Search for scalar and pseudoscalar bosons emitted in nuclear decays via their interactions

A search for light penetrating scalar and pseudoscalar bosons has been performed at the Jülich nuclear-reactor FRJ-1 (Merlin). In nuclear deexcitation processes pseudoscalar particles should be emitted in magnetic transitions and scalar particles in electric transitions. The experiment relies on the detection of the interaction products from the conversion of bosons in the field of an electron or a nucleus with a rotatable multi-scintillator system. The geometrical arrangement of the scintillators allows to distinguish between scalar and pseudoscalar particles via the different angular distributions of the final state photons. We obtain as upper limits for the product of production ratio and interaction cross sectionW for pseudoscalar particles W}<6.9>^–40 cm², and for scalar particles W}<1.3>^–39 cm² with 90% confidence.We gratefully acknowledge the support of this experiment by the KFA Jülich and we are very grateful for most valuable discussions with H. Bechteler, H.R. Koch, O.W.B. Schult, H. Seyfarth and A. Zehnder. We would like to express our thanks to the personnel of the reactor Merlin. We also wish to acknowledge the excellent work of the technical staff of our institute in particular to E. Hermens and R. Pahlke. Thanks to H. Geller and C. Latsch who assisted with the runs.     

Energy transfer to a copper surface by low energy noble gas ion bombardment

The energy transferred to a copper surface by bombardment with Xe⁺, Ar⁺, and He⁺ ions with kinetic energies in the range 100–4000 eV has been studied by our group in previous experiments. There were significant experimental uncertainties for that data at energies below about 200 eV. The present investigation overlaps the previous work, extends the energy range to 10 eV, and includes data for Ne⁺. Particular emphasis is placed on the energy range below 200eV. A specially designed ion source was employed in these experiments. A polycrystalline copper film deposited onto a highly sensitive calorimeter was used as the target material. The results show that the Xe⁺ ion deposits more than 97% of its energy over the entire range investigated whereas the lighter ions deposit a decreasing fraction of their energy below about 1 keV. The decrease is largest for the lightest ion (He⁺). In all cases the deposited energy is about or more than 70% of the incident energy. It will be shown that the present results are in agreement with previous measurements for copper and are qualitatively in good agreement with computer calculations using the TRIM.SP code.On leave from: Institut für Schicht- und Ionentechnik, Forschungszentrum Jülich GmbH, W-5170 Jülich, Fed. Rep. Germany     

Real-space renormalization for arbitrary single-site potential

A simple real-space renormalization in the spirit of Niemeier-van Leeuwen is used to study the critical behavior of a ⁴-model in two and three dimensions. The block spins are defined such that the single-site potential is unchanged under the transformation. Both a first order cumulant approximation and a mean-field truncation are used. For a widely varying double-well potential only a small dependence of the critical exponents upon the detailed structure of the potential is found in agreement with the universality principle. The (nonuniversal) critical temperature is in good agreement with computer simulations. The method can easily be generalized to arbitrary single-site potentials.Work performed at the Institut für Festkörperforschung, Kernforschungsanlage Jülich, D-5170 Jülich, Fed. Rep. Germany     

Polarized He neutron spin filter program at the JCNS

Polarized neutron instruments will occupy about 80% of the Jülich Centre for Neutron Science (JCNS) instrument park. A successful polarized ³He program will be integral to many of these instruments. We have been focusing the developments on spin-exchange optical pumping (SEOP) to polarize the ³He gas in situ. Where possible, in situ polarization using the SEOP method will provide higher time averaged performance of the instruments. Further this allows a custom-built and independent source of polarized ³He to be developed optimized for each instruments demands. In this paper we will: present an argument for the advantages of in situ polarization; describe an in situ polarizer we have constructed, and initial tests of its performance; describe testing of polarization analysis for small angle neutron scattering on biological samples, and our plans for an in situ polarizer for this application.     

Bremsstrahlung from solitons

One dimensional solitons behave like Newtonian particles if subjected to external forces, as has been shown by Fogel et al. for the case of sine-Gordon solitons. We add here the observation that they also emit free radiation—i.e. Bremsstrahlung—if accelerated by an external force. The radiation spectrum is calculated for the sine Gordon case.Work supported in part by the National Science Foundation, Grant DMR 74-23494 and in part by a travel grant from the KFA Jülich     

Hypernuclear properties derived from the Jülich hyperon-nucleon interaction (in comparison with the Nijmegen interactions)

TheG-matrix interactions are derived from the Jülich YN interaction models A and B, and compared with those from the Nijmegen models. The DDHF calculations for heavy A hypernuclei and the shell-model analysis for spin-doublet states of light hypernuclei are performed by use of theG-matrix interactions. It is demonstrated that the OBE models can be tested by the hypernuclear calculations.     

Remarks on conformal invariance

The existence of unitary representations for the special Conformal Group, is investigated for free fields in any dimension, and the connection between the correct transformation properties of the fields and weak conformal invariance pointed out.Partially supported by the Brazilian National Research Council, and K.F.A. Jülich, Germany.On leave of absence from University of Bielefeld, Bielefeld (Germany).     

