Showing papers in "European Physical Journal in 1970"

Laserlight — first example of a second-order phase transition far away from thermal equilibrium

Abstract: We solve the functional Fokker-Planck equation established in a previous paper in the vicinity of laser threshold. The stationary solution is obtained explicitly in the formP=N exp [−ϕ({ū, ū*})]. ϕ has exactly the same form as the Ginzburg-Landau expression for the free energy of a superconductor, if the pair wave function is replaced by the electromagnetic field amplitudeū. This gives us the key for a thermodynamic reinterpretation of all laser phenomena. In particular the laser threshold appears as a second-order phase transition in all details. It is indicated that our theory provides a new formalism also for the Ginzburg-Landau theory.

Scattering of light by slightly rough surfaces or thin films including plasma resonance emission

Abstract: It will be shown that the perturbation theory approach with respect to the amplitude of the roughness for the scattering of light by rough surfaces is equivalent to a model consisting of a smooth surface and surface current sources. This model has an obvious physical meaning and allows a simple calculation of the scattered fields, which are given. The model and the previous one given by Stern are identical up to the position of the surface currents, which have to be placed into the vacuum. Consequently the former explanation has to be corrected, which says that the peak of the scattered radiation at the plasma frequency is generated by surface roughness. We will show that it is possible to generate this maximum by statistical inhomogenities within the metal.

Comparison between measured and calculated RF losses in the superconducting state

Abstract: Results of experiments and of the BCS-theory on the surface resistance of superconductors are presented. It will be shown that agreement between theory and experiment can be achieved by using revised material parameters.

Energieverteilungen bei der Festkörperzerstäubung durch Ionenbeschuß

Abstract: The energy distributions of the neutral particles sputtered from polycrystalline targets of Al, Ti, Ni, Cu and Ag by normally incident Ar+-ions in the 1 keV region have been determined for ejection energies below 20 eV in a direction close to the normal to the target surface. The experimental method employed is strongly connected to the characteristic properties of a low pressure electrodeless hf plasma used as an effective ion source as well as an ionizing medium for the ejected target atoms. The resulting curves always show a maximum at most probable ejection energies between 1 and 5 eV, being approximately half of the surface binding energy. These curves are converted to the corresponding energy distributions for the recoil atoms within the target by an energy dependent factor. It is found that the energy distribution within the bombarded solid decreases monotonically with the inverse square of the energy of the recoils.

Kramers Kronig analysis of the optical properties of small silver particles

Abstract: In order to complete a preceding paper the dielectric constantɛ of the particle material of small silver particles with diameters between 210 and 25 A is computed in the wavelength region 365≦λ≦455 nm from the measured spectra of thesmall particle plasma reasonance absorption. For this purpose a properKramers Kronig relation is derived, and is checked by applying to particles with Drude free electron gas. The results, concerning the silver particles, are that the real part ofɛ changes slightly, whereas the imaginary part is markedly enhanced (up to the ten-fold of the bulk values) if the particle size decreases. This size dependence ofɛ can quantitatively be described with thefree path effect within the accuracy of the measured values. Conversely, thebulk dielectric constant of silver is obtained by applying the free path effect to the measured dielectric constant of the small particles.

Is a subtraction really necessary in the isospin even π N dispersion relation

Abstract: It is shown that the assumption of anunsubtracted fixed-t dispersion relation for the isospin evenπN amplitudeA + is compatible with all data. The prediction for the subtraction function agrees reasonably well with independent determinations. The assumption has the consequence that the ratio of thes-channel helicity flip and non flip amplitudes vanishes in the high energy limit.

Elektronen-Spinpolarisation bei der Photoionisation unpolarisierter Cäsiumatome mit zirkularpolarisiertem Licht

Abstract: Photoelectrons ejected from cesium atoms by circularly polarized light of certain wavelengths are highly spinpolarized according to Fano's theory. Measurements of the spinpolarization of photoelectrons along the wavelength spectrum are reported. The highest degree of spinpolarization obtained experimentally is 100%. Our results reveal a small deviation from the theoretically predicted spinpolarization. Apart from giving information on the influence of spin-orbit interaction on the photoionization process, the Fano-effect turns out to be a simple and efficient method for producing polarized electron beams. Though not designed as a polarized electron source, our present apparatus yields a beam of 0.3·10−10 Ampere with a polarization of 81 ± 3% when a broad unfiltered spectral band is irradiated.

