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Linear Accelerator Input Beam Data Collection for DIAMOND Calculation Systém Setup
KRÁKORA, Martin
The first chapter of the theoretical part of my bachelor's thesis is focused on the theme of radiotherapy in general as well as to its history. Radiotherapy is a young medical field which treats both malignant and non-malignant diseases by ionizing radiation. The roots of this discipline go back to the beginning of the 20th century, when German physicist Wilhelm Conrad Rontgen discovered X-rays. These rays started to be used in the treatment of tumorous diseases; the first case of tumour elimination by these rays was described in 1896. The second theoretical chapter outlines the types of radiotherapy and their clinical applications. The first type of radiotherapy is curative (radical), which is the primary choice for treatment of tumours, with the aim to eradicate the tumour completely and cure the patient. Another type of radiotherapy is adjuvant. This is a "securing" method, indicated in case of assumption that there are still microscopic tumour remains in the patient's body. There is also neoadjuvant radiotherapy, so-called preoperative. It is applied before the medical procedure when it is necessary to reduce the size of the tumour. Another clinically applied type is radiotherapy with palliative intent. This treatment is indicated to patients whose disease is incurable and serve to remove or alleviate the symptoms. The last type is non-tumorous radiotherapy. This method of treatment is used for non-tumorous diseases and it is always the method of the last resort. The following chapter discusses the theme of radiotherapeutic irradiator. These devices include simulator which simulates the irradiation plan and is very important for planning and control in radiotherapy. Linear accelerators are the most often tools used for irradiation. These accelerators use high-frequency beam of photons or electrons for irradiation. Other devices used in radiotherapy include cobalt and cesium irradiators. The fourth chapter deals with planning in radiotherapy. Irradiation plan, which must be approved by a doctor, is put together in the process of planning. This plan is approved in case when the created combination of irradiation fields achieves the most accurate covering of the target volume by a required dose, and at the same time healthy tissues and organs are spared as much as possible. This chapter also mentions the theme of phantoms that are very important for planning in radiotherapy. Phantoms were also used during the measurement within the practical part of the thesis. The fifth chapter is devoted to irradiation techniques used in radiotherapy. All basic techniques used for irradiation are described here one-field irradiation technique, which is the simplest one, two-field irradiation, i.e. contralateral, convergent or tangential techniques. Also three-field irradiation technique the T and Y techniques, as well as the four-field technique BOX and Crossfire techniques. The most complex techniques include five and more fields where three-dimensional conformational radiotherapy is used. The last chapter describes individual planning systems used at the Department of Oncology of České Budějovice Hospital, with which the objectives of the practical part of the bachelor's thesis were achieved. These planning systems include Mephysto mc2, Diamond and Eclipse programs. Independent measurements were carried out within the practical part of the bachelor's thesis, on the basis of which the following hypothesis was confirmed: "A procedure implemented in compliance with methodology No. 4 can shorten the time of measuring of parameters of ionizing radiation beams from linear accelerator to be entered into the DIAMOND computing system." The aim of the thesis was to get data files for entering the source of ionizing radiation (linear accelerator) into the DIAMOND computing system. This objective was achieved and the respective data files are presented in the chapter of Results (the whole version is attached to this thesis on a CD).
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Femtosecond laser spectroscopy of diamond
Bažíková, Sára ; Malý, Petr (advisor) ; Preclíková, Jana (referee)
Due to its extraordinary features and wide bandwidth (5.47 eV), diamond is a very promising material in the field of optoelectronics. By absorbing ultraviolet light, excited charge carriers - electrons and holes - are created in the diamond, which can create excitons due to mutual Coulomb interaction. For low temperatures and high concentrations of photoexcitated carriers, carriers can condense into electron-hole droplets and form an electron-hole liquid. The aim of this diploma thesis is to follow up with previous research at the department and to examine the dynamics of electron-hole liquid in bulk diamond at low temperatures. Using femtosecond laser spectroscopy, we investigate the influence of excitation wavelengths on the dynamics of electron-hole liquid condensation.
