Lithium-doped plastic neutron multiplicity counter and systems and methods thereof

Abstract

The present disclosure relates to a modular, lithium-doped, solid state, organic neutron multiplicity counter apparatus. In some embodiments the apparatus makes use of at least one lithium-doped, solid state, organic scintillator detector element. A readout device is included which is coupled to the lithium-doped, solid state, organic scintillator detector element for collecting information received by the lithium-doped, solid state, organic scintillator detector element. The lithium-doped neutron multiplicity counter apparatus is sensitive to thermal neutrons, fast neutrons and gamma-rays for carrying out neutron multiplicity counting.

Description

LLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POALITHIUM-DOPED PLASTIC NEUTRON MULTIPLICITY COUNTER AND SYSTEMS AND METHODS THEREOFCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a PCT International Application of United States Patent Application No. 63 / 702,918 filed on October 3, 2024. The entire disclosure of the above application is incorporated herein by reference.FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the United States Department of Energy and Lawrence Livermore National Security, LLC for the operation of Lawrence Livermore National Laboratory.FIELD

[0003] The present disclosure relates to multiplicity detectors used to detect for the presence and configuration of special nuclear materials, and more particularly to a highly portable neutron multiplicity counter which is able to directly detect thermal neutrons, fast neutrons and gamma rays, without the use of high voltages for its operation.BACKGROUND

[0004] This section provides background information related to the present disclosure which is not necessarily prior art.

[0005] When assessing an unknown configuration of special nuclear material (SNM), it is important to be able to understand whether there are immediate criticality safety concerns and to assess the unknown material. A neutron multiplicity counter does not simply record that a neutron was counted, but also when it was counted. This pattern of neutron arrival times can inform analysis of SNM size and configuration through the amount of the spontaneously-fissioning isotope and multiplication M (equivalent to ken). As an example of the current state of the art, the MC-15 Portable Neutron Multiplicity Detector relies on pressurized3He tubes nested in high-density polyethylene (HDPE) and is only sensitive to thermal neutrons. By contrast, the instant disclosure below describes a Li-LLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA loaded plastic multiplicity counter (referred to herein as the “MC-Li”) that is lightweight (e.g., under 30 lbs.), uses low-power Silicon Photomultipliers (SiPMs) instead of Photomultipliers (PMTs), and has sensitivity to thermal neutrons, fast neutrons, and gamma-rays that can be time-correlated to discrete events: fission chain neutron capture, fission chain neutron scattering, and gamma-rays direct from fission.

[0006] As mentioned above, an example of the current state of the art relies on pressurized3He tubes nested in HDPE and is only sensitive to thermal neutrons. Users need a rugged, modular, lightweight neutron multiplicity counter that can be right sized for any particular use case to more easily facilitate getting the multiplicity counter to the location of the unknown configuration of material. The multiplicity counter according to the instant disclosure addresses these challenges and others.SUMMARY

[0007] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0008] In one aspect the present disclosure relates to a modular, lithium-doped neutron multiplicity counter apparatus. The apparatus may comprise at least one lithium- doped, solid state, organic scintillator detector element responsive to neutrons and gamma rays. The apparatus may also comprise a readout device coupled to the at least one lithium- doped solid state, organic scintillator detector element for collecting neutron and gamma ray information received by the at least one lithium-doped solid state organic scintillator detector element. The lithium-doped neutron multiplicity counter apparatus is sensitive to thermal neutrons, fast neutrons and / or gamma-rays for carrying out neutron multiplicity counting.

[0009] In another aspect of the present disclosure the readout device comprises a SIPM.

[0010] In another aspect of the present disclosure the at least one lithium-doped scintillator detector element comprises a lithium-doped, solid state organic scintillator detector element.

[0011] In another aspect of the present disclosure the at least one lithium-doped scintillator detector element comprises a lithium-doped, solid state organic scintillator detector element having at least one of a square or rectangular cross section.LLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA

[0012] In another aspect of the present disclosure the at least one lithium-doped, solid state, organic scintillator detector element has a first end and a second end opposite the first end, and wherein the readout device comprises a silicon photomultiplier readout device coupled at one of the first end or the second end.