Resonance spectroscopy of γ-radiation on Au (I) and Au (III) compounds

Abstract: Isomer shift (IS) and electric quadrupole splitting (QS) of the 77 keV γ-rays of Au197 were investigated for a large number of Au (I) and Au (III) compounds at 4.2 °K by nuclear γ-resonance Spectroscopy. A close correlation between the observed isomer shifts and the spectrochemical series of the ligands was observed. For each oxidation state, isomer shift and electric quadrupole splitting show approximately a linear relationship. On the basis of LCAO-MO theory, the experimental results are interpreted by covalency effects in the molecular orbitals, synergic coupling of σ- and π-bonds, and the empirically known donor and acceptor properties of the ligands.

Reactions of excited atoms and molecules with atoms and molecules: IV. Determination of interaction potentials from Penning electron energy distributions

Abstract: Penning electron distributions arising from the ionization of Na and K by He (1s 2s1,3S)-metastables in thermal collisions, as well as the absolute cross section for Penning ionization of Na by He (23S) and relative cross sections for ionization of Na and K by He(21S) and He(23S) are measured.It is shown that under fairly general conditions the well depth ε* of the interaction potential between the metastable and the target particle can be obtained directly from the measured electron distributions. ε*-values are reported for the moleules He(1s 2s1,3S)-Na(2S), K(2S) (2,2Ω), and for He(1s 2s1,3S)-Hg(1S)(1,3Ω). These latter values are obtained from previously published measurements and are to be considered preliminary. Further, additional evidence is given, that Penning ionization with metastables is an electron exchange process.

Ein „ F-Zentrum'' als paramagnetischer Donator in Zinkoxid

Abstract: The ESR line atg≃196 in zinc oxide single crystals has been reinvestigated It is found that the defect responsible for the resonance can be described as anF-center, ie, an electron trapped in an oxygen vacancy TheF-centers act as donors and due to overlapping of their wave functions give rise to donor band conduction This model has been confirmed by studying various methods to produce the centers and by ESR and conductivity measurements down to liquid helium temperature

Mössbauer isomer shifts, hyperfine interactions, and magnetic hyperfine anomalies in compounds of iridium

Abstract: The dependence of the isomer shift of the 73 keVγ-rays of193Ir on the oxidation state was studied in a variety of compounds of trivalent and tetravalent iridium as well as in IrF5 and IrF6. The observed shifts can be attributed to the sielding effect of the varying number of 5d electrons, but there may be additional direct contributions fromσ-bonding electrons. In the hexahalogen complexes with Kramers-degenerate electronic groundstates magnetically ordered phases were found and studied at temperatures between 0.5 and 4.2 K. Between IrF6 and tetravalent [IrCl6]2− and [IrBr6]2− complexes magnetic hyperfine anomalies of up to 10% were observed, which support the presented interpretation of the hyperfine fields in terms of core polarization, orbital and spin-dipolar contributions.

Plasma resonance radiation from non radiative plasmons

Abstract: Non radiative surface plasmons decay into photons on a rough surface. This light emission is studied with gold- and silver foils of different thicknesses. The surface plasmons are excited in this experiment by light. By this way a relatively accurate determination of the optical constants is possible.

Inner shell ionization by heavy, charged particles and associated energy loss of the projectile

Abstract: The process ofL- andM-shell ionization of atoms by heavy, charged particles is analysed in detail by a semiclassical, time-dependent perturbation method. The target electrons are described by non-relativistic hydrogenic wave functions. For the projectile is assumed a well-defined straight-line path. The Coulomb deflection and the screening is partially taken into account.

Single crystal preparation and crystalline electric field parameters of ErAl 2 .

