August 20, 2022
Uranium-234 is an isotope of uranium. In natural uranium and in uranium ores, U-234 occurs as an indirect decay product of uranium-238, but it accounts for only 0.0055% (55 parts per million) of raw uranium because of its decay time. is only 245,500 years about 1 / 18,000 as long as of U-238. The main production pathway of U-234 through nuclear fission is as follows: The U-238 nucleus emits alpha particles to become thorium-234 (Th-234). Next, with a short half-life, the Th-234 nucleus emits beta particles to become protactinium-234 (Pa-234), or more likely a nuclear isomer, denoted Pa-234m. Finally, the Pa-234 or Pa-234m nucleus emits another beta particle to become the U-234 nucleus. The U-234 nucleus decays by alpha emission to thorium-230, except for the fraction (one billionth) of the nucleus that undergoes spontaneous fission. Extraction of relatively small amounts of U-234 from natural uranium would be possible using isotope separation, similar to that used for conventional uranium enrichment. However, there is no real chemical, physical or technical need to isolate U-234. Very small samples of pure U-234 can be extracted through chemical ion exchange - from the plutonium-238 samples that have been somewhat aged to allow decay to U-234 via alpha emission. Enriched uranium contains more U-234 than natural uranium which is a by-product of uranium enrichment to obtain U-235, a concentration of lighter isotopes that are stronger than U-235. The percentage increase of U-234 in enriched natural uranium is acceptable in current nuclear reactors, but recycled (recyclable) uranium may contain higher fractions of U- 234, which is undesirable. This is because U-234 does not fission and tends to absorb neutrons slowly in a nuclear reactor - becoming U-235. U-234 has a neutron capture cross section of about 100 barns for thermal neutrons and about 700 barns for its resonance integral - averaged over neutrons of different intermediate energies. In a nuclear reactor, non-fissile isotopes capture a neutron-producing fission isotope. U-234 is converted to U-235 more easily and thus at a greater rate than U-238 is Pu-239 (via neptunium-239) because U-238 has a much smaller neutron capture cross-section with only 2 ,7 barns. However, reactions (n, 2n) with fast neutrons also convert a small amount of U-235 to U-234, so the spent nuclear fuel may contain about 0.010% U-234, one billion much higher rate than unirradiated uranium.  Depleted uranium contains less than U-234 (about 0.001% ), making depleted uranium's radioactivity about half that of natural uranium. Natural uranium has an "equilibrium" concentration of U-234 at a point where an equal number of decays of U-238 and U-234 will occur.