Whilst the performance of small THGEMs is well known, here we consider the challenges in scaling these up to large area charge readouts. We first verify the expected gain of larger THGEMs by reporting experimental Townsend coefficients for a 10 cm diameter THGEM in low-pressure CF4. Large area 50 cm by 50 cm THGEMs were sourced from a commercial PCB supplier and geometrical imperfections were observed which we quantified using an optical camera setup. The large area THGEMs were experimentally characterised at Boulby Underground Laboratory through a series of gain calibrations and alpha spectrum measurements. ANSYS, Magboltz and Garfield++ simulations of the design of a TPC based on the large area THGEMs are presented. We also consider their implications for directional dark matter research and potential applications within nuclear security.

Muon scattering tomography techniques can be used to image the contents of an enclosed volume by measuring the scattering angle of cosmic ray muons as they pass through a volume using particle tracking detectors. The magnitude of the observed muon scatter varies with the density of the objects within a volume, therefore the technique is well suited to distinguishing dense (high-Z) materials from lower density (low-Z) materials. AWE has been investigating muon scattering tomography techniques for use in the identification of special nuclear material (SNM) in transit cargo for a number of years. As part of this work AWE and our partner institutions have plate chamber technology, and a software suite of reconstruction tools and Monte Carlo simulations that we have used to quantify the capability and limitations of muon tomography techniques for SNM identification.Recent work at AWE has focused on the development of portable detector technologies for the imaging of objects and packages at unfixed locations. It is envisaged that portable detectors will be positioned to the sides of the screened objects rather than at the top and bottom with the object in the centre. This work has involved the further development of our Monte Carlo models to provide a more detailed of the horizontal muon flux and the implementation of new tracking algorithms to identify muons coming from either side of the tracking system. Part of this work has also involved investigating the use of portable wire chamber and silicon tracking detectors. Our work has also focused on examining the potential improvements to image quality afforded by the detection of spallation neutrons from muon interactions inside an object. The work presented will provide an overview of these recent developments and draw conclusions on the use of muon scattering tomography techniques for deployable security imaging applications.

This work presents data obtained from an investigation into muon stimulated neutron emission in combination with the technique of muon scattering tomography. Initial measurements in lead of the neutron emission measured a half-life of 56.9 ± 6.63 ns which is three standard deviations lower than expected, with the error primarily attributed to prompt X-ray emission. A hypothetical detector, based on a muon scattering tomography prototype at AWE was used to examine the data expected from an integrated system. A lifetime 81 ± 3 ns was obtained here. Alongside this a portable muon trigger detector has been developed which aims to be implemented in a deployable muon scattering tomography system. The portable detector successfully measures muons to an accuracy of 20%.

Legacy nuclear waste can contain anything from parts of fuel rods to coveralls worn by the workers, stored inside large concrete containers. It is important to identify the materials present in these containers with techniques that are non-invasive and scalable, in order to be applied for a considerable amount of large volumes. Using muon scattering tomography, we show that it is possible to discriminate uranium blocks from lead, tungsten and plutonium, inside a concrete filled cylinder, by selecting the muon tracks that pass through the volumes of interest. There is very good discrimination between uranium and lead or tungsten for block sizes upwards of 2 × 2 × 2 cm 3 . We even show that we can discriminate between lumps of uranium and plutonium.

Resistive plate chambers (RPC) are particle detectors commonly used by the high energy physics community. Their normal operation requires a constant flow of gas mixture to prevent self-poisoning which reduces the chamber's capability to detect particles. We studied how quickly the efficiency of two RPCs drops when operated in sealed mode, i.e. without refreshing the gas mixture. The test aim is to determine how RPCs could be used as particle detectors in non-laboratory applications, such as those exploiting muon tomography for geological imaging or homeland security.The two sealed RPCs were operated in proportional mode for a period of more than three months, and their efficiencies were recorded continuously and analysed in 8-hours intervals. The results show that the efficiency drops on average by 0.79 +/- 0.01 % every 24 hours of operation and returns close to the initial value after purging the old gas mixture and flushing the chambers with fresh gas.

