• The intensity of a beam is defined as the energy flowing
through 1m x 1m in one second
Inverse Square law
The inverse square law states that the intensity of the radiation from a source varies inversely as the square of the distance from the source
The density achieved on an imaging receptor such as x-ray film is directly proportional to the intensity of the x-ray beam reaching it
Film density ∝Radiation Intensity
However, due to the inverse square law, the intensity falls off rapidly with distance
Radiographers therefore have to take particular note of the distance between the x-ray tube and the imaging receptor and adjust the exposure accordingly
This will ensure that the film or receptor receives the appropriate dose
The inverse square law is crucial to radiation protection
The intensity of radiation falling on unit area in unit time, falls off rapidly with distance
This is due to the squared nature of the inverse relationship
Thus if the distance between radiation source and operator is doubled, the dose is 4 times less
If the distance is trebled, the dose is 9 times less and so on
To weaken or reduce in force, effect, amount or value.
The higher the energy, the deeper the photons penetrate.
So, what happens if we take two x-ray photons of identical energy, but use a high atomic number material and a low atomic number material?
Ionisation occurs when some forms of radiation have sufficient energy to interact with atoms and ‘eject’ their orbital electrons
Such atoms (or the molecules that they form) can then be rendered unstable and reactive with consequent effects
This is the basis of the biological effect of ionising radiations such as x and γrays