Advances in the Static-Argon, Dc-Arc Spectrochemical Source

Abstract

The advanced dc-arc spectrochemical source discussed here was developed by William A. Gordon at N.A.S.A., Lewis Research Center, Cleveland, Ohio. It consists of a dc current arc in a static-argon gas chamber. Figure 1 is a photograph of a typical spectrochemical analysis system. This unit is in operation at the University of Colorado Medical Center in Denver, Colorado, under the direction of Michael Hambidge, M.D. It employs a standard Jarrell-Ash 1.5 meter Paschen-Runge mount direct reading spectrometer. The spectrometer offers a reciprocal linear dispersion of 5.5 Å/millimeter along the focal curve yielding a spectral band pass of 0.4 Å for typical exit slit widths. Photomultipliers are arranged behind the exit slits along the focal curve located in the rear of the spectrograph and each of the currents from these photomultiplier tubes is integrated by storing a charge on separate capacitors. After analysis each capacitor is discharged through an electronic measuring circuit and the signal is recorded. This is the same model spectrometer which is employed at N.A.S.A., Lewis Research Center with the static-argon arc at that location. The inert gas chamber itself is located in front of the entrance slit on the optical bar of the spectrometer. Some of the auxiliary equipment necessary to operate the system is visible on the right side of the photograph. A standard spectrochemical dc-arc supply source is located below the arc chamber. A manifold system containing gas flow valves and a pressure gauge is visible. The gas flow system which controls the argon pressure that is backfilled into the arc chamber is also connected to a vacuum pump located on the floor.