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On Ge: Sb crystals with dopant concentrations, N , ranging between 8 x 10l6 and 1.5 x 10'' cm-3, the temperature and concentration dependences are found of the mobility anisotropy coefficient, K , over the temperature interval 4.2 K 5 T 5 180 K and at T 5 4.2 K. At temperatures T, close to the Hall-coefficient-maximum temperature, the K versus T curve exhibits a minimum at T = Tmin. The temperature Tmin corresponds to the boundary that separates the regions of weak and strong electron scattering. At sufficiently low temperatures, where the scattering is strong (the impurity and band states of electrons are mixed), neither the formulae for classical conductivity nor the formulae of the theory of quantum corrections permit a reliable determination of the value of mobility anisotropy K . Ha KpUCTaJIJIaX Ge

Sub-second time structure of hard X-rays observed during solar flares by spectrometer "IRIS" on a board of CORONAS satellite are discussed. The burst duration of 80ms and FWHM about 30ms are recorded in powerful flare of

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Over the temperature range 2 to 77 K longitudinal and transverse magnetoresistance (MR) measurements are performed on Ge:Sb crystals in magnetic fields u p to 200 kOe. The crystals used are uniaxially compressed along the (1 11) axis and have electron concentrations between 0.82 x 1017 and 6.2 X lo1'A large MR anisotropy is found to arise chiefly from the anisotropy of the energy gap between the Fermi level and the mobility edge. A correlation is shown to exist between the temperature dependences of the negative and positive MR's in high magnetic fields. From an analysis of the concentration and temperature dependences of the MR anisotropy, i t is inferred that for n > n, there exist certain regions of electron concentrations and temperatures where, despite the metallic character of conduction, effects show up which are typical of impurity band charge carriers. P u t another way, the electron states in these regions are intermediate between band states, for which the scattering is weak, and virtually localized states, for which the scattering is strong.

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