Band 26, Heft 3

Auf die Sonderstellung der metrikinvarianten (universell gequantelten) Skalare der Physik wird hingewiesen. Aus ihnen können die übrigen Größen definiert werden mit Hilfe von Länge und Zeit. Eine bevorzugte Stellung haben die alternierenden Differentialformen, weil sie sich als Ganzes wie metrikinvariante Skalare verhalten. Der Begriff orthogonal geht nicht ein.

A method and equipment are described for measuring the spin dependence of slow neutron cross sections. The neutron beam from the High Flux Beam Reactor (HFBR) is polarized by Bragg reflection from a magnetized 92% Co-8% Fe single crystal which process also serves to select the neutron energy. Nuclei in the target are statically polarized in a field of ∼ 35 kOe at temperatures ranging from 0.05 to 0.10 K. Large nuclear polarizations are obtained in polycrystalline ferromagnetic dysprosium metal because of the large magnetic hyperfine interaction. The total angular momenta, /, of the compound states corresponding to the first several resonances in Dy 161 and Dy 163 were determined by measuring the transmission of the target with the neutron beam alternately polarized parallel and antiparallel to the nuclear polarization. Quantitative results at two resonances of opposite spin permit absolute /-value assignments (i. e., the assignments are independent of any knowledge of the absolute signs of the nuclear magnetic moments). Results were as follows: Isotope 163 161 161 161 161 161 161 161 161 163 161 161 E 0 (eV) 1.71 2.72 3.69 4.35 7.75 10.40 10.87 12.65 14.3 16.25 16.7 18.5 J 2 3 2 2 3 2 3 2 (?) 2 3 (?) 2 The hyperfine interaction constants for Dy163, obtained by measuring the nuclear polarization as a function of temperature, were A/k = 0.100 ± 0.005 K, and P/k = 0.008 ± 0.001 K where A and P are, respectively, the magnetic and the electric hyperfine interaction constants.

The Ir-Fe and Ir-Ni alloy systems were studied over the whole composition range by means of the nuclear resonance absorption of the 73 keV y-rays of 193Jr and of the 14.4 keV y-rays of 57Fe. The magnetic hyperfine field at the Ir-nuclei in Ir-Ni alloys decreases approximately linearly with the Ir concentration from - 460 kOe at 4.2 K in very dilute alloys to zero at about 20 at.-% Ir. This behaviour is paralleled by the decrease of the magnetic moment per Ni atom as determined from bulk magnetization measurements. The hyperfine fields at both Ir and Fe were measured for the ferromagnetic bcc phase of the Ir-Fe system. They turned out to be virtually independent of concentration with values of about -1400 kOe and - 330 kOe, respectively. Linewidths increasing with the Ir concentration indicate a distribution of hyperfine fields. The fee phase of the Ir-Fe system has been found to be paramagnetic at 4.2 K throughout the range of its existence. The dependence of the hyperfine fields on concentration is discussed in terms of a rigid 3d-band model combined with local shielding. A discussion of the concentration dependence of the 193 Ir and 57 Fe isomer shifts has to take into account lattice expansion as well as band repopulation effects.

The ferromagnetic transition temperature, the quadrupole interaction, the hyperfine magnetic field, and the isomer shift have been measured in Eu 2 SiO 4 and Eu 3 SiO 5 using the 21.6 keV nuclear gamma resonance in 151 Eu. The isomer shifts found (-0.6 mm/sec for Eu 2 SiO 4 and +0.1 mm/sec for Eu 3 SiO 5 against EuS) are less negative than the values typical for other ionic Eu 2+ compounds. The magnetic hyperfine fields (280 kOe for Eu 2 SiO 4 and 240 kOe for Eu 3 SiO 5 ) are much lower than the Eu 2+ free ion value. A brief qualitative discussion of these hyperfine parameters is given. A rough correlation between the isomer shift and the transition temperature for various divalent Eu compounds is indicated. The effect of trivalent of the silicates is demonstrated.

