The half-life of a radioactive isotope is the
time required for half the quantity of the
isotope to decompose. The half-life of
uranium 238 is 4.5 x 10 raise to 9 years. The half-life of
uranium 234 is 2.5 x 10 raise to 5 years. How much
more greater is the half-life of uranium 238
than uranium 234?
Answers
Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239. 238U cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable. Doppler broadening of 238U's neutron absorption resonances, increasing absorption as fuel temperature increases, is also an essential negative feedback mechanism for reactor control.
Uranium-238,
238
U
Uranium03.jpg
10 gram sample
General
Symbol
238U
Names
uranium-238, U-238
Protons
92
Neutrons
146
Nuclide data
Natural abundance
99.2745%
Half-life
4.468 billion years
Parent isotopes
242Pu (α)
238Pa (β−)
Decay products
234Th
Isotope mass
238.05078826 u
Spin
0
Decay modes
Decay mode
Decay energy (MeV)
Alpha decay
4.267
Isotopes of uranium
Complete table of nuclides
Around 99.284% of natural uranium's mass is uranium-238, which has a half-life of 1.41×1017 seconds (4.468×109 years, or 4.468 billion years).[1] Due to its natural abundance and half-life relative to other radioactive elements, 238U produces ~40% of the radioactive heat produced within the Earth.[2] 238U decay contributes 6 electron anti-neutrinos per decay (1 per beta decay), resulting in a large detectable geoneutrino signal when decays occur within the Earth.[3] The decay of 238U to daughter isotopes is extensively used in radiometric dating, particularly for material older than ~ 1 million years.
Depleted uranium has an even higher concentration of the 238U isotope, and even low-enriched uranium (LEU), while having a higher proportion of the uranium-235 isotope (in comparison to depleted uranium), is still mostly 238U. Reprocessed uranium is also mainly 238U, with about as much uranium-235 as natural uranium, a comparable proportion of uranium-236, and much smaller amounts of other isotopes of uranium such as uranium-234, uranium-233, and uranium-232.[4]