Isotopes of rubidium
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Rubidium (37Rb) has 35 known isotopes, from 72Rb to 106Rb, with naturally occurring rubidium composed of two: stable 85Rb (72.2%) and radioactive 87Rb (27.8%). The primordial radionuclide 87Rb has a half-life of 4.97×1010 years, beta decaying to stable 87Sr. It is, as the element is, widespread on Earth as rubidium readily substitutes for potassium in all minerals. The decay of 87Rb has been used extensively in dating rocks; see rubidium–strontium dating for a more detailed discussion.
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| Standard atomic weight Ar°(Rb) | |||||||||||||||||||||||||||||||||||||||||||||
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Other than 87Rb, the longest-lived radioisotopes are 83Rb with a half-life of 86.2 days, 84Rb with a half-life of 32.82 days, and 86Rb with a half-life of 18.645 days. All other radioisotopes have half-lives less than a day, most less than 20 minutes. Of the isomeric states the most stable is 82mRb at 6.472 hours.
The ground state of 82Rb has a much shorter half-life of 1.2575 minutes. It is used medically in some cardiac positron emission tomography scans to assess myocardial perfusion. It is synthesized through the longer-lived 82Sr, made in a cyclotron, though a generator. It may be administered as the chloride.
List of isotopes
| Nuclide [n 1] |
Z | N | Isotopic mass (Da)[4] [n 2][n 3] |
Discovery year[5][6] |
Half-life[1] [n 4][n 5] |
Decay mode[1] [n 6] |
Daughter isotope [n 7][n 8] |
Spin and parity[1] [n 9][n 5] |
Natural abundance (mole fraction) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Excitation energy[n 5] | Normal proportion[1] | Range of variation | |||||||||||||||||
| 72Rb | 37 | 35 | 71.95885(54)# | 2017 | 103(22) ns | p | 71Kr | 1+# | |||||||||||
| 73Rb | 37 | 36 | 72.950605(44) | 1993 | <81 ns | p | 72Kr | 3/2−# | |||||||||||
| 74Rb | 37 | 37 | 73.9442659(32) | 1977 | 64.78(3) ms | β+ | 74Kr | 0+ | |||||||||||
| 75Rb | 37 | 38 | 74.9385732(13) | 1975 | 19.0(12) s | β+ | 75Kr | 3/2− | |||||||||||
| 76Rb | 37 | 39 | 75.9350730(10) | 1969 | 36.5(6) s | β+ | 76Kr | 1− | |||||||||||
| β+, α (3.8×10−7%) | 72Se | ||||||||||||||||||
| 76mRb | 316.93(8) keV | 1986 | 3.050(7) μs | IT | 76Rb | (4+) | |||||||||||||
| 77Rb | 37 | 40 | 76.9304016(14) | 1972 | 3.78(4) min | β+ | 77Kr | 3/2− | |||||||||||
| 78Rb | 37 | 41 | 77.9281419(35) | 1968 | 17.66(3) min | β+ | 78Kr | 0+ | |||||||||||
| 78m1Rb | 46.84(14) keV | 1972 | 910(40) ns | IT | 78Rb | (1−) | |||||||||||||
| 78m2Rb | 111.19(22) keV | 1996 | 5.74(3) min | β+ (91%) | 78Kr | 4− | |||||||||||||
| IT (9%) | 78Rb | ||||||||||||||||||
| 79Rb | 37 | 42 | 78.9239901(21) | 1957 | 22.9(5) min | β+ | 79Kr | 5/2+ | |||||||||||
| 80Rb | 37 | 43 | 79.9225164(20) | 1961 | 33.4(7) s | β+ | 80Kr | 1+ | |||||||||||
| 80mRb | 493.9(5) keV | 1996 | 1.63(4) μs | IT | 80Rb | (6+) | |||||||||||||
| 81Rb | 37 | 44 | 80.9189939(53) | 1949 | 4.572(4) h | β+ | 81Kr | 3/2− | |||||||||||
