Direct Measurement of Cesium Adsorption on High-Temperature Surfaces Using Radioactive Tracers

A radioactive tracer technique was used for directly measuring adsorbed material on surfaces typical in thermionic energy converters. Previously used techniques did not allow measurements to be made under the conditions expected in an operating diode. In these experiments, cesium tagged with radioactive ¹³⁴Cs was adsorbed onto tantalum surfaces. Cesium arrival rates from 10¹⁶ to 10²¹ atom/(cm² sec) and tantalum surface temperatures from 500 to 1700 K were investigated. The experimental curves were smooth and reproducible, establishing a high level of confidence in the technique.