Production of X-rays Flashcards
What are the main components of an x-ray tube? (5)
Tubehead Collimator Positioning arms Control Panel Circuitry
Describe the 9 components of the tubehead.
- Glass x-ray tube containing - filament, copper block and target
- Step-up transformer - high kV across x-ray tube
- Step-down transformer - low filament mA
- Glass may be leaded with lead-free window
- Lead shield to minimise radiation leakage
- Oil to facilitate heat removal
- Aluminium filter removes low energy, (soft) damaging x-ray photons
- Collimator to restrict the size and shape of the beam
- Beam-indicating device (BID) or spacer “cone” - may be part of the collimator
To produce x-rays, a small electric current is passed through a filament, what is the current?
8-10 mA
What does the small current used to produce x-rays need to be passed through?
A step-down transformer
What happens to the filament during the production of x-rays?
The filament is heated by current due to the excitation of electrons within the wire.
During the production of x-rays, the electrons from the outer shells are lost, what happens to these ‘free’ electrons?
They surround the filament in an electron cloud.
During the production of x-rays, what happens between the cathode and anode?
A large potential difference (SI) is applied.
What does the step-up transformer do?
It changes 240 volts to 50-90 kV
What does the focusing cup do?
Focusing cup points electrons towards target/focal spot of anode.
What happens to electrons as the current is flowing through the filament?
The -vely charged electrons are attracted to the +vely charged anode, they are pulled across by the high voltage kV between the cathode and anode, electrons have high energy and are fast moving.
How do electrons then cause the production of x-rays?
Electrons hit the target and come to a sudden stop, losing energy, the energy is converted to 99% heat and 1% X-rays.
What happens to the heat produced when electrons hit the target?
The heat is absorbed by the copper and dissipated into the surrounding oil.
What happens to the x-rays produced by the electrons hitting the target?
The x-rays radiate in all directions, most are absorbed by the leaded glass and the target directs x-rays towards the unleaded window so a beam of radiation is emitted.
What are the two types of x-ray spectra?
- The continuous spectrum and 2. The Characteristic spectrum.
Describe the continuous spectrum.
Bremsstrahlung or breaking radiation, has a wide range of photon energies.
Describe the characteristic spectrum.
Depends on the material used in the anode, emitted by loss of electrons from the K and L shells.
What are the properties of x-rays? (11)
- Travel in straight lines in free space
- X-Ray photons form a divergent beam
- Can travel through a vacuum
- Can 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 and emit light
Definition of Scattering
Random change in direction after hitting something.
Definition of Absorbtion
Deposition of energy in tissues.
Definition of Intensity
Number of x-ray photons in a defined area of the beam.
Definition of Attenuation
Reduction in intesity of beam due to scattering and absorption.
Definition of Ionisation
Removal of electron from neutral atom to give -ve (electrons) and +ive (atom) ions.
Definition of Penetration
The ability of photons to pass through or into tissues/materials.
What are the four possible interactions of the x-ray beam?
Completely Scattered = with no loss of energy
Absorbed = with total loss of energy
Scattered = with some absorption and loss of energy
Transmitted unchanged
