Final Review Xray production (interactions in the xray tube) Flashcards
electrons interacts with the atomic
nucleus, more energy is lost and a stronger x-ray is
produced; account for the majority of the x-ray beam.
Bremsstrahlung
electrons interact with an
orbital electron from the atom, the pulling down of
another electron from an outer shell causes an x-ray to be
produced; account for a small majority of the x-ray beam
Characteristic Radiation
Be able to label the different interactions based off the diagrams and be able to tell the difference on xray emission spectra (in packet 10 that was handed out)
Xrays versus gamma rays
-xrays are man made process
-xrays originate from electron cloud of atoms
-gamma rays are a neutral process
-gamma rays originate from atomic nucleus through radioactive decay
Velocity of accelerate electrons
Speed of light
Incoming electrons=
incident electrons
Increase kinetic energy of incident electrons also increase:
-Increases quality and quantity
-increases number of target interactions
Bremmstrahlung is the german term for:
“Breaking or slowing radiation”
Bremsstrahlung is responsible for how much percentage of the xrays produced in the xray tube:
85%
Molybdenum
-lower atomic number
-ideal for soft tissues of breast
Mammography
-high atomic number
-high melting points
-similar binding electrons
Tungsten and rhenium
Occur within 2.35-0.5mm of target surface
-heat production
-Bremsstrahlung interactions
-Characteristic interactions
Is a very inefficient process
xray production
The closer the incident electron passes to the nucleus
The higher energy of the photon
Further away to the nucleus
The lower energy of the photon
increased wavelength and decreased frequency =
decreased energy
decreased wavelength and increased frequency =
increased energy
-contains low energy xrays which will be absorbed by the xray tube
-average energy of the beam is 1/3 of the maximum energy
-xrays are an inefficient process
99%heat, 1% converted to xrays
Heterogenous Beam
Portion of beam from tube to the patient; radiation before it enters the patient
Primary Radiation
Radiation emerging from patients body to expose the film; image forming radiation
Remnant Radiation
These 4 prime factors are controlled by the technologist
mA- milliampere
S- seconds time
kVp- kilovoltage peak
SID - source to image distance
The range and intensity of xrays emitted changes with different exposure technique settings on the control panel
Xray emission spectrum
A Brem photon is the result of
The energy difference between the incident electron as it passes (slows) near the nucleus
Brem Radiation involves
An incident electron and the nucleus of an atom
The inner shell of an atom
K shell
How is brem radiation produced
By slowing of an incident electron
-incident electron interacts with electrostatic force field of nucleus
-Mutual repulsion (slows
electron)
-Strong nuclear force
(Keeps them apart and
deflects incident
electron and repulsion
causes a deceleration
of incident electron)
Bremsstrahlung interactions
Brems responsible for wide variety of energies
-produces a continuous spectrum of xrays
-heterogenous xray bream
Results of Brems interactions
-Deceleration yields xray photons energies
-xray production is continuous during deceleration
-accounts for largest portion of total xray beam
-photon energy dependent on how close electron comes to nucleus and rate of deceleration
Brems energy produced dependent on
-how close to the incident photon gets to the nucleus (closer creates increased energy)
- the degree of deceleration of the electron (greater deceleration created increased energy)
Brems process at atomic level :
-high speed electron is attracted to the positively charged nucleus
- interaction with nuclear force fields causes electron to slow down and lose energy
-lost kinetic energy converted to X-ray energy
Two interactions part of X-ray production
Bremmstruhlung interactions and characteristic interactions
True or false
Electron interacts directly with nucleus
False : slim chance an electron will hit or interact with nucleus directly and if that happens all energy will be lost
As incident electron gets closer to nucleus, the following occurs
-photon energy increases due to rate of deceleration
- larger deflection of incident electron
-electrons with small amount of residual kinetic energy, become part of electrical current flow
Characteristic X-ray production involves
Incident electron and inner shell electron
Less of a turn=
Less energy of a photon
The process of adding or removing electrons from an atom is
Ionization
Responsible for 15% of X-rays produced in the X-ray tube
Characteristic
Characteristic process at atomic level
-high speed incident electron interacts with an inner shell (k or l) shell electron or a target atom
-k or l shell electron is ejected , leaving a vacancy
-electron vacancy filled by another electron from an outer shell (characteristic cascade)
-electron transition responsible for producing a characteristic X-ray photon
Binding energy of kshell is
