Material dependence of 2

Calculations of the material dependence of 2H(d,p)3H cross section and neutron-to-proton branching ratio of d+d reactions have been performed including a concept of the 0+ threshold single particle resonance. The resonance has been assumed to explain the enhanced electron screening effect observed in the d+d reaction for different metallic targets. Here, we have included interference effects between the flat and resonance part of the cross section, which allowed us to enlighten observed suppression of the neutron channel in some metals such as Sr and Li. Since the position of the resonance depends on the screening energy that strongly depends on the local electron density. The resonance width, observed for the d+d reactions in the very hygroscopic metals (Sr and Li) and therefore probably contaminated by oxides, should be much larger than for other metals. Thus, the interference term of the cross section depending on the total resonance width provides the material dependences

Interference between broad resonance states and direct reaction mechanisms in nuclear reactions below the Coulomb barrier

Eine breite, isolierte Resonanz in einer Kernreaktion kann unter bestimmten Umständen zur Interferenz mit dem direkten, nur schwach energieabhängigen Reaktionsanteil führen. Dieser selten auftretende Fall kann eine starke Änderung des differentiellen Wirkungsquerschnitts zur Folge haben. Für die Berechnung derartiger Reaktionen müssen die zwei wichtigsten Modelle, das der direkten Reaktionen (hier im Rahmen der Näherung durch gestörte Wellen, DWBA) und das der Resonanzen (hier beschrieben durch die R-Matrix-Parametrisierung) miteinander kombiniert werden. Vorhergehende Messungen haben zu der Vermutung geführt, daß in der Reaktion 6Li(d,alpha)4He ein solcher Fall vorliegen könnte. Zur Vervollständigung der Meßdaten wurde die Reaktion 6Li(d,alpha)4He im Bereich um 100 keV Einschußenergie vermessen, wo bereits von anderen Gruppen eine ungewöhnliche Energieabhängigkeit der Winkelverteilung beobachtet worden ist. Bisherige Analysen waren nicht in der Lage, die Winkelverteilung dieser Reaktion im niederenergetischen Bereich (bis 2 MeV Einschußenergie) auch nur annähernd theoretisch wiederzugeben. Neben den Messungen wurde in dieser Arbeit eine genaue, umfangreiche Analyse der Reaktion 6Li(d,alpha)4He durchgeführt. Dazu wurden zunächst die beiden oben erwähnten Reaktionsmodelle in einheitlicher Weise dargestellt und es wurde eine Methode gezeigt, beide Modelle miteinander zu verknüpfen. Für die konkrete Berechnung wurde ein Programm entwickelt, das in allgemeiner Form eine Anregungskurve für beliebige Reaktionen berechnet. Es baut auf einem älteren Code zur DWBA-Analyse (DWUCK4) auf und ergänzt diesen um eine kohärente Beimischung eines oder mehrerer Resonanzterme. Die besondere Schwierigkeit derartiger Berechnungen besteht in der korrekten Beschreibung der Phasenlage der Übergangsmatrizen, die sonst bei Berechnungen nach nur einem Reaktionsmodell naturgemäß keine Rolle spielt. Die Anwendung der numerischen Berechnungen auf die Reaktion 6Li(d,alpha)4He führt zu einer sehr guten Wiedergabe der Winkelverteilung über einen weiten Energiebereich. Durch die Berücksichtigung des Interferenzeffekts sind die freien Parameter, der Nullreichweitenparameter D02 und das Produkt der reduzierten Partialbreiten der Resonanz gammaalphagammabeta, stark eingegrenzt worden. Im Rahmen dieses Reaktionsmodells ist eine bessere Interpolation der Daten in den astrophysikalisch relevanten Energiebereich möglich. Angewendet auf andere Reaktionen, die eine größere Bedeutung beim Fusionsprozeß in Sternen haben und die schwer zu vermessen sind, könnte dies zu einer Korrektur der Reaktionsraten führen, sofern dort auch eine Interferenz vorliegt. Es werden Kriterien für das Auftreten von Interferenz diskutiert. A broad, isolated resonance in a nuclear reaction can lead under certain circumstances to interference with the direct, only weakly energy dependent reaction contribution. This rarely occurring case may result in a strong modification of the differential cross section. For the calculation of such reactions the two most important models, that of the direct reactions (here in the frame of the Distorted Wave Born Approximation, DWBA) and that of the resonances (described here by R-matrix parametrization) have to be combined. Preceding measurements led to the assumption that in the reaction 6Li(d,alpha)4He such a case might be present. For the completion of the experimental data the reaction 6Li(d,alpha)4He was measured in a projectile energy range around 100 keV where an unusual energy dependence of the angular distribution was already observed by other groups. Past analyses were not nearly able to reproduce the angular distribution of this reaction within the low energy range (up to 2 MeV projectile energy). Apart from the measurements a precise, extensive analysis of the reaction 6Li(d,alpha)4He was performed in this work. At first the two reaction models mentioned above were outlined in a uniform way and a method was presented to link both models together. For the concrete calculation a program was developed which calculates an excitation curve for any reaction in a general form. It is based on an older code for DWBA analysis (DWUCK4) and completes it with a coherent admixture of resonance terms. The special difficulty of such calculations consists in the correct phase of the transition matrices which otherwise does not play a role in calculations performed according to only one reaction model. The application of the numerical calculations to the reaction 6Li(d,alpha)4He leads to a very good description of the angular distribution for a large energy region. The free parameters, the zero-range parameter D02 and the product of the reduced partial widths of the resonance gammaalphagammabeta, were strongly limited by taking into account the interference effect. In the framework of this reaction model a better interpolation of the data into the astrophysically relevant energy region is possible. Applied to other reactions which are of more importance for the fusion processes in stars and which can be measured only with great difficulty, this could lead to a correction of the reaction rates, provided an interference is present. Criteria for interference are discussed

