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Isotopes of uranium

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Isotopesofuranium(92U)
Main isotopes[1] Decay
abun­dance half-life(t1/2) mode pro­duct
232U synth 68.9 y α 228Th
SF –
233U trace 1.592×105y[2] α 229Th
SF –
234U 0.005% 2.455×105y α 230Th
SF –
235U 0.720% 7.038×108y α 231Th
SF –
236U trace 2.342×107y α 232Th
SF –
238U 99.3% 4.468×109y α 234Th
SF –
β−β− 238Pu
Standard atomic weightAr°(U)

Uranium(92U) is a naturally occurringradioactiveelement (radioelement) with nostable isotopes.It has twoprimordial isotopes,uranium-238anduranium-235,that have longhalf-livesand are found in appreciable quantity inEarth's crust.Thedecay producturanium-234is also found. Other isotopes such asuranium-233have been produced inbreeder reactors.In addition to isotopes found in nature or nuclear reactors, many isotopes with far shorter half-lives have been produced, ranging from214U to242U (except for220U). Thestandard atomic weightofnatural uraniumis238.02891(3).

Natural uranium consists of three mainisotopes,238U (99.2739–99.2752%natural abundance),235U (0.7198–0.7202%), and234U (0.0050–0.0059%).[5]All three isotopes areradioactive(i.e., they areradioisotopes), and the most abundant and stable is uranium-238, with a half-life of4.4683×109years(about theage of the Earth).

Uranium-238 is analpha emitter,decaying through the 18-memberuranium seriesintolead-206.Thedecay series of uranium-235(historically called actino-uranium) has 15 members and ends in lead-207. The constant rates of decay in these series makes comparison of the ratios of parent-to-daughter elements useful inradiometric dating.Uranium-233 is made fromthorium-232byneutronbombardment.

Uranium-235 is important for bothnuclear reactors(energy production) andnuclear weaponsbecause it is the only isotope existing in nature to any appreciable extent that isfissilein response tothermal neutrons,i.e., thermalneutron capturehas a high probability of inducing fission. Achain reactioncan be sustained with a large enough (critical) mass of uranium-235. Uranium-238 is also important because it isfertile:it absorbs neutrons to produce a radioactive isotope that decays intoplutonium-239,which also is fissile.

List of isotopes

[edit]


