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.
|Custom Gamma ionization chambers|
By full control of the following processes, Photonis Nuclear Instrumentation can supply custom gamma ionization chambers with the highest quality and reliability levels
- Adaptation of industrialized gamma ionization chambers to customer specific requirements.
- Development of new gamma ionization chambers with our experienced R&D team.
- Long term collaboration with the French Atomic Energy Commission / CEA (theoretical approach, modeling, qualification tests in research reactors.
- Complete manufacturing process on site.
- Support from all the Photonis Group activities, experience and knowledge.
- Certifications & Quality Assurance programs adapted to the customer environment.
- Technical support, applying expertise.
|Examples of custom versions from basic types|
- Gamma sensitivity tailored to individual requirement
- Guard-ring (2 outputs) or coaxial (1 output) structure
- Integral cable or integral connector
- Connector type (BNC, BNCHT, HN or others)
- Adapted external dimensions and mechanical interfaces
- Aluminum or stainless steel structure
- Ruggedized structure for harsh environment (radiation, temperature, humidity, mechanical stress)
- Housing for gamma source
- Lead attenuation for a better relative sensitivity in the high energy range
- Structure: High electrical insulation by use of two coaxial integrated cables in a guard-ring configuration.
- Electrodes: The two electrodes consist of a concentric metal tube assembly, arranged in a guard-ring configuration. The electrodes are made of aluminum or stainless steel.
- Filling gas: The gas type and pressure depend on the required sensitivity. Standard gases are nitrogen or xenon.
- Insulators: As it is necessary to measure extremely low currents, insulators must be of very high quality and radiation resistant. Photonis only uses high-grade alumina insulators from qualified suppliers.
- Integral cable: Integral cables are recommended for the signal and for the high voltage when operating in severe environments
The French Atomic Energy Commission (CEA) selected Photonis as its technological partner for a co-operative development of neutron and gamma detectors when the French nuclear power program took shape in the sixties.
Fuel reprocessing plant – AREVA/COGEMA/ORANO – Numerous gamma ionization chambers – France, Japan.