Volume 22, Issue 4

The energies of the low lying levels and the absolute position of the ground state of the nucleus O 18 are calculated using five velocity-dependent potentials. The calculation is based on the shell model with two outer neutrons in the potential of the Ο 16 core. The interaction potential as well as the core potential are fitted to experimental data, leaving no free parameters in the final result. The wave functions of the harmonic oscillator are used in each case of the five velocity-dependent potentials. An additional computation is carried out using one of these potentials and taking into account the perturbation of the wave functions. It turns out that, for satisfactory application of the velocity-dependent potentials in shell model calculations, this perturbation should be considered.

A general theory of electron diffraction by crystals is developed. The crystals are assumed to be infinitely extended in two dimensions and finite in the third dimension. For the scattering problem by this structure two-dimensionally expanded forms of GREEN’S function and integral equation are at first derived, and combined in single three-dimensional forms. EWALD’S method is applied to sum up the series for GREEN’S function.

In this paper an instability calculation is given for an axially symmetric gas distribution which has a differential rotation and in which a magnetic field is present. It is a generalization of similar calculations given by CHANDRASEKHAR and BEL and SCHATZMAN. The generalization becomes necessary for the study of problems of the formation of planetary systems, and star formation. The instability conditions and the critical wave lengths are calculated for plane-wave-like disturbances. For disturbances running perpendicularly to the axis of rotation instability can occur only if the gas density exceeds a critical value which depends on the differential rotation at the considered distance only as long as pressure gradients and gradients of the magnetic field strength are negligible. If the gas density exceeds this critical value the shortest unstable wave length is proportional to the square root of vT 2 +vB 2 , where v T means the velocity of sound and vB the ALFVÉN-velocity. For disturbances running parallel to the axis of rotation in addition to the JEANS instability a new type of instability occurs due to the simultaneous action of the magnetic field and the differential rotation; for rigid rotation this instability vanishes.

The shock waves produced in T-tubes were investigated with a MACH-ZEHNDER interferometer. The experiments were conducted in hydrogen at an initial pressure of 5 torr. A power crowbar arrangement was used to produce single current pulses. These caused single shock waves to occur with every discharge. Reproducible, non-steady shock waves separated from the discharge plasma were observed at MACH numbers M < 15. By measuring the time dependence of the velocity of the shock front over the entire length of the tube (60 cm) it was found that the shock front behaves in accordance with the homology theory of v. WEIZSÄCKER. From the interferograms it is also possible to determine (but only qualitatively) the drop in density immediately behind the front. As the density jump increases, this drop becomes steeper and steeper—again in agreement with the theory. Moreover, it was shown by side-on photographs taken at various distances from the electrodes that the shock front becomes plane once the shock wave has covered a path ten times longer than the tube diameter.

Scattering experiments of 70 eV electrons from methane and n-heptane are described. The results, namely energy-loss spectra, and the energy and angular distributions of the ejected electrons of these molecules are compared with those of argon. A coincidence technique is used to determine the energy distributions of the probability for formation of the molecular ions. By subtraction of the distributions from the total energy-loss spectra, the distributions of the superexcited states are obtained. In the case of n-heptane, superexcited states are found up to 20 eV above the first ionization potential.

Metastable transitions have been observed in the mass spectra of benzene, hexadeutero-benzene, 1,4-dideuterobenzene and 1,3,5-trideuterobenzene using a double-focusing mass spectrometer. Decomposition maps have been obtained for each substance and decomposition reactions leading to the production of all significant fragment ions have been suggested. Metastable transitions of several doubly-charged species were found. Loss if identity by the H and D atoms of the partly-deuterated benzenes was observed in metastable transitions in their mass spectra, indicating that rapid isomerization occurs before fragmentation.

