Xray production

• What is X-ray a form of?

  Electromagnetic radiation (EMR)
• Who experimented with cathode ray tubes in 1895?

  Wilhelm Rontgen
• What did Rontgen add to the cathode ray tube to allow electron beams to exit?

  A thin aluminum window
• What was the purpose of the cardboard covering in Rontgen's experiment?

  To protect the aluminum from damage
• What fluorescent effect did Rontgen observe during his experiment?

  It was caused by an invisible electron beam
• On what date did Rontgen repeat his experiment?

  November 8, 1895
• What did Rontgen do to test the capacity of his cardboard cover?

  He darkened the room
• What did Rontgen notice from a bench a few feet away from the tube?

  A faint shimmering effect
• What did Rontgen's diary describe about his discovery?

  It was a new kind of invisible light
• What does the 'X' in X-rays stand for?

  Something unknown
• Who was the first person to have a radiograph taken?

  Rontgen's wife, Anna Bertha
• What type of EMR do X-rays demonstrate?

  Both magnetic and electrical properties
• What is the process of X-ray production?

  An energy conversion process involving high-speed electrons
• What voltage is a high-speed electron accelerated to in clinical practice?

  A minimum of 60,000 volts
• How are high-speed electrons produced in an X-ray tube?

  Via thermionic emission at the cathode
• What are the two distinct processes that produce X-ray photons?

  Bremsstrahlung and characteristic radiation
• What is Bremsstrahlung radiation?

  Produced when an electron is slowed by a nucleus
• What is characteristic radiation?

  Produced when an electron ejects an orbital electron
• What occurs during thermionic emission?

  A current is passed through the tungsten filament
• What happens to the outer shell electrons during collisions in thermionic emission?

  They become dislodged from the atom
• What is the 'space charge' in an X-ray tube?

  A cloud of electrons in front of the filament
• What happens when a potential difference is applied across the X-ray tube?

  It accelerates the space charge to the target
• What are the three ways electrons can interact with the target?

  Ionization, proximity to nucleus, orbital interaction
• What is the result of Bremsstrahlung radiation?

  Energy loss is emitted as an X-ray photon
• What is the significance of the K-shell binding energy in tungsten?

  It determines the energy needed to eject K-shell electrons
• What happens below 70 kV in X-ray production?

  Only Bremsstrahlung occurs
• What happens above 70 kV in X-ray production?

  85% Bremsstrahlung and 15% characteristic radiation
• What is the threshold energy for characteristic radiation to occur?

  It must exceed the binding energy of the inner shell
• What is the result of a cascade event in characteristic radiation?

  Electrons fill vacancies, emitting X-ray photons
• What is K-alpha emission?

  The transition of an electron from L-shell to K-shell
• What is K-beta emission?

  The transition of an electron from M-shell to K-shell
• What is the significance of K and L characteristic radiation in medical imaging?

  They are the only significant radiations
• What happens to L-characteristic radiation in conventional imaging?

  It is absorbed by filtration in the X-ray tube
• What is the efficiency of X-ray production?

  1% X-ray photons, 99% heat
• Why is Bremsstrahlung more likely to occur than characteristic radiation?

  It involves interaction with the whole atom
• What is the probability of an incident electron interacting with an atom?

  Higher than undergoing Bremsstrahlung or characteristic processes
• What is the result of an interaction between an incident electron and an atom?

  Loss of kinetic energy and emission of a photon
• What is the summary of X-ray production?

  X-ray production is inefficient, mostly heat
• What are the two processes of X-ray production?

  1. Bremsstrahlung (continuous radiation)

  • Incident electron loses energy due to electrostatic attraction to nucleus
  • KE lost = X-ray photon

  1. Characteristic (ionization)

  • Incident electron ejects an orbital electron
  • Results in cascade event and X-ray photon
• What are the differences between Bremsstrahlung and characteristic radiation?

  • Bremsstrahlung:
  • Always occurs, involves slowing down near nucleus
  • Produces continuous-spectrum X-rays
  • Characteristic:
  • Requires sufficient energy to eject inner-shell electrons
  • Produces specific energy X-rays based on shell transitions