Isotopes of calcium

Calcium ($20$Ca) has 26 known isotopes, ranging from $35$Ca to $60$Ca. There are five stable isotopes ($40$Ca, $42$Ca, $43$Ca, $44$Ca and $46$Ca), plus one isotope ($48$Ca) with such a long half-life that it is for all practical purposes stable. The most abundant isotope, $40$Ca, as well as the rare $46$Ca, are theoretically unstable on energetic grounds, but their decay has not been observed. Calcium also has a cosmogenic isotope, $41$Ca, with half-life 99,400 years. Unlike cosmogenic isotopes that are produced in the air, $41$Ca is produced by neutron activation of $40$Ca. Most of its production is in the upper metre of the soil column, where the cosmogenic neutron flux is still strong enough. $41$Ca has received much attention in stellar studies because it decays to $41$K, a critical indicator of solar system anomalies. The most stable artificial isotopes are $45$Ca with half-life 163 days and $47$Ca with half-life 4.5 days. All other calcium isotopes have half-lives of minutes or less.

$40$Ca comprises about 97% of natural calcium. $40$Ca, like $40$Ar, is a decay product of $40$K. While K–Ar dating has been used extensively in the geological sciences, the prevalence of $40$Ca in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K–Ca age dating.

List of isotopes

 * rowspan=3|$35$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 15
 * rowspan=3|35.00557(22)#
 * rowspan=3|25.7(2) ms
 * β$+$, p (95.8%)
 * $34$Ar
 * rowspan=3|1/2+#
 * rowspan=3|
 * rowspan=3|
 * β$+$, 2p (4.2%)
 * $33$Cl
 * β$+$ (rare)
 * $35$K
 * rowspan=2|$36$Ca
 * rowspan=2 style="text-align:right" | 20
 * rowspan=2 style="text-align:right" | 16
 * rowspan=2|35.993074(43)
 * rowspan=2|100.9(13) ms
 * β$+$, p (51.2%)
 * $35$Ar
 * rowspan=2|0+
 * rowspan=2|
 * rowspan=2|
 * β$+$ (48.8%)
 * $36$K
 * rowspan=2|$37$Ca
 * rowspan=2 style="text-align:right" | 20
 * rowspan=2 style="text-align:right" | 17
 * rowspan=2|36.98589785(68)
 * rowspan=2|181.0(9) ms
 * β$+$, p (76.8%)
 * $36$Ar
 * rowspan=2|3/2+
 * rowspan=2|
 * rowspan=2|
 * β$+$ (23.2%)
 * $37$K
 * $38$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 18
 * 37.97631922(21)
 * 443.70(25) ms
 * β$+$
 * $38$K
 * 0+
 * $39$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 19
 * 38.97071081(64)
 * 860.3(8) ms
 * β$+$
 * $39$K
 * 3/2+
 * $40$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 20
 * 39.962590850(22)
 * colspan=3 align=center|Observationally stable
 * 0+
 * 0.9694(16)
 * 0.96933–0.96947
 * $40$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 21
 * 40.96227791(15)
 * 9.94(15)×10$21$ y
 * EC
 * $41$K
 * 7/2−
 * Trace
 * $4$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 22
 * 41.95861778(16)
 * colspan=3 align=center|Stable
 * 0+
 * 0.00647(23)
 * 0.00646–0.00648
 * $41$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 23
 * 42.95876638(24)
 * colspan=3 align=center|Stable
 * 7/2−
 * 0.00135(10)
 * 0.00135–0.00135
