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Properties and data of the isotope 238U.


Uranium-238 (Uranium I) is the radioisotope of the element Uranium, whose atomic nucleus has 146 neutrons in addition to the element-specific 92 protons, resulting in a mass number of 238.

See also: list of Uranium isotopes.


General data

Name of the isotope:Uranium-238; U-238Namen:Uran ISymbol:238UMass number A:238Atomic number Z:92 (= number of protons)Neutrons N:146Isotopic mass:238.05079(2) u (atomic weight of Uranium-238)Nuclide mass:238.0003273 u (calculated nuclear mass without electrons)Mass excess:47.31058 MeVMass defect:1.93419068 u (per nucleus)Nuclear binding energy:1801.68701328 MeV (per nucleus)
7.5701135 MeV (average binding energy per nucleon)
Separation energy:SN = 6.1537(13) MeV (first neutron)
SP = 7.509(13) MeV (first proton)
Half-life:4.468(6) × 109 aDecay constant λ:4.919326971729 × 10-18 s-1Spin and parity:0+Charge radius:5.8571(33) femtometer fmYear of discovery:1896


Radioactive Decay

Half-life T½ = 4.468(6) × 109 a respectively 1.40902848 × 1017 seconds s.

Decay modeDaughterProbabilityDecay energyγ energy
α234Thca. 100 %4,2699(21) MeV
SZdiv10-5 %


Graphic representation of the uranium-radium series, the natural radioactive decay series of the uranium isotope U-238.


Uranium radium series


Parent Nuclides

Direct parent isotopes are: 242Pu, 238Pa.



Comparison of the natural Uran isotopes including isotopic abundance (proportion of the isotope mixture):


Atomic Mass maQuantityHalf-lifeSpin
Isotopic mixture
238,02891 u100 %
Isotope 234U234,04095(2) u0,0054(5) %2.455(6) × 105 a0+
Isotope 235U235,04393(2) u0,7204(6) %7.04(1) × 108 a7/2-
Isotope 238U238,05079(2) u99,2742(10) %4.468(6) × 109 a0+


Radiation Protection

The German Radiation Protection Ordinance, for example, specifies the following limit values for the isotope Uranium-238 (exemption limits, clearance values and other values as a radioactive or highly radioactive source of radiation (HASS)):

Isotope:U-238+Exemption level:104 BqExemption level per gram:1 Bq/g
Unrestricted handling of solids and liquids.
Activity HASS:Unbegrenzt (UL)Surface contamination:1 Bq cm-2Half-life:4.5 × 109 a


Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear IsomerExcitation EnergyHalf-lifeSpin
238mU2557,9(5) keV280(6) ns0+


Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 146) and isobaric (same nucleon number A = 238) with Uranium-238. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.


OZIsotone N = 146Isobar A = 238


External data and identifiers

Adopted Levels, Gammas:NuDat 238U


Category: Isotopes

Last update: 26.11.2022

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