The role of small silver clusters in photography

Size-selected silver cluster ions have been produced in a mass spectrometer arrangement and have been deposited onto binder-free AgBr microcrystals. Clusters containing less than four silver atoms did not catalyze development (reduction) of the microcrystals. However, application of clusters containing four or more silver atoms rendered the crystals immediately developable in a conventional photographic developer. This for the first time proves directly, that a so-called latent image speck under these conditions of development requires a minimum number of four silver atoms.     

Surface and interface studies with ASPIC

Magnetic properties at surfaces and interfaces have been investigated performing Perturbed Angular Correlation (PAC) measurements in the UHV chamber ASPIC (Apparatus for Surface Physics and Interfaces at CERN) using different PAC probes. The results are: (i) determination of magnetic hyperfine fields of Se on Fe, Co, Ni which are explained by a theoretical study on the magnetic hyperfine fields of 4sp-elements in adatom position on Ni and Fe;(ii) static magnetic hyperfine fields in ultrathin Pd on Ni(0 0 1) which indicate an induced magnetic order in Pd;(iii) the observation of induced fluctuating magnetic interactions in Pd when thick Pd is in contact with Ni. Monolayer-resolved measurements of the magnetic hyperfine fields in magnetized Pd are in accordance with theoretical predictions of the layer dependence of the induced magnetic moments in Pd. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development of a high current pseudospark switch and measurement ofelectron density

The pseudospark, a low-pressure gas discharge in a special geometry, is suitable for high-current switching. A single-channel prototype is tested with a 3.3-μF capacitor bank, voltages up to 30 kV, and peak currents up to 120 kA. The electrical circuit, not comprising any load resistor causes weakly damped sinusoidal pulses of 5-μs duration at 90% current reversal. For lifetime tests, a switch with an alumina insulator and copper seals is used. Hydrogen is the working gas. Several electrode materials like molybdenum, tungsten, graphite and chromium-copper are tested. Optical investigations of the discharge and of plasma parameters are done with an O-ring sealed pseudospark switch. The light of the discharge is observed spectrally integrated with a streak camera. Spectral resolution is obtained by using a high-speed shutter in combination with a monochromator. The radial electron density is determined by measuring the Stark broadening of the Balmer H_β-line. At 60 kA a maximum electron density of about 2×10¹⁷cm^-3 is calculated     

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Solid state nuclear track detectors: Track forming,stabilizing and development processes

Fast moving heavy charged particles passing through solids are mainly losing their energy—in a wide range of velocities—by excitation and ionization processes which result in a more or less stable radiation damage.¹ The radiation damage may consist of broken bonds, free radicals, chemical reaction products, displaced atoms, ionic and electronic defects, dislocation configurations, voids, clusters of defects with and without impurities, nuclei of new phases etc. The nature and stability of this localized radiation damage, termed the “latent” track of the particle depends on the data of the particle and on the physical and chemical properties of the solid. Dielectric materials with low electric and thermal conductivities offer favorable conditions for relatively high local excitation and ionization densities resulting in physical and chemical solid state reactions with relatively stable reaction Products.     

Electron microscopic investigations of tracks of Cf252 fission fragments in quartz glass

Using a single stage carbon replication technique, track pits of Cf²⁵²-fission products in quartz glass could be revealed by transmission electron microscopy with a high degree of resolution. From the shape of the track pits the angles of incidence of the nuclear particles were determined down to extremely small angles. In addition track pits on the fracture surface of irradiated quartz glass samples have been investigated by scanning electron microscopy.     

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