Over 95% of imports entering the United States from outside North America arrive via cargo containers by sea at 329 ports of entry. The current layered approach for the detection only scans 5% of cargo bound for the United States. This is inadequate to protect our country. This research involved the building of a gamma-ray radiation detection system used for cargo scanning. The system was mounted on a spreader bar crane (SBC) at the Port of Tacoma (PoT) and the applicability and capabilities of the system were analyzed. The detection system provided continuous count rate and spectroscopic data among three detectors while operating in an extreme environment. In a separate set of experiments, 60Co and 137Cs sources were positioned inside a cargo container and data were recorded for several count times. The Monte Carlo N-Particle (MCNP) code was used to simulate a radioactive source inside an empty cargo container and the results were compared to experimentally recorded data. The detection system demonstrated the ability to detect 60Co, 137Cs, 192Ir, highly-enriched uranium (HEU), and weapons-grade plutonium (WGPu) with minimum detectable activities (MDA) of 5.9 ± 0.4 microcuries (μCi), 19.3 ± 1.1 μCi, 11.7 ± 0.6 μCi, 3.5 ± 0.3 kilograms (kg), and 30.6 ± 1.3 grams (g), respectively. This system proved strong gamma-ray detection capabilities, but was limited in the detection of fissile materials Additional details of this system are presented and advantages of this approach to cargo scanning over current approaches are discussed.

The work presented here develops a gamma-ray spectral construction and analysis software tool that was used to analyze multi-detector data collected using a digital spectrometer with list mode capabilities. The tool was used to parse the output from three detectors and generate new spectra that the user chooses from post-processing suppression routines, such as simulated anticoincidence and coincidence spectra. Part of this research was also to characterize the improvements in the detection limits and the various detector efficiencies from this method as opposed to creating these spectra using traditional electronic gating systems. A focus is placed on the detection capability improvements for nuclear forensics purposes, particularly the identification and quantification of fission product samples, and structuring the code framework for handling these types of time-dependent samples while increasing the versatility of the detector system. Improvements to the minimum detectable activity for a series of fission products was accomplished through post-processing suppression methods and multi-dimensional spectral data structures are now achievable. / text

Abstract My thesis examines the measurement optimalization when the semiconductor HPGe detectors with a low background and a high relative efficiency are used for achieving low values of MDA (minimum detectable activity). I conducted my research in the Department of Spectrometry of SÚRO (National Radiation Protection Institute) in Prague. In this laboratory the standard geometries of detectors with lower efficiency are used. The aim of this thesis is to offer a proposal of new geometry, sizes and shapes of measurement cells which will better correspond with the demand for higher efficiency of updated detectors. The assignment was to find the best mathematical function to descibe the correlation between efficiency and the direction of the radiation point source towards the detector. This function is derived from experimentally obtained data. To conduct measurements, three kinds of detectors with high relative efficiency used for activity measurements at different geometries were selected. As the source of gamma radiation, the point sources with energies of 46 keV, 661 keV, 1332 keV in different distances and positions were used. The function was applied separatelly to each of the three detectors and to the areas above the detector and sidewards of the detector. The objective of the research was to project new measurement geometries or to optimalize the current ones which could be used also in other detectors with high efficiency. After integrating the function in the cylindrical area above the detector and the annular area sidewards of the detector, areas contributing substantially to the overall efficiency were determined. These areas may be considered to be the optimal sizes for new geometries in given positions. After combining all the optimal areas above the detector, sidewards of the detector and for selected energies and the detector, optimal sizes of a new geometry were found. The function can be used both in the front part and the side part of the detector but its validity is limited. The value of MDA for the particular geometry is in indirect proportion to the efficiency square root and thus this new geometry should lead to minimum values of MDA.

