Elektronenbeugungsaufnahmen an Pb-Bi-Legierungen bei sehr tiefen Temperaturen

By means of electron diffraction the structure of Pb-Bi-films condensed onto a substrate at very low temperatures is investigated. Results are discussed with respect to the resistance measurements ofHasse andSeiberth. A sharp change in resistance normally corresponds to a change in diffraction pattern. Several new phases are observed.     

Zur Anwendung von Austauschpotentialen bei SCF-Rechnungen an Atomen

The statistical exchange potential does not satisfactorily allow for self-exchange in localized electron systems. A simple correction is proposed which is capable of accounting for this leading to overall Hartree-Fock-energies with an accuracy of a few tenths of a per cent. Furthermore it is shown that even for a three-electron system the statistical approximation gives a good core valence exchange energy correction, if the correction ofGombás is used. This is true not only in the case where the valence orbital is explicitly orthogonalized on the core but also when the occupation exclusion operator formalism is used.     

Optische Untersuchungen an CdS-dotierten AgBr-Kristallen bei tiefen Temperaturen

The paper reports on the results of studying the absorption and fluorescence of AgBr crystals doped with CdS. The results are discussed by means of a one-dimensional model of configuration curves.     

Elastische Elektronenstreuung an Titan bei 33 bis 58 MeV

Cross sections for elastic electron scattering were measured for titanium relative to carbon and beryllium at the Darmstadt electron linear accelerator. The energy and angle were varied from 33 to 58 MeV and from 33° to 165°. Phase shift calculations of the scattering cross section show that the rms-radiusR _m determined from the measurements is almost independent of specific assumptions about the charge distribution. For the natural isotopic mixture of titanium the measurements yieldR _m=(3.60±0.04) fm. This result agrees well with measurements of the (2p-1s)-transition energy in the muon-titanium-atom.     

Leitfähigkeitsuntersuchungen an Anthrazen-Kristallen bei Anregung mit Protonenimpulsen

Transient currents in anthracene crystals were measured under bombardment by pulses of 700 keV protons. Electron-hole-pairs are generated by an intrinsic process, the yield varying linearly with the intensity of the bombarding beam. The average energy for pair production is found to be 10⁴ eV. The temperature dependence of the carrier yield can be characterized by an activation energy of 0.07 eV. The results are discussed with regard to different models of the generation process. Drift mobilities of 0.46 cm²/Vsec for electrons and 0.88 cm²/Vsec for holes are determined in good agreement with other authors. A reduction of the current pulse height with the number of bombarding pulses is observed and explained in analogy to the known deterioration of luminescence under ion bombardment. Thereby the higher deterioration constant for the conductivity can be understood.     

Messung der Fehlordnungsenergie an abschreckend kondensierten Metallschichten bei tiefer Temperatur

Metal films are produced with a high degree of disorder by quenching condensation. The stored energy release and the resistivity decrease are measured during annealing of Au-, Pb-, and Sn-films from 20 to 60° K and during crystallization of amorphous Sn-films with a 10 atomic-% Cu-content. The results are compared with earlier measurements on Bi-, Ga-, and Cu-films produced by quenching condensation. The energy released during the crystallization of the amorphous films (Bi, Ga, Sn+10 at.-% Cu) amounts to half of the heat of melting. This is in good agreement with calculations ofOriani andLumsden for the disorder part of the entropy of melting. The recovery of the crystalline Cu-, Au-, Pb-, and Sn-films is described by a crystallization of highly disordered atoms to crystallites formed during condensation. About 30% of all atoms of these films are in this highly disordered state.     

Der Beugungseffekt bei der elastischen Streuung von Ionenstrahlen an Atomen

For the elastic scattering of ion beams at atoms the diffraction of the matter wave at the atom can be observed in the region of small scattering angles and high energies. The diffraction causes undulations in the differential scattering cross section. In this paper a general solution of the diffraction effect is given. The solution holds for the Yukawa type screened Coulomb potential which is well suited for the small angle scattering of-ions at atoms and which contains two parameters. The computations have been made using the partial wave method and the Jeffreys-Born-approximation for the scattering phase shifts. The solution is presented in a form in which the amplitudes and characteristic constants of the first four undulation maxima and minima are given in dependence of a product which contains one of the potential parameters. The characteristic constants are correlated in a characteristic equation with the second potential parameter and the positions of the diffraction extrema. The conditions for the appearance of the diffraction effect are discussed.     

Elastische Streuung von Deuteronen an10B bei niedrigen Energien

The excitation curve for the elastic scattering of deuterons from¹⁰B in the energy range from 1.0 to 2.0 MeV has been measured atθ _L =135°. Strong indications for compound nucleus resonances in¹²C at bombarding energies of approximately 1.0 and 1.9 MeV were observed. Angular distributions from 80 to 175° were determined in 200 keV steps from 1.0 to 2.0 MeV. Optical model analysis were made both for volume absorption and surface absorption potentials. Reasonable fits were obtained at energies up to 1.6 MeV with one set of parameters in both cases, whilst for the higher energies strong deviations were found with the same parameters.     

