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The nature of atmospheric aerosols at Gurushikar, Mt. Abu, Rajasthan where a gamma ray telescope is to be installed, was investigated. Air particulate samples collected on filters were used to estimate the total suspended particulate matter (TSPM) and its elemental composition. The TSPM varied from 31 to 103 μg/m(3) during January to March 1994. The heighest loads were observed during the months of May and June (80-100 μg/m(3)) and lowest during October (20-60 μg/m(3)). The dust was also examined for size, shape and nature of the mineral matter. The particle sizes varied from 100 μm to 5 μm. The course particles (>50 μm) are irregular shaped quartz grains. Some of the medium size (=50 μm) particles were spherical and were highly conducting. These particles were rich in iron content. Correlation coefficients among various elements in the dust showed that it is made up of mainly two components-wind blown ground dust and particulate arising out of wood and coal burning.

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Ni–10 wt% Cr and Ni–20 wt% Cr are irradiated with fast neutrons to fluences of 6.5 × 1021 and 1 × 1022 n/m2, and their isochronal annealing behaviour is studied between 343 and 945 K. On annealing, the resistivity increases between 343 and 575 K and decreases again at higher temperatures. The increase in resistivity is explained on the basis of an increase in local order on annealing. The decrease in resistivity at higher temperature arises because of dissociation of defect clusters.

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