The

alkaline earth metal The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar properties: they are all ...

strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is e ...

(₃₈Sr) has four stable, naturally occurring

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass num ...

s: ⁸⁴Sr (0.56%), ⁸⁶Sr (9.86%), ⁸⁷Sr (7.0%) and ⁸⁸Sr (82.58%). Its

standard atomic weight The standard atomic weight of a chemical element (symbol ''A''r°(E) for element "E") is the weighted arithmetic mean of the relative isotopic masses of all isotopes of that element weighted by each isotope's abundance on Earth. For example, ...

is 87.62(1). Only ⁸⁷Sr is radiogenic; it is produced by decay from the

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...

alkali metal ⁸⁷ Rb, which has a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...

of 4.88 × 10¹⁰ years (i.e. more than three times longer than the current

age of the universe In physical cosmology, the age of the universe is the time elapsed since the Big Bang. Astronomers have derived two different measurements of the age of the universe: a measurement based on direct observations of an early state 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 Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other E ...

investigations; ratios in minerals and rocks have values ranging from about 0.7 to greater than 4.0 (see

rubidium–strontium dating The rubidium-strontium dating method is a radiometric dating technique, used by scientists to determine the age of rocks and minerals from their content of specific isotopes of rubidium (87Rb) and strontium (87Sr, 86Sr). One of the two naturally ...

). Because strontium has an

electron configuration In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon ato ...

similar to that of

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

, it readily substitutes for calcium in

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

s. 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 Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a " rare-earth element". Yttrium is almost always found in co ...

(⁸⁹Sr and heavier isotopes, via beta minus decay) and

rubidium Rubidium is the chemical element with the symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have a density higher ...

(⁸⁵Sr, ⁸³Sr and lighter isotopes, via

positron emission Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (). Positron ...

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. ...

). 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

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 Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, the ...

, the administration of ⁸⁹Sr results in the delivery of

beta particles A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β ...

directly to the area of bony problem, where calcium turnover is greatest. Strontium-90 is a by-product of

nuclear fission Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radio ...

, present in

nuclear fallout Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refers to the radioac ...

. The 1986 Chernobyl nuclear accident contaminated a vast area with ⁹⁰Sr. It causes health problems, as it substitutes for calcium in

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

, preventing expulsion from the body. Because it is a long-lived high-energy

beta Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...

emitter, it is used in SNAP (

Systems for Nuclear Auxiliary Power The Systems Nuclear Auxiliary POWER (SNAP) program was a program of experimental radioisotope thermoelectric generators (RTGs) and space nuclear reactors flown during the 1960s by NASA. Odd-numbered SNAPs: radioisotope thermoelectric generators ...

) devices. These devices hold promise for use in

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, ...

, 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.

List of isotopes

, - , rowspan=2, ⁷³Sr , rowspan=2 style="text-align:right" , 38 , rowspan=2 style="text-align:right" , 35 , rowspan=2, 72.96597(64)# , rowspan=2, >25 ms , β⁺ (>99.9%) , ⁷³Rb , rowspan=2, 1/2−# , rowspan=2, , rowspan=2, , - , β⁺, p (<.1%) , ⁷²Kr , - , ⁷⁴Sr , style="text-align:right" , 38 , style="text-align:right" , 36 , 73.95631(54)# , 50# ms 1.5 µs, β⁺ , ⁷⁴Rb , 0+ , , , - , rowspan=2, ⁷⁵Sr , rowspan=2 style="text-align:right" , 38 , rowspan=2 style="text-align:right" , 37 , rowspan=2, 74.94995(24) , rowspan=2, 88(3) ms , β⁺ (93.5%) , ⁷⁵Rb , rowspan=2, (3/2−) , rowspan=2, , rowspan=2, , - , β⁺, p (6.5%) , ⁷⁴Kr , - , ⁷⁶Sr , style="text-align:right" , 38 , style="text-align:right" , 38 , 75.94177(4) , 7.89(7) s , β⁺ , ⁷⁶Rb , 0+ , , , - , rowspan=2, ⁷⁷Sr , rowspan=2 style="text-align:right" , 38 , rowspan=2 style="text-align:right" , 39 , rowspan=2, 76.937945(10) , rowspan=2, 9.0(2) s , β⁺ (99.75%) , ⁷⁷Rb , rowspan=2, 5/2+ , rowspan=2, , rowspan=2, , - , β⁺, p (.25%) , ⁷⁶Kr , - , ⁷⁸Sr , style="text-align:right" , 38 , style="text-align:right" , 40 , 77.932180(8) , 159(8) s , β⁺ , ⁷⁸Rb , 0+ , , , - , ⁷⁹Sr , style="text-align:right" , 38 , style="text-align:right" , 41 , 78.929708(9) , 2.25(10) min , β⁺ , ⁷⁹Rb , 3/2(−) , , , - , ⁸⁰Sr , style="text-align:right" , 38 , style="text-align:right" , 42 , 79.924521(7) , 106.3(15) min , β⁺ , ⁸⁰Rb , 0+ , , , - , ⁸¹Sr , style="text-align:right" , 38 , style="text-align:right" , 43 , 80.923212(7) , 22.3(4) min , β⁺ , ⁸¹Rb , 1/2− , , , - , ⁸²Sr , style="text-align:right" , 38 , style="text-align:right" , 44 , 81.918402(6) , 25.36(3) d , EC , ⁸²Rb , 0+ , , , - , ⁸³Sr , style="text-align:right" , 38 , style="text-align:right" , 45 , 82.917557(11) , 32.41(3) h , β⁺ , ⁸³Rb , 7/2+ , , , - , style="text-indent:1em" , ^83mSr , colspan="3" style="text-indent:2em" , 259.15(9) keV , 4.95(12) s , IT , ⁸³Sr , 1/2− , , , - , ⁸⁴Sr , style="text-align:right" , 38 , style="text-align:right" , 46 , 83.913425(3) , colspan=3 align=center,

