Isotopes of uranium

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Actinides Half-life Fission products
244Cm 241Pu f 250Cf 243Cmf 10–30 y 137Cs 90Sr 85Kr
232U  f 238Pu f is for
fissile		 69–90 y 151Sm nc➔
4n 249Cf  f 242Amf 141–351 No fission product
has half-life 102
to 2×105 years
241Am 251Cf  f 431–898
240Pu 229Th 246Cm 243Am 5–7 ky
4n 245Cmf 250Cm 239Pu f 8–24 ky
233U    f 230Th 231Pa 32–160
4n+1 234U 4n+3 211–290 99Tc 126Sn 79Se
248Cm 242Pu 340–373 Long-lived fission products
237Np 4n+2 1–2 My 93Zr 135Cs nc➔
236U 4n+1 247Cmf 6–23 My 107Pd 129I
244Pu 80 My >7% >5% >1% >.1%
232Th 238U 235U    f 0.7–12 Gy fission product yield

Uranium (U) is a naturally occurring radioactive element that has no stable isotopes but two primordial isotopes (uranium-238 and uranium-235) that have long half-life and are found in appreciable quantity in the Earth's crust, along with the decay product uranium-234. The average atomic mass of natural uranium is 238.02891(3) u. Other isotopes such as uranium-232 have been produced in breeder reactors.

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 4.4683×109 years (close to the age of the Earth), uranium-235 with a half-life of 7.038×108 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 series into lead-206. The decay series of uranium-235 (historically called actino-uranium) has 15 members that ends in lead-207. 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. 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.

Contents

[edit] Uranium-232

Isotopes of uranium
General
Name, symbol Isotopes of uranium,232U
Neutrons 140
Protons 92
Nuclide data
Natural abundance syn
Half-life 68.9 years
Parent isotopes 236Pu (α)
232Np (β+)
232Pa (β−)
Decay products 228Th
Actinides Half-life Fission products
244Cm 241Pu f 250Cf 243Cmf 10–30 y 137Cs 90Sr 85Kr
232U  f 238Pu f is for
fissile		 69–90 y 151Sm nc➔
4n 249Cf  f 242Amf 141–351 No fission product
has half-life 102
to 2×105 years
241Am 251Cf  f 431–898
240Pu 229Th 246Cm 243Am 5–7 ky
4n 245Cmf 250Cm 239Pu f 8–24 ky
233U    f 230Th 231Pa 32–160
4n+1 234U 4n+3 211–290 99Tc 126Sn 79Se
248Cm 242Pu 340–373 Long-lived fission products
237Np 4n+2 1–2 My 93Zr 135Cs nc➔
236U 4n+1 247Cmf 6–23 My 107Pd 129I
244Pu 80 My >7% >5% >1% >.1%
232Th 238U 235U    f 0.7–12 Gy fission product yield

Uranium 232 (232
92U
140, 232
U, U-232) is an isotope of uranium. It has a half-life of 68.9 years and is a side product in the thorium cycle. It has been cited as an obstacle to nuclear proliferation using 233U as the fissile material, because the intense gamma radiation of 232U's decay products makes the 233U contaminated with it more difficult to handle.

Production of 233U (through the irradiation of 233Th) invariably produces small amounts of 232U as an impurity, because of parasitic (n,2n) reactions on uranium-233 itself, or on protactinium-233:

232Th (n,γ) 233Th (β−) 233Pa (β−) 233U (n,2n) 232U
232Th (n,γ) 233Th (β−) 233Pa (n,2n) 232Pa (β−) 232U

The decay chain of 232U quickly yields strong gamma radiation emitters:

232U (α, 68.9 years)
228Th (α, 1.9 year)
224Ra (α, 3.6 day, 0.24 MeV) (at this point, the decay chain is identical to that of 232Th)
220Rn (α, 55 s, 0.54 MeV)
216Po (α, 0.15 s)
212Pb (β−, 10.64 h)
212Bi (α, 61 s, 0.78 MeV)
208Tl (β−, 3 m, 2.6 MeV)
208Pb (stable)

This makes manual handling in a glove box with only light shielding (as commonly done with plutonium) too hazardous, (except possibly in a short period immediately following chemical separation of the uranium from thorium-228, radium-224, radon-220, and polonium) and instead requiring remote manipulation for fuel fabrication.

Unusually for an isotope with even mass number, 232U has a significant neutron absorption cross section for fission (thermal neutrons 75 barns (b), resonance integral 380 b) as well as for neutron capture (thermal 73 b, resonance integral 280 b).

Lighter:
uranium-231		 Isotopes of uranium is an
isotope of uranium		 Heavier:
uranium-233
Decay product of:
plutonium-236 (α)
neptunium-232 (β+)
protactinium-232 (β−)		 Decay chain
of Isotopes of uranium		 Decays to:
thorium-228 (α)

[edit] Uranium-239

Isotopes of uranium
General
Name, symbol U-239,239U
Neutrons 147
Protons 92
Nuclide data
Natural abundance syn
Half-life 23.45 mins
Decay products 239Np
Decay mode Decay energy
Beta decay 20% 1.28 MeV
Beta decay 80% 1.21 MeV

Uranium-239 is an isotope of uranium. It is usually produced by exposing 238U to neutron radiation in a nuclear reactor. 239U has a half-life of about 23.45 minutes and decays into neptunium-239 through beta decay, with a total decay energy of about 1.29 Mev.[2]. 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.[3]

239Np further decays to plutonium-239, in a second important step which ultimately produces fissile 239Pu (used in weapons and for nuclear power), from 238U in reactors.

