The pairing correlation has long been recognized as the dominant many-body correlation beyond the nuclear mean field. Pairing plays an essential role in many nuclear phenomena including the occurrence of a systematic odd-even staggering (OES) of the nuclear binding energy. Pairing interaction plays, in particular, a significant role in the stability of weakly bound nuclei. Therefore it has been one of the most critical topics in nuclear physics because of the weakly bound structure of all newly discovered nuclei. Beyond the line of stability, pairing interaction is not a residual interaction anymore. Its strength can be of the same order of magnitude as the mean field.  In this thesis we have focused on the pairing interaction in atomic nuclei under extreme conditions to investigate the structure of loosely bound nuclei near the dripline; to probe and globally assess different outcomes of various zero-range pairing interactions and their effect on the loosely bound low angular momentum states. How much can density-dependence in zero-range pairing interaction nuclei affect the line of stability? Calculations predict that pure density-dependent pairing interaction so-called surface interaction enhances the collectivity and gives stronger neutron pairing gap in nuclei far from stability, while, the density dependence pairing interaction does not affect the gap for bound nuclei as much. The odd-even staggering of nuclear binding energies has been investigated to estimate the empirical pairing gap. A 3-point formula Δ(3)C (1/2[B(N,Z)+B(N −2,Z)−2B(N −1,Z)]) is advocated in this thesis, which we believe it is more suitable to measure the magnitude of pairing gap in even-even nuclei. The strength of Δ(3)C can be a good indicator of the two-particle spatial correlation. One-quasiparticle energies and binding energy for those odd nuclei, which can be approximated by spherical symmetry, are calculated to obtain binding energy odd-even staggering (OES) in all known semi-magic even-even nuclei. The pairing strength is fitted globally to all available data on the OES of semi-magic nuclei with Z ≥ 8. The difference between different zero-range density-dependent pairing interactions reduces with this global fitted parameter. The difference between the mean pairing gap and the OES gets larger as we get closer to the dripline. At the end of the thesis, a simple model has been developed which shows that when the mean-field becomes shallower the odd-even staggering of charge radii is reduced.This thesis covers results that are not included in the three published papers and some complementary works on the subject. / Parkopplingen i atomkärnan anses vara den dominerande mångkropparskorrelationen efter kärnmedelfältet. Parkoppling i atomkärnan spelar en viktig roll i många kärnfenomen,inklusive förekomsten av en systematisk udda-jämn förskjutning (OES) av bindningsenergin.Hos svagt bundna atomkärnor däremot spelar parkopplingen en signifikant roll för stabiliteten. Det gäller alla de nyupptäckta neutronrika atomkärnor som karakteriseras aven svag bindningsenergi där således parkopplingen blir ett kritiskt fenomen. När vi lämnar stabilitetslinjen och närmar oss linjen av spontan neutronsönderfall är parkopplingeninte längre obetydlig, utan tvärtom spelar en viktig roll för stabiliteten hos atomkärnan.Dess styrka kan vara av samma storleksordning som medelfältet. I denna avhandling har vi fokuserat på parkopplingen i atomkärnor under extrema villkor i syfte att undersöka strukturen hos löst bundna atomkärnor nära linjen för neutronsönderfall; att utforska och globalt bedöma resultaten av olika parkopplingar baserad på en deltakraft (räckvidd noll) och deras effekt på löst bundna tillstånd med lågt rörelsemängdsmoment. Hur mycket kan ett täthetsberoende i parkopplingen påverka stabilitetslinjen? Beräkningarna förutsäger att ren densitetsberoende växelverkan för parkoppling, så kallad ytväxelverkan, ökar kollektiviteten i atomkärnan och ger ett större pargap för neutroner i kärnor långt ifrån stabilitetslinjen,medan densitetsberoende parkoppling påverkar inte gapet för bundna kärnor i samma omfattning.Udda-jämn-spridning av bindningsenergier har undersökts för att hitta storleken på parkopplingens gap. En 3-punktsformel Δ(3)C (1/2[B(N,Z)+B(N −2,Z)−2B(N −1,Z)]) förespråkas i denna avhandling, som vi anser vara mera lämplig för att mäta storleken på pargapet i jämn-jämna kärnor. Storleken på Δ(3)C kan vara en bra indikator på rumskorrelationen mellan två nukleoner. En-kvasipartikelenergi för de udda kärnorna, som kan approximeras med sfärisk symmetri, beräknas för att erhålla udda-jämn spridning (OES) med avseende på bindningsenergin för alla kända semi-magiska jämn-jämna kärnor. Parkopplingsstyrkan är globalt anpassat med all tillgänglig data på OES vad gäller semi-magiska kärnor med Z ≥ 8. Skillnaden mellan olika täthetsberoende parkopplingar med vår växelverkan minskar med dessa globalt anpassade parametrar. Skillnaden mellan det teoretiska genomsnittliga parkopplingsgapet och OES blir större när vi kommer närmare tröskeln för atomkärnans stabilitet. I slutet av avhandlingen har en schematisk modell utvecklats som, genom attgöra medelfältet grundare, reducerar de udda-jämnt spridda laddningsradierna. Avhandlingen innehåller dessutom resultat som inte ingår i de tre publicerade artiklarna samt några kompletterande arbeten om ämnet. / <p>QC 20171114</p>

