3.2 Types of Radiation Detectors
Radiation detectors are categorized by the physical principles they use to convert radiation energy into a measurable signal. The three major types are gas-filled, scintillation, and semiconductor detectors.
1. Gas-filled Detectors
These detectors contain a gas that is ionized by radiation, creating electron-ion pairs. An applied voltage separates these charges, generating a current pulse that is measured. They are widely used for their simplicity and cost-effectiveness.
- Ionization Chamber: Operates at a low voltage where the collected charge is proportional to the energy deposited. Primarily used for measuring high radiation doses.
- Proportional Counter: Operates at a higher voltage, causing secondary ionization. The output pulse is proportional to the incident radiation energy, allowing for basic spectroscopy.
- Geiger-Müller (GM) Counter: Operates at a very high voltage, causing an avalanche of ionization for any single radiation event. It is highly sensitive and ideal for detecting the presence of radiation, but provides no information about its energy.
2. Scintillation Detectors
These detectors use a special material called a **scintillator** that emits a flash of light when it absorbs radiation energy. This light is then converted into an electrical signal by a photomultiplier tube (PMT) or a silicon photomultiplier (SiPM).
- Scintillation detectors like the NaI(Tl) detector are excellent for **gamma spectroscopy** due to their good energy resolution and high detection efficiency.
- They are commonly used in medical imaging (PET, SPECT) and environmental monitoring.
3. Semiconductor Detectors
Semiconductor detectors use a semiconductor material (like silicon or germanium) where radiation energy creates electron-hole pairs. An applied electric field collects these charges, producing a signal.
- They offer the **best energy resolution** among all detector types.
- They are ideal for precise energy measurements and are widely used in research and advanced analytical applications.
Comparison of Detector Types
| Detector Type | Energy Resolution | Dead Time | Typical Application |
|---|---|---|---|
| Gas-filled | Poor to Moderate | Long (~µs) | Radiation surveys, dose measurement |
| Scintillation | Good | Short (~ns) | Gamma spectroscopy, medical imaging |
| Semiconductor | Excellent | Very Short (~ns) | High-resolution spectroscopy, research |