This thesis presents a method for a small, inexpensive mobile robot equipped with a single high resolution scintillation detector to quickly survey an area and convey information about local sources of gamma radiation to a remote human operator. This is achieved by surrounding the detector with a lead sheath that blocks all gamma rays except those incident along the detector???s axial direction. A horizontal scan is performed by rotating the detector and a directional profile of gamma radiation is constructed. In addition a visual panorama of the local area is assembled using a camera mounted on the detector. A plot of the detector signal versus angle is then overlaid on top of the visual panorama and visible peaks clearly indicate the direction of local gamma radiation sources. Moreover, measuring the energy spectrum of gamma rays in each direction produces a 2D count frequency histogram where distinct peaks indicate the energy and direction of local gamma ray sources allowing the identification of different radio-isotopes.

This thesis considers source localization and tracking when both the signal propagation model and the source motion dynamics are unknown. Algorithms are developed for different scenarios. The algorithms are discussed when a source is stationary or mobile, under the condition when sensors are fixed or mobile. These algorithms exploit the strictly decreasing properties of the model in terms of distance, but do not depend on the form and the values of the models. Therefore, these algorithms could be applied when the signal propagation models and the source motion are unknown. The only assumption made is that the signal propagation strength decreases in distance. For a given performance specification, the optimal number and placement of the sensors is also discussed. Convergence and other properties of the algorithms are established under various noise assumptions.

The thesis is generally focused on summarization of the information related to the high activity sealed sources of ionizing radiation, known as HASS, which are widely used in a variety of sectors in whole world and the Czech Republic as well. The thesis discusses specific cases of actual use of HASS, technical specification, types of occurring radionuclides and examples of use. The biological effects of ionizing radiation on humans related to HASS and some examples of specific adverse events are also described. In the intentions of this thesis is to take into account not only risks arising from incorrect manipulation, but also risks associated with potentially abuse of HASS by terrorist organization. For these reasons, the thesis outlines the basic security requirements associated to the international standards and also mentioned in legislation of CR. In connection with these requirements the suggestion of particular security system on specific workplaces with HASS is than discussed. To supplement the reader's imagination of the real problems of HASS in the Czech Republic, there is created a statistical overview of all HASS located in the Czech Republic. This includes the total number of HASS and the largest area of use devided into various areas of application (medicine, industry, research/education, etc.), representation of most commonly used radionuclides, the geographical distribution of HASS in the Czech Republic and the distribution in terms of the most common activities. The State Office for Nuclear Safety Registry was used as a source for this statistical overview. In the discussion part of the thesis, the real possibility of abuse of HASS and also a possible ways of gain from the perspective of a potential lone striker or a wider terrorist organization is discussed. In general, the following thesis is a logical synthesis of relevant information allowing the reader to obtain a relatively comprehensive view on the whole issue of HASS, especially from the perspective of the broader field of radiation protection emphasized on achieving a socially acceptable security level of all high activity sources of ionizing radiation.

Energy resolution characteristics of silicon surface barrier detector signals amplified by different preamplifiers and spectroscopic amplifiers have been studied. The characterization has been done using alpha particles from an 241Am source and spontaneous fission fragments from two Cf sources. The alpha and spontaneous fission activities of the sources have been measured and the isotopic compositions, ages, and initial activities of the two Cf sources have been calculated using the results from the activity measurements. 82.3% and 82.5% of the spontaneous fission activity of the two sources is found to originate from 252Cf. Heavy ion detection properties of two Si detector setups have been determined by measuring spontaneous fission fragments from one of the Cf sources in coincidence. The mass distribution of fission fragments is derived from the pulse spectra of the coincidence measurements. The conditions for future time resolution measurements have been established. Inquiries on commercially available ultra-thin Si detectors have been made. The purpose is to upgrade detector telescopes to lower the energy threshold of ΔE-ΔE-E identification of particles from neutroninduced nuclear reactions. Three manufacturers of Si detectors with thickness 20-25 µm and active area around 450 mm2 have been listed together with properties of the three offered detectors.

Parallel-plate avalanche counters, PPACs, are commonly used to detect fission fragments. The PPAC detects them and mark (very accurately) the time of detection. Such measurements can be used to measure the neutron energy (via time-of-flight) to study neutron-induced fission.This project report provides a method that, together with the discussed improvements, allows the fabrication of good quality PPAC detectors. Several PPACs are manufactured and the electrodes are built from 0.9 µm thick mylar foils which are evaporated with a 40-80 nm thin layer of aluminum.The developed PPACs are characterized with well known radioactive Cf and Am sources (the source characterization also found in this report), and compared against each other. Additionally, the PPAC signal amplitude spectrum are found to follow theoretical expectations with regards to angular dependence, gas pressure and an applied electrode voltage.At a specific applied electrode voltage and range of gas pressures (3-9 mbar), the measured time resolutions are 2.24-1.38 ns. A trend is observed for finer time resolutions at higher gas pressures. / Parallel-plate avalanche counters, PPACs, används ofta för att detektera fissionsfragment. PPAC:en detekterar fragmenten med väldigt god tidsupplösning och således kan PPAC detektorer användas till att mäta neutron energier (mha. flygtidsmetoden), vilka uppmätts för att studera neutroninducerad fission.Det här projektet och den här rapporten beskriver en metod, med föreslagna förbättringar, som möjliggör tillverkning av PPAC detektorer av bra kvalitet. Under projektet har flera PPACs byggts med elektroder gjorda av 0.9 µm tunn mylar förångade med 40-80 nm aluminium. De tillverkade PPAC detektorerna är karaktäriserade med väl kända radioaktiva Cf- och Am-källor (dessa karaktäriseras även i den här rapporten). Detektorerna är sedan jämförda mot varandra och är funna att följa teoretiska förväntningar med avseende på vinkel-, gastryck- och pålagd elektrodspänningsberoende.Resultaten av projektet, som besvarar flera tidigare frågeställningar och bekräftar vissa antaganden, flyttar utsikten och förståelsen framåt för hur PPACs fungerar och vad forskarna kan uppnå med dem.