Production of Xrays Flashcards
what are the main components of the equipment used to take an xray?
tubehad collimator positioning arm control panel circuitry
component of glass x ray tube?
filament
copper block
target
what kind of transformers are part of the xray tube?
step up transformer high kv across x ray tube
step down transformer low filament mA
what may the glass have?
a lead free window while the rest is leaded
what is the purpose of the lead shield?
minimises radiation leakage
what is the purpose of the oil?
facilitate heat removal
what does the aluminium filter do?
remove soft low energy damaging x rays
what is the purpose of the collimator?
restrict size and shape of beam
what is BID?
beam indicator device
part of collimator
how is an xray produced? what first happens in the filament?
small electric current is passed through 8-10mA
passed through a step down transformer
filament heated by current because of excitation of electrons in the wire
how is an xray produced - what happens to the electrons after the current heats the filament?
electrons lost from the outer shell
produce an electron cloud by free electrons surrounding
step up transformer 240V = 50-90kV
production of an xray, what does the focusing cup do?
focusing cup points electrons towards focal spot on anode
negative electrons attracted to positive charged anode
pulled across by high kv between cathode and anode
electrons = high energy and fast moving
production of an xray, what happens once the electrons are pulled across to the cathode?
electrons hit target and come to a sudden stop
electrons lose energy
energy conversion = 99% heat, 1% xrays
last stage of production of an xray?
heat absorbed by copper dissipated into surrounding oil xrays radiate in all directions most absorbed by leaded glass target = xrays through unleaded window = beam of radiation emitted
2 types of xray spectra?
- continuous spec - brehmstrahlung. eide range of photon energies
- characteristic spec - depends on material in anode, emitted by loss of electrons from k/l shells
x ray properties?
travel in straight lines in free space xray photons form a divergent beam can travel through a vacuum penetrate matter absorbed/scattered human senses cant detect cause - ionisation, biological damage, certain salts to fluoresce
what is scattering?
random change in direction after hitting something
what is absorption?
deposition of energy in the tissues
what is intensity?
no. of xray photons in one area of the beam
what is attenutation?
reduction in intensity of the beam b/c scattering and absorption
what is ionisation?
removal of an electron from a neutral atom to give an electron and a positive ion
what is penetration?
ability of photons to pass through into tissues/materials
what are interactions of an xray beam?
completely scattered with no loss of energy
absorbed with total loss of energy
scattered with some absorption and some loss of energy
transmitted unchaged
interactions of an xray beam at an atomic level?
raleigh scattering
photoelectric effect = pure absorption
conmpton effect = absorption and scatter
pair production = pure absorption
what is the photoelectric effect?
incoming electron interacts with inner K shell
electron ejected with much energy
photoelectron undergoes further interactions
xray photon lost all energy and dissapears
inner shell vacancy replaced by an outer shell electron
excess energy = emmited as light/low energy xray
free electron captured
atomic stability and neutral state
what is the compton effect?
incoming xray photons interact with loosely bound outer shell electron
electron ejected with some energy from xray and becomes compton recoil electron
compton electron can cause ionisaiton
remaining photon energy scattered
may undergo further compoton reactions
may undergo photoelectric reations
escape tissues into clinical environment
