# Isotopes of rubidium

Rubidium ($_{37}$Rb) has 36 isotopes, with naturally occurring rubidium being composed of just two isotopes; $^{85}$Rb (72.2%) and the radioactive $^{87}$Rb (27.8%).
$^{87}$Rb has a half-life of 4.92×10$^{10}$ years. It readily substitutes for potassium in minerals, and is therefore fairly widespread. $^{87}$Rb has been used extensively in dating rocks; $^{87}$Rb decays to stable strontium-87 by emission of a beta particle (an electron ejected from the nucleus). 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. The 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 $^{87}$Sr/$^{86}$Sr 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 $^{87}$Rb, the longest-lived radioisotopes are $^{83}$Rb with a half-life of 86.2 days, $^{84}$Rb with a half-life of 33.1 days, and $^{86}$Rb with a half-life of 18.642 days. All other radioisotopes have half-lives less than a day.
$^{82}$Rb is used in some cardiac positron emission tomography 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 $^{82}$Sr.

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Natural abundance (mole fraction) | Natural abundance (mole fraction) |
| Nuclide | Excitation energy | Excitation energy | Excitation energy | Half-life | Decay mode | Daughter isotope | Spin and parity | Normal proportion | Range of variation |
| $^{72}$Rb | 37 | 35 | 71.95885(54)# | 103(22) ns | p | $^{71}$Kr | 1+# | | |
| $^{73}$Rb | 37 | 36 | 72.950605(44) | <81 ns | p | $^{72}$Kr | 3/2−# | | |
| $^{74}$Rb | 37 | 37 | 73.9442659(32) | 64.78(3) ms | β$^+$ | $^{74}$Kr | 0+ | | |
| $^{75}$Rb | 37 | 38 | 74.9385732(13) | 19.0(12) s | β$^+$ | $^{75}$Kr | 3/2− | | |
| $^{76}$Rb | 37 | 39 | 75.9350730(10) | 36.5(6) s | β$^+$ | $^{76}$Kr | 1− | | |
| $^{76}$Rb | 37 | 39 | 75.9350730(10) | 36.5(6) s | β$^+$, α (3.8×10$^{−7}$%) | $^{72}$Se | 1− | | |
| $^{76m}$Rb | 316.93(8) keV | 316.93(8) keV | 316.93(8) keV | 3.050(7) μs | IT | $^{76}$Rb | (4+) | | |
| $^{77}$Rb | 37 | 40 | 76.9304016(14) | 3.78(4) min | β$^+$ | $^{77}$Kr | 3/2− | | |
| $^{78}$Rb | 37 | 41 | 77.9281419(35) | 17.66(3) min | β$^+$ | $^{78}$Kr | 0+ | | |
| $^{78m1}$Rb | 46.84(14) keV | 46.84(14) keV | 46.84(14) keV | 910(40) ns | IT | $^{78}$Rb | (1−) | | |
| $^{78m2}$Rb | 111.19(22) keV | 111.19(22) keV | 111.19(22) keV | 5.74(3) min | β$^+$ (91%) | $^{78}$Kr | 4− | | |
| $^{78m2}$Rb | 111.19(22) keV | 111.19(22) keV | 111.19(22) keV | 5.74(3) min | IT (9%) | $^{78}$Rb | 4− | | |
| $^{79}$Rb | 37 | 42 | 78.9239901(21) | 22.9(5) min | β$^+$ | $^{79}$Kr | 5/2+ | | |
| $^{80}$Rb | 37 | 43 | 79.9225164(20) | 33.4(7) s | β$^+$ | $^{80}$Kr | 1+ | | |
| $^{80m}$Rb | 493.9(5) keV | 493.9(5) keV | 493.9(5) keV | 1.63(4) μs | IT | $^{80}$Rb | (6+) | | |
| $^{81}$Rb | 37 | 44 | 80.9189939(53) | 4.572(4) h | β$^+$ | $^{81}$Kr | 3/2− | | |
| $^{81m}$Rb | 86.31(7) keV | 86.31(7) keV | 86.31(7) keV | 30.5(3) min | IT (97.6%) | $^{81}$Rb | 9/2+ | | |
| $^{81m}$Rb | 86.31(7) keV | 86.31(7) keV | 86.31(7) keV | 30.5(3) min | β$^+$ (2.4%) | $^{81}$Kr | 9/2+ | | |