Abstract: For the first time the preparation of single crystals of ErAl2 and some isostructural compounds is described. From recently reported susceptibility measurements on ErAl2 single crystals the parameters of the crystalline electric field are calculated to beB 4=+15·10−4°K±30% andB 6=−2.1·10−6 °K±30%. These parameters are discussed in terms of the point charge model. This model describesB 4 andB 6 and the magnetic properties of ErAl2 in good approximation.

The (n, 2n) excitation functions for93Nb and103Rh with special respect to the isomeric states in92Nb and102Rh

Abstract: By means of the activation technique the excitation functions for the reactions93Nb(n,2n)92mNb(10.15d),103Rh(n,2n)102mRh(2.9y), and103Rh(n,2n)102gRh(206d) were measured with an average total uncertainty of about ±8% between 10 and 20 MeV neutron energy. In addition the total93Nb(n, 2n) cross-section was compared with the59Co(n, 2n) cross-section at 16.8 MeV by direct neutron detection using the time-of-flight technique. The results are compared with statistical theory, especially with theoretical expectations for the isomeric cross-section ratios, which are only in reasonable agreement with the experiment if one assumes a ground state spinIg=5 for92Nb andIg=2 for102Rh.

Optical transitions of Ag− centers in alkali halides

Abstract: Ag− centers in alkali halides give rise to a strong absorption band in the 300 nm region (formerly called “B band”). Its resolved triplet structure in CsCl suggests that it corresponds to the C band of the isoelectronic In+ center. Two very weak bands are found in several alkali halides in the 400 nm region. These new bands are assigned to the A and B transitions of the In+-type centers. This is supported by the doublet structure in the A band, and by the temperature dependence of the oscillator strength of the B band. In KCl∶Ag− the ratios of the oscillator strengths are found to befc/fA=610 andfc/fB=3,400 at low temperatures.

Inelastische Streuung langsamer Neutronen an festem und flüssigem Wasserstoff

Abstract: Para-Ortho transitions in solid hydrogen above theλ-point have been measured by inelastic neutron scattering. From the scattered spectra the widths of the rotational lines caused by the quadrupole-quadrupole interaction between the ortho-molecules are determined. The full width at half intensity is found to be 1.22±0.07 and 0.80±0.07 meV for 68 and 27 percent ortho-concentration respectively in good agreement with theoretical values.

The treatment of nuclear reactions by Kohn's variational principle

Abstract: The extension of the Kohn-Hulthen variational principle to the multi-channel reaction problem is discussed. It is shown that this method leads to a unitaryS-matrix. As an application of the method a four channel calculation for the 3/2+ state of5Li is presented.

Diffusion theory of the positive column with two-stage ionization and collisional deexcitation

Abstract: The diffusion theory of the low pressure positive column is extended to account for collisional deexcitation as well as for two-stage ionization by electron impact. This extension results in the equationn″(ξ)+n′(ξ)/ξ+n(ξ)+vn2(ξ)[1+μn(ξ)]-1=0, which is solved numerically for the value ofξ1 which satisfies the boundary conditionn(ξ1)=0 for different values of the parametersν andμ.

Experimentelle und theoretische Untersuchungen von Nichtgleichgewichtseffekten an stationären Heliumplasmen unter Normaldruck

Abstract: Measurements and calculations of temperature, densities and field-strength-current-characteristics of cascaded arcs (0.15 and 0.3 cm radius) burning in Helium under normal pressure are reported. It is shown that the evaluation of measured arc data assuming Saha equilibrium is not in agreement with the detailed solution of the balance equations. The temperature of electrons and heavy particles as well as the density of electrons and neutrals must be determined as independent variables from the rate equation for ground state neutrals, from the equation of state, and from the energy balance of the electron gas and of the total plasma. The latter equation can be replaced by relations between measured intensities and the state variables. The deviations from Saha equilibrium are mainly caused by diffusion of neutral particles into the arc core and of charged particles into the opposite direction. The theoretical results derived from the balance equations are compared with spectroscopic line intensity and line width measurements. The agreement is good even if the equilibrium conditions are strongly violated.

