Chapter 8 X Ray Production Flashcards
X-rays versus gamma rays
-X-rays are man made process
-originate from electron cloud of atoms
-gamma rays are a natural process
-originate from atomic nucleus through radioactive decay
Velocity of accelerate electrons
Speed of light
Increase kinetic energy of incident electrons also increases :
-quality and quantity
- number of target interactions
The three target interactions are
- heat production
-Bremsstrahlung
-characteristic
-high atomic number
-high melting points
-similar binding electrons
Tungsten and rhenium
Molybdenum
-lower atomic number
-ideal for soft tissues of breast
Mammography
Bremsstrahlung is the German term for :
“Breaking or slowing radiation”
Bremsstrahlung is responsible for how much percentage of the X-rays produced in the X-ray tube
85%
Incident electron interacts with electrostatic force field of nucleus (nucleus of tungsten)
Bremsstrahlung
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
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
Brem radiation is produced
By the slowing of an incident electron
Incoming electrons =
Incident electrons
Brems responsible for wide variety of energies
-produces a continuous spectrum of X-rays
-heterogenous X-ray beam
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
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)
Increased wavelength and decreased frequency =
Decreased energy
Decreased wavelength and increased frequency =
Increased energy
Results of Brems :
-deceleration yields X-ray photon energies
-X-ray production is continuous during deceleration
-accounts for largest portion of total X-ray beam
-photon energy dependent on how close electron comes to nucleus and rate of deceleration
Two interactions part of X-ray production
Bremmstruhlung interactions and characteristic interactions
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
Less of a turn=
Less energy of a photon
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
Characteristic X-ray production involves
Incident electron and inner shell electron
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
Cherecteristics responsoble for specific level of energies :
Produces a discrete level of energies
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
Characteristic cascade
The process of an outer shell electron filling a vacancy left in an inner shell
-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 less than 70
Changing (blank) will change the maximum energy of the photons in the X-ray emission spectrum
KVp
The cascade process is associated with:
Characteristic radiation production
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 if primarily determined by
mAs
What can be determined from an X-ray emission spectrum
Maximum photon energy and average photon energy
Characteristic radiation is produced when:
A vacancy in an electron orbit is filled
X-ray tube filtration filters out
Low energy X-rays
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
-Brems and characteristic emissions combined
- consists of “Brems hump” and characteristic peak
-selected KVp will determine maximum keV for any photon
Emission spectrum
Less than 70 KVp is what % is Brems
100%
90 KVp average energy what is your keV
30 keV
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
Characteristic peak energy levels remain unchanged
Change in KVp
-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 the k shell
-binding energy of a k shell tungsten atom is 69.5 keV
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 X-ray beam
X-ray 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
Graph which plots the number of X-rays produced as a function of their energies
X-ray spectrum
Amount or number of X-ray photons in the X-ray beam
X-ray beam quantity
Information that can be obtained from the graph
-continuous curve =Brems
-individual spikes=characteristic
-Maximum beam energy
-average bean energy
Factors which affect beam quality and quantity
KVp, mA , time, filtration, X-ray circuit waveform
-Changes the beam quality
-causes both the average and maximum energy to increase
Kvp
-changes the beam quantity
-causes the total number of X-rays to increase or decrease
Ma
Changes the beam quantity causes the total of number of photons to increase
Proportional relationship
time
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 :
- 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
- 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
