Emission Spectrum Flashcards
Polyenergetic
- 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)
Emission spectrum
- 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
keV
- kilo electron volt
- measurement used for: binding energies and energy of incident electron (coming from the filament)
KVp
- 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)
If the kvp set was 80kvp
- what is the maximum energy?
- what would the average energy be?
- the max energy would be 80 kev
- the average energy would be 24-32 kev (30-40% of 80 kev)
Bremsstrahlung emission spectrum
- energy range from the tube is from 0 to whatever the kvp was set at
- creates a heterogenous or polyenergetic x-ray
How do we calculate the energy of bremsstrahlung emitted radiation?
- 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
Characteristic emission spectrum
- 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
How do we calculate the energy of each emitted photon from a characteristic emission spectrum?
-find the difference between the binding energies of the electron ejected minus the one that took its place
X-ray emission spectrum
- 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
Tungsten
- atomic # 74
- binding energy 69.5
mA-quantity
- 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
Mas
- # 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
MA, time and mAs all affect ____ of x rays
- QUANTITY
- all are directly proportional
KVp
- 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
KVp and the emission spectrum
- as well as moving to the right the spectrum will grow in amplitude (height)
- why? Because the incident electrons hit the anode at a greater speed they create more x-rays (alot more)
KVp
- as the kVp increases:
- we increase the QUALITY of photons created
- there are MORE photons that will reach the image receptor
- because kVp will increase the # as well as the quality of x-rays:
- a tech only has to increase the kVp by 15% to double the amount of photons hitting the receptor
- not directly proportional
As we increase the atomic number of the target material, the efficiency of the characteristic radiation ______
- INCREASES
- why? Because the binding energy for each shell increases
Target material and bremsstrahlung
- as the atomic # increases so does the efficiency with which the target produces bremsstrahlung x-rays
- most positive pull with more protons in nucleus
- able to lose more energy in the form of x-rays
- more x-rays increases the quantity of x-rays produced and therefore the amplitude of our spectrum will increase
Define kilovolt peak
-the measure of the maximum (peak) electrical potential across an X-ray tube; expressed in kilovolt
What effect does kVp have on the speed and energy of the electrons in the X-ray tube
- increasing kVp increases the force with which the incident electrons hit the anode
- increasing the kVp increases the max energy and average energy increases
How will decreasing the kVp change the energy level of the lowest-energy photons?
- nothing happens!
- lowest energy is 0 and it cant be lower than that
How will decreasing the kVp change the energy level of the highest energy photons?
-max of the highest energy photons decreases
How will increasing the kVp change the energy level of the lowest energy photons?
-nothing happens, it doesn’t influence them!
What effect does increasing mAs have on the total x-ray emission spectrum?
- increases the # of electrons sent in 1 second
- increase the quantity of x-rays
- only thing changing is the height (amplitude)
How will decreasing the mAs change the energy level of the lowest energy photons?
It will not change the energy just the quantity
What effect does the atomic # of the target material have on the energy level of the highest-energy photons?
-kVp will always set the energy level regardless of the material and therefore atomic #
