on the barrel reactor in fluid communication with the supply of reactant gas for selectively delivering a jet of reactant gas from the supply to the reaction chamber the nozzle is pivotable relative to the barrel reactor for selectively altering the direction in which the reactant gas jet enters the reaction chamber the positioning device is connected to the nozzle for pivoting the nozzle relative to the barrel reactor to alter the direction in which the reactant gas jet enters the reaction chamber the positioning device is constructed to permit quantitative measurement of the position of the nozzle relative to the barrel reactor thereby permitting reproducible aiming of the nozzle for selecting the direction in which the reactant gas jet enters the reaction chamber application_number US 64418196 A description referring now to the drawings and in particular to fig1 a barrel reactor for use in chemical vapor deposition of a layer of semiconductor material on one face of wafers w is indicated generally at 10 the barrel reactor includes a shell generally designated by 12 defining a reaction chamber 14 in which the wafers w are positioned for chemical vapor deposition the shell comprises an inverted quartz bell jar or reaction chamber vessel 20 a gas ring 22 and a seal plate 24 a lift assembly indicated generally at 30 is positioned generally above the reaction chamber 14 to raise and lower a quartz hanger 32 and a five sided silicon coated graphite susceptor 34 out of and into the bell jar 20.