Production of X-rays

Question 1

What are the components of an x-ray tube?

Answer 1

• control panel: modify time of exposure depending on size of pt, area of exposure and type of film (BW or PA)
• tube head: where domestic supply is converted to x-rays

Question 2

What is the filament/cathode?

Answer 2

• very fine wire made of tungsten
• 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 clouds form around the cathode

Question 3

What is the anode?

Answer 3

• small tungsten embedded in copper
• large potential difference between anode and cathode e.g. 70kV
• negative electrons bombard positive anode
• high energy electrons come to sudden stop or decelerate and evergy form changes
• 99% heat, 1% x-rays

Question 4

Give an overview of the continuous spectrum:

Answer 4

• wide range of photon energies
• small deflections are most common - many low energy photons
• little penetrating power - need filtering out
• large deflections less likely - few high energy photons
• maximum photon energy directly related to kV across the x-ray tube

Question 5

Give an overview of the characteristic spectrum:

Answer 5

• characteristic of anode atom - tungsten
• line spectra relating to K and L shells
• K lines of diagnostic importance with photon energy levels of 58-69.5kV
• L lines are less than 10kV
• X-ray tube needs to be operating above 69.5kV

Question 6

Define:

• scattering:
• absorption:
• intensity:
• attenuation:
• ionisation:
• penetration:

Answer 6

• scattering: random change in direction of photons after hitting something
• absorption: deposition of energy in tissues
• intensity: number of x-ray photons in a defined area of the beam
• attenuation: reduction in intensity of beam due to scattering and absorption
• ionisation: removal of electron from neutral atom to give negative and positive ions
• penetration: the ability of photons to pass through or into tissues/material

Question 7

What are some inteactions which can occur when x-rays hit an object?

Answer 7

X-ray interactions:

• completely scattered with no loss of energy
• absorbed with total loss of energy
• scattered with some absorption and loss of energy
• transmitted unchanged

Question 8

What are the properties of x-rays?

Answer 8

• travel in straight lines in free space
• x-ray photons form a divergent beam
• can travel through a vacuum
• penetrate matter
• can be absorbed or 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

Question 9

What is the radiation dose?

Answer 9

• amount of radiation absorbed by patient
• low energy photons are often absorbed by soft tissues, so most likely to cause biological damage