Table of contents

The mean free path for inelastic interactions of ⁶Li in emulsion is measured and found not to be in systematic agreement with the different known theoretical parameterizations. This may be attributed to the loosely bound structure of ⁶Li nuclei. Possible internal structures of ⁶Li nuclei are investigated via the analysis of the shower particles multiplicity distributions for inclusive and central ⁶Li-Em interactions. In this analysis the experimental P-Em, d-Em and α-Em data are used as inputs for folding the corresponding distributions for ⁶Li-Em interactions. The results from central collisions favour the (α + d) cluster structure for the incident ⁶Li nuclei.

We present an analysis of dielectronic satellite spectra of Ne-like ion resonance lines for elements from Cr to Ni. For these low-Z elements, we use spectra from strongly underionized CO₂-laser produced plasma to minimize the emission from open L-shell ions. This simplifies the spectra and allows the identification of satellite lines caused by radiative transitions from autoionizing states of sodium like ions. Good agreement between the satellite structure calculations and the experimental emission spectra is obtained.

We present an analysis of dielectronic satellite spectra of 2p⁶-2s2p⁶3p Ne-like krypton resonance lines. The satellite structure was registered with high (better than λ/Δλ > 3500) spectral resolution in the emission of a laser irradiated gas puff target. We perform an unambiguous identification of satellite lines caused by radiative transitions from autoionizing states of sodium-like krypton ions. A total of about 20 spectral features are identified, most of them for the first time. Very good agreement between the satellite structure calculations and experimental emission spectra is obtained.

Fourier transform spectroscopy has been applied for recording spectra of palladium in the wavelength region 1900-5000 Å. 596 classified Pd II lines are given with high wavelength accuracy. 32 new energy levels were obtained. A total of 129 levels belonging to the 4d⁹, 4d⁷5s², 4d⁸5s, 4d⁸6s, 4d⁸5d and 4d⁸5p configurations are reported.

The probabilities and cross sections of the helium 1s^{2 1}S → 2s^{2 1}S excitation in collisions of protons, antiprotons and multicharged ions with helium atoms have been calculated with allowance for the configuration interaction at ion energies ranging from 0.1 to 10 MeV/u. The mechanisms for the helium 2a^{2 1}S autoionizing state excitation are determined, the role of the continuous spectrum states at the helium double-electron excitation is examined. The criterion of the helium atom nucleus effective charge choice at the description of a collision process is established. The comparison of the present results with the available experimental data and with the results received in different theoretical approaches has been made.

The motion of an individual electron in a FEL in a field configuration consisting of an ideal quadrupole-wiggler field and uniform axial-guide field, is shown to be nonintegrable in Hamiltonian formulations and can become chaotic for certain initial conditions. The presence of chaos, which is induced by the transverse spatial inhomogenieties in the wiggler field; and the self-fields produced by the space charge and current, poses limits on the wiggler field amplitude and the beam size for beam propagation in Free-Electron Laser operation. Upon plotting Poincaré surface-of-section maps, it is shown that the electron dynamics is chaotic.

An alternative approach to the Pomraning-Eddington method was proposed to bypass the choice of the weight functions used for enforcing the boundary conditions. This approach, where variational technique is used in the integral form of the radiative transfer equation to find the constants of integration, extends the range of the validity of the Pomraning-Eddington method. The method is applied to an anisotropic radiative transfer problem in turbid media. The boundaries of the medium are allowed to possess specular reflection. Different phase functions are considered and results are presented.

Mie-series for cross-sections of light scattering from spherical particles are converted into integral form with a simple integrand. The transformation is due to essential compensations in the (electrically polarized) part of the Mie cross-section.

A new approximate formula for cross-sections is obtained, having a wide region of validity, overlapping with that of van de Hulst's formula.

The magnetofluid dynamic stability of two streaming fluids cylindrical interface has been developed based on the linear perturbation technique. Each of the two fluids is perfectly conducting, non-viscous and incompressible. The model is acting upon the capillary, inertia, pressure gradient and electromagnetic forces. The outer fluid is bounded by a solid cylindrical interface. A general dispersion relation is derived and studied analytically and the results are confirmed numerically. The capillary force is, acting along the fluids interface, destabilizing only for long symmetric wavelengths while it is stabilizing for all others. The electromagnetic forces are strongly stabilizing in each fluid. Above a certain value of the applicable magnetic field strength, the stabilizing influence of a magnetic field suppresses completely the capillary instability. The thicker the outer fluid cylinder the greater is the destabilizing influence of surface tension for the same values of the magnetic field intensity and the densities ratio of (outer-interior) fluids. The latter is strongly stabilizing for the same values of the magnetic field intensity and the outer fluid thickness.