[0013] In another aspect of the present disclosure the readout device comprises a first silicon photomultiplier coupled at the first end and a second silicon photomultiplier coupled at the second end.

[0014] In another aspect of the present disclosure the at least one lithium-doped, solid state, organic scintillator detector element comprises a plurality of similarly shaped, parallel arranged, lithium-doped scintillator detector elements forming a modular panel-like configuration enabling removal and replacement of one or more of the lithium-doped, scintillator detector elements.

[0015] In another aspect of the present disclosure the apparatus further comprises a digital acquisition system in communication with the readout device for performing neutron multiplicity counting and recording a time of arrival for neutrons detected by the lithium-doped, solid state, organic scintillator detector element.

[0016] In another aspect of the present disclosure the apparatus further comprises a centralized digital acquisition system in communication with the first and second silicon photomultipliers, for analyzing the information obtained by the first and second silicon photomultipliers.

[0017] In another aspect of the present disclosure the apparatus further comprises a computer in communication with the digital acquisition system.

[0018] In another aspect of the present disclosure the apparatus further comprises a display device for visually displaying data relating to the information obtained by the readout device.

[0019] In another aspect of the present disclosure the apparatus further comprises a DC voltage generating subsystem for generating a DC voltage applied to the at least one lithium-doped, solid state, organic scintillator detector element.

[0020] In another aspect the present disclosure relates to a modular, lithium- doped neutron multiplicity counter apparatus. The apparatus may comprise a sensing subsystem including a plurality of parallel arranged, elongated, lithium-doped, solid state, organic plastic scintillator detector bars each having a first end and a second end. The apparatus may also comprise at least one silicon photomultiplier (SiPM) positioned adjacentLLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA a first end of the sensing subsystem. At least one of the plurality of parallel arranged, elongated, lithium-doped, solid state, organic plastic scintillator bars may be interchangeably removable to enable modularity and reconfigurability of the sensing subsystem. The apparatus is sensitive to thermal neutrons, fast neutrons, and gammarays.

[0021] In another aspect of the present disclosure the apparatus further comprises an additional silicon photomultiplier positioned adjacent the second end of the sensing subsystem.

[0022] In another aspect of the present disclosure the apparatus further comprises a centralized data acquisition system in communication with the silicon photomultiplier and the additional silicon photomultiplier, for analyzing neutron and gamma ray related information provided by the silicon photomultiplier and the additional silicon photomultiplier.

[0023] In another aspect of the present disclosure the apparatus comprises a computer in communication with the centralized data acquisition system.

[0024] In another aspect of the present disclosure the apparatus comprises a display responsive to at least one of the computer or the data acquisition system for displaying neutron multiplicity counting data to a user.

[0025] In still another aspect the present disclosure relates to a method for detecting and coincidence counting neutrons and gamma rays emitted from a special nuclear material. The method may also comprise using a lithium-doped, solid state, organic neutron sensitive detector to detect arrivals of fast neutrons, thermal neutrons and gamma rays emitted from the special nuclear material. The method may involve collecting information pertaining to arrival times of the fast neutrons and the thermal neutrons detected by the lithium-doped, solid state, organic neutron sensitive detector. The method may also involve using an analysis subsystem to analyze the collected information using a neutron coincidence counting operation to identify an existence of the special nuclear material as well as information relating to at least one of a physical size or characteristic of the special nuclear material.

[0026] In another aspect of the present disclosure using the lithium-doped, solid state, organic neutron sensitive detector comprises using a plurality of adjacent, parallel arranged, elongated, solid state, organic lithium-doped plastic bars to receive the fast neutrons, the thermal neutrons and the gamma rays.LLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA

[0027] In another aspect of the present disclosure the method comprises using selectively removable adjacent, parallel arranged, elongated, solid state, organic lithium- doped plastic bars which are selectively removable to create a modular, reconfigurable detector panel.

