1) Isotope 1) Isotope of thorium 2) Radioactive isotope 3) Radioactive thorium isotope 4) Thorium isotope 5) Thorium-230, alternatively 
(from the article `ionium-thorium dating`) method of establishing the time of origin of marine sediments according to the amount of ionium and thorium they contain....is normally in equilibrium with uranium-234 but is found to be virtually absent in modern corals even though uranium-234 is present. Over a long ... [2 related articles]
Former term for thorium-230. ... Origin: G. Ion, going ... (05 Mar 2000) ... 
Type: Term Pronunciation: ī-ō′nē-ŭm Definitions: 1. Former term for thorium-230.
a naturally occurring radioactive isotope of thorium. Symbol: Io; at. no.: 90; at. wt.: 230.