Growth atomic mechanisms of pulsed laser deposited La modified- $\mathsf{PbTiO_3}$ perovskites

The microstructure and morphology of 100/001-oriented La modified-PbTiO₃ (PLT) films grown by pulsed laser deposition have been analyzed and elucidated within the framework of morphology evolution models, such as the Dynamic Scaling Theory and Structure Zone Model. The experimental results were obtained from X-ray diffraction, atomic force microscopy and cross-section scanning electron microscopy. PLT grows with a compact columnar microstructure. The columns are formed by coherently grouped grains and show oblique walls and rounded tops. Connecting the experimental results with the morphology evolution models, the growth mechanisms involved in the deposition process were identified. While inside each column, the existing Pb vacancies govern the coarsening and coalescence of the grains, a non-local effect of geometric shadowing of the incident particle flux during growth controls competition between columns and their coarsening.Received: 18 June 2003, Published online: 22 September 2003PACS: 68.55.-a Thin film structure and morphology - 81.15.Fg Laser deposition - 77.84.Dy Niobates, titanates, tantalates, PZT ceramics, etc.E. Vasco: Current address: Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich, GermanyC. Polop: Current address: I. Physikalisches Institut, RWTH-Aachen, 52056 Aachen, Germany     

Self-consistent alloy treatment of the periodic anderson model: Susceptibility and specific heat of intermediate valence compounds

To describe the electronic properties of mixed valence compounds we study the periodic Anderson model within the frame of the alloy analog approximation. In this approach the model Hamiltonian is replaced by the sum of two single-particle alloy Hamiltonians the parameters of which have to be determined self-consistently. The alloy problem is solved within the coherent potential approximation. In contrast to other treatments of the periodic Anderson model this approximation scheme is exact in both trivially solvable limits of vanishing hybridization and Coulomb repulsion, respectively. For model parameters corresponding to a mixed valence situation only nonmagnetic solutions of the self-consistency equations exist. After discussing the limit of small hybridization analytically we numerically calculate the magnetic susceptibility and the electronic specific heat as a function of temperature for realistic values of the hybridization and Coulomb repulsion. The results are in very good qualitative agreement with experimental data.Work performed within the research program of the Sonderforschungsbereich 125 Aachen/Jülich/Köln     

Invariances of 2d representations characterized by incommensurate wave vectors

The projection operator technique has been used to derive the forms of invariants of real two-dimensional and complex one-dimensional irreducible representations. The representations are characterised by the wave vectors which do not belong to the high-symmetry points of the Brillouin zone. For these active representations and for all space groups a complete list of invariants is given.The work was partially performed during our stay in Departement Natuurkunde, Universiteit Antwerpen (UIA), Wilrijk, Belgium (R.S.) and in Institut für Festkörperforschung, KFA, Jülich, BRD, (K.P)     

Self-consistent theory of pairbreaking in kondo superconductors

A theory is presented for the calculation of equilibrium properties of superconductors containing magnetic impuritiesof finite concentration. The theory is based on the Nagaoka-Suhl approach to thes — d model and treats finite impurity concentrations within a self-consistentT-matrix-approximation. An integral equation is derived for the pairbreaking parameter which describes de-pairing of Cooper pairs by spin flip scattering. Numerical solutions of this equation are used to compute the phase diagram in the temperature-concentration-plane and the transition-temperature-dependence of the upper critical field. These calculations are in good agreement with experimental data on LaCeAl₂-samples. In addition, the recent discovery of three normal superconducting transitions in LaCeY is discussed quantitatively.Work performed within the research program of the Sonderforschungsbereich 125 Aachen/Jülich/Köln     

Vertex form factors of the rho-meson nucleon interaction at low momentum transfer

We calculated the one pion loop contributions to the form factors of the rho-nucleon interaction within a field theoretical model using effective Lagrangians. The results show that the tensor interaction is likely to be described well within such an approach. We obtain a magnetic coupling in the range of 3.5–7.1 atQ ²=0, depending on the choice of pion-nucleon form factor and a dipole form for theQ ² dependence tensor form factor with a scale of roughly 900 MeV for space-like momentum transfer. The results agree with the findings of the recent analysis of thep-N interaction and support a small scale parameter (0.5 GeV) for the pion-nucleon form factor.This work is supported by BMFT (06BO7027) and COSY-KFA Jülich (41140512)     

Generalized transfer formalism and application to random Ising models

We derive an exact formula for the critical temperature of any planar Ising model built up by periodic repetition of an elementary cell. It is shown that the weight of models with analytic free energy increases with increasing size of the elementary cell. As an application we discuss phase diagrams of Ising models with restricted randomness where the coupling arrangement is governed by the probability law of the popular binary distribution.Work performed within the research program of the Sonderforschungsbereich 125 Aachen/Jülich/Köln; also part of: P. Hoever, Dissertation, Köln 1981 (unpublished)     

