Isotopes of strontium

The alkaline earth metal strontium (Sr) has four stable, naturally occurring isotopes: ⁸⁴Sr (0.56%), ⁸⁶Sr (9.86%), ⁸⁷Sr (7.0%) and ⁸⁸Sr (82.58%). It has a relative atomic mass of 87.62(1).

Only ⁸⁷Sr is radiogenic; it is produced by decay from the radioactive alkali metal ⁸⁷Rb, which has a half-life of 4.88 × 10¹⁰ years. Thus, there are two sources of ⁸⁷Sr in any material: primordial that formed during nucleosynthesis along with ⁸⁴Sr, ⁸⁶Sr and ⁸⁸Sr, as well as that formed by radioactive decay of ⁸⁷Rb. The ratio ⁸⁷Sr/⁸⁶Sr is the parameter typically reported in geologic investigations; ratios in minerals and rocks have values ranging from about 0.7 to greater than 4.0. Because strontium has an electron configuration similar to that of calcium, it readily substitutes for Ca in minerals.

Thirty-one unstable isotopes are known to exist, the longest-lived of which are ⁹⁰Sr with a half-life of 28.9 years and ⁸⁵Sr with a half-life of 64.853 days. Of importance are strontium-89 (⁸⁹Sr) with a half-life of 50.57 days, and strontium-90 (⁹⁰Sr). They decay by emitting an electron and an antineutrino ($\bar{\nu}_e$) in beta decay (β⁻ decay) to become yttrium:

$\mathrm{{}^{89}_{38}Sr}\rightarrow\mathrm{{}^{89}_{39}Y} + e^- + \bar{\nu}_e$

$\mathrm{{}^{90}_{38}Sr}\rightarrow\mathrm{{}^{90}_{39}Y} + e^- + \bar{\nu}_e$

⁸⁹Sr is an artificial radioisotope used in treatment of bone cancer. In circumstances where cancer patients have widespread and painful bony metastases, the administration of ⁸⁹Sr results in the delivery of beta particles directly to the area of bony problem, where calcium turnover is greatest.

⁹⁰Sr is a by-product of nuclear fission found in nuclear fallout and presents a health problem since it substitutes for calcium in bone, preventing expulsion from the body. Because it is a long-lived high-energy beta emitter, it is used in SNAP (Systems for Nuclear Auxiliary Power) devices. These devices hold promise for use in spacecraft, remote weather stations, navigational buoys, etc., where a lightweight, long-lived, nuclear-electric power source is required. The 1986 Chernobyl nuclear accident contaminated a vast area with ⁹⁰Sr.

The lightest isotope is ⁷³Sr and the heaviest being ¹⁰⁷Sr.

