Study of radiation damage in metals by positron annihilation. [Neutron irradiation]

Positron annihilation is a sensitive technique for probing defects in metals and it has recently been shown to be a valuable tool for the study of radiation damage. After an introduction to the three basic experimental methods (angular correlation, Doppler broadening, and lifetime measurements), the interaction of positrons with lattice defects is reviewed. Results for the annealing of damage after low temperature irradiation are used to show that positron annihilation has provided new information on annealing kinetics. The role of positron techniques in characterizing complex defect structures resulting from high-temperature neutron irradiation is reviewed and the possible utility of positron annihilation as a nondestructive monitor of property changes is pointed out

Galileo's stream: A framework for understanding knowledge production

We introduce a framework for understanding knowledge production in which: knowledge is produced in stages (along a research to development continuum) and in three discrete categories (science and understanding, tools and technology, and societal use and behavior); and knowledge in the various stages and categories is produced both non-interactively and interactively. The framework attempts to balance: our experiences as working scientists and technologists, our best current understanding of the social processes of knowledge production, and the possibility of mathematical analyses. It offers a potential approach both to improving our basic understanding, and to developing tools for enterprise management, of the knowledge-production process.

Acoustic laser cleaning of silicon surfaces

We investigate the detachment of small particles from silicon surfaces by means of acoustic waves generated by laser-induced plasma formation at the back side of the sample. It is demonstrated that sufficiently high acoustic intensities can be reached to detach particles in the submicron regime. In order to study this acoustic laser cleaning in more detail, we have developed an interference technique which allows one to determine the elongation and acceleration of the surface with high temporal resolution, the basis for an analysis of the nanomechanical detachment process, which takes place on a temporal scale of nanoseconds. We find that the velocity of the detaching particles is significantly higher than the maximum velocity of the substrate surface. This indicates that not only inertial forces, but also elastic deformations of the particles, resulting from the acoustic pulse, play an important role for the cleaning process