We have developed a novel algorithm based on Markov random fields capable of detecting special nuclear material in large-scale volumes such as cargo containers, using cosmic muons as probes. Since the amount of muon scattering is dependent on the Z2 of the material traversed, strong scattering in a localized area is indicative of high-Z material being present. For scanning purposes in freight harbors and similar, a decision should be made in 1 minute. We will show that our algorithm is capable of identifying a solitary uranium block in a cargo container with 100% accuracy in 1 minute, and suffers only a minor degradation of performance for the same block shielded by a large rock volume.

Muon scattering tomography (MST) allows the identification of shielded high atomic number (high-Z) materials by measuring the scattering angle of cosmic ray muons passing through an inspection region. Cosmic ray muons scatter to a greater degree due to multiple Coulomb scattering in high-Z materials than low-Z materials, which can be measured as the angular difference between the incoming and outgoing trajectories of each muon. Measurements of trajectory are achieved by placing position sensitive particle tracking detectors above and below the inspection volume. By localising scattering information, the point at which a series of muons scatter can be used to reconstruct an image, differentiating high, medium and low density objects.MST is particularly useful for differentiating between materials of varying density in volumes that are difficult to inspect visually or by other means. This paper will outline the experimental work undertaken to develop a prototype MST system based on drift chamber technology. The planar drift chambers used in this prototype measure the longitudinal interaction position of an ionising particle from the time taken for elections, liberated in the argon (92.5%), carbon dioxide (5%), methane (2.5%) gas mixture, to reach a central anode wire. Such a system could be used to enhance the detection of shielded radiological material hidden within regular shipping cargo.

Distributed networks of robust, low-cost, radiation detectors offer the ability to track and locate materials across a number of applications. Individual sensors must be positioned to collectively optimise both the sensing and communication roles of the network and ruggedized to achieve consistent detection performance under a range of environmental conditions. Here we consider the interplay between the modelled optimisation of sensor location and required signal communication. The performance of a purely static sensor network was compared to configurations including mobile sensor units. A random sequential deposition method was applied to locate static sensors and simulations performed with a radiological source moving along both random and pre-defined trajectories. A variety of statistics were used to assess the performance of the network and compared to models where a proportion of sensors were allowed to travel along pre-defined paths. Statistics included the number of interactions, frequency and length of time between the source and deployed sensor coverage, the total area of coverage afforded by the sensors, the area encompassed by the travelling source and the number of sensors deployed. In addition initial experiments were conducted exploring aerial configurations, bandwidth and frequency step as a function of sensor separation. The ranging capabilities of the Atmel AT86RF233 chip were tested with bandwidths from 10 to 100 MHz and from frequencies of 500 kHZ to 4 MHz. These results may influence the choice of future static and mobile sensor configurations.

Muon Scattering Tomography (MST) is a technique for using the scattering of cosmic ray muons to probe the contents of enclosed volumes. As a muon passes through material it undergoes multiple Coulomb scattering, where the amount of scattering is dependent on the density and atomic number of the material as well as the path length. Hence, MST has been proposed as a means of imaging dense materials, for instance to detect special nuclear material in cargo containers. Algorithms are required to generate an accurate reconstruction of the material density inside the volume from the muon scattering information and some have already been proposed, most notably the Point of Closest Approach (PoCA) and Maximum Likelihood/Expectation Maximisation (MLEM) algorithms. However, whilst PoCA-based algorithms are easy to implement, they perform rather poorly in practice. Conversely, MLEM is a complicated algorithm to implement and computationally intensive and there is currently no published, fast and easily-implementable algorithm that performs well in practice. In this paper, we first provide a detailed analysis of the source of inaccuracy in PoCA-based algorithms. We then motivate an alternative method, based on ideas first laid out by Morris et al, presenting and fully specifying an algorithm that performs well against simulations of realistic scenarios. We argue this new algorithm should be adopted by developers of Muon Scattering Tomography as an alternative to PoCA.

