The Omega3/LHCl pixel detector readout chip comprises a matrix of 128 X 16 readout cells of 50 mu m X 500 mu m and peripheral functions with 4 distinct modes of initialization and operation, together more than 800 000 transistors. Each cell contains a complete chain of amplifier, discriminator with adjustable threshold and fast-OR output, a globally adjustable delay with local fine-tuning, coincidence logic and memory. Every cell can be individually addressed for electrical test and masking, First results have been obtained from electrical tests of a chip without detector as well as from source measurements, The electronic noise without detector is similar to 100 e(-) rms. The lowest threshold setting is close to 2000 e(-) and non-uniformity has been measured to be better than 450 e(-) rms at 5000 e(-) threshold. A timewalk of < 10 ns and a precision of < 6 ns rms on a delay of 2 mu s have been measured. The results may be improved by further optimization

Alpha spectroscopy was used to study the mechanism of electrostatic collection of thoron daughters from the air. The results indicate that ThA atoms are primarily collected on negatively charged surfaces. Atoms of ThB produced by decay of ThA already attached to the collecting surface are injected by recoil into the surface layers of solids and are suitable for use in radiotracer experiments.

Semi-insulating GaAs detector structures have been studied by transport ͓current-voltage ͑I-V͒ curves͔ and scanning electron microscope voltage ͑potential͒ contrast methods. The saturated part of I-V curves, suitable for radiation detection, is due to the velocity controlled high field transport mechanism while the sharp increase of current with voltage is ascribed to the impact ionization. It is shown that a modified voltage contrast method is able to reveal the actual potential distribution and to contribute to the optimization of the radiation detector structures.

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