Uranium-238 (²³⁸U)

Data nuklida

Unsur

Uranium (U, Z = 92)

Nomor massa (A)

238

Proton (Z)

92

Neutron (N)

146

Massa atom

238.050786936 ± 0.000001601 u

Waktu paruh

4,463 miliar tahun (± 0,003 miliar tahun)

Mode peluruhan

Peluruhan alfa (α) ( 100 %)

Inti anak

Torium-234 (²³⁴Th)

Kelimpahan alami

0.992 742(10)

Tahun penemuan

1896

Sumber data

IAEA Atomic Mass Data Center (NUBASE) and IUPAC CIAAW, via PubChem

Kegunaan isotop uranium

• 234U (with a half-life of 2.432×105 years) is a daughter product of 238U (with a half-life of 4.47×1010 years) and makes up only 0.0054 percent of the total uranium today. During the decay of the parent radionuclide 238U nucleus (first to 234Th (with a half-life of 24 days) by alpha decay, then to 234Pa (with a half-life of 6.7 h) by beta-minus, and finally to 234U by beta-minus), the energy released will damage the chemical and physical bonds holding the 234U product nuclei in a mineral. As a result, 234U may be leached more easily from water or rock samples than 238U and the isotope-amount ratio n(234U)/n(238U) will vary depending on the extent of water-rock interaction.
• The three natural radioactive decay chains beginning with 238U, 235U, and 232Th each have comparable half-lives that are much longer than the radioactive isotopes that follow until the production of stable isotopes of 206Pb, 207Pb, and 208Pb, respectively. When undisturbed, the activities of daughter isotopes in each decay chain are equal to their parents and one can measure the accumulation of the stable isotopes of lead to date the time that has elapsed since a mineral became a closed system (a system that does not exchange matter with its surroundings). Rocks formed hundreds of millions to billions of years ago can be dated using this technique. If a mineral is disturbed at some point during the decay and isotopes in the decay chain are preferentially removed from the system, the equilibria in a decay sequence will be disturbed. For example, one can measure the excess of 230Th (with a half-life of 7.56×104 years) relative to the 234U parent radionuclide to date carbonates (speleothems or corals) that are less than 5×105 years old.
• Nuclei of 235U are split when bombarded by thermal neutrons. The process is known as nuclear fission and can release tremendous amounts of energy per uranium nucleus. The nucleus that splits will release additional neutrons that, if slowed down sufficiently, can cause subsequent fission events. When properly controlled, 235U fission can be used to generate heat to drive steam turbines, which in turn produces electricity (Fig. IUPAC.92.1). If the fission process is not controlled, then a rapid and explosive release of energy will occur, similar to that of nuclear weapons. Uranium depleted in 235U by fission in nuclear reactors (and hence greatly enriched in 238U compared to “natural” uranium) is used in the manufacture of DUCRETE concrete (Fig. IUPAC.92.2). The incorporation of the large 238U nuclei makes this material an effective absorber of neutrons and gamma rays, and DUCRETE concrete is used to reduce fluxes of neutrons and high-energy photons. The alpha particles produced by the decay of 238U are effectively absorbed by the concrete and do not pose a health risk. DUCRETE is being proposed as a suitable material for the storage of radioactive waste,.

Reaksi inti

• Peluruhan alfa uranium-238

Isotop uranium lainnya

²¹⁵U, ²¹⁶U, ²¹⁷U, ²¹⁸U, ²¹⁹U, ²²⁰U, ²²¹U, ²²²U, ²²³U, ²²⁴U, ²²⁵U, ²²⁶U, ²²⁷U, ²²⁸U, ²²⁹U, ²³⁰U, ²³¹U, ²³²U, ²³³U, ²³⁴U, ²³⁵U, ²³⁶U, ²³⁷U, ²³⁹U, ²⁴⁰U, ²⁴¹U, ²⁴²U, ²⁴³U

Pelajari

Kimia inti Simulasi peluruhan ²³⁸U Bagan nuklida