X-ray Production
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97 Terms
What can electrons do when they move between orbits?
They can move in and out of orbits and give off energy as light, heat, radio waves and X-rays
How does electromagnetic radiation travel?
As waves or packets of energy
What is the electromagnetic spectrum?
The range of electromagnetic radiation arranged according to wavelength, frequency and energy
What is ionising radiation?
High-energy radiation that removes electrons from atoms, changing their chemical composition and potentially damaging living tissue.
What can happen to the nucleus of an atom?
It can lose or gain charged particles, forming radiation particles such as alpha, beta and gamma
Can gamma rays pass through lead?
Some gamma rays can pass through lead
What is cosmic radiation?
High-energy radiation originating from the solar system that reaches Earth and produces a shower of particles
What is terrestrial radiation?
Radiation produced by the natural decay of radioactive materials within the Earth
Where can terrestrial radioactive materials be found?
In minerals such as rock, soil, vegetation and groundwater
What is internal radiation exposure?
Radiation exposure caused by radioactive material decaying inside the body
How can radioactive material enter the body?
Through inhalation or ingestion.
What does the X-ray tube head contain?
A glass container containing the anode and cathode
What are the functions of the glass container in an X-ray tube?
It protects the elements from corrosion, provides electrical insulation and is heat resistant
What charge does the cathode have?
Negative
Why is the cathode negatively charged?
It is the source of negatively charged electrons
What is the filament made of?
Tungsten
How thick is the tungsten filament?
Approximately 0.2 mm thick
Why is tungsten used for the filament?
It is a good thermionic emitter and gives off many electrons.
What is the melting point of tungsten?
Approximately 3,422°C
Why is the high melting point of tungsten important?
It allows the filament to withstand the heat produced during X-ray generation
What is the purpose of the focusing block/cup?
It directs the electrons towards the anode rather than allowing them to spread out
What is thermionic emission?
The process where heat causes electrons to be emitted from the cathode filament.
What is a space charge?
A cloud of negatively charged electrons that builds up around the cathode filament
What is the space charge effect?
The negatively charged electron cloud repels new electrons and limits further electron emission
What is the approximate mA limit used in diagnostic radiography?
1000 mA
What is the effect of using a small mA?
It produces a narrow electron beam and is suitable for small parts and small exposures
What can a narrow electron beam improve?
Spatial resolution and image sharpness
What is spatial resolution?
The ability to produce a sharp, well-defined image with clearly separated details
Why do electrons naturally spread apart?
They are negatively charged and repel each other
How does the focusing cup help the electron beam?
Its negative charge narrows and directs the electrons into a straight, well-aligned beam
What is the charge of the anode?
Positive
What is the main function of the anode?
It attracts electrons, absorbs them and produces X-rays
Why does the anode attract electrons?
It is positively charged and the electrons are negatively charged
What surrounds the anode?
A copper stem
Why is copper used around the anode?
It efficiently removes heat
Why is the tungsten target on the anode angled?
To allow the X-rays to be narrowed and directed at an angle
What surrounds the X-ray tube?
Oil and lead casing
What is the purpose of the oil?
To help absorb and remove heat
What is the purpose of the lead casing?
To absorb scattered X-rays
What percentage of the electron energy becomes X-rays?
Approximately 1%
What percentage of the electron energy becomes heat?
Approximately 99%
How is the heat from X-ray production managed?
Using a copper block and oil casing
What are the two types of anodes?
Stationary and rotating anodes
What is a stationary anode?
An anode where the electron beam is focused on one small area
What is a disadvantage of a stationary anode?
The heat is concentrated in one small area.
What are the advantages/features of a stationary anode?
It has a simple design and low heat capacity
What type of exposures are stationary anodes suitable for?
Low exposures
Where are stationary anodes commonly used?
Dental radiography
What are the main features of a rotating anode?
It has a complex design and high heat capacity
What type of exposures can rotating anodes handle?
High exposures
Why does a rotating anode help with heat?
It spreads the heat over a larger area of the target
What is an induction motor?
A motor that turns the anode without directly contacting it
What are the three parts of an induction motor?
Stator, rotor and bearing.
What is the stator?
The external electromagnet component that drives the rotation of the anode
What is the rotor?
