Isotopes of strontium

The alkaline earth metal strontium (38Sr) has four stable, naturally occurring isotopes: 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.0%) and 88Sr (82.58%). Its standard atomic weight is 87.62(1).

Isotopes of strontium (38Sr)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
82Sr synth 25.36 d ε 82Rb
83Sr synth 1.35 d ε 83Rb
β+ 83Rb
γ –
84Sr 0.56% stable
85Sr synth 64.84 d ε 85Rb
γ –
86Sr 9.86% stable
87Sr 7% stable
88Sr 82.6% stable
89Sr synth 50.52 d β− 89Y
90Sr trace 28.90 y β− 90Y
Standard atomic weight Ar°(Sr)

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 (i.e. more than three times longer than the current age of the universe). Thus, there are two sources of 87Sr in any material: primordial, formed during nucleosynthesis along with 84Sr, 86Sr and 88Sr; and that formed by radioactive decay of 87Rb. The ratio 87Sr/86Sr is the parameter typically reported in geologic investigations;[4] ratios in minerals and rocks have values ranging from about 0.7 to greater than 4.0 (see rubidium–strontium dating). Because strontium has an electron configuration similar to that of calcium, it readily substitutes for calcium in minerals.

In addition to the four stable isotopes, thirty-two unstable isotopes of strontium are known to exist, ranging from 73Sr to 108Sr. Radioactive isotopes of strontium primarily decay into the neighbouring elements yttrium (89Sr and heavier isotopes, via beta minus decay) and rubidium (85Sr, 83Sr and lighter isotopes, via positron emission or electron capture). The longest-lived of these isotopes, and the most relevantly studied, are 90Sr with a half-life of 28.9 years, 85Sr with a half-life of 64.853 days, and 89Sr (89Sr) with a half-life of 50.57 days. All other strontium isotopes have half-lives shorter than 50 days, most under 100 minutes.

Strontium-89 is an artificial radioisotope used in treatment of bone cancer;[5] this application utilizes its chemical similarity to calcium, which allows it to substitute calcium in bone structures. 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 cancerous portions of the bone, where calcium turnover is greatest. Strontium-90 is a by-product of nuclear fission, present in nuclear fallout. The 1986 Chernobyl nuclear accident contaminated a vast area with 90Sr.[6] It causes health problems, as 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.

In 2020, researchers have found that mirror nuclides 73Sr and 73Br were found to not behave identically to each other as expected.[7]

List of isotopes
Nuclide
[n 1]		 Z N Isotopic mass (Da)
[n 2][n 3]		 Half-life
[n 4]		 Decay
mode
[n 5]		 Daughter
isotope
[n 6][n 7]		 Spin and
parity
[n 8][n 4]		 Natural abundance (mole fraction)
Excitation energy Normal proportion Range of variation
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 9] 0+ 0.0056 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 0.0975–0.0999
86mSr 2955.68(21) keV 455(7) ns 8+
87Sr[n 10] 38 49 86.9088774970(91) Stable 9/2+ 0.0700 0.0694–0.0714
87mSr 388.533(3) keV 2.815(12) h IT (99.7%) 87Sr 1/2−
EC (.3%) 87Rb
88Sr[n 11] 38 50 87.9056122571(97) Stable 0+ 0.8258 0.8229–0.8275
89Sr[n 11] 38 51 88.9074507(12) 50.57(3) d β− 89Y 5/2+
90Sr[n 11] 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]
106Sr[8] 38 68
107Sr[8] 38 69
108Sr[9] 38 70
This table header & footer:
  1. mSr – 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. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  5. Modes of decay:
    EC:Electron capture
    IT:Isomeric transition
    n:Neutron emission
    p:Proton emission
  6. Bold italics symbol as daughter – Daughter product is nearly stable.
  7. Bold symbol as daughter – Daughter product is stable.
  8. ( ) spin value – Indicates spin with weak assignment arguments.
  9. Believed to decay by β+β+ to 84Kr
  10. Used in rubidium–strontium dating
  11. Fission product

References
  1. Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  2. "Standard Atomic Weights: Strontium". CIAAW. 1969.
  3. Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  4. Dickin, Alan P. (2018). Radiogenic Isotope Geology (3 ed.). Cambridge: Cambridge University Press. ISBN 978-1-107-09944-9.
  5. Reddy, Eashwer K.; Robinson, Ralph G.; Mansfield, Carl M. (January 1986). "Strontium 89 for Palliation of Bone Metastases". Journal of the National Medical Association. 78 (1): 27–32. ISSN 0027-9684. PMC 2571189. PMID 2419578.
  6. Wilken, R.D.; Diehl, R. (1987). "Strontium-90 in environmental samples from Northern Germany before and after the Chernobyl accident". Radiochimica Acta. 41 (4): 157–162. doi:10.1524/ract.1987.41.4.157. S2CID 99369165.
  7. "Discovery by UMass Lowell-led team challenges nuclear theory". Space Daily. Retrieved 2022-06-26.
  8. Ohnishi, Tetsuya; Kubo, Toshiyuki; Kusaka, Kensuke; et al. (2010). "Identification of 45 New Neutron-Rich Isotopes Produced by In-Flight Fission of a 238U Beam at 345 MeV/nucleon". J. Phys. Soc. Jpn. 79 (7). Physical Society of Japan: 073201. arXiv:1006.0305. Bibcode:2010JPSJ...79g3201T. doi:10.1143/JPSJ.79.073201.
  9. Sumikama, T.; et al. (2021). "Observation of new neutron-rich isotopes in the vicinity of 110Zr". Physical Review C. 103 (1): 014614. Bibcode:2021PhRvC.103a4614S. doi:10.1103/PhysRevC.103.014614. hdl:10261/260248. S2CID 234019083.
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