|
| |
|
|
Microscopic nuclear models for open-shell nuclei
Herko, Jakub ; Knapp, František (advisor)
Title: Microscopic nuclear models for open-shell nuclei Author: Jakub Herko Institute: Institute of Particle and Nuclear Physics Supervisor: Mgr. František Knapp, Ph.D., Institute of Particle and Nuclear Physics Abstract: Since the nucleus is a quantum many-body system consisting of con- stituents whose mutual interaction is not satisfactorily known, it is necessary to use approximate methods when describing the nucleus. Basic approximate approaches in the microscopic theory of the nucleus are the Hartree-Fock the- ory, Tamm-Dancoff approximation and random phase approximation. They are described in the first chapter of this thesis. The main aim was to develop mi- croscopic models for open-shell nuclei with two valence particles or holes. They are described in the second chapter, which contains detailed derivations of the relevant formulae. These methods have been numerically implemented. The re- sults of the calculations of the nuclear spectra and the electromagnetic transition probabilities are presented in the third chapter. Keywords: Tamm-Dancoff approximation, random phase approximation, open- shell nuclei, nuclear spectra, electromagnetic transition probabilities ii
|
|
|
Microscopic nuclear models for open-shell nuclei
Herko, Jakub ; Knapp, František (advisor) ; Kvasil, Jan (referee)
Title: Microscopic nuclear models for open-shell nuclei Author: Jakub Herko Institute: Institute of Particle and Nuclear Physics Supervisor: Mgr. František Knapp, Ph.D., Institute of Particle and Nuclear Physics Abstract: Since the nucleus is a quantum many-body system consisting of con- stituents whose mutual interaction is not satisfactorily known, it is necessary to use approximate methods when describing the nucleus. Basic approximate approaches in the microscopic theory of the nucleus are the Hartree-Fock the- ory, Tamm-Dancoff approximation and random phase approximation. They are described in the first chapter of this thesis. The main aim was to develop mi- croscopic models for open-shell nuclei with two valence particles or holes. They are described in the second chapter, which contains detailed derivations of the relevant formulae. These methods have been numerically implemented. The re- sults of the calculations of the nuclear spectra and the electromagnetic transition probabilities are presented in the third chapter. Keywords: Tamm-Dancoff approximation, random phase approximation, open- shell nuclei, nuclear spectra, electromagnetic transition probabilities ii
|
|
|
Giant monopole resonances in deformed nuclei
Božík, Daniel ; Kvasil, Jan (advisor) ; Mareš, Jiří (referee) ; Knapp, František (referee)
Title: Giant monopole resonances in deformed nuclei Author: Daniel Božík Department: Institute of particle and nuclear physics Supervisor: prof. RNDr. Jan Kvasil, DrSc., ÚČJF, MFF UK Abstract: The study of giant monopole resonances is important, because of its di- rect connection to the incompressibility of the nuclear matter, and its importance has risen with new experimental data obtained in recent years from the experi- ments TAMU and RCNP. The current work brings a study of the giant monopole resonances for chains of spherical (Pb, Sn, Zr) as well as deformed (Sm, Mo, Cd) isotopes. The calculations were carried out within the HFB + SRPA method, which was developed at MFF UK in cooperation with JINR Dubna and the University of Erlangen. We were as first able to confirm, from the microscopic theory, the appearance of a double-peak structure of GMR strength functions for deformed nuclei, and its connection with E0-E2 coupling. We showed the importance of using strength functions in the study of GMR. Keywords: HFB, SRPA, giant monopole resonances 1
|
|
|
Theoretical description of nuclear collective excitations
Repko, Anton ; Kvasil, Jan (advisor) ; Knapp, František (referee) ; Mareš, Jiří (referee)
Density functional theory is a preferred microscopic method for calculation of nuclear properties over the whole nuclear chart. Besides ground-state properties, which are calculated by Hartree-Fock theory, nuclear excitations can be described by means of Random Phase Approximation (RPA). The main objective of the present work is to give the RPA formalism for spherically symmetric nuclei, using the techniques of angular-momentum coupling. Various auxiliary topics, such as Hartree-Fock theory, Coulomb integral, center-of-mass corrections and pairing, are treated as well. RPA method is derived also for axially deformed nuclei. The derived formulae are then implemented in the computer code and utilized for calculation of some physical results. After thorough investigation of the precision aspects of the calculation, the following topics are treated as examples: toroidal nature of the low-energy (pygmy) part of the E1 resonance, giant resonances of various multipolarities in deformed nucleus 154Sm, and magnetic dipole (M1) transitions in deformed 50Cr. Powered by TCPDF (www.tcpdf.org)
|
|
|
Quantum computing in many-body physics
Brandejs, Jan ; Cejnar, Pavel (advisor) ; Knapp, František (referee)