| 81mRb | 86.31(7) keV | 1977 | 30.5(3) min | IT (97.6%) | 81Rb | 9/2+ | |||||||||||||
| β+ (2.4%) | 81Kr | ||||||||||||||||||
| 82Rb | 37 | 45 | 81.9182090(32) | 1949 | 1.2575(2) min | β+ | 82Kr | 1+ | |||||||||||
| 82mRb | 69.0(15) keV | 1953 | 6.472(6) h | β+ | 82Kr | 5− | |||||||||||||
| 83Rb | 37 | 46 | 82.9151142(25) | 1950 | 86.2(1) d | EC | 83Kr | 5/2− | |||||||||||
| 83mRb | 42.0780(20) keV | 1968 | 7.8(7) ms | IT | 83Rb | 9/2+ | |||||||||||||
| 84Rb | 37 | 47 | 83.9143752(24) | 1947 | 32.82(7) d | β+ (96.1%) | 84Kr | 2− | |||||||||||
| β− (3.9%) | 84Sr | ||||||||||||||||||
| 84mRb | 463.59(8) keV | 1950 | 20.26(4) min | IT | 84Rb | 6− | |||||||||||||
| 85Rb[n 10] | 37 | 48 | 84.9117897360(54) | 1921 | Stable | 5/2− | 0.7217(2) | ||||||||||||
| 85mRb | 514.0065(22) keV | 1952 | 1.015(1) μs | IT | 85Rb | 9/2+ | |||||||||||||
| 86Rb | 37 | 49 | 85.91116744(21) | 1941 | 18.645(8) d | β− (99.9948%) | 86Sr | 2− | |||||||||||
| EC (0.0052%) | 86Kr | ||||||||||||||||||
| 86mRb | 556.05(18) keV | 1951 | 1.017(3) min | IT | 86Rb | 6− | |||||||||||||
| 87Rb[n 10][n 11][n 12] | 37 | 50 | 86.909180529(6) | 1921 | 4.97(3)×1010 y | β− | 87Sr | 3/2− | 0.2783(2) | ||||||||||
| 88Rb | 37 | 51 | 87.91131559(17) | 1939 | 17.78(3) min | β− | 88Sr | 2− | |||||||||||
| 88mRb | 1373.8(3) keV | 2009 | 123(13) ns | IT | 88Rb | (7+) | |||||||||||||
| 89Rb | 37 | 52 | 88.9122781(58) | 1940 | 15.32(10) min | β− | 89Sr | 3/2− | |||||||||||
| 90Rb | 37 | 53 | 89.9147976(69) | 1951 | 158(5) s | β− | 90Sr | 0− | |||||||||||
| 90mRb | 106.90(3) keV | 1967 | 258(4) s | β− (97.4%) | 90Sr | 3− | |||||||||||||
| IT (2.6%) | 90 Rb | ||||||||||||||||||
| 91Rb | 37 | 54 | 90.9165373(84) | 1951 | 58.2(3) s | β− | 91Sr | 3/2− | |||||||||||
| 92Rb | 37 | 55 | 91.9197285(66) | 1960 | 4.48(3) s | β− (99.99%) | 92Sr | 0− | |||||||||||
| β−, n (0.0107%) | 91Sr | ||||||||||||||||||
| 93Rb | 37 | 56 | 92.9220393(84) | 1960 | 5.84(2) s | β− (98.61%) | 93Sr | 5/2− | |||||||||||
| β−, n (1.39%) | 92Sr | ||||||||||||||||||
| 93mRb | 4423.1(15) keV | 2010 | 111(11) ns | IT | 93Rb | (27/2−) | |||||||||||||
| 94Rb | 37 | 57 | 93.9263948(22) | 1961 | 2.702(5) s | β− (89.7%) | 94Sr | 3− | |||||||||||
| β−, n (10.3%) | 93Sr | ||||||||||||||||||
| 94m1Rb | 104.2(2) keV | 2008 | 130(15) ns | IT | 94Rb | (0−) | |||||||||||||
| 94m2Rb | 2074.9(14) keV | 2016 | 107(16) ns | IT | 94Rb | (10−) | |||||||||||||
| 95Rb | 37 | 58 | 94.929264(22) | 1967 | 377.7(8) ms | β− (91.3%) | 95Sr | 5/2− | |||||||||||
| β−, n (8.7%) | 94Sr | ||||||||||||||||||
| 95mRb | 835.0(6) keV | 2009 | <500 ns | IT | 95Rb | 9/2+# | |||||||||||||
| 96Rb | 37 | 59 | 95.9341334(36) | 1967 | 201.5(9) ms | β− (86.3%) | 96Sr | 2− | |||||||||||
| β−, n (13.7%) | 95Sr | ||||||||||||||||||
| 96m1Rb[n 13] | 0(200)# keV | (1981)[n 14] | 200# ms [>1 ms] |
1(+#) | |||||||||||||||
| 96m2Rb | 1134.6(11) keV | 1999 | 1.80(4) μs | IT | 96Rb | (10−) | |||||||||||||
| 97Rb | 37 | 60 | 96.9371771(21) | 1969 | 169.1(6) ms | β− (74.5%) | 97Sr | 3/2+ | |||||||||||
