Radiothorium

noun

1. A radio-element produced by the disintegration of thorium and intermediate between mesothorium, of which it is a product, and thorium emanation, of which it is the parent. It closely resembles thorium in its chemical properties, and was discovered by Hahn in 1905.
2. an earlier name for the thorium isotope thorium-228, given by its discoverer Otto Hahn. It is a radioactive substance formed as one of series of products in the chain of radioactive decay of thorium. Its immediate predecessor in the chain is Actinium-228, and it decays by alpha emission to radium-224 with a half-life of 1.91 years. The name radiothorium was given prior to the full understanding of the nature of isotopes of elements.
3. The radioactive isotope thorium-228
4. radioactive isotope of thorium with mass number 228