National Repository of Grey Literature 48 records found  previous9 - 18nextend  jump to record: Search took 0.00 seconds. 
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.
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.
Study of reaction cross-sections 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 cross-sections mainly cross-sections 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 cross-sections 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 cross-section values and also...
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 cross-sections (SACS) of 55 Mn(n,2n)54 Mn, 90 Zr(n,2n)89 Zr, 127 I(n,2n)126 I reactions in well-defined LR-0 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 cross-sections 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/B-VII.0, ENDF/B-VII.1, JEFF-3.1, JEFF-3.2, JENDL-3.3, JENDL-4, ROSFOND-2010, CENDL-3.1 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.
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.
Photon strength functuins in 160Tb from two-step gamma cascade measurement
Kroll, Jiří ; Krtička, Milan (advisor) ; Cejnar, Pavel (referee)
Title: Photon strength functions in nucleus 160 Tb from the two-step γ cascades measurements Author: Jiří Kroll Department: Institute of Particle and Nuclear Physics Supervisor: Mgr. Milan Krtička, Ph.D. Supervisor's e-mail address: krticka@ipnp.troja.mff.cuni.cz Abstract: Photon strength functions have been a subject of a study for more than fifty years. A number of 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 the present time. In the present work the analysis of measurements of the two-step γ cascades following the slow neutron capture on the 159 Tb nucleus is used for study of photon strength functions. Results of the experimental data analysis are compared with the outputs of the Monte Carlo simulations based on the validity of so called Extreme Statistical Model. Comparison of experimental data with outcomes of simulations thus becomes the basic tool for studying correctness of theoretical models. Keywords: Photon strength function, Energy level density, Extreme Statistical Model
Surgical treatment of calcaneal fractures. Optimalization of the position of a sustentacular screw
Pazour, Jan ; Džupa, Valér (advisor) ; Krtička, Milan (referee) ; Obruba, Petr (referee)
The present study focuses on the operative treatment of intraarticular calcaneal fractures. Oste- osynthesis of calcaneal fractures through an extensile lateral approach accompanies an incre- ased risk of wound healing complications. The less invasive surgical approaches reduce these risks but achieving a fracture reduction is harder. Another problem is a technically demanding placement of a sustentacular screw. The incorrect placement of a sustentacular screw is followed by an increased risk of the screw penetration into the talocalcaneal joint. A too-long screw can threaten the anatomical structures around sustentaculum tali. Finally, the malposition of the screw can negatively influence the stability of the osteosynthesis. The purpose of the study was to compare the results of the treatment of calcaneal fractures using a plate osteo- synthesis through an extensile lateral approach and the less invasive intramedullary fixation with C-nail using a sinus tarsi approach from the perspective of the incidence of wound healing complications, stability of the osteosynthesis and the functional results. Furthermore, the impact of various positions of the sustentacular screw on the stability of osteosynthesis was also ana- lyzed. The thesis consists of two sections - clinical and experimental. In the...

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1 Krtička, Miroslav
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