The Mössbauer scattering of the 145.4 keV γ-rays of 141 Pr was observed in a number of praseodymium compounds. From the isomer shifts between trivalent and tetravalent fluorine compounds the value Δ/(r 2 ) = + 12 · 10 -3 fm 2 was derived for the change of the nuclear charge radius. The magnetic moment of the 145.4 keV state, μ 7 / 2 = (2.8 ± 0.2) μN, was deduced from the magnetic hyperfine pattern observed with scatterers of antiferromagnetic PrO 2 .

Experimental K-X-ray intensity ratios Kα 2 /Kα 1 , Kα 3 /Kα , Kβ 1 /Kα 1 , Kβ 2 /Kβ 1 , Kβ 3 /Kβ 1 , Kβ 4 /Kβ 1 and Kβ 5 /Kβ 1 have been determined for several elements with 63≤Z≤92. These ratios agree very well with the results of a fully relativistic calculation of transition probabilities by Rosner and Bhalla. The theoretical values are tested with an accuracy of better than one per cent for the ratios Kα 2 /Kα 1 , Kβ 2 /Kβ 1 and Kβ 3 /Kβ 1 .

The Yb174 (n,γ) -spectrum has been measured in the energy region of 26 -1500 keV. More than half of the observed 239 y-lines were placed in a level scheme. Precise energies have been determined for the states and their deexcitation has been studied in detail. New rotational bands, with the configurations { ([624 ↑] n + [512 ↑] n + [514 ↓] n ) 3/2 +[642 ↓]}, [651 ↓] and [642 ↓] are proposed at 1067, 1356 and 1937 keV. Calculations show that these bands strongly mix through Coriolis coupling. Additional and previously unknown states of the [624 ↑] and [633 ↑] bands are proposed. Level energies and y-branching ratios are explained reasonably well through a multi­ band mixing calculation of the configurations with negative parity.

Measurements of Neutron-Scattering-Amplitudes using the Christiansen-Filter- Technique By means of Christiansen-Filters it is possible to make use of the high accuracy achieved for the scattering amplitudes of liquids also for solids in form of powders. We investigated the scattering law for the small angle scattering of Neutrons by Christiansen-Filters and found a good agreement between theory and experiment. Using powders of several elements we could measure the scattering amplitudes of the elements with an uncertainty within ± 0.2% to ± 1%. We got for the bound atoms of Al: a = (3.449±0.009) F; Nb: a = (7.11 ± 0.04 ) F; Cr: a = (3.532 ± 0.010) F; Te: a= (5.43 ± 0.04 ) F; Sb: a = (5.641 ± 0.012) F; and Ta: a = (6.91 ± 0.07) F. Si: a = (4.159±0.006) F;

Die Bestimmung der kohärenten Streuamplitude des gebundenen Schwefelatoms mit Hilfe des Neutron-Schwerkraftrefraktometers des Forschungsreaktors München ergab a = (2,847 + 0,001) F. Der totale Wirkungsquerschnitt von flüssigem Schwefel (135 °C und 176 °C) für Neutronen- Energien 4 · 10 -3 > E > 0,15 · 10 -3 eV wurde gemessen. Der Beitrag der Selbstdiffusion des Schwefels zum inelastischen Streuquerschnitt wird beredinet.

Approximately 165 conversion electron lines from slow neutron capture in 199Hg have been measured with the beta spectrometer at the reactor FRM between 900 keV and 8 MeV. The high energy K-conversion coefficients of El and Ml transitions are separated distinctly and agree very well with theoretical calculations, which have been performed by several groups recently. High energy L-conversion electron coefficients have been measured for the first time with such a degree of accuracy that different multipole orders are separated and a comparison with theoretical values is possible. 6 known levels above 2 MeV have been assigned 1 + and 14 new levels have been established. 145 lines have been placed into the level scheme and new level energies have been calculated. A new 0 + level has been found at 1856.97 ± 0.1 keV.

