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The Tandem Laboratory at Uppsala University, a national research infrastructure forworld-leading materials analysis, has a long history of performing hydrogen measurementusing NRA (Nuclear Reaction Analysis). This project intents to diversify the infras-tructure for hydrogen measurement by investigating the feasibility of an advanced ERCS(Elastic Recoil Coincidence Scattering) system, enabling finer detection limits. The sys-tem, based on a DSSD (Double-sided Silicon Strip Detector) and a 64 channel dataacquisition system, is set up, tested and calibrated using both single- and triple peakα-radiation sources. Results indicate that all but 14 front segments work correctly. Thestatus of three segments could not be determined due to faulty pre-amplifier channels.Two of the segment faults were found to be caused by snapped electrode connections onthe DSSD. The status of half the backside rings could not be determined due to a faultypre-amplifier. Despite this, the energy spectrum of a 241Am α-particle source was mea-sured with good resolution, showing a clear energy peak corresponding to the 5486 keVα-particles with FWHM equaling 270 keV. Calculations indicate an average dead timefor the working channels of 1.37 %. Measurements on a 239Pu-241Am-244Cm α-particlesource resulted in three main peaks with energies at 5155 keV, 5486 keV and 5805 keV,corresponding to the three peaks of the α-source. Results indicated FWHMs of 208 keV,190 keV and 169 keV respectively, with an average dead time of 32.8 %. These resultsdemonstrate that the detector is in working condition. Furthermore, the pre-amplifiershave been examined and any dead channels are accounted for.

Nuclear weapons are an ever-present danger which threatens our very existence, which is whymany call for total nuclear disarmament. To do this, we need to know how many nuclear bombsthere are in the world. However, to be sure that the true number is given, we must useapproximations and simulations to determine the nuclear capacity of a given country.Additionally, to know that these numbers are accurate, sensitivity studies are carried out.In this case, such a study was executed to measure the sensitivity of design and operationalparameters of three reactors: Ågesta, NRX, and CANDU, with respect to their plutoniumproduction and quality. The parameters of interest are power density, fuel temperature, fueldensity, fuel rod thickness, moderator temperature, moderator density, coolant temperature,coolant density, pitch, initial enrichment, and cycle length.The study relied on the simulation tool Serpent, which is a Monte-Carlo code for nuclearreactions. The parameters of interest were altered one at a time, usually by ±10% of theirnominal value, to see how the amount of plutonium changes, as well as its quality.The result showed that the power density and initial enrichment had the greatest impact onplutonium production, however, the biggest factor in terms of plutonium grade was the cyclelength. After just 30 days, the plutonium will decrease from weapon’s grade to reactor gradequality, which marks the clearest difference between how a reactor would be run for civilian orweapon purposes. Other parameters like fuel temperature and coolant temperature and densitydid not affect the plutonium in any significant fashion.

To further the understanding and knowledge about fusion plasmas and their behaviour during different conditions, it is important to be able to collect information about the plasma and the processes occurring within it. Visible spectroscopy, or the study of the visible wavelength light emitted by the plasma, is a useful tool in this search for knowledge. This thesis is based on experiments where visible wavelength light has been measured and analysed in order to determine quantities about the emitting source. Doppler shift measurements of spectral lines have been utilised to determine the toroidal rotation velocities of plasma impurity ions and to study the correlation with mode rotation and the effect of active feedback control of the resistive wall modes. Information on the impurities present in the plasma has been determined and the calibrated intensities of spectral lines has yielded impurity concentrations, particle fluxes and electron temperature and densities. Ion temperatures have been determined from Doppler broadening measurements. The measured vibrational and rotational band structure of deuterium molecular spectra has been analysed in order to calculate rotational and vibrational temperatures, relative populations and molecular particle fluxes. The effect of the molecular flux on simple calculations of atomic flux has also been studied. Specific molecular states and transitions of deuterium have also been probed with synchrotron radiation to study the level and transition energies. The measurement and analysis of visible wavelength light has been demonstrated to be a sensitive diagnostic tool in the quest for increased knowledge about fusion plasmas and molecular structure. / QC 20101215

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The main goal of the GBAR (Graviational Behaviour of Antihydrogen at Rest) experiment is to investigatethe gravitational effect on antimatter by measuring the classical free fall of an antihydrogen atom. The requiredpositrons are created by pair production inside a tungsten target and are moderated using a tungsten mesh. In thisthesis, two schemes are examined to determine the feasibility of replacing the tungsten moderator with a solid neonmoderator which would increase the moderation efficiency from η+,W ≈ 10−3 to η+,Ne ≈ 10−2. For the first scheme,the moderator is placed directly behind the target. We determined the power deposition inside the moderator tobe approximately 60 W which is at least one order of magnitude larger than the available cooling power to keep theneon at the required temperature. For the second scheme, a combination of magnetic fields is applied to separatethe electrons from the positrons before hitting the moderator. The field configuration was optimized leading to 11%to 16% of positrons hitting the moderator that have mostly small kinetic energies. Finally, an energy consideringscoring function was developed which values slow positrons higher and the relevant magnetic fields were optimizedwith respect to reaching the maximal score.

