# Isotopes of strontium

The alkaline earth metal strontium ($_{38}$Sr) has four stable, naturally occurring isotopes: $^{84}$Sr (0.56%), $^{86}$Sr (9.86%), $^{87}$Sr (7.0%) and $^{88}$Sr (82.58%). Its standard atomic weight is 87.62(1).
Only $^{87}$Sr is radiogenic; it is produced by decay from the radioactive alkali metal $^{87}$Rb, which has a half-life of 4.88 × 10$^{10}$ years (i.e. more than three times longer than the current age of the universe). Thus, there are two sources of $^{87}$Sr in any material: primordial, formed during nucleosynthesis along with $^{84}$Sr, $^{86}$Sr and $^{88}$Sr; and that formed by radioactive decay of $^{87}$Rb. The ratio $^{87}$Sr/$^{86}$Sr 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 (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 $^{73}$Sr to $^{108}$Sr. Radioactive isotopes of strontium primarily decay into the neighbouring elements yttrium ($^{89}$Sr and heavier isotopes, via beta minus decay) and rubidium ($^{85}$Sr, $^{83}$Sr and lighter isotopes, via positron emission or electron capture). The longest-lived of these isotopes, and the most relevantly studied, are $^{90}$Sr with a half-life of 28.9 years, $^{85}$Sr with a half-life of 64.853 days, and $^{89}$Sr ($^{89}$Sr) 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; 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 $^{89}$Sr 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 $^{90}$Sr. 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 $^{73}$Sr and $^{73}$Br were found to not behave identically to each other as expected.

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Natural abundance (mole fraction) | Natural abundance (mole fraction) |
| Nuclide | Excitation energy | Excitation energy | Excitation energy | Half-life | Decay mode | Daughter isotope | Spin and parity | Normal proportion | Range of variation |
| $^{73}$Sr | 38 | 35 | 72.96570(43)# | 25.3(14) ms | β$^+$, p (63%) | $^{72}$Kr | (5/2−) | | |
| $^{73}$Sr | 38 | 35 | 72.96570(43)# | 25.3(14) ms | β$^+$ (37%) | $^{73}$Rb | (5/2−) | | |
| $^{74}$Sr | 38 | 36 | 73.95617(11)# | 27.6(26) ms | β$^+$ | $^{74}$Rb | 0+ | | |
| $^{75}$Sr | 38 | 37 | 74.94995(24) | 85.2(23) ms | β$^+$ (94.8%) | $^{75}$Rb | (3/2−) | | |
| $^{75}$Sr | 38 | 37 | 74.94995(24) | 85.2(23) ms | β$^+$, p (5.2%) | $^{74}$Kr | (3/2−) | | |
| $^{76}$Sr | 38 | 38 | 75.941763(37) | 7.89(7) s | β$^+$ | $^{76}$Rb | 0+ | | |
| $^{76}$Sr | 38 | 38 | 75.941763(37) | 7.89(7) s | β$^+$, p (0.0034%) | $^{75}$Kr | 0+ | | |
| $^{77}$Sr | 38 | 39 | 76.9379455(85) | 9.0(2) s | β$^+$ (99.92%) | $^{77}$Rb | 5/2+ | | |
