found: Work cat.: Johnson, E.H. Hydrogen maser frequency comparison with a cesium beam standard, 1966:p. ii (abstract, "A direct measurement of the hyperfine energy-level splitting (splitting the energy band into sublevels) of the hydrogen atom has been made by comparing the frequency of an atomic hydrogen maser and a cesium-beam frequency standard") p. 1 ("A direct comparison between a hydrogen maser and a cesium beam tube frequency standard has been made ...")
found: McGraw-Hill dictionary of scientific and technical terms, 2003:p. 361 ("cesium electron tube -- (electr[onics]) -- an electronic device used as an atomic clock, producing electromagnetic energy that is accurate and stable in frequency. Also known as cesium beam tube")
found: Academic Press dictionary of science and technology, 1992:p. 395 ("cesium electron tube -- electronics -- a tube that generates electromagnetic energy at highly stable frequency for use in atomic clocks")
notfound: Chambers dictionary of science and technology, 1999