Investigation of photon--photon angular correlations in atomic mercury.

Abstract: By application of the time differential coincidence technique developed in nuclear spectroscopy, for the first time the angular correlation of light quanta of atomic decays was observed. The experiments were carried out with the 73 S 1-63 P 1-61 S o-cascade of mercury excited by electron impact at energies of 50 eV. The two transitions of 4358 and 2536 A were selected by interference filters and detected by photomultipliers. Time differential coincidence spectra were measured at the two angular positions 0=90 ° and 0=180 °. It was found that the excitation of the 73 S 1-state by the electron beam leads to no alignment. Therefore the usual γ-γ angular correlation theory is applicable. Perturbations occur by static interaction with external magnetic fields and by free hyperfine interaction in the odd isotopes of mercury. The interaction frequencies of the free hyperfine interaction are in all cases too high to be resolved. Measurements were performed using mercury of natural abundances, with and without external magnetic fields. First of all the spin rotation in the magnetic field of the earth (690 mG) was observed, giving for theg-factor of the 63 P 1-state $$g(Hg, 6^3 P_1 ) = 1.35 \pm 0.10.$$ This value is in agreement with the more precise values determined by other techniques. Shielding of the earth's field gave a nearly unattenuated angular correlation, with an integral attenuation factor of $$G_2 = 0.98 \pm 0.06.$$ The value of the angular correlation coefficientA 2. $$A_2 = - 0.188 \pm 0.009,$$ is in good agreement with the expected average value for the natural isotope mixture $$\overline {A_2^{theor} } = - 0.196.$$ A third measurement in an external magnetic field of 5.6 G showed several complete spin rotations. A nice fit was possible by using the superposition of all six participating cascades in the hyperfine level schemes of the different isotopes. The theoretical anisotropies,g F -values, and intensities were inserted according to natural isotope abundances. From the time differential measurements also a value for the lifetime of the Hg-63 P 1-level was derived. The result $$\tau (Hg, 6^3 P_1 ) = (120 \pm 2) nsec$$ is in agreement with earlier measurements. Further applications of the method are discussed.

Stationary collisionless shock waves in an initial plasma with high ion temperature

Abstract: Stationary collisonless shock waves propagating perpendicularly to an initial magnetic field are produced by the fast-rising magnetic field\((\dot B = 7 \cdot 10^{10} G/sec)\) of a theta pinch (coil diameter 16 cm, coil length 60 cm).

A Si(Li) detector system for conversion coefficient measurements and application to the decays of51Cr and87Y

Abstract: An electron detector system with a 3 mm × 100 mm2 Si(Li) detector with a cooled FET and vacuum air lock for changing sources was constructed. The absolute efficiency was measured as a function of energy for use in the measurement ofK conversion coefficients. With the Si(Li) and a Ge(Li) detector, theK conversion coefficient of the 320 keV transition in51V was measured to be 0.00156 ± 0.00008 where theK conversion coefficients of the 661 and 279 keV transitions in137Ba and203Tl were used as standards. From absolute detection efficiency measurements, theK conversion coefficients of the 388 and 483 keV transitions in87Sr were measured to be 0.16 ± 0.02 and 0.0024 ± 0.0003, respectively.

Messung von Temperatur-Verteilungen im N 2 -Kaskadenbogen bis 26000 °K

Abstract: On a stationary, flowless and cylindrical nitrogen arc (1 atm, 5 mm O), the radial temperature distributions are measured spectroscopically for the current range of 5–570 A in steps of between 5 and 50 A. At the highest current of 570 A the power input amounts to 18 kW/cm arc length and to 12 kW/cm2 wall load. The temperatures attain a maximum of 26,000 °K corresponding to a degree of ionisation of 115%. The emission ofN III-lines confirms the occurance of a partially double ionisation of the nitrogen. The intensities of molecular bands together with severalN I- andN II-lines are measured side on be means of electronic registration, whilst that of the lineN III 4103 A is recorded photographically.

