x-ray production

Question 1

components of a x-ray tube

Answer 1

tube insert, tube housing and light-beam diaphragm

Question 2

tube housing

Answer 2

provides protection from radiation and electrical hazards such as electrical shock, radiation leakage, overheating and filtration

Question 3

light beam diaphragm

Answer 3

provides protection from radiation hazards from the tube insert such as radiation and scattered radiation

Question 4

results of scattered radiation

Answer 4

• contribution to patients dose
• degrades image quality
• controls field size of beam
• protects body parts that aren’t required on a radiograph

Question 5

x-ray photon production

Answer 5

• produced when fast-moving electrons are suddenly stopped by the impact with a metal target
• kinetic energy of the electrons is converted into x-ray photons and into heat (99%)

Question 6

thermionic emission

Answer 6

• when a material is heated, the KE of the atoms within the material increases, increasing the severity of the collisions of the atoms
• outer electrons of a material are more loosely bound than inner electrons
• collisions of energetic atoms near the surface of the material imparts sufficient KE to cause some of the material to be liberated from the material
• each electron that is liberated will leave with a net positive charge

Question 7

space charge effect (thermionic emission)

Answer 7

state of equilibrium - electrons that are liberated from the material equals the rate of electrons that are attracted back into the material, creating an electron cloud

Question 8

thermionic work function

Answer 8

minimum energy needed to liberated an electron from a material

Question 9

materials used in x-ray tubes

Answer 9

molybdenum, tungsten, rhenium, graphite

Question 10

tube current

Answer 10

• passage of current through the filament causes the filament to heat, causing electrons to be liberated by thermionic emission.
• liberated electrons are drawn towards the positive anode to form the tube current
• the liberated electrons ae then accelerated towards the metal target to create x-ray photons

Question 11

acceleration of electrons

Answer 11

liberated electrons will strike the anode with greater KE, producing more energetic X-ray photons

Question 12

generation of heat

Answer 12

when the filament electrons interact with the shell electrons, the shell electrons are briefly excited, energy is emitted in the form of low energy electromagnetic radiation (heat)

Question 13

process of bremsstrahlung radiation

Answer 13

• inelastic collisions with atomic nuclei
• filament electrons are suddenly decelerated
• the deceleration causes the filament electrons to lose some KE which may be converted into x-ray photons

Question 14

maximum photon energy

Answer 14

• a filament electron is suddenly halted by impacted directly with the positively charged nucleus causing the filament to lose all of its KE which is then converted into an X-ray photon

Question 15

inherent filtration

Answer 15

low x-ray photons are filtered by the tube insert and the cooling surrounding the tube insert

Question 16

added filtration

Answer 16

low energy x-ray photons can also be removed from the beam by adding aluminium or copper filtration

Question 17

characteristic production

Answer 17

photons are produced at fixed energies depending on the atomic number of the metal target anode