[en] The low field dc magnetic properties and the magnetic relaxation behaviour of some high-temperature superconductors and a conventional extreme type 2 superconductor have been studied. It was found that the magnetic relaxation behaviour of the conventional Chevrel phase superconductor PbMo₆S₈ and the high temperature superconductors YBa₂Cu₃O₇ and Bi₂Sr₂CaCu₂O₈ show major similarities that can be attributed to the common property of these materials; and extremely short coherence length. At low fields the time decay of the magnetization is small and follows a logarithmic law, as predicted in the classical Anderson-Kim flux creep model, whereas at higher fields a large and non-logarithmic decay, which qualitatively is predicted by both the collective creep theory and the vortex glass model, is found. The anisotropic properties of the high-temperature superconductor Bi₂Sr₂CaCu₂O₈ were examined. At low fields the behaviour could be described within the anisotropic 3D Ginzburg-Landau theory with an effective mass anisotropy of the order of 20. Measurements at low fields of the zero-field-cooled relaxation in sintered samples of YBa₂Cu₃O₇ showed that thermally activated intergranular flux motion exists in granular high-temperature superconductors. The intergranular creep is much smaller than the giant intragranular flux creep measured at higher fields. When cooling a sintered sample of Bi^_Sr₂CaCu₂O₈ in a very small magnetic field a novel feature of high-T_c superconductors was revealed; instead of the anticipated negative (diamagnetic) signal the susceptibility attained a positive value. The effect was named 'anti-Meissner effect' since the behaviour was opposite to the ordinary Meissner effect. The phenomenon is consistent with the idea of spontaneous orbital moments that could exist in a material containing Josephson weak links

[en] Experimental and theoretical investigations of the electron structure of metals in external magnetic fields have been performed. The experimental technique is based on the de Haas - van Alphen effect and reveals the anisotropic behaviour of the Zeeman splitting of cyclotron orbits on the Fermi surface. For the X-centered hole pockets in Pt a variation of the cyclotron orbit g factor, g_c, from ∼0.5 to ∼3.4 was found. On the double X-pocket holes in Ir g_c varies from ∼0.5 to ∼2, but with a different anisotropic behaviour between the two X pockets. For the calculations of the Zeeman splitting, the agreement is excellent with experimental results in the alkali metals Na, K, and Rb, while Cs shows large discrepancy. In the transition metals investigated the agreement is very good for Pd but worse in Ir and Pt. For the noble metals the calculated anisotropic behaviour of the Zeeman splitting agrees with the experiments. Field-induced spin and orbital moments and the corresponding paramagnetic susceptibility have been calculated for the metals mentioned above and for Li, Rh, α-Ce, fcc-U, and fcc-Pu. With a few exceptions the estimates of the total susceptibilities agree with experimental values. The transition metals are shown to possess an unexpectedly large orbital contribution to the magnetization due to the orbital term in H_z. In the f system, the spin - orbit energy is suppressed by the Zeeman energy and the induced spin and orbital moments are parallel, in spite of the fact that the f shell is less than half filled. The high-field magnetization of Pd and α-Ce is investigated by performing calculations for field strengths up to several thousand tesla. The magnetization curves are dominated by density of states effects and no metamagnetic phase transitions are revealed

[en] Radiohalogens are widely used in nuclear medicine, both as tool for diagnostic in vivo imaging, and in radionuclide therapy. This study deals with the use of radiohalogens; separation, precursor synthesis, labeling and biological behavior. The focus is on ²¹¹At and ¹²⁴I, the former being a candidate for nuclide therapy and the latter potentially useful for diagnostic imaging and Auger-electron based radiotherapy. For astatine the separation, labeling and some biological behavior is described, and for iodine the latter two. Astatine was separated from an irradiated bismuth target by dry distillation. A novel cryotrap was developed for the isolation of astatine and subsequent synthesis of radiolabeled compounds. 5-[²¹¹At]astato-2'-deoxyuridine (AUdR) and N-succinimidyl-4-[²¹¹At]astatobenzoate (SAB) were synthesized in 95% respectively 90% radiochemical yields. The former is incorporated into DNA of proliferating cells and can therefore be used as an endoradiotherapeutic agent. The latter is a conjugate for the astatination of proteins. Human epidermal growth factor (hEGF) was tagged with astatine using three approaches: a) direct labeling of native hEGF, b) conjugation with SAB, and c) direct labeling of an hEGF - 7-(3-aminopropyl)-7,8-dicarba-nido-undecaborate(1-) conjugate. The overall labeling yields were 3.5% for direct labeling, 44% for SAB and 70% for the hEGF-nido-carborane conjugate. A new route to N-succinimidyl 3- and 4- [¹²⁴I]iodobenzoate, two reagents for radioiodination of proteins is described affording 90% radiochemical yield. Three radioiodinated analogs of PK11195, 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)isoquinoline-3-carboxyam ide, a peripheral-type benzodiazepine receptor antagonist, were synthesized. All three analogs were obtained in >90% radiochemical yield. Synthesis and application of 5-[¹²⁴I]iodo-2'-deoxyuridine (IUdR) is presented. The closo-dodecaborate anion was evaluated as prosthetic group for radioiodination of macromolecules. Its inertness to in vivo dehalogenation was demonstrated by low thyroidal radioiodine uptake in the rat (0.07% ID/g, 20 h post injection)

