Production of x-rays m3 Flashcards
What is the Domestic electricity supply?
- 220/240 volts
- 50 Hertz
- 13 amp current (usually)
- Circuits can be fused at 3, 5 or 13 amps
- Immersion heaters, older cookers etc. may have 30 amp circuits.
What does the dental x-ray tube look like?
What is the The filament /cathode?
Very fine wire made of tungsten
A small current passed along it 8-10mA
Electrons are excited
Wire gets hot – may give off light
Electrons are lost from outer shells/orbits round the nucleus
Electron cloud forms around the cathode
What is the anode?
Small tungsten target embedded in copper
Large potential difference between anode & cathode – e.g. 70kV
-ve electrons bombard +ve anode
High energy electrons come to sudden stop or decelerate & energy form changes
99% HEAT 1% X-RAYS
What are the 2 main types of collisions at the atomic level?
1.Continuous spectrum
- Bremsstrahlung or breaking radiation
- Wide range of photon energies
2.Characteristic spectrum
- Depends on material used in anode
- Emitted by loss of electrons from K & L shells
How is Bremsstrahlung radiation formed?
- Negatively charged electron from the cathode is attracted to the positively charged atom of tungston within the anode
- As it moves around the nucleus it loses alot of its energy
- most of the energy given off is heat but we also get some Bremsstrahlung radiation being produced
There are a wide range of photon energies, what happens in Small deflections?
Wide range of photon energies
Small deflections are most common – many low energy photons
Little penetrating power – need filtering out or they will be absorbed by the body
Absorbed radiation gives rise to the x-ray dose
Large deflections are less likely – few high energy photons
Maximum photon energy directly related to kV across the x-ray tube
Characteristic radiation is the second type of radiation to be produced how does this happen?
- Incident electron has a direct hit with electron in K shell and knocks the K shell electron out (called the ejected orbital electron) and the initial electron is also expelled from within the atom as a incident electron
- K shell is now unstable with electron deficent
- Gap needs filled in so an electron from L shell drops down to K shell to make it stable again
- But then that electron has too much binding energy so it gets rid of the excess energy as an x-ray photo
What are the defintions for Scattering, Absorption and Intensity.
Scattering = random change in direction after hitting something.
Absorption = deposition of energy in tissues.
Intensity = number of x-ray photons in a defined area of the beam.
What are the definitions of Attenuation, Ionisation and Penetration?
Attenuation = reduction in intensity of beam due to scattering & absorption.
Ionisation = removal of electron from neutral atom to give -ve (electron) & +ve (atom) ions.
Penetration = the ability of photons to pass through or into tissues/materials
What are the different ways x-rays can interact? (4 ways)
- Completely scattered with no loss of energy
- Absorbed with total loss of energy
- Scattered with some absorption & loss of energy
- Transmitted unchanged
What are the properties of x-rays?
- Travel in straight lines in free space
- X-ray photons form a divergent beam
- Can travel through a vacuum
- Penetrate matter
- Can be absorbed
- Can be scattered
- Not detectable by human senses
- Produce a latent image on film emulsion
- Cause ionisation
- Can cause biological damage
- Cause certain salts to fluoresce & emit light
What is the Radiation Dose?
The radiation dose is the amount of radiation absorbed by the patient.
Low energy photons often are absorbed by soft tissues
What is the summary of Electromagnetic Radiation?
- Divided into ionising & non-ionising radiation
- Some properties are harmful to living tissues
- Properties depend on the wavelength
- Biological harm is not limited to ionising radiation
