<p>Quantum chromodynamics has interesting limits both in the low and the high-energy region. In the low energy region one has phenomenology of meson interactions which are still not clearly understood. In the high-energy region one wants to find a new theory which will envelope gravity and the standard model in the quantum framework, possibly via some kind of string theory.</p><p>In this thesis some aspects are touched upon including both these limits. On the one hand we look at meson scattering close to threshold and try to describe cross sections via phenomenological models such as the two-step model. We then go on and dwell upon noncommutative geometry, a framework which has been successful in describing certain aspects of the theory of strings.</p><p>The low-energy calculations gave some insight into the need for finding better understanding of the theories of mesons. The work on noncommutative geometry was on the other hand fruitful in gaining understanding of certain connections between different star products and their relations on a local level.</p>

High power fusion plasmas produced in the world’s largest facility for magnetic confinement experiments (JET), have been studied using the neutron emission measured with the magnetic proton recoil (MPR) spectrometer. The MPR has been used to observe plasmas since 1996 including those of deuterium-tritium leading to several fusion records and corresponding observational achievements of neutron emission spectroscopy. Noteworthy are novel studies of the complex states of fuel ions arising through plasma heating by neutral beam (NB) injection and radio frequency (RF) power. This thesis concerns the analysis of MPR data on the neutron emission from NB heated discharges alone and in combination with RF. A main objective of these studies has been the effect of supra-thermal fuel ion reactions on the fusion power as compared to the basic thermal component. The analysis was based on dedicated models to describe the velocity distributions of the ion population under the influence of the NB and RF heating in a parametric form allowing trial neutron spectra to be calculated and fitted to the data to select the kinetic state of the fuel ions that best described the MPR observations. Spectral signatures of different underlying plasma states and phenomena were identified and results from up to five different ion reaction contributions to the fusion power were demonstrated besides the global plasma features of toroidal rotation. Moreover, the thesis presents examples of derived detailed plasma information from MPR data such as the kinetic energy densities for the thermal and supra-thermal parts of the fuel ion population as well as the synergetic coupling of RF power to the fast ions from NB injection. The results constitute a stepping-stone for neutron emission spectroscopy as a main diagnostic for ITER and other future fusion experiments on thermonuclear ignition.

Quantum chromodynamics has interesting limits both in the low and the high-energy region. In the low energy region one has phenomenology of meson interactions which are still not clearly understood. In the high-energy region one wants to find a new theory which will envelope gravity and the standard model in the quantum framework, possibly via some kind of string theory. In this thesis some aspects are touched upon including both these limits. On the one hand we look at meson scattering close to threshold and try to describe cross sections via phenomenological models such as the two-step model. We then go on and dwell upon noncommutative geometry, a framework which has been successful in describing certain aspects of the theory of strings. The low-energy calculations gave some insight into the need for finding better understanding of the theories of mesons. The work on noncommutative geometry was on the other hand fruitful in gaining understanding of certain connections between different star products and their relations on a local level.

<p>Resonant states are multiply excited states in atoms and ions that have enough energy to decay by emitting an electron. The ability to emit an electron and the strong electron correlation (which is extra strong in negative ions) makes these states both interesting and challenging from a theoretical point of view. The main contribution in this thesis is a method, which combines the use of <i>B </i>splines and complex rotation, to solve the three-electron Schrödinger equation treating all three electrons equally. It is used to calculate doubly excited and triply excited states of ⁴<i>S</i> symmetry with even parity in He^-. For the doubly excited states there are experimental and theoretical data to compare with. For the triply excited states there is only theoretical data available and only for one of the resonances. The agreement is in general good. For the triply excited state there is a significant and interesting difference in the width between our calculation and another method. A cause for this deviation is suggested. The method is also used to find a resonant state of ⁴<i>S</i> symmetry with odd parity in H^2-. This state, in this extremely negative system, has been predicted by two earlier calculations but is highly controversial.</p><p>Several other studies presented here focus on two-electron systems. In one, the effect of the splitting of the degenerate H(<i>n=</i>2) thresholds in H^-, on the resonant states converging to this threshold, is studied. If a completely degenerate threshold is assumed an infinite series of states is expected to converge to the threshold. Here states of ¹<i>P</i> symmetry and odd parity are examined, and it is found that the relativistic and radiative splitting of the threshold causes the series to end after only three resonant states. Since the independent particle model completely fails for doubly excited states, several schemes of alternative quantum numbers have been suggested. We investigate the so called DESB (Doubly Excited Symmetry Basis) quantum numbers in several calculations. For the doubly excited states of He^-mentioned above we investigate one resonance and find that it cannot be assigned DESB quantum numbers unambiguously. We also investigate these quantum numbers for states of ¹<i>S </i>even parity in He. We find two types of mixing of DESB states in the doubly excited states calculated. We also show that the amount of mixing of DESB quantum numbers can be inferred from the value of the cosine of the inter-electronic angle. In a study on Li^-the calculated cosine values are used to identify doubly excited states measured in a photodetachment experiment. In particular a resonant state that violates a propensity rule is found.</p>

