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51.
Th. Rubehn W. F. J. Müller R. Bassini M. Begemann-Blaich Th. Blaich A. Ferrero C. Groß G. Imme I. Iori G. J. Kunde W. D. Kunze V. Lindenstruth U. Lynen T. Möhlenkamp L. G. Moretto B. Ocker J. Pochodzalla G. Raciti S. Reito H. Sann A. Schüttauf W. Seidel V. Serfling W. Trautmann A. Trzcinski G. Verde A. Wörner E. Zude B. Zwieglinski 《Zeitschrift für Physik A Hadrons and Nuclei》1995,353(2):197-204
Electromagnetic fission of238U projectiles at E/A =600 and 1000 MeV was studied with the ALADIN spectrometer at the heavy-ion synchrotron SIS. Seven different targets (Be, C, Al, Cu, In, Au and U) were used. By considering only those fission events where the two charges added up to 92, most of the nuclear interactions were excluded. The nuclear contributions to the measured fission cross sections were determined by extrapolating from beryllium to the heavier targets with the concept of factorization. The obtained cross sections for electromagnetic fission are well reproduced by extended Weizsäcker-Williams calculations which include E1 and E2 excitations. The asymmetry of the fission fragments' charge distribution gives evidence for the excitation of the double giant-dipole resonance in uranium.Communicated by V. Metag 相似文献
52.
A. Weidinger J. Erxmeyer H. Glückler Ch. Niedermayer O. Laforsch J. Groß M. Mehring 《Hyperfine Interactions》1994,86(1):609-614
Hydrogenated YBa2Cu3O7 with [H]/cell=2.0 was studied by X-ray diffraction, SR and1H-NMR. For the first time, the hydride phase (16% larger c-axis) known from thin film experiments was seen in a bulk sample. A comparison of the SR and NMR results shows that the 15 mT site (2 MHz in SR) is the stable position for the proton and muon. The three other muon sites (4 MHz line and two exponentially decaying components) are metastable. 相似文献
53.
Two new ditopic receptors for α,ω-alkanediyldiammonium cations based on a tetraazamacrocyclic (cyclidene) nickel(II) complex bearing two crown-ether residues were synthesized. The studies of the host-guest interaction between the receptors and a series of α,ω-diammonium salts by NMR titration in acetonitrile-d3 showed that 1:1 complexes are formed with Kassoc∼103-105 M−1. Receptor 1 with benzo-15-crown-5 arms showed substantial selectivity in binding of trimethylene- and tetramethylenediammonium dications, and 1-2 orders of magnitude weaker binding of shorter (C2) or longer (C5 and C6) diammonium cations. Receptor 2 with benzo-18-crown-6 arms showed higher affinity to all studied diammonium cations, but the recognition of the length of α,ω-diammonium cations was less pronounced. 相似文献
54.
U. Groß P. Dietrich G. Engler D. Prescher J. Schulze K. Lunkwitz A. Ferse 《Journal of fluorine chemistry》1982,20(1):33-52
The present work studies the changes in polymer structure and the mechanism of the decomposition of polytetrafluoroethylene resin (PTFE) exposed to high energy radiation (electron beam). Spectroscopic and kinetic observations are used to interpret the degradation process. For the first time the decomposition of PTFE has been carried out on a preparative scale and new results obtained by analysing the degradation products. The radiation-induced degradation of PTFE is accompanied by thermal degradation under certain irradiation conditions. This is due to an increase in temperature of the polymer caused by retardation of highly accelerated electrons (heat accumulation effect).The kinetics are discussed in terms of the reactions and recombination of radicals produced by high-energy radiation both in the polymer melt and the polymer surface. These are related to the overall rate of decomposition.The primary radicals formed by decomposition of PTFE in an inert atmosphere (N2, Ar) react to produce perfluorinated alkanes and alkenes. In the presence of reactive gases the decomposition fragments originated will react rapidly; e.g. if oxygen is present in the reactive area the radicals form perflourinated peroxyl and oxyl radicals which finally stabilize themselves by CC-scission to perfluorocarbon acid fluorides and carbonyldifluorides. 相似文献
55.
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56.
Electron impact mass spectra of 65 pyrrolidine-N-oxyl derivatives have been assigned on a ‘peak-to-subgraph’ basis. On average, 50% of the total ion current is represented by structurally significant fragments associated with the nitroxide group. Secondary fragmentation is, as a rule, of a minor importance (30%), and fragments due to functional groups other than NO· seldom contribute more than 10% of the total ion current An enhanced specificity of fragmentation is observed when one or more of the 2,2, 5,5-methyl groups is replaced by a longer aliphatic chain or an aromatic group. 相似文献
57.
Zusammenfassung Ein Verfahren zur Bestimmung von Tellurspuren mit Hilfe der Simultankomparationsmethode wurde ausgearbeitet, das auf der Bichromat-Ferriin-Reaktion beruht. Ferriin wird von Tellur(IV) reduziert; dieser Prozeß wird von Bichromat induziert. Bei diesem Verfahren werden die Tellurspuren durch Natriumhypophosphitreduktion mit Arsen oder Selen als Träger abgeschieden, der Metallniederschlag wird mit Salpetersäure zu Tellur(IV) oxydiert, die zu untersuchenden Proben und die Standardreihe gleichzeitig gestartet und verglichen. Mit dieser Methode kann Tellur auch in Mikrogrammengen mit einem Fehler von weniger als ±10% bestimmt werden. Störend wirken nur die Pt-Metalle und Au(III).
Determination of tellurium in microgram amounts with the aid of the simultaneous comparation method
Summary A procedure has been worked out for the determination of traces of tellurium with the aid of the simultaneous comparation method, and based on the bichromate-ferriin reaction. Ferriin is reduced by tellurium(IV); this process is induced by bichromate. In this procedure the traces of tellurium are precipitated by means of sodium hypophosphite-reduction with arsenic or selenium as carriers. The metal precipitate is oxidized to tellurium(IV) with nitric acid; the samples under investigation and the standard series are started at the same time and compared. By means of this method it is possible to determine tellurium, even in microgram amounts, with an error of less than ± 10%. Only the platinum metals and gold(III) interfere.相似文献
58.
Pavel Arsenyan Olga Pudova Juris Popelis Edmunds Lukevics 《Tetrahedron letters》2004,45(15):3109-3111
A series of thiophene-based homologues with a silicon core surrounded by mono-, bi-, terthiophene, and their derivatives with alkylsilyl linkages has been prepared using hydrosilylation and Stille coupling methods. 相似文献
59.
Reductive amination of 4′-formyl[benzo-15-crown-5] with sodium cyanoborohydride in the NH4Ac/MeOH medium followed by acid addition and extraction with CHCl3 unexpectedly lead to the isolation of the salt (B15C5-CH2-NH3)+-(H3BCNBH2CN)− with an unusual dicyanodiborohydride anion. The self-complementary 4′-ammoniomethyl[benzo-15-crown-5] cation was found to exist as a supramolecular dimer in the solid state, acetonitrile solution, and gas phase as revealed by X-ray crystallography, NMR and mass spectrometry, respectively. 相似文献
60.
The 1O2-induced degradation of spiro[1,8a]dihydroindolizines - a new photochromic system - may involve dioxetanes as intermediates giving fulvenylesters . 相似文献