How Xrays Are Produced Flashcards
Label the components of the X-ray machine? (4)
Cone
X-ray head
Arm
X-ray control box
What comprises the tube head?
Metal housing
Transformers
Step up transformer
Step down transformer
X-ray tube
Oil
Collimators lined with lead
Aluminum filters
Aiming cylinderWhat does the X-ray tube consist of?
Cathode
Anode
Cathode
- charged
Tungsten filament
Produces electrons to be accelerated
Molybdenum focusing cup
Anode
\+ charged Focal spot (tungsten) located in a copper stalk
Step up transformer
Will increase voltage
PROPEL ELECTRONS FROM CATHODE TO ANODE.
The max energy of the X-ray photon is equal to the voltage the step up transformer is set at
Step down transformer
Reduces incoming voltage
Creates electrons as the cathode at the filament
What is Bremsstrahlung X-rays?
Created when high speed electrons interact with tungsten nuclei in the target resulting in a spectrum of X-rays with different energies.
Accounts for the bulk of X-ray photons produced
High energy bremsstrahlung X-ray
Electrons directly collide with a nucleus, producing a high energy photon (keV) - that is equal in energy to. The incident electron
Medium energy bremsstrahlung X-ray
Produced by electrons passing close to the nucleus causing deflection and deceleration of the electron. The deceleration causes the electron to lose some energy in the form of photon radiation.
Low energy bremsstrahlung X-ray
Produced when the electrons pass at a distance from the nucleus. They are deflected and slowed somewhat producing a low energy photon.
Path not altered dramatically
What is characteristic radiation?
Electrons collide with an orbiting inner electron ejecting it from orbit. The electron in the higher ring will drop down to the lower ring to fill in. This drop releases energy. The energy. Is released in the form of a photon
Inner ring has the lowest binding energy
Accounts only for a small fraction of X-rays
The X-ray tube is a vacuum tube - why?
No gas molecules for the electrons to hit into, no oxidation or burnout (combustion)
What is the focal spot?
Where the stream of X-ray photons originate.
Placed at an angle to shoot the X-ray photons out and creat an effective focal spot for sharp images
What is a molybdenum cup?
Found in the cathode - focuses the electrons towards the anode and narrows the beam of electrons
What is the auto transformer?
Controlled by the kVp dial on the control panel. This transformer varies the voltage to the step up transformer to abide the desired high energy kVp to the tube
What is the most frequent malfunction of the X-ray tube?
Filament burnout
The X-ray unit should be left on all day to prevent this for as long as possible. Turning it on on off with keep heating and cooling the filament
Why should you change the exposure time between field of teeth?
Molars - have more tissue to pass through
Incisors- less tissue
What is the tube current mA?
The quantity if radiation produced
As mA is increased the number of electrons increases
More collisions more radiation
More collisions means more radiation. T or F
True
Increasing kVp increases the X-ray penetration of matter. T or F
True
What is tube voltage kVp?
The energy used to propel the electron to strike the target.
Increasing the kVp increases in efficiency of the conversion of electonr energy into x ray photons.
Increase = more quantity and quality of radiation
What is a collimator?
A metal barrier used to reduce the size of the X-ray beam. Lined with lead - absorbs stray photons
The intensity if the xray beam is inversely proportional to the he square of the he distance between the source and the target. T or. F
True - the X-rays will ospreys out decreasing intensity. Having an effect on exposure
What is coherent scattering?
Low energy photons are deflected by Outer ring electrons - emits a secondary photon at a different angle
Creates a foggy look on film
What is photoelectric absorption?
Incident electrons are absorbed by an atom by interacting with inner shell electrons,
This makes the lighter areas of film
Depends on density and thickness - gives contrast to films
Photon strikes - electron ejected and quickly absorbed
What is Compton scattering?
Photon interacts with an outer orbital electron
Accounts of 49% of interactions in dental radiography
Scattered electrons darken and degrade the image - no useful info
Photons strikes outer electron - lower energy photon ejected sling with a recoil electron
How is the beam attenuated (refined)?
Lower energy photons are more readily absorbed
Higher energy photons transmit easier through absorber. T or F
True
Compton scattering vs Coherent scattering
Compton - higher energy photon, creates darkness on the film. Accounts for majority of scatter.
Coherent - low energy photon, creates fuzziness, accounts for little scattering
