102 research outputs found

    Rhetorik und Philosophie in der FrĂĽhgeschichte der philosophischen Ă„sthetik

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    Klinische Studien an (krebskranken) Minderjährigen, unter besonderer Bedachtnahme der ethischen Aspekte und der Versicherung des medizinischen Risikos

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    Diese rechtswissenschaftliche Dissertation bespricht neben den rechtlichen Rahmenbedingungen bezüglich klinischer Studien an (krebskranken) Minderjährigen auch die ethischen Fragen, die in diesem Kontext auftreten. Darüber hinaus wird dieser Arbeit Lebendigkeit verliehen, indem durch Experteninterviews ein guter Einblick in die Praxis gewährleistet wird. Die zentralen Erkenntnisinteressen der Dissertation sind: das Aufzeigen von Wechselbeziehungen zentraler Begriffe und Definitionen in diesem Themenfeld; die Vorstellung relevanter philosophischer und risikoethischer (Entscheidungs-)Theorien vor dem Hintergrund dieser Thematik; ein prägnanter, auch für Nicht- Juristen verständlicher, Überblick über die rechtlichern Rahmenbedingungen klinischer Studien, die Handhabung dieser Normen in praxi und die Thematisierung auftretender Probleme vor allem im Hinblick auf die Probandenversicherung sowie die Aufklärung über die wahre Rolle, Funktion, Bedeutung und Tätigkeit von Ethikkommissionen. Zur Erforschung dieser Themenbereiche bediente sich die Verfasserin nicht nur einer äußerst umfangreichen Literaturrecherche, sondern auch der Feldforschung. Auf deren Grundlage, ergänzt durch eine umfangreiche Dokumentenanalyse, konnte aus juristischer sowie ethischer Perspektive ein fundierter Überblick über die medizinische Forschung an Kindern gegeben werden. Durch die genannte Methodenkombination gelang es außerdem theoretische Argumentationen und Grundlagen mit Praxen in Verbindung zu bringen und Konnexitäten sowie Widersprüche dieser beiden Ebenen von einem ethischen Blickwinkel aus aufzuzeigen.The intent of this jurisprudential dissertation is to present the legal regulations concerning clinical trials involving minors (who have cancer) and related ethical questions. Additionally, interviews with experts in the field were included to add the aspect of real-life practice to the theories presented. The cognitive interests of the dissertation are: the identification of interrelations of the various terms and definitions central to the field; the presentation of relevant philosophical and ethical (decision) theories in relation to the topic; a concise overview of the legal regulations for clinical trials, easy to understand without necessity of a legal background; the application of said regulations in real-life situations; the analysis of problems related to clinical trials insurance as well as the clarification of the function, importance, and practice of ethic committees. The author of this dissertation used the methods of extensive literature research as well as fieldwork in her research of the aspects mentioned above. Based on her findings in combination with comprehensive document analysis the author managed to create a well-founded overview of medical research involving children from a legal as well as an ethical point of view. Additionally, the methodology mentioned above made it possible to link theoretical arguments and basic principles of the matter as well as practice and show the connectivities and contradictions of these levels from an ethical point of view

    Nuclear Fission Research at IRMM

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    The Institute for Reference Materials and Measurements (IRMM) will celebrate its 45th anniversary in 2005. With its 150-MeV Geel Electron Linear Accelerator (GELINA) and 7-MV Van de Graaff accelerator as multi-purpose neutron sources, it served the nuclear physics community for this period.The research in the field of nuclear fission was focused in recent years on both the measurement and calculation of fission cross sections, and the measurement of fission fragment properties.Fission cross sections were determined for 233Pa and 234U; the fission process was studied in the resolved resonance region of 239Pu(n,f) and for 251Cf(nth,f). These measurements derive their interest from accelerator driven systems, the thorium fuel cycle, high temperature reactors, safety issues of current reactors, and basic physics. The measurements are supported by several modeling efforts that aim at improving model codes and nuclear dataJRC.D.5-Neutron physic

