The neutron is a valuable tool in many fields of science due to its properties regarding electric charge and magnetic moment. However, these properties also makes it difficult to detect. Through simulation one can optimize the detector environment to best correspond with the needs for a specific experiment. In this project, a detector environment is simulated, consisting of a neutron and gamma point source and one detector for each type of particle. The simulated results were in good agreement with the underlying theory and the simulation can, therefore, be used in future work.

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The quality grades are what determines the value of sawn timber. Therefore the grading process is essential for the profitability of a sawmill. At a modern sawmill in northern Sweden, a CT Log Computed Tomography is used in the saw line to optimize the cutting solutions by virtual 3D reconstruction of the log features. By adjusting the position of the log according to the optimal solution before cutting, the aim is to increase the quality and final resale value of the sawn timber. However, measurement errors in the virtual and final grading systems cause inconsistencies that decrease the agreement in grading. The grading process uses a rule-based system based on the Nordic Timber Grading Rules, which depends strongly on the size and shape of knots. If knots are measured incorrectly they could falsely exceed the allowed value for a certain quality, resulting in an inaccurate quality grade. The results from this initial project, show that using multivariate modeling instead of the traditional rule-based grading system improves the agreement between the virtual and final grading. The accuracy in grading increases with up to 19%, resulting in an agreement of 73%. A better agreement between the two systems would allow the process to take advantage of the full potential of the CT, increasing the profitability of the sawmill. The results are promising, but before implementing the method in the sawmill further testing and development have to be done to ensure optimal improvement.

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The potential for characterizing the spin and mass of dark matter at the Large Hadron Collider (LHC) given a 5 sigma confidence level discovery has been studied. The search for dark matter is one of the big open question in particle physics as observations predict 84 percent of the matter in the universe to be dark matter, however no detection has been made. In this study two production channels at the LHC of weakly interacting massive particles with different spin have been studied in the framework of a simplified model. The processes if detected have the signature of a mono-jet and missing transverse energy. The assumption made is that the dark matter is a scalar or a Dirac fermion particle and interacts with the top quark and a Beyond the Standard Model color charged mediator via a loop process. The considered mediators are a scalar top partner and a fermionic top partner. The results from recasting conclude that in a narrow region in the mass-mass-plane for the dark matter and the mediator a search is adequate and given a discovery characterization of the spin and mass is possible.

The present master thesis concerns a study of collimator designs for a high-spatial-resolution Gamma Emission Tomography (GET) instrument for used fuels utilizing Monte Carlo simulation codes. Designing a collimator for this purpose is a multilateral process that requires many interconnected and conflicting objectives to be taken into consideration. The purpose is to design a high-spatial-resolution GET system that combines in the best way the properties of a high detector count-rate, high photopeak to total spectrum ratio, low detector dead time and low leaking background radiation through the collimator material. As to achieve the best trade-off among these objectives, the GEANT4 and the Serpent 2 simulation codes were implemented. Used fuel contains various γ-ray emitting radionuclides and depending on the burnup history and cooling time their absolute intensities vary (i.e. for higher γ-ray intensity from the fuel, bigger collimator length is demanded). For this reason, Serpent 2 was used to produce long- and short-cooled fuel gamma emission spectra of low and high burnup. According to the obtained spectra, the collimator slit dimensions and material were determined. As far as the collimator length and material is concerned, the GEANT4 simulation toolkit was used to deal with shielding problems by applying the geometry splitting/Russian roulette variance reduction techniques. Serpent 2 simulations were performed in order to determine the transmitted signal intensity through the slit for various slit height and width dimensions. Finally, it was investigated the peak-to-total ratio change for different slit sizes and when a cavity structure was added along the slit length. / Denna uppsats handlar om kollimatordesign för hög rumsupplösning i gammaemissionstomografi (GET) av använt kärnbränsle genom att använda Monte Carlo-simuleringskoder. Att konstruera en kollimator för detta syfte är en process som kräver hänsyn till sammankopplande och ibland konflikterande målsättningar. Målet är att designa en GET-system som på bästa sätt kombinerar följande specifikationer: hög räknehastighet i detektorn, hög peak-to-total ratio, låg detektors dödtid och låg bakgrund från läckage genom skärmingsmaterialet. För att uppnå bästa möjliga resultat mellan dessa punkter användes simuleringskoderna GEANT4 och Serpent 2. Använt kärnbränsle innehåller varierande radionuklider och beroende på deras utbränning och nedkylningstid deras emissioner (absolutintensitet) varierar (t.ex större kollimatorers längd krävs vid högre intensitet från bränslet). Serpent 2 har använts för att beräkna gammaemisionsspektra för lång- och kort-kylda bränslen med låga och höga utbränningar. Med dessa hypotetiska bränslen, har spaltdimensioner och material undersökts. Beträffande spaltlängden och materialval användes GEANT4 genom att tillämpa variansreduktionsteknikerna geometry splitting/Russian roulette. Spaltbredden och spalthöjden hittades med Serpent 2 genom att beräkna transmissionssignal genom spalter av varierande dimensioner. Slutligen, undersöktes hur peak-to-total ratio ändras för olika spaltmått och även när en kavitet introduceras i kollimatorn.

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