Materials Performance in a Radiation Environment
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Radiation Damage in Metallic Materials The first article, by H. Ullmaier, begins with a broad description of defect production that can apply to displacement damage in all solid-state materials. The author then focuses on production of both individual defects and multipledisplacement events (cascades). These cascades can involve thousands of displacements. Subsequent defect reactions can greatly reduce the number of nascent displacements but can also create stable MRS BULLETIN/APRIL 1997
damage aggregates such as vacancy clusters (voids), which are famous for their role in the swelling of irradiated materials. The remainder of the article describes how these and other damage aggregates can significantly affect properties such as ductility, hardness, density, and deformation under load.
Radiation Effects in Ceramics In this article, G.P. Pells considers damage effects in a broad group of ceramic materials, including (1) crystalline oxides such as alumina, (2) compounds that can easily exist in both crystalline and glassy forms (for example silica), and (3) alkali halides (e.g., sodium chloride). Some ceramics, including the latter two, can suffer damage from purely ionizing radiation through a process known as radiolysis. This phenomenon complicates attempts to control the properties of these materials and challenges materials scientists to understand its influence. This article addresses the effects of irradiation on those properties degraded by total accumulated damage dose—for example, thermal and mechanical changes. Properties that can be degraded by irradiation flux as well as fluence are also considered—namely optical absorption, electrical conductivity, and dielectric loss.
Radiation Effects in Graphite and Carbon-Based Materials Author T.D. Burchell discusses damage effects in the broad family of carbonbased materials. Graphite, one of the materials in this class, has the distinction of having caused great consternation due to its unexpected response to irradiation—namely swelling and energy release in graphite moderators for fission reactors. Properties of carbon-based ma-
terials are particularly sensitive to fabrication techniques, and so the author begins with an examination of that subject. Radiation-damage mechanisms are considered next, with special attention given to the strongly directional nature of atomic arrangements in graphitic materials. Stored energy receives due attention, as do dimensional changes, which can range from shrinkage to breakaway swelling. A review of physical property changes, including strength and thermal conductivity, concludes this article.
Irradiation of Plastics: Damage and Gas Evolution In the final article of this theme issue, D. Evans and M.A. Crook examine the nature of radiation damage in polymeric materials, including those containing inorganic fiber reinforcement. The authors begin with a discussion of the interaction of radiation with polymers, which can suffer structural damage from ionization effects. This is followed by a consideration of the chemical struct
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