Analysis of Sources and Sinks of Mercury in the Urban Water Cycle of Frankfurt am Main, Germany

Mercury (Hg) is still a focus of environmental research, since its levels in fish frequently exceed the Environmental Quality Standard (EQS) of 20 µg/kg for biota defined by the European Water Framework Directive (Directive 2008/105/EC). Current Hg levels in Abramis brama from German rivers are in the range of 73–346 µg/kg wet weight (2009) and exceed the EQS by a factor of 3.7–17.3. Therefore, it is important to identify the sources of Hg pollution in the aquatic environment and to develop effective strategies for reducing the input into associated river systems. The aim of the present study was to analyze Hg in the urban water cycle of the city of Frankfurt am Main, Germany. Samples were taken from the river Main crosscutting the city and its tributaries. In addition, precipitation, stormwater runoff, effluents of two municipal WWTPs, and stormwater management structures such as combined sewer overflows and stormwater retention basins have been analyzed. Loads of Hg have been determined based on the measured concentrations and a Hg mass balance for the aquatic system was created. A total of 160 water samples were analyzed by cold vapor atomic fluorescence spectroscopy (CVAFS) according to US EPA Method 1631. Results from the mass balance have shown that approximately 5 kg Hg/a enter and 15 kg Hg/a leave the study area of Frankfurt am Main via the river Main. The largest amount of Hg (24.58 kg/a) throughout the urban water cycle of Frankfurt am Main is transported via wastewater. However, municipal WWTPs in Frankfurt am Main have been identified as the largest Hg sink, since 99.7% (24.5 kg/a) of the Hg is shifted from the sewage water and stormwater during treatment into the sewage sludge. Thus, the increase of the Hg load in the river Main from 5 to 15 kg/a has to be attributed to other sources such as 3 industrial WWTPs, groundwater and non-treated stormwater runoff during heavy rain events

Recovery of Rare Earth Elements from NdFeB Magnets by Chlorination and Distillation

A sustainable separation concept for large-scale recycling of NdFeB magnets under atmospheric pressure was developed by utilizing a combination of two separation concepts known from the literature: (I) selective pre-separation by in situ chlorination and evaporation of ground oxidized NdFeB material and (II) subsequent distillation for high-purity recovery of all recyclable chlorinated material components, especially its Rare Earth Elements (REEs). Theoretically, simplified estimations of the time conversion curves at 1173 K, 1273 K, and 2000 K of a single particle resulted in the idea of realizing chlorination in some kind of combustion chamber, fluidized bed, or continuous combustion chamber. After chlorination, all non-volatile components, such as REE chlorides, are condensed out of the vapor phase in a single-stage phase separator. For subsequent fine separation by distillation (1292–1982 K for Rare Earth Chlorides and 418–867 K at 2500 kPa for boron and zirconium chloride recovery), simplified simulations were performed in a total-reflux column under ideal phase equilibrium conditions to show the estimated minimum separation effort. Using two composition examples from the literature, high-purity separation of the major Rare Earth Chlorides within a twelve-stage distillation column as a residual heavy boiling product has been demonstrated to be potentially technically feasible

Material dependence of

Calculations of the material dependence of 2H(d,p)3H cross section and neutron-to-proton branching ratio of d+d reactions have been performed including a concept of the 0+ threshold single particle resonance. The resonance has been assumed to explain the enhanced electron screening effect observed in the d+d reaction for different metallic targets. Here, we have included interference effects between the flat and resonance part of the cross section, which allowed us to enlighten observed suppression of the neutron channel in some metals such as Sr and Li. Since the position of the resonance depends on the screening energy that strongly depends on the local electron density. The resonance width, observed for the d+d reactions in the very hygroscopic metals (Sr and Li) and therefore probably contaminated by oxides, should be much larger than for other metals. Thus, the interference term of the cross section depending on the total resonance width provides the material dependences

Material dependence of 2H(d,p)3H cross section at the very low energies

Calculations of the material dependence of 2H(d,p)3H cross section and neutron-to-proton branching ratio of d+d reactions have been performed including a concept of the 0+ threshold single particle resonance. The resonance has been assumed to explain the enhanced electron screening effect observed in the d+d reaction for different metallic targets. Here, we have included interference effects between the flat and resonance part of the cross section, which allowed us to enlighten observed suppression of the neutron channel in some metals such as Sr and Li. Since the position of the resonance depends on the screening energy that strongly depends on the local electron density. The resonance width, observed for the d+d reactions in the very hygroscopic metals (Sr and Li) and therefore probably contaminated by oxides, should be much larger than for other metals. Thus, the interference term of the cross section depending on the total resonance width provides the material dependences

Charged-particle channels in the bêta-decay of 11Li

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