Nuclide
[n 1] 		Historic
name 		Z N Isotopic mass(Da)[6]
[n 2][n 3] 		Half-life[1]
 Decay
mode[1]
[n 4] 		Daughter
isotope
[n 5][n 6] 		Spinand
parity[1]
[n 7][n 8] 		Natural abundance(mole fraction)
Excitation energy[n 8] Normal proportion[1] Range of variation
214U[7] 92 122 0.52+0.95
−0.21ms 		α 210Th 0+
215U 92 123 215.026720(11) 1.4(0.9) ms α 211Th 5/2−#
β+? 215Pa
216U[8] 92 124 216.024760(30) 2.25+0.63
−0.40ms 		α 212Th 0+
216mU 2206 keV 0.89+0.24
−0.16ms 		α 212Th 8+
217U[9] 92 125 217.024660(86)# 19.3+13.3
−5.6ms 		α 213Th (1/2−)
β+? 217Pa
218U[8] 92 126 218.023505(15) 650+80
−70μs 		α 214Th 0+
218mU 2117 keV 390+60
−50μs 		α 214Th 8+
IT? 218U
219U 92 127 219.025009(14) 60(7) μs α 215Th (9/2+)
β+? 219Pa
221U 92 129 221.026323(77) 0.66(14) μs α 217Th (9/2+)
β+? 221Pa
222U 92 130 222.026058(56) 4.7(0.7) μs α 218Th 0+
β+? 222Pa
223U 92 131 223.027961(63) 65(12) μs α 219Th 7/2+#
β+? 223Pa
224U 92 132 224.027636(16) 396(17) μs α 220Th 0+
β+? 224Pa
225U 92 133 225.029385(11) 62(4) ms α 221Th 5/2+#
226U 92 134 226.029339(12) 269(6) ms α 222Th 0+
227U 92 135 227.0311811(91) 1.1(0.1) min α 223Th (3/2+)
β+? 227Pa
228U 92 136 228.031369(14) 9.1(0.2) min α (97.5%) 224Th 0+
EC(2.5%) 228Pa
229U 92 137 229.0335060(64) 57.8(0.5) min β+(80%) 229Pa (3/2+)
α (20%) 225Th
230U 92 138 230.0339401(48) 20.23(0.02) d α 226Th 0+
SF? (various)
CD(4.8×10−12%) 208Pb
22Ne
231U 92 139 231.0362922(29) 4.2(0.1) d EC 231Pa 5/2+#
α (.004%) 227Th
232U 92 140 232.0371548(19) 68.9(0.4) y α 228Th 0+
CD(8.9×10−10%) 208Pb
24Ne
SF (10−12%) (various)
CD? 204Hg
28Mg
233U 92 141 233.0396343(24) 1.592(2)×105y α 229Th 5/2+ Trace[n 9]
CD (≤7.2×10−11%) 209Pb
24Ne
SF? (various)
CD? 205Hg
28Mg
234U[n 10][n 11] Uranium II 92 142 234.0409503(12) 2.455(6)×105y α 230Th 0+ [0.000054(5)][n 12] 0.000050–
0.000059
SF (1.64×10−9%) (various)
CD (1.4×10−11%) 206Hg
28Mg
CD (≤9×10−12%) 208Pb
26Ne
CD (≤9×10−12%) 210Pb
24Ne
234mU 1421.257(17) keV 33.5(2.0) ms IT 234U 6−
235U[n 13][n 14][n 15] Actin Uranium
Actino-Uranium 		92 143 235.0439281(12) 7.038(1)×108y α 231Th 7/2− [0.007204(6)] 0.007198–
0.007207
SF (7×10−9%) (various)
CD (8×10−10%) 215Pb
20Ne
CD (8×10−10%) 210Pb
25Ne
CD (8×10−10%) 207Hg
28Mg
235m1U 0.076737(18) keV 25.7(1) min IT 235U 1/2+
235m2U 2500(300) keV 3.6(18) ms SF (various)
236U Thoruranium[10] 92 144 236.0455661(12) 2.342(3)×107y α 232Th 0+ Trace[n 16]
SF (9.6×10−8%) (various)
CD (≤2.0×10−11%)[11] 208Hg
28Mg
CD (≤2.0×10−11%)[11] 206Hg
30Mg
236m1U 1052.5(6) keV 100(4) ns IT 236U 4−
236m2U 2750(3) keV 120(2) ns IT (87%) 236U (0+)
SF (13%) (various)
237U 92 145 237.0487283(13) 6.752(2) d β− 237Np 1/2+ Trace[n 17]
237mU 274.0(10) keV 155(6) ns IT 237U 7/2−
238U[n 11][n 13][n 14] Uranium I 92 146 238.050787618(15)[12] 4.468(3)×109y α 234Th 0+ [0.992742(10)] 0.992739–
0.992752
SF (5.44×10−5%) (various)
β−β−(2.2×10−10%) 238Pu
238mU 2557.9(5) keV 280(6) ns IT (97.4%) 238U 0+
SF (2.6%) (various)
239U 92 147 239.0542920(16) 23.45(0.02) min β− 239Np 5/2+ Trace[n 18]
239m1U 133.7991(10) keV 780(40) ns IT 239U 1/2+
239m2U 2500(900)# keV >250 ns SF? (various) 0+
IT? 239U
240U 92 148 240.0565924(27) 14.1(0.1) h β− 240Np 0+ Trace[n 19]
α? 236Th
241U[13] 92 149 241.06031(5) ~40 min[14][15] β− 241Np 7/2+#
242U 92 150 242.06296(10)[13] 16.8(0.5) min β− 242Np 0+
This table header & footer:
  1. ^mU – Excitednuclear isomer.
  2. ^( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. ^# – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. ^ Modes of decay:
    CD: Cluster decay
    EC: Electron capture
    SF: Spontaneous fission
  5. ^Bold italics symbolas daughter – Daughter product is nearly stable.
  6. ^Bold symbolas daughter – Daughter product is stable.
  7. ^( ) spin value – Indicates spin with weak assignment arguments.
  8. ^ab# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  9. ^Intermediate decay product of237Np
  10. ^Used inuranium–thorium dating
  11. ^abUsed inuranium–uranium dating
  12. ^Intermediatedecay productof238U
  13. ^abPrimordialradionuclide
  14. ^abUsed inUranium–lead dating
  15. ^Important in nuclear reactors
  16. ^Intermediate decay product of244Pu,also produced byneutron captureof235U
  17. ^Neutron capture product, parent of trace quantities of237Np
  18. ^Neutron capture product; parent of trace quantities of239Pu
  19. ^Intermediate decay product of244Pu