    Prediction of Fission Mass Yield Distributions Based on Cross-Section Evaluations

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    The statistical model for fission cross-section evaluations has been extended by including the concept of multi-modality of the fission process. The three most dominant fission modes, i.e. the two asymmetric standard I (S1) and standard II (S2) modes and the symmetric super long mode, are taken into account. Based on calculations of the nuclear surface within the multi-modal random neck rupture model, separate outer fission barriers are considered for each mode, while the inner barriers and isomeric wells are assumed to be the same. Deconvoluted fission cross-sections for the S1, S2 and super long modes of 235,238U(n,f) and 237Np(n,f), based on experimental branching ratios, were calculated for the first time in the incident neutron energy range from 0.01 to 5.5 MeV, providing good agreement with the experimental fission cross-section data. In this way, branching ratios can also be deduced for incident neutron energies when no experimental data exist, and used for the prediction of the corresponding fragment mass yield distributions.JRC.D.5-Neutron physic

    Calculations of Neutron Multiplicities and Spectra for Different Actinides

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    The neutron balance in present day reactor systems is a crucial quantity, which needs continuous attention. Refinements in modelling of the prompt neutron multiplicities and spectra are the key to improved predictions of critically benchmark exercises. 235U and 252Cf are key isotopes, since the latter is an important prompt neutron spectrum standard and the former is the main isotope of today's fuel cycle. Hence, improved models to describe prompt neutron characteristics for the above mentioned isotopes are highly appreciated. Based on experimental fission yield and total kinetic energy data, new calculations of the prompt neutron multiplicity and spectra for 235U(n,f) in the incident neutron energy range up to 50 MeV and for 252Cf(SF) have been performed. For 235U(n,f) a new fission cross section calculation was necessary up to 50 MeV prior to being able to deduce the partial fission cross sections above the fist fission chance and the corresponding cross-section ratios, important quantities entering the multiplicity and spectrum modelling. For 252Cf(SF), the multi-modality of the fission process was taken into account. Additionally, a more realistic fission fragment residual temperature distribution as well as an anisotropy of the prompt neutron emission has been introduced leading to improved agreement with experimental results.JRC.D.5-Neutron physic

    Prompt fission neutron emission in the reaction 235U(n,f)

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    Experimental activities at JRC-Geel on prompt fission neutron (PFN) emission in response to OECD/NEA nuclear data requests are presented in this contribution. Specifically, on-going investigations of PFN emission from the reaction 235U(n,f) in the region of the resolved resonances, taking place at the GELINA facility, are presented. The focus of this contribution lies on studies of PFN correlations with fission fragment properties. The experiment employs a scintillation detector array for neutron detection, while fission fragment properties are determined via the double kinetic energy technique using a position sensitive twin ionization chamber. This setup allows us to study several correlations between properties of neutron and fission fragments simultaneously. Results on PFN correlations with fission fragment properties from the present study differ significantly from earlier studies on this reaction, induced by thermal neutrons.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

    Prompt fission neutron emission calculations and description of sub-barrier fission cross section resonances for 234U(n,f)

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    Prompt emission quantities of 234U(n,f) (average quantities as a function of fragment mass, average quantities as a function of total kinetic energy (TKE) and total average quantities) have been calculated within the Point-by-Point model. The recently measured fission fragment distributions at incident energies (En) ranging from 0.2 MeV to 5 MeV have been used The insensibility of the fragment pair multiplicity νpair to the partition of total excitation energy (TXE) between complementary fully accelerated fission fragments has been confirmed. This gives confidence in the predicted total average prompt emission data as a function of En and of average quantities as a function of TKE at different incident energies of 234U(n,f). The systematic behaviour of experimental ratios νH/νpair as a function of heavy fragment mass number AH together with the TXE partition based on modeling at scission allow the parameterization of the excitation energy ratio E*H/TXE. This opens up the possibility to provide ν(A) of 234U in the absence of any experimental data. For the first time the calculation of (TKE) at many En revealed two interesting aspects: the slope dTKE/dν does not vary with En and the flattening of at low TKE values is more pronounced at low incident energies. The correlation between the sub-barrier resonant behaviour of the fission cross-section of fertile actinides (characterizing the pre-scission stage) and the visible fluctuations of their fission fragment and prompt neutron emission data (characterizing the post-scission stage), already discussed in the case of 238U(n,f) is outlined and quantitatively supported by 234U(n,f), too. The pronounced vibrational resonances in the experimental fission cross-section of 234U, are for the first time well described by model calculations without any adjustment, due to our statistical model for reaction cross-section calculation including a refined fission model with sub-barrier effects.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

