Isotopes of rubidium

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. Relative atomic mass is 85.4678(3).

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

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 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 4.92×10¹⁰ years.

Table

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)×10^10 y	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. Fission product
5. Primordial radionuclide
6. Used in rubidium-strontium dating

Notes

• 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

1. "Universal Nuclide Chart". nucleonica. (registration required (help)).

• Isotope masses from:
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
• Isotopic compositions and standard atomic masses from:
  • J. R. de Laeter; J. K. Böhlke; P. De Bièvre; H. Hidaka; H. S. Peiser; K. J. R. Rosman; P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry 75 (6): 683–800. doi:10.1351/pac200375060683.
  • M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005.
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.