[en] Mercury and radioactive caesium have received immense attention in Sweden during the past decades, as common contaminants in fish. This thesis examines how the Hg and ¹³⁷Cs levels in fish from 79 circumneutral lakes are affected by various environmental factors. In addition, the observed contaminant levels in the fish are compared to observations from more acidic lakes. Partial least square regression models (PLS) were used to assess the influence of 46-53 environmental predictors on Hg and ¹³⁷Cs levels in perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.). Linear regression intercepts of contaminant concentration vs. fish size were used as estimates of lake specific contaminant level in fish, in the cases when the contaminant content had a clear size-dependency. Differences in land use in the catchment areas were found to be a good predictor of both Hg and ¹³⁷Cs levels in the fish. Lowest levels were found in lakes draining arable land. High Hg levels in both species were predominantly found in forest lakes, whereas high ¹³⁷Cs levels were observed in Wetland lakes. The Hg and ¹³⁷Cs levels in the fish were negatively correlated to the cation concentration in lake water, but had a positive relationship to the amount of humic matter, i.e. low contaminant levels in hard-water lakes and high levels in brown-water lakes. No effect of lake pH was found on Hg or ¹³⁷Cs levels in either species. The Hg contents in perch and roach were of the same magnitude as in fish from more acidic lakes. The radiocaesium deposition in the close vicinity of lakes had a more profound effect on the ¹³⁷Cs levels in fish than more distant deposition

[en] Heavy residues were measured with inclusive radiochemical methods. In collisions of the heavy projectile Xe with Au, a side wise focusing of target residues towards intermediate angels was for the first time observed in the angular distribution. A possible explanation to this is that the heavy residues are produced in deep-inelastic collisions, in which no full damping is achieved as a consequence of the faster interaction times. In the study of the Ar and Th reaction at several energies it was shown that the heavy residue production does not account for the missing events in the folding angle distributions of the same system. It is concluded that the missing cross section is more likely to appear in multifragment emission events. In interactions at intermediate energies, the excited target-like complex may fission or survive fission by evaporating particles to form a heavy residue. The angular momentum acquired by the complex in a collision can influence the decay path. For this reason, experiments using counter techniques were completed to infer the linear and angular momentum transfer. These measurements showed that in peripheral collisions the transfer of angular and linear momentum to a fissioning nucleus are correlated in an unexpected simple dependence. The systematics appears to be applicable to a series of similar measurements at intermediate and low energies. The degree of alignment of the angular momentum also appears to follow a universal correlation as a function of reaction Q-value in these reactions. 108 refs, 30 figs

[en] The high sensitivity and capacity of flow cytometric analysis made it possible to study the effects of ionizing radiation at lower doses than used in earlier studies. Based on the analysis of one million cells per dose group of inbred mice, a linear dose response relationship was determined with high significance in the region 3-20 mGy/day. It is expected that the relationship is also linear below 3 mGy, since 3 mGy is the cellular dose absorbed from a single hit of low-LET ionizing radiation. Ascorbic acid, a radical scavenger, had no radioprotective effect when given at high concentrations to mice that were γ-irradiated at a very low dose rate for 35 days. This indicates that direct ionization of DNA is the dominating mechanism of chromosome breakage at such low dose rates. The time-course for maturation and transport of erythrocytes from mouse bone marrow and spleen to peripheral blood was determined. This assay can also be used for erythrocytes from mouse spleen, offering possibilities to study the effects of compounds distributed to the spleen. The suitability of four species of small wild rodents for micronucleus assays monitoring genotoxic agents was studied. The bank vole and field vole did not respond to low doses of γ-irradiation. On the other hand, the wood mouse and yellow-necked mouse responded to the same low doses suggesting that they can be used for monitoring. Background frequencies of micro nucleated erythrocytes and sensitivity to radiation differed more between individuals of the wild species than between inbred laboratory mice. micro nucleated erythrocytes were flow sorted onto slides and used for fluorescent in situ hybridization with a centromere-specific DNA probe. There was good correlation between the presence of centromeres and a high mean DNA content in micronuclei induced by aneugenic agents causing malsegregation of chromosomes

