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Gamma-spectrometry in reactor physics at LR-0 Rez experimental reactor
Burianová, Nicola ; Švadlenková, Marie (advisor) ; Krtička, Milan (referee)
The first part of this bachelor's thesis deals with the basics of the semiconductor gamma-ray spectrometry theory that is used at experimental reactor LR-0 in Research center in Řež. The measurement results are applied in reactor physics. The second part describes the measurement of a fuel pin, which was performed in order to determine gamma permeability of lead shielding of the semiconductor detector for specific type of colimator. Experimental results are compared with those calculated at the LR-0 using MCNP method.
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Studium fotonových silových funkcí z termálního záchytu neutronů
Bauer, Karel ; Krtička, Milan (advisor) ; Cejnar, Pavel (referee)
This thesis deals with the description of $\gamma-$ray deexcitation of neutron resonances produced in thermal neutron capture below neutron separation energy. A subject of this thesis is obtaining information on absolute value of \textit{photon strength function} (PSF) achieved from primary transitions in thermal neutron capture. The aim is to map and bring new information on absolute value of photon strength function (PSF) in $^{156}$Gd and $^{158}$Gd. The method which was used in this thesis can lead to refusion of several models of PSF a level density. Powered by TCPDF (www.tcpdf.org)
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Processing of two-step γ cascade data from 151Eu(n,γ)152Eu reaction
Schusser, Jakub ; Krtička, Milan (advisor) ; Cejnar, Pavel (referee)
1 Photon strength functions in terms of statistical approach to a nuclear decay describe the probability distribution of photon emission by given nucleus. They can be studied using two step gamma cascades. The two step gamma cascade method was firstly introduced in fifties of the 20th century. Our aim is to study two step gamma cascades following thermal neutron capture in 151 Eu. The experiment was performed at the Nuclear Physics Institute ASCR in Řež near Prague. The acquired emission spectra of photons from thermal neutron capture will be processed by energetic and efficiency calibration and after further processing will be compared to the output of theoretical models.
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Influence of the Detection Threshold on the Response of the C6D6 Detectors
Knapová, Ingrid ; Krtička, Milan (advisor) ; Pěč, Viktor (referee)
Scintillation C6D6 detectors are used for radiative capture cross-section measurements in various neutron time-of-flight facilities (n_TOF in CERN, GELINA in IRMM Geel). To determinate cross-section with the help of Pulse Height Weighting Technique we usually neglect influence of undetectable energy, derived from two phenomena - internal conversion and detection threshold for low photon energies. However, in some cases their impact cannot be completely omitted and due to lack of knowledge it has not been the subject of research yet. The purpose of this thesis is to study the influence of these two effects from simulations of neutron radiative capture induced photon spectra. Two nuclei: 197 Au and 238 U were used for testing.
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Use of activation detectors for neutron field measurement in models of ADTS
Chudoba, Petr ; Wagner, Vladimír (advisor) ; Krtička, Milan (referee)
Accelerator driven transmutation systems could be a solution to the problem with long-lived nuclear waste and opening the way to thorium fuel cycle. Due to intensive neutron source based on spallation reaction are these systems very litle dependent on the arrangement of the core and fuel quality. These systems can transmute the spent fuel, eventually 232Th or 238U without affecting maintenance of fission reaction. Additionally subcritical blanket ensures high safety. For these systems it is necessary to know the cross sections of reactions of fast neutrons produced in the spallation reaction with different materials. This data is necessary not only for the selection of appropriate construction materials, but also for creation of programs simulating accelerator driven transmutation systems. This thesis is focused on the experimental determination of cross sections of reactions 89Y(n,2n)88Y and 89Y(n,3n)87Y with neutron energies from 17,6 to 33,6 MeV. Yttrium is analyzed for its (n,xn) threshold reactions, which makes it appropriet activation detector for study of the neutron fields in model configurations of accelerator driven transmutation systems. The obtained cross sections are unique, in that so far there are no experimental data for used neutron energies.
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Photon strength functions in Gd isotopes studied from resonance neutron capture
Kroll, Jiří ; Krtička, Milan (advisor) ; Kvasil, Jan (referee) ; Granja, Carlos (referee)
Title: Photon strength functions in Gd isotopes studied from resonance neutron capture Author: RNDr. Jiří Kroll Department: Intitute of particle and nuclear physics Supervisor: doc. Mgr. Milan Krtička, Ph.D., Intitute of particle and nuclear physics Abstract: Photon strength functions have been studied for more than sixty years. A number of theoretical models was proposed to describe experimental data during that time. However, the correctness of these models is still very questionable and its verification is the subject of very intensive experimental and theoretical activity at present time. In this thesis the analysis of spectra of γ rays following the radiative capture of neutrons on isolated neutron resonances of 152,154−158 Gd nuclei is used to study photon strength functions. Experimental data were measured using segmented DANCE calorimeter that is installed at Los Alamos Neutron Scattering Center in New Mexico, USA. Experimental spectra are then compared with the outputs of Monte Carlo simulation of nuclear elec- tromagnetic decay, performed by DICEBOX code, that is based on the validity of the so-called Extreme Statistical Model. The response of the detector system to generated γ cascades was subsequently calculated using the Geant4 code. An analysis of the data clearly indicates that magnetic...
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Photon strength functions in 196Pt from two-step gamma cascade measurement
Kloc, Michal ; Krtička, Milan (advisor) ; Cejnar, Pavel (referee)
Photon strength functions (PSFs), using the statistical approach to a nuclear decay, seem to be a suitable tool for the description of the electromagnetic transitions in a nucleus. Since the early 50's, when PSFs were first introduced, a plenty of theoretical models were proposed however their validity is still a question. In this work the data from the measurement of so called Two step cascades in the nucleus 196Pt using the reaction 195Pt(n,gamma)196Pt are processed. The experiment was performed at the Nuclear Physics Institute ASCR in Řež near Prague. We assume that these experimental spectra contain important information on PSFs. Comparison of the processed data with a few Monte Carlo simulations is also a part of this thesis.
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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.
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Photon strength functuins in 177Lu from two-step gamma cascade measurement
Valenta, Stanislav ; Krtička, Milan (advisor) ; Kvasil, Jan (referee)
The subject of the study made in this work are photon strength functions. Many models, both based on theoretical as well as phenomenological approaches, were proposed for these quantities, describing the gamma decay of the nucleus, during last 50 year. However, the correctness of these models is still questionable and its verification is the subject of intensive experimental and theoretical activity at the present time. The results of the analysis of measurements of the two-step cascades following thermal neutron capture on the 176Lu nucleus are compared with the outputs of the Monte Carlo simulations based on the validity of the so-called Extreme Statistical Model. Comparison of experimental data with outcomes of simulations thus becomes the basic tool for studying correctness of theoretical models. The experiment analyzed in the present work provides information mainly about E1 and M1 photon strength functions, especially about the so-called scissors resonance.
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