Isotopes of calcium

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Isotopes of calcium  (20Ca)
Main isotopes [1] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
40Ca96.9% stable
41Ca trace 9.94×104 y ε 41K
42Ca0.647%stable
43Ca0.135%stable
44Ca2.09%stable
45Ca synth 162.61 d β 45Sc
46Ca0.004%stable
47Casynth4.536 dβ 47Sc
48Ca 0.187%5.6×1019 y ββ 48Ti
Standard atomic weight Ar°(Ca)

Calcium (20Ca) has 26 known isotopes, ranging from 35Ca to 60Ca. There are five stable isotopes (40Ca, 42Ca, 43Ca, 44Ca and 46Ca), plus one isotope (48Ca) with such a long half-life that it is for all practical purposes stable. The most abundant isotope, 40Ca, as well as the rare 46Ca, are theoretically unstable on energetic grounds, but their decay has not been observed. Calcium also has a cosmogenic isotope, 41Ca, with half-life 99,400 years. Unlike cosmogenic isotopes that are produced in the air, 41Ca is produced by neutron activation of solid 40Ca in rock and soil. Most of its production is in the upper metre of the soil column, where the cosmogenic neutron flux is still strong enough. The most stable artificial isotopes are 45Ca with half-life 162.61 days and 47Ca with half-life 4.536 days. All other calcium isotopes have half-lives of minutes or less.

Contents

Stable 40Ca comprises about 97% of natural calcium and is mainly created by nucleosynthesis in stars (alpha process). Similarly to 40Ar, however, some atoms of 40Ca are radiogenic, created through the radioactive decay of 40K. While K–Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca in nature initially impeded the proliferation of K-Ca dating in early studies, with only a handful of studies in the 20th century. Modern techniques using increasingly precise Thermal-Ionization (TIMS) and Collision-Cell Multi-Collector Inductively-coupled plasma mass spectrometry (CC-MC-ICP-MS) techniques, however, have been used for successful K–Ca age dating [4] [5] similar in method to Rb-Sr dating, as well as determining K losses from the lower continental crust [6] and for source-tracing calcium contributions from various geologic reservoirs. [7] [8]

Stable isotope variations of calcium (most typically 44Ca/40Ca or 44Ca/42Ca, denoted as 'δ44Ca' and 'δ44/42Ca' in delta notation) are also widely used across the natural sciences for a number of applications, ranging from early determination of osteoporosis [9] to quantifying volcanic eruption timescales. [10] Other applications include: quantifying carbon sequestration efficiency in CO2 injection sites [11] and understanding ocean acidification, [12] exploring both ubiquitous and rare magmatic processes, such as formation of granites [13] and carbonatites, [14] tracing modern and ancient trophic webs including in dinosaurs, [15] [16] [17] assessing weaning practices in ancient humans, [18] and a plethora of other emerging applications.

List of isotopes


Nuclide
Z N Isotopic mass (Da) [19]
[n 1]
Half-life [1]
[n 2]
Decay
mode
[1]
[n 3]
Daughter
isotope

