Isotopes of strontium

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The alkali earth metal strontium (Sr) has four stable, naturally occurring isotopes: ⁸⁴Sr (0.56%), ⁸⁶Sr (9.86%), ⁸⁷Sr (7.0%) and ⁸⁸Sr (82.58%). 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: that formed during primordial nucleo-synthesis 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.

Sixteen unstable isotopes are known to exist. Of greatest importance is strontium-90 (⁹⁰Sr) with a half-life of 28.78 years. It is a by-product of nuclear fission which is found in nuclear fallout and presents a health problem since it substitutes for calcium in bone, preventing expulsion from the body. Strontium-90 decays by emitting an electron and an anti-neutrino ( $\bar{\nu}_e$ ) in beta decay (β⁻ decay) to become yttrium-90 (⁹⁰Y):

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

Because strontium-90 is one of the best long-lived high-energy beta emitters known 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.
Standard atomic mass: 87.62(1) u

[edit] Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
nuclide symbol	excitation energy			half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
⁷³Sr	38	35	72.96597(64)#	>25 ms	1/2-#
⁷⁴Sr	38	36	73.95631(54)#	50# ms [>1.5 µs]	0+
⁷⁵Sr	38	37	74.94995(24)	88(3) ms	(3/2-)
⁷⁶Sr	38	38	75.94177(4)	7.89(7) s	0+
⁷⁷Sr	38	39	76.937945(10)	9.0(2) s	5/2+
⁷⁸Sr	38	40	77.932180(8)	159(8) s	0+
⁷⁹Sr	38	41	78.929708(9)	2.25(10) min	3/2(-)
⁸⁰Sr	38	42	79.924521(7)	106.3(15) min	0+
⁸¹Sr	38	43	80.923212(7)	22.3(4) min	1/2-
⁸²Sr	38	44	81.918402(6)	25.36(3) d	0+
⁸³Sr	38	45	82.917557(11)	32.41(3) h	7/2+
^83mSr	259.15(9) keV			4.95(12) s	1/2-
⁸⁴Sr	38	46	83.913425(3)	STABLE	0+	0.0056(1)	0.0055-0.0058
⁸⁵Sr	38	47	84.912933(3)	64.853(8) d	9/2+
^85mSr	238.66(6) keV			67.63(4) min	1/2-
⁸⁶Sr	38	48	85.9092602(12)	STABLE	0+	0.0986(1)	0.0975-0.0999
^86mSr	2955.68(21) keV			455(7) ns	8+
⁸⁷Sr	38	49	86.9088771(12)	STABLE	9/2+	0.0700(1)	0.0694-0.0714
^87mSr	388.533(3) keV			2.815(12) h	1/2-
⁸⁸Sr	38	50	87.9056121(12)	STABLE	0+	0.8258(1)	0.8229-0.8275
⁸⁹Sr	38	51	88.9074507(12)	50.57(3) d	5/2+
⁹⁰Sr	38	52	89.907738(3)	28.90(3) a	0+
⁹¹Sr	38	53	90.910203(5)	9.63(5) h	5/2+
⁹²Sr	38	54	91.911038(4)	2.66(4) h	0+
⁹³Sr	38	55	92.914026(8)	7.423(24) min	5/2+
⁹⁴Sr	38	56	93.915361(8)	75.3(2) s	0+
⁹⁵Sr	38	57	94.919359(8)	23.90(14) s	1/2+
⁹⁶Sr	38	58	95.921697(29)	1.07(1) s	0+
⁹⁷Sr	38	59	96.926153(21)	429(5) ms	1/2+
^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	0+
⁹⁹Sr	38	61	98.93324(9)	0.269(1) s	3/2+
¹⁰⁰Sr	38	62	99.93535(14)	202(3) ms	0+
¹⁰¹Sr	38	63	100.94052(13)	118(3) ms	(5/2-)
¹⁰²Sr	38	64	101.94302(12)	69(6) ms	0+
¹⁰³Sr	38	65	102.94895(54)#	50# ms [>300 ns]
¹⁰⁴Sr	38	66	103.95233(75)#	30# ms [>300 ns]	0+
¹⁰⁵Sr	38	67	104.95858(75)#	20# ms [>300 ns]

[edit] 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.

[edit] References

Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
- Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
- National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
- David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.