Irradiated cubic single crystal SiC as a high temperature sensor
Radiation is known to cause point defects formation in different materials. In the case of cubic SiC single crystal radiation flux on the order of 2⋅10 20 neutrons/cm 2 at 0.18 MeV causes over 3% volume lattice expansion. Radiation-induced strain (measurable by X-Ray diffraction) can be relieved when the annealing temperature exceeds the temperature of irradiation. Based on this effect the original technology of maximum temperature measurement was developed a while ago. Single crystal SiC sensor small size (200-500 microns), wide temperature range (150-1450 °C), “no-lead” installation, and exceptional accuracy make it very attractive for use in small, rotating and “hard-to-access” parts, including, but not limited to gas turbine blades, space shuttle ceramic tiles, automobile engines, etc. With the advances in X-Ray diffraction measurements, crystal and thin film growth techniques, it is the time to revise and update this technology. Modeling radiation damage, as well as annealing effects are also beneficial.
Experimental and Computational Studies of Ion-Solid Interactions in Silicon Carbide
Experimental and computational results on ion-beam-induced defect production, damage accumulation, and thermal recovery in SiC are reviewed. The accumulation and recovery of disorder on the Si and C sublattices have been determined experimentally by ion-channeling methods. Atomic-level simulations are used to determine defect production, cascade-overlap effects, and defect migration energies. Energetic Si and C collision cascades, with energies up to 50 keV, primarily produce single interstitials, mono-vacancies, antisite defects, and small defect clusters. Overlapping of Si and C cascades results in the interaction of defects and clusters that stimulates cluster growth and produces long-range structural disorder. For energetic Au cascades, nanoscale amorphous clusters are produced directly within about 25% of the Au cascades, along with point defects and smaller clusters. The disordering behavior and the changes in volume and elastic modulus obtained experimentally and from molecular dynamics simulations are in good agreement, thus providing atomic-level interpretation of experimentally observed features. Simulations of close-pair production and recombination in SiC indicate that the activation energies for recombination of most close pairs range from 0.24 to 0.38 eV. Multi-axial channeling measurements indicate annealing below 300 K results in relaxation of some interstitials to lower-energy configurations. Long-range migration energies for interstitial and vacancies havemore » likewise been determined by computational methods.« less
Experience of using rating scales for the assessment of vocational trainees in general practice.
For two years trainers in the northern half of the south western region have been asked to assess their trainees with a condensed version of the new Manchester rating scales for vocational training in general practice and to send copies to the regional adviser. The condensed version retains the 23 scales but does not include the subscales. Trainers' workshops and comments from individuals suggested that no radical improvements to the scales were required and that they were an adequate statement of what was required from trainees. The response rate of 89% for returning at least one assessment and 38% for returning all three suggested that use of this condensed version would be more feasible than using the full version of the scales. Analysis of 86 first assessments and 48 sets of three assessments showed a range of variation both in trainee ratings and use of individual scales that was consistent with expectations. A lack of significant rank correlations between the scales indicated that each of the scales measured a different characteristic of behaviour. We suggest that the most useful way to achieve systematic assessment of vocational trainees is by the use of the 23 main rating scales, with regional variations where appropriate.