Showing papers by "Paul Scherrer Institute published in 1988"

Optical Superresolution Using Solid-State Cameras And Digita; Signal Processing

Abstract: A common problem in optical metrology is the determination of the exact location of an edge (a black/white transition). The use of cameras for this task has been restricted in the past because of their limited number of pixels and the lack of methods for subpixel accuracy edge detection. Analysis of the optical and electronic parts of modern solid-state cameras shows that it is possible to determine the exact location of an edge to subpixel accuracy, independently of the system's modulation transfer function. A novel algorithm for this purpose is presented together with an expression for the precision of the edge location as a function of pixel noise and edge step height. Experimental verification was carried out using a modified CCD camera coupled to an intelligent framestore (smart camera). Under optimum conditions the measured accuracy for the edge position was better than 1/140 of the pixel period, corresponding to less than 120 nm on the sensor surface of the camera. Applications of this novel method in metrology and micrometrology are discussed.

Short‐Range Order and Atomic Displacements in Ni–20 at% Cr Single Crystals

Abstract: Ni–20 at% Cr single crystals aged at 741, 828, and 973 K for up to 480 h are investigated by elastic diffuse neutron scattering. The contributions due to short-range order and atomic size effect are separated by a least-squares fitting procedure. The short-range order with diffuse intensity maxima at l 1/2 0 positions increases with decreasing ageing temperature. In comparison, the intensity due to atomic displacements is weak. For the three ageing temperatures investigated the effective pair potentials, determined from the Clapp-Moss high temperature approximation as well as with an inverse Monte-Carlo method, are very similar. Ni–20 At% Cr-Einkristalle, die bei 741, 828 und 973 K bis zu 480 h ausgelagert wurden, werden mit elastischer diffuser Neutronenstreuung untersucht. Die Beitrage von Nahordnung und atomaren Verzerrungen werden nach der Methode der kleinsten Fehlerquadrate separiert. Die Nahordnung mit Intensitatsmaxima an l 1/2 0 Positionen nimmt mit abnehmender Auslagerungstemperatur zu. Vergleichsweise niedrig ist der Beitrag der atomaren Verzerrungen. Bei den drei Auslagerungstemperaturen werden sehr ahnliche effektive Paarpotentiale gefunden, sowohl nach der Clapp-Moss-Hochtemperaturnaherung als auch nach einer inversen Monte-Carlo-Methode.

Adsorption of Cu and Ag atoms on Si(111) surfaces: Local density functional determination of geometries and electronic structures

Abstract: The electronic structures, adsorption geometries, chemisorption energies, and vibrational frequencies of single Cu and Ag atoms on Si(111) surfaces are determined by self‐consistent total energy calculations using first principles, local density functional theory, with a numerical basis for a cluster of 20 Si atoms. The binding energy results reveal that both Cu and Ag adsorb in threefold hollow sites with equilibrium heights of 0.74 A (Cu) and 1.48 A (Ag) above the plane of the surface Si atoms. The adsorption energies are found to be 92 kcal/mol for Cu and 72 kcal/mol for Ag. Assuming a rigid substrate, the calculated frequencies of the perpendicular vibrational modes are 58 cm−1 for Cu and 90 cm−1 for Ag. The lateral diffusion barriers, assuming an unreconstructed rigid Si(111) surface, are found to be 12 and 8 kcal/mol for Cu and Ag, respectively. Calculations for Cu and Ag atoms being moved towards the interior of the cluster, including geometric relaxation of the nearest‐neighbor Si atoms, demonstra...

The seasonal variation of 20 elements in 1st and 2nd year needles of Norway spruce, Picea abies (L.) Karst

Abstract: The concentration of 20 elements (including eight nutritional elements) in spruce needles was monitored by taking samples at nine different dates in a single year. On each date the youngest and the 1-year-old needles were collected at four different sites. The needles were washed with an organic solvent to remove surface contamination before analysis by instrumental neutron activation. Although the sites showed widely different concentrations for the same element, they could be treated as a uniform population using normalized concentration values. Taking the time dependence of the concentration and the ratio of the concentrations in new and old needles as criteria, the following three groups of elements could be distinguished: 9 group I —Ca, Sr, Ba, and Mn; group II — Al, Br, Co, Fe, Hg, La, Sc, Sb, and Zn; group III — K, Rb, Cs, P, and Cl. Mg and Na did not fit into any of these groups. Within group I and III elements the strongest variations occur during the growing season (late spring and early summer) and the weakest during the dormant season; the variation is greater in the younger needles. Group II elements show an approximately linear increase throughout the year in both the younger and older needles. The concentrations of elements of groups I and II increase with time, while those of group III decrease. Na is unique insofar as its concentration is influenced by foliar uptake of road de-icing salt. The concentration of elements belonging to the same group shows strong inter-element correlations. The grouping of elements deduced here shows similarities with the chemical nature of the elements and with their transportability within the plant.