Resonant states are multiply excited states in atoms and ions that have enough energy to decay by emitting an electron. The ability to emit an electron and the strong electron correlation (which is extra strong in negative ions) makes these states both interesting and challenging from a theoretical point of view. The main contribution in this thesis is a method, which combines the use of B splines and complex rotation, to solve the three-electron Schrödinger equation treating all three electrons equally. It is used to calculate doubly excited and triply excited states of 4S symmetry with even parity in He-. For the doubly excited states there are experimental and theoretical data to compare with. For the triply excited states there is only theoretical data available and only for one of the resonances. The agreement is in general good. For the triply excited state there is a significant and interesting difference in the width between our calculation and another method. A cause for this deviation is suggested. The method is also used to find a resonant state of 4S symmetry with odd parity in H2-. This state, in this extremely negative system, has been predicted by two earlier calculations but is highly controversial. Several other studies presented here focus on two-electron systems. In one, the effect of the splitting of the degenerate H(n=2) thresholds in H-, on the resonant states converging to this threshold, is studied. If a completely degenerate threshold is assumed an infinite series of states is expected to converge to the threshold. Here states of 1P symmetry and odd parity are examined, and it is found that the relativistic and radiative splitting of the threshold causes the series to end after only three resonant states. Since the independent particle model completely fails for doubly excited states, several schemes of alternative quantum numbers have been suggested. We investigate the so called DESB (Doubly Excited Symmetry Basis) quantum numbers in several calculations. For the doubly excited states of He- mentioned above we investigate one resonance and find that it cannot be assigned DESB quantum numbers unambiguously. We also investigate these quantum numbers for states of 1S even parity in He. We find two types of mixing of DESB states in the doubly excited states calculated. We also show that the amount of mixing of DESB quantum numbers can be inferred from the value of the cosine of the inter-electronic angle. In a study on Li- the calculated cosine values are used to identify doubly excited states measured in a photodetachment experiment. In particular a resonant state that violates a propensity rule is found.

<p>Measuring lifetimes of excited nuclear states can give important information on the internal structure of the nucleus. This thesis is based on two experiments performed in Italy and in the USA in order to deduce the lifetimes of excited states in ¹⁶⁵Lu and ¹⁰⁷Cd. The lifetimes were measured using the Recoil Distance Method and the reduced transition probabilities between states have been calculated from the lifetimes in a model independent way. In the analysis of the data from the experiment on ¹⁶⁵Lu, the shape of the nucleus is investigated using a collective rotational model to describe the observed excited states. A possibility of a triaxial shape of this nucleus is discussed. In the second experiment the obtained reduced transition probabilities for the nucleus ¹⁰⁷Cd are compared to theoretical predictions for vibrational and rotational excitation modes</p>

<p>A facility for studies of elastic neutron scattering in the 50–130 MeV range has been developed. In addition to elastic neutron scattering, it has been used for (n,p) and (n,d) reaction experiments. The performance of the device has been illustrated in measurements of the (n,p) and (n,n) cross sections on ¹H and ¹²C.</p><p>Elastic neutron scattering from ¹²C and ²⁰⁸Pb has been studied at 96 MeV in the 10–70 degree interval. The achieved energy resolution, 3.7 MeV, is about one order of magnitude better than for any previous experiment above 65 MeV incident energy. The present experiment represents the highest neutron energy where the ground state has been resolved from the first excited state in neutron scattering. A novel method for normalization of the absolute scale of the cross section has been used. The estimated normalization uncertainty, 3 %, is unprecedented for a neutron-induced differential cross section measurement on a nuclear target.</p><p>The results are compared with modern optical model predictions, based on phenomenology or microscopic nuclear theory. The data on ²⁰⁸Pb are in general in good agreement with the theory models.</p><p>All theory models fail to describe the ¹²C data in the 30–50 degree interval, where the models predict a saddle structure not displayed by the present experimental data. Various reasons for this discrepancy have been investigated. For the other parts of the angular range studied, the agreement is good.</p><p>These measurements have to a large degree been motivated by needs in various application areas, i.e., nuclear waste incineration by fast neutrons and biomedical effects caused by neutrons. The implications of the present results on these applications are discussed.</p>

