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!