Observationally Stable Stable nuclides are nuclides that are not radioactive and so (unlike radionuclides) do not spontaneously undergo radioactive decay. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes. Th ...

Believed to decay by β⁺β⁺ to ⁸⁴Kr , 0+ , 0.0056 , 0.0055–0.0058 , - , ⁸⁵Sr , style="text-align:right" , 38 , style="text-align:right" , 47 , 84.912933(3) , 64.853(8) d , EC , ⁸⁵Rb , 9/2+ , , , - , rowspan=2 style="text-indent:1em" , ^85mSr , rowspan=2 colspan="3" style="text-indent:2em" , 238.66(6) keV , rowspan=2, 67.63(4) min , IT (86.6%) , ⁸⁵Sr , rowspan=2, 1/2− , rowspan=2, , rowspan=2, , - , β⁺ (13.4%) , ⁸⁵Rb , - , ⁸⁶Sr , style="text-align:right" , 38 , style="text-align:right" , 48 , 85.9092607309(91) , colspan=3 align=center, Stable , 0+ , 0.0986 , 0.0975–0.0999 , - , style="text-indent:1em" , ^86mSr , colspan="3" style="text-indent:2em" , 2955.68(21) keV , 455(7) ns , , , 8+ , , , - , ⁸⁷SrUsed in

, style="text-align:right" , 38 , style="text-align:right" , 49 , 86.9088774970(91) , colspan=3 align=center, Stable , 9/2+ , 0.0700 , 0.0694–0.0714 , - , rowspan=2 style="text-indent:1em" , ^87mSr , rowspan=2 colspan="3" style="text-indent:2em" , 388.533(3) keV , rowspan=2, 2.815(12) h , IT (99.7%) , ⁸⁷Sr , rowspan=2, 1/2− , rowspan=2, , rowspan=2, , - , EC (.3%) , ''⁸⁷Rb'' , - , ⁸⁸Sr

Fission product Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release ...