| $^{77}$Sr | 38 | 39 | 76.9379455(85) | 9.0(2) s | β$^+$, p (0.08%) | $^{76}$Kr | 5/2+ | | |
| $^{78}$Sr | 38 | 40 | 77.9321800(80) | 156.1(27) s | β$^+$ | $^{78}$Rb | 0+ | | |
| $^{79}$Sr | 38 | 41 | 78.9297047(80) | 2.25(10) min | β$^+$ | $^{79}$Rb | 3/2− | | |
| $^{80}$Sr | 38 | 42 | 79.9245175(37) | 106.3(15) min | β$^+$ | $^{80}$Rb | 0+ | | |
| $^{81}$Sr | 38 | 43 | 80.9232114(34) | 22.3(4) min | β$^+$ | $^{81}$Rb | 1/2− | | |
| $^{81m1}$Sr | 79.23(4) keV | 79.23(4) keV | 79.23(4) keV | 390(50) ns | IT | $^{81}$Sr | (5/2)− | | |
| $^{81m2}$Sr | 89.05(7) keV | 89.05(7) keV | 89.05(7) keV | 6.4(5) μs | | | (7/2+) | | |
| $^{82}$Sr | 38 | 44 | 81.9183998(64) | 25.35(3) d | EC | $^{82}$Rb | 0+ | | |
| $^{83}$Sr | 38 | 45 | 82.9175544(73) | 32.41(3) h | β$^+$ | $^{83}$Rb | 7/2+ | | |
| $^{83m}$Sr | 259.15(9) keV | 259.15(9) keV | 259.15(9) keV | 4.95(12) s | IT | $^{83}$Sr | 1/2− | | |
| $^{84}$Sr | 38 | 46 | 83.9134191(13) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.0056(2) | |
| $^{85}$Sr | 38 | 47 | 84.9129320(30) | 64.846(6) d | EC | $^{85}$Rb | 9/2+ | | |
| $^{85m}$Sr | 238.79(5) keV | 238.79(5) keV | 238.79(5) keV | 67.63(4) min | IT (86.6%) | $^{85}$Sr | 1/2− | | |
| $^{85m}$Sr | 238.79(5) keV | 238.79(5) keV | 238.79(5) keV | 67.63(4) min | β$^+$ (13.4%) | $^{85}$Rb | 1/2− | | |
| $^{86}$Sr | 38 | 48 | 85.9092607247(56) | Stable | Stable | Stable | 0+ | 0.0986(20) | |
| $^{86m}$Sr | 2956.09(12) keV | 2956.09(12) keV | 2956.09(12) keV | 455(7) ns | IT | $^{86}$Sr | 8+ | | |
| $^{87}$Sr | 38 | 49 | 86.9088774945(55) | Stable | Stable | Stable | 9/2+ | 0.0700(20) | |
| $^{87m}$Sr | 388.5287(23) keV | 388.5287(23) keV | 388.5287(23) keV | 2.805(9) h | IT (99.70%) | $^{87}$Sr | 1/2− | | |
| $^{87m}$Sr | 388.5287(23) keV | 388.5287(23) keV | 388.5287(23) keV | 2.805(9) h | EC (0.30%) | $^{87}$Rb | 1/2− | | |
| $^{88}$Sr | 38 | 50 | 87.905612253(6) | Stable | Stable | Stable | 0+ | 0.8258(35) | |
| $^{89}$Sr | 38 | 51 | 88.907450808(98) | 50.563(25) d | β$^−$ | $^{89}$Y | 5/2+ | | |
| $^{90}$Sr | 38 | 52 | 89.9077279(16) | 28.91(3) y | β$^−$ | $^{90}$Y | 0+ | | |
| $^{91}$Sr | 38 | 53 | 90.9101959(59) | 9.65(6) h | β$^−$ | $^{91}$Y | 5/2+ | | |
| $^{92}$Sr | 38 | 54 | 91.9110382(37) | 2.611(17) h | β$^−$ | $^{92}$Y | 0+ | | |
| $^{93}$Sr | 38 | 55 | 92.9140243(81) | 7.43(3) min | β$^−$ | $^{93}$Y | 5/2+ | | |
| $^{94}$Sr | 38 | 56 | 93.9153556(18) | 75.3(2) s | β$^−$ | $^{94}$Y | 0+ | | |
| $^{95}$Sr | 38 | 57 | 94.9193583(62) | 23.90(14) s | β$^−$ | $^{95}$Y | 1/2+ | | |
| $^{96}$Sr | 38 | 58 | 95.9217190(91) | 1.059(8) s | β$^−$ | $^{96}$Y | 0+ | | |
