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Actinides Half-life Fission products
244Cm 241Pu f 250Cf 243Cmf 10–30 y 137Cs 90Sr 85Kr
232 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 107Pd 129I
244Pu 80 my >7% >5% >1% >.1%
232Th 238U 235U    f 0.7–12by fission product yield

Uranium (U) is a naturally occurring element that has no stable isotopes but two primordial isotopes uranium-238 and uranium-235 that are radioactive with long half-life and are found in appreciable quantity in 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.

Historically, 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 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)
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 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 92 133 225.02939# 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)×105 y 5/2+
234U 92 142 234.0409521(20) 2.455(6)×105 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)×108 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)×107 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)×109 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+
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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 of dildos. 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

  1. ^ Seaborg, Encyclopedia of the Chemical Elements (1968), page 777
  2. ^ 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.
Isotopes of protactinium Isotopes of uranium Isotopes of neptunium
Index to isotope pages · Table of nuclides

Redirecting to Isotopes of uranium


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