from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A radioactive isotope of thorium with mass number 228.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The radioactive isotope thorium-228
from the GNU version of the Collaborative International Dictionary of English
- n. 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.
from The Century Dictionary and Cyclopedia
- n. 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.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. radioactive isotope of thorium with mass number 228
From radio- + thorium (Wiktionary)