| $^{97}$Sr | 38 | 59 | 96.9263756(36) | 432(4) ms | β$^−$ (99.98%) | $^{97}$Y | 1/2+ | | |
| $^{97}$Sr | 38 | 59 | 96.9263756(36) | 432(4) ms | β$^−$, n (0.02%) | $^{96}$Y | 1/2+ | | |
| $^{97m1}$Sr | 308.13(11) keV | 308.13(11) keV | 308.13(11) keV | 175.2(21) ns | IT | $^{97}$Sr | 7/2+ | | |
| $^{97m2}$Sr | 830.83(23) keV | 830.83(23) keV | 830.83(23) keV | 513(5) ns | IT | $^{97}$Sr | (9/2+) | | |
| $^{98}$Sr | 38 | 60 | 97.9286926(35) | 653(2) ms | β$^−$ (99.77%) | $^{98}$Y | 0+ | | |
| $^{98}$Sr | 38 | 60 | 97.9286926(35) | 653(2) ms | β$^−$, n (0.23%) | $^{97}$Y | 0+ | | |
| $^{99}$Sr | 38 | 61 | 98.9328836(51) | 269.2(10) ms | β$^−$ (99.90%) | $^{99}$Y | 3/2+ | | |
| $^{99}$Sr | 38 | 61 | 98.9328836(51) | 269.2(10) ms | β$^−$, n (0.100%) | $^{98}$Y | 3/2+ | | |
| $^{100}$Sr | 38 | 62 | 99.9357833(74) | 202.1(17) ms | β$^−$ (98.89%) | $^{100}$Y | 0+ | | |
| $^{100}$Sr | 38 | 62 | 99.9357833(74) | 202.1(17) ms | β$^−$, n (1.11%) | $^{99}$Y | 0+ | | |
| $^{100m}$Sr | 1618.72(20) keV | 1618.72(20) keV | 1618.72(20) keV | 122(9) ns | IT | $^{100}$Sr | (4−) | | |
| $^{101}$Sr | 38 | 63 | 100.9406063(91) | 113.7(17) ms | β$^−$ (97.25%) | $^{101}$Y | (5/2−) | | |
| $^{101}$Sr | 38 | 63 | 100.9406063(91) | 113.7(17) ms | β$^−$, n (2.75%) | $^{100}$Y | (5/2−) | | |
| $^{102}$Sr | 38 | 64 | 101.944005(72) | 69(6) ms | β$^−$ (94.5%) | $^{102}$Y | 0+ | | |
| $^{102}$Sr | 38 | 64 | 101.944005(72) | 69(6) ms | β$^−$, n (5.5%) | $^{101}$Y | 0+ | | |
| $^{103}$Sr | 38 | 65 | 102.94924(22)# | 53(10) ms | β$^−$ | $^{103}$Y | 5/2+# | | |
| $^{104}$Sr | 38 | 66 | 103.95302(32)# | 50.6(42) ms | β$^−$ | $^{104}$Y | 0+ | | |
| $^{105}$Sr | 38 | 67 | 104.95900(54)# | 39(5) ms | β$^−$ | $^{105}$Y | 5/2+# | | |
| $^{106}$Sr | 38 | 68 | 105.96318(64)# | 21(8) ms | β$^−$ | $^{106}$Y | 0+ | | |
| $^{107}$Sr | 38 | 69 | 106.96967(75)# | 25# ms [>400 ns] | | | 1/2+# | | |
| $^{108}$Sr | 38 | 70 | | | | | | | |
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* ↑ $^m$Sr – Excited nuclear isomer.
* ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
* ↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
* 1 2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* ↑ Modes of decay: EC:Electron capture IT:Isomeric transition n:Neutron emission p:Proton emission
* ↑ Bold italics symbol as daughter – Daughter product is nearly stable.
* ↑ Bold symbol as daughter – Daughter product is stable.
* ↑ ( ) spin value – Indicates spin with weak assignment arguments.
* ↑ Believed to decay by β$^+$β$^+$ to $^{84}$Kr
* ↑ Used in rubidium–strontium dating
* 1 2 3 Fission product