Page 11 - Radiation Safety

Properties of Gas-Filled Detector:
- Sensitive to environmental condition
(temperature & pressure)
- Higher sensitivity (dose and energy) compare
to semiconductor detector

Functioning Principle of Gas-Filled Detector:
- - Radiation cause ionisation in the gas
Ion Saturation - - Electric field causing the negative ion move to
Ion pairs created

anode and positive ion move to cathode
Current flow is measured as dose reading

Characteristic of Gas in detector:
- Noble gas (not easy to ionised)
- Do not oxidise the wall of detector (metal)
- E.g.: Argon, Krypton, Xenon

Limited
Recombination Ion Saturation Proportional Region G-M region
Proportional
Voltage not strong Detector: Detector: Detector:
enough to Ionisation Chamber Gas Flow Proportional/ Geiger-Müeller
separate ion pairs (IC) Gas Proportional

Ion pairs will - Good accuracy - Good accuracy - Gas multiplication
recombined and - Increase in dose - Gas multiplication - Pulse mode
causing loss of (intensity) increase - Pulse mode - Highest sensitivity
signal (dose in signal - Discrete energy can be detected Seldom used - Fast response
reading) - Current mode using multi-channel analyser (MCA)
- Higher sensitivity

- Not affected by - Increase in voltage, increase in - Not affected by
changes in voltage pulse size voltage
- Not affected by - Increase in energy, increase in pulse - Dead time
variation in energy size - Poor accuracy