Actinides vs fission products

[edit]
Actinides and fission products by half-life
Actinides[16]bydecay chain Half-life
range (a) 		Fission productsof235Ubyyield[17]
4n 4n+ 1 4n+ 2 4n+ 3 4.5–7% 0.04–1.25% <0.001%
228Ra№ 4–6 a 155Euþ
248Bk[18] > 9 a
244Cmƒ 241Puƒ 250Cf 227Ac№ 10–29 a 90Sr 85Kr 113mCdþ
232Uƒ 238Puƒ 243Cmƒ 29–97 a 137Cs 151Smþ 121mSn
249Cfƒ 242mAmƒ 141–351 a

No fission products have ahalf-life
in the range of 100 a–210 ka...

241Amƒ 251Cfƒ[19] 430–900 a
226Ra№ 247Bk 1.3–1.6 ka
240Pu 229Th 246Cmƒ 243Amƒ 4.7–7.4 ka
245Cmƒ 250Cm 8.3–8.5 ka
239Puƒ 24.1 ka
230Th№ 231Pa№ 32–76 ka
236Npƒ 233Uƒ 234U№ 150–250 ka 99Tc₡ 126Sn
248Cm 242Pu 327–375 ka 79Se₡
1.33 Ma 135Cs₡
237Npƒ 1.61–6.5 Ma 93Zr 107Pd
236U 247Cmƒ 15–24 Ma 129I₡
244Pu 80 Ma

... nor beyond 15.7 Ma[20]

232Th№ 238U№ 235Uƒ№ 0.7–14.1 Ga

Uranium-214

[edit]

Uranium-214 is the lightest known isotope of uranium. It was discovered at the Spectrometer for Heavy Atoms and Nuclear Structure (SHANS) at the Heavy Ion Research Facility inLanzhou,Chinain 2021, produced by firing argon-36 at tungsten-182. It alpha-decays with a half-life of0.5 ms.[21][22][23][24]

Uranium-232

[edit]
Main article:Uranium-232

Uranium-232 has a half-life of 68.9 years and is a side product in thethorium cycle.It has been cited as an obstacle tonuclear proliferationusing233U, because the intensegamma radiationfrom208Tl(a daughter of232U, produced relatively quickly) makes233U contaminated with it more difficult to handle. Uranium-232 is a rare example of aneven-even isotopethat isfissilewith both thermal and fast neutrons.[25][26]

Uranium-233

[edit]
Main article:Uranium-233

Uranium-233 is a fissile isotope that is bred fromthorium-232as part of the thorium fuel cycle.233U was investigated for use in nuclear weapons and as a reactor fuel. It was occasionally tested but never deployed in nuclear weapons and has not been used commercially as a nuclear fuel.[27]It has been used successfully in experimental nuclear reactors and has been proposed for much wider use as a nuclear fuel. It has a half-life of around 160,000 years.

Uranium-233 is produced by neutron irradiation of thorium-232. When thorium-232 absorbs aneutron,it becomesthorium-233,which has a half-life of only 22 minutes. Thorium-233beta decaysintoprotactinium-233.Protactinium-233 has a half-life of 27 days and beta decays into uranium-233; some proposed molten salt reactor designs attempt to physically isolate the protactinium from further neutron capture before beta decay can occur.

Uranium-233 usually fissions on neutron absorption but sometimes retains the neutron, becominguranium-234.The capture-to-fission ratio is smaller than the other two major fissile fuels,uranium-235andplutonium-239;it is also lower than that of short-livedplutonium-241,but bested by very difficult-to-produceneptunium-236.

Uranium-234

[edit]
Main article:Uranium-234

234U occurs in natural uranium as an indirect decay product of uranium-238, but makes up only 55 parts permillionof the uranium because itshalf-lifeof 245,500 years is only about 1/18,000 that of238U. The path of production of234U is this:238Ualpha decaystothorium-234.Next, with a shorthalf-life,234Thbeta decaystoprotactinium-234.Finally,234Pa beta decays to234U.[28][29]

234Ualpha decaystothorium-230,except for a small percentage of nuclei that undergospontaneous fission.

Extraction of small amounts of234U from natural uranium could be done usingisotope separation,similar to normal uranium-enrichment. However, there is no real demand inchemistry,physics,or engineering for isolating234U. Very small pure samples of234U can be extracted via the chemicalion-exchangeprocess, from samples ofplutonium-238that have aged somewhat to allow some alpha decay to234U.

