Verdampfung von Uranspaltprodukten in Wasserstoff, Stickstoff und Sauerstoff

Zusammenfassung Die Verdampfung der Spaltprodukte Germanium, Arsen, Molybdän, Ruthenium, Cadmium, Zinn, Antimon und Tellur aus bestrahltem U₃O₈ im Wasserstoff-, Stickstoff- und Sauerstoffstrom wurde zwischen 900 und 1500° C untersucht. Bei 1500° C verdampfen die meisten dieser Elemente innerhalb 1 Std mit hoher Ausbeute.

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Summary The volatization of the fission products germanium, arsenic, molybdenum, ruthenium, cadmium, tin, antimony and tellurium from neutron-irradiated uranium oxide in flowing hydrogen, nitrogen or oxygen of atmospheric pressure was investigated between 900 and 1500° C. At 1500° C, most of these elements are volatized with high yield within one hour.

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Herrn Prof. Dr. F. Strassmann danken wir herzlich für die Förderung dieser Arbeit, Herrn I. Bonner für seine Mitarbeit, den Betriebsstäben der Forschungsreaktoren Frankfurt und München, insbesondere Herrn Dr. G. Wolf (Frankfurt), für Bestrahlungen und dem Bundesministerium für wissenschaftliche Forschung für finanzielle Beihilfen.

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Herrn Prof. Dr. W. Geilmann zum 75. Geburtstag gewidmet.

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Aus einer Dissertation, Mainz 1963.     

Coulometrisches Verfahren zur Bestimmung von Gesamt-, Carbonat- und Nichtcarbonat-Kohlenstoff in magmatischen, metamorphen und sediment?ren Gesteinen

Zusammenfassung Für die Bestimmung von Gesamt-, Carbonat- und Nichtcarbonat-Kohlenstoff in magmatischen, metamorphen und sedimentären Gesteinen (auch bei höheren Anteilen an organischem C) ist ein Verfahren nach dem Prinzip der coulometrischen Titration geeignet. Der Gesamt-Kohlenstoff wird ermittelt durch Erhitzung der auf <0,125 mm zerkleinerten Probe bei etwa 1250°C im Sauerstoffstrom ohne irgendwelche Zusätze. Zur Bestimmung von Nichtcarbonat-Kohlenstoff wird eine bestimmte Menge Gesteinspulver mit Salzsäure versetzt und auf einem Aluminiumblock HCl abgeraucht. Der Carbonat-Kohlenstoff entweicht als CO₂. Zurück bleibt der Nichtcarbonat-Kohlenstoff, welcher wie der Gesamt-Kohlenstoff coulometrisch bestimmt wird. Der Carbonat-Kohlenstoff bzw. die äquivalente Menge CO₂ ergibt sich dann aus der Differenz von Gesamt- zu Nichtcarbonat-Kohlenstoff. Das Verfahren ist anwendbar auf Kohlenstoffgehalte in Gesteinen von etwa 10 ppm bis 20 Gew.-% bei mittleren Standardabweichungen von etwa 0,0002–0,05% C (Richtwerte). Die Analysendauer für eine Probe beträgt etwa 3–5 min.

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Coulometric method for the determination of total, carbonate, and non-carbonate carbon in igneous, metamorphic, and sedimentary rocks

For the measurement of total carbon the sample, ground finer than 0.125 mm and without the addition of any reagents, is ignited in a current of oxygen at about 1250°C. Non-carbonate carbon can be analysed after another portion of the sample is treated with conc, hydrochloric acid and evaporated on a hot plate; the carbonates are decomposed and the carbonate carbon is removed as carbon dioxide. The residue is non-carbonate carbon which is also determined by the coulometric method. The difference between total carbon and non-carbonate carbon corresponds to carbonate carbon or its equivalent as carbon dioxide. The method is applicable to carbon contents in rocks from 10 ppm to 20 wt.-%. The standard deviation is approximately 0.0002 to 0.05% C. Each carbon analysis takes about 3 to 5 min.

     

Untersuchung von Heterostrukturen der Mischkristallreihe GaAs/AlAs mit dem Rasterelektronenmikroskop

The investigation of heterojunctions of the mixed crystals series GaAs/AlAs by means of different scanning electron microscopic techniques yields that the utilization of the cathodoluminescence is highly suited for detecting small energy gap differences. Compared with the secondary electron contrast and the imaging by backscattered electrons, resp., it is clearly advantagoeus with respect to an identification specific tot he material. The course of the intensity profile with increasing primary electron energy permits to indicate a qualitative correlation with the value of the band gap. This is demonstrated with two heterojunctions with strongly different dopings. The Y-modulation technique is successful in displaying an orientation-dependent portion of the image contrast of homo- and heterojunctions of multiple structures.     

Steplike transmission of light through a metal-dielectric multilayer structure due to an intensity-dependent sign of the effective dielectric constant

We numerically study light propagation through a specially designed nonlinear nanoscale metal-dielectric multilayer structure with a linear effective dielectric constant just below zero. The calculated dependence of the output intensity on the input intensity shows a steplike behavior. It rests upon an intensity-dependent change of the effective dielectric constant from negative (low-transmission state) to positive (high-transmission state) values, corresponding to a transition of the optical properties from metalliclike to dielectriclike. The study of the transient behavior of the structure demonstrates a switching time of around 1 ps.     

Aeolian transport of sand

The airborne transport of particles on a granular surface by the saltation mechanism is studied through numerical simulation of particles dragged by turbulent air flow. We calculate the saturated flux q_s and show that its dependence on the wind strength u_* is consistent with several empirical relations obtained from experimental measurements. We propose and explain a new relation for fluxes close to the threshold velocity u_t, namely, q_s=a(u_*-u_t)^α with α≈2. We also obtain the distortion of the velocity profile of the wind due to the drag of the particles and find a novel dynamical scaling relation. We also obtain a new expression for the dependence of the height of the saltation layer as function of the strength of the wind.     

Synthetic and Biological Studies on New Urea and Triazole Containing Cystobactamid Derivatives

Cystobactamids belong to the group of arene-based oligoamides that effectively inhibit bacterial type IIa topoisomerases. Cystobactamid 861-2 is the most active member of these antibiotics. Most amide bonds present in the cystobactamids link benzoic acids with anilines and it was found that some of these amide bonds undergo chemical and enzymatic hydrolysis, especially the one linking ring C with ring D. This work reports on the chemical synthesis and biological evaluation of thirteen new cystobactamids that still contain the methoxyaspartate hinge. However, we exchanged selected amide bonds either by the urea or the triazole groups and modified ring A in the latter case. While hydrolytic stability could be improved with these structural substitutes, the high antibacterial potency of cystobactamid 861-2 could only be preserved in selected cases. This includes derivatives, in which the urea group is positioned between rings A and B and where the triazole is found between rings C and D.     

Applied Infrared Photoluminescence in Lead Salt Crystals

Results on applied infrared photoluminescence investigations of lead salt chalcogenides are presented. Interpretations of spectra and wafer maps are given. The results obtained may be applied to the investigation of material properties important for laser and detector fabrication.     

Infrared photoluminescence - a tool for HgCdTe crystal research

Material and structural parameters of narrow-gap p-type HgCdTe are investigated by infrared photoluminescence. The method is used for analyzing the energy gap, the carrier lifetime, and heterointerfaces and to monitor defects like inclusions. The spatial distribution of the quantities mentioned has been investigated by applying the mapping technique known for III – V semiconductors. The methods is a powerful tool for both crystal growth and device manufacturing.