Neutron Detector Fluence Measurement via Prompt-Delayed Event Segmentation
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Solution Overview
Problem
Current neutron detection systems face challenges in accurately measuring high-energy neutron fluence due to dead-time effects, particularly in high flux densities, which lead to underestimation of the actual flux density and incorrect determination of equivalent dose in radiation protection applications.
Innovation Solution
A method involving a neutron detector with a carbon-containing moderator and a counter tube, where events are recorded and analyzed over time intervals, using a decay law to evaluate the number of high-energy neutrons by accounting for the generation and decay of low-energy neutrons from high-energy interactions, allowing for the determination of fluence without dead-time influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a neutron detector with moderator and counter tube is used to detect high-energy neutrons, then the detection capability is improved, but dead-time effects cause underestimation of flux density at high flux densities
Solution Approach 1:
The measurement process is segmented into multiple time intervals (first time interval for prompt events, second time interval for delayed events). By dividing the measurement into temporal segments, the system can distinguish between different types of neutron interactions and avoid dead-time effects in the prompt event measurement, while still capturing the total flux through the delayed events.
Solution Approach 2:
The system performs preliminary measurement of prompt events in the first time interval, then uses this information to correct the measurement by adding the delayed events from the second time interval. This preliminary action allows the system to account for dead-time effects before finalizing the flux density calculation.
2Productivity
If the detector processes events quickly to maintain high count rate, then productivity is improved, but dead-time effects increase causing underestimation of flux density
Solution Approach 1:
The system uses periodic time intervals to separate prompt event measurement from delayed event measurement. By implementing periodic action with distinct time windows, the system can maintain high productivity in prompt event processing while periodically accounting for delayed events to ensure measurement precision.
3Reliability
If the detector uses a lead intermediate layer to thermalize high-energy neutrons, then the detection of low-energy neutrons is improved, but the generation of low-energy neutrons causes dead-time effects in the counter tube
Solution Approach 1:
The measurement is segmented into two temporal phases: prompt events (first time interval) and delayed events (second time interval). This segmentation allows the system to distinguish between neutrons detected directly and those thermalized in the lead layer, enabling accurate flux density measurement despite the dead-time effects introduced by the lead intermediate layer.
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 enables reliable and accurate measurement of high-energy neutron fluence by distinguishing between prompt and delayed events, correcting for dead-time underestimation and providing a proportional counter value that accurately represents the high-energy neutron flux, thus ensuring a correct determination of equivalent dose.
Implementation Method 1
high-energy neutrons can carry out so-called inelastic scattering processes, as a result of which low-energy neutrons are generated
Implementation Method 2
Thermal neutrons can be detected by nuclear reactions such as 3He(n,p)3H and 10B(n,α)7Li
Implementation Method 3
the fast neutrons can also be detected 'directly' in such a way that they carry out elastic collisions with the nuclei of the counting gas in a proportional counter, as a result of which protons are knocked out of the nuclei
Implementation Method 4
In a detector, each neutron pulse generated at a distance from the detector by a loss event is associated with so-called 'prompt' and 'delayed' events. Prompt events are caused by neutrons that were not slowed down on their way to the detector and thus essentially hit the detector at the time of the loss event. The delayed events come about as a result of thermal neutrons or neutrons thermalized on their way to the detector and occur in the detector at a time interval of 2 to 3 ms relative to the loss event.
Data Source
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AI summary
The invention relates to a method for measuring the number of strikes of high-energy neutrons in a predetermined detection volume. The aim of determining the flow of high-energy neutrons is achieved by a method comprising the following steps: provision of a neutron detector (1) comprising a moderator device (2), which is composed of a material containing carbon and a counting tube (4) that is filled with counting gas, said counting tube (4) being configured to detect neutrons; a measurement is carried out, during which the number of events that occur in the counting tube (4) are determined as temporal functions; a start time (S1, S2, S3) is defined; an evaluation time window (f1) is defined after the start time; the events that have been measured in the evaluation time window (f1) are evaluated and a counter value is output, said value being dependent on the number of strikes of high-energy neutrons in the detector at the start time (S1, S2, S3) and on the result of the evaluation.