If solids are bombarded by ions, positive secondary ions (SI) of all elements of the target material are emitted. The mass analysis of these SI permits conclusions to be drawn about the composition of the target material. An arrangement based upon this kind of ion production is called an ion-bombardment ion source. In this paper it was investigated whether or not this ion source is suitable for quantitative analysis of solids by mass spectrometry. For this purpose the SI yield γ + of 27 elements was measured at constant bombardment conditions (12 keV A + -ions, 45° incidence). γ + is approximately 1% for 10 elements — Si, Mn, Fe, Co, Ni, Rh, Ta, W, Os, and U. Aluminium shows the largest, gold the smallest SI yield. Yields differ by a factor of 1000 for different elements. The influence of the ionization energy on the SI yield is discussed. The yield is independent of the concentration in the range 0.02—20%.

The electrical conductivity of pure Na 2 SO 4 , Rb 2 SO 4 and Cs 2 SO 4 and of the nine equimolar mixtures LiNaSO 4 , LiRbSO 4 , LiCsSO 4 , NaKSO 4 , NaRbSO 4 , NaCsSO 4 , KRbSO 4 , KCsSO 4 and RbCsSO 4 has been measured up to 1145°C. From the measurements we have estimated the number of cations taking part in cooperative motions in these salts. The relation between the TOBOLSKY parameter and the conductivities is discussed.

Thermal diffusion in the molten systems LiNO 3 —AgNO 3 , KNO 3 —AgNO 3 , RbNO 3 —AgNO, and CsNO 3 —AgNO 3 was detected by means of chemical analysis. Two types of cells were used: the elementary effect was measured directly in cells with vertical temperature gradients, and the coefficient of thermal diffusion (D') was estimated from the steady-state separation obtained in convection cells (horizontal temperature gradient). A discussion of possible sources of error shows for both methods that the results might be systematically lower than corresponding to ideal conditions. In all systems AgNO 3 was enriched at the cold side. There are indications that the SORET-coefficient varies with the composiiton of the mixture and the temperature. Thus for the LiNO 3 — AgNO 3 system, depending on the conditions, the SORET coefficient ranged from 2 × 10 -3 to 5.5 × 10 -3 degr. -1 , while it was about 1.8 × 10 -3 -5 degr. -1 over a wide concentration range for the KNO 3 —AgNO 3 system, and about 1.3 × 10 -3 degr. -1 over the investigated ranges for the RbNO 3 —AgNO 3 and CsNO 3 —AgNO 3 systems. Also isotope effects were measured with the convection cell, giving SoRET-coefficients of the order of 10 -5 to 4 × 10 -5 degr. -1 for 6 Li— 7 Li as well as for 39 K— -41 K, which is in agreement with previous investigations.

Cosmic ray exposure ages of more than 60 iron meteorites have been determined using the 41 K/ 40 -K-method. Isotope fractionation processes and the reproducibility of age values have been studied. Iron meteorites with ages of 900, 700, 600, 400 × 10 6 y (and hexahedrites with ages of 10 to 100 × 10 6 y according to WÄNKE) are abundant, such with ages exceeding 1 × 10 9 y are rare. Correlations have been found between exposure ages and structural classes as well as Ga—Ge-groups. These prove that the remarkable groupings of iron meteorites according to some of their structural and compositional features are indeed due to the fact that it were only a few distinct parent iron masses which essentially contributed to the production of iron meteorites. Some of these parent masses supplied the meteorites mainly in one or two “catastrophic” collisions and break-up events, others in a quasi-continuous series of events over a period of many hundreds of million years. More specified, the results are as follows: Medium and fine octahedrites of the Ga—Ge-group III have, essentially, been produced in two major collisions 600 and 700 × 10 6 y ago, fine octahedrites of the Ga—Ge-group IV a in one collision about 400 × 10 6 y ago. These events alone supplied already about 50% of all iron meteorites. Hexahedrites, coarse octahedrites of the Ga—Ge-group I and nickel-rich ataxites reveal, on the other hand, age distributions which appear rather continuous. Mean interplanetary life times deduced from these distributions are about 100 × 10 6 y for hexahedrites (according to WANKE), 500 × 10 6 y for nickel-rich ataxites and 700 × 10 6 y for coarse octahedrites of the Ga — Ge-group I. The differences in the statistics of meteorite production events for different meteorite classes indicate that fundamental dissimilarities may exist in the parent iron masses and parent celestial bodies. Accordingly, one model is proposed for explaining the data on hexahedrites, coarse octahedrites of the Ga—Ge-group I, and ataxites, another one for explaining the data on the medium and fine octahedrites of the Ga—Ge-groups III and IV a: The hexahedrites, coarse octahedrites and ataxites are fragments of a multiplicity of nickel-iron inclusions (“pools” according to URET) within the surface layers of Moon, Mars and asteroids (Mars-asteroids), respectively. These fragments, together with stone meteorites, have been produced in a multiplicity of crater-forming impacts by comets on Moon, Mars or asteroids. Rather compact and large nickel-iron masses, perhaps fragments of asteroidal nickel-iron cores are considered as being the parent masses of the fine octahedrites and medium octahedrites of the Ga—Ge-groups III und IV a. The meteorites of each group have been produced either when such a nickel-iron mass as a projectile hit another asteroid or when a comet hit the nickel-iron mass. Mainly surface material is expected to survive the catastrophe in form of structurally undisturbed meteorites, of which a considerable portion may have been exposed to cosmic rays to a measurable degree prior to the collision. Possible conclusions from a comparison of 41 K/ 40 K-age values with 36 Ar/ 36 Cl- and similar ages are reconsidered.

