Dosimetry 5 Flashcards
1
Q
What is TLD?
A
- Thermoluminescence dosimetry
- Uses small crystals and many different materials
- It is a passive dosimeter, using no cables but also does not give an instant reading after radiation
- They have many different applications
2
Q
What is the mechanism within a TLD?
A
- Ionising particles interact with crystals, exciting electrons from valence to conduction bands
- Some electrons become trapped in intermediate bands and do not return to valence
- Impurities in the crystal produce electron traps
- When heated, electrons leave traps, return to valence band and release visible light
- Collect light, proportional to the absorbed dose
3
Q
What are the advantages of TLD?
A
- Wide dose range
- Can be reused
- No wires attached to the patient
- Small
- No external bias (no high voltage applied)
- Does not require temperature/pressure corrections
4
Q
What are the disadvantages of TLD?
A
- No immediate readout
- TL signal fades with time
- Can be sensitive to ambient/UV light
- The TL Reader can be unstable
5
Q
How does radiographic film work?
A
- Reduction of silver halide into silver
- Requires processing and therefore there are problems with reproducibility
- Is a two dimensional dosimeter
- as high spatial resolution
- It has a high atomic number so has variations of response
