Tech Help - Processing "A" Activation Electrodes Open Valve Processing Method. The example described below relates to 50mA electrodes. When processing other sizes the current settings should be adjusted to suit the relevant electrode size as stated in the table. [All current ratings are in milliamps] Shell Rating Starting Current Shell Bombardment Maximum Current Helium Rinse Current 20 100 300 200 30 150 400 500 50 200 600 500 90 / 100 250 600 / 700 500 120 300 800 / 900 500 Setting Up Insert mercury into the pumping tubulation reservoirs. 400 milligrams is recommended [3 - 4mm ball] Seal the tubes to the manifold Whenever possible pump two tubes together Connect a reliable temperature indicator at the centre of one of the tubes. A good quality temperature gauge is recommended for accurate temperature measurement, although a piece of newspaper is often used.   Bombarding Open the main valve slowly. The tube will begin to evacuate. At 10 millibars [6 torr] pressure switch on the current Allow the pressure to continue falling. At approximately 3 millibars [2 torr] the tubes will strike [light up]. Close the main valve and set the current to 200mA. And allow bombardment to continue. The pressure will increase initially due to vaporisation of moisture. By opening and closing the main valve the pressure can be reduced to 3 millibars [2 torr]. Increasing the current slightly if necessary to effect correct heating of the tubes until tube temperature reaches between 150° C - 170° C. Increase the current to 600mA This increase should take place when the tube temperature reaches between 150° C - 170° C. [slight brown charring on the newspaper]. Open fully the main valve. Allow the bombarding to continue until all electrode shells are glowing bright orange/red along their whole length [shell temperature 900° C] and the tube temperature reaches 250° C [At this temperature the piece of newspaper will be burned brown and may even have burnt in two]. Switch off the current. Allow the tubes to evacuate to between 10-2 and 2 x 10-2 [10 - 20 microns] and the tube temperature to fall to approximately 100° C.   Helium Rinse This serves two purposed. Firstly, any residual gases left in the tubes will be diluted by the Helium. Secondly, the rinse will indicate whether adequate bombardment tool place.[See Masonlite Technical Sheet HR1] Introduce 5 millibars [4 torr] of Helium gas. Switch on current and increase to 500mA. Allow the tubes to burn for one minute. If the gas discharge colour remains a consistent straw yellow, this indicates a clean, well bombarded tube. Switch off the current. Open fully the main valve. Allow the tubes to evacuate fully. When the tube temperature has fallen to at least 50° C and a vacuum of 10-3 [1 micron] is achieved the tubes can be filled with the required amount of rare gas and sealed off for ageing in.

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