Kelum Gamage

Real-Time, Fast Neutron Coincidence Assay of Plutonium With a 4-Channel Multiplexed Analyzer and Organic Scintillators

The design, principle of operation and the results of measurements made with a four-channel organic scintillator system are described. The system comprises four detectors and a multiplexed analyzer for the real-time parallel processing of fast neutron events. The function of the real-time, digital multiple-channel pulse-shape discrimination analyzer is described together with the results of laboratory-based measurements with 252Cf, 241Am-Li and plutonium. The analyzer is based on a single-board solution with integrated high-voltage supplies and graphical user interface. It has been developed to meet the requirements of nuclear materials assay of relevance to safeguards and security. Data are presented for the real-time coincidence assay of plutonium in terms of doubles count rate versus mass. This includes an assessment of the limiting mass uncertainty for coincidence assay based on a 100 s measurement period and samples in the range 0-50 g. Measurements of count rate versus order of multiplicity for 252Cf and 241Am-Li and combinations of both are also presented.

A digital approach to neutron–γ imaging with a narrow tungsten collimator aperture and a fast organic liquid scintillator detector

A digital neutron-γ imaging technique for mixed radiation field is described. The imaging system is based upon an organic liquid scintillator detector, a narrow tungsten collimator, fast digitiser and adjustable equatorial mount. Radioactive sources have been attached to a vertical plane and the digitiser has been used to digitise neutron and γ events. The digitised events have been discriminated using pulse gradient analysis and images have been generated of the count distribution in the source plane.

Resilient communication for smart grid ubiquitous sensor network

We explored the adaptation of the USN architecture for SG communication.We reviewed existing communication technologies that can be deployed in SG USN.Vulnerability and challenges of the USN architecture for SG were highlighted.The choice of communication technologies reduces complexity in SG communication.A secure and QoS aware USN middleware can guarantee requirements of SG application. Smart grid combines a set of functionalities that can only be achieved through ubiquitous sensing and communication across the electrical grid. The communication infrastructure must be able to cope with an increasing number of traffic types which is as a result of increased control and monitoring, penetration of renewable energy sources and adoption of electric vehicles. The communication infrastructure must serve as a substrate that supports different traffic requirements such as QoS (i.e. latency, bandwidth and delay) across an integrated communication system. This engenders the implementation of middleware systems which considers QoS requirements for different types of traffic in order to allow prompt delivery of these traffic in a smart grid system. A heterogeneous communication applied through the adaptation of the Ubiquitous Sensor Network (USN) layered structure to smart grid has been proposed by the International Telecommunication Union (ITU). This paper explores the ITUs USN architecture and presents the communication technologies which can be deployed within the USN schematic layers for a secure and resilient communication together with a study of their pros and cons, vulnerabilities and challenges. It also discusses the factors that can affect the selection of communication technologies and suggests possible communications technologies at different USN layers. Furthermore, the paper highlights the USN middleware system as an important mechanism to tackle scalability and interoperability problems as well as shield the communication complexities and heterogeneity of smart grid.

A 4-channel multiplex analyzer for real-time, parallel processing of fast scintillators

The design, principle of operation and the results of the first measurements made with a 4-channel multiplexed analyzer for real-time parallel processing of fast scintillation detectors is described. Recent advancements in the performance of organic scintillation media for the detection of fast neutrons, not least the reduction in hazard and the recent advent of plastic scintillation materials exhibiting Pulse Shape Discrimination (PSD), has highlighted the possibility of using multiple detectors in systems based on detectors exploiting these media. In this paper a real-time, digital multiple-channel PSD analyzer is described based on a single-board solution with an integrated high-voltage supply and graphical user interface. It has been developed to meet the requirements of nuclear materials assay of relevance to safeguards and security, and tested in a variety of related laboratory-based environments.

Resilient wireless communication networking for Smart grid BAN

The concept of Smart grid technology sets greater demands for reliability and resilience on communications infrastructure. Wireless communication is a promising alternative for distribution level, Home Area Network (HAN), smart metering and even the backbone networks that connect smart grid applications to control centres. In this paper, the reliability and resilience of smart grid communication network is analysed using the IEEE 802.11 communication technology in both infrastructure single hop and mesh multiple-hop topologies for smart meters in a Building Area Network (BAN). Performance of end to end delay and Round Trip Time (RTT) of an infrastructure mode smart meter network for Demand Response (DR) function is presented. Hybrid deployment of these network topologies is also suggested to provide resilience and redundancy in the network during network failure or when security of the network is circumvented. This recommendation can also be deployed in other areas of the grid where wireless technologies are used. DR communication from consumer premises is used to show the performance of an infrastructure mode smart metering network.

