Time-Gated Dual Detector for Shielded SNM Identification
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Solution Overview
Problem
Conventional radiation portal monitors (RPMs) face challenges in detecting special nuclear materials (SNM) due to low radiation emission and shielding, leading to high nuisance alarm rates from natural backgrounds, and existing upgrades have not significantly improved detection probability.
Innovation Solution
The method involves using gamma detectors to indirectly detect neutron radiation in the 3-8 MeV energy range, correlating radiation signatures in time to enhance the signal-to-background ratio, and employing a dual-detector setup with a first radiation detector sensitive to low background fission signatures and a second detector for gamma or x-ray radiation, with time-gated data acquisition to suppress background noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RPMs use thermal neutron detectors with moderating material to detect SNM, then neutron detection capability is provided, but the detection probability remains low and nuisance alarm rates from NORM sources become unacceptably high
Solution Approach 1:
The detection system is segmented into multiple independent detector types (fast neutron detectors, thermal neutron detectors, gamma detectors) that operate in parallel. Each detector type targets specific radiation signatures, allowing the system to cross-validate signals and distinguish true SNM detections from NORM background sources, thereby reducing nuisance alarms while maintaining detection capability
Solution Approach 2:
The system changes the detection parameters by using fast neutron detectors with energy thresholds set to detect high-energy neutrons (>0.1 MeV) characteristic of fission, rather than relying solely on thermal neutron detection. This parameter change in energy threshold and detector response time allows differentiation between fission neutrons and neutrons from NORM sources, reducing false positives
2Measurement precision
If RPMs use higher resolution gamma detectors such as NaI scintillation crystals or high purity germanium detectors to improve detection, then gamma detection resolution is improved, but substantial improvement in achieving detection goals is not demonstrated
Solution Approach 1:
The system merges multiple detection modalities (fast neutron detection, thermal neutron detection, gamma spectroscopy) into a single integrated RPM system. By combining these detector types and their respective strengths, the system achieves superior SNM detection probability that neither detector type could achieve alone, while the multi-modal approach provides cross-validation to reduce false alarms
3Object-affected harmful factors
If SNM is shielded by neutron or gamma shielding, then the radiation signature is suppressed, but detection becomes very difficult with conventional RPMs
Solution Approach 1:
The fast neutron detectors are designed to detect high-energy neutrons before they are fully moderated or absorbed by shielding materials. By detecting neutrons in their high-energy state closer to the source, the system can identify SNM even when conventional thermal neutron detection and gamma spectroscopy are blocked or suppressed by shielding
Solution Approach 2:
The system uses multiple detector types as intermediaries to detect different aspects of the radiation field. When one detection path is blocked by shielding, other detector types can still detect alternative radiation signatures (e.g., fast neutrons when thermal neutrons are blocked, or vice versa), providing redundant detection paths that overcome shielding effects
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
This approach increases the probability of detecting shielded SNM while reducing nuisance alarms, providing a higher detection probability than typical RPMs with lower susceptibility to false positives.
Implementation Method 1
said at least one first radiation detector detects neutron radiation or high energy gamma radiation of a typical energy between 3 MeV and 9 MeV
Implementation Method 2
said at least one first radiation detector detects high energy gamma radiation of a typical energy between 3 MeV and 9 MeV
Implementation Method 3
said at least one second radiation detector detects gamma or x-ray radiation
Implementation Method 4
said at least one second radiation detector detects gamma or x-ray radiation
Implementation Method 5
nuclear material emitting in a time correlated manner at least a first radiation and a second radiation
Implementation Method 6
the data being acquired by said at least one second radiation detector within said predetermined time windows being analyzed separately from data acquired by said at least one second radiation detector outside said time window
Data Source
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AI summary
The invention relates to a method for obtaining information or signatures about the presence and/or the nature of a nuclear radiation source (11), especially in a homeland security application, said nuclear radiation source (11) emitting in a time or angle correlated manner at least a first radiation and a second radiation. The method comprises the steps of detecting said first radiation by means of at least one first radiation detector (D1) and detecting said second radiation by means of at least one second radiation detector (D2), whereby the detection of said second radiation is triggered by said detection of said first radiation in a manner that is adapted to the radiation's correlation structure, thereby increasing the signal-to-background ratio for the detection of said second radiation.