Scintillation Detector Pulse Shape Discrimination
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Solution Overview
Problem
Current radiation measurement devices for homeland security applications require multiple detectors to measure gamma and neutron radiation, making them bulky and complex, especially for detecting fast neutrons, which are difficult to detect using small portable instruments.
Innovation Solution
A method utilizing a single scintillation crystal detector with pulse shape discrimination capabilities, capable of distinguishing between gamma radiation and fast neutrons by analyzing light decay times, and optionally using a Li-Glass window for thermal neutron detection, allowing for a lightweight, portable handheld device to measure both types of radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple detectors are used to detect both gamma radiation and neutrons, then the detection capability is improved, but the device complexity and size increase
Solution Approach 1:
The patent combines gamma radiation detection and neutron detection into a single scintillation detector by using a dual-layer crystal structure. The first scintillation crystal layer detects gamma radiation while the second scintillation crystal layer detects neutrons through nuclear reactions, eliminating the need for separate detectors and reducing overall device complexity.
Solution Approach 2:
The scintillation detector is designed to perform multiple detection functions simultaneously - it can detect both gamma radiation and neutrons using the same detector assembly. This is achieved by utilizing different interaction mechanisms within the scintillation crystal layers, allowing one detector to replace what would traditionally require multiple specialized detectors.
2Weight of moving object
If a scintillation crystal is used for neutron detection, then the device portability is improved, but the ability to distinguish neutron signals from gamma signals deteriorates
Solution Approach 1:
The scintillation detector is divided into two distinct crystal layers with different properties. The first layer is optimized for gamma detection while the second layer contains isotopes with high neutron interaction cross-sections. This segmentation allows each layer to specialize in detecting specific radiation types, improving signal discrimination while maintaining portability.
Solution Approach 2:
Different regions of the scintillation detector have different material compositions tailored to specific detection needs. The second crystal layer incorporates isotopes like lithium-6 or boron-10 that have high neutron interaction cross-sections, creating local regions optimized for neutron detection while other regions remain optimized for gamma detection.
3Productivity
If a single isotope with large neutron interaction cross-section is used, then the neutron detection efficiency is improved, but the gamma radiation detection capability is reduced
Solution Approach 1:
The detector uses separate crystal layers where the first layer maintains high gamma detection efficiency with standard scintillation materials, while the second layer incorporates isotopes with high neutron interaction cross-sections. This segmentation allows each layer to optimize for its specific detection target without compromising the other capability.
Solution Approach 2:
The scintillation detector employs composite material structure with two different crystal layers. The first layer uses conventional scintillation material for gamma detection, while the second layer uses composite materials containing neutron-sensitive isotopes embedded in a scintillation matrix, allowing both detection functions to coexist with optimized performance.
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
Enables the detection of both fast neutrons and gamma radiation with high count rates in a compact, portable device, leveraging advanced digital signal processing and pulse shape analysis to separate and measure radiation types effectively, even in high-dose scenarios necessary for homeland security.
Implementation Method 1
Gamma radiation entering the scintillation crystal, is mostly absorbed or scattered by electrons within the scintillation crystal, whereby the recoil electrons recombine over time, thereby emitting light
Implementation Method 2
Connected to the window is a photo detector, mostly a PMT, measuring the amount of light seen
Implementation Method 3
fast neutrons, that is neutrons with (kinetic) energies of 500 keV and more... following a nuclear reaction
Implementation Method 4
a Li-Glass window between the scintillation crystal and the photo detector... allowing neutrons with energies of less than 1 keV - thermal neutrons - to interact with the Li-Glass
Data Source
Figure 1~3
AI summary
The invention relates to a 1. Method of measurement of both gamma radiation and neutrons with energies above 500keV - fast neutrons - for the use in home-land security applications, preferably in portable handheld devices, utilizing a scintillation crystal, said scintillation crystal having a first light decay time (T1) following the interaction of a gamma quant with the scintillation crystal and a second and shorter light decay time (T2) following the interaction of a fast neutron with the scintillation crystal, a photo detector together with an amplifier, as well as sampling Analog to Digital Converters - ADC - and a digital signal processing device including a Multi-Channel-Analyzer, said devices selected in a way they are able to perform a pulse shape discrimination, being able to distinguish light decay times of a few nanoseconds up to several microseconds, and to process count rates of more than 10 counts per second for interactions of gamma quanta and of more than 1 count per second for interactions of neutrons with the scintillation crystal, comprising the steps of allowing gamma quanta and neutrons to interact with the scintillation crystal, collecting the light, emitted by the scintillation crystal, guiding it to a glass window optically coupled to the scintillation crystal and letting that light interact with a photo detector, amplifying the signal output from the photo detector with a suitable amplifier, preferably a photomultiplier tube - PMT - thus generating an amplifier output signal, digitizing the amplifier output signal, determining the charge collection time for each interaction measured, determining the light decay time of the scintillator from said charge collection time for each interaction measured, separating the signals with a first decay time (T1) from those with a second decay time (T2), determining the total charge (Q1) collected for each signal with a first decay time (T1), that total charge being a measure for the energy deposed in the scintillation crystal, sorting said total charge signals (Q1) in a spectrum, i.e. with by using a Multi-Channel-Analyzer (MCA), said spectrum representing the energy distribution of the gamma quants having deposed at least 10 keV and therefore at least a part of their energy in the scintillation crystal, counting the signals with a second decay time (T2) and determining the count-rate, that is the number of signals per given time interval, that count rate being a measure for the number of neutrons having deposed at least part of their energy in the scintillation crystal.