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CATHY GULLI'S STORY about vitamin consumption in Canada and its potential hazards was informative ('How vitamins can be hazardous to your health,' Health, April 21). In it she quotes Gerry [...]

Single crystals of silicon were irradiated with neutron doses ranging from 2.5 × 1018 n cm-2 up to 2.5 × 1019 n cm-2 (E>0.1 MeV). Diffuse X-ray scattering from the irradiated and isochronal annealed samples was measured near the (440) reflection. There are two distinct annealing stages, one at 200°C and another at 600°C. From the variation of the size and the shape of the interstitial and vacancy clusters we identify the mobile defects. We conclude that at 200°C the divacancy is migrating while at 600°C interstitials are mobile. Thereby, single interstitials being evaporated is more likely than complete interstitial clusters becoming mobile.

Measurements of diffuse X-ray scattering close to Bragg reflections, of lattice parameter changes and of glasslike, or amorphous, scattering from α-quartz single crystals after irradiation in the range of dose from 3 to 49 × 1018 fast neutrons per square centimeter are reported. The measurements close to Bragg reflections and the lattice parameter changes lead to the conclusion that the neutrons create defective regions. The crystalline matrix is heavily strained by the defective regions and the symmetry and magnitude of the strain field is determined. During annealing no appreciable change of the size and the form of the defective regions is observed. The annealing seems to be closely connected to the α-β quartz phase transition.The amorphous scattering is very similar in a fully amorphized crystal and in heavily irradiated vitreous silica. In more lightly irradiated samples this amorphous scattering seems to grow with increasing irradiation in proportion to the number of defective (amorphized) regions produced by the neutron damage.

We measure diffuse X-ray scattering close to Bragg reflections in aluminium single crystals after irradiation with fast-neutrons at 4.6 K. Detailed evaluation of the data demonstrates that interstitials are located in cascades (radius rK = 50 Å). Within a cascade the institials form small clusters. The average number of three interstitials per cluster is independent of dosage up to 2.4 × 1018 n/cm2.During annealing the small clusters grow and finally form interstitial loops. For this growth long-range migration of the interstitials out of their cascade is observed.

Single crystals of silicon were irradiated with neutron doses ranging from 2.5 × 1018 n cm-2 up to 2.5 × 1019 n cm-2 (E>0.1 MeV). Diffuse X-ray scattering from the irradiated and isochronal annealed samples was measured near the (440) reflection. There are two distinct annealing stages, one at 200°C and another at 600°C. From the variation of the size and the shape of the interstitial and vacancy clusters we identify the mobile defects. We conclude that at 200°C the divacancy is migrating while at 600°C interstitials are mobile. Thereby, single interstitials being evaporated is more likely than complete interstitial clusters becoming mobile. [ABSTRACT FROM PUBLISHER]

Several letters to the editor are presented in response to articles in previous issues including "How vitamins can be hazardous to your health," in the April 21, 2008 issue, "The space where Tory principles used to be," in the April 28, 2008 issue, and "Righteous crusader or civil rights menace?," in the April 21, 2008 issue.