No description available.

The non-trivial structure of the QCD vacuum gives rise to a P and CP violating term in the QCD Lagrangian. The fact that we do not see an observable CP violation in the strong interaction despite this CP violating theta term is called the Strong CP Problem. In this thesis, we analyze an observable consequence of this theta vacuum term in the decay of the ground state neutral Sigma hyperon. Due to the SU(3) flavor symmetry, the current upper bound of the neutron electric dipole moment can be translated to an angular asymmetry in the decay distribution of the Σ0 particle. The selfanalyzing weak decay of the Λ hyperon means that any P violation in the initial Σ0 → Λγ decay will result in an asymmetry in the angular distribution of the final decay products. Studying the Sigma and anti-Sigma hyperon decays, we get an idea of C and CP violation in the decay chain. The effect of the production process of the Σ0 hyperon on the angular distribution of the final products is also worked out. A significant angular asymmetry in the decay will mean not only physics beyond the Standard Model, but also physics beyond the CP violating term in the QCD Lagrangian

Fission yields represent the probability of producing a certain nuclide in a fission event, and are important observables for fission research. For applications, accurate knowledge of the yields is fundamental at all stages of the fuel cycle of nuclear reactors, e.g., for reactivity calculations, or to estimate (spent) fuel inventory. Fission yields also help in the basic understanding of the fission process, for nucleosynthesis models, and for radioactive ion beam production. This thesis was developed in the framework of the AlFONS project, the objective of which was to measure neutron-induced fission yields of relevance for partitioning and transmutation of spent fuel. The work is performed at the IGISOL-4 facility in JYFL (University of Jyväskylä). The first part of this thesis work is dedicated to the development and characterisation of a suitable 9Be(p(30MeV),nx) neutron source for IGISOL-4. The neutron energy spectrum and the neutron yield from a 5mm thick converter were studied with Monte Carlo simulations. Two characterisation campaigns that validated the MCNPX code were also performed. At the maximum current available from the cyclotron at JYFL, a total neutron yield between 2 and 5×1012 neutrons/(sr s) can be obtained. This satisfies the design goal for studies of fission yields. The neutron source was used in the measurement of fission yields from high-energy neutron-induced fission of natU at IGISOL-4, discussed in the second part of this thesis. The fission products were online-separated with a dipole magnet. The isobars, with masses in the range A = 128-133, were identified using γ-spectroscopy. Data for the relative yields of tin and antimony, as well as isomeric yield ratios for five nuclides will be reported. The yields show trends not observed in the ENDF/B-VII.1 evaluation, and only in part confirmed by the GEF model. The final part of this thesis concerns a study of the performance of different nuclear model codes, that aim at describing the states of the fission fragments right after scission. Reproduction of experimental data serves to benchmark the models and it indicates, to some extent, how reliably the results can be extrapolated to regions where no data exist. A methodology to compare and test these models has been developed, which was implemented in the DEℓFIN code. DEℓFIN takes the excited fission fragments, defined by the model under test, and de-excites them in a standardised way using the nuclear model code TALYS. Eliminating any variability in the way the final observables are extracted helps focusing on each model's assumptions. DEℓFIN was tested on five models, and interesting features in the prompt neutron multiplicity were found for some of them. This study will promote a better understanding of the ideas used in the development of fission models.

