Nested Moderator Shells for Portable Neutron Spectrometry
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Solution Overview
Problem
Current neutron spectrometry methods, such as the Bonner Sphere System, are bulky, heavy, and laborious to use, limiting their practicality for routine measurements in nuclear reactor environments, despite providing high sensitivity and wide energy response.
Innovation Solution
A neutron spectrometer featuring a Helium-3 thermal neutron counter surrounded by multiple removable cylindrical moderator shells, allowing varying moderator thickness for energy-specific responses, with data acquisition controlled by a personal computer for efficient energy distribution analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Bonner Sphere System is used for neutron spectrometry, then high sensitivity and wide energy response are achieved, but the device becomes bulky, heavy, and laborious to use
Solution Approach 1:
The moderating assembly is divided into multiple separate spherical moderators of different sizes that can be individually positioned around the detector. This segmentation allows the system to achieve various energy responses by combining different sized moderators, while maintaining a compact configuration that is easier to handle and transport compared to a single large fixed assembly.
Solution Approach 2:
The system transitions from a fixed static moderating assembly to a dynamic configuration where moderators can be added, removed, or repositioned around the detector. This dynamic capability allows the instrument to adapt to different measurement requirements and energy ranges, while also enabling easier transport and deployment by removing unnecessary moderators from the configuration.
2Reliability
If the Bonner Sphere System is used for neutron spectrometry, then high sensitivity and wide energy response are achieved, but the measurement process becomes laborious
Solution Approach 1:
The detector system is designed to measure multiple energy ranges simultaneously by positioning different sized moderators around it. A single measurement configuration can provide information across thermal to fast neutron energies, eliminating the need for sequential measurements with different assemblies and significantly improving measurement efficiency and productivity.
Solution Approach 2:
Multiple spherical moderators of different sizes are combined around a single detector to create a unified measurement system that captures neutron spectrum information across wide energy ranges in one measurement. This merging of functions eliminates the laborious process of switching between different moderating assemblies and provides comprehensive spectral data efficiently.
3Reliability
If simple thermal neutron counters are used, then high neutron counting efficiency is achieved, but the device cannot measure neutron energy distribution
Solution Approach 1:
Spherical moderators act as intermediary elements that transform fast neutrons into thermal neutrons before they reach the detector. By varying the size and amount of moderating material, the system can selectively thermalize neutrons of different energies, allowing the simple thermal neutron counter to indirectly measure the energy distribution of the original neutron field while maintaining high counting efficiency.
Solution Approach 2:
The system changes the physical parameter of neutron energy by using moderators to thermalize fast neutrons before detection. By controlling the moderating process through selection of different sized spheres and amounts of moderating material, the system can adapt the energy range measured while maintaining the high efficiency of thermal neutron detection, thus achieving both counting efficiency and energy measurement capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables a more portable, compact, and efficient measurement of neutron energy spectra, retaining high sensitivity and wide energy response, facilitating routine measurements in nuclear reactors and other neutron-exposed locations.
Implementation Method 1
U.S. Patent No. 3,102,198 to Bonner (1963) describes the now commonly used and commercially available Helium-3 thermal neutron counter. It is a thermal neutron counter that uses Helium as a counting gas that is enriched with the Helium-3 isotope. This gas offers a high detection efficiency for thermal neutron through the 3He(n,p)3H reaction
Implementation Method 2
Incident energetic neutrons are slowed down through collisions with the hydrogen atoms present in the moderator. When they reach thermal energies, the neutrons are then efficiently detected by the thermal neutron counter at the centre of the moderator
Implementation Method 3
This gas offers a high detection efficiency for thermal neutron through the 3He(n,p)3H reaction
Data Source
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AI summary
A neutron spectrometer is disclosed, which consists of a Helium-3 proportional counter connected by cable to signal and data processing circuits, and a series of moderator shells and moderator lids. The series of cylindrical moderator shells are designed to fit within one another, like Russian Matryoshka dolls, with the counter at the center. Small air gaps are introduced between the shells so that removal of one shell from another is facilitated. The counter is placed within the smallest cylindrical moderator shell, and then a circular lid matching the smallest shell is placed on the opening of the first shell to close the first shell. This first closed shell is then placed within a second shell, which shell is closed with its corresponding circular lid. The cable is routed through the series of shells. A method for using the invention is also disclosed, wherein the counter reading is taken from the fully-assembled neutron spectrometer. Then the outer cylindrical shell and circular lid pair is removed, and another measurement of the counter is recorded. This is continued until the last shell is removed, and a measurement is recorded using the bare counter.