Gamma ray sources
Metallic cesium is used in photoelectric cells and infrared detectors, because of its property of being readily ionized by light energy.
The most important cesium compounds are the hydroxide, the carbonate, the iodide and the bromide. Cesium hydroxide is used as an electrolyte in alkaline storage batteries for use in subzero climates. Cesium carbonate has been used in specialty glasses. The iodide and bromide are used in some scintillation counters because they emit electrons when exposed to radiation. Cesium bromide is also used to measure the epitaxial film thickness of semiconductors
The atomic clock uses cesium as the time measuring element based on the precise movement of its outer electrons.