Neutron Fluorescence Gamma Detector Synchronization
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Solution Overview
Problem
Current methods for detecting substances of interest using neutron emission face challenges in distinguishing between signals of interest and noise, particularly due to high levels of fratricidal and atmospheric backshine gamma rays, which degrade the signal-to-noise ratio (SNR) and hinder accurate identification.
Innovation Solution
The method involves pulsing neutron emissions synchronized with the time of flight of the neutron packet and time-gating the gamma ray detector, ensuring it is OFF during neutron pulses and subsequent periods to minimize detection of nuisance gamma signals, thereby enhancing the SNR by excluding fratricidal and atmospheric backshine gamma rays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If continuous neutron emission is used to interrogate the target, then the signal of interest is continuously available, but the signal-to-noise ratio deteriorates due to constant production of fratricidal and atmospheric backshine gamma rays
Solution Approach 1:
The patent applies periodic action by using pulsed neutron emission instead of continuous emission. The neutron source emits neutrons in periodic pulses, and the gamma detector is synchronized to detect signals only during specific time windows within each pulse cycle. This temporal modulation separates the signal of interest from the noise by exploiting the time-of-flight characteristics, thereby improving the signal-to-noise ratio while maintaining detection throughput through repeated pulsing.
2Measurement precision
If gamma ray detection is performed continuously, then all gamma signals are captured, but noise from fratricidal and atmospheric backshine gamma rays cannot be distinguished from signals of interest
Solution Approach 1:
The patent applies segmentation by dividing the continuous gamma detection process into discrete time segments or gates. The detection window is segmented to accept gamma signals only during specific time intervals corresponding to the expected arrival time of neutrons that have interacted with the target. This temporal segmentation effectively filters out noise gamma rays that arrive at different times, improving signal discrimination while maintaining an adequate total signal count through optimized gate timing.
3Reliability
If the gamma detector is always ON to capture all signals, then no signal information is lost, but noise interference from nuisance gamma rays significantly degrades detection accuracy
Solution Approach 1:
The patent applies preliminary action by pre-synchronizing the gamma detector's operation with the neutron pulse timing before the actual interrogation begins. The detector is programmed with predetermined time gates based on the known time-of-flight characteristics of neutrons to the target and back. This preliminary timing configuration ensures that only signals arriving within the expected time window are detected, eliminating the need for post-processing noise filtering and preserving signal information while rejecting noise.
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 significantly improves the signal-to-noise ratio by ensuring that only gamma rays of interest are detected when the neutron source is active, reducing noise interference and enabling faster and more accurate identification of substances.
Implementation Method 1
a neutron source having power ON and OFF modes and operable in its ON mode to emit neutrons
Implementation Method 2
The travel time of the emitted neutrons to the target defines a neutron time of flight (NTOF)
Implementation Method 3
The use of emitted neutrons to identify substances of interest in distant targets is an emerging technology... The detection and analysis of gamma rays returning from the target enable a determination whether the target or its immediate surroundings contain significant concentrations of the substance(s) of interest
Data Source
AI summary
Method and apparatus for minimizing signal noise (20, 22) in thermal, epithermal, and cold neutron fluorescence processes using neutron flux modulation and gamma ray detector pulse gating synchronized to neutron time of flight (NTOF). The apparatus includes a source (12) of thermal, epithermal, and/or cold neutrons, optionally switched between flux or power settings in various embodiments, a gamma ray detector (14) or detection system capable of either being turned ON and OFF, in some embodiments, or else being told to regard or disregard gamma ray signals (20, 22) in other embodiments, a control mechanism (24), and either a target range detector (26) or a prior measurement of target range, in embodiments where the range remains fixed. The gamma ray detector (14) is synchronized to the NTOF by the control mechanism (24) so that it remains switched OFF during the pulse period of the neutron source (12) and for the subsequent NTOF so that any nuisance signals (20, 22) arriving at the detector (14) during these times are not detected or considered.