A simple apparatus for determining column density and absolute photoabsorption cross sections

This article presents a simple measuring apparatus that is capable of measu ring column density and absolute photoabsorption cross sections. The appara tus includes a simple high-temperature heatpipe furnace, an MKS Instruments Baratron, a hydrogen discharge lamp, and an optical detecting system. The heatpipe furnace provides an absorbing medium with a steady total pressure in a closed system so that the column density can be obtained using the ide al gas relation. The apparatus is designed for a working temperature range below 1000 K and a pressure range up to 10 Torr. Encountered experimental d ifficulties and their found solutions will be discussed in detail. In this work, the absolute photoabsorption cross section of Mg is measured near the 3s threshold using this apparatus. The absolute photoabsorption cross sect ion result at the 3s threshold, which is 2.1 +/- 0.3 Mb, is in good agreeme nt with hook method data (2.36 Mb). (C) 2000 American Institute of Physics. [S0034-6748(00)03403-1].