Uranium-238

Properties and data of the isotope ²³⁸U.

Content

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.

General data

Name of the isotope:Uranium-238; U-238Other names:Uran ISymbol:²³⁸U or 23892UMass number A:238 (= number of nucleons)Atomic 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:S_N = 6.1537(13) MeV (first neutron)
S_P = 7.509(13) MeV (first proton)Half-life:4.468(6) × 10⁹ aDecay constant λ:4.919326971729 × 10^-18 s^-1Specific activity α:12447.428554556 Bq g^-1
3.364169879609 × 10^-7 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Charge radius:5.8571(33) femtometer fmYear of discovery:1896

Radioactive Decay

Half-life T_½ = 4.468(6) × 10⁹ a respectively 1.40902848 × 10¹⁷ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²³⁴Th	ca. 100 %	4.2699(21) MeV
SZ	div	10^-5 %

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

Parent Nuclides

Direct parent isotopes are: ²⁴²Pu, ²³⁸Pa.

Occurrence

Comparison of the natural Uranium isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):

	Atomic Mass m_a	Quantity	Half-life	Spin
Uranium Isotopic mixture	238.02891 u	100 %
Isotope ²³⁴U	234.04095(2) u	0.0054(5) %	2.455(6) × 10⁵ a	0+
Isotope ²³⁵U	235.04393(2) u	0.7204(6) %	7.04(1) × 10⁸ a	7/2-
Isotope ²³⁸U	238.05079(2) u	99.2742(10) %	4.468(6) × 10⁹ a	0+

Nuclear Isomers

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

Nuclear Isomer	Excitation Energy	Half-life	Spin
^238mU	2557.9(5) keV	280(6) ns	0+

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.

OZ	Isotone N = 146	Isobar A = 238
87	²³³Fr
88	²³⁴Ra
89	²³⁵Ac
90	²³⁶Th	²³⁸Th
91	²³⁷Pa	²³⁸Pa
92	²³⁸U	²³⁸U
93	²³⁹Np	²³⁸Np
94	²⁴⁰Pu	²³⁸Pu
95	²⁴¹Am	²³⁸Am
96	²⁴²Cm	²³⁸Cm
97	²⁴³Bk	²³⁸Bk
98	²⁴⁴Cf	²³⁸Cf
99	²⁴⁵Es
100	²⁴⁶Fm
101	²⁴⁷Md