Production of x-rays Flashcards
what is the domestic electricity supply?
220/240v
50 Hz
13 amp
complete the sentence
A is converted to B within the x ray tube
a- domestic electrical supply
b-x rays
draw the dental xray tube
check notes
where is the filament found within the xray tube?
at the cathode
what is the fine wire filament made from?
tungsten
why is tungsten used in the xray tube?
-because it has a high melting pt and a lot of heat is generated during xray production
-it has a high tensile strength so can be pulled into very fine wire (filament)
what size of current passes along the filament?
8-10 mA
what is a step down transformer and why is it needed?
current must pass through step down transformer as amp of electrical supply is 13 A
what is the step down transformer made of?
copper
what happens to electrons in the cathode?
-as current passes along filament- electrons get excited and vibrate
-wire gets hot and gives off light
-excited electrons are lost from outer shells and form electron cloud around cathode within focusing cup
what is the anode made from?
copper with a tungsten target
what is the potential difference between the anode and the cathode?
50-90 kV
why is a step up transformer needed?
because the domestic electrical supply is only 220/240V the voltage will become 70kV
what happens to the high energy electrons when they are pulled towards the anode?
the electrons suddenly stop at anode changing their form into 99% heat and 1% X-rays
what are the two types of collisions that give rise to x-rays ?
continuing spectrum and characteristic spectrum
what occurs during continuing spectrum collision?
-free electrons around cathode are attracted to positive nucleus of tungsten
-electrons slow down/change direction as they reach the tungsten target
-as they slow/deflect energy is lost and released as X-rays
what happens if electrons pass close to the nucleus of tungsten?
they slow significantly and significantly change direction- giving most of their energy to photons producing x-rays
what happens if electrons pass further away from nucleus?
they do not slow or change direction as much- therefore giving off less energy to photons producing X-rays
why should low energy photons be filtered within the X-ray tube?
because they do not produce a quality image and therefore will be absorbed by the patient unnecessarily
-they have little penetration power
what are low energy X-rays absorbed by?
normally soft tissues (superficial structures)
what are X-rays produced by as?
bremstraulling radiation
is there a wide range of energies produced with continuous spectrum?
yes- electrons all have different energy and produce a wide range of photon energies.
what is the maximum photon energy produced?
directly related to the keV of energy across the x ray tube
what happens during characteristic radiation?
-an incident electron directly hits an electron within the K shell knocking this electron out (ejected orbital electron)
-k shell is now unstable
-electron from L shell drops to K shell
-the excess binding energy from the L shell is released as xray photon
-the cycle continues for each shell
what kV must x ray tube operate ate for characteristic spectrum to be produced?
above 69.5kV (if below this will only produce branstraulling radiation)
what are the energy levels of K shells?
58-69 kV
what ways can x-rays interact?
-scattered no energy loss
-absorbed-total energy loss
-mix of both
-transmitted unchanged
what is an internal scatter?
when an xray passes down into the patients body
in free space, how do X-rays travel?
in a straight line
how do multiple X-rays travel?
divergently in a beam
can X-rays travel through vacuum ?
yes
are x rays detectable by humans?
no
what do X-rays do?
produce image on film emulsion
do x rays cause ionisation?
yes
do x rays cause biological damage?
yes
what is the radiation dose?
the amount of radiation absorbed by the patient
