Composite gamma-neutron detection system

• US 8,389,941 B2
• Filed: 12/22/2010
• Issued: 03/05/2013
• Est. Priority Date: 06/11/2008
• Status: Active Grant

• Current Assignee: Rapiscan Systems Incorporated (OSI Systems Incorporated)
• Original Assignee: Rapiscan Systems Incorporated (OSI Systems Incorporated)
• Inventors: Bendahan, Joseph, Morton, Edward James
• Primary Examiner(s): Kim, Kiho
• Application Number:
  US12/976,861
• Publication Number:
  US 20110204243A1
• Time in Patent Office: 804 Days
• Field of Search: 25039001-39012, 250391-395, 2502691-2698
• US Class Current: 250/363.02
• CPC Class Codes: G01T 1/16 Measuring radiation intensity G01T1/29 takes precedence ; self-powered detectors G01T3/006; using an ionisation chamber filled with a liquid or solid, e.g. frozen liquid, dielectric G01T3/008
• CPC Class Codes: G01T 1/167 Measuring radioactive content of objects, e.g. contamination whole body counters G01T1/163
• CPC Class Codes: G01T 1/208 Circuits specially adapted for scintillation detectors, e.g. for the photo-multiplier section
• CPC Class Codes: G01T 3/06 with scintillation detectors
• CPC Class Codes: G01V 5/222 measuring scattered radiation
• CPC Class Codes: G01V 5/281 detecting special nuclear material [SNM], e.g. Uranium-235, Uranium-233 or Plutonium-239
• CPC Class Codes: H01J 40/04 Electrodes
• CPC Class Codes: H01J 43/08 Cathode arrangements construction of photo cathodes H01J40/06, H01J40/16, H01J47/00, H01J49/08
• CPC Class Codes: H01J 43/18 Electrode arrangements using essentially more than one dynode
• CPC Class Codes: H01J 43/30 Circuit arrangements not adapted to a particular application of the tube and not otherwise provided for

Abstract

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.

Claims

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 ⁶Li or ¹⁰B.

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.