Does radioactive dating with isotopes of uranium and thorium
U) is a naturally occurring radioactive element that has no stable isotope.It has two primordial isotopes, (uranium-238 and uranium-235), that have long half-lives and are found in appreciable quantity in the Earth's crust. Other isotopes such as uranium-232 have been produced in breeder reactors.U-234 has a neutron capture cross-section of about 100 barns for thermal neutrons, and about 700 barns for its resonance integral—the average over neutrons having various intermediate energies.In a nuclear reactor non-fissile isotopes capture a neutron breeding fissile isotopes.Protactinium-233 has a half-life of 27 days and beta decays into uranium-233; some proposed molten salt reactor designs attempt to physically isolate the protactinium from further neutron capture before beta decay can occur.
Finally, Pa-234 nuclei each emit another beta particle to become U-234 nuclei.
In addition to isotopes found in nature or nuclear reactors, many isotopes with far shorter half-lives have been produced, ranging from years (close to the age of the Earth).
Uranium-238 is an α emitter, decaying through the 18-member uranium series into lead-206.
Enriched uranium contains more U-234 than natural uranium as a byproduct of the uranium enrichment process aimed at obtaining U-235, which concentrates lighter isotopes even more strongly than it does U-235.
The increased percentage of U-234 in enriched natural uranium is acceptable in current nuclear reactors, but (re-enriched) reprocessed uranium might contain even higher fractions of U-234, which is undesirable.