<p>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.</p>

Transmutation of plutonium and minor actinides in accelerator-driven systems (ADS) is being envisaged for the purpose of reducing the long-term radiotoxic inventory of spent nuclear reactor fuel. For this reason, the physics of sub-critical systems are being studied in several different experimental programs across the world. Three of these experiments have been studied within the scope of the present thesis; the MUSE experiments in France, the Yalina experiments in Belarus and the SAD experiments in Russia. The investigations of the MUSE experiments have focused on three different neutronic parameters; the neutron energy spectrum, the external neutron source efficiency and the dynamic neutron source response. It has been shown that the choice of external neutron source has negligible effect on the neutron energy spectrum in the core. Therefore, from this point of view, the MUSE experiments can be considered representative of an ADS. From the analyses of different reactivity determination methods in the Yalina experiments, it can be concluded that the slope fit method gives results in good agreement with the results obtained by the Monte Carlo method MCNP. Moreover, it was found that the Sjöstrand method underestimates keff slightly, in comparison with MCNP and the other investigated methods. In the radiation shielding studies of the SAD experiments, it was shown that the entire part of the effective dose detected at the top of the biological shielding originates from the proton-induced spallation reactions in the target. Thus, it can be concluded that the effective dose is directly proportional to the proton beam power, but independent of the reactivity of the sub-critical core. In order to study the energy gain of an ADS, i.e., the core power divided by the proton beam power, the proton source efficiency, ψ*, has been studied for various ADS models. ψ* is defined in analogy with the neutron source efficiency, φ*, but relates the core power directly to the source protons instead of to the source neutrons. φ* is commonly used in the physics of sub-critical systems, driven by any external neutron source (spallation source, (D,D), (D,T), 252Cf spontaneous fission etc.). On the contrary, ψ* has been defined only for ADS studies, where the system is driven by a proton-induced spallation source. The main advantages of using ψ* instead of φ* are that the way of defining the external source is unique and that ψ* is proportional to the energy gain. An important part of this thesis has been devoted to studies of ψ* as a function of different system parameters, thereby providing a basis for an ADS design with optimal properties for obtaining a high core power over beam power ratio. For instance, ψ* was found to decrease considerably with increasing spallation target radius. / QC 20101005

This thesis presents measurements of fundamental properties of singly charged ionic systems including spectral wavelengths, lifetimes of excited states and branching fractions with the main focus on time resolved laser spectroscopy of stored ions providing lifetime measurements of metastable states. The results of these measurements have been used to determine energy levels and transition probabilities of the studied systems. The included experimental data are compared with results from calculations which provides evaluations of different theoretical models. The presented results have been applied by others to the field of atomic astrophysics in order to deduce electron densities and elemental abundances in ejecta of the supermassive star eta Carinae and have also been followed by additional work of theoreticians interested in comparisons with laboratory data. The thesis is a result of several collaborations in which Stockholm University has been providing lifetime measurements of metastable states, Lund Observatory and the National Institute of Standards and Technology have been providing wavelength and branching fraction measurements, Lund Laser Centre has been providing lifetime measurements of short-lived states and calculations have been performed by theoretical physicists from Université de Mons-Hainaut, Université de Liège, Queen's University of Belfast and Laboratoire Aimé Cotton.

In 1789 a German chemist, Martin Heinrich Klaproth, announced the discovery of a new element: uranium; few years later, the head of father of the modern chemistry, Antoine Lavoisier, was swept away by guillotine: a new era was destined to be opened, either where energy would have been produced in large scale by nuclear processes delivering hundreds of times the energy of chemical processes or where a mass of people, revolutionary or not, would have been melted down into a couple of seconds. After a quite long time, on the 2nd December 1942, the first nuclear reactor has been put into operation by Enrico Fermi in Chicago; few years later, came also the dark side utilization of fissile materials in Hiroshima and Nagasaki. Since those moments, three power plants generations succeeded, until the current one which is the generation IV of nuclear reactors. The latter has the goal of generating electricity in a safe manner, for the core is designed to provide an effective passive cooling of the decay heat. Amid generation IV of nuclear power plants, the Gas Turbine – Modular Helium Reactor, designed by General Atomics, is the only core with an energy conversion efficiency of 50%; the above consideration, coupled to construction and operation costs lower than ordinary Light Water Reactors, renders the Gas Turbine – Modular Helium reactor rather unequaled. In the present studies we investigated the possibility to operate the GT-MHR with two types of fuels: LWRs waste and thorium; since thorium is made of only fertile 232Th, we tried to mix it with pure 233U, 235U or 239Pu; ex post facto, only uranium isotopes allow the reactor operation, that induced us to examine the possibility to use a mixture of uranium, enriched 20% in 235U, and thorium. We performed all calculations by the MCNP and MCB codes, which allowed to model the reactor in a very detailed threedimensional geometry and to describe the nuclides transmutation in a continuous energy approach; finally, we completed our studies by verifying the influence of the major nuclear data libraries, JEFF, JENDL and ENDF/B, on the obtained results. / <p>QC 20100922</p>

Diss. Uppsala : Univ., 2004.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2007. / Härtill 8 uppsatser.

This thesis describes the recent improvements of the SMILETRAP Penning trap mass spectrometer and a number of interesting high precision mass measurements, which have been performed using the improved apparatus, and are relevant in todays fundamental physics problems. The mass of the hydrogen-like 24,26Mg ions as well as the masses of the hydrogen- and lithium-like 40Ca ions are presented in this work that are indispensable input values when evaluating g-factor measurements of the bound electron. In both cases the uncertainty in the masses was improved by one order of magnitude compared to the literature values known so far. The mass of 7Li has been measured and a new mass value has been obtained with an unprecedented relative uncertainty of 6.3x10-10. A large deviation of 1.1 μu (160ppb) compared to the literature value has been observed. In order to find the reason of this large deviation and to look for possible systematics we have measured the mass of 4He and 6Li and concluded that the 6Li(n,γ)7Li reaction Q-value used in the literature when calculating the 7Li mass is wrong by about 1 keV. The mass difference between 3He and 3H (Δ m (3H -3He)) is the Q-value of the tritium β-decay. An accurate knowledge of the tritium Q-value is of importance in the search for a finite rest mass of the electron neutrino. By adding a measurement of the mass of 3He1+ to previous mass measurement of 3H1+ and 3He2+ we have improved our previous Q-value by a factor of 2. At the moment our Q-value is the most accurate and more importantly it is based on the correct atomic mass values.

In this thesis, options for efficient transmutation of transuranium elements are discussed. The focus is on plutonium, americium and curium mainly because of their long-term contribution to the radiotoxicity of spent nuclear fuel. Two innovative helium-cooled core designs are proposed, dedicated to the transmutation of actinides. The performance of the more promising of the two is studied in realistic transient fuel cycle scenarios. During the 1150 day irradiation cycle, a minor actinide consumption of 355 kg/GWth·year is achieved. An analysis of the efficiency of spallation neutron sources in helium-cooled cores is also performed. It is shown that the proton source efficiency, ψ∗, is improved by about 10% when helium is used as coolant, rather than lead-bismuth eutectic. Further, a proposal is made to transmute actinides in the upper part of a BWR core. A net consumption of transuranics is shown possible in the BWR park already when 50% of the BWR fuel is of the proposed evolutionary type. The thesis concludes that efficient transmutation of transuranic elements in dedicated helium-cooled subcritical cores is possible. But, in many instances fuel cycles without dedicated cores may lead to comparable final states. Especially, the evolutionary BWRfuel proposed seems interesting. / QC 20100820

<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.