711 mm this tube 53 u2032 has an angled tip 91 u2032 allowing a maximum melt surface area to be exposed to dopant gasses flowing from the tip additionally the moveable tube 53 u2032 includes a guide 201 aligning the quartz tube 53 u2032 and a perforated disk 203 preventing the dopant from exiting the tube 53 u2032 into the silicon melt 17 when the dopant material trapped in the tube 53 u2032 argon gas can be introduced into the feed tube assembly 15 u2032 causing the dopant laden argon to travel down the feed tube assembly 15 u2032 under sublimation and exit the angled tip 91 u2032 at the upper surface of the silicon melt this second embodiment of the feed assembly 10 u2032 operates as follows the process is similar to the process described for the first embodiment except the actuator 19 advances the quartz tube 53 u2032 of the feed tube assembly 15 u2032 so the angled tip 91 u2032 is positioned at the upper surface of the silicon melt the locking member 125 of the brake assembly 25 is tightened to lock the magnetic slide 89 in position thus locking the angled tip 91 u2032 of moveable tubes 53 u2032 in position at the upper surface of the silicon melt the dopant held in the vessel and valve assembly 11 is released when the valve 43 in the dopant cartridge 41 is.