All other isotopes have half-lives shorter than 55 days, most under 100 minutes.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)[1][n 1]	daughter isotope(s)[n 2]	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
^73Sr	38	35	72.96597(64)#	>25 ms	β^+ (>99.9%)	^73Rb	1/2−#
					β^+, p (<.1%)	^72Kr
^74Sr	38	36	73.95631(54)#	50# ms [>1.5 µs]	β^+	^74Rb	0+
^75Sr	38	37	74.94995(24)	88(3) ms	β^+ (93.5%)	^75Rb	(3/2−)
					β^+, p (6.5%)	^74Kr
^76Sr	38	38	75.94177(4)	7.89(7) s	β^+	^76Rb	0+
^77Sr	38	39	76.937945(10)	9.0(2) s	β^+ (99.75%)	^77Rb	5/2+
					β^+, p (.25%)	^76Kr
^78Sr	38	40	77.932180(8)	159(8) s	β^+	^78Rb	0+
^79Sr	38	41	78.929708(9)	2.25(10) min	β^+	^79Rb	3/2(−)
^80Sr	38	42	79.924521(7)	106.3(15) min	β^+	^80Rb	0+
^81Sr	38	43	80.923212(7)	22.3(4) min	β^+	^81Rb	1/2−
^82Sr	38	44	81.918402(6)	25.36(3) d	EC	^82Rb	0+
^83Sr	38	45	82.917557(11)	32.41(3) h	β^+	^83Rb	7/2+
^83mSr	259.15(9) keV			4.95(12) s	IT	^83Sr	1/2−
^84Sr	38	46	83.913425(3)	Observationally Stable[n 3]			0+	0.0056(1)	0.0055–0.0058
^85Sr	38	47	84.912933(3)	64.853(8) d	EC	^85Rb	9/2+
^85mSr	238.66(6) keV			67.63(4) min	IT (86.6%)	^85Sr	1/2−
					β^+ (13.4%)	^85Rb
^86Sr	38	48	85.9092607309(91)	Stable			0+	0.0986(1)	0.0975–0.0999
^86mSr	2955.68(21) keV			455(7) ns			8+
^87Sr[n 4]	38	49	86.9088774970(91)	Stable			9/2+	0.0700(1)	0.0694–0.0714
^87mSr	388.533(3) keV			2.815(12) h	IT (99.7%)	^87Sr	1/2−
					EC (.3%)	^87Rb
^88Sr[n 5]	38	50	87.9056122571(97)	Stable			0+	0.8258(1)	0.8229–0.8275
^89Sr[n 5]	38	51	88.9074507(12)	50.57(3) d	β^−	^89Y	5/2+
^90Sr[n 5]	38	52	89.907738(3)	28.90(3) y	β^−	^90Y	0+
^91Sr	38	53	90.910203(5)	9.63(5) h	β^−	^91Y	5/2+
^92Sr	38	54	91.911038(4)	2.66(4) h	β^−	^92Y	0+
^93Sr	38	55	92.914026(8)	7.423(24) min	β^−	^93Y	5/2+
^94Sr	38	56	93.915361(8)	75.3(2) s	β^−	^94Y	0+
^95Sr	38	57	94.919359(8)	23.90(14) s	β^−	^95Y	1/2+
^96Sr	38	58	95.921697(29)	1.07(1) s	β^−	^96Y	0+
^97Sr	38	59	96.926153(21)	429(5) ms	β^− (99.95%)	^97Y	1/2+
					β^−, n (.05%)	^96Y
^97m1Sr	308.13(11) keV			170(10) ns			(7/2)+
^97m2Sr	830.8(2) keV			255(10) ns			(11/2−)#
^98Sr	38	60	97.928453(28)	0.653(2) s	β^− (99.75%)	^98Y	0+
					β^−, n (.25%)	^97Y
^99Sr	38	61	98.93324(9)	0.269(1) s	β^− (99.9%)	^99Y	3/2+
					β^−, n (.1%)	^98Y
^100Sr	38	62	99.93535(14)	202(3) ms	β^− (99.02%)	^100Y	0+
					β^−, n (.98%)	^99Y
^101Sr	38	63	100.94052(13)	118(3) ms	β^− (97.63%)	^101Y	(5/2−)
					β^−, n (2.37%)	^100Y
^102Sr	38	64	101.94302(12)	69(6) ms	β^− (94.5%)	^102Y	0+
					β^−, n (5.5%)	^101Y
^103Sr	38	65	102.94895(54)#	50# ms [>300 ns]	β^−	^103Y
^104Sr	38	66	103.95233(75)#	30# ms [>300 ns]	β^−	^104Y	0+
^105Sr	38	67	104.95858(75)#	20# ms [>300 ns]

1. Abbreviations:
   EC: Electron capture
   IT: Isomeric transition
2. Bold for stable isotopes, bold italic for nearly-stable isotopes (half-life longer than the age of the universe)
3. Believed to decay by β⁺β⁺ to ⁸⁴Kr
4. Used in rubidium-strontium dating
5. Fission product

Notes

• Evaluated isotopic composition is for most but not all commercial samples.
• The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
• 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.