caesium vs cesium 137

caesium and cesium 137 both are nouns.

Word	Noun	Adjective	Verb	Adverb
caesium	Yes	No	No	No
cesium 137	Yes	No	No	No

As nouns, cesium 137 is a hyponym of caesium; that is, cesium 137 is a word with a more specific, narrower meaning than caesium:

caesium: a soft silver-white ductile metallic element (liquid at normal temperatures); the most electropositive and alkaline metal
cesium 137: a radioactive isotope of cesium used in radiation therapy

caesium (noun)	cesium 137 (noun)
a soft silver-white ductile metallic element (liquid at normal temperatures); the most electropositive and alkaline metal	a radioactive isotope of cesium used in radiation therapy