Qucosa – Hemholtz-Zentrum Dresden-Rossendorf
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Establishment of the Physical and Technical Prerequisites for the Determination of the Relative Biological Effectiveness of Low-energy Monochromatic X-rays
Get PDFA superconducting electron linear accelerator of high brilliance and low emittance (ELBE) is under operation at Forschungszentrum Rossendorf since January 2003. The first stage of ELBE is based on an electron energy of 20 MeV, whereas in the future a 40 MeV beam will be provided. The relativistic electron beam is used to drive various kinds of secondary radiation sources. Among all, X-rays in a wide energy range can be obtained. One method for production of intensive, quasi-monochromatic Xrays in the energy range 10 - 100 keV, tunable in photon energy, is by channeling of relativistic electrons in a perfect crystal. This unconventional photon source with variable time structure will be optimised and used for radiobiological studies. Its first test operation was in October 2003. This thesis is part of the first radiobiological project – the determination of relative biological effectiveness (RBE) of the X-rays in this energy range. The most important aspects of medical application of low-energy X-rays are imaging and radiation therapy, but they can also be helpful in the study of radiation effects in living matter. However, the RBE depends on the photon energy, dose range, cell line and biological endpoint. Up to now no definitive conclusions can be made about their biological effectiveness due to the large spread of the published data. Therefore, in order to precisely determine the RBE, studies have to be performed at an intensive, tunable photon source, for several practically relevant cell lines and biological endpoints. The possibility of using channeling radiation (CR) for medical applications has been widely discussed in the literature, but building and optimisation of a dedicated source is for the first time performed at the ELBE accelerator
Low Energy Ion Beam Synthesis of SiNanocrystals for Nonvolatile Memories – Modeling and Process Simulations
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Unterstützung der ukrainischen Aufsichtsbehörde beim Ausbau der verbesserten betrieblichen KKW-Überwachung (Teil 3)
Get PDFIn Analogie zu den Systemen für die KKW Saporoshje und Rovno wurden für die drei Blöcke des KKW Südukraine und für den ersten Block des KKW Chmelnitzky technische Systeme zur verbesserten betrieblichen Überwachung eingerichtet. Dazu werden der Aufsichtsbehörde vor Ort und im Krisenzentrum in Kiew einmal pro Minute für jeden Block bis zu 51 sicherheitsrelevante technologische und 16 radiologische Parameter zur Bewertung mittels moderner technischer Ausrüstungen online zur Verfügung gestellt. Die entwickelte Auswertesoftware gestattet die Darstellung der Bewertungsergebnisse in Form von Tabellen, Grafiken und Schemata. Außerdem ermöglicht ein Archivmodus Trendanalysen. Mit der Integration der für die geschützte Warte gelieferten Ausrüstungen in das am Standort des KKW Saporoshje betriebene Fernüberwachungssystem ist es nunmehr möglich, die wesentlichen sicherheitsrelevanten Parameter des gesamten Standortes auch bei außergewöhnlichen Ereignissen mit Hilfe moderner Technik zu erfassen und zu bewerten
Modelling of in-vessel retention after relocation of corium into the lower plenum
Get PDFConsidering the unlikely core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Worldwide several experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work. At the Institute of Safety Research of the FZR a finite element model has been de-veloped simulating the thermal processes and the viscoplastic behaviour of the ves-sel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal and the mechanical calculations are sequentially and recursively coupled. The model is capable of evalu-ating fracture time and fracture position of a vessel with an internally heated melt pool. The model was applied to pre- and post test calculations for the FOREVER test se-ries representing the lower head RPV of a PWR in the geometrical scale of 1:10. These experiments were performed at the Royal Institute of Technology in Stock-holm. The results of the calculations can be summarised as follows: # The creeping process is caused by the simultaneous presence of high tem-perature (>600 °C) and pressure (>1 MPa) # The hot focus region is the most endangered zone exhibiting the highest creep strain rates. # The exact level of temperature and pressure has an influence on the vessel failure time but not on the failure position # The failure time can be predicted with an uncertainty of 20 to 25%. This uncer-tainty is caused by the large scatter and the high temperature sensitivity of the viscoplastic properties of the RPV steel. # Contrary to the hot focus region, the lower centre of the vessel head exhibits a higher strength because of the lower temperatures in this zone. The lower part moves down without significant deformation. Therefore it can be assumed, that the vessel failure can be retarded or prevented by supporting this range. # The development of a gap between melt crust and vessel wall could not be proofed. First calculations for a PWR geometry were performed to work out differences and commonalities between prototypic scenarios and scaled experiments. The results of the FOREVER-experiments cannot be transferred directly to PWR geometry. The geometrical, mechanical and thermal relations cannot be scaled in the same way. Because of the significantly higher temperature level, a partial ablation of the vessel wall has to be to expected in the PWR scenario, which is not the case in the FOREVER tests. But nevertheless the FOREVER tests are the only integral in-vessel retention experiments up to now and they led to a number of important insights about the behaviour of a vessel under the loading of a melt pool and pressure
