Ionising Radiation Flashcards
1
Q
Where do gamma rays originate?
A
- Produced by a radionuclide
- Loses energy to become stable via emitting gamma rays
2
Q
What is a radionuclide?
A
Atom with unstable nucleus
3
Q
Why is Technetium99m used in RNI?
A
- Short half-life
- Only gamma photons released during decay
- energy of 140KeV
- ease of production
- easy to make organ specific
4
Q
Why do anterior and posterior images differ in RNI?
A
- Gamma rays emitted from body in ALL directions
- Xrays only produce shadow
5
Q
What does the collimator do?
A
-Removes gamma rays which don’t travel in a direction perpendicular to the crystals
6
Q
What do the sodium iodide crystals do?
A
- Produce light when activated with thallium
- Converts gamma rays into light (scintillations)
- intensity of the light is proportional to the energy of the gamma ray incident
7
Q
What do photomultiplier tubes do?
A
- Absorb light and convert to electrons
- Multiplies initial current produced by the light
8
Q
What does the event localisation circuitry do?
A
- Light detected by photomultiplier quadrants with specific coordinates
- Coordinates detected by position analyser
9
Q
What happens in pulse height analysis?
A
- Output from photomultiplier tubes sent to PHA (pulse height analysis)
- PHA removes gamma rays which have undergone attenuation process previously