The linear excitation of long wavelength oscillations in the electron beam-plasma system is investigated. Under the condition of quasineutrality the unperturbed densities of the beam and plasma are considered to be arbitrary (i.e. no restriction about these densities). The linear dispersion relations and growth rates describing the interactions between cold beam-cold plasma, hot beam-cold plasma and cold beam-hot plasma are obtained. It is shown that at ω ≪ ω_p the growth rate is reduced by a factor 1/1 + (ω_b/ω_p)². Also, for the two cases hot beam-cold plasma, cold beam-hot plasma and under the condition n_op ≪ n_ob, it is found that the long wavelength oscillations become unstable at the same time.

The well-known approach of kinetic theory of nonlinear wave interaction in plasma, based on the introduction of many-index nonlinear dielectric tensors, is applied to obtain the expressions for nonlinear current-densities as well as for generated quasistationary magnetic fields. A transition to the case of cold magnetoactive plasma is proceeded. The results appear to be in agreement with those obtained in the limits of the hydrodynamic approach.

The effects of shear in the E × B rotation velocity are studied in connection with the recently discovered electron temperature gradient driven instability induced by conducting end plates. The transition between the temperature gradient driven mode and the Helmholtz-Kelvin instability is studied.

The modulational instability development of Langmuir and electromagnetic waves is reviewed in highly collisional plasmas where the characteristic frequency Ω of the modulated perturbations is much less than v_eff, the effective electron collision frequency. All calculations are based on Braginskii's system of hydrodynamic equations in collision-dominated plasmas and use a simple and universal formalism including new methods developed for description of the modulational effects in arbitrary media. It is demonstrated that the modulational instability for the situation considered is mostly determined by collisional effects (differential Joule heating nonlinearity), in contrast to the wellknown modulational instability in collisionless plasmas (where ponderomotive force nonlinearity dominates). Rates and thresholds of the instabilities are found in various limits. Coupled nonlinear Langmuir and sound waves are presented. Theory taking into account combined effect of the differential Joule heating, ponderomotive force and relativistic electron mass variation on the instability of electromagnetic waves is presented. Effects of magnetic fields are briefly discussed.

Introducing the Dyson-Maleev transformation, the coherent-state ansatz and the time-dependent variation principle, we obtain two partial differential equations of motion in type-I antiferromagnets. Employing the method of multiple scales, we reduce these equations into the envelope function equations and force the amplitude function to satisfy a nonlinear Schrödinger equation. Using the inverse-scattering transformation, we discuss solitary magnon localization, two magnon bound states and gap solitons.

In May 1993 the first in a series of Euroconferences organized within the Human Capital and Mobility programme of the Commission of the European Communities (CEC) was arranged at Studsvik, Sweden, by the Studsvik Neutron Research Laboratory (NFL). According to the CEC objectives, a Euroconference should be a meeting at the cutting edge of scientific or technical knowledge and it should give young and promising European researchers, through their active participation in such a meeting, the possibility to benefit from contacts with high level scientists. In order to achieve this goal the international organizing committee, consisting of Prof. U. Dahlborg (chairman, NFL and Royal Institute of Technology (KTH), Stockholm), Prof. R. Scherm (Braunschweig and Grenoble), Dr. H. Gamari-Seale (Athens), Prof. M. Fontana (Parma), Prof. M. M. R. R. Costa (Coimbra), Dr. F. J. Bermejo (Madrid), and Dr. M. Dahlborg (secretary, Stockholm and Nancy), decided that the first Euroconference at Studsvik should not be too large but that the intimate character of the meeting was more important. Thus, the maximum number of participants was set at about 70. Out of these, the participation of 22 young researchers, the majority of them were coming from less-favored regions in Europe, was completely financed by the CEC but the conference was also co-sponsored by the Swedish Natural Research Council. It was considered by the committee to be a very important task of the Euroconference to show the young scientists, some of whom did not have any experience in the use of the neutron scattering technique, what they may achieve by adding the technique to their research arsenal.

The subject for this first Euroconference was chosen to be Neutrons in Surface Science and at Interfaces. The five day meeting was divided in two parts. The first two days were of school-type intended to give the young participants a firm background in the theory and the experimental technique, as well as to demonstrate the applicability of the neutron scattering technique to different scientific research problems. To this end the invited scientists, Prof. S . Dietrich (Wuppertal), Prof. P. Mangin (Nancy), Dr. R. Richardson (Bristol), Dr. R. K. Thomas (Oxford) and Prof. J. W. White (Canberra) gave reviews of different fields of surface science while Dr. J. Penfold (Rutherford) was covering the experimental techniques used in neutron reflectometry. During the remaining three days a regular international conference with invited and contributed lectures by senior and young scientists was arranged. Invited lecturers to the conference were Dr. J. J. Benattar (Saclay), Dr. J. M. Gay (Marseille), Prof. F. Mezei (Berlin) and Prof. D. Richter (Jülich).

Professor Clifford G. Shull, who the day before the Euroconference started received the well renowned Aminoff prize from the Royal Academy of Sciences in Stockholm for his outstanding contribution to the development of neutron diffraction, was specially invited to visit Studsvik during the conference where he also gave his much appreciated academy lecture.