[0028] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. Reference numerals indicate corresponding parts throughout the several views of the drawings in which:

[0030] Figure 1 is a high level block diagram of one embodiment of a neutron multiplicity counter system in accordance with the present disclosure;

[0031] Figure 2 is a perspective view of one example of the neutron multiplicity counter shown in Figure 1 ;

[0032] Figure 3 is a perspective view of the neutron multiplicity counter of Figure 2 but with a cover panel removed to reveal the detector elements arranged therewithin;

[0033] Figure 4 is a plan view of another embodiment of a neutron detector panel in accordance with the present disclosure where each of the detector elements has a square shape;

[0034] Figure 5 is a plan view of another embodiment of a neutron detector panel in accordance with the present disclosure where differently sized and shaped detector elements are used to form a single detector panel; and

[0035] Figure 6 is a graph showing a graph illustrating a distribution of thermal neutrons, fast neutrons and gamma rays based on the pulse shape of their waveforms.DETAILED DESCRIPTION

[0036] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0037] The present disclosure relates to a neutron and gamma ray detection system which has sensitivity to both thermal and fast neutrons. It will be appreciatedLLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA immediately that at the present time, it is believed that there is no commercial neutron multiplicity counter that has sensitivity to both thermal and fast neutrons through direct interactions using a homogeneous detection medium material. Other multiplicity counters rely on thermalization to try to detect fast neutrons, whereas the systems and methods described herein can detect thermal neutrons directly through neutron capture and fast neutrons through proton recoil. Additionally, X, Y can be reconstructed through which individual bar fires, while the Z information is identified through the dual ended readout feature, providing some level of imaging not possible with other neutron multiplicity counters.

[0038] The systems and methods described herein operate by sensing neutrons through either scintillation emission from proton recoils or neutron captures on Lithium. Gamma-rays can also be detected using the systems and methods described herein from Compton scatters. Light emitted from particle interactions will travel to a detector system described herein, where the amount of light is directly proportional to the energy. These components within the detector system (e.g., acting as photosensors) will send a signal to a data acquisition system (e.g., DAQ or ASICS / FPGA combination). Additionally, particle types are discriminated using pulse shape discrimination (“PDS”) where waveform analysis can be used to evaluate the ratio of relayed light relative to prompt light as a function of energy through a standard Qtail / Qtotal analysis or by using a Gaussian mixture model to identify particles as fast neutrons, thermal neutrons, and gamma-rays. A central small computer may interface with the data acquisition system or ASICS / FPGA combination, and a small screen may be provided to visualize neutron multiplicity events and neutron correlations to provide real time assessments of unknown items.

[0039] Referring to Figure 1 , one example of a neutron multiplicity counter system 10 is shown in accordance with the present disclosure. The system 10 in this example includes a new Lithium-based multiplicity counter 12, which will be referred to hereafter simply as the “MC-Li” system 12. The MC-Li system 12 in this example has a plurality of Li-doped plastic scintillator detector elements 12i-12e stacked adjacent to one another, which in one example are shaped like rectangular elongated bars, and which form a neutron and gamma ray sensing subsystem. Collectively, the detector elements 12i-12e form what may be viewed as a neutron and gamma ray detector component 13.

[0040] In one example, as shown in Figure 1 , the MC-Li system 12 also has dual data readout subsystems 12a and 12b arranged on opposing sides of the detector elementsLLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA12i-126. The dual data readout subsystems 12a and 12b, in one embodiment, may be low power silicon photomultipliers (“SIPMs”), and will be referred to throughout the following discussion as the “SIPMs 12a and 12b”.

[0041] In one embodiment the SIPMs 12a and 12b may both be in communication with a centralized data acquisition subsystem (hereinafter “DAQ”) 14. In some embodiments an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA) may be used as a data acquisition system. In another embodiment separate DAQs may be coupled to the SIPMs 12a and 12b. In another embodiment a computer 16 or suitable electronic processor (hereinafter simply “computer” 16) may be in communication with the DAQ 14. In one embodiment the DAQ 14 includes a position sensitive detector (PSD) for assisting in the analysis of thermal neutrons and fast neutrons. If included, the computer 16 may include a memory 18 (e.g., non-volatile RAM / ROM, etc.) which stores a database 20 of information helpful or needed for operation of the system 10, as well as algorithms and / or software modules 22 helpful or needed for operating the system 10 and evaluating data obtained from the MC-Li 12. A DC voltage generating subsystem 24 may be included for applying a DC input voltage to the MC-Li system 12.