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Laser spectroscopy of crystalline and nanocrystalline diamond
Zukerstein, Martin ; Trojánek, František (advisor) ; Preclíková, Jana (referee)
The aim of this thesis is a study of NV centres in crystalline and nanocrystalline diamond by laser spectroscopy methods. In the theoretical part we discuss the laser spectroscopy methods, the studied material - diamond and the NV colour centres. In the experimental part we discuss the influence of nanoparticle size on luminescence spectra. We measure the luminescence of samples at room and also at low temperatures depending on the intensity and wavelength of the excitation. We study the photo-conversion of negatively charged state of NV centres to the neutral in detail. We make the time resolved measurements of the luminescence on streak camera for characterization the dynamical properties of the studied samples. The result is the comparison of lifetimes of the states in NV centres in selected samples.
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Multiphoton absorption of ultrafast laser pulse
Zukerstein, Martin ; Trojánek, František (advisor) ; Schmoranzerová, Eva (referee)
Nonlinear optics is constantly developing and in terms of future applications very perspective field of physics. With high-intensity pulsed lasers we are able to study interesting phenomena in matter that we cannot observe with common sources of light. The aim of this thesis is a study of the multiphoton absorption of high-intensity pulses in diamond using z-scan technique. It theoretically describes this nonlinear phenomenon using quantum theory. The next section author took a measurement of the two-photon absorption and found the two-photon absorption coefficients in different samples. Diamond was chosen as the sample material. This material has absolutely unique properties that rank it highly in future applications for optoelectronic devices.
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Studium optických nelinearit v polovodičích a polovodičových nanostrukturách
Kozák, Martin ; Trojánek, František (advisor) ; Herynková, Kateřina (referee) ; Kužel, Petr (referee)
This Ph.D. thesis is focused on the study of optical nonlinearities and dynamics of excited charge carriers in monocrystalline diamond, nanocrystalline diamond and silicon. The dynamics of high density carriers in bulk diamond is investigated in detail (the transition from excitons and free carriers to electron-hole liquid or plasma). We study the picosecond dynamics of electron-hole liquid condensation using several techniques of time-resolved optical spectroscopy and demonstrate its evaporation by femtosecond laser pulses. We also propose two new optical techniques for measurement of lifetime, diffusion coefficient and surface recombination velocity of excitons in diamond. The results obtained by these techniques are described theoretically using diffusion equation and compared with the results obtained by the transient grating diffraction measurement. Further we study two- and three- photon absorption and nonlinear refractive index in diamond. In nanocrystalline diamond we study the second and third harmonic generation and its physical origin. In superlattices of silicon nanocrystals in SiO2 matrix we investigate the nonlinear transient absorption dynamics and carrier diffusion.
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Diamond wheels and their use in the stone industry
Skryja, Jan ; Kolář, Ladislav (referee) ; Jaroš, Aleš (advisor)
This bachelor thesis deals with stone sawing during stone processing. It is divided into theoretical and practical parts. In the theoretical part diamond blades, the sawing process and stone extraction are described. The practical part is focused on the wear of circular saws in granite circular sawing. The wear is determined for two diamond cutting blades made by different manufacturers and is determined by the blade weight loss and segments height loss as a function of time. Both measured values show linear dependence. The results are the basis for a future comparison of the two diamond blades on the economic side, which is not the subject of this work.
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Study of semiconductors by methods of laser spectroscopy
Dzurňák, Branislav ; Trojánek, František (advisor) ; Oswald, Jiří (referee) ; Herynková, Kateřina (referee)
Title: Study of semiconductors by methods of time resolved laser spectroscopy: Luminescence spectroscopy of nanocrystalline diamond Author: Branislav Dzurňák Department: Department of Chemical Physics and Optics Supervisor: doc. RNDr. František Trojánek, Ph.D. Abstract: The PhD thesis is focused on optical properties of nanocrystalline diamond prepared by chemical vapour deposition method. Photoluminescence of nanocrystalline diamond samples and effects of ambient temperature, pressure, pH and UV irradiation on it are studied by laser spectroscopy. Results suggest the keyrole of water and air adsorbates which affect the energy states in the sub-bandgap region of diamond. Photoluminescence decay of samples of different surface termination and structure and its dependency on ambient pressure and temperature is studied by methods of ultrafast (picosecond and nanosecond scale) laser spectroscopy. Results are analysed by power-law decay function which fits well the luminescence decay curves and also describes the dynamics of charge carriers in states localised within the bandgap. The model of interaction of nanocrystalline diamond with air adsorbates is proposed. Non-linear optical properties of nanocrystalline diamond are also studied, namely the generation of second and third harmonic frequency. The thesis...
