Muon Tomography System Research Articles

Development of a muon detector based on a plastic scintillator and WLS fibers to be used for muon tomography system

Muon tomography is a useful method for monitoring special nuclear materials (SNMs) such as spent nuclear fuel inside dry cask storage. Multiple Coulomb scattering of muons can be used to provide information about the 3-dimensional structure and atomic number(Z) of the inner materials. Tomography using muons is less affected by the shielding material and less harmful to health than other measurement methods.We developed a muon detector for muon tomography, which consists of a plastic scintillator, 64 long wavelength-shifting (WLS) fibers attached to the top of the plastic scintillator, and silicon photomultipliers (SiPMs) connected to both ends of each WLS fiber. The muon detector can acquire X and Y positions simultaneously using a position determination algorithm.The design parameters of the muon detector were optimized using DETECT2000 and Geant4 simulations, and a muon detector prototype was built based on the results. Spatial resolution measurement was performed using simulations and experiments to evaluate the feasibility of the muon detector. The experimental results were in good agreement with the simulation results. The muon detector has been confirmed for use in a muon tomography system.

Optimization Study of a Muon Tomography System for Imaging of Nuclear Waste Containers

Optimization Study of a Muon Tomography System for Imaging of Nuclear Waste Containers

Feasibility study of a prototype muon tomography system based on a plastic scintillator and WLS fibers

Muon tomography is a technique for monitoring special nuclear material, such as uranium, inside the shielding material. It is a 3D imaging system capable of identifying atomic number (Z) using muon particles, high energy natural radiation. The following technique shows an advantage in no radiation exposure due to its usage of naturally occurring cosmic ray muons.In this study, a prototype muon tomography system was developed using four muon detectors in top and bottom structures. The four muon detectors based on a plastic scintillator and WLS fibers were implemented in the previous study. Two detectors above the target object and the other two below the target object measure a muon’s incoming and outgoing trajectories, respectively. Four detectors constituting the prototype were connected by coincidence to confirm the muon detection.The purpose of this study was to develop the prototype muon tomography system and to reconstruct the image of the high-Z material, such as lead and uranium. The performance of the prototype was confirmed by imaging under various conditions, such as measurement time, position, and thickness changes, using lead blocks. In addition, the feasibility of the prototype was verified by performing imaging using three materials with different atomic numbers, such as lead, iron, and aluminum.

A High Spatial Resolution Muon Tomography Prototype System Based on Micromegas Detector

Cosmic ray muon has strong penetrating power and no ionizing radiation hazards, which makes it an ideal probe for detecting special nuclear materials (SNMs). In this article, a high spatial resolution muon tomography system based on Micromegas detectors is proposed to optimize the imaging time and quality. The proposed system includes eight Micromegas detectors based on the thermal bonding technique and a scalable readout system. In addition, a multiplexing method based on position encoding is developed to reduce the number of electronics channels by order of magnitude. The spatial resolution of the proposed system with encoding readout can reach a value of hundred micrometers. Finally, a tomography test is performed, and test results show that this proposed system can image 2-cm objects and distinguish different materials.

Design and characterization of a Muon tomography system for spent nuclear fuel monitoring

In recent years, monitoring of spent nuclear fuel inside dry cask storage has become an important area of national security. Muon tomography is a useful method for monitoring spent nuclear fuel because it uses high energy muons that penetrate deep into the target material and provides a 3-D structure of the inner materials.We designed a muon tomography system consisting of four 2-D position sensitive detector and characterized and optimized the system parameters. Each detector, measuring 200 × 200 cm2, consists of a plastic scintillator, wavelength shifting (WLS) fibers and, SiPMs. The reconstructed image is obtained by extracting the intersection of the incoming and outgoing muon tracks using a Point-of-Closest-Approach (PoCA) algorithm.The Geant4 simulation was used to evaluate the performance of the muon tomography system and to optimize the design parameters including the pixel size of the muon detector, the field of view (FOV), and the distance between detectors. Based on the optimized design parameters, the spent fuel assemblies were modeled and the line profile was analyzed to conduct a feasibility study. Line profile analysis confirmed that muon tomography system can monitor nuclear spent fuel in dry storage container.