The spinning part that turns the target disc at high speed.
Why does the rotor turn the target disc at high speed?
To help prevent overheating
What is the bearing?
Low-friction spheres between the rotor and X-ray tube that allow the rotor to rotate freely
What is the function of the glass envelope?
It creates an air-free vacuum around the cathode and anode
Why is a vacuum needed inside the X-ray tube?
To prevent corrosion and allow the electrons to travel between the cathode and anode
What is the function of the tube housing?
To prevent X-rays from being emitted throughout the examination room
What are the charges of the anode and cathode?
Anode = positive (+), Cathode = negative (-).
What happens during a heat-producing collision?
High-speed electrons collide with the metal target and lose energy, which is mainly converted into heat
Approximately how much electron energy becomes heat?
About 99%
Approximately how much electron energy becomes X-rays?
Less than 1%
Where do the electrons involve in X-ray production come from?
The cathode filament
Why do electrons interact with the anode?
They have been accelerated and interact with the tungsten target
How is heat produced when electrons interact with the anode?
Electrons are deflected or displaced by outer-shell electrons and lose energy, which is converted into heat
How is the heat produced at the anode managed?
By the copper block and oil
What is an X-ray-producing collision?
A collision where a fast-moving electron is suddenly decelerated or interacts near the nucleus of a target atom, producing an X-ray
What happens when an incoming electron passes close to the nucleus?
It is slowed down and deflected, causing a large loss of energy
What happens to the energy lost by the electron during deceleration?
It is released as an X-ray photon
What is the Bremsstrahlung spectrum?
A continuous range of X-ray energies produced when high-speed electrons are slowed down or deflected by the electric field of an atomic nucleus
What does "Bremsstrahlung" mean?
Braking radiation
Why is the Bremsstrahlung spectrum continuous?
Electrons can lose any amount of their kinetic energy during interactions with the nucleus
What can be manipulated when taking an X-ray of different materials?
The voltage and exposure settings
What is characteristic radiation?
X-ray radiation produced when a high-energy electron removes an inner-shell electron and an outer-shell electron fills the resulting vacancy
What happens when a high-energy electron collides with an inner-shell electron?
Both electrons can be ejected, leaving a hole in the inner shell
What happens after an inner-shell electron is removed?
An electron from an outer shell moves into the empty space
What happens when the outer-shell electron moves into the inner shell?
It loses energy, which is emitted as an X-ray photon
How much does characteristic radiation contribute to the total X-ray photons produced?
It makes a relatively small contribution
Below what voltage will K-line characteristic radiation not produce an image?
69.5 kV
What voltage range do dental X-ray machines operate within?
Approximately 60–90 kV
What is the source of electrons in an X-ray tube?
The cathode filament
How are electrons produced at the cathode?
Through thermionic emission
How are electrons accelerated through the X-ray tube?
By a voltage measured in kVp
What happens to electrons when they reach the anode?
They interact with the tungsten atoms and decelerate, producing X-rays
What does kVp control in X-ray production?
The maximum energy of the Bremsstrahlung radiation
What is the maximum Bremsstrahlung energy at 100 kVp?
100 keV
What is the maximum Bremsstrahlung energy at 75 kVp?
75 keV
What is the basic process of Bremsstrahlung X-ray production?
Electrons are produced at the cathode, accelerated across the tube and then decelerated near the tungsten nucleus at the anode.
What happens when an electron passes close to the nucleus?
It is strongly slowed and deflected, losing energy as an X-ray photon
What happens if an electron passes very close to the nucleus?
It loses a large amount of energy and may completely change direction, producing a higher-energy X-ray photon
What happens if an electron passes further from the nucleus?
It experiences less deflection and loses less energy
What law of energy applies to X-ray production?
Energy cannot be created or destroyed; it can only be transferred
What determines the energy of Bremsstrahlung radiation?
How close the electron passes to the nucleus
What happens to the energy of the Bremsstrahlung X-ray as the electron passes closer to the nucleus?
More energy is lost by the electron and released as an X-ray photon
What is an analogy for Bremsstrahlung radiation?
Throwing a ball at a glass window: the ball slows and transfers energy to the glass, similar to an electron losing energy when deflected by a positively charged nucleus.