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 arc lamp. The x rays are obtained from a molybdenum-anode x-ray tube at an accelerating potential of 25.3 kV. The spectral distribution of x rays which produce the absorption signal consists mainly of the Mo Kα and Kβ fluorescence peaks at 17.5 and 19.6 keV, respectively. Plane-wave illumination of the lamp and two-dimensional detection of the transmitted x rays allow us to probe the Hg atom density in all regions of the lamp, simultaneously, with a spatial resolution of 170 μm. A complete two-dimensional map of the density is obtained by Abel inversion of the absorption data. This map extends all the way out to the arc-envelope boundary and includes the cold regions of the discharge behind the electrodes. A temperature map of the discharge is obtained by combining the density information with an optical emission measurement of the core temperature at a single axial location.