Begin by ensuring all valves are closed except for the evacuate valve and starting the pumps on the EXC controller. Pressure on the high-vacuum side of the system may be monitored via the TC gauge at the intake of the turbo pump (the Varian 843). Wait until this gauge begins to read (i.e. below 1 torr) then open the main valve to evacuate the entire manifold. The TC gauge will 'bottom-out' at which point the system is below 10-4 torr. Continue pumping for 10 minutes or more to clear the system of impurities. Start the RGA program on the PC and turn on the unit. Using the utilities menu 'connect' to the RGA head. Select ANALOG SCAN mode and perform a scan of the residual gases left in the system. Be sure to turn the TOTAL PRESSURE indicator on. You may use the AUTO-SCALE feature on the GRAPH menu to scale it for proper display. Save this trace and data two ways: First, by using the "Save as Windows MetaFile" option in the file menu (the image is to be included into the report using a word-processor and is small at about 12K per image ... it is optional, though, as you may recreate it in any spreadsheet program) - save to a directory (and later to a USB key) for later printing and inclusion into the lab report (Make sure you label it 'Background'). Second, and MOST IMPORTANTLY, save the PRESSURE DATA from the trace using the "Save as ASCII Data" option - this is a data file with two columns, one amu and one pressure in torr - this is required for each sample since the trace is not good enough for quantitative analysis. This file may be opened or imported into any spreadsheet program.
17.30, 7.79E-007 17.40, 1.30E-007 17.50, 2.86E-007 17.60, 1.65E-006 17.70, 4.20E-006 17.80, 5.24E-006 17.90, 6.32E-006 18.00, 6.08E-006 18.10, 6.20E-006 18.20, 5.13E-006 18.30, 3.22E-006 18.40, 1.34E-007
Ensure you understand why peaks occur only at integers for atomic mass and why an element with an atomic mass listed as "35.45" will NOT show-up at 34.5 amu (!)
First, obtain a BACKGROUND trace showing gases in a system under high vacuum. Open the evacuate valve and pump the mainfold down to high vacuum. After five minutes of pumping, turn the RGA on and run a trace (collecting pressure data in a file) showing gases in the system. After the trace is stable (i.e. it remains unchanged after several sweeps through the range of atomic masses) stop the trace and turn off the filament using the proper icon. Save this trace as "backgnd".
Now admit air into the manifold and sample it as follows:
Again, stop the scan, turn off the filament, and save this trace on disk as 'Air'.
We must now pump the air out of the manifold before using the next gas. FIRST, you must TURN OFF THE RGA FILAMENT! Stop the scan then turn off the filament using the filament icon if not already done. Check it twice - these are $360.00 each! Now that the RGA is off it is safe to bring the pressure higher than 10-4 torr. If the filament is left on above a preset limit an interlock system will trip and power to the RGA will be cut - if this occurs the pressure at the RGA head must be reduced again and the RGA re-initialized from the connect menu. Now open the evacuate valve and pump the residual gases out of the manifold for five minutes.
With a clean manifold, close the evacuate and sample valves and admit 2 torr of PURE HELIUM GAS into the manifold. Using the same procedure as before (and optimal sample pressure of between 1 * 10-5 and 3 * 10-5 torr), sample the helium gas and save a trace as 'Helium'.
Now, let's see what happens if the sample pressure _is_ too low. Repeat the above trace using helium but this time set the total pressure much lower than optimal, at between 1 * 10-6 and 3 * 10-6 torr.
When done, stop the scan, turn off the filament, and save this trace on disk as 'He-low'.
We must now pump the helium out of the manifold before using the next gas (pump for another five minutes). With a clean manifold, close the evacuate and sample valves and admit 2 torr of NEON GAS into the manifold. Using the same procedure as before (and optimal sample pressure of between 1 * 10-5 and 3 * 10-5 torr), sample the neon gas and save a trace as 'Neon'.
Finally run another trace on carbon dioxide gas.
When done, evacuate the manifold, close all valves, and shut down the vacuum system.
For this experiment, an abbreviated lab report is required (word processed, never hand-written) with the same format as PHTN1300. Answer each question in the form "4a., 4b., 4c. ..." with each new question (#4, #5, etc) beginning on a new page. Do NOT answer an entire question (e.g. question 4) as a single paragraph without identification of sub-parts ('a', 'b', etc). Submit the lab report in a bound folder NOT simply a pile of loose, stapled papers nor a thick binder!