What is "thorium-228"

radiothorium \ra`di*o*tho"ri*um\ (r[=a]`d[i^]*[o^]*th[^o]r"[=e]*[u^]m), n. (Chem.) 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.

n. (context isotope English) A radioactive isotope of thorium, (nuclide 228 90 Th), having a half-life of 1.4 x 10¹⁰ years; it occurs naturally, and is a source of nuclear energy

n. radioactive isotope of thorium with mass number 228 [syn: radiothorium]