In this thesis, I study numerical and semi-analytical models of self-gravitating protostellar discs, with the aim of furthering our understanding of the role of disc-self gravity in planet formation. At the time of writing, the ALMA era of observational astronomy is upon us. Therefore, I place my research into this context with synthetic images of both numerical and semi-analytical models. I begin with an examination into the apparent lack of convergence, with increasing resolution, of the fragmentation boundary in Smoothed Particle Hydrodynamics (SPH) simulations of a protostellar disc. I run a suite of SPH with different numerical implementations, and find that even very similar implementations can fundamentally change the final answer. I analyse a suite of SPH simulations that fragment to form gravitationally bound objects, with the motivation of informing future population synthesis model development. I find that fragment-fragment and fragment-disc interaction dominates the orbital evolution of the system even at very early times, and any attempt to produce a population of objects from the gravitational instability process must include these interactions. Before a disc fragments, it will go through a self-gravitating phase. If the disc cools globally on a timescale such that it is balanced by heating due to gravitational stresses, the disc will be in a state of quasi-equilibrium. So long as the disc mass is sufficiently low, and spirals are sufficiently tightly wound, then angular momentum transport can be described by the local approximation, for which there is an analytical description. Using this analytical description, I develop an existing 1D model into 3D, and examine a wide range of parameter space for which disc self-gravity produces significant non-axisymmetry. Using radiative transfer calculations coupled with synthetic observations, I determine that there is a very narrow range of parameter space in which a disc will have sufficiently large gravitational stresses so as to produce detectable spirals, but the stresses not be so large as to cause the disc to fragment. By developing a simple analytical prescription for dust, I show that this region of parameter space can be broadened considerably. However, it requires grains that are large enough to become trapped by pressure maxima in the disc, so I conclude that if self-gravitating spiral arms are detected in the continuum, it is likely that at least some grain growth has taken place.

The goal of the thesis was to analyse the space arrangement of the gamma - spektrometry laboratory at the RC SÚJB České Budějovice in order to design an optimal regime in a radiological emergency.

A fresh perspective on covert channels is presented in this work. A new class, air-gap covert channels, is defined as an unintentional communication channel established between systems that are physically and electronically isolated from one another. A specific class of air-gap covert channel is studied in depth, out-of-band covert channels (OOB-CCs), which are defined as policy-breaking communication channels established between isolated, physically unmodified systems. It is shown that OOB-CCs can be categorized by the physical channel that they communicate over: acoustic, light, seismic, magnetic, thermal, and radio-frequency, and the hardware that is required at the transmitter and receiver to make covert communication possible. In general, OOB-CCs are not as high-bandwidth as conventional radio-frequency channels; however, they are capable of leaking sensitive information that requires low data rates to communicate (e.g., text, recorded audio, cryptographic key material). The ability for malware to communicate information using a specific type of OOB-CC, the covert-acoustic channel, is also analyzed. It is empirically demonstrated that using physically unmodified, commodity systems (e.g., laptops, desktops, and mobile devices), covert-acoustic channels can be used to communicate at data rates of hundreds of bits per second, without being detected by humans in the environment, and data rates of thousands of bits per second when nobody is around to hear the communication. Defence mechanisms to counter covert-acoustic channels are also proposed and evaluated, and, as a result, best practices for the designers of secure systems and secure facilities are presented. Additionally, the covertness of OOB-CCs, i.e., the amount of data that can be leaked before the channel is detected, is also determined for classical communication channels as well as for covert-acoustic channels.