<p>The fuel assemblies used at the Swedish nuclear power plants contain typically between 100 and 300 fuel rods. An experimental technique has been demanded for determining the relative activities of specific isotopes in individual fuel rods without dismantling the assemblies. The purpose is to validate production codes, which requires an experimental relative accuracy of <2 % (1 σ).</p><p>Therefore, a new, non-destructive tomographic measurement technique for irradiated nuclear fuel assemblies has been developed. The technique includes two main steps: (1) the gamma-ray flux distribution around the assembly is recorded, and (2) the interior gamma-ray source distribution in the assembly is reconstructed. The use of detailed gamma-ray transport calculations in the reconstruction procedure enables accurate determination of the relative rod-by-rod source distribution.</p><p>To investigate the accuracy achievable, laboratory equipment has been constructed, including a fuel model with a well-known distribution of ¹³⁷Cs. Furthermore, an instrument has been constructed and built for in-pool measurements on irradiated fuel assemblies at nuclear power plants.</p><p>Using the laboratory equipment, a relative accuracy of 1.2 % was obtained (1 σ). The measurements on irradiated fuel resulted in a repeatability of 0.8 %, showing the accuracy that can be achieved using this instrument. The agreement between rod-by-rod data obtained in calculations using the POLCA–7 production code and measured data was 3.1 % (1 σ).</p><p>Additionally, there is a safeguards interest in the tomographic technique for verifying that no fissile material has been diverted from fuel assemblies, i.e. that no fuel rods have been removed or replaced. The applicability has been demonstrated in a measurement on a spent fuel assembly. Furthermore, detection of both the removal of a rod as well as the replacement with a non-active rod has been investigated in detail and quantitatively established using the laboratory equipment.</p>

<p>Reaction cross sections were measured for protons at 65.5 MeV, for deuterons at 37.8, 65.5, 97.4 MeV, for ³He at 96.4, 137.8, 167.3 MeV, and for ⁴He at 69.6, 117.2, 163.9 and 192.4 MeV. Targets were ⁹Be, ¹²C, ¹⁶O, ²⁸Si, ^40,48Ca, ^58,60Ni, ^{112,116,118,120,124}Sn and ²⁰⁸Pb. ⁴⁸Ca and ¹¹⁸Sn targets were used only for some of the measurements. Rest of the targets have been measured for all energies and projectiles but ⁴He at 69.6 MeV where reaction cross sections were measured for ⁹Be, ¹²C, ¹⁶O, ²⁸Si, ⁴⁰Ca targets. A modification of a standard attenuation technique was used. Details of the experimental design are presented.</p><p>Experimental uncertainties were 2-3% for p, 3% for d and 3-10% for ^3,4He. </p><p>A strong forward peaking of the reaction products was observed for ^3,4He. Therefore the standard reaction cross section measurement technique was not applicable for these projectiles. The forward peaking is also responsible for the increase of experimental uncertainties for these projectiles. The forward peaking of the reaction products is not known for other projectiles and has also not been observed with ^3,4He at different - both higher and lower - energies. Possible explanations for this phenomenon are discussed.</p><p>Optical model calculations of the reaction cross sections are in good agreement with the measured values.</p><p>The measurements were performed with beams from the Gustav Werner cyclotron at the The Svedberg Laboratory, Uppsala.</p>

<p>The reaction cross section gives the probability that a particle will undergo a nonelastic process when passing through a nuclear medium. Therefore reaction cross section data are of importance both for theoretical studies and for applications in such diverse fields as medicine, biology, astrophysics and accelerator-driven transmutation of nuclear waste.</p><p>There exist many data sets with angular distributions of elastic scattering, but very few measurements of the complementary reaction cross section have been performed. The measurement is in principle simple but has in practice proved to be very difficult to perform, and the relatively limited amount of experimental data displays some serious inconsistencies.</p><p>Results from measurements of reaction cross sections are presented for:</p><p>• ³He on ⁹Be, ¹²C, ¹⁶O, ²⁸Si, ⁴⁰Ca, ^58,60Ni, ^{112,116,118,120,124}Sn and ²⁰⁸Pb at 96, 138 and 167 MeV</p><p>• protons on ¹²C, ⁴⁰Ca, ⁹⁰Zr and ²⁰⁸Pb at six energies in the energy range 80-180 MeV, and on </p><p>⁵⁸Ni at 81 MeV. </p><p>Experimental uncertainties were 3-9% for ³He and 1.5-8% for protons.</p><p>The apparatus and the experimental method used for the measurements of reaction cross sections, using a modified attenuation technique, is described. The detection method enables simultaneous measurements of reaction cross sections for five different sizes of the solid angles in steps from 99.0 to 99.8% of the total solid angle. The final results are obtained by extrapolation to the full solid angle.</p><p>Experimental results are compared with predictions from optical model calculations using phenomenological global optical potentials.</p><p>Phenomenological parametrizations of reaction cross sections for scattering of projectiles on targets are presented. The parametrizations show that reaction cross sections are very sensitive to matter distributions at very large radii of both the projectile and the target. For protons the derived relations makes it possible to predict the reaction cross sections on targets for which no experimental data exist.</p>