Messung der Fehlordnungsenergie an abschreckend kondensiertem Kupfer bei tiefer Temperatur

Copper films are produced by quenching condensation on a substrate at low temperature. A stored energy release of 216 cal/mole and a resistivity decrease of 1.8μΩcm are observed during annealing from 20 to 60 °K. In this temperature range the recovery of the films is described by a crystallisation of highly disordered material between small crystallites, which are produced during condensation. About 14 atomic-% of the whole film substance take part in this process. The stored energy-resistivity ratioE/Δ? found is 1.9 cal/g/gm/gWcm in the whole temperature range from 20 to 60 °K. This value is in good agreement with the stored energy measurements on neutron-bombarded copper.     

Bestimmung der Empfindlichkeit bei Tc-99-NMR-Messungen an einem 250-MHz-Spektrometer

By means of different concentrations the signal-to-noise ratios of Tc-99-NMR spectra were determined applying well measurable Tc-samples [tetrabutylammoniwn pertechnetate, TBA (TcO₄)J and a 250 MHz-spectrometer. The signal-to-noise ratios of the spectra were determined by using the integrated routines of the firm's software and accumulating different number of scans. By fittings of data of the signal-to-noise ratio dependence and by extrapolation the minimum Tc-concentralion could be empirically found out. Applying a duration of measurements of 12 hours about 10^?7 molar concentrations can be determined.     

Erfahrungen bei der Anwendung der 85Kr-Methode zur Temperaturmessung an Motorkolben

Am Beispiel von Untersuchungen am Kolben eines Dieselmotors wird ein Verfahren der Bestimmung maximaler Temperaturen beschrieben, welche in dem Element auftreten, das mit Hilfe des Isotops ⁸⁵Kr markiert ist. Die Brauchbarkeit dieses Verfahrens für die Motoruntersuchungen wurde nachgewiesen, sowie die Möglichkeiten seiner Anwendiung bei der Korrelation der Verteilung maximaler Temperaturen im Kolben mit dem Motorverschleiß und besonders mit dem Spiel-zwischen dem Kolben und dem Zylinder und den Einstellungen der Einspritzapparatur.     

Elastische und unelastische Streuung von Deuteronen an Aluminium bei 11,8 MeV

Using the 11.8 MeV deuteron beam of a cyclotron, a study has been made of the angular dependence of the deuteron spectrum from interactions on Al²⁷. Separation of the deuterons from other products of the deuteron reactions was accomplished by recordingdE/dx, measured by a three fold proportional counter, andE, measured by a CsI-counter, on an oscilloscope screen. The experimental inelastic angular distributions have the shape of a direct interaction process. The elastic angular distribution shows pronounced diffraction maxima.     

Statistische Schwankungen bei Strommessungen an Detektoren für ionisierende Strahlung

Unter vereinfachenden Voraussetzungen für die Energieübertragung werden Beziehungen für den relativen mittleren quadratischen Schwankungsfehler bei Strommessungen an Ionisationskammern und anderen proportional verstärkenden Detektoren für β- und Quantenstrahhmg abgeleitet und experimentell überprüft. Analog zum Schwankungsfehler bei Impulsdichtemessungen ist das Quadrat des relativen Schwankungsfehlers für Strommessungen umgekehrt proportional dem Ionisations- bzw. Detektorstrom und der Integrationszeitkonstanten. Ferner hängt der Schwankungsfehler von den Kammerabmessungen, von der Teilchen- oder Quantenenergie und vom Fülldruck ab. Aus dem Zusammenhang zwischen Schmankungsfehler, Ionisationsstrom und Zeitkonstante ergibt sich eine natürliche Grenze für die mit einer Ionisationskammer bei vorgegebenem Sclwankungsfehler und vorgegebener Zeitkonstante kleinste meβbare Dosisleistung bzw. Strahlungsintensität.     

Modellunabhängige Beschreibung kugelsymmetrischer Ladungsverteilungen bei der Streuung schneller Elektronen an Atomkernen

A method is given to evaluate in a model independent way cross sections for scattering of fast electrons by nuclei. For this purpose the charge distribution in the nucleus will not, as usual, be described by means of the charge densityρ(r), but by the first moment functionT(Q): $$T(Q) = \int\limits_0^Q {r(Q')dQ'} .$$ The integration has to be performed over this part of the charge distribution in which the charge will increase from the value 0 to the valueQ. ThusT(Q) gives the first moment of this part. It will be shown that this function can be fixed by elastic scattering within certain limits.