科学研究費補助金 研究種目:試験研究(B)(1) 課題番号:05555158 研究代表者:谷川 恭雄 研究期間:1993-1994年度

NIL

Dans le cadre des activités de maintenance des centrales nucléaires, les personnes intervenant sur des chantiers en zone contrôlée doivent effectuer des mesures de contamination surfacique sur leurs outils, gants, sur tenue de travail et sur les parties de leur corps susceptible d’être contaminées (cou et tête par exemple). Or, les mesures de contamination surfacique bêta ne peuvent pas toujours être réalisées au plus près des chantiers. Le bruit de fond gamma présent à ces endroits étant élevé et fluctuant, ce dernier perturbe les appareils utilisés habituellement pour la mesure de contamination surfacique. L’objectif principal de ce travail était de concevoir un appareil de mesure adapté à la détection de contamination surfacique bêta de quelques Bq/cm2 (typiquement < 4 Bq/cm2), dans une ambiance gamma de quelques dizaines de µSv/h (typiquement < 100 µSv/h) et fluctuante (typiquement de l’ordre de 30% en 1 seconde). / In the framework of the nuclear power plants maintenance, the onsite workers incontrolled areas must performed some surface contamination controls of their tools, gloves, workingsuits and over their body parts which may be contaminated (neck and head for instance). However,surface beta contamination measurements can’t always been done as close as possible of the working location. The onsite ambient gamma background, being high and fluctuating, may disturb the radiation protection devices commonly used for surface contamination measurements.The main goal of this work was to conceive a radiation protection device adapted to the betasurface contamination of about a few Bq/cm2 (< 4Bq/cm2 typicaly) in a fluctuating (typicaly 30%variation per second) ambient gamma background of a few μSv/h (typicaly <100 μSv/h).

Surface contamination occurs in nuclear facilities, something that is important to detect easily and efficiently. Using today’s methods to detect nuclear surface contamination may cause certain inconsistencies as the human operator is solely trusted to keep the detector at the correct distance and move it at the correct speed. This thesis project aims to address the problem of inconsistent measurements with respect to the current measurement methods. A system is designed to monitor the measurement process with regards to detector velocity and height. The system will trigger a warning when the minimum detectable activity is too high, as it would lead to inconsistent results. This system consists of a cart-detector setup with a scintillation detector and velocity measurement device(s). Software will utilize the measurement data to implement the aforementioned monitoring. The system aims to be compliant with international standards, such as the ISO 11929 and the ISO 7503 standards, and will thus make use of these standards. The result of the part-analysis for each component of the system showed a large inaccuracy regarding the Intertial Measurement Units (IMUs); hence, the robotic wheels were chosen as the main method of measuring speed for this project. The robotic wheels and the detector were shown to be sufficiently accurate for the desired measurements. The Raspberry Pi 4 model B, the on- board computer, was also shown to be performance-wise and property-wise well suited for the project. This project showed that there is a theoretical way to implement the speed of a moving detector-rig into the Minimum Detectable Activity (MDA) formula. However, the implementation investigated in this project suggests that full compatibility with ISO 7503 was not achievable. / Radioaktiv ytkontaminering förekommer i kärnkraftverk, vilket är viktigt att upptäcka snabbt och effektivt. Dagens metoder för att upptäcka radioaktiv ytkontaminering kan lida av viss osäkerhet eftersom man förlitar sig helt på att operatören kan manövrera detektorn på rätt höjd och hastighet. Detta examensarbete behandlar en lösning till det ovan nämnda problemet. Ett ”proof-of-concept”-system som kan övervaka mätprocessen designas. Genom att mäta hastighet och känna till höjden över marken kan en varning meddelas användaren när den minsta detekterbara aktiviteten (MDA) når ett tröskelvärde. Det färdiga systemet är en plattform på hjul med en scintillator- detektor monterad tillsammans med en eller flesta hastighetsmätningsenheter. Systemet bör vara kompatibelt med internationella standarder, till exempel ISO 11929 och ISO 7503. Resultaten från den utvärdering av varje individuell komponent som gjorts visade på en stor mätosäkerhet i de två utvärderade IMUerna. Detta medförde att robothjulen valdes som enda källa för hastighetsmätning. Robothjulen, samt detektorn påvisade god mätsäkerhet, väl lämpad för detta projekt. Även mikrodatorn, Raspberry Pi 4 model B, visade sig vara lämplig sett till prestanda och egenskaper. Projektet resulterade i att det är trott att det finns en lämpligt sätt att i teorin implementera hastighet som en parameter i formeln för MDA. Det är dock värt att nämna att resultaten tyder på att det i denna implementation inte var möjligt att uppnå fullständig kompabilitet ISO 7503.