Modern Determination of Vertical Deflections Using Digital Zenith Cameras

At the beginning of the 21st century, a significant technological change took place in geodetic astronomy. In Zurich and Hannover, digital zenith camera systems were developed based on digital imaging sensors (charge-coupled device) that strongly improved the degree of automation, efficiency, and accuracy of the observation of the direction of the plumb line and its vertical deflection. This paper describes the instrumental design of the new digital zenith camera systems and gives an overview of the data processing with focus on the models used for astrometric data reduction and tilt correction. Results of frequently repeated observations of vertical deflections and comparison measurements show an accuracy of vertical deflection measurements of better than 0.1 arc sec. Application examples for vertical deflection data from zenith camera observations, such as the high-precision local gravity field determination in engineering projects and gravity field validation are summarized

Vacancy Clusters at Nanoparticle Surfaces

The authors detect vacancy clusters at Au nanoparticle surfaces using a combination of positron lifetime spectroscopy, 1- detector, and 2-detector measurements of Doppler broadening of annihilation radiation. Gold nanoparticles are formed by MeV implantation of gold ions into MgO (100) followed by annealing. Clusters of two Mg and two O vacancies (v{sub 4}) are attached to the gold nanoparticle surfaces within the projected range (R{sub p})

Application of the Positron Lifetime Spectroscopy as Method of Non-Destructive Testing

In order to show the suitability of the Positron Lifetime Spectroscopy (POLIS) as a method of Non-Destructive Testing (NDT) several iron alloys / steels were mechanically damaged (tensile stress, fatigue, creeping). The positron annihilation parameters show clear changes during all applied kinds of damage. After tensile stress as well as after creeping a homogeneous distribution of damage in the sample was detected. During the very first elastic cycle of a fatigue experiment, a change in the defect structure occurs in well annealed materials. A modified spectrometer for in the field mapping is presented

Ergebnisse bei der Entwicklung der Positronenannihilation als Methode zur zerstörungsfreien Werkstoffprüfung

Crystal lattice defects especially dislocations gave an important effect on mechanical material properties. Positron annihilation is a very sensitive method to detect dislocations, vacancies and especially microvoids in metals. It is shown that correlations between positron life time and material tension exist. Large effects are found even in the elastic range. Positron annihilation is shown to have a potential in NDE. Unfortunately there is a leck of knowledge concerning the behaviour of positrons in steels. Annealing experiments are helpful to understand microstructural processes at different temperatures

Characterization of microstructure of plastically deformed and and thermally treated carbon steel by means of positron annihilation life-time spectroscopy in comparison with micromagnetic methods

Positron annihilation is a very sensitive method for detecting crystal lattice defects. Using positron life-time measurements separate information can be obtained about deslocations, vacancies and vacancy clusters in meatls. Also micromagnetics is very sensitive to the microstructure in steels if they are ferromagnetic. The paper compares positron life-time measurement and micromagnetics during thermal annealing of plastically deformed pure nickel and a carbon steel. The advantage of positron annihilation is insensitivity to macroscopic residual stresses, the disadvantage is a long measuring time. Both methods can give complemantary information about the microstructure of the materia