X-Ray Production

Question 1

parts of x-ray machine

Answer 1

tubehead
collimator
positioning arm
control panel
circuitry

Question 2

what is inside the xray tube

Answer 2

glass envelope
cathode
anode

Question 3

glass envelope use

Answer 3

maintains vacuum so electrons can travel from cathode to anode

leaded glass to absorb photons not in desired direction

Question 4

cathode use

Answer 4

filament = electron release
- made of tungsten

focusing cup = repels electrons at filament, focuses electrons at anode target
- molybdenum

Question 5

anode use

Answer 5

target = produces photons and heat
- made of tungsten
- focal spot where electrons collide and create photons

heat-dissipating block = target embedded in metal
- copper
- thermal conduction which reduces overheating

Question 6

step up and step down transformer

Answer 6

step up -
increases potential difference across xray tube to 60-70kV

step down -
decreases potential difference across filaments to 10V

Question 7

what does electron volts (eV) measure

Answer 7

kinetic energy gained by electrons as they accelerate from cathode to anode

if 70kV = each electron has 70keV of kinetic energy reaching anode

Question 8

in the xray tube, what metals attenuate the photons

Answer 8

copper and tungsten

Question 9

penumbra effect

Answer 9

blurring of radiographic image due to focal spot not being a single point, but a small area

need a focal spot to reduce superimposition and creation of blurry image

this increases heat concentration however

so angle target instead

Question 10

components of xray tubehead

Answer 10

xray tube
metal shielding [lead]

aluminium filtration
- removes lower energy xrays which do not contribute to image

oil
- disspitates heat

spacer cone
- fsd, set distance, indicates direction of beam

Question 11

collimator

Answer 11

lead diaphragm at end of spacer cone
reduces pt dose
crops xray beam to match size
rectangular best
50x40mm

reduce surface area irradiation by 50%
increases collimation errors

Question 12

how is heat and x-ray produces via electrons

Answer 12

heat -
outer shell electrons of tungsten atoms at target

xray -
inner shell electrons and nuclei of tungsten at target

Question 13

order of heat dissipation

Answer 13

heat
->
tungsten target
->
copper block
->
oil in tubehead
->
air

Question 14

why do xray tubes operate at 70kV

Answer 14

so bombarding electrons have sufficient energy to displace K shell electrons

Question 15

continuous radiation

Answer 15

continuous range of xray photon energy

maximum photon energy matches peak voltage

bombarding electrons interacts with nucleus of target atom

Question 16

characteristic radiation

Answer 16

produces specific energies of xray photons, characteristic to the element used at the target

photon energy depend on binding energy of electron shells

bombarding electron interacts with inner shell electrons of target atom