Volume 21, Issue 12

Using a semi-empirical theory of interaction between neutrons in atomic nuclei, the average energy of a neutron, the equation of state, and the pressure-compressibility relation is computed for a neutron gas of very high density (n ≈ 10 15 gcm -3 ). The results are applied to the computation of the mass and the radius of a neutron star as a function of the central density. For the critical mass, above which a neutron star cannot exist, a value of 0.96 solar masses is found.

The plasma in thermodynamic equilibrium has been extensively discussed under the assumption that all particles can be classified as “bound” or “classically free”. Under this assumption simple models led to divergencies of the partition functions of bound and free particles as well as to discrepancies of the predicted level shift. On the basis of a quantum-mechanical treatment we develop an “adapted free-bound approximation” for the eigenstates and a classical approximation for the partition function of the free particles. It is a decisive feature of the analysis that it takes freebound interaction into account. The results produce values for the free-bound limit and the limit of the series continuum. They also remove the divergence difficulties.

Previous investigations derived the SAHA equation for a plasma in equilibrium applying the free-bound concept valid for an isolated electron-ion pair. In our investigation of the “adapted free-bound model” (I) we have shown that due to the free-bound interaction the demarcation between free and bound states is shifted by Δ χ =—e 2 /r 0 . We study the influence of this shift of the ionization limit on the effective ionization energy in SAHA’S equation. At the same time we account by interpolation for the contributions of the quasi-free highly correlated particles. The lowering of the free-bound limit causes an increase of the effective lowering of the ionization energy in SARA’S equation beyond the well-known e 2 /D-term resulting from the free-free interaction. This additional term itself is of the order O (e 2 /D) and therewith much stronger than the correction found from higher order correlations of the free particles. On the other hand it is much smaller than the lowering of the free-bound limit.

Weakly ionized plasmas bounded by insulated walls have been studied for the limiting cases of very low and very high pressure in numerous papers. These investigations base the particle kinetics either on the model of “collision dominated motion” or on the model of “inertia dominated motion”. Corresponding model regions are matched neglecting the transition region. We consider a weakly ionized plasma bounded by insulated walls. Its particle production is due to electron collisions and its particle destruction due to wall recombination. Describing the electrons as in quasiequilibrium and ion-neutral interaction by constant mean free time collisions it is possible to derive for arbitrary plasma pressure an integrodifferential equation valid throughout the plasma core, the transition region and the sheath. No matching of model regions is required. The well-known LANGMUIR and SCHOTTKY theories are shown to be asymptotic solutions of this general treatment.

The beam plasma exists in at least two states: The “quiescent” state with low pressures and the "turbulent" state with high pressures of the neutral gas (argon in most experiments). The quiescent state is described theoretically. It is shown that the system should transport growing waves with frequencies just below the upper hybrid frequency ωH 2 =ω p 2 +ω c 2 . These oscillations are found experimentally for ω p > k 1 ω c , where k 1 has a value of about 0.35 in the experiments described. Increasing the pressure and the plasma density as well raises the amplitude of the oscillations. Then at the critical pressure the turbulent state with high density is produced very abruptly. The essential feature of this second state is the high energy loss of the beam particles. The dependence of the losses on the parameters of the system is studied in detail. The maximum losses may attain 50% of the original beam energy. Some other properties of the system are described.

Microwave measurements were made of the electron density and the electron collision frequency in the plasma between the shock front and the discharge plasma of electromagnetically produced shock waves. These investigations were carried out in argon and hydrogen at p o =2 mm Hg initial pressure and velocities ranging from M=5 to M=20. At higher velocities the discharge plasma advances right into the shock front. A 4-mm-microwave transmission interferometer was used. A system of LECHER wires in the measuring arm of the interferometer provided a spatial resolution of approximately 1 to 2 mm and proved successful in measuring the electron density distribution between the shock front and the following discharge plasma. In the case of hydrogen the rise of the electron density in the shock front is caused by compression of the precursor electrons. In argon, on the other hand, most of the electrons are produced behind the shock front. A typical relaxation of the electron density towards equilibrium was measured. It was also possible to measure the electron collision frequency in argon as a function of time (and hence of the distance from the shock front).

Time behaviour, threshold currents and power output of the most intensive induced transitions are investigated in pulsed argon- and xenon-ionlasers in the visible and ultraviolet region. In the 7 mm diameter tube transitions of higher ionized atoms are favoured compared to smaller diameter tubes. Pressure dependence of threshold currents and curent dependence of induced peak power are measured. By observing discharge current, spontaneous sidelight and laser output at the same time, information is obtained about possible excitation mechanisms for various transitions.

Aus der Grenzwertformel F(λ) =λ·G -1 werden für die Ordnung n=3 die Vorzeichen und Zahlenwerte der Wechselwirkungsgrößen f 12 (λ), f 13 (λ) und / 23 (λ) nach Formeln allgemein berechnet. Dieses Modell wird zur Vorzeichen- und Bereichsabschätzung der Wechselwirkungskraftkonstanten von hinreichend stark frequenzgekoppelten Molekülen des Typs XYZ mit C s -Symmetrie verwandt. Für diesen Molekültyp XYZ mit C s -Symmetrie lassen sich für Valenzwinkel α mit 90° ≦ α < 180° vollständig analytische Vorzeichenregeln aufstellen, die keine zusätzlichen numerischen Auswertungen erfordern. Zur Veranschaulichung dieser Vorzeichenregeln und Bereichsabschätzungen dienen die Moleküle HOCl, DOCl und NOF als Zahlenbeispiele.