A muon tracker based on resistive plate chambers is described, with particular emphasis on the hardware and the read-out electronic. The tracker is used to measure the angular scattering of cosmic muons as they traverse a suitcase-sized volume. The solution adopted, based on pick-up strips and independent read-out channels, allowed us to achieve a spatial resolution of 500 m m, which is sufficient to discriminate between high-Z and low-Z materials.

We present a novel approach to the detection of special nuclear material using cosmic rays. Muon Scattering Tomography (MST) is a method for using cosmic muons to scan cargo containers and vehicles for special nuclear material. Cosmic muons are abundant, highly penetrating, not harmful for organic tissue, cannot be screened against, and can easily be detected, which makes them highly suited to the use of cargo scanning. Muons undergo multiple Coulomb scattering when passing through material, and the amount of scattering is roughly proportional to the square of the atomic number Z of the material. By reconstructing incoming and outgoing tracks, we can obtain variables to identify high-Z material. In a real life application, this has to happen on a timescale of 1 min and thus with small numbers of muons. We have built a detector system using resistive plate chambers (RPCs): 12 layers of RPCs allow for the readout of 6 x and 6 y positions, by which we can reconstruct incoming and outgoing tracks. In this work we detail the performance of an algorithm by which we separate high-Z targets from low-Z background, both for real data from our prototype setup and for MC simulation of a cargo container-sized setup. (c) British Crown Owned Copyright 2013/AWE

Resistive Plate Chambers(RPCs) offer simple construction and efficient detection of charge particles over a large area with nano-second precision. Traditionally, large strips or pads that cover the entire area of induced charge are used to pick up the signal. The signal is then connected to a binary read-out. This approach gives moderate spatial resolution, typically of the order of a centimetre. However using fine-pitch pick-up strips, with the induced signal spread over several strips and analogue read-out, allows much better spatial resolution to be obtained than is possible with wide strips and binary readout.

This work describes the performance of a muon tracker built with high resolution glass resistive plate chambers. The tracker is the result of a collaboration between University of Bristol and the Atomic Weapon Establishment to develop a reliable and cost effective system to scan shipping containers in search of special nuclear materials. The current setup consists of 12 detection layers, each comprised of a resistive plate chamber read out by 1.5 mm pitch strips. For most of the layers we achieved an efficiency better than 95%, a purity above 95% and a signal-to-noise ratio better than 300. A spatial resolution better than 500μm was obtained for most layers, thus satisfying the main requirements to apply resistive plate chambers to cosmic ray tomography.

Resistive Plate Chambers (RPCs) are widely used in high energy physics for both tracking and triggering purposes. They have good time resolution and with finely segmented readout can also give a spatial resolution of better than 1 mm. RPCs can be produced cost-effectively on large scales, are of rugged build, and have excellent detection efficiency for charged particles. Our group has successfully built a Muon Scattering Tomography (MST) prototype, using 12 RPCs to obtain tracking information of muons going through a target volume of similar to 50cm x 50cm x 70cm, reconstructing both the incoming and outgoing muon tracks. We describe a readout system for fine-pitch RPCs using MAROC3 readout chips capable of scaling to a large system.

Tomographic imaging using cosmic ray muons has a range of applications including homeland security and geological imaging. To this end, we have developed a technique to calculate the most probable muon trajectory through a scattering material, given its measured entry and exit trajectories. This method has the potential to improve tomographic algorithms, in particular by replacing the muon paths assumed by the Point Of Closest Approach (POCA) method, with more realistic paths. These paths can be calculated for arbitary matter distributions, rather than just the point scatterers assumed by POCA.