Two satellite meetings were arranged in connection with the Euroconference, one, a course organized within the Graduate School Programme in Materials Science at the Royal Institute of Technology (KTH), Stockholm, by Prof. U. Dahlborg, on Thermal Neutrons in Applied Sciences and Material Technology and the other the annual Neutron Scattering Days at NFL, this year devoted to The Use of Neutrons for Studies of Residual Stress and arranged by Prof. K. Sköld (Studsvik). To both these meetings well renowned international experts, Prof. M. Schlenker (Grenoble), Dr. R. McGreevy (Studsvik), Dr. R. Illić (Ljubljana), Prof. T. Eriksen (Stockholm) and Dr. T. Holden (Chalk River) were invited.

Hopefully, the proceedings of the Euroconference are giving a flavor of the quality of the contributions. However, the collection of contributed papers does not illustrate all the activity at the Euroconference. In addition every young scientist was presenting a poster on his or her research and, as mentioned above, there were a large number of invited talks as well as some oral contributions. The vivid discussions both during the school and the conference as well as the stimulating atmosphere created by all the participants, young and less young, are not revealed in the proceedings but are nevertheless remembered with pleasure.

X-ray reflectivity at glancing angles is a very sensitive method which can be applied to the study of very different kinds of physical problems involving ultra thin films. In this paper we show: first, how we have solved a problem which dates back over three centuries: the structure of the Newton black film, second, how to investigate thermally induced capillary waves on a Langmuir monolayer of amphiphilic molecules and, finally, how to determine, with a very high accuracy, the density of a thin film of silica.

A study of monochromator-type neutron mirrors, produced under different sputtering conditions by a triode sputtering system is presented, and the effect on the magnetic behaviour and the film structure is revealed. Special attention was paid to the dependence of the interface roughness in respect to the deposition parameters. A structural characterization of the specimen was performed by x-ray reflectometry and diffraction, supported by transmission electron microscopy and electron diffraction studies, made on ultramicrotom cuts oriented perpendicular to the surface. SQUID magnetometry and polarized neutron reflectometry in combination with a simulation of the reflection data on the Co₁₁Fe₈₉-Si system was used to examine the magnetization profile and its evanescence near the chemical interface. Mößbauer spectroscopy clarified the model of interpretation.

Measurements performed by means of Small Angle Neutron Scattering (SANS), Incoherent Quasi Elastic Neutron Scattering (IQENS) and Fourier Transform Infrared (FTIR) techniques on reversed water-in-oil micelles are presented and analysed. This ternary system, constituted by water/surfactant Me⁺ⁿ(AOT)_n/oil forms droplets whose shapes and sizes have been determined by SANS. Moreover a strong confinement effect for the H₂O molecules, whose dynamical properties reflect themselves on the O-H stretching band (FTIR) and on the low frequency diffusive motions (IQENS), is revealed.

Neutron diffraction and quasielastic scattering are well-suited techniques for surface melting studies. Indeed, they allow measurements of disorder and translational diffusion in the quasi-liquid layer which intervenes at the solid-vapour interface (surface) of a crystal, when the bulk melting temperature is approached. The principal results of neutron scattering studies of van der Waals films deposited on powdered graphite and MgO substrates are reviewed.

On the spectrometer MURN at the pulsed reactor IBR-2 dry Portland cement, silica fume, and a hydrating Portland cement paste were studied by small-angle neutron scattering (SANS). By using the TOF-method a momentum transfer from 0.07 nm^-1 to 7 nm^-1 is detectable.

Every component (dry cement powder, clinker minerals, hydrating cement pastes) shows a different scattering behaviour. In the measured Q-region the hardening cement paste does not show a Porod-like behaviour of SANS-curves. In contrast the Porod's potential law holds for dry powder samples of clinker minerals and silica fume. In experiments carried out to observe the hydration progress within the first 321 days the characteristics of the scattering curves (potential behaviour, the radius of gyration, and the macroscopic scattering cross section at Q = 0 nm^-1) were measured. Some evolution of the inner structure of the hardened cement paste was noted.

Incoherent Quasi-Elastic Neutron Scattering, ultrasonic velocity and density measurements on poly(ethylene oxide) aqueous solutions are presented. The neutron analysis indicates the existence of strongly confined water and furnish an estimated value of the confined region size of ∼3 Å. The behaviour of the excess adiabatic compressibility as a function of concentration and temperature shows the presence of a more compact arrangement in which up to two water molecules for each monomeric unity are allowed.

The structure and physical properties of the NdBa_2-xSr_xCu₃O₇ system has been studied in relation to the strontium content x. The orthorhombic structure transforms to tetragonal beyond x = 0.6, single phase samples are produced in the range of x = 0.0 to 1.0 and all the studied samples are superconductors.

The orthorhombic HoNiSn compound with space group Pnma is antiferromagnetic below 4.2 K. The magnetic structure of this compound is of a sine modulated type with a propagation vector k = [0.3593, 0.3337, 0.0]. The holmium magnetic moment is equal to 8.5 μ_B and its direction lies in the (a, b) plane.