Thesis (M.Med. (Diagnostic Radiology)) -- University of Limpopo, 2022 / BACKGROUND: Ionizing radiation is detrimental to growing cells. The potential risk of any dose of radiation in growing cells can lead to permanent damage of basic cellular structure resulting in a high risk of developing cancer in children. Therefore, paediatric doctors need sufficient knowledge to protect their patients from late effects of radiation resulting from medical use. Most studies report poor knowledge of radiation safety measures among doctors. PURPOSE: The purpose of this study is to assess the knowledge of radiation safety and radiation doses among paediatric doctors in Pietersburg and Mankweng Hospitals, Limpopo province, South Africa. OBJECTIVE: To assess the paediatric doctors’ knowledge of radiation doses used in radiological diagnostic imaging examinations, as well as their knowledge of radiation safety measures. METHODOLOGY: This is a survey of paediatric doctors in the paediatrics general ward, paediatric oncology, intensive care and neonatal units, and paediatric surgery department, at Pietersburg and Mankweng Hospitals. A self-administered questionnaire with 23 items on knowledge of radiation safety and radiation doses emitted during normal radiological examinations is used to collect the data in May 2021. Data are analysed using Statistical Package for Social Sciences (SSPS) version 26.0 software. Chi-squared test is used to analyse the relationship between variables. Analysis of variance (ANOVA) is used to analyse the differences between variables. A p value of <0.05 is considered statistically significant. A total score of 50% in each section is used to denote adequate knowledge. The result are presented in charts and tables. RESULTS: Out of 52 paediatric doctors, 47 completed the questionnaire achieving a 90.4% response rate. Majority of participants were females (n = 31; 66%). Overall, only 10 (21.2%) of the participants scored 50% and above, including three consultants, two registrars, two medical officers and one medical officer intern. Twenty-five (53.1%) participants scored 50% and above on knowledge of radiation safety. Nearly half (44.7%) of the doctors were familiar with the concept of ALARA principle in radiation dose optimisation. Three participants scored more than 50% in the knowledge of radiation doses section. Only five (10.6%) and 17 (36%) participants correctly identified MRI and ultrasound, respectively, as the radiological diagnostic modalities that do not utilize ionizing radiation. CONCUSION: The level of knowledge of radiation safety and radiation doses among the paediatric doctors are poor. A very small number of the paediatric doctors were able to identify non-ionizing radiation modalities that can be used as an alternative to reduce radiation exposure to paediatrics during radiological investigations. Paediatric doctors will benefit from courses on radiation safety and radiation doses to improve their knowledge and/or eliminate unwarranted exposure of their patients to ionizing radiation.

Ion induced charge collection dynamics within Integrated Circuits (ICs) is important due to the presence of ionizing radiation in the IC environment. As the charge signals defining data states are reduced by voltage and area scaling, the semiconductor device will naturally have a higher susceptibility to ionizing radiation induced effects. The ionizing radiation can lead to the undesired generation and migration of charge within an IC. This can alter, for example, the memory state of a bit, and thereby produce what is called a "soft" error, or Single Event Upset (SEU). Therefore, the response of ICs to natural radiation is of great concern for the reliability of future devices. Immunity to soft errors is listed as a requirement in the 1997 National Technology Roadmap for Semiconductors prepared by the Semiconductor Industry Association in the United States. To design more robust devices, it is essential to create and test accurate models of induced charge collection and transport in semiconductor devices. A heavy ion microbeam produced by an accelerator is an ideal tool to study charge collection processes in ICs and to locate the weak nodes and structures for improvement through hardening design. In this dissertation, the Ion Beam Induced Charge Collection (IBICC) technique is utilized to simulate recoil effects of ions in ICs. These silicon or light ion recoils are usually produced by the elastic scattering or inelastic reactions between cosmic neutrons or protons and the lattice atoms in ICs. Specially designed test structures were experimentally studied, using microbeams produced at Sandia National Laboratories. A new technique, Diffusion Time Resolved IBICC, is first proposed in this work to measure the average arrival time of the diffused charge, which can be related to the first moment (or the average time) of the arrival carrier density at the junction. A 2D device simulation tool, the MEDICI code, and heavy-ion microbeams are used to calculate and measure charge collection and relative arrival time on stripe-like test junctions. The MEDICI simulation is in qualitative and sometimes even quantitative agreement with the microbeam measurements. The amount of charge collection and the magnitude of average arrival time for diffused charge collection can be crucial to understanding and mitigating radiation induced circuit malfunctions during normal IC operations.