Numerical evaluation of a muon tomography system for imaging defects in concrete structures

Among numerous applications of muon tomography, deployment in civil structures has caught attraction of many recently. In this work, the appropriateness of muon scattering tomography to detect defects in concrete structures has been studied numerically. A few basic concrete structures that are frequently used in civil construction have been considered as test cases. A simulation has been performed on Geant4 platform where an imaging setup built with several layers of gaseous ionization detectors, having a specific spatial resolution for tracking the muons, has been modeled. The images of the test cases with and without the defect have been simulated for variable exposure of cosmic muons on the basis of their scattering from the composite concrete structures. The images have been compared using t-test to evaluate the performance of the imaging setup in identifying the defects. Further processing of the images has been done with a pattern recognition method proposed in our earlier work to examine the credibility of the method of defect identification in civil works. The efficacy of the said method has been evaluated in terms of the PRM-score devised in this work. The limitation and advantages of the present application of the muon scattering tomography encompassing the imaging and image processing technique in nondestructive evaluation of concrete structures have been discussed.

Development of Sealed MRPC with extremely low gas flow for muon tomography

A muon tomography system named Tsinghua University cosmic ray Muon tomography (TUMUTY) facility based on Multi-Gap Resistive Plate Chamber (MRPC) has been built in Tsinghua University in 2012. Our research is focused on developing a muon non destructive testing system that will be used in homeland security operations such as custom inspections, airport security and so on. The gases normally used to operate MRPCs (C2F4H2, SF6 and i-C4H10.) have a high global warming potential. Eco-gas is a choice to solve this problem, but it will greatly increase the overall cost of the system. On the other hand, we can also reduce the greenhouse pollution by lowering the airflow to the chamber. In this paper, a sealed MRPC prototype filled only with C2F4H2 has been designed and studied. The prototype has a sensitive area of 500 mm⋅500 mm, and it can work very well at an extremely low gas flow of 0.5 ml/min. Moreover, we also studied the performance of the detector under a mode without gas exchange. The result shows that the detector can work for more than 60 hours without gas exchange. Under this mode, the average gas flow of the detector reduces to 0.05 ml/min.

Complementary non-destructive detection of nuclear materials with passive neutron and gamma-ray detectors, and a large-volume muon tomography system

Abstract Experimental demonstrations are reported of the complementarity of passive gamma-ray spectroscopy, passive neutron counting, and passive muon scattering tomography, in the simultaneous detection of shielded nuclear material. The demonstrations were applied to a number of experimental configurations that emulate various scenarios that may be encountered in the context of nuclear safeguards, or the security of nuclear facilities. In each case, the experimental analysts were blind to the contents of each configuration as they attempted to deduce the presence or absence of nuclear materials using data collected simultaneously from the three detection techniques. Analysis of data collection times was at first restricted to 10 minutes, and then to 2 hours, both with nuclear material (if present), and without nuclear material (as background from the shielded arrangement). The results of these experiments show how these techniques complement each other in the detection of shielded nuclear material.

The performance study of MRPCs used for muon tomography

Muon tomography system built by 2-D readout high spatial resolution Multi-gap Resistive Plate Chamber (MRPC) detector is a project in Tsinghua University. In 2013, we had developed a prototype of muon tomography system named TUMUTY, now we try to develop larger sensitive area and smarter structure MRPC detector to upgrade the system to a car detection system, which is used to detect high Z metal hidden in cars or other objects. For the system, 2 layers × 3 detectors are needed to get the incident particle's track, and the setting is the same for the outgoing track. Therefore, there will four layers containing twelve detectors in total, and its detection area will reach 1× 3 m2. An encoding readout method is suggested to minimize the number of the readout electronics, which reduces the complexity and the cost of the system. In this paper, we measured the performance of 12 MRPCs used for the system.

Performance study of large area encoding readout MRPC

Muon tomography system built by the 2-D readout high spatial resolution Multi-gap Resistive Plate Chamber (MRPC) detector is a project of Tsinghua University. An encoding readout method based on the fine-fine configuration has been used to minimize the number of the readout electronic channels resulting in reducing the complexity and the cost of the system. In this paper, we provide a systematic comparison of the MRPC detector performance with and without fine-fine encoding readout. Our results suggest that the application of the fine-fine encoding readout leads us to achieve a detecting system with slightly worse spatial resolution but dramatically reduce the number of electronic channels.

