what is the binding energy in the tungsten?
0.08 keV
in the P shell, what is the binding energy in the tungsten?
0.008 keV
how do you find the photon energy of a shell?
- the difference in binding energy
- subtract the shell with the vacancy from the farther shell that’s filling up the shell
- the radiographer subtracts the binding energy of the farther shell (shell providing electron) from the closer shell (shell with vacancy) ??????
how are characteristics photons named?
- named for the shell being filled in each case.
- Ex.) If an outer-shell electron is filling a K shell, regardless of where that filling electron is coming from, the photon produced is called K characteristic.
how to find an energy of a characteristic photons?
- one must know the shell-binding energies of the element and the shells involved
what is an example of finding a photon energy?
A filament electron removes a K-shell electron, and an L-shell electron fills the vacancy:
K-shell binding energy = 69.5 keV
L-shell binding energy = 12.1 keV
69.5 − 12.1 = 57.4 keV
The energy of the K-characteristic photon produced is 57.4 keV.
define bremstrahlung
- means breaking radiation
- the filament electron misses all of the orbital electrons and interacts with the nucleus of the target atom
- The attraction causes the filament electron to slow down and change direction and, in doing so, lose kinetic energy.
- The closer the filament electron passes to the nucleus, the stronger the attraction.
- the stronger the resultant brems photon
how to find the energy of a Brems photon?
- subtracting the energy that the filament electron leaves the atom with from the energy it had upon entering.
- Ex.) a filament electron enters an atom with 100 keV of energy, passes very close to the nucleus, and leaves with 30 keV of energy.
The brems photon produced is 70 keV
100 keV − 30 keV = 70 keV
what are the 2 reasons why most of the photons are Brems?
- he filament electron is more likely to miss the orbital electrons of the target atom, because they are in constant motion and the atom is mostly empty space
- All lower settings (below a kVp of 70) result in a beam made up entirely of brems
define filtration
- the use of material to absorb x-ray photons from the x-ray beam
- can be used in inherent, added, or compensating filter
define inherent filtraton
- inheret to the tube assembly (tube and housing)
what is the primary contributor to the inherent filter?
- the target window
- equals to 0.5mm Al equivalent
what happens when the filament electron passes nearby the nucleus of an atom?
- there is a very strong attraction
- the nucleus has a strong binding energy, therefore, the attraction will be greater with the net charge difference
What is a result from a strong attraction between an atom and an electron?
- the more energy the filament electron loses and the stronger the resultant brems photon.
how are bremsstrahlung interactions produced?
- when filament electrons miss all of the orbital electrons of the target atom and interact with the nucleus
what are other ways to avoid radiation exposure?
- time
- distance
- shielding
define electron stream
- where the cloud travels
define actual focal spot
- portion where the electrons hit the anode angle
define effective focal spot
- the principle
- where all the photons go after the clash with the anode
what are the focus spots?
- filaments
how many focus spots do we have?
- 2
- small filament
- large filament
what are the factors of a small focus spot?
- we’ll get better resolution
- heat is increased
what are the factors of a large focus spot?
- less resolution (lack of detail)
- heat will decrease