N4A1  Instrumentation for Homeland and National Security, Muon Tomography

Thursday, Nov. 5  08:30-10:10  Town and Country

Session Chair:  Nathan Hilton, Sandia National Labs, United States; Peter Vanier, Brookhaven National Laboratory, United States

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(08:30) N4A1-1, Augmentation of a Muon Scattering Tomography Scanning System Using Large Area Scintillator Detectors

L. F. Thompson1, J. Boakes2, J. Burns2, T. Deakin3, S. Quillin2, C. Steer2

1Department of Physics and Astronomy, University of Sheffield, Sheffield, UK
2AWE, Aldermaston, UK
3Lablogic Systems Ltd., Sheffield, UK
Muon scattering tomography systems permit the passive detection of shielded special nuclear materials (SNM) when passive emission rates are close to background due to heavy shielding. The design and performance of a scalable trigger panel for a drift chamber based muon tracking system is reported. The trigger design is based on a wavelength shifting fibre readout of injection molded tiles, and was chosen to provide good muon trigger efficiency and to cover the large areas required for cosmic ray muon tomography systems. An integral aspect of the design was to make the overall cost of the trigger panel as inexpensive as possible. We have observed a muon trigger efficiency of 86% at the trigger panel farthest from the PMT. Initial source tests also indicate a 3.4% efficiency for 1.4MeV gamma-rays. Injection molded scintillator tile based detectors are an inexpensive way to provide passive radiation sensitivity over large detector areas required for cosmic ray muon tomography. We have demonstrated their use as both a cosmic ray muon trigger and passive radiation sensor in a single module providing operational and cost benefits.

(08:50) N4A1-2, Position-Sensitive Plastic Scintillator Designed for Cosmic-Ray Muon Imaging of Dry Storage Cask

C. Liao, H. Yang

Nuclear Engineering and RHP, Oregon State University, corvallis, United States
The overarching goal of this project is to develop an imaging system to monitor the content of a dry storage cask (DSC) with cosmic ray muons. The imaging technique utilizing multiple Coulomb scattering was demonstrated to be a good non-destructive assay method for high-Z materials, such as used nuclear fuel assemblies in DSCs. In this work, we present a prototype design of the Muon Imaging system, which contains four identical position-sensitive muon detectors, forming two muon trackers. Specifically, we introduce our design of the position-sensitive plastic scintillator. Each position-sensitive detector is a single layer of a plastic scintillator plane with size of 32 cm by 32 cm by 2.5 cm. 32 parallel grooves with 2 mm width, 4 mm depth pitch are curved on each side of the scintillator plane. The directions of the grooves on the top and bottom sides are perpendicular to each other, and the pitch between two adjacent grooves is 1 cm. EJ-200 was chosen as the scintillator material. Bunches of wavelength shifting (WLS) optical fibers are embedded in each groove for light readout. The optical fibers from each channel are coupled to Hamamatsu H8500C MAPMTs. The PMT signals are then passed on to the Anger logic resistive network to reduce the cost of reading all channels. Monte Carlo simulation results showed excellent position resolution of the designed position-sensitive plastic scintillator. Some preliminary tests are presented as well. Experimental results will be presented and discussed in full submission.

(09:10) N4A1-3, Energy Measurement and Application on Material Discrimination in Muon Tomography

Z. Luo1,2, X. Wang1,2, Z. Zeng1,2, Y. Wang1,2, M. Zeng1,2, J. Cheng1,2, H. Yi1,2

1Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education, Tsinghua University, Beijing, China
2Department of Engineering Physics, Tsinghua University, Beijing, China
In muon tomography, the RMS of Multiple Coulomb Scattering angle of muon through a material is not only related to the physical property of the material but also related to the energy of muon. However, in most cases, the average energy of muon is adopted in imaging instead of actual energy because of the lack of energy measurement. Although the result with average muon energy is acceptable to some extent, the reconstructed scattering density of the material of interest may have some deviation which may lead to the misjudgment of elements and reduce the material discrimination ability of muon tomography system. In this paper, the benefit for distinguishing material with segmented muon energy has been studied and a multi-layer Time of Flight method has been proposed to measure the muon energy. The difference in RMS of scattering angle between high Z materials such as Pb and W can be expanded with segmented energy acquired with this method via Monte Carlo simulation, thus promoting the material discrimination ability of muon tomography system.

(09:30) N4A1-4, Improved Muon Tracking for Plastic-Scintillator-Based Muon Scattering Tomography

D. Waller, J. T. Brown, J. Connor, A. Jones, T. A. Jones, I. Watson, K. Moats

Radiological Analysis and Defence, Defence Research and Development Canada, Ottawa, Ontario, Canada
Following the successful demonstration of a plastic-scintillator-based muon scattering tomography (MST) system by the Cosmic Ray Inspection and Passive Tomography (CRIPT) collaboration, R&D effort is ongoing at DRDC to develop a portable MST system that could be used to image “small” objects (less than one cubic metre in volume). In order to make more compact muon tracking detectors, but maintain the same track angular resolution, the position resolution of the CRIPT muon detectors must be improved. We use overlapping, triangular, scintillator bars with wavelength shifting fibres to detect muons; improved position resolution can be achieved for these detectors by increasing the average number of photons detected per muon. To detect more photons, we have switched from multi-anode photomultiplier tubes to higher quantum efficiency silicon photomultipliers, and we are investigating different optical coupling materials (liquids, gels, glues) to improve the transmission of scintillation photons from the scintillator bars to the wavelength shifting fibres. In our first set of experiments with small Cs-137 and Sr-90 sources, we have demonstrated that the light yield is increased significantly by injecting optical adhesive between the wavelength shifting fibre and the scintillator; however, some material incompatibility issues have been encountered. We report on the light yield measurements using a range of optical couplers and the long-term aging concerns for some of these materials.

(09:50) N4A1-5, Drift Chamber Tracking Detectors for Muon Scattering Tomography

J. Burns1, S. Quillin1, S. Snow2, M. Stapleton1, C. Steer1

1AWE plc, Aldermaston, Reading, United Kingdom
2Department of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
Muon Scattering Tomography (MST) allows the density of different materials to be identified within an enclosed volume by measuring the scattering angle of cosmic ray muons passing through objects within the physical space of a detection system. Cosmic ray muons scatter to a greater degree in dense (high-Z) materials than low-Z materials via the multiple Coulomb scattering process. By measuring the trajectory of a deflected muon as it enters and exits an inspection volume it is possible to quantify the magnitude of the scattering induced and locate the point of maximum scattering within the volume. As most of the scattering occurs within high-Z materials more of the localised scattering points are distributed around the areas containing high density materials. These localised scattering points can be used to construct an image of the materials within a volume. One particular application of MST is the location of shielded special nuclear material (SNM) hidden within cargo containers. This paper will detail the design, construction and performance of a prototype MST system based on drift chamber detectors. The thirty six planar drift chambers used in this system measure the longitudinal position of the muon interaction from the time taken for electrons, liberated from an argon, carbon dioxide, methane gas mixture to reach a positively charged anode wire. These drift chambers were arranged in twelve individual detector layers, six above and below the inspection volume respectively to track the trajectory of an incoming and outgoing muon.