Affiliation: | (1) Institute of Physics, Czechosl. Acad. Sci., Na Slovance 2, 180 40 Praha 8, Czechoslovakia;(2) Institute of Electronics, Bd. Lenin 72, 1184 Sofia, Bulgaria;(3) Faculty of Nuclear Science and Physical Engineering, V Holeovikách 2, 180 00 Praha 8, Czechoslovakia |