Název práce: Kvantové výpočty v mnohočásticové fyzice Autor: Jan Brandejs Katedra: Ústav částicové a jaderné fyziky Vedoucí bakalářské práce: prof. RNDr. Pavel Cejnar, Dr., DSc., Ústav částicové a jaderné fyziky Abstrakt: Při simulaci mnohočásticových kvantových systém· obvykle dochází k exponenciální explozi výpočetní složitosti. Kvantové počítače umožňují ten- to problém principiálně vyřešit. Díky práci R. Feynmanna je známo, že axiomy teorie složitosti vychází z fyzikálních zákon·. Situace se změní, zavedeme-li do výpočetního procesu mimo klasické fyziky i kvantovou teorii. Ukazuje se, že pro efektivní simulaci kvantového systému je vhodné použít jiný, lépe kontrolovatelný kvantový systém. Realizace výpočtu s využitím q-bit· a kvantového paralelismu pak ve vybraných případech vede k zásadní redukci složitosti. Kvantové počítače potenciálně umožňují realizaci výpočt· a simulací, které jsou s klasickými počíta- či prakticky neproveditelné. Zejména na poli kvantové chemie vyvstává možnost přímočaré aplikace. Tato práce je zaměřena na použití kvantových počítač· pro mnohočásticové problémy a obsahuje analýzu složitosti kvantové simulace atomo- vých jader. Klíčová slova: kvantový počítač, kvantová simulace, mnohočásticová fyzika
|
|
|
Microscopic calculations of nuclear properties with realistic nucleon-nucleon interaction
Herko, Jakub ; Knapp, František (advisor) ; Kvasil, Jan (referee)
Title: Microscopic calculations of nuclear properties with realistic nucleon-nucleon interaction Author: Jakub Herko Department: Institute of Particle and Nuclear Physics Supervisor: Mgr. František Knapp, Ph.D., Institute of Particle and Nuclear Phy- sics Abstract: A significant problem of nuclear physics is the fact that the nucleus is quantum many-body system consisting of constituents whose mutual interac- tion is unknown. Therefore, it is necessary to use approximative methods when describing the nucleus. In the microscopic theory of the nucleus we often use the mean-field approximation, in which we consider non-interacting nucleons moving in external field. One approach to obtain an optimal mean-field is the Hartree- Fock method. The first part of this work is theoretical and describes methods of the microscopic theory of the nucleus, especially the Hartree-Fock method, with emphasis on formalism of the second quantization. The second part describes a practical implementation of the Hartree-Fock method in calculations of certain properties of the nuclei and calculations that go beyond this method and include the residual interaction using the perturbation theory. Keywords: Hartree-Fock method, nuclear binding energies, single-particle spectra, many-body perturbation theory
|
|
|
Quantal and thermal phase transitions in atomic nuclei
Dvořák, Martin ; Cejnar, Pavel (advisor) ; Knapp, František (referee)
In this bachelor work phase transitions in atomic nuclei are studied. The main attention is paid to quantal phase transitions between nuclear ground states of different symmetry. First, the interacting boson model in its simplest version, IBM-1, is introduced. The correspondence between the IBM and the geometric model of nuclei is indicated and possible shapes of the nucleus in the ground state are introduced. In the next step, critical and degenerated critical points of the potential derived from the IBM-1 are investigated in detail, especially their dependence on parameter values of the potential. Degenerated critical points are classified using the catastrophe theory. The special values of potential parameters are found for which phase transitions of the first and second order occur. Finally, the possibility of substitution of the potential by canonical catastrophic functions in a vicinity of degenerated critical points is discussed.
|
|
|
Photon strength functions in 162Dy from two-step gamma cascade measurement
Chudoba, Petr ; Krtička, Milan (advisor) ; Knapp, František (referee)
Photon strength functions quantities, which describe deexcitation of nucleus by emiting gamma rays within statistical model of the nucleus. Information about these quantities can be gained from study of two-step gamma cascades. The thesis is focused on processing of experimental data from measurement of these cascades in 162Dy nucleus. Data were acquired using experimental set-up istalled on the research reactor in Řež near Prague. In the experiment the 161Dy targed was bombarded by thermal neutrons. Following gamma deexcitation of 162Dy nucleus was measured by coincident spectrometer composed of two semi-conductor detectors. The aim of the thesis is to perform energy and efficiency calibration and to process experimental data into the form of two-step gamma cascades spectra. In adition, a comparsion of the two-step cascades spectra with the outcome of simulations of a few basic models of photon strength functions is made.
|
|
|
Gigantické rezonance v atomových jádrech
Repko, Anton ; Kvasil, Jan (advisor) ; Knapp, František (referee)
Skyrme functional is commonly used for the description of ground-state and dynamical properties of atomic nuclei. To describe the dynamical properties in the microscopic self-consistent way, we employed Separable Random Phase Approximation (SRPA) based on Skyrme functional. This work describes theory of Skyrme Hartree-Fock and SRPA and presents numerical calculation of E1 and M1 giant resonances in spherical nuclei Ca-40 - Fe-56. There is some evidence for non-zero ground-state deformation of the nucleus Fe-56, so it is treated also with such assumption. The results obtained for various parametrizations are compared to the experimental data.
|
guest ::
