Isotopes of strontium

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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 standard atomic mass of 87.62(1) u.

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.

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 anti-neutrino (\bar{\nu}_e) in beta decay 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 which is 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 which is 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[edit]

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) a 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. ^ a b c Fission product

Notes[edit]

  • 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[edit]

  1. ^ http://www.nucleonica.net/unc.aspx


Isotopes of rubidium Isotopes of strontium Isotopes of yttrium
Table of nuclides