In Gamma Detectors, the gamma radiations produce electrons by interacting with the cathode material and the filling gas.
These electrons ionize the gas and the charge carriers are collected by the electrodes. The resulting anode pulse is detected by a load circuit. The primary electrons are created by several interaction mechanisms:
- Photoelectric effect
- Compton scattering
- Pair production
The mechanism efficiency depends on gamma quanta energy, cathode material and thickness, filling gas type and pressure. Detector sensitivity is therefore very dependent on the detector design, but is always energy-dependent. Due to the dominance of the photoelectric effect, the maximum sensitivity occurs at about 80 keV. At high gamma energies (> 500 keV), the sensitivity can fall to one hundredth of the maximum for the same mechanical design.