In this master thesis a thorough analysis of data collected in an experiment performed at the JYFL accelerator laboratory in Finland using a reaction with a 47-Ti beam on a 58-Ni target is presented. The prompt emitted gamma rays from the fusion-evaporation products were detected in the gamma-ray spectrometer JUROGAM II, while the recoils were detected in the GREAT spectrometer. The main aim of this work was to use triple gamma-ray coincidences to find out if it is possible to discover new levels and transitions in proton-rich nuclides such as 103-Sn and 101-In.  A recoil triggered gamma-cube of coincident gamma rays was constructed and analyzed with the program levit8r from the Radware software package. From an intensity estimation of the data it was concluded that 102-Ag was the strongest reaction channel and emission of 3-7 particles in the fusion-evaporation reaction was favoured. By analyzing peaks in double-gated spectra of the gamma-cube, three new levels and seven new gamma-ray transitions up to an excitation energy of 8644 keV and an angular momentum of 22 h were proposed as a continuation of rotational band B3 published in a recent article on 102-Ag. From plots of the alignment of the newly proposed transitions no band crossing was observed, just a smooth continuation of the band. The efficiency of the charged particle detector, UoYTube, was deduced to be about 66% for proton detection, while the probability to detect one random proton was about 10%.

The Environmental Radioactivity Laboratory (ERL) of iThemba LABS conducts research into levels of natural and anthropogenic radioactivity in the environment. The laboratory-based measurements are conducted using a low-background Hyper Pure Germanium (HPGe) detector system. A critical aspect of such measurements involves calibrating the detector about energy and detection efficiency. The present study details experiment that were carried to determine both energy and efficiency calibrations for various sample geometries using gamma-ray spectrometry. The measurements using reference sources of known activity were carried out using two sample holders (Marinelli Beaker (1000 ml) and, a cylindrical pill bottle (100 ml)), and a point source. The IAEA reference materials (RGU-1, RGTh-1 ore and RGK-1) were prepared and used to fill the Marinelli beaker and pill bottles. Certified reference point sources (⁶⁰Co, ¹⁵²Eu, ¹³⁷Cs, ²²Na, ²⁴¹Am and ¹³³Ba) were obtained from the National Metrology Institute of South Africa (NMISA). Experiments consisted of exposing the HPGe detector to various gamma-ray sources prepared using various sample holders and the point source geometry. The counting time for each measurement was 24 hours. Each spectrum was analysed by inserting region of interests around suitably selected photo-peaks and the counts associated with these photo-peaks were automatically determined and corrected for background by the software. The full energy peak detection efficiency was then determined from the background corrected counts, the known activity of the source and the implicit in measurement (solid angle). The experimental and simulated spectra using point sources and volume sources were compared. Both experimental and simulated spectra presented showed a good agreement in terms of shape and varying intensities as expected. Additional photo-peaks were observed from ²²Na, ⁶⁰Co, ¹³³Ba and ¹⁵²Eu (point sources) and ²³²Th and ²³⁸U (volume sources) experimental spectra these effects were not observed in the simulated spectra. These additional peaks observed are the result of coincidence summing in some of gamma emitting radionuclides. Efficiencies that were experimentally determined, were compared with the calculated efficiencies from Monte Carlo simulations using MCNPX. Efficiency calibration parameters (power fit function) for the volume sources were determined from experimental and simulated data; a = 2.58; b = -0.75 experimental and a = 1.01; b = 0.65 simulated (100 mL pill bottle) and a = 2.07; b = -0.75 experimental and a = 1.61; b = 0.66 simulated (1 L Marinelli beaker). The simulated parameters for the efficiency as determined can be used for future calculations of activity concentrations when the 100 mL pill bottle or 1 L Marinelli Beaker sample holder is used. Further improvement in these calculations can be achieved by considering the sample density. The simulation input files used to generate these values is available and can be modified to match any sample holder geometry, as well as any density that might be required in future counting.