[en] The increasing demand for characterization of nuclear fuel, both from an operator and authority point of view, motivates the development of new experimental and, preferable, non-destructive methods. In this thesis, some methods based on nuclear spectroscopic techniques are presented. Various parameters of irradiated fuel are shown to be determined with high accuracy and confidence by utilizing gamma-ray scanning, tomography and passive neutron assay. Specifically, fuel parameters relevant for a secure storage of spent nuclear fuel in a long-term repository, such as e.g. burnup and decay heat, are shown to be determined with adequate accuracy. The techniques developed are expected to be implemented in the planned encapsulation facility in Sweden. Also, a device for tomographic measurements of the spatial distribution of thermal power in nuclear fuel assemblies has been built, tested and evaluated. The device utilizes single photon emission computed tomography (SPECT) in order to reconstruct the gamma-ray source distribution within a fuel assembly. The device is expected to be an important tool for validating reactor core simulators regarding new fuel designs

[en] Neutron emission spectroscopy measurements were performed at the Joint European Torus (JET) to study fusion plasmas of deuterium-tritium. The instrument used, the magnetic proton recoil (MPR) neutron spectrometer, was designed and optimised for plasmas of high fusion power (P_F). It has been successfully operated at the world record level of P_F = 16 MW attained at JET. This resulted in a range of new plasma diagnostic observations whose quality and scope would increase even further with higher P_F values. Indeed, the MPR is a prototype for the diagnosis of plasmas where thermonuclear ignition is reached (P_F ≅ 1 GW), as is the aim of the next step tokamak. This thesis describes the principles of the MPR neutron spectrometer as well as the set-up of the experiment at JET. The performance and diagnostic capabilities are illustrated based on the results obtained. Particular emphasis is given to the focal plane detector of the MPR and to its monitoring system which was a direct result of this thesis work. A special study was also done to quantify how the average thermal motion of the ions in the plasma affects the neutron emission spectrum compared to their collective motion due to plasma rotation. The analysis of the MPR data was focused on plasmas with radio frequency (RF) heating. To this end, a new analysis model was developed to derive information on the heated ion population. For instance, it is shown how the RF perturbs the thermal equilibrium of the fuel ion population which is approximately described as a triple temperature plasma state. The results and methods presented are new contributions to the field of fusion plasma diagnostics, and new insight has been provided on the plasma response to RF heating

[en] A magnetic proton recoil (MPR) spectrometer has been designed and constructed for use at the Joint European Torus (JET) tokamak. It was installed at JET in October 1996 and has subsequently been in continuous use during the first main deuterium-tritium (DT) operation in 1997, which culminated in the production of a record plasma generating 16.1 MW fusion power. This thesis describes the MPR spectrometer, including calibration and characterization procedures, and the JET experiments. Special emphasis is given to the focal plane detector and its response to radiation, which is a part of the total spectrometer response function. The result from this development and characterization work is presented. The data taking and reduction procedures are also described. Results from the first measurements in D-plasmas on the triton burnup neutron energy distribution are presented and compared with calculations. Examples of results obtained for DT-plasmas are reported which represent the first use of neutron spectrometry for measurements of plasma rotation and fast ion components in radio frequency heated plasmas. The forthcoming use of neutron spectrometry, especially for studies of ignited plasmas, is outlined in view of gained operating experience of the new technique and the achieved results

[en] Developments and analysis techniques aiming at a best possible performance and understanding of the DELPHI RICH detector are the main subjects of this thesis. A high precision of the measured Cherenkov angle is crucial for a good particle identification. In order to achieve this for the DELPHI RICH detector, a careful calibration of its photon detectors and a precise alignment of its components has been performed. A charged particle produces typically 5 to 10 Cherenkov photons that are detected among numerous background signals from various sources. Most of these background signals are identified and removed. A generally good performance, essentially in agreement with the expectations, has been achieved. The implementation of the DELPHI RICH detector - one of the first large scale applications of the RICH technique - was a great challenge. Now, the DELPHI RICH detector has been fully operational since 1994 providing exceptionally pure and efficient identification of fast charged hadrons over nearly the full solid angle and a wide momentum range. A large number of important physics results relying on the RICH technique have been produced. One example is the first and unique measurement of the strange quark asymmetry at the Z⁰ peak. The measurements of the production rates of various types of hadrons in Z⁰ decays are other examples