characteristic and continuous radiation Flashcards
what electrons are involved in heat production
outer shell electrons
bombarding electron loses kinetic energy which is converted to heat
how is heat dissipated in an x ray tube
initially by heat dissipating copper block surrounding target, then oil in tube head then surrounding air
what electrons are involved during x ray producing interactions
inner shell electrons
what are the 2 classifications of x ray interactions
characteristic radiation
continuous radiation
what is continuous radiation
bombarding electron avoids all outer shell electron and passes close to or into target nucleus
The positive charge causes it to be rapidly decelerated and deflected and the lost kinetic energy is released as x ray photons
what energy is contained within x ray photons produced by continuous radiation
wide range of energies are produced depending how close the bombarding electrons come to the target nucleus
the closer they come the greater the energy
Greatest energy that can be achieved is seen when an electron collides directly with the target nucleus stopping it completely and giving out maximum kinetic energy (rare)
what is the maximum energy an x ray photon can have when produced via continuous radiation and when is this seen
seen when bombarding electron hits target nucleus directly losing the maximum amount of kinetic energy possible
numerical value of this is identical to the voltage of x ray tube e.g dental x ray tube = 70kV which would produce a max photon energy of 70keV (kilo electron volts)
Why is filtration important with regards to continuous radiation
majority of x ray photons produced by continuous radiation are of low energy
these low energy photons are to not contribute to the x ray image but are still absorbed by the patient increasing the patient dose
aluminium sheet is therefore used as a filter to stop these reaching the patient
what is characteristic radiation
occurs when the bombarding electron collides with an inner cell electron and either
- displaces it to a more outer shell (excitation)
- removes it completely (ionisation)
The remaining orbiting electrons then re arrange themselves to refill the innermost shells.
When an electron drops to a lower level it loses energy (its binding energy) which is emitted as a photon of specific energy
what energy is contained within x ray photons produced by characteristic radiation
values are very specific to element in question
photon energy = the difference between the binding energies of the two shells involved
example:
Tungsten (target)
K shell binding energy - 69.5 kEv
L shell binding energy - 10.2keV
M shell binding energy - 2.5 keV
if electron dropped from M shell to K shell - photon with 67keV released
If electron dropped from M to L - photon with 7.7keV released
characteristic vs continuous
what do bombarding electrons interact with
continuous - target nucleus
characteristic - inner shell electrons
characteristic vs continuous
what energy are the photons produced
characteristic - specific energies that are characteristic of target element - dependent on binding energies of electron shells
continuous - continuous range of energy values with maximum energy matching voltage of x ray machine