An exploratory investigation of the electron reconstruction efficiencyat the LHCb is presented. The study is done through simulations ofparticle interaction with the full LHCb detector setup, both by firingsingle particles into the detector and by generating the decay of Bmesons into J/psi K, where the J/psi decays into dileptons. PreviousLHCb analysis of the decay has shown a large yield difference betweenthe number of electron versus muon final states, around a factor offour. The kinematical dependence on the reconstruction efficiency ofthe leptons is studied and found to be non-discriminatory. Theelectronic channel loss of yield is compared to the muonic channel withthe purpose of finding in which reconstruction and selection steps theyield discrepancy factor originates. A total factor of 1.8 is found,which combined with the L0 trigger factor of 2 makes the resultcomparable to the observed factor. A large loss of yield from ageometrical selection, which requires electrons to be in the acceptanceof the electromagnetic calorimeter or in the pre-shower detector,triggers a study of the performance of electrons failing thisrequirement. The performance is determined by looking at how well theparticles are identified, using both LHCb data and simulations. Thefailing electrons are found to perform well, therefore the requirementis considered superfluous and avoiding it would increase the electronfinal state yield with around 14.5%.

The Division of Applied nuclear physics at Uppsala university, isregularly performing high-precision measurements on isomeric fissionyield ratios (IYR). Its aim is to explore the physics behind nuclearfission, in particular how angular momentum is generated. Thedepartment has developed a method to obtain the root mean square(rms) values of the primary fission fragment angular momentumdistribution (Jrms). However, several assumptions are made in themodel; thus this project aims to assess the sensitivity of the modelparameters. In particular, the focus is on assessing the mean andwidth of the excitation energy distribution, as well as thecorrelation between the excitation energy and the angular momentum.The task is to implement a method that builds upon the previousmodel. The method that was implemented is based on random sampling,which randomises values of the parameters in a specific rangedepending on the type of distribution.Three types of distributions (Normal, Rayleigh and Poisson) of theexcitation energy were tested, and it seemed to have little effecton the system. The fact that the distributions are symmetric orantisymmetric seemed to have negligible impact.The nucleus that was studied was 134I after the fission process withparent nucleus 235U in the thermal energy range. The IYR was plottedagainst four parameters: Jrms, a proportionality constant (A)between the energy and angular momentum, the intrinsic energy (Eint)and the spread of the energy (E).Their mean values and spread wasacquired from a fission simulations software called GEF. Using theseas inputs to another software TALYS, one can acquire the isomericyield ratios (IYR) for the nucleus with different neutron channels.Jrms has the most impact, and had a clear interval which gave a IYRvalue close to experiments. The three other parameters showed noclear correlation which results in the conclusion: the IYR says verylittle about the fragments excitation energy but quite a lot aboutits angular momentum in the case of 134I with the assumptions made.

The purpose of this project is to study the plasma delay time phenomenon in preparation for the construction of the VERDI spectrometer. To accomplish this, simulations of the spontaneous fissioning process of Cf-252 were created using the fission code GEF, as well as MATLAB. GEF has produced one million fission events, from which the time of flight and kinetic energy of each fission fragment have been calculated with classical mechanics, to replicate the experiment. To imitate the plasma delay time phenomenon, three different models, found in the literature, have been compared. Accounting for other realistic resolution effects and using the first model as the plasma delay time phenomenon, the absolute errors of the mass-yields reaches up to 4 u, whereas the second and third model display absolute errors up to 3 u. Furthermore, it is found that, despite the significant differences in the models' dependencies, the resulting effects are quite similar. All models are found to have a narrowing influence on the pre-neutron emission mass- yield distributions, resulting in an increased peak-to-valley ratio. In the detection of fission fragments, a higher peak-to-valley resolution is often associated with a better mass resolution. This study shows that the plasma delay time could have a misleading influence in regards to estimating an experimental mass resolution.

Time-resolved Fourier spectroscopy has been applied to the observation of Rydberg O(I) and O(,2) infrared emission from a pulsed discharge at 0.1 torr. The emission of a 2.5 meter long column through the negative glow was observed with a newly designed discharge apparatus. A computer-controlled interferometer step-servo was developed to enable 100 microsecond time- and 0.12 cm('-1) spectral-resolution capabilities. The Rydberg features were enhanced with respect to those of contaminates by signal processing methods that utilized their individual temporal behavior. Line position determinations of the 7h - 5g, 7g - 5f, 5g - 4f and 6g - 4f O(I) lines have been made to an accuracy of 0.015 cm('-1). Polarization constants of the O(II) core have been deduced from this data. Nine newly observed and four previously observed line-like features have been attributed to Rydberg O(,2).