Formal scattering theory approach to S-matrix relations in supersymmetric quantum mechanics.

Abstract: Combining the methods of scattering theory and supersymmetric quantum mechanics we obtain relations between the $S$ matrix and its supersymmetric partner. These relations involve only asymptotic quantities and do not require knowledge of the dynamical details. For example, for coupled channels with no threshold differences the relations involve the asymptotic normalization constant of the bound state removed by supersymmetry.

Optimizing deposition parameters of electron beam evaporated TiO 2 films

Abstract: A study of the major deposition parameters including source material, oxygen partial pressure, substrate temperature, and deposition rate affecting the optical quality of electron beam evaporated TiO(2) films is presented. After careful optimization of these parameters it is possible to reproducibly deposit TiO(2) films from TiO(2) source material mixed with 5% CeO(2) at an oxygen partial pressure of 5 x 10(-5) Torr, a substrate temperature of 320 degrees C, and a deposition rate of 2 A/s.

Corrosion Behaviour of British Magnox Waste Glass in Pure Water

Abstract: The corrosion behaviour of Magnox Waste (MW) glass in deionized water has been investigated under the aegis of the Japanese-Swedish-Swiss (JSS) project. The studies carried out at PSI and BNFL included static leaching and corrosion layer characterization. The results were used by HMI to derive the modelling parameters for the MW glass with the PHREEQE/GLASSOL codes. The silica concentration was found to strongly influence the corrosion rate of the glass. The MW glass selectively retains Cs due to the formation of a Cs-Mg-Al-Si-O-rich layer on its surface.

A Natural Analogue Study of Radionuclide Migration in a Water Conducting Fracture in Crystalline Rock

Abstract: A suite of elements including U, Th and the REE are examined in a rock drillcore, from the Böttstein granite of northern Switzerland, which is intersected by a (suspected) water carrying fracture. Examination of the natural decay series indicates a nonfractionated loss of U throughout the core over the last 300000 years or so. There has also been a more recent addition of \" 4 U and 2 3 0 Th to the rock in the vicinity of the fracture. REE data indicate the importance of previous alteration of the rock for later radionuclide uptake.

Process for the decontamination of surfaces

Abstract: In this decontamination process, the surfaces contaminated with radioactive substances, in particular on components of cooling circuits in nuclear reactors, are treated in a first treatment step with an aqueous decontamination solution, containing chromic acid and permanganic acid, at a temperature in the range from 270 to 350 K, in particular at usual room temperature. The contaminated surface layers are thus oxidized by means of the permanganic acid, while the effect of the chromic acid is that the modified surface layers do not adhere firmly. In a second treatment step, the surface layers thus modified are removed by a chemical treatment in the same temperature range, as a result of dissolution, or/and removed by mechanical or hydraulic action. Aqueous solutions of organic acids are suitable for the chemical treatment in the second treatment step, it also being advantageously possible to add reducing agents and complexing agents and/or corrosion inhibitors.

Polarization observables in. pi. d-italic-arrow-right elastic scattering: Analyzing powers tau/sub 22/ and iT/sub 11/

Abstract: The composite spin observable tau/sub 22/equivalent(T/sub 22/+T/sub 20// ..sqrt..6 ) has been measured at five incident pion energies between 134 and 294 MeV, in an angular range between 90/sup 0/ and 170/sup 0/, using a tensor-polarized deuterium target. New, accurate data for the vector analyzing power iT/sub 11/ were obtained at the same time. In combination with the results reported in part I of this series, our measurements allow us to determine the three analyzing powers T/sub 20/, T/sub 21/, and T/sub 22/, separately, and compare them with existing theoretical calculations, all of which fail, in one way or another, to reproduce the entire data set.

The study of prompt and delayed muon induced fission

Abstract: The mean life times of negative muons bound to actinide nuclei have been measured by detecting the time difference between a stopped muon and the arrival of fragments from delayed fission after muon capture. The deduced capture ratesΛc are 1.392(4)·107/s for237Np, 1.290(7)·107/s for242Pu and 1.240(7)·107/s for244Pu. The results are compared with published data for the fission and the neutron decay channels and for the electron decay of the bound muon. Including a former measurement ofΛc for239Pu, an isotopic dependence of the muon capture rates in the Pu isotopes is clearly observed.