Es wird ein Tabellenwerk beschrieben, das bei der Analyse von Rotationsspektren asymmetrischer Kreisel von Nutzen ist. Es werden Formeln für Erwartungswerte angegeben, die sich aus den tabellierten Werten in einfacher Weise berechnen lassen. Die Anwendungsmöglichkeiten werden erläutert.

In dieser Arbeit wird eine Berechnung des Ammoniakmoleküls mit der Valenzstrukturmethode unter gleichzeitiger Berücksichtigung von Konfigurationswechselwirkung (VB-CI-Methode) und Hybridisierung der Einelektronenfunktionen der L-Schale des N-Atoms durchgeführt. Als Einelektronenfunktionen werden „SLATER-Orbitals“ verwendet. Die benutzten Abschirmkonstanten und die beiden Kernabstände werden durch eine grobe Variation optimalisiert. Mit einem Satz von 12 Funktionen für den Grundzustand des Moleküls, der durch eine symmetrische Singulettfunktion ( 1 A-Funktion) charakterisiert ist, wird eine Näherung der Potentialkurve für das Durchschwingen des N-Atoms durch die Ebene der Η-Atome berechnet. Die so erhaltene Höhe des Potentialwalls ist etwa um einen Faktor 3 zu groß, so daß sich eine Berechnung der Inversionsaufspaltung nicht durchführen läßt. Für die optimale Zustandsfunktion ergibt sich ein Energiewert von —56,0565 DRY, was einer Bindungsenergie von 62,7% des experimentellen Wertes entspricht. Die Kernabstände NH und HH ergeben sich zu 2,0415 a. E. bzw. 3,085 a. E., d. h. um 6,5% bzw 0,3% größer als die experimentellen Werte. Außerdem wird das Dipolmoment des Moleküls in Abhängigkeit von der Pyramidenhöhe und für die optimalen Abschirmkonstanten und Kernabstände in Abhängigkeit vom Hybridisierungswinkel berechnet. Beim für die Energieberechnung optimalen Winkel ergibt sich ein Dipolmoment von 0,755 a. E., das um etwa 30% höher als der experimentelle Wert von 0,574 a. E. ist. Weiterhin werden Elektronendichten in zwei Ebenen des Moleküls berechnet und in Form von Linien gleicher Dichte graphisch dargestellt. Schließlich werden noch einige angeregte Zustände des Moleküls berechnet.

It is well known that in the initial energy spectra of hydrocarbon fragment ions formed by electron impact, satellite ion groups occur which are believed to be mainly due to the fragmentation of doubly charged ions into two singly charged fragments. By using an electron energy of 150 eV a new type of satellite was observed in the initial energy spectra of C 1 H k + and C 2 Hl + fragment ions from hydrocarbons with three and more carbon atoms. The n-paraffins were investigated systematically up to n-decane. Because the initial energy of these satellites is nearly twice the initial energy of the already well known “first” satellites, it is suggested that these newly discovered “second” satellites are due to an analogous fragmentation process of the type A +++ →B + + C ++ . Therefore, a careful search was made for the corresponding doubly charged fragment ions of high kinetic energy. Well pronounced satellite groups of doubly charged fragment ions were, indeed, found. Their momentum approximately equals the momentum of the corresponding “second” satellites of singly charged fragments, which supports the suggested mechanism.

Within the last two years the FANO factor F for Ge (Li)-detectors, which defines the theoretical limit for the resolution in the area of spectroscopy in regard to the detector, was found out experimentally several times. The values obtained for F vary between 0.7 and 0.15. In order to find out the reasons for these variations the dependence of the energy resolution on the electric field was examined at various gamma-energies for several Ge (Li)-detectors. Even at very high electric fields (several kilovolts/cm) still a field dependence especially at high gamma-energies appeared, which could be explained in terms of charge collection time. As condition for an exact determination of the FANO factor the extrapolation of the resolution to field strength infinity is set up; with this method the value of the FANO factor for Ge (Li)-detectors, used here, was estimated to 0.20 ±0.05.

Mit Hilfe des BoLLINGER—THOMAS-Verfahrens wurde das Szintillationsabklingen von CsJ-Kristallen verschiedener Tl-Konzentration im Temperaturbereich von —160 °C bis +145°C im Hinblick auf die Verwendung zur Teilchendiskriminierung untersucht. Zur Anregung der Szintillationen dienten α-Teilchen und γ-Quanten. Die Güte der Teilchendiskriminierung bei Zimmertemperatur für Kristalle verschiedenen TI-Gehaltes wurde nach der Nulldurchgangsmethode geprüft.

A procedure is described for preparing thin plane single crystal foils from the solid suitable for transmission electron diffraction. The essential point is to thin down the foils by mechanical polishing to thicknesses of about 1 μm before applying chemical or sputtering procedures.

Die zwischen 90 °K und 500 °K gemessenen Wärmeleitfähigkeiten von GaP und AlSb zeigen einen Temperaturverlauf, der auf einen Einfluß der optischen Phononen hindeutet. Die experimentellen Gitterwärmeleitfähigkeiten von III—V-Halbleitern bei DEBYE-Temperatur werden analysiert und unter einfachen Annahmen gelingt eine Auftrennung in Wärmeleitungsbeiträge von akustischen und optischen Phononen. Der akustische Anteil kommt durch Überlagerung der Wechselwirkung von akustischen mit akustischen und von akustischen mit optischen Phononen zustande.