, style="text-align:right" , 38 , style="text-align:right" , 50 , 87.9056122571(97) , colspan=3 align=center, Stable , 0+ , 0.8258 , 0.8229–0.8275 , - , ⁸⁹Sr , style="text-align:right" , 38 , style="text-align:right" , 51 , 88.9074507(12) , 50.57(3) d , β⁻ , ⁸⁹Y , 5/2+ , , , - , ⁹⁰Sr , style="text-align:right" , 38 , style="text-align:right" , 52 , 89.907738(3) , 28.90(3) y , β⁻ , ⁹⁰Y , 0+ , , , - , ⁹¹Sr , style="text-align:right" , 38 , style="text-align:right" , 53 , 90.910203(5) , 9.63(5) h , β⁻ , ⁹¹Y , 5/2+ , , , - , ⁹²Sr , style="text-align:right" , 38 , style="text-align:right" , 54 , 91.911038(4) , 2.66(4) h , β⁻ , ⁹²Y , 0+ , , , - , ⁹³Sr , style="text-align:right" , 38 , style="text-align:right" , 55 , 92.914026(8) , 7.423(24) min , β⁻ , ⁹³Y , 5/2+ , , , - , ⁹⁴Sr , style="text-align:right" , 38 , style="text-align:right" , 56 , 93.915361(8) , 75.3(2) s , β⁻ , ⁹⁴Y , 0+ , , , - , ⁹⁵Sr , style="text-align:right" , 38 , style="text-align:right" , 57 , 94.919359(8) , 23.90(14) s , β⁻ , ⁹⁵Y , 1/2+ , , , - , ⁹⁶Sr , style="text-align:right" , 38 , style="text-align:right" , 58 , 95.921697(29) , 1.07(1) s , β⁻ , ⁹⁶Y , 0+ , , , - , rowspan=2, ⁹⁷Sr , rowspan=2 style="text-align:right" , 38 , rowspan=2 style="text-align:right" , 59 , rowspan=2, 96.926153(21) , rowspan=2, 429(5) ms , β⁻ (99.95%) , ⁹⁷Y , rowspan=2, 1/2+ , rowspan=2, , rowspan=2, , - , β⁻, n (.05%) , ⁹⁶Y , - , style="text-indent:1em" , ^97m1Sr , colspan="3" style="text-indent:2em" , 308.13(11) keV , 170(10) ns , , , (7/2)+ , , , - , style="text-indent:1em" , ^97m2Sr , colspan="3" style="text-indent:2em" , 830.8(2) keV , 255(10) ns , , , (11/2−)# , , , - , rowspan=2, ⁹⁸Sr , rowspan=2 style="text-align:right" , 38 , rowspan=2 style="text-align:right" , 60 , rowspan=2, 97.928453(28) , rowspan=2, 0.653(2) s , β⁻ (99.75%) , ⁹⁸Y , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n (.25%) , ⁹⁷Y , - , rowspan=2, ⁹⁹Sr , rowspan=2 style="text-align:right" , 38 , rowspan=2 style="text-align:right" , 61 , rowspan=2, 98.93324(9) , rowspan=2, 0.269(1) s , β⁻ (99.9%) , ⁹⁹Y , rowspan=2, 3/2+ , rowspan=2, , rowspan=2, , - , β⁻, n (.1%) , ⁹⁸Y , - , rowspan=2, ¹⁰⁰Sr , rowspan=2 style="text-align:right" , 38 , rowspan=2 style="text-align:right" , 62 , rowspan=2, 99.93535(14) , rowspan=2, 202(3) ms , β⁻ (99.02%) , ¹⁰⁰Y , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n (.98%) , ⁹⁹Y , - , rowspan=2, ¹⁰¹Sr , rowspan=2 style="text-align:right" , 38 , rowspan=2 style="text-align:right" , 63 , rowspan=2, 100.94052(13) , rowspan=2, 118(3) ms , β⁻ (97.63%) , ¹⁰¹Y , rowspan=2, (5/2−) , rowspan=2, , rowspan=2, , - , β⁻, n (2.37%) , ¹⁰⁰Y , - , rowspan=2, ¹⁰²Sr , rowspan=2 style="text-align:right" , 38 , rowspan=2 style="text-align:right" , 64 , rowspan=2, 101.94302(12) , rowspan=2, 69(6) ms , β⁻ (94.5%) , ¹⁰²Y , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n (5.5%) , ¹⁰¹Y , - , ¹⁰³Sr , style="text-align:right" , 38 , style="text-align:right" , 65 , 102.94895(54)# , 50# ms 300 ns, β⁻ , ¹⁰³Y , , , , - , ¹⁰⁴Sr , style="text-align:right" , 38 , style="text-align:right" , 66 , 103.95233(75)# , 30# ms 300 ns, β⁻ , ¹⁰⁴Y , 0+ , , , - , ¹⁰⁵Sr , style="text-align:right" , 38 , style="text-align:right" , 67 , 104.95858(75)# , 20# ms 300 ns, , , , , , - , ¹⁰⁶Sr , style="text-align:right" , 38 , style="text-align:right" , 68 , , , , , , , , - , ¹⁰⁷Sr , style="text-align:right" , 38 , style="text-align:right" , 69 , , , , , , , , - , ¹⁰⁸Sr , style="text-align:right" , 38 , style="text-align:right" , 70 , , , , , , ,

References

* Isotope masses from: ** * Isotopic compositions and standard atomic masses from: ** ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** {{Authority control Strontium

Strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is e ...