69.5
Characteristic can be produced at what amount of keV
70 or higher
What kind of energy spectrum does Brem produce
Continuous
The process of an outer shell electron filling a vacancy left in an inner shell
Characteristic cascade
-hole in inner shell and must be filled by electron from any outer shell
- electron energy difference
-secondary photon produced
Characteristic cascade
What shell is of diagnostic value
K shell
Brems is produced at what keV
anything is less than 70
The cascade process is associated with:
Characteristic radiation production
Changing (blank) will change the maximum energy of the photons in the X-ray emission spectrum
KVp
A technologist can control the quantity of the X-rays striking the patient by adjusting the
mA
The maximum kinetic energy of a projectile electron accelerated across an X-ray tube depends on the
Kilovoltage
Beam quantity is primarily determined by
mAs
What can be determined from an xray spectrum
Maximum photon energy and average photon energy
-Brems and characteristic emissions combines
-consists of a “brems hump” and characteristic peak
-selected kvp will determines maximum kev possible for any photon
Emission Spectrum
Characteristic radiation is produced when:
A vacancy in an electron orbit is filled
How kilovoltage effects emission spectrum
Created potential difference
-determines the speed of the electrons in tube current
-greater speed results in greater quantity and quality of primary beam
-Increasing electron speed will increase xray beam penetribilty
Example:
kvp is increasing, shift to the right, increases average energyaverage and maximum energ increased when kvp is increase
How mA affects the emission spectrum
Unit to measure tube current or number of electrons flowing per unti time
-mA directly proportional to quantity of xrays produced
-double the mA will double the number of xray photons produced
Example:
mA is increasing so its doubling quantity but mA does not affect the energy of the xray beam
xray tube filtration filters out
low energy xrays
When an incident electron approaches a positive charged nucleus of a tungsten atom
The incident electron slows down due to electrostatic attraction
Controls the projectile electron energy , intensity, maximum energy and the average energy of the X-ray beam
kvp
Controls the number of projectile electrons striking the anode and the intensity of the X-ray beam
mA
Less than 70 KVp is what % is Brems
100%
Approximately 30-40% of selected KVp
Average keV
Higher KVp =
higher average energy
kvp is your…
energy (quality)
mA is your…
Quantity
Changes in mA and KVp for regarding emission spectrum
Characteristic peak energy levels remain unchanged
Change in KVp regarding emission spectrum
Changes beam amplitude and average energy
Change in generator type
Produce a beam with higher average energy
Characteristic energy produced dependent on
-binding energy of a k shell
-tungsten atom is 69.5 keV
aluminum filtration added to xray beam to absorb low energy photons (reduced patient exposure)
Beam filtration
-added to primary beam to alter its intensity(wedge filter or trough filter)
-used to image nonuniform anatomic areas
-thicker part of filter lines up with thinner part allowing fewer xray photons to reach atomic area
compensating filtration
Value of the photon energy equals to :
The difference of the binding energy of the ionized shell and the transitioning electron
Penetrating ability of the xray beam
xray beam quality
Amount of material required to reduce the X-ray beam intensity to one half its original value
Half value layer
Factors which affect beam quality
-kvp
-filtration
Changes the beam quality by changing photon wavelength and an increase causes both the average and maximum energy to increase
kvp
Factors which affect beam quality and quantity
KVp, mA , time, filtration, X-ray circuit waveform
Brems interaction in order:
- High speed incident electron comes close to the nucleus of a tungsten atom
- Positive nuclear force field causes the incident electron to change direction
- The high speed electron decelerates
- The lost kinetic energy is converted to an X-ray photon
Characteristic intersection in order :
1.High speed projectile electron passes near a K or L shell electron or a tungsten atom
- The incident electron ejects the inner shell electron
- A vacancy is created in the orbital shell
4.The unstable atom attempts to return to the normal state by filling the vacancy with the outer shell electrons
- The movement of outer shell electrons creates a characteristic cascade
- The potential energy of each orbital electrons movement is converted to a characteristic photon
Energy or motion, type of energy exhibited by incident electrons
kinetic
what happens to the kvp when the frequency decreases, energy decreases, and wavelength increases
kvp decreases
What happens to the kvp when frequency increases, energy increases and wavelength decreases
kvp increases
what happens to the number of photons when exposure time is increased
number of xray photons increase
