Thesis (M.A.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 26-28.

Made available in DSpace on 2016-01-13T13:27:32Z (GMT). No. of bitstreams: 0 Previous issue date: 1993-09-28. Added 1 bitstream(s) on 2016-01-13T13:33:01Z : No. of bitstreams: 1 000854600.pdf: 1022046 bytes, checksum: 14be557a18bce93d838ba01c104f9da9 (MD5) / Estudamos o conceito de radiação em dois contextos aparentemente distintos: radiação proveniente de uma carga clássica, pontual, e radiação proveniente de um detetor de Unruh-DeWitt. Rederivamos os campos de uma carga em movimento hiperbólico e mostramos através deste exemplo que radiação não é geralmente covariante. Calculamos as taxas de emissão para detetores em movimento uniformemente acelerado e movimento uniforme através do vácuo de Minkowski. Concentramos em detetores ligados por tempo finito / We study the concept of radiation in two apparently distinct contexts: radiation coming from a classical pointlike charge, and radiation coming from an Unruh-DeWitt detector. We rederive the fields for a charge in hyperbolic motion and use this example to show that the concept of radiation is not a generally covariant one. We calculate the emission rates for uniformly accelerated and inertial detectors going through the Minkowski vacuum. We concentrate on finite-time detectors

Orientador: George Emanuel Avraam Matsas / Banca: Ruben Aldrovandi / Banca:Alfredo Takashi Suzuki / Resumo: Estudamos o conceito de radiação em dois contextos aparentemente distintos: radiação proveniente de uma carga clássica, pontual, e radiação proveniente de um detetor de Unruh-DeWitt. Rederivamos os campos de uma carga em movimento hiperbólico e mostramos através deste exemplo que radiação não é geralmente covariante. Calculamos as taxas de emissão para detetores em movimento uniformemente acelerado e movimento uniforme através do vácuo de Minkowski. Concentramos em detetores ligados por tempo finito / Abstract: We study the concept of radiation in two apparently distinct contexts: radiation coming from a classical pointlike charge, and radiation coming from an Unruh-DeWitt detector. We rederive the fields for a charge in hyperbolic motion and use this example to show that the concept of radiation is not a generally covariant one. We calculate the emission rates for uniformly accelerated and inertial detectors going through the Minkowski vacuum. We concentrate on finite-time detectors / Mestre

A micro heavy water concentration unit using the G.S. process was constructed to study possible process improvements. The deuterium isotope exchange was performed successfully in this unit. It was found that the use of monoethanolamine (MEA) in conjunction with the G.S. process had little or no effect on the recovery fraction of heavy water from the feed. However, the experiments indicated that the gas rate could be increased to attain a higher production rate, or equivalently, for the same production rate the size of the towers could be slightly reduced. The improvement was found only marginally attractive particularly because one more stage could be needed to recover the MEA which was introduced in the feed water.

Low temperature radiative properties of the layered transition metal dichalcogenides 2H-MoS2, 2H-WS2 and 2H-WSe 2 are investigated. Synthetically grown crystals of all three materials, natural 2H-MoS2 single crystals and several 2H-MoS2 and 2H-WS2 commercial powders are studied. Steady-state photoluminescence (PL) measurements performed on the samples reveal two distinct radiative regions in the near infrared. The first region consisting of several sharp lines is produced by bound excitons related to the halogen transport agent intercalated within the van der Waals gap of the layered compounds. The second weaker region, composed of a broad spectral band, originates from the radiative recombination between an intrinsic crystal lattice defect center and the valence band in the conditions of a strong electron-phonon coupling. Time decay analysis of the bound excitonic radiative transitions is performed with time-resolved and PL intensity ratio measurements. The spectral and temperature dependence of the total radiative emissions of all three compounds are described in the framework of a two-channel kinetic recombination model in thermal equilibrium conditions. A configuration coordinate diagram is also constructed for 2H-MoS 2. PL intensity measurements performed on the 2H-MoS2 and 2H-WS2 synthetic crystals reveal a sublinear PL dependence on excitation intensity. Finally a technique developed to intercalate halogen molecules in natural 2H-MoS2 single crystals is described.

