What is Thorium 232 – Definition

Thorium 232

Thorium 232, which alone makes up nearly all natural thorium, is the most common isotope of thorium in the nature. This isotope has the longest half-life (1.4 x 10¹⁰ years) of all isotopes with more than 83 protons. In fact, its half-life is considerably longer than the age of earth. Therefore ²³²Th belongs to primordial nuclides.²³²Th decays via alpha decay into ²²⁸Ra . ²³²Th  occasionally decays by spontaneous fission with very low probability of 1.1 x 10^-9 %.

²³²Th is a fertile isotope. ²³²Th is not capable of undergoing fission reaction after absorbing thermal neutron, on the other hand ²³²Th can be fissioned by fast neutron with energy higher than >1MeV. ²³²Th does not meet also alternative requirement to fissile materials. ²³²Th is not capable of sustaining a nuclear fission chain reaction, because too many of neutrons produced by fission of ²³²Th have lower energies than original neutron.Isotope ²³²Th is key material in the thorium fuel cycle. Radiative capture of a neutron leads to the formation of fissile ²³³U. This process is called nuclear fuel breeding. 

Uranium 233 breeding

²³²Th is the predominant isotope of natural thorium. If this fertile material is loaded in the nuclear reactor, the nuclei of ²³²Th absorb a neutron and become nuclei of ²³³Th. The half-life of ²³³Th is approximately 21.8 minutes. ²³³Th decays (negative beta decay) to ²³³Pa (protactinium), whose half-life is 26.97 days. ²³³Pa decays (negative beta decay)  to ²³³U, that is very good fissile material. On the other hand proposed reactor designs must attempt to physically isolate the protactinium from further neutron capture before beta decay can occur.

What is Thorium

Thorium is a naturally-occurring chemical element with atomic number 90 which means there are 90 protons and 90 electrons in the atomic structure. The chemical symbol for thorium is Th. Thorium was discovered in 1828 by norwegian mineralogist Morten Thrane Esmark. Joens Jakob Berzelius, the swedish chemist, named it after Thor, the Norse god of thunder.Thorium  is a naturally-occurring element and it is estimated to be about three times more abundant than uranium. Thorium is commonly found in monazite sands (rare earth metals containing phosphate mineral).Thorium has 6 naturally occurring isotopes. All of these isotopes are unstable (radioactive), but only ²³²Th is relatively stable with half-life of 14 billion years, which is comparable to the age of the Earth (~4.5×10⁹ years). Isotope ²³²Th belongs to primordial nuclides and natural thorium consists primarily of isotope ²³²Th. Other isotopes (²³⁰Th, ²²⁹Th, ²²⁸Th, ²³⁴Th and ²²⁷Th) occur in nature as trace radioisotopes, which originate from decay of ²³²Th, ²³⁵U and ²³⁸U.

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Thorium