Noun
mesothorium (plural mesothoriums)
(physics) Certain products of the radioactive decay of thorium, mainly isotopes of radium and actinium
There, in the space of a few months, using extremely primitive apparatus, Hahn discovered mesothorium I, mesothorium II, and – independently from Bertram Boltwood – the mother substance of radium, ionium (later identified as thorium-230). Source: Internet
In subsequent years, mesothorium I (radium-228) assumed great importance because, like radium-226 (discovered by Pierre and Marie Curie ), it was ideally suited for use in medical radiation treatment, while costing only half as much to manufacture. Source: Internet