Thesis (M.A.)--Boston University. Note: Page 24 is missing. / Many animals, invertebrates as well as vertebrates, have demonstrated an ability to somehow sense ionizing irradiation. This recognition is often apparent by a behavioral response which can be correlated with the x-ray stimulus in some way. The fiddler crab, Uca pugilator, was found to exhibit a behavioral response to ionizing irradiation. When the x-ray machine was turned off, the animal would respond instantaneously by a marked hesitation in its general movement after which it would resume its normal activity. This response suggests the animal's ability to somehow be aware of irradiation. Previous work in this area suggested that the photoreceptors were the primary site of stimulation. The fiddler crab's photoreceptors, located at the ends of protruding eye-stalks, are particularly easily excised. When the eye stalks were rer1oved, the response to x-rays was no longer evident. A parallel series of experiments were done with ltght as the stimulus. With intact eyestalks, the animal showed the same off response, and with the eyestalk removed, the subject exhibited no such response. The possibility of a direct stimulation of nervous structures as well as that of an indirect activation by the x-ray evoked release of bioactive substances is discussed. After considering the sinus gland, which was also removed along with the photoreceptors, as a possible site of x-ray reception, a strong implication that the photoreceptors are the primary locus of x-ray sensitivity in the fiddler crab was stated. The marked dose rate dependency of the animal's response to x-rays was noted, and a possible explanation was suggested.

A formação de pares e ANTPOT._ hPOT.+ é o efeito imediato da ação da radiação sobre a matéria. Nos vidros boratos sem impurezas, os elétrons liberados durante o processo de irradiação são capturados por estados metaestáveis das vacâncias de oxigênio cujos níveis estão distribuídos em torno de uma profundidade média de aproximadamente 0,2eV abaixo da base da banda de condução. Nessas vacâncias são formados os centros de elétrons do boro (BEC). Os buracos correspondentes deixados na banda de valência se estabilizam em sítios de oxigênio que ligam átomos de boro tri-coordenados a átomos de boro tetra-coordenados, formando assim os centros de buracos boro-oxigênio (BOHC), com energia de aproximadamente 1,0eV acima do topo da banda de valência. Nos vidros boratos com baixa concentração de impurezas, tais como o ferro e hidrogênio, comumente encontradas em muitas amostras, uma parcela específica dos elétrons e buracos produzidos pela irradiação é neutralizada por íons dessas impurezas, sob condições que dependem da afinidade química e do estado de oxidação do sistema. Com isso, as concentrações de BEC e BOHC diminuem imediatamente após a irradiação da amostra. Como os vidros boratos são bons isolantes elétricos, espera-se que cada par (BEC POT. -, BOHC POT. +) se forme a partir de átomos que sejam primeiros ou segundos vizinhos na matriz vítrea estando, portanto, a uma distância suficientemente pequena para formarem dipolos elétricos metaestáveis. A mesma hipótese vale para o caso envolvendo impurezas onde, por exemplo. o par ([Fe POT. 2+]POT. -, BOHC POT. +) formaria também um dipolo elétrica local metaestável. Em nosso trabalho usamos a técnica de análise de impedância para estudar a presença desses dipolos em vidros previamente expostos à radiação ionizante. Estudamos os vidros Al IND. 2 O IND. 3.3BaO (Ax) e 2/7(100-x)Al IND. 2 O IND. 3.5/7(100-x)B IND. 2O IND. 3.xBaO (Bx) (mol %), ) onde x é a porcentagem de álcali no vidro. Determinamos experimentalmente as constantes dielétricas epsilon dos vidros Ax (para x=30) Bx (para x=20, 30 e 40) e comparamos os resultados. Constatamos que o vidro B20 apresenta uma curva de resposta em baixas freqüências que indica uma relaxação dipolar bem acentuada em relação aos demais vidros. Observamos também, através de nossos espectros de impedância, a presença de dipolos elétricos induzidos por raio x. / The immediate effect of the action of the ionizing radiation on the matter is the formation of e-h+ pairs. For the borate glasses free of impurities the electrons released during the irradiation process are trapped by metastable states of oxygen vacancies whose levels are distributed among an average value of about 0.2 eV below the bottom of the conduction band. At these vacancies the formation of boron electron centers (BEC) take place. The holes left in the valence band are stabilized at the oxygen sites bridging tri-coordinated to tetra-coordinated borons, fonning the boron-oxygen hole centers (BOHC) with average energy of about 1.0 eV above the top of valence band. In borate glasses with low content of impurities such as iron and hydrogen that are often found in most samples, a specific fraction of the electrons and holes are scavenged by the ions of these impurities, under conditions that are dependent of the chemical affinity and of the oxidation state of the system. As a consequence, the BEC and BOHC concentrations decrease immediately after the sample irradiation. As the borate glasses are good electrical insulators, it is expected that each pair (BEC-, BOHC+) be formed from atoms occupying the first or second nearest neighboring sites in the glassy matrix so that the distance among them is sufficiently small to the metastable electrical dipoles being formed. The same hypothesis is valid for the case involving impurities where, e.g. the ([Fe2+], BOHC+) pair is a local metastable electrical dipole. In this work the technique of impedance analysis is applied to study the presence of these dipoles in glasses previously submitted to the ionizing radiation. We studied the glasses of composition Al2O3.6B2O3.3BaO (Ax) and 2/7(100-x)Al2O3.5/7(100- X)B2O3.xBaO (Bx) (mol %), where x is the alkali percent fraction in the glass. Experimental evaluation of dielectric constants \' was performed for the Ax (x = 30) and Bx (x = 20, 30 and 40) and the results were compared. It was found that the B20 glass shows a feature that indicates a greater dipolar relaxation as compared with the other samples. It was demonstrated, also by impedance spectroscopy, the presence of dipoles induced by x-ray.

