1. Measurements of the Absolute Absorbance/Transmittance of Ar using a Gas Flow System Bob Azmoun; SUNY Stonybrook, BNL 1/22/03

2. Absorbance Vs. Pressure Sample chamber passed a He leak check. Increasing pressure is the result of out-gassing. Out-gassing substance unknown. Gas flow system is necessary. Sample chamber passed a He leak check. Increasing pressure is the result of out-gassing. Out-gassing substance unknown. Gas flow system is necessary. Schematic of VUV apparatus Absorbance/Transmit- tance measured with respect to vacuum.

3. Simple Gas Flow System Schematic of simple gas flow system. The transmittance through a static volume of gas shows rapid decline as a function of time. The transmittance improves with increasing flow time. The level of out- gassing/contamination is unknown using this set-up. The transmittance through a static volume of gas shows rapid decline as a function of time. The transmittance improves with increasing flow time. The level of out- gassing/contamination is unknown using this set-up.

4. More Sophisticated Gas Flow System Schematic of more sophisticated gas flow system. New gas system doesn’t show improvements in gas purity over simpler system (yet). New system provides concentration levels of O 2 and H 2 O. After by-passing the sample chamber in the gas flow circuit, the concentrations of O 2 and H 2 0 dropped to: [O 2 ]=7.4ppm; [H 2 O]=35.0ppm. New gas system doesn’t show improvements in gas purity over simpler system (yet). New system provides concentration levels of O 2 and H 2 O. After by-passing the sample chamber in the gas flow circuit, the concentrations of O 2 and H 2 0 dropped to: [O 2 ]=7.4ppm; [H 2 O]=35.0ppm.

5. Identifying the Out-gassing substances. Data Ref.: Zaidel’ & Shreider, VUV Spectroscopy Absorption Coefficient of Water Vapor.Absorption coefficient of Oxygen.

6. Final Remarks If indeed water vapor is the primary contaminant as the data suggests, then the gas purity may be dramatically improved by both baking out the sample chamber first and allowing for a longer flow period.