Neutron Scatter Camera Angular Resolution via Detector Plane Separation
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Solution Overview
Problem
Current neutron detection technologies are inadequate for imaging and locating small amounts of fissile materials like plutonium or highly enriched uranium, as they struggle to detect low-energy fission neutrons and differentiate between various neutron sources, especially in scenarios with high-Z shielding.
Innovation Solution
A neutron scatter camera system that uses liquid scintillator cells and pulse shape discrimination to image and differentiate neutron sources by measuring proton recoil energy and time-of-flight, allowing for precise localization and identification of fission neutrons, even in the presence of high-Z shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional neutron detection technologies are used, then the detection process is simple, but the ability to detect low-energy fission neutrons and differentiate between neutron sources is insufficient
Solution Approach 1:
The detection system is segmented into two distinct detector planes (first and second detector planes) separated by a distance. Each plane independently detects scattered neutrons, allowing the system to measure both scattering angles and time-of-flight. This segmentation enables precise neutron source differentiation by capturing spatial and temporal information from multiple detection points.
Solution Approach 2:
The invention adds a temporal dimension to neutron detection by measuring time-of-flight between two spatially separated detector planes. This transforms the detection from a single-point spatial measurement to a combined space-time measurement, enabling differentiation of neutron sources based on both direction and energy characteristics.
2Productivity
If detector planes are placed close together, then detection efficiency is high, but angular resolution deteriorates
Solution Approach 1:
The system optimizes the separation distance between detector planes as a key parameter. By carefully selecting the distance between the first and second detector planes, the invention achieves a balance where sufficient separation provides adequate angular resolution while maintaining reasonable detection efficiency. This parameter optimization resolves the contradiction between efficiency and precision.
3Reliability
If high-Z shielding materials are present, then neutron penetration is improved, but neutron detection and source localization becomes difficult
Solution Approach 1:
The system uses feedback from multiple measurement parameters (scattering angle from spatial distribution and energy from time-of-flight) to reconstruct neutron source location. By analyzing the correlated information from both detector planes, the system can penetrate high-Z shielding and still accurately locate sources through iterative reconstruction algorithms that account for shielding effects.
Solution Approach 2:
The detection system employs a composite approach combining organic scintillator materials in the detector planes with appropriate shielding materials. This composite structure allows the system to maintain sensitivity to scattered neutrons while providing necessary shielding, enabling source localization even when high-Z materials are present in the interrogation scenario.
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 system effectively detects and images fission neutrons, differentiates between neutron sources, and pinpoints the source location with high accuracy, achieving a significant signal-to-noise ratio and improved sensitivity, especially in scenarios with high-Z shielding.
Implementation Method 1
A neutron scatter camera system that uses liquid scintillator cells and pulse shape discrimination to image and differentiate neutron sources
Implementation Method 2
Particle scatter cameras use conservation of energy and momentum for the collision between an incident neutron (no) and a proton (p) from the detector to calculate the direction of origin for the neutron
Implementation Method 3
the energy of the recoiling neutron is determined from the time-of-flight (TOF) between the two detectors
Implementation Method 4
A neutron scatter camera system that uses liquid scintillator cells and pulse shape discrimination to image and differentiate neutron sources
Data Source
AI summary
An instrument that will directly image the fast fission neutrons from a special nuclear material source wherein the neutron detection efficiency is increased has been described. Instead of the previous technique that uses a time-of-flight (TOF) between 2 widely spaced fixed planes of neutron detectors to measure scatter neutron kinetic energy, we now use the recoil proton energy deposited in the second of the 2 scatter planes which can now be repositioned either much closer together or further apart. However, by doubling the separation distance between the 2 planes from 20 cm to a distance of 40 cm we improved the angular resolution of the detector from about 12° to about 10°. A further doubling of the separation distance to 80 cm provided an addition improvement in angular resolution of the detector to about 6° without adding additional detectors or ancillary electronics. The distance between planes also may be dynamically changed using a suitable common technique such as a gear- or motor-drive to toggle between the various positions. The angular resolution of this new configuration, therefore, is increased at the expanse of detection sensitivity. However, the diminished sensitivity may be acceptable for those applications where the detector is able to interrogate a particular site for an extended period.