Enriched uraniumcontains more234U than natural uranium as a byproduct of the uranium enrichment process aimed at obtaininguranium-235,which concentrates lighter isotopes even more strongly than it does235U. The increased percentage of234U in enriched natural uranium is acceptable in current nuclear reactors, but (re-enriched)reprocessed uraniummight contain even higher fractions of234U, which is undesirable.[30]This is because234U is notfissile,and tends to absorb slowneutronsin anuclear reactor—becoming235U.[29][30]

234U has aneutron capturecross section of about 100barnsforthermal neutrons,and about 700 barns for itsresonance integral—the average over neutrons having various intermediate energies. In a nuclear reactor, non-fissile isotopes capture a neutron breeding fissile isotopes.234U is converted to235U more easily and therefore at a greater rate thanuranium-238is toplutonium-239(vianeptunium-239), because238U has a much smaller neutron-capturecross sectionof just 2.7 barns.

Uranium-235

[edit]
Main article:Uranium-235

Uranium-235 makes up about 0.72% of natural uranium. Unlike the predominant isotopeuranium-238,it isfissile,i.e., it can sustain afissionchain reaction.It is the onlyfissile isotopethat is aprimordial nuclideor found in significant quantity in nature.

Uranium-235 has ahalf-lifeof 703.8million years.It was discovered in 1935 byArthur Jeffrey Dempster.Its (fission) nuclearcross sectionfor slowthermal neutronis about 504.81barns.For fastneutronsit is on the order of 1 barn. At thermal energy levels, about 5 of 6 neutron absorptions result in fission and 1 of 6 result in neutron capture forminguranium-236.[31]The fission-to-capture ratio improves for faster neutrons.

Uranium-236

[edit]
Main article:Uranium-236

Uranium-236has a half-life of about 23 million years; and is neither fissile with thermal neutrons, nor very good fertile material, but is generally considered a nuisance and long-livedradioactive waste.It is found in spentnuclear fueland in the reprocessed uranium made from spent nuclear fuel.

Uranium-237

[edit]

Uranium-237has a half-life of about 6.75 days. It decays intoneptunium-237bybeta decay.It was discovered by Japanese physicistYoshio Nishinain 1940, who in a near-miss discovery, inferred the creation of element 93, but was unable to isolate the then-unknown element or measure its decay properties.[32]

Uranium-238

[edit]
Main article:Uranium-238

Uranium-238 (238U or U-238) is the most commonisotopeofuraniumin nature. It is notfissile,but isfertile:it can capture a slowneutronand after twobeta decaysbecome fissileplutonium-239.Uranium-238 is fissionable by fast neutrons, but cannot support a chain reaction because inelastic scattering reducesneutron energybelow the range where fast fission of one or more next-generation nuclei is probable. Doppler broadening of238U's neutron absorption resonances, increasing absorption as fuel temperature increases, is also an essential negative feedback mechanism for reactor control.

About 99.284% of natural uranium is uranium-238, which has a half-life of 1.41×1017seconds (4.468×109years). Depleted uranium has an even higher concentration of238U, and even low-enriched uranium (LEU) is still mostly238U. Reprocessed uranium is also mainly238U, 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 asuranium-234,uranium-233,anduranium-232.

Uranium-239

[edit]

Uranium-239is usually produced by exposing238U toneutron radiationin a nuclear reactor.239U has a half-life of about 23.45 minutes andbeta decaysintoneptunium-239,with a total decay energy of about 1.29 MeV.[33]The most common gamma decay at 74.660 keV accounts for the difference in the two major channels of beta emission energy, at 1.28 and 1.21 MeV.[34]

239Np then, with a half-life of about 2.356 days, beta-decays toplutonium-239.

Uranium-241

[edit]

In 2023, in a paper published inPhysical Review Letters,a group of researchers based in Korea reported that they had founduranium-241in an experiment involving238U+198Pt multinucleon transfer reactions.[35][36] Its half-life is about 40 minutes.[35]

References

[edit]
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  16. ^Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability afterpolonium(84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap isradon-222with a half life of less than fourdays). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
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    "The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk248with a half-life greater than 9 [years]. No growth of Cf248was detected, and a lower limit for the β−half-life can be set at about 104[years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]. "
  19. ^This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
  20. ^Excluding those "classically stable"nuclides with half-lives significantly in excess of232Th; e.g., while113mCd has a half-life of only fourteen years, that of113Cd is eightquadrillionyears.
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