Thorium-228 is an isotope of thorium which has 90 electrons and protons and 138 neutrons. It has a half life of 1.9116 years. It is highly unstable and is not found in nature. When it decays, it emits an alpha particle and turns into Radium-224. Occasionally it decays by the unusual route of cluster decay, emitting a nucleus of oxygen-20.
Th-228 has an atomic weight of 228.0287411 grams/mole. Uranium-232 decays to this nuclide by alpha emission.