Composite gamma-neutron detection system
View Patent ↗The present invention provides a gamma-neutron detector based on mixtures of thermal neutron absorbers that produce heavy-particle emission following thermal capture. The detector consists of one or more thin screens embedded in transparent hydrogenous light guides, which also serve as a neutron moderator. The emitted particles interact with the scintillator screen and produce a high light output, which is collected by the light guides into a photomultiplier tube and produces a signal from which the neutrons are counted. Simultaneous gamma-ray detection is provided by replacing the light guide material with a plastic scintillator. The plastic scintillator serves as the gamma-ray detector, moderator and light guide. The neutrons and gamma-ray events are separated employing Pulse-Shape Discrimination (PSD). The detector can be used in several scanning configurations including portal, drive-through, drive-by, handheld and backpack, etc.
1. A system for detection of neutrons and gamma rays, comprising:
a plurality of scintillator screens comprising thermal neutron absorber materials, said materials interacting with neutrons to emit heavy particles, and said heavy particles interacting with scintillator screens to produce light,
a plurality of light guides into which said scintillator screens are embedded, said light guides serving as a neutron moderating medium,
a first photodetector which receives the produced light through said light guides, and converts the light to a measurable signal,
a plastic scintillator for producing light on interaction with gamma-rays,
a reflector placed between said plastic scintillator and said scintillator screens to prevent cross-contamination between optical signals from the neutron and gamma detection materials, wherein the reflector is positioned in parallel to said plastic scintillator and said scintillator screens,
a second photodetector which collects the produced light from said plastic scintillator, and converts the light to a measurable signal, and
a first counter and a second counter for counting pulses generated by the first photodetector and the second photodetector, respectively.
2. The system of claim 1 wherein the second counter is a Multi-Channel Analyzer (MCA) that is used to measure the spectra of the gamma rays.
3. The system of claim 1 , wherein the thermal neutron absorber materials comprise 6 Li or 10 B.
4. The system of claim 1 , wherein said plastic scintillator comprises of polyvinyl toluene (PVT).
5. The system of claim 1 further comprising a Pulse-Shape Discrimination (PSD) circuit that separates the neutron and gamma-ray events measured by the first photodetector.
6. The system of claim 1 , wherein the plurality of scintillator screens comprise silver activated zinc sulfide (ZnS(Ag)) phosphorous.
7. The gamma-neutron detector of claim 1 wherein each of the plurality of scintillator screens comprise neutron sensitive material having a density of up to 30% by volume of the scintillator screen.
8. The system of claim 1 wherein the plastic scintillator comprises at least one of an organic solid scintillator, an inorganic solid scintillator, or a liquid scintillator positioned between glass layers.
9. The system of claim 1 further comprising a second gamma-sensitive scintillation panel.
10. The system of claim 9 wherein the plastic scintillator and second gamma-sensitive scintillation panel are thicker than each of said plurality of scintillator screens.
11. The system of claim 9 wherein the plastic scintillator and second gamma-sensitive scintillation panel have a faster decay time than the neutron detector.
12. The system of claim 9 wherein the plastic scintillator, second gamma sensitive scintillation panels and at least one neutron detector are angled relative to a direction of incoming radiation.
13. The system of claim 1 wherein pulse shapes of the generated measurable signals are analyzed to discriminate between gamma interactions and neutron interactions.
14. A portal gantry detection system having a top, right, and left side wherein said top, left, and right sides each comprise the system of claim 1 .
15. A mobile detection system comprising a boom wherein said boom comprises the system of claim 1 .