Derp 3/2-Analogzustand in51V

Abstract: In an investigation ofT=7/2 analogue states in51V the50Ti(p, γ) excitation curve has been measured for proton bombarding energies 1280–1480 keV and 2340–2660 keV. From the (p, γ) resonances 29 new virtual levels in the region of 9316–9510 keV excitation energy in51V were determined. The strong resonance atEp=1 371 keV has been identified as the isobaric analogue state of the51Ti ground state by determining spin and parity of this resonance to be 3/2−. There is no evidence for a strong analogue resonance in51V corresponding to the 1.16 MeVp1/2 state in51Ti. The γ-decay of thep3/2 analogue state has been studied by measuring branching ratios and angular distributions of primary γ-transitions with a Ge(Li) detector.M1E2 mixing ratios have been determined for these transitions. The total width of the resonance for γ-decay is found to be Γγ=1.6±0.4 eV. New bound levels in51V have been introduced at 3576, 4651 and 4661 keV excitation energy. TheJπ values of the 3085, 4770, and 4863 keV states are determined to be 5/2−, 5/2−, 3/2−, respectively. The analogue-antianalogueM1 transition strength is found to be considerably reduced compared to the situation ins-d shell nuclei.

He5 scattering states in the refined cluster function representation

Abstract: As a first application of the refined cluster model reaction theory we calculated the scattering states of He5 using a specific ansatz for the nucleon-nucleon forces. He4-n and H3-d channels are considered only. Our results agree qualitatively with the experimental values if available; in particular we were able to explain the narrow resonance in theD3/2 He4-n channel as a consequence of the strong coupling to theS3/2T-d channel.

Messung der spezifischen Wärme von abschreckend kondensierten Indium-, Blei- und Wismut-Schichten bei tiefer Temperatur

Abstract: Thin metal films are evaporated onto a cooled Be-foil at 25–32 °K in high vacuum. After condensation the films have a large degree of disorder. The specific heat is measured in the temperature range from 5–8 °K after condensation and after annealing. No differences in the specific heat are found for disordered and annealed In- and Pb-films. The specific heat of amorphous Bi-films, however, is 1.7 times larger than that of crystalline films. The results are discussed together with investigations of disordered films by superconducting tunneling.

Levels of118Sn populated in the decay of118In and118Sb isomers

Abstract: Gamma-rays in the disintegration of 5.0 s (1+), 8.5 s (7−, 8−), and 4.4 min (4+, 5+)118In isomers and of 3.5 min (1+) and 5.1 h (8−)118Sb isomers have been investigated using Ge(Li) detectors and Ge(Li)-NaI(Tl) coincidence spectrometers. The decay schemes of these isomers have been constructed incorporating 17 levels in the product nucleus,118Sn, at the following energies (in keV): 0 (0+), 1229.5 (2+), 1757.5 (0+), 2043.1 (2+), 2056.4 (0+), 2280.3 (4+), 2321.3 (5−), 2326.4 (1+, 2+), 2402.7 (4+), 2488.8 (4+), 2496.5 (0+), 2575.2 (7−), 2677.3, 2733.7 (2+), 2929.8, 2963.5 (4+), and 3137.1 (0+). The structure of118Sn is briefly discussed in view of results from recent quasiparticle-model calculations.

Local current commutators

Abstract: The predictive power of current algebra relations is discussed using models for the spectral functions of current commutator matrix elements. The functions constructed fulfill the requirements of covariance, locality and spectrum conditions. Thus, the current algebra constraints can easily be imposed. In these models the formfactors are described by superpositions of poles. For simplicity only spin zero states are taken into account.

Experimental study of the isomeric states 101m Ru, 103m Ru and 101m Tc

Abstract: In natural Ruthenium isomeric states were produced by photonuclear reactions with LINAC Bremsstrahlung of 26 MeV. They were identified as: 526.6±0.7 keVT 1/2=22.5±0.5 μsec in101Ru 192.0±0.2 keVT 1/2=760±50 μsec in101Tc 210.9±0.2 keVT 1/2=1560±50 μsec in103Ru The experimental techniques are described.