Isotopes of rubidium

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.

Isotopes of rubidium (₃₇Rb)

Main isotopes[1] Decay Isotope abun­dance half-life (t1/2) mode pro­duct 82Rb synth 1.2575 m β+ 82Kr 83Rb synth 86.2 d ε 83Kr 84Rb synth 32.82 d β+ 84Kr β− 84Sr 85Rb 72.2% stable 86Rb synth 18.645 d β− 86Sr 87Rb 27.8% 4.97×1010 y β− 87Sr
Standard atomic weight Ar°(Rb)
	85.4678±0.0003[2] 85.468±0.001 (abridged)[3]
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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]	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)#	103(22) ns	p	71Kr	1+#
73Rb	37	36	72.950605(44)	<81 ns	p	72Kr	3/2−#
74Rb	37	37	73.9442659(32)	64.78(3) ms	β+	74Kr	0+
75Rb	37	38	74.9385732(13)	19.0(12) s	β+	75Kr	3/2−
76Rb	37	39	75.9350730(10)	36.5(6) s	β+	76Kr	1−
					β+, α (3.8×10−7%)	72Se
76mRb	316.93(8) keV			3.050(7) μs	IT	76Rb	(4+)
77Rb	37	40	76.9304016(14)	3.78(4) min	β+	77Kr	3/2−
78Rb	37	41	77.9281419(35)	17.66(3) min	β+	78Kr	0+
78m1Rb	46.84(14) keV			910(40) ns	IT	78Rb	(1−)
78m2Rb	111.19(22) keV			5.74(3) min	β+ (91%)	78Kr	4−
					IT (9%)	78Rb
79Rb	37	42	78.9239901(21)	22.9(5) min	β+	79Kr	5/2+
80Rb	37	43	79.9225164(20)	33.4(7) s	β+	80Kr	1+
80mRb	493.9(5) keV			1.63(4) μs	IT	80Rb	(6+)
81Rb	37	44	80.9189939(53)	4.572(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	81.9182090(32)	1.2575(2) min	β+	82Kr	1+
82mRb	69.0(15) keV			6.472(6) h	β+ (>99.67%)	82Kr	5−
					IT (<0.33%)	82Rb
83Rb	37	46	82.9151142(25)	86.2(1) d	EC	83Kr	5/2−
83mRb	42.0780(20) keV			7.8(7) ms	IT	83Rb	9/2+
84Rb	37	47	83.9143752(24)	32.82(7) d	β+ (96.1%)	84Kr	2−
					β− (3.9%)	84Sr
84mRb	463.59(8) keV			20.26(4) min	IT	84Rb	6−
					β+ (<0.0012%)	84Kr
85Rb[n 10]	37	48	84.9117897360(54)	Stable			5/2−	0.7217(2)
85mRb	514.0065(22) keV			1.015(1) μs	IT	85Rb	9/2+
86Rb	37	49	85.91116744(21)	18.645(8) d	β− (99.99%)	86Sr	2−
					EC (.0052%)	86Kr
86mRb	556.05(18) keV			1.017(3) min	IT (>99.7%)	86Rb	6−
					β− (<0.3%)	86Sr
87Rb[n 10][n 11][n 12]	37	50	86.909180529(6)	4.97(3)×1010 y	β−	87Sr	3/2−	0.2783(2)
88Rb	37	51	87.91131559(17)	17.78(3) min	β−	88Sr	2−
88mRb	1373.8(3) keV			123(13) ns	IT	88Rb	(7+)
89Rb	37	52	88.9122781(58)	15.32(10) min	β−	89Sr	3/2−
90Rb	37	53	89.9147976(69)	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	90.9165373(84)	58.2(3) s	β−	91Sr	3/2−
92Rb	37	55	91.9197285(66)	4.48(3) s	β− (99.99%)	92Sr	0−
					β−, n (0.0107%)	91Sr
93Rb	37	56	92.9220393(84)	5.84(2) s	β− (98.61%)	93Sr	5/2−
					β−, n (1.39%)	92Sr
93mRb	4423.1(15) keV			111(11) ns	IT	93Rb	(27/2−)
94Rb	37	57	93.9263948(22)	2.702(5) s	β− (89.7%)	94Sr	3−
					β−, n (10.3%)	93Sr
94m1Rb	104.2(2) keV			130(15) ns	IT	94Rb	(0−)
94m2Rb	2074.9(14) keV			107(16) ns	IT	94Rb	(10−)
95Rb	37	58	94.929264(22)	377.7(8) ms	β− (91.3%)	95Sr	5/2−
					β−, n (8.7%)	94Sr
95mRb	835.0(6) keV			<500 ns	IT	95Rb	9/2+#
96Rb	37	59	95.9341334(36)	201.5(9) ms	β− (86.3%)	96Sr	2−
					β−, n (13.7%)	95Sr
96m1Rb[n 13]	0(200)# keV			200# ms [>1 ms]			1(+#)
96m2Rb	1134.6(11) keV			1.80(4) μs	IT	96Rb	(10−)
97Rb	37	60	96.9371771(21)	169.1(6) ms	β− (74.5%)	97Sr	3/2+
					β−, n (25.5%)	96Sr
97mRb	76.6(2) keV			5.7(6) μs	IT	97Rb	(1/2,3/2)−
98Rb	37	61	97.941632(17)	115(6) ms	β−(85.65%)	98Sr	(0−)
					β−, n (14.3%)	97Sr
					β−, 2n (0.054%)	96Sr
98m1Rb	73(26) keV			96(3) ms	β−	98Sr	(3+)
98m2Rb	178.5(4) keV			358(7) ns	IT	98Rb	(2−)
99Rb	37	62	98.9451192(43)	54(4) ms	β− (82.7%)	99Sr	(3/2+)
					β−, n (17.3%)	98Sr
100Rb	37	63	99.950332(14)	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)	31.8(33) ms	β− (72%)	101Sr	3/2+#
					β−, n (28%)	100Sr
102Rb	37	65	101.960008(89)	37(4) ms	β−, n (65%)	101Sr	(4+)
					β− (35%)	102Sr
103Rb	37	66	102.96440(43)#	26(11) ms	β−	103Sr	3/2+#
104Rb	37	67	103.97053(54)#	35# ms [>550 ns]
105Rb[5]	37	68
106Rb[5]	37	69
This table header & footer: view

1. ^mRb – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Bold half-life – nearly stable, half-life longer than age of universe.
5. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
6. Modes of decay:

   EC:	Electron capture
   IT:	Isomeric transition
   n:	Neutron emission
   p:	Proton emission

7. Bold italics symbol as daughter – Daughter product is nearly stable.
8. Bold symbol as daughter – Daughter product is stable.
9. ( ) spin value – Indicates spin with weak assignment arguments.
10. Fission product
11. Primordial radionuclide
12. Used in rubidium–strontium dating
13. Order of ground state and isomer is uncertain.

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

• Isotopes of strontium
• Isotopes of krypton
• Isotopes of selenium