[0042] The detector elements 12i-12e may take a wide variety of shapes and dimensions, but in one example each detector element has an elongated, square cross- sectional configuration resembling a tube, a circular cross section is also permited. The detector elements 12i-12e are also shown in Figures 2 and 3, wherein in Figure 3 a cover panel 13a is removed from a frame portion 13b to reveal the detector elements within a detector panel 13’. In one specific embodiment each detector element 12i-12e has dimensions of about 5.5 cm x 5.5 cm x 48 cm (about 2.16” x 2.16” x 18.9”) which form a single detector “panel” having dimensions of about 33 cm tall x 48 cm wide x 5.5 cm thick (i.e., about 13” tall x 18.9” wide x 2.16” thick). In one embodiment each of the detector elements 12i-12e is formed from plastic doped with Lithium. Again, however, a greater or lesser number of the detector elements may be used to meet the needs of specific applications, and the present disclosure is not limited to the use of only six detector elements. For example, in some embodiments the detector elements may be square shaped, as shown in the detector panel 13’ of Figure 4. Figure 5 shows another embodiment where a mixture of differently shaped detector elements are used which form a detector panel 13”.LLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA

[0043] For any of the above described detector panels 13, 13’ or 13”, the detector elements used may be made from a lithium-doped, suitable scintillating plastic, for example and without limitation, EJ-299-50. In other embodiments the plastic may be EJ-270, or lithium doped in any amorphous organic scintillator such as plastic or glass, for example, and the present disclosure is not limited to using detectors formed from only one specific type of plastic.

[0044] It will also be appreciated that the overall shape and configuration of the MC-Li system 12 may vary widely, and is not limited to the rectangular, panel-like configuration shown in Figures 2 and 3. In addition, two or more of the MC-Li systems 12 may be disposed adjacent to one another to form a three dimensional, cube-like configuration, rather than a one dimensional, panel-like configuration. This could create a calorimeter for neutron spectroscopy or allow a higher efficiency to fast neutrons.

[0045] It will be appreciated that the above dimensions for the detector elements 12i-126may vary considerably to meet the needs of a specific application. A significant advantage of the MC-Li 12 system is that it is modular, which allows additional detector elements to be added or subtracted, if desired, to tailor the MC-Li system 12 for a desired application, specific form factor and / or areal coverage.

[0046] Another significant advantage of the MC-Li system 12 described herein is that it provides its detection capability using only a single row (i.e., one-dimensional panel) of detector elements 12i-12e, which form a single panel detector (i.e., versus a plurality of rows which form a plurality of adjacent panels of detectors, which would form a cube-like configuration. Previously constructed neutron detectors typically have required the use of row ratios (i.e., multiple rows of detectors) to identify the level of moderation. However, the MC-Li system 12 of the instant disclosure provides the same understanding by taking a ratio of the fast neutrons to the thermal neutrons in situ from the PSD 14a. Therefore, this feature removes the need for two rows (i.e., just a single row of vertically stacked, homogenous detector elements 12i-12e), thus enabling a significantly smaller, lighter-weight detector having a configuration of a panel rather than a 3D configuration.

[0047] In the embodiment shown in Figure 1 , the MC-Li 12 system comprises one detector panel 13 that contains one (1 ) row of six (6) plastic detector elements or bars 12i- 126. In one embodiment the geometry of the MC-LI 12 may be selected to replicate the cross-sectional area of existing multiplicity counters, while each detector element 12i-12e is selected to maximize coverage with the SiPM. Each detector element 12i-12e is read outLLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA using the dual ended SiPMs 12a and 12b, thus allowing for X, Y, Z interaction information. In one embodiment the centralized DAQ 14 may be a CAEN DT2730, commercially available from CAEN S.p.A. of Viareggio, Italy. The detector is designed to be modular, such that a user can add or remove bars depending on the desired form factor and areal coverage. Users of the current state of the art typically use row ratios to identify the level of moderation. However, the detector of the instant disclosure provides the same understanding by taking a ratio of the fast neutrons to the thermal neutrons in situ from the PSD.