Following their introduction in the physics community in the early '80s the use of Resistive Plate Chambers (RPCs) as charged particles detectors has constantly increased. Low cost per unit area, good time resolution and easy of operation are some of the features that contributed to such large adoption and that make RPCs interesting for several applications not necessarily related to physics. We built a prototype detector to track cosmic muons and exploit the information provided by estimating the multiple coulomb scattering angle to determine the type of materials they traversed. Simulations show that the technique could be used to inspect a cargo container in a time of the order of minutes.The detector we built consists of six planes, each one providing X-Y readout over a 50 cm x 50 cm area. The readout scheme we adopted, based on multiplexing chips used in high energy physics, allowed us to use a limited amount of electronic output channels while still obtaining a spatial resolution lower than 1 mm. An overview of the detector and of the analysis performed on the data is provided.

Resistive plate chambers (RPCs) are widely used in high energy physics for both tracking and triggering pur- poses, due to their excellent time resolution, rate capabil- ity, and good spatial resolution. RPCs can be produced cost-effectively on large scales, are of rugged build, and have excellent detection efficiency for charged particles. Our group has successfully built a muon scattering tomogra- phy (MST) prototype, using 12 RPCs to obtain tracking information of muons going through a target volume of 50 cm◊ 50 cm◊ 70 cm, reconstructing both the incoming and outgoing muon tracks. The required spatial granularity is achieved by using 330 readout strips per RPC with 1.5 mm pitch. The RPCs have shown an efficiency above 99 % and an estimated intrinsic resolution below 1.1 mm. Due to these qualities, RPCs serve as excellent candidates for usage in volcano radiography.

We present a novel method to detect special nuclear material using cosmic rays. Muon Scattering Tomography (MST) is a method in homeland security for scanning cargo containers and vehicles for special nuclear material with cosmic muons. These are abundant, highly penetrating, not harmful against organic tissue, cannot be screened against, and can easily be detected. Muons undergo multiple Coulomb scattering when passing through material, and the amount of scattering is proportional to the ℤ2 of the material. By reconstructing incoming and outgoing tracks, we can obtain variables to determine the ℤ of the target material. In a real life application, this has to happen on a timescale of 1 min and thus with small numbers of muons. We have built a detector system using resistive plate chambers (RPCs). 12 layers of RPCs allow for the readout of 6 × and 6 y positions, by which we can reconstruct incoming and outgoing tracks. In this work we detail the performance of two algorithms by which we separate high-ℤ targets from low-ℤ background.

The spin-dependent momentum density of Gd7Pd3 was probed by the magnetic Compton scattering technique with elliptically polarized synchrotron radiation. A contribution to the spin moment from Pd 4d electrons was observed, at 2 and 280 K, alongside a large Gd 4f moment and a smaller Gd 5d moment. The total spin moment, at 2 K, was determined as 50.8 +/- 0.7 mu(B) (f.u.)(-1). The Gd 4f contribution to the spin moment was determined as 43.4 +/- 1.8 mu(B) (f.u.)(-1), the Gd 5d moment as 4.4 +/- 0.7 mu B (f.u.)(-1) and the Pd 4d spin moment contribution as 2.9 +/- 1.1 mu B (f.u.)(-1), where f.u. represents a formula unit. At 280 K the total spin moment was 27.3 +/- 0.9 mu(B) (f.u.)(-1) with individual contributions determined as a Gd 4f spin moment of 23.8 +/- 1.1 mu B (f.u.)(-1), a Gd 5d contribution of 2.2 +/- 0.5 mu B (f.u.)(-1) and a Pd 5d spin moment of 1.2 +/- 0.6 mu B (f.u.)(-1).

The observation of magnetic effects in X-ray scattering dates from the second decade of the twentieth century, before becoming associated with gamma ray phenomena in the quest to understand neutrino helicity, some thirty years later. The paradigm-changing studies in both realms of coherent and incoherent magnetic scattering also predate the availability of synchrotron radiation, which crucially possesses the polarization properties that make it a potent probe of magnetization. This review will cover the historical development, summarize the underlying interpretive theory and conclude with an example of recent research on rare earth compounds.