Hydrogen Trapping Studies in Fusion First Wall Materials
Hydrogen trapping in the first wall of fusion reactors is one of the most serious materials problems facing the designers of magnetic confinement devices. The release of this trapped hydrogen from the near surface region of the first wall during a tokamak discharge has been shown to play a major role in the hydrogen fueling of today's plasmas, while trapped hydrogen isotopes will directly influence the on-site tritium inventory and the structural properties of future D-T reactors. This paper summarizes the laboratory ion implantation sttidies on the hydrogen trapping characteristics of first wall materials. Emphasis is placed on the near term materials problems associated with austenitic stainless steels that are currently in use in magnetic confinement devices. Hydrogen trapping experiments involving more exotic first wall structural and coating materials are briefly reviewed.
Interaction of hydrogen with radiation defects in metals
The interaction of hydrogen (deuterium) with radiation defects in Mo and Ni was observed by the hydrogen permeation method from a glow discharge plasma for self-interstitial atoms (SIAs) and by depth profiling of implanted gas for vacancies (V). On the basis of the analogies with the free metal surface the model of interaction of hydrogen with vacancy defects is suggested. Using the known values of the adsorption and solution heats, the binding energies of hydrogen with vacancy and vacancy clusters are estimated for some metals (V, Nb, Ta, α-Fe, W, Pd, Cu, Au, Al). Good correlation is observed for calculated and experimental values.
The Limits of Vulnerability in Explaining Fear of Crime: A Comparative Neighborhood Analysis
Recent research on the fear of crime in the United States has focused on the sources of fear. Many of these studies have identified neighborhood-level variables that are related to fear, but most have examined the differences in fear among individual residents of one or more cities. There has been substantially less research on the differences in the sources of fear among residents of different areas within a single city. This article examines the causes of fear through a comparative analysis of three different neighborhoods in San Francisco. An analysis of covariance model is used to assess the importance of differences in the sources of fear that may be associated with an individual's neighborhood of residence. The findings demonstrate that age, as a measure of physical vulnerability previously associated with fear among individuals, is not related to fear in neighborhoods where residents express the greatest general concern about crime. It is concluded that in those urban areas where crime problems are regular features of the neighborhood environment, measures of physical vulnerability are less important in predicting differences in fear among individuals.