A procedure for growing hcp argon single crystals doped with oxygen is described. The hcp crystal structure is confirmed by birefingence and neutron scattering experiments. The birefringence at 77 °K of a hcp argon single crystal doped with 2% oxygen is determined to be n e -n 0 = + (2.11 ± 0.63) · 10 -6 . From this result one can calculate the Lorentz field factors, obtaining f o = (333 328.6 ± 1.4) · 10 -6 and f e = (333 342.7 ± 2.8) · 10 -8 . Using Ewald's theory of structural birefringence to determine σ = c/a from the measured birefringence yields σ = (163 451 ± 3) · 10 -5 . This value definitely excludes the ideal hcp structure (σ = 1.63299), in contrast with the results of X-ray measurements.

The sudden change of nuclear charge (β-decay) produces a finite probability for the excitation of the outer electron shell. The emission spectrum of a gaseous Xe 133 -source exhibits light from the daughter Cs + , excited by the sudden change of nuclear charge, as shown by a spectral analysis. The probability for this excitation, p ∼ 6 · 10 -2 per β-decay, is found in coincidence with the β-particles from the upper part of the β-spectrum; this value is lowered if also the low-energy part of the β-spectrum is included in observation; this seems to indicate a breakdown of the sudden approximation around 20 keV. The absolute values of p for Kr 85 and Xe 133 are discussed. The photon yield from the Kr 85 -decay in solid state for high E β is not a constant, as it is in the gaseous state, but decreases with E β , suggesting nonradiative transitions induced by the β-recoil.

Very cold neutrons (typical wavelengths are about 10 2 Å) are available by recently developed techniques 2. The features of the scattering of these “ultracold” neutrons are investigated in the present paper discussing a few examples of magnetic scattering. The diffraction of neutrons by the vortex lattice in superconductors is treated as an example of elastic scattering, while in most other cases the scattering is inelastic. We discuss the scattering by ferromagnetic magnons at low temperatures and the critical scattering from an isotropic ferromagnet above the critical tempera­ture. Simple models are used to derive the total cross sections. It is shown that relevant information about the inealsticity can be gained by the measurement of total cross sections in these cases.

A precise transmission measurement of the cross sections of Bismuth, Lead, Silicone and Carbon for 130 eV neutrons (Co-resonance) has been carried out. A new resonance method has been applied, using epithermal reactor neutrons, which have been scattered twice from Co-foils. - We obtained the total 130 eV cross sections: Bi: 9,182 ± 0,007 b, Pb: 11,295 ± 0,009 b, Si:2,0442 ± 0,0018 b, C: 4,746 ± 0,007 b. From these results the coherent nuclear scattering lengths (bound), Bi: 8,646 ± 0,005 fm, Pb : 9,524 ± 0,004 fm, C: 6,660 ± 0,006 fm, have been calculated, under consideration of various corrections (absorption, Schwinger-scattering, Incoherence, Neutron-Electron-Interaction, energy-dependence of nuclear-scattering).

Es wurde eine systematische Untersuchung der (n,n'γ) -Querschnitte für 14 MeV-Neutronen an gg-Kernen im Massenbereich A = 46 - 88 durchgeführt und die Querschnitte für die Anregung des ersten 2 + -Niveaus für 19 Kerne im genannten Massenbereich wurden gemessen. Die Ergebnisse können durch das statistische Modell der Kernreaktionen befriedigend erklärt werden.

Gamma radiation from the capture of neutrons in natural Se and in enriched 76 Se and 80 Se has been studied with different Ge (Li)-detectors, with a Ge(Li)-NaJ pair spectrometer and with a Ge (Li) -Ge (Li) two-paramater γ-γ coincidence system. These measurements resulted in a considerable improvement of the level schemes of 77 Se, 78 Se and 81 Se. The 81 Se and the 107 Ag level schemes are compared, and the applicability of phonon-particle coupling to low-lying states of 81 Se is discussed. In the case of 77 Se, some properties may be possibly better described by the Nilsson model. It is rather clear, however, that both models can only be regarded as limited approximations and that more refined models are required for Se nuclei. The well-known, unusually small isomeric cross section ratio of 81 Se, and the weak population of p-single-quasiparticle states by primary transitions from the capture state 80 Se + n, which shows up in our measurements, may be understood by assuming a capture state containing a doorway state with a simple collective excitation.

