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Isotopes of uranium

Uranium (U)
Standard atomic mass: 238.02891(3) u
The element has no stable isotopes. However, it has a characteristic terrestrial isotopic composition and thus an atomic mass can be given.

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Isotopes of uranium were known as:

uranium II : ²³⁴U
actino-uranium : ²³⁵U
uranium I : ²³⁸U

Naturally occurring uranium is composed of three major isotopes, uranium-238 (99.28% natural abundance), uranium-235 (0.71%), and uranium-234 (0.0054%). All three isotopes are radioactive, creating radioisotopes, with the most abundant and stable being uranium-238 with a half-life of 4.51×10⁹ years (close to the age of the Earth), uranium-235 with a half-life of 7.13×10⁸ years, and uranium-234 with a half-life of 2.48×10⁵ years.^[1]

Uranium-238 is an α emitter, decaying through the 18-member uranium natural decay series into lead-206.^[2] The constant rates of decay in these series makes comparison of the ratios of parent to daughter elements useful in radiometric dating. Uranium-233 is made from thorium-232 by neutron bombardment.

The isotope uranium-235 is important for both nuclear reactors and nuclear weapons because it is the only isotope existing in nature to any appreciable extent that is fissile, that is, can be broken apart by thermal neutrons.^[2] The isotope uranium-238 is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope plutonium-239, which also is fissile.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
nuclide symbol	excitation energy			half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
²¹⁷U	92	125	217.02437(9)	26(14) ms [16(+21-6) ms]	1/2-#
²¹⁸U	92	126	218.02354(3)	6(5) ms	0+
²¹⁹U	92	127	219.02492(6)	55(25) µs [42(+34-13) µs]	9/2+#
²²⁰U	92	128	220.02472(22)#	60# ns	0+
²²¹U	92	129	221.02640(11)#	700# ns	9/2+#
²²²U	92	130	222.02609(11)#	1.4(7) µs [1.0(+10-4) µs]	0+
²²³U	92	131	223.02774(8)	21(8) µs [18(+10-5) µs]	7/2+#
²²⁴U	92	132	224.027605(27)	940(270) µs	0+
²²⁵U	92	133	225.029391(12)	61(4) ms	5/2+#
²²⁶U	92	134	226.029339(14)	269(6) ms	0+
²²⁷U	92	135	227.031156(18)	1.1(1) min	(3/2+)
²²⁸U	92	136	228.031374(16)	9.1(2) min	0+
²²⁹U	92	137	229.033506(6)	58(3) min	(3/2+)
²³⁰U	92	138	230.033940(5)	20.8 d	0+
²³¹U	92	139	231.036294(3)	4.2(1) d	(5/2)(+#)
²³²U	92	140	232.0371562(24)	68.9(4) y	0+
²³³U	92	141	233.0396352(29)	1.592(2)E+5 y	5/2+
²³⁴U	92	142	234.0409521(20)	2.455(6)E+5 y	0+	[0.000054(5)]	0.000050-0.000059
^234mU	1421.32(10) keV			33.5(20) µs	6-
²³⁵U	92	143	235.0439299(20)	7.04(1)E+8 y	7/2-	[0.007204(6)]	0.007198-0.007207
^235mU	0.0765(4) keV			~26 min	1/2+
²³⁶U	92	144	236.045568(2)	2.342(3)E+7 y	0+
^236m1U	1052.89(19) keV			100(4) ns	(4)-
^236m2U	2750(10) keV			120(2) ns	(0+)
²³⁷U	92	145	237.0487302(20)	6.75(1) d	1/2+
²³⁸U	92	146	238.0507882(20)	4.468(3)E+9 y	0+	[0.992742(10)]	0.992739-0.992752
^238mU	2557.9(5) keV			280(6) ns	0+
²³⁹U	92	147	239.0542933(21)	23.45(2) min	5/2+
^239m1U	20(20)# keV			>250 ns	(5/2+)
^239m2U	133.7990(10) keV			780(40) ns	1/2+
²⁴⁰U	92	148	240.056592(6)	14.1(1) h	0+
²⁴¹U	92	149	241.06033(32)#	5# min	7/2+#
²⁴²U	92	150	242.06293(22)#	16.8(5) min	0+

Notes

Evaluated isotopic composition is for most but not all commercial samples.
The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
Commercially available materials may have been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the given mass and composition can occur.
Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References

^ Seaborg, Encyclopedia of the Chemical Elements (1968), page 777
^ ^a ^b The decay series of uranium-235 (also called actino-uranium) has 15 members that ends in lead-207, protactinium-231 and actinium-227.

Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
- Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
- National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005). your mum
- David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.

Isotopes of protactinium	Isotopes of uranium	Isotopes of neptunium
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Category: Isotopes of uranium

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