Ionization of a polarized hydrogen atomic beam in an ECR discharge

Abstract: The production of an intense beam of polarized hydrogen ions with an ECR ionizer has been investigated. A deuteron tensor polarization of up to 85% of the theoretical value has been observed. The intensity is significantly improved compared to an electron beam ionizer.

Positive muons in bismuth: determination of their sites, detection of a large local lattice contraction and giant associated electric field gradients, evidence for short and long range diffusion

Abstract: Using a high purity Bi single crystal the temperature and orientation dependence of the zero and transverse field muon spin relaxation rate has been studied in detail. The results imply that the μ+ occupies one of the two possible interstitial sites in the distorted rhombohedral crystal structure of Bi below 10 K and the other site above 80 K. At both sites the nearest neighbor Bi atoms are found to be shifted towards the μ+ by ≈10% of their nominal distance, implying a large local lattice contraction. In concomitance extremely strong electric field gradients are manifest at the nn Bi nuclei. An almost temperature independent reduced relaxation rate in the temperature range from 20 K to 60 K is interpreted in terms of short range diffusion along a limited chain of alternating types of sites. Above 100 K both long range and short range diffusion are indicated.

Model dependence of charge-symmetry breaking in the neutron-proton interaction.

Abstract: The effects of charge-symmetry breaking of nuclear forces can be observed in neutron-proton elastic scattering as a difference between neutron and proton analyzing powers. A formalism has previously been developed and applied to compute these effects in terms of electromagnetic interactions, one-boson exchange potentials, the two-pion exchange potential, and possible quark effects. The results were found to be in agreement with the one existing measurement. Here we extend this work and study in detail how these charge-symmetry breaking predictions vary with the particular choice for the nucleon-nucleon force. We compare predictions for Reid soft-core, Paris, coordinate-space Bonn, and hybrid quark-meson potentials. We show in particular that charge-symmetry breaking measurements can place strong restrictions on models of the nucleon-nucleon interaction.

Currents, magnetization and AC-losses of YBa2Cu3O7 superconductors in rapidly changing magnetic fields

Abstract: In YBa2Cu3O7 samples of different shape time dependent magnetization currents were induced at 4.2K by the application of rapid magnetic field changes. This contactless method allows the study of the intergrain and intragrain currents in the resistive flux flow state.

Evidence for a resonance in positron-electron scattering at 810 keV centre-of-mass Energy

Abstract: A monoenergetic positron (e+) beam (ΔT/T<5·10−4) from the Stuttgart pelletron accelerator and a 4.6 mg/cm2 Be target has been employed to investigatee+e−scattering in the MeV region in a large solid angle with high statistics by means of a novel positionsensitive detector system. Superimposed on the Bhabha scattering, a structure has been found at ane+ kinetic energy of 2263 keV (810 keV excitation energy in thee+e−rest frame). From the energy-integrated resonance cross-section of\(\sigma _{res} \cdot \Gamma _{res}^{e^ + e^ - } \) ≅30 b·eV (c.m.) and the standard resonance cross-section we estimate partial resonance widths\(\Gamma _{res}^{e^ + e^ - } \) ≅72 meV or 24 meV for total angular momenta J=0 or J=1, respectively. The structure, which has not been predicted within the framework of quantum electrodynamics, coincides with one of the sum energies of the correlatede+e−lines observed in heavy-ion collisions.

Determination of the partial electron capture- and spontaneous-fission half-lives of254No

Abstract: The isotope254No was produced in the fusion reaction48Ca +208Pb. Using the velocity filter SHIP and radiochemical techniques it was found that the nuclide254No with a half-life of 55 s decays byα, EC, and spontaneous-fission. Deduced partial half-lives are (61±2) s forα-decay, (550−160+370) s for EC and [2.2−1.0+2.0]×104 s for spontaneous fission.

Near-Field Geochemistry of Vitrified HLW in a Sedimentary Host Rock

Abstract: The Project Gewahr 1985 (PG'85) safety analysis considered the practicality of HLW disposal in the crystalline bedrock of Northern Switzerland. More recently, an alternative disposal option in the argillaceous sediments overlying the crystalline basement has been examined. This paper examines some aspects of the performance of the near-field engineered barriers in an argillaceous environment, with specific comparison to the PG'85 crystalline case. Two phenomena are considered in particular detail: oxidation of the host rock during the operational phase and the related failure mode of the steel tunnel liner.

Off-shell effects inpp↔πd spin observables

Abstract: We show that spin observables inpp↔πd are fairly sensitive to small changes in the off-shell πN helicity amplitudes. This is illustrated at proton laboratory kinetic energies ofTp=515 MeV andTp=578 MeV. A reduction of the helicity-flip amplitude by 13% brings the predictions of the relativistic rescattering model much closer to experiment.