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Dynamics of photoexcited charge-carriers in diamond
Popelář, Tomáš ; Malý, Petr (advisor) ; Herynková, Kateřina (referee)
Title: Dynamics of photoexcited charge carriers in diamond Author: Bc. Tomas Popelar Department: KCHFO MFF UK Supervisor: prof. RNDr. Petr Maly DrSc., KCHFO MFF UK Abstract: In this work we examine the luminescence from diamond in the strong excitation regime by one-photon or two-photon absorption of femtosecond laser beam. Measured sample was very pure type IIa diamond prepared by CVD method which was held in cryostat in order to measure temperature dependant luminescence in range from 12 K to 300 K. The signal was collected and analyzed either by spectrograph or streak camera so we gained time-integrated and time-resolved results. We analyzed only the part of the spectrum containing contributions from electron-hole liquid (for low temperatures), free excitons and probably exciton complexes. For higher temperatures where the condensation is not possible the contribution from e-h plasma was too weak compared to free excitons and was only detectable by time-resolved measurements. Other time-dependant results were obtained by pump and probe experiment with which we examined a change of life- times based on mode of excitation (one-photon or two-photon one) and also an influence of other beams on the condensation into electron-hole drops. Keywords: CVD diamond, dynamics, e-h liquid, excitons
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Superconductivity in disordered systems
Šopík, Břetislav ; Lipavský, Pavel (advisor) ; Novotný, Tomáš (referee) ; Munzar, Dominik (referee)
Author: Mgr. Břetislav Šopík Thesis advisor: doc. Pavel Lipavský, CSc. Ph.D. thesis Superconductivity in disordered systems Abstract We study some aspects of the superconductivity in disordered systems - namely the superconductivity in a boron-doped diamond. We also apply theoretical methods originally developed in the field of the disordered systems to the theory of superconductivity. In the case of the boron-doped diamond we focus on the question of the dependence of the critical temperature Tc on boron doping. We discuss the impact of the boron distribution correlations on the Tc as well. First, we evaluate the density of states at the Fermi energy N0 within the dynamical cluster approximation. We discuss the Tc as a function of N0 within the BCS, the McMillan and the Belitz theory. In the case of 100 samples, the simplified Belitz theory gives the best agreement with experimental data. For 111 samples the McMillan theory is sufficient. We also show that the difference of 100 and 111 samples in the N0 dependence of Tc can be explained as given by attractive correlations in the boron distribution. Applying the concept of the coherent potential approximation, we re- move a self-interaction from the Galitskii-Feynman T-matrix approxima- tion. This correction has no effect in the normal state but makes the...
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(100) substrate processing optimization for fabrication of smooth boron doped epitaxial diamond layer by PE CVD
Mortet, Vincent ; Fekete, Ladislav ; Ashcheulov, Petr ; Taylor, Andrew ; Hubík, Pavel ; Trémouilles, D. ; Bedel-Pereira, E.
Boron doped diamond layers were grown in an SEKI AX5010 microwave plasma enhanced chemical vapour deposition system. Effect of surface preparation, i.e. polishing and O2/H2 plasma etching on epitaxial growth on type Ib (100) HPHT synthetic diamonds were investigated. Using optimized substrate preparation, smooth (RRMS ~ 1 nm) boron doped diamond layers with metallic conduction and free of un-epitaxial crystallites were grown with a relatively high growth rate of 3.7 μm/h. Diamond were characterized by optical microscopy, optical profilometry, atomic force microscopy and Hall effect.
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