I report on the derivation, development and computer implementation of methods for computing the energies and forces between small rigid polarizable molecules, that are defined by the center-of-mass moments of their electronic and nuclear charge distributions and their linear response moments. The formalism is based on compact and efficient storage and manipulation of symmetric Cartesian tensors of arbitrary rank, and a general formula for the Cartesian gradients of one-dimensional interaction (kernel) potentials. The theory is applied to many-body interactions among water molecules. Permanent moments of the water molecule are computed up to the 9th order with quantum-chemistry software and their basis-set dependence is investigated. Response moments up to the 5th order are similarly investigated. Kernel potentials for electronic, nuclear and polarized interactions are suggested and compared to interaction energies from symmetry-adapted perturbation-theory. I discuss vibrational degrees of freedom and report on a novel method for fitting high rank moment tensors to a flexible geometry. The method is based on decomposition of the tensor into a sum of outer products of vectors, which are defined in the lab-frame by the molecular geometry. I show that the formalism, which is based on an asymptotic expansion, can give good results at all ranges.

The recent development of perovskite-based solar cells have shown a remarkably fast increase in power conversion efficiency making them a promising low-cost alternative to conventional cells. The most successful class of materials however, the lead-halide perovskites, are held back due to toxicity and stability issues significantly limiting their use. Because of this, the investigation of new, lead-free, light-absorber materials as a replacement is an important step towards improved solar cells. The focus of this licentiate thesis is the study of bismuth-based materials and their photovoltaic properties through electronic structure calculations. Specifically, the cubic-phase AgBi2I7 under gradual substitution of either bromine or antimony is investigated using density functional theory under periodic boundary conditions. This enables calculations of the system's energy levels and band structure. Furthermore, the energy variance of the employed model of the system is sampled with respect to its level of ion disorder to obtain a better understanding of the distribution of ions within the crystal. The materials are found to have good optical properties but comparatively low efficiencies. The introduced substitutions allow fine-tuning of the system's band gap and is shown to increase the overall performance of the solar cells. In addition, spin-orbit coupling effects are demonstrated to be important when treating these bismuth-based systems. The crystal structure is found to have a significant preference for separating its silver ions and cation vacancies.

Measurements of atomic and ionic data has been an active research area since the beginning of spectroscopic studies. The experimental data deduced from thesestudies are of great interest for our understanding of fundamental as well as applied physics. The metastability of certain energy levels has been used toexplain phenomena in widely different fields ranging from the principles of the laser to observations of forbidden spectral lines originating fromastrophysical objects. Eventhough measurements of radiative lifetimes have been carried out for many decades new interesting results are still found in theexplanation of phenomena observed in these studies. The technological development in the field of atomic physics has provided researchers with several toolswhich have opened up completely new possibilities in recent years. Atoms and ions can now be stored for long times which allows studies of extremely weakprocesses. In this thesis results from studies of weak radiative decays of metastable levels are presented. The measurements were carried out utilizing a laserprobing technique together with ions stored in the ion storage ring CRYRING at the Manne Siegbahn laboratory in Stockholm, Sweden. The longest radiativelifetime measured so far in a storage ring, 89 s in singly ionized barium, is presented along with a completely new method for determining extremelylong radiative lifetimes. The thesis also includes new interesting results from lifetime measurements in argon which revealed the unexpected importance of an E3 decay channel. This is to the best of our knowledge the first ever observation of an E3 transition rate of this magnitude in a singlycharged ion. All lifetime measurements are presented with complementary calculations by our collaborators at Université de Mons-Hainaut and Université de Liège, Belgium. The studies of BaII are also part of a collaboration with the Institute of solid state physics of the Bulgarian Academy of Sciences.

This master thesis deals with simultaneous measurement and discrimination of temperature and strain using fiber Bragg gratings(FBGs). Saab Avionics is seeking for a further development of the overheat detection system that gives a warning when a heat leakage is detected. A further development is to distinguish between temperature and strain and give a warning when strain occurs that correspond to a temperature increase of 10°C. The present work was performed for Saab Avionics and the experiments were carried out in Kungliga Tekniska Högskola(KTH) at department of Laser Physics.  The aim of this thesis was to study some methods for simultaneous measurement of temperature and strain with FBGs and try to discriminate them. Two methods were investigated, a sensor design containing a boron-codoped germanosilicate fiber and a germanosilicate fiber and fibers with different cladding diameters. The gratings were heated in an oven and stressed with solder between a translation stage and a stationary stage. For the boron-codoped germanosilicate fiber the temperature sensitivity was ~ 2 times lower than the germanosilicate fiber, while they had similar strain responses. For the second sensor design with different cladding diameters, for a 80 μm cladding diameter the strain response was ~ 2.5 times higher that the 125 μm cladding diameter, while for a 100 μm cladding diameter the strain response is ~ 1.6 times higher than the 125 μm cladding diameter. For a 125 μm, a 100 μm and a 80 μm cladding diameter the temperature sensitivities were similar.