Isotopes of rubidium

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Rubidium (Rb) has 32 isotopes, with naturally occurring rubidium being composed of just two isotopes; 85Rb (72.2%) and the radioactive 87Rb (27.8%). Normal mixes of rubidium are radioactive enough to fog photographic film in approximately 30 to 60 days. Standard atomic mass is 85.4678(3) u.

87Rb has a half-life of 4.92×1010 years. It readily substitutes for potassium in minerals, and is therefore fairly widespread. 87Rb has been used extensively in dating rocks; 87Rb decays to stable strontium-87 by emission of a negative beta particle. During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residual magma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. Highest ratios (10 or higher) occur in pegmatites. If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the 87Sr/86Sr ratio. The dates indicate the true age of the minerals only if the rocks have not been subsequently altered. See rubidium-strontium dating for a more detailed discussion.

Other than 87Rb, the longest-lived radioisotopes are 83Rb with a half-life of 86.2 days, 84Rb with a half-life of 33.1 days and 86Rb with a half-life of 18.642 days. All other radioisotopes have half-lives less than a day.

82Rb is used in some cardiac PET scans to assess myocardial perfusion. It has a half-life of 1.273 minutes. It does not exist naturally, but can be made from the decay of 82Sr.

Rubidium-87[edit]

Rubidium-87 is an isotope of rubidium. Rubidium-87 was the first and the most popular atom for making Bose–Einstein condensates in dilute atomic gasses. Even though rubidium-85 is more abundant, rubidium-87 has a positive scattering length, which means it is mutually repulsive, at low temperatures. This prevents a collapse of all but the smallest condensates. It is also easy to evaporatively cool, with a consistent strong mutual scattering. There is also a strong supply of cheap uncoated diode lasers typically used in cd writers which can operate at the correct wavelength.

Rubidium-87 has an atomic mass of 86.9091835 u, and a binding energy of 757,853 keV. Its atomic percent abundance is 27.835%, and has a half-life of 4.92×1010 years.

Table[edit]

nuclide
symbol
Z(p) N(n)  
isotopic mass (u)
 
