Radiation-damage studies with hyperfine-interaction methods

The paper discusses contributions of hyperfine-interaction methods to the investigation of radiation damage, particularly to problems connected with the interaction of impurities with structural point defects. The subject is treated by means of some selected examples of recent research with Mössbauer spectroscopy, perturbed angular correlation, perturbed angular distribution, and nuclear orientation.     

Comparative performance study of ICP mass spectrometers by means of U "isotopic measurements"

The performance of four commercially available ICPMS instruments of three different types was compared by means of uranium "isotopic measurements". Examined were two quadrupole sector (different generation, different manufacturer), one single detector double focusing magnetic sector and one multiple collector double focusing magnetic sector instruments. The same samples of the IRMM-072 series were used under routine conditions to measure the 233U/235U and the 233U/238U ratios which, in these samples, vary over almost three orders of magnitude from approximately 1 to approximately 2 x 10(-3). Within expanded (k = 2) uncertainties, good agreement was observed between the certified values and the data internally corrected for mass-discrimination effects. The magnitude of the evaluated uncertainties was different for each type of instrument. With the multiple collector instrument, expanded uncertainties varied from +/- 0.04% to +/- 0.24% for the 233U/235U ratio, and from +/- 0.08% to +/- 0.27% for the 233U/238U ratio. They were approximately 1 to 5 times larger with the single detector magnetic sector instrument, and approximately 10 to 25 times larger with both quadrupole sector instruments. With the multiple collector instrument, repeatability of the measurements seemed to be limited by the difficulty of correcting properly for instrumental background, whereas with the single detector magnetic sector instrument the counting statistics was the only limitation (on smallest ratios). Apparent mass-discrimination was clearly found to be larger but more reproducible (and hence easier to correct for) in the case of magnetic sector instruments than for both quadrupole sector instruments. If space charge effects were the main source of mass-discrimination for all instruments, these results are in contradiction with the hypothesis of the size of mass-discrimination decreasing with the acceleration voltage. With the single detector magnetic sector instrument in particular (when operated by changing the ion energy only), our results pointed at more than only one major source of mass-discrimination, with variable size depending on the ratios measured.     

Higher aliphatic aldehyde polymers,VII: poly(n-decaldehyde)

n-Decaldehyde (DA) was polymerized to crystalline poly(n-decaldehyde) (PDA) of reasonable molecular weight in methylcyclohexane (MCH) solvent with lithiumtert-butoxide (LTB) as the initiator under carefully controlled temperature conditions. The polyacetal structure ofPDA was established by IR and PMR spectroscopy as well as by the characteristic degradation of the polymer in the presence of 2,4-dinitrophenylhydrazine.PDA had the dual melting behavior typical of aliphatic polyaldehydes with four or more side chain carbon atoms. The DSC scans of crystallinePDA in the first, or side chain, transition region showed as many as three endothermic peaks between 45 and 65°C. The X-ray diffraction pattern of crystalline PDA was similar to that which had been observed for other polyaldehydes but with a larger unit cell.PDA was extruded at 53°C in a capillary rheometer and gave a filament whose X-ray diffraction pattern indicated medium orientation effects.

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Zusammenfassung Die Polymerization vonn-Decaldehyd zu einem krystallinen Polymeren von mittlerem Molekulargewicht wurde mit Lithium-tert-butylat in Methylcyclohexan unter genauer Temperaturkontrolle durchgeführt. Poly(n-decaldehyd) (PDA) wurde mittels spektroskopischen Methoden (IR und PMR) charakterisiert, und durch Abbau in der Gegenwart von 2,4-Dinitrophenylhydrazin wurde die Polyacetalstructur des Polymeren bestätigt.PDA hat einen Doppelschmelzpunkt ähnlich anderer aliphatischer Polyaldehyde mit mehr als vier Kohlenstoffatome in der Seitenkette.DSC-Untersuchungen zeigten in der ersten Übergangsregion, der der Seitenkettenkristallisation, daß drei endotherme Spitzen zwischen 45 und 65° beobachtet werden konnten. DasDebye-Scherrer-Diagramm des krystallinenPDA war ähnlich dem anderer Polyaldehyde, aber mit größerer Einheitszelle.PDA wurde bei einer Temperatur von 53°C in einem Rheometer extrudiert und gab Fasern, deren Röntgenstreuung mittlere Orientierung zeigte.

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Part Vl:J. Starr andO. Vogl, J. Polymer Sci., Polym. Chem. Ed. (in press.).     

Die Konstitution des Laburnins

Zusammenfassung Durch Überführung des Laburnins in (+)-Pseudoheliotridan, die auf zweifache Weise gelang, wurde bewiesen, daß diesem Nebenalkaloid des Cytisins die Konstitution eines 1-Oxymethyl-pyrrolizidins (I) zukommt. Da die Konfiguration des Pseudoheliotridans bekannt ist, ist damit auch die des Laburnins gegeben.Herrn Prof. Dr.L. Ebert zum 60. Geburtstag in Verehrung gewidmet.     

Darstellung und Charakterisierung von Kopf-Kopf-Polymeren. 1. Mitt. Kopf-Kopf-Poly(methylcinnamat)

Ohne Zusammenfassung     

Diffusion in ordered Fe-Si alloys

The measurement of the diffusional Mössbauer line broadening in single crystalline samples at high temperatures provides microscopic information about atomic jumps. We can separate jumps of iron atoms between the various sublattices of Fe-Si intermetallic alloys (D0₃ structure) and measure their frequencies. The diffusion of iron in Fe-Si samples with Fe concentrations between 75 and 82 at% shows a drastic composition dependence: the jump frequency and the proportion between jumps on Fe sublattices and into antistructure (Si) sublattice positions change greatly. Close to Fe₃Si stoichiometry iron diffusion is extremely fast and jumps are performed exclusively between the three Fe sublattices. The change in the diffusion process when changing the alloy composition from stoichiometric Fe₃Si to the iron-rich side is discussed.     

H?here aliphatische Polyaldehyde. 3. Mitt. Kristallstruktur, Kristallinit?t und Umwandlungen in der Schmelze von isotaktischem Poly-n-heptaldehyd

Ohne Zusammenfassung     

The nature of point defects produced by cold working of metals studied with Mössbauer spectroscopy and perturbed γ-γ angular correlation

We report on the production of point defects by cold working of Al, Cu, Ag, Pt and Au doped with the Mössbauer impurity⁵⁷Co. In our experiments no mobile interstitials were observed, while regarding vacancies the defect patterns are similar to those found after quenching and irradiation. The same observations for these hosts were made in recent experiments in which the PAC probe¹¹¹In was used.     

Diffusion studies

Mössbauer spectroscopy represents a unique method to determine the frequency and the vector of diffusion jumps in solids. The elementary diffusion event can thus be studied in a microscopic way. In order to get maximum information experiments have to be performed on single crystals.Mössbauer studies of long-range diffusion, on the one hand, have proved the reliability of the method but also demonstrated the considerable technical effort which is necessary. Investigations of localized diffusion (diffusion in a cage), on the other hand, have been successful in various fields of physics and biophysics.