The change of the shearmodulus of pure polycrystalline Al, Cu and Pt due to reactor neutron irradiation at 4 °K has been studied. The shearmodulus was determined by measuring the vibrational frequencies of a helical spring in two different modes (between 50 and 300 Hz) together with internal friction and electrical resistance. Large relative decreases of the shearmodulus ΔG/G per molar fraction c of Frenkel defects were found, namely ΔG/Gc - 47, - 39, - 67 for Al, Cu and Pt, respectively. The absolute values are much larger than expected from lattice theory. The effects cannot be explained by a relaxation of the defects.

The precipitation of lithium dissolved in germanium crystals and the re-solution of the precipitates during heating has been studied by means of anomalous transmission of x-rays. The effective absorption coefficient depends sensitively on the spacial distribution of lithium interstitials, and is enhanced enormously if pair correlations increase, as is the case during clustering. On the basis of Dederidis' theory and knowledge about the Geli phase diagram, the experiments provide relations between concentration and radius of the precipitates, distortion parameters, and average and local concentration of lithium interstitials.

In high purity Ta-foils the damage production during electron irradiation at 4.5 °K has been studied using electrical resistivity measurements. The observed dose curves show a strong saturation effect, i. e., the effective damage rates decrease with increasing defect densities. Two mechanisms contribute to this radiation annealing effect: 1) Spontaneous recombination of newly produced interstitials or vacancies with vacancies or interstitials already present in the crystal (direct re­ combinations) and 2) spontaneous recombination of close Frenkel pairs under the influence of nearby low energy recoil events (subthreshold events). The contribution of both direct recombin­ations and subthreshold events can be separated by subthreshold test irradiations as well as by radiation doping experiments. Both methods yield mutually consistent results. From these one can deduce a value of the spontaneous recombination volume of about 50 atomic volumes and a value for the cross section for the spontaneous recombination of a close Frenkel pair by subthreshold energy transfers from 1.2 MeV electrons of about 90,000 barns.

The prompt γ-radiation emitted in 235U thermal fission has been investigated in a multiparameter experiment, γ-yield, time-distribution, energy spectrum and nuclear anisotropy of the emission have been measured, especially γ-yield and anisotropy as a function of fragment mass and γ-energy. The mass dependence of the primary spins of the fragments can be deduced from these measurements. A value of 7 h̶ for the average primary spin and an increase of the primary spins within each fission product group is obtained. This dependence is explained within an adiabatic model of scission due to the mass dependence of the deformation of the fragments.

Rotational Structure in the 21.22 eV Photoelectron-Spectrum of H 2 : The form of the vibrational steps in the 21.22 eV potoelectron-Spectrum of H 2 was analysed using a retarding field electron energy spectrometer with 10 meV resolution and a computer programme for a least squares fit analysis. Even though the broadening caused by the thermal motion of the H 2 molecules during the photoionization process prevented the complete resolution of the rotational structure, it is possible to conclude from the results that the angular momentum of the nuclear rotation does not change in the photoionization process of H 2 molecules with 21.22 eV photons.

The formation of a steady helical instability in a wall-stabilized hydrogen arc at low currents is investigated experimentally. To determine the onset-point of the instability theoretically the basic equations of electrodynamics and the balance of mass, momentum and energy are solved in the limiting case of vanishing growth-rate of the instability, taking into account the dissipative terms as well as the temperature dependence of the density. It turns out that the destabilizing J X B-forces, which try to deflect the arc by a convective heat-transfer, are balanced by the thermal stabilization of the tube-wall as well as by the unsym metrical energy-production in the curved arc. Onset-point and pitch of the helix result from the theory in full agreement with the measurements.

The D 1 ∏ u - X 1 ∑ g + system of H 2 and D 2 shows strong predissociation. High resolution m easurements on the line widths of isolated absorption lines have been carried out, showing the influence of rotation on the predissociation probability of the corresponding rotational states. Their lifetime decreases with increasing rotation of the molecule and with decreasing mass due to the coupling of electronic and rotational motion. Both results are in excellent agreement with theoretical predictions given by Kronig. The shape of the absorption lines broadened by predissociation was found to be typically asymmetric. They are of the Beutler type, well known form the autoionisation of the rare gases.

