TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The reaction chamber comprises an annular wall and has a generally circular cross-section having a center and a radius R, where the core region extends from the center to less than 0.975R (preferably less than 0.4R) or at least 0.5R (preferably at least 0.9R) and the peripheral region extends from the center region to the annular wall. The reaction chamber is not partitioned into separate portions. The fluidized bed reactor comprises an annular inner chamber formed between a reaction chamber wall and an outer shell, where the process comprises maintaining a pressure in the inner chamber greater than 1 bar (preferably 5-20 bar) below the pressure within the reaction chamber. The fluidized bed reactor comprises a distributor for distributing gases into the reaction chamber.    TECHNOLOGY FOCUS - POLYMERS - Preferred Process: The temperature of the first feed gas/the second feed gas is less than 400 degrees C (preferably less than 100 degrees C) prior to entry into the reaction chamber. The temperature of the second feed gas is at least 300 degrees C (preferably 450-600 degrees C). The pressure in the fluidized bed reactor is at least 4 (preferably 4-20) bar. In the process, a spent gas is withdrawn from the fluidized bed reactor, where the pressure of the spent gas is at least 3 (preferably 4-20) bar. In the process, at least 4% (preferably 100%) of the silane introduced into the fluidized bed reactor is introduced through the core region. In the process, particulate polycrystalline silicon is withdrawn from the fluidized bed reactor, where the Sauter mean diameter of the particulate polycrystalline silicon is 600-2000 or 800-1300 mu m. The average residence time of gas introduced into the reaction chamber is less than 20 (preferably 0.1-20) seconds. In the process, at least 150 (preferably 100-1000) kg/hour of silicon, deposits on the silicon particles per square meter of reaction chamber cross-section. The reaction chamber is heated to at least 500 degrees C (preferably 700-800 degrees C). Preferred Components: The concentration by volume of silane in the first feed gas is at least 25% (preferably 50-200%) greater than the concentration by volume of silane in the second feed gas. The second feed gas comprises less than 15 (preferably 1-5) vol.% of silane. The second feed gas consists essentially of compounds other than silane. The second feed gas consists essentially of one or more compounds comprising silicon tetrachloride, hydrogen, argon or helium. The first feed gas comprises less than 60 (preferably 2-20) vol.% of silane. The overall concentration of silane in feed gases introduced into the reaction chamber is less than 12 (preferably less than 8) or 1-15 (preferably 10-15) vol.%. EXAMPLE - Hydrogen was fed into the peripheral region of the reaction chamber and a silane-containing gas was introduced into the core of the reaction chamber, where the gas introduced into the core region of the reactor contains 4.8 vol.% and the gas was entered at a temperature of 395 degrees C, and the gas introduced into the peripheral region of the reactor contains no silane and the gas was entered at a temperature of 600 degrees C. The overall silane concentration in the gases fed into the reactor was maintained at 2 vol.%. The ratio of the surface area of the core region to the surface area of the peripheral region of the reaction chamber was 1:2. Pressure of the reactor gas discharge was maintained at 20 bar absolute, the reaction chamber was maintained at 700 degrees C, and the obtained mixtures were worked up to give polycrystalline silicon.