

Fission chambers
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Fission chambers
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Product [a] | Diameter[b] (mm) | Sensitive Length[b] (mm) | Thermal Neutron Sensitivity[b][c][d] | Fast Neutron (2.5MeV) Sensitivity[b][d][e] | Typical Material | Type[i] | |
---|---|---|---|---|---|---|---|
Pulse (cps/nv) | D.C. (A/nv) | Pulse (cps/nv) | |||||
FC165 | 25.4 | 57 | 0.12 | [g] | 2.86x10-4 [f] | Stainless Steel[h] | Coaxial |
FC167 | 25.4 | 127 | 0.14 | [g] | 2.90x10-4 [f] | Stainless Steel[h] | Coaxial |
CFUM | 25.4 | 120 | x10-1 | x10-14 | - | Aluminium | Coaxial |
FC550 | 36.8 | 116 | 0.48 | [g] | 9.54x10-4 [f] | Stainless Steel[h] | Coaxial |
CFUL | 48 | 211 | 1 | 2.00x10-13 | - | Aluminium | Coaxial |
FC1400 | 50.8 | 508 | 1.16 | 3.38x10-13 | 2.43x10-3 [f] | Aluminium | Coaxial |
FC1199 | 50.8 | 900 | 1.22 | 2.46x10-13 | 2.08x10-3 [f] | Aluminium | Coaxial |
CFUG | 80 | 220 | 4 | 8.0x10-13 | - | Aluminium | Coaxial |
CFUC | 48 | 220 | 0.6 | 9.00x10-14 | - | Inconel[h] | Guard Ring |
FC765 | 76.2 | 213 | 0.6 | 1.20x10-13 | 1.33x10-3 [f] | Aluminium | Guard Ring |
FC1330 | 76.2 | 371 | 2 | 4.0x10-13 | - | Aluminium | Guard Ring |
CFUP | 76.5 | 180 | 0.7 | 1.40x10-13 | - | Aluminium | Guard Ring |
PFC16 | 66.3 | [44.4][j] | 0.0011 | [g] | 2.77x10-5 [f] | Stainless Steel[h] | Parallel Plate |
PFC82 | 124.2 | [101.6][j] | 0.0057 | [g] | 1.42x10-4 [f] | Stainless Steel[h] | Parallel Plate |
PFC338 | 61 | 52.8 [32.8][j] | [g] | [g] | 5.85x10-4 | Stainless Steel[h] | Parallel Plate |
[a] Significant catalogue of fission chamber designs and variants available. Table shows the most popular variants
[b] Nominal values stated
[c] At 1000µg/cm2 of 235U unless otherwise stated. Alternative coating materials and densities are available which will alter performance.
[d] Standard tolerance on these devices is ±20%
[e] At 1000µg/cm2 of 238U unless otherwise stated. Alternative coating materials and densities are available which will alter performance.
[f] Estimated from mono-energetic neutron testing of PFC338/450/U238 and theoretical sensitivity factor determined from cross-section ratio (≈9x10-4)
[g] Simple reconfiguration required to optimise performance for this operational mode.
[h] May be suitable for high temperature (300°C to 600°C) or very high temperature (>600°C) operations, subject to specific configurations.
[i] Design, materials and manufacturing process are common among most of these devices. Consequently, operation capability is common and may be transferable.
[j] Active length [window diameter], where applicable.
Description
Exosens fission chambers are capable of operating in pulse, fluctuation (Campbell or Mean-Squared-Voltage), or current modes to deliver accurate, reliable neutron flux measurements across startup, operational, and safety-critical conditions. Engineered for resilience in high-radiation and high-temperature applications, we offer a full range of high-sensitivity and high-flux models — including custom solutions tailored to your needs.
Fission chambers are highly sensitive neutron detectors designed to measure neutron flux in environments, such as nuclear reactors, research facilities, fusion power and nuclear fuel cycle facilities. They operate by detecting fission reactions initiated by incoming neutrons interacting with a fissile material deposited within the chamber. The resulting fission fragments ionize the gas inside the chamber, generating electrical pulses proportional to the neutron flux.
Gas-filled neutron detectors are designed to operate in three modes:
- Pulse mode analyzes and counts individual detector pulses.
- Fluctuation, or Campbell / Mean-Squared-Voltage mode, is used to analyze the fluctuations in the signal.
- Current mode is used to measure the mean of the direct current from the detector.
Fission chambers offer a robust solution for a wide range of neutron flux levels and maintain performance stability, even in harsh radiation and high-temperature conditions. Their fast response time, wide dynamic range, and resilience make them critical for reactor monitoring, safety systems, and experimental applications.
What We Offer:
We supply a comprehensive range of fission chambers optimized for demanding applications. Our portfolio includes:
- High-sensitivity chambers for low-flux measurements.
- High-flux capable chambers for power reactor monitoring and control.
- Customized designs tailored to specific reactor conditions or experimental needs.
- Harsh environment models for extended lifetimes in high temperatures and radiation levels.
Our expertise ensures reliability, precision, and safety in all neutron detection applications, supporting the operational excellence and regulatory compliance of nuclear facilities worldwide.
Custom fission chambers
With full control of the following processes, Exosens can supply custom Exosens fission chambers with the highest quality and reliability levels:
- Adaptation of industrialized fission chambers to customer-specific requirements utilizing significant operational experience
- Development of new fission chambers with our experienced research and development teams.
- Long-term collaboration with internationally renowned organizations for modeling, qualification tests in research reactors and development.
- Complete manufacturing and test process on site.
- Support from all the Exosens group activities, experience, and knowledge.
- Highly regulated Quality Assurance programs adapted to the customer’s environment.
- Expertise in design and manufacture of nuclear instrumentation to solve customer challenges. .
- Export control, as an Authorized Economic Operator, Exosens acts in accordance with the EU international regulations.
- Fissile material management & product storage
- Calibration measurements in high radiation flux
Examples of custom versions from basic types
- Neutron and gamma sensitivity tailored to individual requirements.
- Guard-ring (2 outputs) or unguarded (1 output) designs, as well as coaxial and parallel plate configurations
- Materials for high temperature (>3000°C) and very high temperature (>600°C) operation.
- Adapted mechanical interface for installation (Customized external dimensions, springs, threads, hooks).
- LOCA (Loss Of Coolant Accident) and post-LOCA protection.
- Ruggedized structure for harsh environment (radiation, temperature, humidity, mechanical stress).
- Integral cables or integral connectors.
- Coaxial or triaxial mineral-insulated cable, as well as organic cables.
- Customized connector type (BNC, HN, SHV and many others)

Main features
Structure configuration: Coaxial, parallel plate, unguarded or guard-ring.
Structure material: Various material types utilized including aluminium, stainless steel, titanium and nickel alloy.
Integral cable: Integral mineral insulated, or organic cables options are available.
Connector: Customized connector type (BNC, HN, SHV and many others)
Insulators: Exosens only uses high-grade, radiation-resistant insulators from qualified suppliers to ensure the measurement of extremely low currents.
References
- Research Reactors
- Boiling Water Reactor (BWR
- MAGNOX
- Advanced Gas-cooled Reactor (AGR)
- CANada Deuterium Uranium reactor (CANDU)
- Pressurized Heavy-Water Reactor (PHWR)
- Pressurized Water Reactor (PWR)
- Water-Water Energetic Reactor (VVER)
- Training Research Isotopes General Atomics (TRIGA)
- Fast Breeder Reactor (FBR)
- Research Reactors
- High temperature gas-cooled reactors
- Sodium cooled fast reactors
- Thorium high temperature reactor
- Fusion reactors