Emission Spectrum Flashcards
1
Q
Polyenergetic
A
- many energies
- the x-ray beam consists of a wide range of energies known as the x-ray emission spectrum
- x ray beam consists of:
- bremsstrahlung (speeding along and influenced by positive charge of nucleus)
- characteristic (k shell interactions)
2
Q
Emission spectrum
A
- a graph of the number of x-ray photons and the range of energies the photons possess at a given exposure setting
- affected by changing several parameters: kVp, mAs, target material, filtration, voltage waveform
3
Q
keV
A
- kilo electron volt
- measurement used for: binding energies and energy of incident electron (coming from the filament)
4
Q
KVp
A
- peak energy being sent across the tube
- ex if 80 kvp is set, it means the max energy crossing the tube is 80 keV
- some electrons are at the highest energy, majority are around 30-40% of the peak energy
- many of the low energy incident electrons end up creating heat (99% of them)
5
Q
If the kvp set was 80kvp
- what is the maximum energy?
- what would the average energy be?
A
- the max energy would be 80 kev
- the average energy would be 24-32 kev (30-40% of 80 kev)
6
Q
Bremsstrahlung emission spectrum
A
- energy range from the tube is from 0 to whatever the kvp was set at
- creates a heterogenous or polyenergetic x-ray
7
Q
How do we calculate the energy of bremsstrahlung emitted radiation?
A
- subtract the incoming vs the outgoing energy of the incident electron
- max incoming it could be is the kvp set
- provides a range of energies from 0 to the max kvp set
8
Q
Characteristic emission spectrum
A
- only occurs between certain energies, usually above 70 kvp
- why? Because an incident electron travelling below 70 kev cannot knock an electron out of the k shell of a tungsten atom (k shell of tungsten- binding energy of 69.5 kev) often represented by a spike or line at 69 kev
9
Q
How do we calculate the energy of each emitted photon from a characteristic emission spectrum?
A
-find the difference between the binding energies of the electron ejected minus the one that took its place
10
Q
X-ray emission spectrum
A
- the general shape is always the same, but its relative position can change
- the larger the area under the curve, the higher the x-ray intensity or quantity
11
Q
Tungsten
A
- atomic # 74
- binding energy 69.5
12
Q
mA-quantity
A
- the number of electrons available to move from cathode to anode
- as we increase our mA, we INCREASE the number of electrons boiled off at the filament
- increasing the mA, proportionally increases the # of photons at all energy levels
- therefore increasing the AMPLITUDE of the spectrum
13
Q
Mas
A
- # of electrons sent in 1 second
- exposure time determines how long the electrons will pass from cathode to anode
- like mA, exposure time is directly proportional to the number of electrons crossing the tube
- therefore directly proportional to the number of x-rays created
14
Q
MA, time and mAs all affect ____ of x rays
A
- QUANTITY
- all are directly proportional
15
Q
KVp
A
- will affect the quality and quantity of the x-rays (mainly the quality)
- ⬆️ the kVp we are ⬆️the force with which the incident electrons hit the anode
- why? the max energy increases, average energy increases
- this means that the average x-ray energy is higher as the kVp is increased
- this improves the QUALITY of the x-ray (quality refers to strength of radiation)
- a stronger x-ray photon is better able to penetrate our patients