| β−, n (25.5%) | 96Sr | ||||||||||||||||||
| 97mRb | 76.6(2) keV | 2012 | 5.7(6) μs | IT | 97Rb | (1/2,3/2)− | |||||||||||||
| 98Rb | 37 | 61 | 97.941632(17) | 1971 | 115(6) ms | β−(85.65%) | 98Sr | (0−) | |||||||||||
| β−, n (14.3%) | 97Sr | ||||||||||||||||||
| β−, 2n (0.054%) | 96Sr | ||||||||||||||||||
| 98m1Rb | 73(26) keV | 1980 | 96(3) ms | β− | 98Sr | (3+) | |||||||||||||
| 98m2Rb | 178.5(4) keV | 2009 | 358(7) ns | IT | 98Rb | (2−) | |||||||||||||
| 99Rb | 37 | 62 | 98.9451192(43) | 1971 | 54(4) ms | β− (82.7%) | 99Sr | (3/2+) | |||||||||||
| β−, n (17.3%) | 98Sr | ||||||||||||||||||
| 100Rb | 37 | 63 | 99.950332(14) | 1978 | 51.3(16) ms | β− (94.3%) | 100Sr | 4−# | |||||||||||
| β−, n (5.6%) | 99Sr | ||||||||||||||||||
| β−, 2n (0.15%) | 98Sr | ||||||||||||||||||
| 101Rb | 37 | 64 | 100.954302(22) | 1992 | 31.8(33) ms | β− (72%) | 101Sr | 3/2+# | |||||||||||
| β−, n (28%) | 100Sr | ||||||||||||||||||
| 102Rb | 37 | 65 | 101.960008(89) | 1995 | 37(4) ms | β−, n (65%) | 101Sr | (4+) | |||||||||||
| β− (35%) | 102Sr | ||||||||||||||||||
| 103Rb | 37 | 66 | 102.96440(43)# | 2010 | 26(11) ms | β− | 103Sr | 3/2+# | |||||||||||
| 104Rb | 37 | 67 | 103.97053(54)# | 2018 | 35# ms [>550 ns] |
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| 105Rb[7] | 37 | 68 | 2021 | ||||||||||||||||
| 106Rb[7] | 37 | 69 | 2021 | ||||||||||||||||
| This table header & footer: | |||||||||||||||||||
- mRb – Excited nuclear isomer.
- ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
- # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
- Bold half-life – nearly stable, half-life longer than age of universe.
- # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
- Modes of decay:
EC: Electron capture IT: Isomeric transition n: Neutron emission p: Proton emission - Bold italics symbol as daughter – Daughter product is nearly stable.
- Bold symbol as daughter – Daughter product is stable.
- ( ) spin value – Indicates spin with weak assignment arguments.
- Used in rubidium–strontium dating
- Order of ground state and isomer is uncertain.
- Half-life not measured, only circumstantial evidence for the isomeric state
Rubidium-87
Rubidium-87 is one of two natural isotopes of rubidium, with an abundance of 27.835%, and a half-life of 4.97×1010 years, with beta decay to strontium-87, a stable isotope.
During fractional crystallization of igneous rock, 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. The highest ratios (10 or higher) occur in pegmatites. The age of a mineral, if it has not been subsequently altered, is determined by the parent and daughter abundances, the half-life, and the original content of the daughter, here strontium; the 87Sr/86Sr ratio helps in its calculation. See rubidium-strontium dating for further detail.
Rubidium-87 was the first and the most popular atom for making Bose–Einstein condensates in dilute atomic gases. 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.
See also
Daughter products other than rubidium