Made available in DSpace on 2014-10-09T12:32:55Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:05Z (GMT). No. of bitstreams: 1 03635.pdf: 2626366 bytes, checksum: 40e4590eefc4ec60a78bc25814cc9bdb (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:32:55Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:05Z (GMT). No. of bitstreams: 1 03635.pdf: 2626366 bytes, checksum: 40e4590eefc4ec60a78bc25814cc9bdb (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Call number: LD2668 .T4 1955 S67 / Master of Science

Thesis (Ph.D. 1974) from the Dept. of Physics, University of Adelaide.

Thesis (Ph.D.) - Carleton University, 2005. / Includes bibliographical references (p. 148-161). Also available in electronic format on the Internet.

Thesis (doctoral)--Vrije Universiteit te Amsterdam. / Bibliography: p. 97-100.

Thesis (M.S. in Physics)--United States Naval Postgraduate School, 1959. / "Physics and Mathematics" -t.p. Includes bibliographical references (p. 33).

Part A of two Project Reports; Part B can be found at: http://hdl.handle.net/11375/17692 / <p> A number of recently published papers have been critical of the values of CE and Cλ by the ICRU as absorbed dose conversion factors for ionization chambers used in electron or photon beams.</p> <p> This report examines the subject in light of these recent works. Presented is a review of both theoretical and experimental results published to date along with the results of experimental work carried out at this facility. The present study concentrated on the measurement of the absorbed dose conversion factors for electrons and 25 NW photons. It also attempted to determine how the conversion factors might be influenced by such factors as chamber design buildup cap thickness and composition, and phantom composition.</p> <p> Measurements were made using electrons with 10 to 32 MeV initial energy and a 25 MeV photon beam, all produced by a Sagittaire Model Therac 40 linear accelerator. Checks on the stability of the measurement system were made using a 60Co source. Fricke ferrous sulfate dosimetry was used for absorbed dose measurement in the determination of CE.</p> <p> The results of the study would indicate that there is little or no effect on the measured values of CE or Cλ introduced by either the sleeves or phantoms for the radiation qualities studied. The results of the absorbed dose conversion factor study would indicate that the values recommended by the ICRU are sufficiently accurate for use in most instances. The data would tend to support the arguement that if there is an error in one of the ICRU derivations, the error in theory lies in the CE determination rather than that for Cλ.</p> / Thesis / Master of Engineering (MEngr)

Tendo em vista a importância da calibração de instrumentos medidores de radiação e do conhecimento das principais características destes instrumentos, diversos tipos de câmaras de ionização foram intercomparados em termos de seus coeficientes de calibração e dependência energética, em feixes padrões de raios X, níveis radioterapia, radiodiagnóstico e radioproteção. Foi realizada uma intercomparação de activímetros utilizados em medicina nuclear, com três radionuclídeos: 67Ga, 201Tl e 99mTc. Todos os activímetros que participaram da intercomparação apresentaram resultados dentro dos limites recomendados pela norma CNEN-NE-3.05. Para completar o conjunto de qualidades de radiação do Laboratório de Calibração de Instrumentos do IPEN, foram estabelecidos feixes de radiação-X, nível radioproteção e radioterapia de energias baixas, seguindo recomendações internacionais. Três metodologias para a obtenção de coeficientes de calibração de câmaras de ionização não seladas em feixes de radiação-X foram estudadas e comparadas. Um conjunto de câmaras de ionização Victoreen, especialmente projetado para uso em intercomparações laboratoriais, foi submetido a testes de caracterização. O desempenho destas câmaras mostrou que elas podem ser utilizadas em feixes de radiação-X nível radioproteção de maneira segura, visto que nestes feixes estas câmaras apresentaram resultados em conformidade com recomendações internacionais. No entanto, seu uso em feixes de radioterapia e de radiodiagnóstico deve ser feito com algumas considerações, pois especialmente nos testes de dependência energética e de tempo de estabilização, estas câmaras não atenderam às respectivas recomendações internacionais. Este trabalho apresenta dados sobre o desempenho de diversos modelos de câmaras de ionização em diferentes feixes de radiação-X, fornecendo uma ferramenta para a escolha do instrumento mais adequado para a realização de medições em feixes de radiação ionizante / Since the calibration of radiation measurement instruments and the knowledge of their major characteristics are very important subjects, several different types of ionization chambers were intercompared in terms of their calibration coefficients and their energy dependence, in radiotherapy, diagnostic radiology and radioprotection standard beams. An intercomparison of radionuclide calibrators for nuclear medicine was performed, using three radionuclides: 67Ga, 201Tl and 99mTc; the results obtained were all within the requirements of the national standard CNEN-NE-3.05. In order to complete the range of radiation qualities of the Calibration Laboratory of IPEN, standard radiation beam qualities, radiation protection and low energy radiation therapy levels, were established, according international recommendations. Three methodologies for the calibration of unsealed ionization chambers in X-ray beams were studied and compared. A set of Victoreen ionization chambers, specially designed for use in laboratorial intercomparisons, was submitted to characterization tests. The performance of these Victoreen ionization chambers showed that they are suitable for use in radioprotection beams, because the results obtained agree with international recommendations. However, these Victoreen ionization chambers can be used in radiotherapy and diagnostic radiology beams only with some considerations, since their performance in these beams, especially in relation to the energy dependence and stabilization time tests, did not agree with the international recommendations for dosimeters used in radiotherapy and diagnostic radiology beams. This work presents data on the performance of several types of ionization chambers in different X-ray beams, that may be useful for choosing the appropriate instrument for measurements in ionizing radiation beams.

A mamografia é um exame realizado no mamógrafo, que utiliza raios X para obter imagens da anatomia interna da mama. Para que esta imagem seja capaz de fornecer um diagnóstico correto, é necessário que os equipamentos passem constantemente por programas de controle de qualidade para que se possa garantir que as pacientes submetidas a este exame não estejam recebendo dose além da necessária, evitando-se assim possíveis efeitos biológicos indesejados. As câmaras de ionização são detectores muito utilizados para se realizar o controle de qualidade de equipamentos que utilizam radiação, como os mamógrafos. No presente trabalho foram utilizadas quatro câmaras de ionização desenvolvidas no Laboratório de Calibração de Instrumentos do IPEN LCI/IPEN, que foram submetidas a testes de caracterização em feixes padrões de radiação X do LCI. Elas apresentaram resultados satisfatórios, dentro dos limites estabelecidos pelas normas nacionais e internacionais. Como aplicação, estas câmaras de ionização foram utilizadas para testes de controle de qualidade em quatro mamógrafos clínicos de diferentes instituições quanto à repetibilidade e linearidade da taxa de kerma no ar. Os resultados obtidos nestes testes encontram-se dentro dos limites recomendados pelas normas nacionais e internacionais. / Mammography is an examination in mammography, which uses X-rays to obtain images of the internal anatomy of the breast. To provide a correct diagnosis, it is necessary that the equipment constantly undergo quality control programs to ensure that patients submitted to this examination do not receive more than the necessary dose, thus avoiding unwanted possible biological effects. The ionization chambers are widely used detectors to perform the quality control program of equipment with radiation, as mammographers. In the present study, four different special ionization chambers, developed at the Calibration Laboratory of Instruments of IPEN - LCI / IPEN, were submitted to the characterization tests in standard X radiation beams at the LCI. The results were satisfactory, within the limits estabilished by national and international standards. As an application, the ionization chambers were used for quality control tests in four mammography clinics from different institutions, as the repeatability and linearity of the air kerma rate. The results obtained in these tests were within the limits recommended by national and international standards.