A plastic scintillator-based muon tomography system with an integrated muon spectrometer

A muon scattering tomography system which uses extruded plastic scintillator bars for muon tracking and a dedicated muon spectrometer that measures scattering through steel slabs has been constructed and successfully tested. The atmospheric muon detection efficiency is measured to be 97% per plane on average and the average intrinsic hit resolution is 2.5mm. In addition to creating a variety of three-dimensional images of objects of interest, a quantitative study has been carried out to investigate the impact of including muon momentum measurements when attempting to detect high-density, high-Z material. As expected, the addition of momentum information improves the performance of the system. For a fixed data-taking time of 60s and a fixed false positive fraction, the probability to detect a target increases when momentum information is used. This is the first demonstration of the use of muon momentum information from dedicated spectrometer measurements in muon scattering tomography.

Design and characterization of a small muon tomography system

Muon tomography is a useful method for monitoring special nuclear materials (SNMs) because it can provide effective information on the presence of high-Z materials, has a high enough energy to deeply penetrate large amounts of shielding, and does not lead to any health risks and danger above background. We developed a 2-D muon detector and designed a muon tomography system employing four detector modules. Two top and two bottom detectors are, respectively, employed to record the incident and the scattered muon trajectories. The detector module for the muon tomography system consists of a plastic scintillator, wavelength-shifting (WLS) fiber arrays placed orthogonally on the top and the bottom of the scintillator, and a position-sensitive photomultiplier (PSPMT). The WLS fiber arrays absorb light photons emitted by the plastic scintillator and re-emit green lights guided to the PSPMT. The light distribution among the WLS fiber arrays determines the position of the muon interaction; consequently, 3-D tomographic images can be obtained by extracting the crossing points of the individual muon trajectories by using a point-of-closest-approach algorithm. The goal of this study is to optimize the design parameters of a muon tomography system by using the Geant4 code and to experimentally evaluate the performance of the prototype detector. Images obtained by the prototype detector with a 420-nm laser light source showed good agreement with the simulation results. This indicates that the proposed detector is feasible for use in a muon tomography system and can be used to verify the Z-discrimination capability of the muon tomography system.

Toward a RPC-based muon tomography system for cargo containers.

A large area scanner for cosmic muon tomography is currently being developed at University of Bristol.Thanks to their abundance and penetrating power, cosmic muons have been suggested as ideal candidates to scan large containers in search of special nuclear materials, which are characterized by high-Z and high density. The feasibility of such a scanner heavily depends on the detectors used to track the muons: for a typical container, the minimum required sensitive area is of the order of 100 2. The spatial resolution required depends on the geometrical configuration of the detectors. For practical purposes, a resolution of the order of 1 mm or better is desirable. A good time resolution can be exploited to provide momentum information: a resolution of the order of nanoseconds can be used to separate sub-GeV muons from muons with higher energies.Resistive plate chambers have a low cost per unit area and good spatial and time resolution; these features make them an excellent choice as detectors for muon tomography.In order to instrument a large area demonstrator we have produced 25 new readout boards and 30 glass RPCs. The RPCs measure 1800 mm× 600 mm and are read out using 1.68 mm pitch copper strips.The chambers were tested with a standardized procedure, i.e. without optimizing the working parameters to take into account differences in the manufacturing process, and the results show that the RPCs have an efficiency between 87% and 95%. The readout electronics show a signal to noise ratio greater than 20 for minimum ionizing particles. Spatial resolution better than 500 μm can easily be achieved using commercial read out ASICs. These results are better than the original minimum requirements to pass the tests and we are now ready to install the detectors.

The design and performance of a scintillating-fibre tracker for the cosmic-ray muon tomography of legacy nuclear waste containers