The mobility of the inert gases argon and xenon in pure and doped single crystals of KBr was studied. The gases were introduced by ion bombardment. The recently established system of stages was used to interpret the results. Normal volume diffusion was found for xenon at low gas concentration, the activation enthalpy being 1.4 ± 0.2 eV. This release was independent of doping, thus favoring a transport process for xenon independent of single vacancies. As most probable alternative, a mobility via small vacancy clusters, e. g. vacancy pairs was suggested. Trapping of xenon was found at higher xenon concentrations. This retarded release was shown to depend on doping and was more pronounced in crystals with an excess of cation vacancies. The diffusion of argon occurred with a similar activation enthalpy, but was most probably due to an interstitial motion.

The hyperfine structure of 99 Tc (IV) in mixed crystals of K 2 [TcCl e ] — K 2 [PtCl 6 ] and K 2 [TcF,] —K 2 [PtF e ] was measured at 3 cm wavelength and at 1.7°K and 77°K respectively. The parameters of the chloro-complex are g max =1.9896, g min =1.9876, A max =1.361 × 10 -2 cm -1 , A min = 1.337 × 10 -2 cm -1 ; in addition to the Δm=0 transitions, the forbidden Δm= ±1 transitions were observed. The parameters of the polycrystalline fluoro-complex were determined to g=3.884, A=3.34 × 10 -2 cm -1 , B=1.76 × 10 -2 cm- 1 .

Das Mikrowellenspektrum des Tertiärbutylchloracetylens wurde im Bereich zwischen 8000 und 24 000 MHz untersucht. Durch Vermessen der Mikrowellenspektren einer Reihe von isotopensubstituierten Molekülen im natürlichen Vorkommen konnten nach der Methode der r s -Strukturbestimmung die Gesamtlänge der linearen Kette sowie die Abstände C—Cl und C—C ≡ C bestimmt werden. Die Quadrupolfeinstruktur konnte zum Teil aufgelöst und die Kernquadrupolkopplungskonstante ermittelt werden. Obwohl das Molekül einem symmetrischen Kreisel entspricht, ist das Spektrum sehr komplex durch das Auftreten sehr vieler angeregter Schwingungsfreiheitsgrade. Es gelang, fast alle stärkeren angeregten Schwingungsfreiheitsgrade zuzuordnen, wobei aus den Intensitätsverhältnissen die entsprechenden Schwingungsfrequenzen ermittelt werden konnten. Die Ergebnisse stimmen befriedigend mit den früher von uns vermessenen Ultrarot- und Raman-Spektren überein. Die Strukturdaten entsprechen der gleichzeitig von uns mittels Elektronenbeugung bestimmten Struktur.

