Neutron Scatter Camera for SNM Source Imaging
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Solution Overview
Problem
Current neutron detection technologies struggle to accurately image and locate sources of fission neutrons from special nuclear materials (SNM) like plutonium or highly enriched uranium, especially when concealed behind thick shielding, due to limitations in detecting lower energy neutrons and distinguishing them from background radiation.
Innovation Solution
A neutron scatter camera system that uses a pair of detectors with liquid scintillator cells and pulse shape discrimination to measure proton recoil energy and time-of-flight, allowing for the imaging and differentiation of neutron sources by reconstructing probability cones and reducing gamma contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional neutron counting techniques are used, then the detection process is simple, but the sensitivity for detecting solar neutrons and fission neutrons is insufficient
Solution Approach 1:
The detector system is divided into two separate detector arrays positioned at different locations, allowing the system to capture scattered neutrons from multiple angles and improve sensitivity through spatial segmentation of the detection process
Solution Approach 2:
The system transitions from simple neutron counting to three-dimensional imaging by adding spatial dimensionality through the use of two detector arrays and reconstructing probability cones in 3D space, enabling precise localization of neutron sources
2Measurement precision
If fast neutron imaging techniques are used at high energies, then it is easier to determine interaction parameters, but the proton recoil range is limited at SNM neutron energies
Solution Approach 1:
The system uses scattered neutrons as intermediaries that carry information from the neutron source through the first detector to the second detector, allowing measurement of interaction parameters without requiring direct measurement of short-range proton recoils
Solution Approach 2:
The system replaces direct mechanical measurement of proton recoil (which is limited by short range at low energies) with a time-of-flight measurement system that uses electromagnetic timing to determine neutron energy, bypassing the mechanical limitation
3Measurement precision
If neutron scatter camera is used to image fission neutrons, then the source location can be determined, but gamma contamination affects the detection accuracy
Solution Approach 1:
The system converts gamma contamination from a harmful factor into a useful discriminator by using pulse shape discrimination to identify and separate gamma events from neutron events, transforming the interference into a means for improving detection accuracy
Solution Approach 2:
The system changes the parameter being measured from simple neutron counting to pulse shape analysis, using the temporal characteristics of the scintillation signal to differentiate between neutron and gamma interactions
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 neutron sources, differentiates between various neutron sources, and pinpoints their location with high accuracy, achieving a significant reduction in gamma contamination and improving signal-to-noise ratio through spatial filtering and better penetration through high-Z shielding.
Implementation Method 1
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 2
The incident neutron scatters in the first detector and then again in the second detector. The angle of the first scatter (θ1) is related to the energy given to the proton in the first scatter, Ep
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 a pair of detectors with liquid scintillator cells and pulse shape discrimination to measure proton recoil energy and time-of-flight
Implementation Method 5
This defines a probability cone which can be back projected onto a virtual image plane. An image is formed by overlapping these cones over many events
Data Source
AI summary
An instrument that will directly image the fast fission neutrons from a special nuclear material source has been described. This instrument can improve the signal to background compared to non imaging neutron detection techniques by a factor given by ratio of the angular resolution window to 4π. In addition to being a neutron imager, this instrument will also be an excellent neutron spectrometer, and will be able to differentiate between different types of neutron sources (e.g. fission, alpha-n, cosmic ray, and D-D or D-T fusion). Moreover, the instrument is able to pinpoint the source location.