Development and applications of polarized electron spectroscopy to solids and surfaces

Recent milestones in the development of spin-polarized electron spectroscopy, along with trends in current applications to magnetic solids and surfaces, are reviewed. Emphasis is placed on the work performed in the Jülich-Cologne area since 1978 as it was originally promoted also by Bernd Mühlschlegel.Dedicated to B. Mühlschlegel on the occasion of the 60th birthday     

The mean jump number of a vacancy in annealing experiments

In this paper we shall calculate the mean jump number ¯n which a vacancy makes during its life in a nearly perfect lattice, before it is absorbed in a sink. We suppose that the sinks are unfillable and that there is no interaction between the vacancies. The dependence of ¯n on the shape and size of the sink in the f.c.c. lattice will be discussed.The author is indebted to Dr. K. Míek and L. Smrka for stimulating discussions and Dr. J. Polák for critical remarks.This paper was read at the International Conference on Vacancies and Interstitials in Metals in KFA Jülich, September 1968.     

Flow Measurements with Gundestrup Probe: Problems and Solutions

Electrical probes are an excellent tool for local measurements of basic plasma parameters, fluctuations and plasma flow studies. However, the application of a probe diagnostics is usually accompanied by theoretical restrictions, practical limitations and problems. In this paper we describe the new probe system recently developed for the TOMAS toroidal device (Forschungszentrum Jülich, Germany). This system comprises multi-collector Gundestrup probe for flow measurements and Langmuir probe for plasma characterization. During development of such a system, several physical and technical issues, which are common for probe applications, were solved or essentially suppressed.     

On Suhl's dispersion equations for dilute magnetic alloys in a finite magnetic field

A one dimensional, nonlinear, singular integral equation was recently shown to be equivalent to Suhl's dispersion equations for the Kondo-problem of a half-spin magnetic impurity in a finite magnetic field. We investigate this integral equation further analytically and numerically and obtain numerical solutions which we use for a calculation of transport coefficients. The normal part of the scattering potential of the magnetic impurity is included via ans-wave phase shift. The transport coefficients are universal functions of the ratiosT/T _K andB/B _K of the temperatureT and the zero magnetic field Kondo-temperatureT _K and of the magnetic inductionB and the Kondo magnetic inductionB _K. We find maxima in the electrical and thermal resistivities as functions ofT/T _K forBB _K. These are typical Kondo phenomena, and can be influenced by. Interference of and the phases of Kondo-scattering amplitudes leads to dramatic effects in the thermopower and the Hall coefficient.SFB 125The numerical part of this work was performed at the Institut für Festkörperforschung, Kernforschungsanlage Jülich, F.R. Germany     

The superconducting transition temperature of Pb1−x Mn x films

Results of the superconducting transition temperatureT _c of amorphous and microcrystalline films of lead doped with manganese as magnetic impurity are reported in this work. The amorphous films show an Abrikosov-Gor'kov behaviour, whereas for the crystalline films there is a much smaller depression and a peak for higher Mn concentrations, which indicates a region of coexistence of superconductivity and magnetic ordering as a spinglass.Supported by the Deutsche Forschungsgemeinschaft in the Sonderforschungsbereich 125, Fehlordnung in Metallen — Aachen, Jülich, Köln     

Statistical theory of pinning on point defects

The statistical treatment of pinning on point defects is given including the correlations of the number of defects in neighbouring volumes (the interaction of these volumes with the fluxoid is taken as the elementary interaction causing the pinning). For higher defect densities, the agreement with the experiments on niobium is better than with the previous theory. This method of correlations seemed suitable for study the effect of cutting-off the small elementary interactions and for the replacement of the Gauss distribution function by the Poisson distribution function for the number of defects in the elementary volumes. Both these efforts give negative results with respect to the experiments; so far we are therefore not able to explain quantitatively the large increase of the pinning force at small defect densities and small magnetic fields, as well as its decrease to zero always for fields smaller thanH _c2 . The attractive interaction between the flux lines in type II superconductors with small Ginzburg-Landau parameter could give a qualitative explanation of the enhancement of the pinning at small defect densities.Part of this work was performed during the author's stay at the Institut für Festkörperforschung, KFA Jülich. The kind hospitality of this institute and many valuable discussions, especially with Dr. H.Ullmaier, are acknowledged.     

The massive thirring model as continuum limit of the Heisenberg model

The continuum limit of the lattice fermion version of the anisotropic spin-1/2 Heisenberg chain is reconsidered. It is shown that certain matrix elements of the Heisenberg Hamiltonian converge towards corresponding matrix elements of a massive Thirring model as previously suggested by Luther and Peschel. However, the result is only to first order consistent with the exactly known spectral and critical properties of the two models. Going beyond previous results in addition to the coupling constant of the massive Thirring model the kinetic energy coefficient comes out correctly to the first order of the lattice fermion interaction, too. Emphasizing the role of the underlying Hilbert spaces the discrepancy in higher orders is explained.Work performed within the research program of the Sonderforschungsbereich 125 Aachen, Jülich, Köln