The continuous spectrum of gamma radiation which accompanies the capture of orbital electrons has been recently calculated independently by Glauber and Martin (1954), and by Hess (1955). Both calculations take into account the influence of the nuclear charge on the wave functions but otherwise involve different methods and approximations, the conclusions being also quite different: the intensity of the gamma radiation is an order of magnitude lower according to Hess than according to Glauber and Martin. The purpose of the calculations presented in this thesis has been to settle this disagreement and to explain its origin. To this effect the high energy part of the gamma spectrum, which is almost entirely determined by the contributions of the capture of the 1s and 2s electrons, has been computed for the case of A³⁷ for which experimental data are available. In view of the low nuclear charge of A³⁷ (z = 18), the non-relativistic Coulomb wave functions could be used, and, apart from neglecting screening effects, the calculations are exact although partly numerical. In particular, the retardation effects which were neglected by Glauber and Martin have rigorously been taken into account. The conclusions are: first, approximations used by Hess were partly inconsistent, although the method was in principle correct; second, taking into account retardation effects results in a gamma spectrum whose intensity amounts to 0.81 of the intensity obtained by Glauber and Martin at 135 Kev, and to 0.24 at 675 KeV (the gamma spectrum limit being 816 KeV). The gamma spectrum of A³⁷ determined by Lindqvist and Wu (1955) seems to agree quite well with Glauber and Martin's result. However, Lindqvist and Wu measured only relative intensities and had to apply many instrumental corrections so that it is not yet clear whether the measured spectrum would not agree as well with the spectrum computed in this thesis. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A discussion is given of the many uses of photo-conductive cells, especially of those of the lead sulphide type. A Factor of Merit for radiation detectors as proposed by Clark Jones is presented, which is intended to cover all types of detectors, and which is applied to the lead sulphide cells studied. Other Factors of Merit are also mentioned. From information obtained the Factors of Merit are evaluated for the cells. These Factors of Merit are found to vary with the temperature of the cell layer. It is found that limiting noise is not due to Johnson noise, but rather to radiation fluctuations; and that the ultimate sensitivity has been reached in some cells. The cells are assumed to be type II detectors according to Clark Jones's classification. It is found that the engineering limit proposed by R. J. Havens does not apply here. Particularly good agreement between various expressions for the Factor of Merit is shown, assuming a type II detector. A description of the apparatus is given in some detail. A black body radiator and associated temperature control, a 900 cycles per second tuned amplifier, a wide band preamplifier and a multi vibrator used in measuring time constants of such cells are described. The methods of measurement of responsivity to noise ratio, of noise, of time constants, frequency response curves and spectral response of a detector are outlined. It is found that the black body is optically aligned; tests show that the response of a cell is directly proportional to the intensity of the illumination. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The effect of low closes of radiation is of primary importance if we wish to understand the basic mechanisms of radiation damage. In vitro experiments performed at clinically relevant doses can also lead to better understanding of radiotherapy protocols and fractionation regimes. The availability of accurate data at low doses can facilitate the examination of survival models which describe dose-effect relationships. Most cellular radiobiology experiments are performed at high doses (3 to 30 Cray). The errors in these experiments, while acceptable at high doses, are too large to allow determination of radiobiological parameters, such as oxygen enhancement ratio (OER) and relative biological effectiveness (RBE), at low doses (0 to 3 Cray). These experiments are limited in the low dose region because we are measuring only the surviving fraction, in a population of predominantly surviving cells, and because there is an uncertainty of 10 to 15% in the number of cells plated. We have developed a technique to assay cell survival at low doses. The exact number of cells plated is determined microscopically. After incubation, the number of killed cells and the number of surviving cells are both determined, by microscopic examination. While extremely labour intensive, this technique yields survival data, in the low dose region, which is much more accurate than the data obtained using classical methods. This technique can be used to measure many radiobiological parameters. We have chosen to examine the effect of oxygen at low doses. Our results clearly demonstrate that, for asynchronous Chinese Hamster Ovary (CHO) cells, the radiosensitizing effect of oxygen is reduced at lower doses. A Picker X-ray source (280 kVp, HVL 1.7 mm Cu) was used for these experiments. The choice of a survival model has important implications in the low dose region. The predictions of three different survival models regarding the effect of oxygen at low doses are discussed. This technique can be used to complement the classical "high dose assay" to obtain data that encompasses a large dose range. This will be especially valuable, for example, when attempting to fully describe radiobiological parameters, or when examining survival models. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Objective: To examine the effect of treatment and tumour factors on the overall survival (OS) of patients completing chemo-radiation (CRT) for stage IIB cervical cancer. Materials and methods: Retrospective audit of 228 patients with stage IIB cervical cancer treated between 1995 and 2010, who received CRT with at least 45 Gy external beam radiation, two to four brachytherapy insertions, and one or more cycles of concurrent weekly cisplatin (40mg/m², capped at 60 mg/week). Results: Mean tumour size was 5.5cm, bilateral parametrial involvement in 40% of patients, lateral parametrial involvement in 50%, and vaginal spread in 43%. Mean total dose to Point A was 83 Gy (range 61-96) linear quadratic equivalent dose to 2 Gy/fraction. Mean overall treatment time (OTT) was 45 days. The average weekly haemoglobin (AWHB) during treatment was 11.6 g/dL (range 8.8-15.5). Blood transfusions before or during chemo-radiation were given in 33% of patients. Two thirds of patients completed five or six cycles of weekly cisplatin. Reasons for fewer than five cycles were: scheduling failure, neutropaenia, and/or renal impairment. No outcome differences were observed for Monday vs. Thursday cisplatin administration. The 5-year OS was 60%. Patients completing fewer than six cycles had a worse OS (55 vs. 76%, p=0.02). By multiple regression analysis for OS, only six cycles of cisplatin, squamous histology, and AWHB>10g/dL were significant. Conclusions: Maintaining HB>10 and administering six cycles of weekly cisplatin at the dose regimen used appear to be requirements for maximal benefit during CRT of stage IIB cervical cancer.

The reported median survival time for patients who are diagnosed with high grade astrocytomas and who undergo postoperative radiotherapy is of the order of 24 to 40 weeks. The course of radiotherapy administered to these patients takes up a considerable portion of their expected survival time. Therefore, any means of reducing the treatment time may contribute to an enhanced quality of life for these patients. A potentially useful method for the reduction of the treatment time may be achieved with the use of continuous low dose rate external beam radiotherapy, where the treatment is administered over a 12 to 24 hour period. A relationship between fractionated and continuous low dose rate irradiation has been reported for skin, however, no such relationship has been reported for the brain. Low dose rate protocols that are equivalent in effect to fractionated (conventional) protocols can be derived using the linear quadratic theory, provided that quantitative radiobiological data for normal tissue (brain) is known. Thus, the aim of the current study is to test the radiation tolerance of the rat brain to low dose rate and fractionated radiation in order to establish the values for the parameters of the linear quadratic model.