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Study of gamma decay in 168Er from neutron capture
Knapová, Ingrid ; Krtička, Milan (advisor) ; Gunsing, Frank (referee) ; Veselý, Petr (referee)
The γ-ray emission process in highly-excited nuclei is typically described within the statistical model of nucleus using the two main ingredients - the level density (LD) and the photon strength functions (PSFs). The knowledge of LD and PSFs is essential in the modeling of nuclear reactions with applications in astrophysics or advanced nuclear reac- tors. In this work, we studied the multi-step γ-ray cascade spectra following the radiative neutron capture 167 Er(n, γ)168 Er measured with the Detector for Advanced Neutron Cap- ture Experiments in Los Alamos National Laboratory. The experimental γ-ray spectra were compared with the simulated spectra exploiting the dicebox Monte Carlo code for simulation of radiative decay to test different models of LD and PSFs. Furthermore, the measured spectra allowed us to determine the population of the isomeric state in 168 Er with 109 ns half-life and compare it with the simulated isomeric population, which provides an important test of the applicability of the statistical model. The simulated isomeric population was found to be significantly lower than the experi- mental one if no structure effects are assumed above the excitation energy of the isomer. If we adopt the decay scheme up to excitation energy well above 2 MeV, we obtain the simulated isomeric ratio...
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Analysis of photon data from neutron capture on 170Tm
Špringlová, Kamila ; Krtička, Milan (advisor) ; Vorobel, Vít (referee)
The subject of this thesis is to study modes of γ decay of 170 Tm; knowledge of quan- tities describing γ decay form an important step in understanding an atomic nucleus. A description of γ decay of excited states of a heavy atomic nucleus above excitation energy of a few MeV is usually performed within the statistical model using the level density and photon strength functions. There have been numerous attempts to introduce models for these quantities, however, there are still contradictions with experimental data. This thesis focuses on analyzing experimental data from γ decay of excited 170 Tm nucleus formed by a slow neutron capture on 169 Tm. Specifically, the so-called sum-energy and multistep γ cascade spectra were prepared and the impact of several parameters used in the data processing was tested. The γ rays emitted from the radiative neutron capture were detected with a highly-segmented high-efficiency scintillation detector DANCE at Los Alamos National Laboratory. The full analysis is then completed by comparing the experimental data with predictions based on various level density and photon strength functions models. The whole process is very complex and its first step is a conversion of raw data to the form that can be compared with simulations, which is the subject of this thesis. 1
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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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Study of statistical decay in well deformed rare-earth 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 well-deformed rare-earth nuclei. In this thesis the ana- lyses of γ-ray spectra measured by two different experimental setups are pre- sented. The two-step γ cascades measurements with odd gadolinium targets were performed at the research reactor LVR-15 at the Research Centre Řež. In the multi-step γ cascades experiments the γ rays following resonance ne- utron capture on 161−163 Dy targets were measured with the highly-segmented γ-ray calorimeter Detector for Advanced Neutron Capture Experiments in the Los Alamos Neutron Science Center at Los Alamos National Labora- tory. Experimental spectra were compared...
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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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