    Prediction of the prompt neutron multiplicity distribution ν(A) for 235U(n,f) and 239Pu(n,f) in the incident energy range of multichance Fission

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    Measurements of fission fragment data at incident energies (En) up to several tens of MeV require prompt neutron multiplicity distribution ν(A) to determine the preneutron fragment properties. Those ν(A) data are not readily experimentally available. Consequently, model predictions of ν(A) at En where multichance fission occurs are needed. The Point-by-Point model of prompt emission provides the individual ν(A) of compound nuclei of the main and secondary nucleus chains that are undergoing fission at any En. Total ν(A) calculations for n + 235U and n + 239Pu are presented together with systematic behaviors of individual ν(A) with increasing energy.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

    Properties of the Reaction 238U(n,f) at the Vibrational Resonances

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    Recent fission cross-section calculations for the reaction 238U(n, f), based on an extended statistical model, predict a significant change of fission fragment properties, such as the mean mass by dA = 1.5 and a notable increase in total kinetic energy in the region of the vibrational resonance at an incident neutron energy En = 0.9 MeV. This model includes individual fission cross-sections by the asymmetric standard 1 (S1) and standard 2 (S2) as well as the symmetric super-long (SL) mode. In order to verify the model predictions, a dedicated experiment on 238U has been carried out to measure fission-fragment mass yield distributions for incident neutron energies from En = 2.0 MeV down to 0.9 MeV, where the fission characteristics at the vibrational resonance at En = 0.9 MeV were investigated for the first time. The previously reported distinct structure in the angular anisotropy around En = 1.2 and 1.6 MeV was observed at En = 0.9 MeV as well. The predicted large changes in fission fragment mass yield and total kinetic energy could not be confirmed. In the resonance the mean total kinetic energy is only about 0.5 MeV higher than at En = 1.8 MeV. At the same time, a slight decrease of the mean heavy fragment mass was observed, probably indicating a slightly increased contribution of the S1 fission mode.JRC.D.5-Neutron physic

    Neutron Multiplicity Correlations with Fission Fragment Mass and Energy from

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    There exists experimental evidence for strong fluctuations of the average neutron multiplicity from resonance to resonance in 239Pu(n,f). These fluctuations have been shown to impact nuclear reactor benchmarks by reducing the criticality. The fluctuating neutron multiplicity can be explained as a consequence of the competition between direct fission and the (n,Îłf) process. However, there is also evidence for fluctuations of the fission fragment mass yields from resonance to resonance. The mass yield fluctuations may also contribute to fluctuations of the neutron multiplicity averaged over all fission fragment masses. In order to model the contribution to the neutron multiplicity fluctuations by the fission fragment mass yield fluctuations new data on the correlations between fission fragment properties and neutron multiplicities are in need. We present experiments carried out to determine prompt neutron multiplicity correlations with fission fragment masses and total kinetic energies in the reaction 239Pu(n,f). The experiment has been performed at the GELINA facility at JRC-Geel. A twin position-sensitive Frisch-grid ionization chamber is used for fission fragment identification via the double kinetic energy technique. An array of scintillation detectors is employed for neutron counting. Correlations between average neutron multiplicities and fission fragment properties have been measured with improved resolution in both mass and TKE, compared to data from the literature
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