| Rb | 37 | 45 | 81.9182090(32) | 1.2575(2) min | β$^+$ | $^{82}$Kr | 1+ | | |
| $^{82m}$Rb | 69.0(15) keV | 69.0(15) keV | 69.0(15) keV | 6.472(6) h | β$^+$ (>99.67%) | $^{82}$Kr | 5− | | |
| $^{82m}$Rb | 69.0(15) keV | 69.0(15) keV | 69.0(15) keV | 6.472(6) h | IT (<0.33%) | $^{82}$Rb | 5− | | |
| $^{83}$Rb | 37 | 46 | 82.9151142(25) | 86.2(1) d | EC | $^{83}$Kr | 5/2− | | |
| $^{83m}$Rb | 42.0780(20) keV | 42.0780(20) keV | 42.0780(20) keV | 7.8(7) ms | IT | $^{83}$Rb | 9/2+ | | |
| $^{84}$Rb | 37 | 47 | 83.9143752(24) | 32.8(07) d | β$^+$ (96.1%) | $^{84}$Kr | 2− | | |
| $^{84}$Rb | 37 | 47 | 83.9143752(24) | 32.8(07) d | β$^−$ (3.9%) | $^{84}$Sr | 2− | | |
| $^{84m}$Rb | 463.59(8) keV | 463.59(8) keV | 463.59(8) keV | 20.26(4) min | IT | $^{84}$Rb | 6− | | |
| $^{84m}$Rb | 463.59(8) keV | 463.59(8) keV | 463.59(8) keV | 20.26(4) min | β$^+$ (<0.0012%) | $^{84}$Kr | 6− | | |
| $^{85}$Rb | 37 | 48 | 84.9117897360(54) | Stable | Stable | Stable | 5/2− | 0.7217(2) | |
| $^{85m}$Rb | 514.0065(22) keV | 514.0065(22) keV | 514.0065(22) keV | 1.015(1) μs | IT | $^{85}$Rb | 9/2+ | | |
| $^{86}$Rb | 37 | 49 | 85.91116744(21) | 18.645(8) d | β$^−$ (99.99%) | $^{86}$Sr | 2− | | |
| $^{86}$Rb | 37 | 49 | 85.91116744(21) | 18.645(8) d | EC (.0052%) | $^{86}$Kr | 2− | | |
| $^{86m}$Rb | 556.05(18) keV | 556.05(18) keV | 556.05(18) keV | 1.017(3) min | IT (>99.7%) | $^{86}$Rb | 6− | | |
| $^{86m}$Rb | 556.05(18) keV | 556.05(18) keV | 556.05(18) keV | 1.017(3) min | β$^−$ (<0.3%) | $^{86}$Sr | 6− | | |
| $^{87}$Rb | 37 | 50 | 86.909180529(6) | 4.97(3)×10$^{10}$ y | β$^−$ | $^{87}$Sr | 3/2− | 0.2783(2) | |
| $^{88}$Rb | 37 | 51 | 87.91131559(17) | 17.78(3) min | β$^−$ | $^{88}$Sr | 2− | | |
| $^{88m}$Rb | 1373.8(3) keV | 1373.8(3) keV | 1373.8(3) keV | 123(13) ns | IT | $^{88}$Rb | (7+) | | |
| $^{89}$Rb | 37 | 52 | 88.9122781(58) | 15.32(10) min | β$^−$ | $^{89}$Sr | 3/2− | | |
| $^{90}$Rb | 37 | 53 | 89.9147976(69) | 158(5) s | β$^−$ | $^{90}$Sr | 0− | | |
| $^{90m}$Rb | 106.90(3) keV | 106.90(3) keV | 106.90(3) keV | 258(4) s | β$^−$ (97.4%) | $^{90}$Sr | 3− | | |
| $^{90m}$Rb | 106.90(3) keV | 106.90(3) keV | 106.90(3) keV | 258(4) s | IT (2.6%) | $^{90}$ Rb | 3− | | |
| $^{91}$Rb | 37 | 54 | 90.9165373(84) | 58.2(3) s | β$^−$ | $^{91}$Sr | 3/2− | | |
| $^{92}$Rb | 37 | 55 | 91.9197285(66) | 4.48(3) s | β$^−$ (99.99%) | $^{92}$Sr | 0− | | |
| $^{92}$Rb | 37 | 55 | 91.9197285(66) | 4.48(3) s | β$^−$, n (0.0107%) | $^{91}$Sr | 0− | | |
| $^{93}$Rb | 37 | 56 | 92.9220393(84) | 5.84(2) s | β$^−$ (98.61%) | $^{93}$Sr | 5/2− | | |
| $^{93}$Rb | 37 | 56 | 92.9220393(84) | 5.84(2) s | β$^−$, n (1.39%) | $^{92}$Sr | 5/2− | | |
| $^{93m}$Rb | 4423.1(15) keV | 4423.1(15) keV | 4423.1(15) keV | 111(11) ns | IT | $^{93}$Rb | (27/2−) | | |
| $^{94}$Rb | 37 | 57 | 93.9263948(22) | 2.702(5) s | β$^−$ (89.7%) | $^{94}$Sr | 3− | | |
| $^{94}$Rb | 37 | 57 | 93.9263948(22) | 2.702(5) s | β$^−$, n (10.3%) | $^{93}$Sr | 3− | | |
| $^{94m1}$Rb | 104.2(2) keV | 104.2(2) keV | 104.2(2) keV | 130(15) ns | IT | $^{94}$Rb | (0−) | | |