Abtrennung von Uran aus wässriger Lösung durch Calix[6]arene mittels Flüssig-Flüssig-Extraktion sowie Festphasen-Extraktion
Get PDFDie Uranspeziation in ausgewählten Sicker- und Grubenwässern des ehemaligen Uranbergbaus wurde mittels spektroskopischer Methoden (TRLFS, LIPAS) untersucht. Deren Kenntnis in Abhängigkeit vom pH-Wert ermöglicht die Optimierung der Uranabtrennung mittels uranophiler Calixarene. Mittels Flüssig-Flüssig-Extraktion wurde gezeigt, dass COOH-derivatisierte Calix[6]arene als effektive Extraktionsmittel für die selektive Uranylabtrennung aus umweltrelevanten Wässern bei pH-Werten größer 4 geeignet sind und für Praxisanwendungen eingesetzt werden können. Extraktionskonstanten wurden bestimmt. Die durch Fixierung dieser Calixarenderivate auf Polyester dargestellten calixarenmodifizierten Vliese sind in der Lage Uranylionen aus synthetischen Grubenwässern in Anwesenheit von Konkurrenzionen abzutrennen. Die Untersuchungen zur Reversibilität der Uranbindung an calixarenausgerüsteten Polyestervliesen haben gezeigt, dass eine fast vollständige Regenerierung der calixarenmodifizierten Vliese mittels verdünnter Mineralsäuren möglich ist. Die regenerierten textilen Filtermaterialien können für weitere Uranabtrennungszyklen eingesetzt werden. Nach Auswahl geeigneter Calixarenderivate ist eine Übertragung des entwickelten Abtrennungsprinzipes auf weitere Actinide (z.B. Np, Pu) bzw. Schwermetall-Kontaminanten (z.B. As, Cd, Pb) möglich
Investigation of acoustic waves generated in an elastic solid by a pulsed ion beam and their application in a FIB based scanning ion acoustic microscope
Get PDFThe rapid growth of the microelectronics industry in the last decades made it possible to produce structures in the sub-micrometer scale on silicon chips and to reach an integration scale under 100 nm. Decreasing the size and increasing the complexity of these structures make a control of quality and defects investigation more difficult. During a long time ultrasound devices are being used for nondestructive investigation of materials, like ultrasound microscopes, scanning photo-acoustic microscopes or scanning electron-acoustic microscopes, where acoustic waves are generated by acoustic transducers, focused laser or electron beams, respectively. The aim of this work is to investigate more precisely the acoustic wave generation by pulsed and periodically modulated ion beams in different solid materials depending on the beam parameters and to demonstrate the possibility to apply an intensity modulated focused ion beam (FIB) for acoustic emission and for nondestructive investigation of the internal structure of materials on a microscopic scale. The combination of a FIB and an ultrasound microscope in one device can provide the opportunity of nondestructive investigation, production and modification of micro- and nanostructures simultaneously. The FIB spot size in modern systems is comparable with that of a focused electron beam and the penetration depth of ions with energy of 20-60 keV is lower than 100 nm. This makes it possible to reach a sub-micrometer resolution of a scanning ion acoustic microscope. On the other hand side a FIB with energy of 20-60 keV is a good tool which can be used for the fabrication of nanostructures using ion milling, implantation or ion beam assisted deposition techniques. The bulk ultrasound emission in a solid was investigated using a pulsed high energy ion beam focused on aluminum, copper, iron and silicon samples. Oxygen, silicon and gold ion beams were applied in charge states from 1+ to 4+ with the pulse duration of 0.5 - 4 µs and an energy of 1.5 - 10 MeV. Intensity of the detected acoustic waves shows a linear dependence on the energy of the incident ions, on the ion flux as well as on the pulse duration. No influence of the ion charge and ion mass to the emission of acoustic waves was observed. The ion acoustic effect was applied for a nondestructive material inspection using intensity modulated FIB providing by the IMSA-100 FIB system with an accelerating potential of 30-35 kV. The achieved lateral resolution of this scanning ion acoustic microscope is in the micrometer range depending on the sample material and the beam modulation frequency. The resolution can be improved by increasing the frequency. The maximal modulation frequency which was obtained at IMSA-100 is about 2 MHz corresponding to lateral resolution of 4-5 µm on silicon. Using this microscope, some images of integrated microstructures on a silicon chip were obtained using the lock-in technique for filtering of the signal from the noise and increasing of the total imaging time. The possibility to visualize near sub-surface structure was demonstrated. Due to the strong sputtering effect and the long time of irradiation the imaged structures were significantly damaged. Si2+, Ge2+, Ga+ and Au+ ions were used. All these ions are quite heavy and have high sputtering coefficients. Long-time imaging improves the quality of acoustic images, i. e. the signal-to-noise ratio is reduced with the square root from the pixel time, but leads to significant erosion of the imaged structure
