Radiation physics 1

Question 1

What are x-rays

Answer 1

• Part of the electromagnetic spectrum
• Travel in straight lines at the speed of light
• Can travel through materials and through a vacuum

Question 2

How is the x-ray produced

Answer 2

An electron beam is produced from a cathode which hits an anode and produces an x-ray beam

Question 3

Describe what happens at the cathode

Answer 3

• An electric current is passed through the filament, heating it up
• Some electrons get enough energy to sit in a cloud surrounding it - this is called thermionic emission
• Electrons from the cathode at a high voltage are attracted to the positive anode

Question 4

What an increase in cause the number of x-rays to increase

Answer 4

• Increasing current
• Increasing time
• Increasing mass

Question 5

Explain how x-ray images are formed

Answer 5

X-rays can be
- Transmitted: travel through the patient to the detector
- Scattered: X-rays travel into the patient and scattered at different angles
- Absorbed: energy deposited into the patient; photoelectric effect; compton scatter

Question 6

Describe the photoelectric effect

Answer 6

• X-ray photon knocks an electron out, so a photon is scattered
• Reduces contrast in the image

Question 7

Describe the compton scatter

Answer 7

• Incoming x-ray photon knocks an electron out, so a photon is scattered
• Reduces contrast in the image