Neutron assay in mixed radiation fields with a 6Li-loaded plastic scintillator

A novel technique for assay of thermal and fast neutrons in a 6Li-loaded plastic scintillator is presented. Existing capture-gated thermal neutron detection techniques were evaluated with the 6Li-loaded plastic scintillator studied in this work. Using simulations and experimental work, shortcomings in its performance were highlighted. As a result, it was proposed that by separating the combined fast and thermal neutron events from gamma events, using established pulse shape discrimination techniques, the thermal neutron events could then be assayed. Experiments were conducted at the National Physical Laboratory, Teddington, performing neutron assays with seven different neutron fields using the proposed technique. For each field, thermal and fast neutron content was estimated and were shown to corroborate with the seven synthesised fields.

An analytical approach to γ-ray self-shielding effects for radioactive bodies encountered nuclear decommissioning scenarios

A novel analytical approach is described that accounts for self-shielding of γ radiation in decommissioning scenarios. The approach is developed with plutonium-239, cobalt-60 and caesium-137 as examples; stainless steel and concrete have been chosen as the media for cobalt-60 and caesium-137, respectively. The analytical methods have been compared MCNPX 2.6.0 simulations. A simple, linear correction factor relates the analytical results and the simulated estimates. This has the potential to greatly simplify the estimation of self-shielding effects in decommissioning activities.

Ground Penetrating Radar as a Contextual Sensor for Multi-Sensor Radiological Characterisation

Radioactive sources exist in environments or contexts that influence how they are detected and localised. For instance, the context of a moving source is different from a stationary source because of the effects of motion. The need to incorporate this contextual information in the radiation detection and localisation process has necessitated the integration of radiological and contextual sensors. The benefits of the successful integration of both types of sensors is well known and widely reported in fields such as medical imaging. However, the integration of both types of sensors has also led to innovative solutions to challenges in characterising radioactive sources in non-medical applications. This paper presents a review of such recent applications. It also identifies that these applications mostly use visual sensors as contextual sensors for characterising radiation sources. However, visual sensors cannot retrieve contextual information about radioactive wastes located in opaque environments encountered at nuclear sites, e.g., underground contamination. Consequently, this paper also examines ground-penetrating radar (GPR) as a contextual sensor for characterising this category of wastes and proposes several ways of integrating data from GPR and radiological sensors. Finally, it demonstrates combined GPR and radiation imaging for three-dimensional localisation of contamination in underground pipes using radiation transport and GPR simulations.

First Results of Using a UVTron Flame Sensor to Detect Alpha-Induced Air Fluorescence in the UVC Wavelength Range

In this work, a robust stand-off alpha detection method using the secondary effects of alpha radiation has been sought. Alpha particles ionise the surrounding atmosphere as they travel. Fluorescence photons produced as a consequence of this can be used to detect the source of the alpha emissions. This paper details experiments carried out to detect this fluorescence, with the focus on photons in the ultraviolet C (UVC) wavelength range (180–280 nm). A detector, UVTron R9533 (Hamamatsu, 325-6, Sunayama-cho, Naka-ku, Hamamatsu City, Shizuoka Pref., 430-8587, Japan), designed to detect the UVC emissions from flames for fire alarm purposes, was tested in various gas atmospheres with a 210Po alpha source to determine if this could provide an avenue for stand-off alpha detection. The results of the experiments show that this detector is capable of detecting alpha-induced air fluorescence in normal indoor lighting conditions, as the interference from daylight and artificial lighting is less influential on this detection system which operates below the UVA and UVB wavelength ranges (280–315 nm and 315–380 nm respectively). Assuming a standard 1r2 drop off in signal, the limit of detection in this configuration can be calculated to be approximately 240 mm, well beyond the range of alpha-particles in air, which indicates that this approach could have potential for stand-off alpha detection. The gas atmospheres tested produced an increase in the detector count, with xenon having the greatest effect with a measured 52% increase in the detector response in comparison to the detector response in an air atmosphere. This type of alpha detection system could be operated at a distance, where it would potentially provide a more cost effective, safer, and faster solution in comparison with traditional alpha detection methods to detect and characterise alpha contamination in nuclear decommissioning and security applications.

Pulse shape discrimination characteristics of stilbene crystal, pure and 6Li loaded plastic scintillators for a high resolution coded-aperture neutron imager

Pulse shape discrimination performances of single stilbene crystal, pure plastic and 6Li loaded plastic scintillators have been compared. Three pulse shape discrimination algorithms have been tested for each scintillator sample, assessing their quality of neutron/gamma separation. Additionally, the digital implementation feasibility of each algorithm in a real-time embedded system was evaluated. Considering the pixelated architecture of the coded-aperture imaging system, a reliable method of simultaneous multi-channel neutron/gamma discrimination was sought, accounting for the short data analysis window available for each individual channel. In this study, each scintillator sample was irradiated with a 252Cf neutron source and a bespoke digitiser system was used to collect the data allowing detailed offline examination of the sampled pulses. The figure-of-merit was utilised to compare the discrimination quality of the collected events with respect to various discrimination algorithms. Single stilbene crystal presents superior neutron/gamma separation performance when compared to the plastic scintillator samples.