Ausgehend von den nach verschiedenen Verfahren erhaltenen Kraftfeldern von SiF 4 und SiCl 4 werden für SiBr 4 und SiJ 4 Kraftkonstantensätze angegeben. Zur Berechnung der Grundschwingungen von SiCl 3 Br, SiCl 2 Br 2 und SiClBrs eignen sich Kraftkonstanten, die direkt oder nach geeigneter Mittelung bzw. Abstufung von SiCl 4 und SiBr 4 übertragen werden. Eine Neuaufnahm e des Raman- Spektrums von SiClBr 3 ergibt, daß ν 6 in Übereinstimmung mit der Berechnung bei 161 cm -1 liegt.

Die Raman- und Fern-IR-Spektren der Verbindungen TiCl n Br 4-n (n = 0 - 4) wurden aufgenommen und durch Kraftfelder wiedergegeben, die sich von TiCl 4 und TiBr 4 herleiten. Die Ergebnisse erweisen eindeutig die Anwesenheit aller Zwischenglieder in statistischer Verteilung, sichern die lückenlose Zuordnung der gemessenen Spektren und bestätigen die Übertragbarkeit von Kraftkonstanten für eine Gruppe von Übergangsmetall-Verbindungen.

The electron paramagnetic resonance of copper (II)-tetrammine nitrate in solution of methanol and water has been investigated. The data obtained from the spectra at room temperature and 97 °K together with the optical transition energies determined from single crystal polarized absorption spectra at 77 °K by other authors were used to calculate the LCAO-MO bonding parameters. The bonding orbital of the ammonia molecule cannot be described by the concept of sp 2 hybridization which was exclusively used in the theory. Therefore a calculation of the overlap integral S(n) for α bonding and of the superhyperfine splitting was carried out in terms of an arbitrary hybridization parametern. For ammonia, n was taken from the Duncan-Pople hybrid wave function for the lone pair orbital. The o bonding and the out-of-plane π bonding appear to have a moderate degree of covalency (α = Ϭ = 0.91; α’= 0.49). The covalent in-plane n bonding is somewhat stronger (β = 0.87) but is by no means so strongly covalent as is observed in compounds with ligands which do not exclusively coordinate through the lone pair electrons. At low temperature nine ligand nuclear superhyperfine structure lines corresponding to the interaction of four magnetically equivalent nitrogen nuclei have been observed. The value of α' derived from the superhyperfine splitting is in excellent agreement with that obtained from the copper nucleus hyperfine structure.

A method is presented for the calculation of the electrostatic interaction energy in a crystal lattice taking into account the real charge distribution of the particles. For this purpose the charge distribution of a particle is represented by a superposition of multipole moments. The crystal potential is expanded into amultipole expansion, the resulting lattice sums being evaluated according to Ewald's method. The present paper is restricted to the treatment of molecules or molecule-ions of cylindrical symmetry.

In the paper of Neckel , Kuzmany , and Vinek 5 a procedure was proposed for the calculation of the electrostatic interaction energy of a crystal lattice provided the multipole moments of the particles are known. In the present paper a method for calculating multipole moments using LCAO-MO-wave functions is discussed. The multipole moments for the [FHF] - -ion and the Madelung energy of KHF 2 , RbHF 2 and CsHF 2 are evaluated. The results are com pared with calculations obtained by using a point charge model. For KHF 2 , RbHF 2 and CsHF 2 , the total lattice energies are evaluated.

Investigations on motions of hydrogen atoms in metals, on rotational diffusion in molecular solids and on fluctuations of protons at hydrogen bonds are reviewed as examples for experiments with incoherent neutron scattering requiring high resolution.

Anelastic strains exceeding elastic strains up to a factor of 30 have been observed close to the critical point of H in Nb. The temperature dependence of the relaxation strength follows a Curie-Weiß law for temperatures (T - T c )/T c ≥ 6-10 -3 .