[n 4]
Spin and
parity [1]
[n 5] [n 6]
Natural abundance (mole fraction)
Normal proportion [1] Range of variation
35Ca201535.00557(22)#25.7(2) ms β+, p (95.8%)34Ar1/2+#
β+, 2p (4.2%)33Cl
β+ (rare)35K
36Ca201635.993074(43)100.9(13) msβ+, p (51.2%)35Ar0+
β+ (48.8%)36K
37Ca201736.98589785(68)181.0(9) msβ+, p (76.8%)36Ar3/2+
β+ (23.2%)37K
38Ca201837.97631922(21)443.70(25) msβ+38K0+
39Ca201938.97071081(64)860.3(8) msβ+39K3/2+
40Ca [n 7] 202039.962590850(22) Observationally stable [n 8] 0+0.9694(16)0.96933–0.96947
41Ca202140.96227791(15)9.94(15)×104 y EC 41K7/2−Trace [n 9]
42Ca202241.95861778(16)Stable0+0.00647(23)0.00646–0.00648
43Ca202342.95876638(24)Stable7/2−0.00135(10)0.00135–0.00135
44Ca202443.95548149(35)Stable0+0.0209(11)0.02082–0.02092
45Ca202544.95618627(39)162.61(9) dβ45Sc7/2−
46Ca202645.9536877(24)Observationally stable [n 10] 0+4×10−54×10−5–4×10−5
47Ca202746.9545411(24)4.536(3) dβ47Sc7/2−
48Ca [n 11] [n 12] 202847.952522654(18)5.6(10)×1019 yββ [n 13] [n 14] 48Ti0+0.00187(21)0.00186–0.00188
49Ca202948.95566263(19)8.718(6) minβ49Sc3/2−
50Ca203049.9574992(17)13.45(5) sβ50Sc0+
51Ca203150.96099566(56)10.0(8) sβ51Sc3/2−
52Ca203251.96321365(72)4.6(3) sβ (>98%)52Sc0+
β, n (<2%)51Sc
53Ca203352.968451(47)461(90) msβ (60%)53Sc1/2−#
β, n (40%)52Sc
54Ca203453.972989(52)90(6) msβ54Sc0+
55Ca203554.97998(17)22(2) msβ55Sc5/2−#
56Ca203655.98550(27)11(2) msβ56Sc0+
57Ca203756.99296(43)#8# ms [>620 ns]5/2−#
58Ca203857.99836(54)#4# ms [>620 ns]0+
59Ca203959.00624(64)#5# ms [>400 ns]5/2−#
60Ca204060.01181(75)#2# ms [>400 ns]0+
61Ca [21] [n 15] 204161.02041(86)#1# ms1/2−#
This table header & footer:
  1. ()  Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  2. Bold half-life  nearly stable, half-life longer than age of universe.
  3. Modes of decay:
    EC: Electron capture
    n: Neutron emission
    p: Proton emission
  4. Bold symbol as daughter  Daughter product is stable.
  5. () spin value  Indicates spin with weak assignment arguments.
  6. #  Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  7. Heaviest observationally stable nuclide with equal numbers of protons and neutrons
  8. Believed to undergo double electron capture to 40Ar with a half-life no less than 9.9×1021 y
  9. Cosmogenic nuclide
  10. Believed to undergo ββ decay to 46Ti
  11. Primordial radionuclide
  12. Believed to be capable of undergoing triple beta decay with very long partial half-life
  13. Lightest nuclide known to undergo double beta decay
  14. Theorized to also undergo β decay to 48Sc with a partial half-life exceeding 1.1+0.8
    −0.6
    ×1021 years [20]
  15. Discovery of this isotope is unconfirmed

Calcium-48

About 2 g of calcium-48 Calcium-48 carbonate.png
About 2 g of calcium-48

Calcium-48 is a doubly magic nucleus with 28 neutrons; unusually neutron-rich for a light primordial nucleus. It decays via double beta decay with an extremely long half-life of about 5.6×1019 years, though single beta decay is also theoretically possible. This decay can analyzed with the sd nuclear shell model, and it is more energetic (4.27  MeV) than any other double beta decay. [22] It is used as a precursor for neutron-rich [23] and superheavy [24] isotopes.

Calcium-60

Calcium-60 is the heaviest known isotope as of 2020. [1] First observed in 2018 at Riken alongside 59Ca and seven isotopes of other elements, [25] its existence suggests that there are additional even-N isotopes of calcium up to at least 70Ca, while 59Ca is probably the last bound isotope with odd N. [26] Earlier predictions had estimated the heaviest even isotope to be at 60Ca, and 59Ca unbound. [25]

In the neutron-rich region, N = 40 becomes a magic number, so 60Ca was considered early on to be a possibly doubly magic nucleus, as is observed for the 68Ni isotone. [27] [28] However, subsequent spectroscopic measurements of the nearby nuclides 56Ca, 58Ca, and 62Ti instead predict that it should lie on the island of inversion known to exist around 64Cr. [28] [29]

See also

Daughter products other than calcium

References

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Further reading