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Molecular dynamics simulations have been used to generate a comprehensive database of surviving defects due to displacement cascades in bulk tungsten. Twenty one data points of primary knock-on atom (PKA) energies ranging from 100 eV (sub-threshold energy) to 100 keV (∼780×E d , where E d is the average displacement threshold energy) have been completed at 300 K, 1025 K and 2050 K. Within this range of PKA energies, two regimes of power-law energy-dependence of the defect production are observed. A distinct power-law exponent characterizes the number of Frenkel pairs produced within each regime. The two regimes intersect at a transition energy which occurs at approximately 250×E d . The transition energy also marks the onset of the formation of large self-interstitial atom (SIAs) clusters (size 14 or more). The observed defect clustering behavior is asymmetric, with SIA clustering increasing with temperature, while the vacancy clustering decreases. This asymmetry increases with temperature such that at 2050 K (∼0.5T m ) practically no large vacancy clusters are formed, meanwhile large SIA clusters appear in all simulations. The implication of such asymmetry on the long-term defect survival and damage accumulation is discussed. In addition, rare <100>{110} SIA loops are observed.

The relative stability of single He defects in bcc and fcc metals is investigated using ab initio calculations based on density functional theory. The results indicate that the tetrahedral position is energetically more favorable for a He interstitial than the octahedral site in bcc metals, but the relative stability of He defects in fcc metals varies, depending on local environments. The He formation energies in bcc Fe and fcc Ni at the tetrahedral and octahedral positions with and without spin polarization are investigated. It is of interest to find that the magnetism of host atoms does not directly affect the relative stabilities of He in interstitial sites in bcc Fe and fcc Ni.

constitution and alteration of the surface layers. Calcite, aragonite, Ca(OH),, and unhydrated material can be detected. ' S. Goto, M. Dairnon, G . Hosaka, and R. Kondo, "Composition and Morphology ofHydrated Tricalcium Silicate," J . A m . Cclrrim. So<.Tricalcium Silicate Pastesl 2 Bemardo Mafchese, "Scanning Electron Microscopy Contribution to the Study of Bernardo Marchese, "Scanning Electron Microscopy Contribution to thc Study of I' Bemardo Marckse, "Scanning Electron Microscopy Contribution to the Study of Bemardo Marchcse, "Discussion of the Paper 'Studies on the Hydration of I6 Bemardo Marchese. "SEM Toweraohv ofTwin Fracture Surfaccs of Alite Pastes 1." Cpm. C'orzcr, RPS., 3 [2] 149-61 (1973).

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