| $^{94m2}$Rb | 2074.9(14) keV | 2074.9(14) keV | 2074.9(14) keV | 107(16) ns | IT | $^{94}$Rb | (10−) | | |
| $^{95}$Rb | 37 | 58 | 94.929264(22) | 377.7(8) ms | β$^−$ (91.3%) | $^{95}$Sr | 5/2− | | |
| $^{95}$Rb | 37 | 58 | 94.929264(22) | 377.7(8) ms | β$^−$, n (8.7%) | $^{94}$Sr | 5/2− | | |
| $^{95m}$Rb | 835.0(6) keV | 835.0(6) keV | 835.0(6) keV | <500 ns | IT | $^{95}$Rb | 9/2+# | | |
| $^{96}$Rb | 37 | 59 | 95.9341334(36) | 201.5(9) ms | β$^−$ (86.3%) | $^{96}$Sr | 2− | | |
| $^{96}$Rb | 37 | 59 | 95.9341334(36) | 201.5(9) ms | β$^−$, n (13.7%) | $^{95}$Sr | 2− | | |
| $^{96m1}$Rb | 0(200)# keV | 0(200)# keV | 0(200)# keV | 200# ms [>1 ms] | | | 1(+#) | | |
| $^{96m2}$Rb | 1134.6(11) keV | 1134.6(11) keV | 1134.6(11) keV | 1.80(4) μs | IT | $^{96}$Rb | (10−) | | |
| $^{97}$Rb | 37 | 60 | 96.9371771(21) | 169.1(6) ms | β$^−$ (74.5%) | $^{97}$Sr | 3/2+ | | |
| $^{97}$Rb | 37 | 60 | 96.9371771(21) | 169.1(6) ms | β$^−$, n (25.5%) | $^{96}$Sr | 3/2+ | | |
| $^{97m}$Rb | 76.6(2) keV | 76.6(2) keV | 76.6(2) keV | 5.7(6) μs | IT | $^{97}$Rb | (1/2,3/2)− | | |
| $^{98}$Rb | 37 | 61 | 97.941632(17) | 115(6) ms | β$^−$(85.65%) | $^{98}$Sr | (0−) | | |
| $^{98}$Rb | 37 | 61 | 97.941632(17) | 115(6) ms | β$^−$, n (14.3%) | $^{97}$Sr | (0−) | | |
| $^{98}$Rb | 37 | 61 | 97.941632(17) | 115(6) ms | β$^−$, 2n (0.054%) | $^{96}$Sr | (0−) | | |
| $^{98m1}$Rb | 73(26) keV | 73(26) keV | 73(26) keV | 96(3) ms | β$^−$ | $^{98}$Sr | (3+) | | |
| $^{98m2}$Rb | 178.5(4) keV | 178.5(4) keV | 178.5(4) keV | 358(7) ns | IT | $^{98}$Rb | (2−) | | |
| $^{99}$Rb | 37 | 62 | 98.9451192(43) | 54(4) ms | β$^−$ (82.7%) | $^{99}$Sr | (3/2+) | | |
| $^{99}$Rb | 37 | 62 | 98.9451192(43) | 54(4) ms | β$^−$, n (17.3%) | $^{98}$Sr | (3/2+) | | |
| $^{100}$Rb | 37 | 63 | 99.950332(14) | 51.3(16) ms | β$^−$ (94.3%) | $^{100}$Sr | 4−# | | |
| $^{100}$Rb | 37 | 63 | 99.950332(14) | 51.3(16) ms | β$^−$, n (5.6%) | $^{99}$Sr | 4−# | | |
| $^{100}$Rb | 37 | 63 | 99.950332(14) | 51.3(16) ms | β$^−$, 2n (0.15%) | $^{98}$Sr | 4−# | | |
| $^{101}$Rb | 37 | 64 | 100.954302(22) | 31.8(33) ms | β$^−$ (72%) | $^{101}$Sr | 3/2+# | | |
| $^{101}$Rb | 37 | 64 | 100.954302(22) | 31.8(33) ms | β$^−$, n (28%) | $^{100}$Sr | 3/2+# | | |
| $^{102}$Rb | 37 | 65 | 101.960008(89) | 37(4) ms | β$^−$, n (65%) | $^{101}$Sr | (4+) | | |
| $^{102}$Rb | 37 | 65 | 101.960008(89) | 37(4) ms | β$^−$ (35%) | $^{102}$Sr | (4+) | | |
| $^{103}$Rb | 37 | 66 | 102.96440(43)# | 26(11) ms | β$^−$ | $^{103}$Sr | 3/2+# | | |
| $^{104}$Rb | 37 | 67 | 103.97053(54)# | 35# ms [>550 ns] | | | | | |
| $^{105}$Rb | 37 | 68 | | | | | | | |
| $^{106}$Rb | 37 | 69 | | | | | | | |
| This table header & footer: view ||||||||||
* ↑ $^m$Rb – 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.
* 1 2 3 # – 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.
* 1 2 Fission product
* ↑ Primordial radionuclide
* ↑ Used in rubidium–strontium dating
* ↑ Order of ground state and isomer is uncertain.

## Rubidium-87

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.
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 4.92×10$^{10}$ years.