Near-edge x-ray-absorption fine structure in uranium compounds

For a number of metallic and nonmetallic U systems as well as a few Th compounds, the near-edge x-ray-absorption fine-structure spectra, taken by transmission and total-electron-yield techniques, are reported at the L$_3$, M$_3$, M$_4$,5, N$_4$,5, and O$_4$,5, thresholds. At L$_3$ and M$_3$, similar spectra with analogous information are observed. While in the metallic U systems, the white lines at L$_3$ and M$_3$ show only minor variations in position and relative peak height, a shift of ≃4 eV is observed between UCl$_3$ and UF$_4$, representing mainly the difference in Coulomb interaction between a 2p3/2 core hole and the 5f configurations. The spectra at the M$_4$,5 and N$_4$,5 thresholds are dominated by intense absorption peaks due to 3d-5f and 4d-5f transitions probing directly the unoccupied 5f states. No multiplet structure due to 3d-5f or 4d-5f exchange interaction is resolved, but the linewidths of the M4,5 peaks in the metallic U systems are found to decrease by ≃20% with increasing U-U distance, reflecting a narrowing of the unoccupied 5f bands. The spectra at the O4,5 thresholds, on the other hand, show well-resolved structures, which are atomiclike for ThF4 and UF4 and may be described by spin-orbit and exchange splitting of the 5d$^9$5f$^1$ and 5d$^9$5f$^3$ final states, respectively. In metallic U systems, the O4,5 structures are broadened and partly lost, presumably due to the more itinerant nature of the 5f states. Additional relatively weak peaks are observed in the M$_4$,5 and O$_4$,5 spectra of Th metal, ThO$_2$, UO$_2$, and UF$_4$ at energies from ≃15 to 38 eV above threshold, which are assigned to multiple-scattering resonances

X-RAY ABSORPTION ON URANIUM SYSTEMS AT VARIOUS THRESHOLDS

We have studied the near edge X-ray absorption fine structure of various metallic and non-metallic U compounds at the L3, M3, M4,5, N4,5, and O4,5 thresholds using transmission and total-electron-yield techniques. At the L3 thresholds, a chemical shift of ≈4 eV between trivalent and tetravalent U compounds is observed, which drops to ≈2eV between the latter and hexavalent U systems. This indicates extended 5f character and a 5f count close to two in the high oxidation states. The M4,5 thresholds are characterised by intense absorption peaks due to 3d-5f transitions which show no multiplet structure from 3d-5f exchange interaction. However, the linewidths of the M4,5 peaks decrease by ≈20% with increasing U-U distance in metallic systems, indicating a narrowing of the 5f band. The soft X-ray absorption spectra at the N4,5 thresholds behave very similarly to the M4,5 edges, except for a vanishing intensity of transitions into the continuum. Rich structures from 5d-5f exchange interaction are observed at the O4,5 edges of non-metallic U compounds, becoming broadened and partly vanishing in metallic systems, presumably due to the more itinerant nature of the 5f states

4f Occupation and hybridization from M-shell excitations in Rare-Earth materials

M-shell excitations in Rare-Earth (RE) materials were studied using synchrotron radiation and total electron yield detection in UHV. In mixed-valent compounds of the heavy RE's (Sm, Eu, Tm), the M<SUB>4,5</SUB> spectra are identified as superpositions of quasi-atomic 3d<SUP>9</SUP>4f<SUP>n+1</SUP> multiplet structures, providing quantitative information on the mean valence ν̅(4f occupation) of the RE ions, even in highly dilute systems. The method employed in deriving quantitative values for ν̅ is described in some detail. Effects of 4f/valence-band hybridization on the M<SUB>4,5</SUB> spectra are investigated for Ce systems: the 3d<SUP>9</SUP>4f<SUP>2</SUP> multiplet structure seen in γ-like Ce compounds is found to collapse in α-like systems, where satellites at about 5 eV higher energies are additionally observed. The method is also applied to dilute Ce systems, such as Ce in a Pd matrix, which is found to be α-like. In addition, M<SUB>3</SUB>-edge spectra are presented for a series of Ce compounds, and their relation to L<SUB>3</SUB>-edge spectra is discussed

НЕОДНОРОДНОСТЬ ХИМИЧЕСКОГО СОСТАВА МЕЖЗВЕЗДНОЙ СРЕДЫ ПО ДАННЫМ HDE 226868 (Cyg X-1) И α Cam // Ученые записки КФУ. Физико-математические науки 2011 N2

Методом моделирования синтетического спектра с учетом не-ЛТР-эффектов определены химические составы атмосфер О-сверхгигантов HDE 226868 (оптический компонент Cyg X-1) и α Cam, имеющих близкие физические характеристики, но расположенных на расстоянии 2.5-2.7 кпк друг от друга. Среднее содержание элементов группы CNO, а также Al, S и Zn в HDE 226868 на 0.15-0.30 dex превосходит содержание этих элементов в α Cam. Установленное различие содержаний находится в качественном соответствии с распределением тяжелых элементов в диске Галактики, полученным в работе Лака и др. в результате исследования 50 галактических цефеид. Данный факт является подтверждением неоднородности распределения тяжелых элементов на масштабе порядка 2 кпк и соответствует представлениям о сохранении индивидуальных характеристик <<сверхоблаков>> в межзвездной среде на шкале времени более одного миллиарда лет

"Rostocker künstliches Herz"--gegenwärtiger Stand und Ausblick.

The authors report on their experiences gained by animal experiments (calf) and their attempts (human corpses) concerning adaptation of the apparatus to the human thorax. At the present time they do not see a chance for its routine clinical use. The main reason why is the impossibility to install the extrathoracic driving system into the thoracic cage and last not least the wear of the material used for the heart chambers

Erfahrungen mit dem Rostocker künstlichen Herz.

A totally artificial heart--the Rostock totally artificial heart (Rostock TAH) was implanted in calves. We can give the following deductions after 27 examinations: -- The Rostock TAH was tested successfully in endurance test about 7 months; it show no sign of wear. -- The surgical technique of the implantation was standardised and a successful experimentation is possible. -- The longest survival time was 15 days. The hemodynamic early results were very good in 3 other animals. -- Modifications of the Rostock TAH were taken up relating to the dimensions of the artificial ventriculi and by mounting a screw cap for avoiding an air embolism. -- Adaption tests in the corpse show that the present form of the artificial heart is not ideal for a possible application in man. -- The problem is still existing in developing a suitable drive system locates intrathoracically. The present drive and control system on a pneumatic base is qualified only for the animal experiment but not for a possible application in man