quality and intensity of x ray beam

Question 1

define intensity

Answer 1

An X-ray beam is composed of photons of electro-magnetic radiation. They are of high energy (short wavelength) photons that are described as ionising radiation.‘Ionising’ means that they are able to eject electrons from their atoms. This results in the release of energised electrons with negative charge and the remaining atoms, which now have a positive charge. The electrons and the positively charged atoms are called ions(charged particles).
Intensity is a measure of quantity of radiation flowing in unit ti

Question 2

method of describing the intensity

Answer 2

How we measure intensity
As it travels through air, the X-ray beam causes ionisation of the air and this enables the radiation to be detected by a measuring instrument known as an ionisation chamber

The air ionisation chamber measures the amount of charge created in the air it contains in C kg-1. In simpler terms the intensity of the beam refers to the number of photon within it i.e. the higher the number the greater the intensity.

Question 3

factors affecting intensity

Answer 3

Factors affecting intensity
Material placed in the path of the x ray beam will remove some of the photons
The higher the atomic number of that material the greater the amount of photons removed
Scattering is the redirection of some of the photons in the beam

Question 4

quality of x ray beam

Answer 4

Quality
Penetrating power of the x ray beam
Average photon energy
The more high energy photons the better the penetrating power
Higher quality beams require greater thickness of material to reduce intensity
X ray beams are heterogenous

Quality of the x ray beam
This describes the penetrating power of the X-ray beam. When compared to light, quality is the ‘colour’ of the beam.
Quoting its average photon energy or wavelength can indicate the quality of such radiation.
‘The more high energy (shorter wavelength) photons that there are in the beam, the higher is its penetrating power’
Higher quality beams require a greater thickness of material to reduce their intensity. The half-value layer is a useful way of comparing the penetrating power of X-ray beams.
In radiography we relate to quality to
Generating voltage
Half value layer
Beam filtration
Effective photon energy or effective waveleng

Question 5

factors affecting x ray output

Answer 5

Tube voltage(kvp)- affects quality because peak kv determines maximum photon energy

• Increase the penetrating power
• Increase the half value layer as it is more penetrating
• For tungsten kv must be at least 70 for k emissions to occur
• Higher kv will give the electrons more energy and makes the whole process more efficient
• Voltage waveform affects both quality and intensity

Question 6

filters

Answer 6

Filtration- Filters are inserted into the X-ray beam to improve the quality of the beam. Unfortunately they reduce the intensity.
A filter consists of a thin sheet of metal such as aluminium (Z=13), copper (Z=29), molybdenum (Z = 42) or palladium, which has the effect of absorbing most of the low energy (long wavelength) radiation. This will reduce patent’s skin dose.