MEASUREMENT OF THE HG DISTRIBUTION IN A HIGH-PRESSURE ARC LAMP BY X-RAY-ABSORPTION

We have used an x-ray absorption technique to measure the distribution of Hg atoms in a pure-Hg high-pressure are lamp. The x rays are obtai ned from a molybdenum-anode x-ray tube at an accelerating potential of 35.3 kV. The spectral distribution of x rays which produce the absorp tion signal consists mainly of the Mo K alpha and K beta fluorescence peaks at 17.5 and 19.6 keV, respectively. Plane-wave illumination of t he lamp and two-dimensional detection of the transmitted x rays allow us to probe the Hg atom density in all regions of the lamp, simultaneo usly, with a spatial resolution of 170 mu m. A complete two-dimensiona l map of the density is obtained by Abel inversion of the absorption d ata. This map extends all the way out to the arc-envelope boundary and includes the cold regions of the discharge behind the electrodes. A t emperature map of the discharge is obtained by combining the density i nformation with an optical emission measurement of the core temperatur e at a single axial location. (C) 1998 American Institute of Physics.