Lighter:
Uranium-238		 Isotopes of uranium is an
isotope of Uranium		 Heavier:
Uranium-240
Decay product of:
Protactinium-239 (β-)		 Decay chain
of Isotopes of uranium		 Decays to:
Neptunium-239 (β-)


[edit] Table

nuclide
symbol		 historic
name		 Z(p) N(n)  
isotopic mass (u)
 		 half-life decay
mode(s)[4][n 1]		 daughter
isotope(s)[n 2]		 nuclear
spin		 representative
isotopic
composition
(mole fraction)		 range of natural
variation
(mole fraction)
excitation energy
217U 92 125 217.02437(9) 26(14) ms
[16(+21-6) ms]		 1/2-#
218U 92 126 218.02354(3) 6(5) ms α 214Th 0+
219U 92 127 219.02492(6) 55(25) ms
[42(+34-13) ms]		 α 215Th 9/2+#
220U 92 128 220.02472(22)# 60# ns α 216Th 0+
β+ (rare) 220Pa
221U 92 129 221.02640(11)# 700# ns α 217Th 9/2+#
β+ (rare) 221Pa
222U 92 130 222.02609(11)# 1.4(7) ms
[1.0(+10-4) ms]		 α 218Th 0+
β+ (10−6%) 222Pa
223U 92 131 223.02774(8) 21(8) ms
[18(+10-5) ms]		 α 219Th 7/2+#
224U 92 132 224.027605(27) 940(270) ms α 220Th 0+
225U 92 133 225.02939# 61(4) ms α 221Th (5/2+)#
226U 92 134 226.029339(14) 269(6) ms α 222Th 0+
227U 92 135 227.031156(18) 1.1(1) min α 223Th (3/2+)
β+ (.001%) 227Pa
228U 92 136 228.031374(16) 9.1(2) min α (95%) 224Th 0+
EC (5%) 228Pa
229U 92 137 229.033506(6) 58(3) min β+ (80%) 229Pa (3/2+)
α (20%) 225Th
230U 92 138 230.033940(5) 20.8 d α 226Th 0+
SF (1.4×10−10%) (various)
β+β+ (rare) 230Th
231U 92 139 231.036294(3) 4.2(1) d EC 231Pa (5/2)(+#)
α (.004%) 227Th
232U 92 140 232.0371562(24) 68.9(4) y α 228Th 0+
CD (8.9×10−10%) 208Pb
24Ne
CD (5×10−12%) 204Hg
28Mg
SF (10−12%) (various)
233U 92 141 233.0396352(29) 1.592(2)×105 y α 229Th 5/2+
SF (6×10−9%) (various)
CD (7.2×10−11%) 209Pb
24Ne
CD (1.3×10−13%) 205Hg
28Mg
234U[n 3][n 4] Uranium II 92 142 234.0409521(20) 2.455(6)×105 y α 230Th 0+ [0.000054(5)][n 5] 0.000050-
0.000059
SF (1.73×10−9%) (various)
CD (1.4×10−11%) 206Hg
28Mg
CD (9×10−12%) 184Hf
26Ne
24Ne
234mU 1421.32(10) keV 33.5(20) ms 6-
235U[n 6][n 7][n 8] Actin Uranium
Actino-Uranium		 92 143 235.0439299(20) 7.04(1)×108 y α 231Th 7/2- [0.007204(6)] 0.007198-
0.007207
SF (7×10−9%) (various)
CD (8×10−10%) 186Hf
25Ne
24Ne
235mU 0.0765(4) keV ~26 min IT 235U 1/2+
236U 92 144 236.045568(2) 2.342(3)×107 y α 232Th 0+
SF (9.6×10−8%) (various)
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 β- 237Np 1/2+
238U[n 6][n 4][n 7] Uranium I 92 146 238.0507882(20) 4.468(3)×109 y α 234Th 0+ [0.992742(10)] 0.992739-
0.992752
SF (5.45×10−5%) (various)
β-β- (2.19×10−10%) 238Pu
238mU 2557.9(5) keV 280(6) ns 0+
239U 92 147 239.0542933(21) 23.45(2) min β- 239Np 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 β- 240Np 0+
α (10−10%) 236Th
241U 92 149 241.06033(32)# 5# min β- 241Np 7/2+#
242U 92 150 242.06293(22)# 16.8(5) min β- 242Np 0+
  1. ^ Abbreviations:
    CD: Cluster decay
    EC: Electron capture
    IT: Isomeric transition
    SF: Spontaneous fission
  2. ^ Bold for stable isotopes, bold italics for nearly-stable isotopes (half-life longer than the age of the universe)
  3. ^ Used in uranium-thorium dating
  4. ^ a b Used in uranium-uranium dating
  5. ^ Intermediate decay product of 238U
  6. ^ a b Primordial radionuclide
  7. ^ a b Used in Uranium-lead dating
  8. ^ Important in nuclear reactors

[edit] 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.

[edit] References

  1. ^ Seaborg, Encyclopedia of the Chemical Elements (1968), page 777
  2. ^ CRC Handbook, 57th Ed. p. B-345
  3. ^ CRC Handbook, 57th Ed. p. B-423
  4. ^ http://www.nucleonica.net/unc.aspx
Isotopes of protactinium Isotopes of uranium Isotopes of neptunium
Index to isotope pages · Table of nuclides
Retrieved from "http://en.wikipedia.org/w/index.php?title=Isotopes_of_uranium&oldid=460967614#Uranium-239"
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