[0048] For passive characterization of an unknown configuration of material, sensitivity to both fast and thermal neutrons can determine both the total multiplication and the prompt multiplication. Prompt multiplication is especially helpful given the elegant, closed-form analytic formula that relates material geometric configuration. The present system 10 uses fission chain restart theory, which allows for a far more detailed analysis than a basic Bohnel theory against which prior detectors are analyzed. Large amounts of moderator greatly diminish the neutron emissions. When a neutron is lost, there is a gain in gamma-ray, and the acquisition of that gamma-ray preserves the timing information from the parent neutron. The gamma-rays that result from neutron capture are surrogates for thermal neutrons. Inelastic scattering offers further information: these gamma-rays are surrogates for fast neutrons. A sensitivity to high-energy neutron capture gamma-rays makes the assay of large, highly moderated configurations of material possible while inelastic scatter gamma-rays can augment sensitivity to fast neutrons.

[0049] As mentioned above, the Li-loaded plastic multiplicity counter MC-Li 10 according to the instant disclosure is lightweight, and in some embodiments may weigh only about 7 kg (e.g., 15 lbs.). The MC-Li 12 in some embodiments uses low-power SiPMs, typically 50 V - 100 V per detector element 12i-12e. Thus, this feature removes the need for two rows of detector elements, enabling a smaller, slimmer, lighter-weight detector. The low voltage requirement of the SIPM 12 also facilitates in-field maintenance and repair.

[0050] The MC-L1 12 system provides detector elements 12i -12& which have triple PSD capable material, and more specifically which are sensitive to thermal neutrons, fast neutrons, and gamma-rays. Advantageously the MC-Li 12 removes the need for the use of HDPE or Cd, and the use of dual SiPMs 12a and 12b readouts enables XYZ neutron moderation sensitivity.LLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA

[0051] Although the SIPMs 12a and 12b, and the DAQ 14, described herein are expected to be especially popular, the present disclosure is not limited to these components. For example, the detector elements 12i-12e may be nominal design includes 6 Li-doped plastic bars, SiPMs, and a centralized DAQ the conceptual innovation also includes the ability to use any scintillating plastic in various configurations (thinner or shorter bars), coupled to various choices for the photosensors (SIPM, PMTs, etc.), and various electronics such as a centralized data acquisition system, and ASCIS and FPGA-based readout. The product will also include a small computer and screen display to give operators real time evaluation of the unknown item and save data that can be transmitted to others for further analysis.

[0052] Referring to Figure 6, a pulse shape discrimination plot 400 is shown from a Li-doped PSD plastic detector with dual ended SiPM readout, such as that similar or identical to the system 10 of Figure 1. Clear features demonstrate sensitivity to thermal neutrons and fast neutrons while also identifying gamma-rays. Information on the level of moderation can be gleaned with only one row of material (i.e., from just a one-dimensional detector panel such as detector panel 13 of Figure 1 ). By placing cuts on the thermal neutron island and the fast neutron band, the ratio of the two can provide the level of moderation.

[0053] Although the description contains many details and specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the present exemplary embodiments thereof. Other implementations, enhancements and variations can be made based on what is described and illustrated in this document. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products. Certain features that are described in this document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that suchLLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA operations be performed in the particular order shown or in a sequential order, or that all illustrated operations can be performed, to achieve desirable results. Moreover, the separation of various system or apparatus components in the embodiments described above should not be understood as requiring such separation in all embodiments.

[0054] Therefore, it will be appreciated that the scope of the instant disclosure fully encompasses other embodiments which may become obvious to those skilled in the art. In the claims, reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above-described exemplary embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device to address each and every problem sought to be solved in order that it be encompassed by the present claims. Furthermore, no element or component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.” Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0055] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not toLLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0056] When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0057] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0058] Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Claims

LLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POACLAIMSWhat is claimed is:1 . A modular, lithium-doped neutron multiplicity counter apparatus, comprising: at least one lithium-doped, solid state, organic scintillator detector element responsive to neutrons and gamma rays; a readout device coupled to the at least one lithium-doped solid state, organic scintillator detector element for collecting neutron and gamma ray information received by the at least one lithium-doped solid state organic scintillator detector element; wherein the lithium-doped neutron multiplicity counter apparatus is sensitive to thermal neutrons, fast neutrons and / or gamma-rays for carrying out neutron multiplicity counting.

2. The apparatus of claim 1 , wherein the readout device comprises a silicon photomultiplier (SIPM).

3. The apparatus of claim 1 , wherein the at least one lithium-doped scintillator detector element comprises a lithium-doped, solid state organic scintillator detector element.

