NOVELTY - Introducing a first gas and a second gas into a reaction chamber of a reactor, involves introducing the first gas into the first gas plenum and through the peripheral openings into the reaction chamber, where the first gas passes through the channel portion and throttle potion of the distribution openings; and introducing the second gas through the second gas plenum and through the central openings into the reaction chamber, where the second gas passes through the channel portion and throttle potion of the distribution openings.    USE - In the introduction of first gas such as hydrogen and second gas e.g. silane into reaction chamber of reactor (claimed) for the production of polycrystalline silicon which is used in integrated circuits and photovoltaic (i.e. solar) cells.    ADVANTAGE - The method limits or reduces the amount of deposits that form on the reactor walls, thereby increasing the productivity of the reactor; and uses hydrogen as a peripheral gas, which decreases the probability of wall deposits falling to the bottom of the reactor causing reactor downtime.    DETAILED DESCRIPTION - Introducing a first gas and a second gas into a reaction chamber of a reactor, where the reactor comprises at least one reaction chamber wall and a gas distribution unit for distributing the first gas and the second gas into the reaction chamber, where the distribution unit comprises a distributor having several distribution openings including at least one peripheral opening and at least one central opening, where the distribution openings have a channel portion and a throttle portion, the distribution unit further comprises an inlet block, an outer annular ring, an inner annular ring concentric to the outer annular ring, a product withdrawal tube concentric to the outer annular ring and inner annular ring and that extends through the distributor and inlet block, the space between the distributor, inlet block, outer annular ring and inner annular ring defining a first gas plenum, the space between the distributor, inlet block, inner annular ring and the product withdrawal tube defining a second gas plenum, involves introducing the first gas into the first gas plenum and through the peripheral openings into the reaction chamber, where the first gas passes through the channel portion and throttle potion of the distribution openings; and introducing the second gas through the second gas plenum and through the central openings into the reaction chamber, where the second gas passes through the channel portion and throttle potion of the distribution openings.