The rotational spectrum of pyridazine in the vibrational ground state is reported for the parent species and three isotopically substituted species. The r s coordinates of the ring atoms have been reliably determined with the exception of the α coordinate of the Cl and the C4 atoms which is obviously too small for the application of KRAITCHMAN’S equations. The dipole moment was calculated from the STARK effect as μ α =4.22 D. The quadrupole coupling constants, from hfs measurements, are χ αα =— 4.64, χ bb =1.38, χ cc =3.27 MHz. The only non-diagonal quadrupole coupling tensor element has been less accurately determined from the variation of the hfs upon rotation of the principal axes system by isotopic substitution of one N 15 nucleus.

The microwave spectrum of isobutyronitrile has been investigated in the region from 5 — 30 GHz. A and C type transitions have been observed. No splittings due to internal rotation of the methyl groups could be detected and a lower bound of 2.6 kcal/mole for the barrier height is established. Values for the rotational constants are 7.940 95 ± 0.000 04, 3.968 039 ± 0.000 010 and 2.901 030 ± 0.000 010 GHz. The nuclear quadrupole coupling constants are χ αα =—3.90 5 ±0.01 0 MHz, χ bb =2.07 7 ±0.02 MHz and χ cc =1.82 8 ±0.01 7 MHz.

The size distribution of Barkhausen discontinuities was measured along the hysteresis cycle during the decomposition of non-ferromagnetic nickel hydride at room temperature. The results confirm our earlier conception that this process is comparable to the precipitation of alloys. During the decomposition, firstly superparamagnetic particles are formed. They increase in size to monodomain and multi-domain particles successively, and finally grow together to compact nickel.

To get information on extremely small organic deposits in ultra high vacuum systems the sensitivity of most of the conventional methods for thickness measurements is not high enough. On the other hand the radioactive tracer method has shown its high sensitivity and wide versatility in many fields. Tritium with a half life of 12.3 γ and a mean β-energy of 5.4 keV was choosen as tracer isotope. A method is described for Tritium-labelling diffusion pump oils with specific activities up to 100 mC/g. Using the liquid scintillation counting technique one can detect deposits down to below 10 10 molecules/cm 2 . First results with this Tritium labelled pump fluid are given under different operating conditions in an all metal ultra high vacuum system.

Für das homogene magnetische Sektorfeld mit gekrümmten Feldbegrenzungen und schrägem Ein- und Austritt wird die Gleichung des Nebenstrahls eines Ionenbündels mit radialer und axialer Öffnung relativ zu dessen Mittelstrahl in dritter Näherung bestimmt. Damit werden die Bildfehlerkoeffizienten 3. Ordnung gewonnen. Die Streufeldeinwirkungen werden ebenfalls in dritter Näherung behandelt, wobei die im Streufeldbereich stattfindende Gesamtablenkung durch das Modell eines „Ersatzstrahlenganges“ mit Knickung und Versetzung des Strahls an einer zu bestimmenden „Ersatzfeldgrenze“ beschrieben wird. Numerische Beispiele werden angegeben. Bisher 1-12 waren entsprechende Rechnungen nur bis in 2. Näherung durchgeführt.

Kurze Rubinstäbe wurden quasikontinuierlich bei variabler Kühlmitteltemperatur betrieben. Der Temperaturgang von Schwelle, Wirkungsgrad und Emissionsspektrum wurde gemessen. Dabei ergab sich ein unerwarteter Effekt: Bei einem VERNEUILLE-Stab nahm die Schwelle unterhalb einer Kühlmitteltemperatur von — 5°C stark zu, während sie bei einem nach dem CZOCHRALSKI-Verfahren gezogenen Stab den Erwartungen gemäß abnahm. Erklärungsmöglichkeiten sind Anregungsprozesse in hochliegenden Energieniveaus und vom Herstellungsverfahren abhängige, durch das Pumplicht induzierte Absorptionszentren, deren Lebensdauer mit sinkender Temperatur zunimmt.