Uranium-234


Uranium-234

Infobox isotope


background = #fc6
text_color =
isotope_name = Uranium-234
isotope_filename =
alternate_names =
mass_number =234
symbol =U
num_neutrons =142
num_protons =92
abundance =0.0055%
halflife =246,000 years
error_halflife =
decay_product = Thorium-230
decay_mass =230
decay_symbol =Th
parent = Plutonium-238
parent_mass =238
parent_symbol =Pu
parent_decay = a
parent2 = Protactinium-234
parent2_mass = 234
parent2_symbol = Pa
parent2_decay = b-
parent3 = Neptunium-234
parent3_mass = 234
parent3_symbol = Np
parent3_decay = b+
mass =
spin =
excess_energy =
error1 =
binding_energy =
error2 =
decay_mode1 =Alpha decay
decay_energy1 =
decay_mode2 =
decay_energy2 =
decay_mode3 =
decay_energy3 =
decay_mode4 =
decay_energy4 =
Uranium-234 is an isotope of Uranium. In natural uranium and uranium ore, 234U occurs as an indirect decay product of 238U, but it makes up only 0.0055% of the raw uranium because its half-life of just 246,000 years is only about 1/18,000 as long as the half-life of 238U.

Large-scale extraction of 234U from natural uranium would only be feasible by isotope separation similar to that used for uranium enrichment, and there is no industrial demand for isolating U-234. Pure samples of U-234 can be extracted (by ion exchange) from pure plutonium-238 which has been aged to allow some of it to decay to 234U.

Enriched uranium contains more U-234 than natural uranium as a side-effect of enrichment for U-235, which concentrates lighter isotopes even more. The increased level of U-234 in enriched natural uranium is acceptable in current nuclear reactors but re-enriched reprocessed uranium may contain higher levels which are undesirable.

234U has a neutron absorption cross section of 100 barns for thermal neutrons, and 700 barns for resonance integral, an average over neutrons of various intermediate energies. Hence, in a thermal reactor, it is converted to fissile 235U at a faster rate than the much larger amount of 238U (with an absorption cross section of 2.7) is converted to 239Pu. Thus spent nuclear fuel should contain only some of the 234U that was in the fresh fuel.

Depleted uranium contains much less U-234 (around 0.001% [ [http://www.who.int/mediacentre/factsheets/fs257/en/ WHO | Depleted uranium] ] ) which makes the radioactivity of depleted uranium about one-half of that of natural uranium, since natural uranium has an "equilibrium" concentration of 234U, and therefore an equal number of decays of 238U and 234U will occur. Depleted uranium also contains less U-235, but in spite of its half-life which is shorter than U-238's, the concentration of U-235 in natural uranium is low enough so that the U-235 depletion does not result in a significant reduction in radioactivity.

Isotope|element=Uranium
lighter=Uranium-233
heavier=Uranium-235
before=Plutonium-238 (α)
Protactinium-234 (β-)
Neptunium-234 "'(β+)
after=Thorium-230 "'(α)

ee also

*Uranium-uranium dating

References


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