Thesis (M. Phil.)--University of Hong Kong, 1989.

Telomeres are regions of repetitive DNA bound with a set of specialized proteins required to protect chromosomes from fusing with each other and from eliciting DNA damage response. Dysfunctional telomere maintenance can lead to premature cellular senescence, premature organismal aging and cancer predisposition. In the last few years the evidence has emerged indicating a link between dysfunctional maintenance of telomeres and defective DNA damage response. The objective of this project was to explore further this link by examining effects of some DNA damage response proteins on telomeres that have not been examined before and examining DNA damage response in cells in which telomeres are dysfunctional as a result of alterations in genes not directly involved in DNA damage response. We have developed a method, termed IQ-FISH, for accurate identification of average telomere length in interphase cells from individuals with defective DNA damage response. By applying IQ-FISH we could successfully measure telomere lengths in cell lines from patients that are heterozygous (+/-) and cell lines from patients or animals that are homozygous (-/-) with respect to mutations in these genes. We then analysed telomere length and function, as well as DNA damage response, in lymphoblastoid cell lines originating from BRCA1 and BRCA2 carriers (+/-) and also a single fibroblast cell line from a patient with bi-allelic mutations in BRCA2 (-/-). In addition we have analysed a mouse embryonic stem cell line in which Brca1 was deleted (Brca1-/-) by gene targeting. Our results show lack of correlation between DNA damage response and telomere maintenance in heterozygous cell lines (with the exception of one BRCA1+/- cell line) but a clear positive correlation in the case of cell lines with homozygous mutations. Finally, as a model for telomere dysfunction we have chosen cell lines from Dyskeratosis Congenita (DC) patients. DC is a rare progressive congenital disorder which results in premature aging. DC is primarily a disorder of dysfunctional telomere maintenance and we used cell lines from patients with mutations in DKC1, a gene encoding a protein termed Dyskerin which forms a part of the telomerase enzyme complex. Our results indicate that DC cells with dysfunctional DKC1 may have a dysfunctional DNA damage response.

Thesis (Ph. D.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed January 28, 2008) Includes bibliographical references (p. 117-131).

Thesis (M. Sc.)--University of Canterbury, 2008. / Typescript (photocopy). "May 2008." Includes bibliographical references (p. 55-60). Also available via the World Wide Web.

Στη διπλωματική αυτή παρουσιάζονται οι μετρήσεις των επιπέδων της μη-ιονίζουσας ακτινοβολίας σε διάφορες περιοχές της Ελλάδας είτε σε συνεχή βάση μέσω εγκατεστημένων μετρητικών σταθμών (μετρήσεις 24ωρου) είτε με περιοδικές μετρήσεις με τη χρήση συχνοεπιλεκτικού πεδιόμετρου (μετρήσεις ad hoc). Οι μετρήσεις πραγματοποιήθηκαν μέσω του Προγράμματος ΕΡΜΗΣ το οποίο αναπτύσσεται από το Εργαστήριο Κινητών Ραδιοεπικοινωνιών του Εθνικού Μετσόβιου Πολυτεχνείου και το Εργαστήριο Ραδιοεπικοινωνιών του Αριστοτελείου Πανεπιστημίου Θεσσαλονίκης. / In this document are presented the measurements of the levels of non-ionizing radiation either on a 24hour basis or ad hoc. The measurements are conducted by the HERMES program which is being implemented by the Mobile Radio-Communications Laboratory of the National Technical University of Athens and the Radiocommunications Laboratory of the Aristotle University of Thessaloniki.

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