Tomographic imaging techniques using the Coulomb scattering of cosmic-ray muons are increasingly being exploited for the non-destructive assay of shielded containers in a wide range of applications. One such application is the characterisation of legacy nuclear waste materials stored within industrial containers. The design, assembly and performance of a prototype muon tomography system developed for this purpose are detailed in this work. This muon tracker comprises four detection modules, each containing orthogonal layers of Saint-Gobain BCF-10 2mm-pitch plastic scintillating fibres. Identification of the two struck fibres per module allows the reconstruction of a space point, and subsequently, the incoming and Coulomb-scattered muon trajectories. These allow the container content, with respect to the atomic number Z of the scattering material, to be determined through reconstruction of the scattering location and magnitude. On each detection layer, the light emitted by the fibre is detected by a single Hamamatsu H8500 MAPMT with two fibres coupled to each pixel via dedicated pairing schemes developed to ensure the identification of the struck fibre. The PMT signals are read out to standard charge-to-digital converters and interpreted via custom data acquisition and analysis software.The design and assembly of the detector system are detailed and presented alongside results from performance studies with data collected after construction. These results reveal high stability during extended collection periods with detection efficiencies in the region of 80% per layer. Minor misalignments of millimetre order have been identified and corrected in software. A first image reconstructed from a test configuration of materials has been obtained using software based on the Maximum Likelihood Expectation Maximisation algorithm. The results highlight the high spatial resolution provided by the detector system. Clear discrimination between the low, medium and high-Z materials assayed is also observed.

FIRST IMAGES FROM THE CRIPT MUON TOMOGRAPHY SYSTEM

The CRIPT Cosmic Ray Imaging and Passive Tomography system began data taking in September 2012. CRIPT is a “proof of principle” muon tomography system originally proposed to inspect cargo in shipping containers and to determine the presence of special nuclear materials. CRIPT uses 4 layers of 2 m x 2 m scintillation counter trackers, each layer measuring two coordinates. Two layers are used to track the incoming muon and two for the outgoing muon allowing the trajectories of the muon to be determined. The target volume is divided into voxels, and a Point of Closest Approach algorithm is used to determine the number of scattering events in each voxel, producing a 3D image. The system has been tested with various targets of depleted uranium, lead bricks, and tungsten rods. Data on the positional resolution has been taken and the intrinsic resolution is unfolded with the help of a simulation using GEANT4. The next steps include incorporation of data from the spectrometer section, which will assist in determining the muon's momentum and improve the determination of the density of the target.

Design of a muon tomography system with a plastic scintillator and wavelength-shifting fiber arrays

Recently, monitoring nuclear materials to avoid nuclear terrorism has become an important area of national security. It can be difficult to detect gamma rays from nuclear material because they are easily shielded by shielding material. Muon tomography using multiple -Coulomb scattering derived from muons can be utilized to detect special nuclear materials (SNMs) such as uranium-235 and plutonium-239. We designed a muon tomography system composed of four detector modules. The incident and scattered muon tracks can be calculated by two top and two bottom detectors, respectively. 3D tomographic images are obtained by extracting the crossing points of muon tracks with a point-of-closest-approach algorithm. The purpose of this study was to optimize the muon tomography system using Monte Carlo simulation code. The effects of the geometric parameters of the muon tomography system on material Z-discrimination capability were simulated and evaluated.

China: Elementis — inorganic pigments

Tomographic imaging techniques using the Coulomb scattering of cosmic-ray muons are increasingly being exploited for the non-destructive assay of shielded containers in a wide range of applications. One such application is the characterisation of legacy nuclear waste materials stored within industrial containers. The design, assembly and performance of a prototype muon tomography system developed for this purpose are detailed in this work. This muon tracker comprises four detection modules, each containing orthogonal layers of Saint-Gobain BCF-10 2 mm-pitch plastic scintillating fibres. Identification of the two struck fibres per module allows the reconstruction of a space point, and subsequently, the incoming and Coulomb-scattered muon trajectories. These allow the container content, with respect to the atomic number Z of the scattering material, to be determined through reconstruction of the scattering location and magnitude. On each detection layer, the light emitted by the fibre is detected by a single Hamamatsu H8500 MAPMT with two fibres coupled to each pixel via dedicated pairing schemes developed to ensure the identification of the struck fibre. The PMT signals are read out to standard charge-to-digital converters and interpreted via custom data acquisition and analysis software.The design and assembly of the detector system are detailed and presented alongside results from performance studies with data collected after construction. These results reveal high stability during extended collection periods with detection efficiencies in the region of 80% per layer. Minor misalignments of millimetre order have been identified and corrected in software. A first image reconstructed from a test configuration of materials has been obtained using software based on the Maximum Likelihood Expectation Maximisation algorithm. The results highlight the high spatial resolution provided by the detector system. Clear discrimination between the low, medium and high-Z materials assayed is also observed.