half-life[n 1] decay
mode(s)[1][n 2]
daughter
isotope(s)[n 3]
nuclear
spin
representative
isotopic
composition
(mole fraction)
range of natural
variation
(mole fraction)
excitation energy
71Rb 37 34 70.96532(54)# p 70Kr 5/2−#
72Rb 37 35 71.95908(54)# <1.5 µs p 71Kr 3+#
72mRb 100(100)# keV 1# µs p 71Kr 1−#
73Rb 37 36 72.95056(16)# <30 ns p 72Kr 3/2−#
74Rb 37 37 73.944265(4) 64.76(3) ms β+ 74Kr (0+)
75Rb 37 38 74.938570(8) 19.0(12) s β+ 75Kr (3/2−)
76Rb 37 39 75.9350722(20) 36.5(6) s β+ 76Kr 1(−)
β+, α (3.8×10−7%) 72Se
76mRb 316.93(8) keV 3.050(7) µs (4+)
77Rb 37 40 76.930408(8) 3.77(4) min β+ 77Kr 3/2−
78Rb 37 41 77.928141(8) 17.66(8) min β+ 78Kr 0(+)
78mRb 111.20(10) keV 5.74(5) min β+ (90%) 78Kr 4(−)
IT (10%) 78Rb
79Rb 37 42 78.923989(6) 22.9(5) min β+ 79Kr 5/2+
80Rb 37 43 79.922519(7) 33.4(7) s β+ 80Kr 1+
80mRb 494.4(5) keV 1.6(2) µs 6+
81Rb 37 44 80.918996(6) 4.570(4) h β+ 81Kr 3/2−
81mRb 86.31(7) keV 30.5(3) min IT (97.6%) 81Rb 9/2+
β+ (2.4%) 81Kr
82Rb 37 45 81.9182086(30) 1.273(2) min β+ 82Kr 1+
82mRb 69.0(15) keV 6.472(5) h β+ (99.67%) 82Kr 5−
IT (.33%) 82Rb
83Rb 37 46 82.915110(6) 86.2(1) d EC 83Kr 5/2−
83mRb 42.11(4) keV 7.8(7) ms IT 83Rb 9/2+
84Rb 37 47 83.914385(3) 33.1(1) d β+ (96.2%) 84Kr 2−
β (3.8%) 84Sr
84mRb 463.62(9) keV 20.26(4) min IT (>99.9%) 84Rb 6−
β+ (<.1%) 84Kr
85Rb[n 4] 37 48 84.911789738(12) Stable 5/2− 0.7217(2)
86Rb 37 49 85.91116742(21) 18.642(18) d β (99.9948%) 86Sr 2−
EC (.0052%) 86Kr
86mRb 556.05(18) keV 1.017(3) min IT 86Rb 6−
87Rb[n 5][n 6][n 4] 37 50 86.909180527(13) 4.923(22)×1010 a β 87Sr 3/2− 0.2783(2)
88Rb 37 51 87.91131559(17) 17.773(11) min β 88Sr 2−
89Rb 37 52 88.912278(6) 15.15(12) min β 89Sr 3/2−
90Rb 37 53 89.914802(7) 158(5) s β 90Sr 0−
90mRb 106.90(3) keV 258(4) s β (97.4%) 90Sr 3−
IT (2.6%) 90 Rb
91Rb 37 54 90.916537(9) 58.4(4) s β 91Sr 3/2(−)
92Rb 37 55 91.919729(7) 4.492(20) s β (99.98%) 92Sr 0−
β, n (.0107%) 91Sr
93Rb 37 56 92.922042(8) 5.84(2) s β (98.65%) 93Sr 5/2−
β, n (1.35%) 92Sr
93mRb 253.38(3) keV 57(15) µs (3/2−,5/2−)
94Rb 37 57 93.926405(9) 2.702(5) s β (89.99%) 94Sr 3(−)
β, n (10.01%) 93Sr
95Rb 37 58 94.929303(23) 377.5(8) ms β (91.27%) 95Sr 5/2−
β, n (8.73%) 94Sr
96Rb 37 59 95.93427(3) 202.8(33) ms β (86.6%) 96Sr 2+
β, n (13.4%) 95Sr
96mRb 0(200)# keV 200# ms [>1 ms] β 96Sr 1(−#)
IT 96Rb
β, n 95Sr
97Rb 37 60 96.93735(3) 169.9(7) ms β (74.3%) 97Sr 3/2+
β, n (25.7%) 96Sr
98Rb 37 61 97.94179(5) 114(5) ms β(86.14%) 98Sr (0,1)(−#)
β, n (13.8%) 97Sr
β, 2n (.051%) 96Sr
98mRb 290(130) keV 96(3) ms β 97Sr (3,4)(+#)
99Rb 37 62 98.94538(13) 50.3(7) ms β (84.1%) 99Sr (5/2+)
β, n (15.9%) 98Sr
100Rb 37 63 99.94987(32)# 51(8) ms β (94.25%) 100Sr (3+)
β, n (5.6%) 99Sr
β, 2n (.15%) 98Sr
101Rb 37 64 100.95320(18) 32(5) ms β (69%) 101Sr (3/2+)#
β, n (31%) 100Sr
102Rb 37 65 101.95887(54)# 37(5) ms β (82%) 102Sr
β, n (18%) 101Sr
  1. ^ Bold for isotopes with half-lives longer than the age of the universe (nearly stable)
  2. ^ Abbreviations:
    EC: Electron capture
    IT: Isomeric transition
  3. ^ Bold for stable isotopes
  4. ^ a b Fission product
  5. ^ Primordial radionuclide
  6. ^ Used in rubidium-strontium dating

Notes[edit]

  • 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.
  • 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[edit]

  1. ^ http://www.nucleonica.net/unc.aspx


Isotopes of krypton Isotopes of rubidium Isotopes of strontium
Table of nuclides