An attempt to study ionizing radiation fronts in Cs vapour

Criteria are developed for the design of an experiment to study steady radiation fronts in Cs vapor. According to these criteria, a pulsed light source of supposedly sufficient intensity (≃10²²photons/cm²-sec) and pulse length (≃90ys) was built, and an absorption tube for Cs vapor inside an oven was developed (through several models) which produced a maximum absorber density of ≃10¹⁸particles/cm³. Light and electrical probe measurements were carried out to detect ionizing radiation fronts in the cesium. While the light measurements were inconclusive due to stray light problems, the probe measurements showed that photoionization takes place but at a much lower rate than expected. A subsequent study of the light source confirmed that indeed the light source, a constricted capillary arc, driven by a 90μs square current pulse, has a much lower intensity in the test section of the absorption tube than is required to drive a front. The low intensity of this light pulse rendered the initial aim of the experiment namely the study of steady ionization fronts in cesium vapor, unattainable with the available apparatus.