 
 

Study of statistical decay in well deformed rareearth nuclei
Valenta, Stanislav ; Krtička, Milan (advisor) ; Pospíšil, Stanislav (referee) ; Veselý, Petr (referee)
The γ decay of highly excited nuclear levels can be described within the statistical model of nucleus in terms of the level density and a set of photon strength functions. The knowledge of these quantities enables more accurate calculations of reaction rates in many different reactions which are important especially in nuclear astrophysics and in the development of advanced nuclear reactors. Despite the fact that the photon strength functi ons have been studied for decades, there are still contradicting experimental results regarding the low energy behavior of dipole strength. One of these ca ses is the shape of electric dipole photon strength function and the strength of the scissors mode in welldeformed rareearth nuclei. In this thesis the ana lyses of γray spectra measured by two different experimental setups are pre sented. The twostep γ cascades measurements with odd gadolinium targets were performed at the research reactor LVR15 at the Research Centre Řež. In the multistep γ cascades experiments the γ rays following resonance ne utron capture on 161−163 Dy targets were measured with the highlysegmented γray calorimeter Detector for Advanced Neutron Capture Experiments in the Los Alamos Neutron Science Center at Los Alamos National Labora tory. Experimental spectra were compared...


Cross section measurement in reactor spectrum: 55Mn(n,2n), 90Zr(n,2n), 127I(n,2n)
Burianová, Nicola ; Košťál, Michal (advisor) ; Krtička, Milan (referee)
This diploma thesis deals with the validation of spectral average crosssections (SACS) of 55 Mn(n,2n)54 Mn, 90 Zr(n,2n)89 Zr, 127 I(n,2n)126 I reactions in welldefined LR0 reactor spectrum. The measurement of SACS for selected reactions is of high interest because they are used for the practical reactor dosimetry. Various experiments for description of neutron field in reactor and detector characterization, which are necessary for validation, are described. The spectral average crosssections are derived from Net Peak Areas of irradiated samples measured using a semiconductor high purity germanium detector. Obtained result were compared with MCNP6 calculations using ENDF/BVII.0, ENDF/BVII.1, JEFF3.1, JEFF3.2, JENDL3.3, JENDL4, ROSFOND2010, CENDL3.1 and IRDFF nuclear data libraries. Notable discrepancies were found in 90 Zr(n,2n)89 Zr and 127 I(n,2n)126 I reactions. This thesis also contains a theoretical basis for the interaction of neutrons with matter.


Study of reaction crosssections important for advanced nuclear systems
Chudoba, Petr ; Wagner, Vladimír (advisor) ; Krása, Antonín (referee) ; Krtička, Milan (referee)
The doctoral thesis is focused on measurements of neutron crosssections mainly crosssections of (n,xn) threshold reactions. With the dawn of advanced nuclear systems such as fast reactors of GenIV, accelerator driven system or even fusion reactors, monitoring of fast neutron fields will gain on importance. The activation detectors are one of the viable options how to monitor these neutron fields and (n,xn) reactions would be one of the best options how to do such monitoring. There is one condition though. We need to have good cross section data in high neutron energy region. Unfortunately, the current situation is rather bad. There is only a small amount of reliable data for neutron energies above 20 MeV and with increasing energy, the situation gets only worse. For this reason, we measure the crosssections of (n,xn) reactions on perspective materials such as yttrium, gold and tantalum with neutron energies from 17.4 up to 94 MeV. In this thesis, the measurements together with motivation and methodology are described. Obtained results are in agreement with existing data. Severe discrepancies were observed between the predictions and experimental data for high order (n,xn) reactions. This problem is discussed and solved. The results in this region are in form of crosssection values and also...


Linearity of light yield in JUNO neutrino experiment
Tměj, Tomáš ; Vorobel, Vít (advisor) ; Krtička, Milan (referee)
The aim of the work is measurement of linearity of liquid scintillator light yield. Knowledge of deviation from the light yield linearity is essential for interpretation of the data measured in the neutrino experiment JUNO. The method is based on use of Compton scattering in the tested scintillator and on precise spectroscopy of the scattered gamma radiation.


Photon strength functions in 168Er from multistep gamma cascade measurement at DANCE
Knapová, Ingrid ; Krtička, Milan (advisor) ; Pěč, Viktor (referee)
Subject of the thesis is study of photon strength functions describing the gamma decay of the nucleus. During last 50 years a number of theoretical models for these quantities were proposed, however, their accuracy is still de batable and its verification has recently been a subject of intensive experimental and theoretical research. In this work measurement of multistep gamma cas cades following the radiative neutron capture on target nucleus 167 Er is used to analyse photon strength functions. The experiment was performed with DANCE calorimeter located in Los Alamos Neutron Scattering Center. The experimen tal spectra are compared with Monte Carlo simulations of electromagnetic decay using the DICEBOX algorithm, based on assumptions of Extreme Statistical Model. Comparison of experimental and simulated spectra is a fundamental tool for studying correctness of theoretical models of photon strength functions. This study provides information mainly about E1 and M1 photon strength functions, especially properties of the socalled scissor mode are analysed.


Studium fotonových silových funkcí z termálního záchytu neutronů
Bauer, Karel ; Krtička, Milan (advisor) ; Cejnar, Pavel (referee)
A subject of this thesis is to gain information on absolute photon strength function below the neutron separation energy. This energy range is known as a "lowtail" energy region of E1 resonance. The absolute photon strength function is obtained by normalizing the total average intensity for several energy ranges to the average intensities from thermal neutron capture spectrum for which an absolute calibration is experimentally known. The absolute photon strength function is investigated by means of statistical method. Everything seems to be compatible with information on studied Gd isotopes. However, disclosed method can potentially lead to rejection of combination of PSF and LD models. Powered by TCPDF (www.tcpdf.org)


Gammaspectrometry in reactor physics at LR0 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 gammaray spectrometry theory that is used at experimental reactor LR0 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 LR0 using MCNP method.


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)