4. The apparatus of claim 3, wherein the at least one lithium-doped scintillator detector element comprises a lithium-doped, solid state organic scintillator detector element having at least one of a square, rectangular, circular, or cylindrical cross section.

5. The apparatus of claim 1 , wherein the at least one lithium-doped, solid state, organic scintillator detector element has a first end and a second end opposite the first end, and wherein the readout device comprises a silicon photomultiplier readout device coupled at one of the first end or the second end.

6. The apparatus of claim 5, wherein the readout device comprises a first silicon photomultiplier coupled at the first end and a second silicon photomultiplier coupled at the second end.LLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA7. The apparatus according to claim 1 , wherein the at least one lithium-doped, solid state, organic scintillator detector element comprises a plurality of similarly shaped, parallel arranged, lithium-doped scintillator detector elements forming a modular panel-like configuration enabling removal and replacement of one or more of the lithium-doped, scintillator detector elements.

8. The apparatus of claim 1 , further comprising a digital acquisition system in communication with the readout device for performing neutron multiplicity counting and recording a time of arrival for neutrons detected by the lithium-doped, solid state, organic scintillator detector element.

9. The apparatus of claim 6, further comprising a centralized digital acquisition system in communication with the first and second silicon photomultipliers, for analyzing the information obtained by the first and second silicon photomultipliers.

10. The apparatus of claim 8, further comprising a computer in communication with the digital acquisition system.1 1 . The apparatus of claim 1 , further comprising a display device for visually displaying data relating to the information obtained by the readout device.

12. The apparatus of claim 1 , further comprising a DC voltage generating subsystem for generating a DC voltage applied to the at least one lithium-doped, solid state, organic scintillator detector element.

13. A modular, lithium-doped neutron multiplicity counter apparatus, comprising: a sensing subsystem including a plurality of parallel arranged, elongated, lithium- doped, solid state, organic plastic scintillator detector bars each having a first end and a second end; at least one silicon photomultiplier (SiPM) positioned adjacent a first end of the sensing subsystem;LLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA at least one of the plurality of parallel arranged, elongated, lithium-doped, solid state, organic plastic scintillator bars being interchangeably removable to enable modularity and reconfigurability of the sensing subsystem; and wherein the apparatus is sensitive to thermal neutrons, fast neutrons, and gammarays.

14. The apparatus of claim 13, further comprising an additional silicon photomultiplier positioned adjacent the second end of the sensing subsystem.

15. The apparatus of claim 14, further comprising a centralized data acquisition system in communication with the silicon photomultiplier and the additional silicon photomultiplier, for analyzing neutron and gamma ray related information provided by the silicon photomultiplier and the additional silicon photomultiplier.

16. The apparatus of claim 15, further comprising a computer in communication with the centralized data acquisition system.

17. The apparatus of claim 16, further comprising a display responsive to at least one of the computer or the data acquisition system for displaying neutron multiplicity counting data to a user.

18. A method for detecting and coincidence counting neutrons and gamma rays emitted from a special nuclear material, the method comprising: using a lithium-doped, solid state, organic neutron sensitive detector to detect arrivals of fast neutrons, thermal neutrons and gamma rays emitted from the special nuclear material; collecting information pertaining to arrival times of the fast neutrons and the thermal neutrons detected by the lithium-doped, solid state, organic neutron sensitive detector; using an analysis subsystem to analyze the collected information using a neutron coincidence counting operation to identify an existence of the special nuclear material as well as information relating to at least one of a physical size or characteristic of the special nuclear material.LLNL Ref.: IL-13942-PCT JT / TDHDP Ref.: 16336-000251 -WO-POA19. The method of claim 18, wherein using a lithium-doped, solid state, organic neutron sensitive detector comprises using a plurality of adjacent, parallel arranged, elongated, solid state, organic lithium-doped plastic bars to receive the fast neutrons, the thermal neutrons and the gamma rays.

20. The method of claim 19, wherein one or more of the plurality of adjacent, parallel arranged, elongated, solid state, organic lithium-doped plastic bars are selectively removable to create a modular, reconfigurable detector panel.

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