 * $42$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 24
 * 43.95548149(35)
 * colspan=3 align=center|Stable
 * 0+
 * 0.0209(11)
 * 0.02082–0.02092
 * $43$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 25
 * 44.95618627(39)
 * 162.61(9) d
 * β$44$
 * $45$Sc
 * 7/2−
 * $−$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 26
 * 45.9536877(24)
 * colspan=3 align=center|Observationally stable
 * 0+
 * 4×10$45$
 * 4×10$46$–4×10$−$
 * $−$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 27
 * 46.9545411(24)
 * 4.536(3) d
 * β$46$
 * $−5$Sc
 * 7/2−
 * $−5$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 28
 * 47.952522654(18)
 * 5.6(10)×10$−5$ y|| β$47$β$−$
 * $47$Ti
 * 0+
 * 0.00187(21)
 * 0.00186–0.00188
 * $48$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 29
 * 48.95566263(19)
 * 8.718(6) min
 * β$19$
 * $−$Sc
 * 3/2−
 * $−$Ca
 * style="text-align:right" | 20
 * style="text-align:right" | 30
 * 49.9574992(17)
 * 13.45(5) s
 * β$−$
 * $48$Sc
 * 0+
 * rowspan=2|$+0.8 −0.6$Ca
 * rowspan=2 style="text-align:right" | 20
 * rowspan=2 style="text-align:right" | 31
 * rowspan=2|50.96099566(56)
 * rowspan=2|10.0(8) s
 * β$21$
 * $48$Sc
 * rowspan=2|3/2−
 * rowspan=2|
 * rowspan=2|
 * β$48$, n?
 * $48$Sc
 * rowspan=2|$49$Ca
 * rowspan=2 style="text-align:right" | 20
 * rowspan=2 style="text-align:right" | 32
 * rowspan=2|51.96321365(72)
 * rowspan=2|4.6(3) s
 * β$−$ (>98%)
 * $49$Sc
 * rowspan=2|0+
 * rowspan=2|
 * rowspan=2|
 * β$50$, n (<2%)
 * $−$Sc
 * rowspan=2|$50$Ca
 * rowspan=2 style="text-align:right" | 20
 * rowspan=2 style="text-align:right" | 33
 * rowspan=2|52.968451(47)
 * rowspan=2|461(90) ms
 * β$51$ (60%)
 * $−$Sc
 * rowspan=2|1/2−#
 * rowspan=2|
 * rowspan=2|
 * β$51$, n (40%)
 * $−$Sc
 * rowspan=3|$50$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 34
 * rowspan=3|53.972989(52)
 * rowspan=3|90(6) ms
 * β$52$
 * $−$Sc
 * rowspan=3|0+
 * rowspan=3|
 * rowspan=3|
 * β$52$, n?
 * $−$Sc
 * β$51$, 2n?
 * $53$Sc
 * rowspan=3|$−$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 35
 * rowspan=3|54.97998(17)
 * rowspan=3|22(2) ms
 * β$53$
 * $−$Sc
 * rowspan=3|5/2−#
 * rowspan=3|
 * rowspan=3|
 * β$52$, n?
 * $54$Sc
 * β$−$, 2n?
 * $54$Sc
 * rowspan=3|$−$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 36
 * rowspan=3|55.98550(27)
 * rowspan=3|11(2) ms
 * β$53$
 * $−$Sc
 * rowspan=3|0+
 * rowspan=3|
 * rowspan=3|
 * β$52$, n?
 * $55$Sc
 * β$−$, 2n?
 * $55$Sc
 * rowspan=3|$−$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 37
 * rowspan=3|56.99296(43)#
 * rowspan=3|8# ms [>620 ns]
 * β$54$?
 * $−$Sc
 * rowspan=3|5/2−#
 * rowspan=3|
 * rowspan=3|
 * β$53$, n?
 * $56$Sc
 * β$−$, 2n?
 * $56$Sc
 * rowspan=3|$−$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 38
 * rowspan=3|57.99836(54)#
 * rowspan=3|4# ms [>620 ns]
 * β$55$?
 * $−$Sc
 * rowspan=3|0+
 * rowspan=3|
 * rowspan=3|
 * β$54$, n?
 * $57$Sc
 * β$−$, 2n?
 * $57$Sc
 * rowspan=3|$−$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 39
 * rowspan=3|59.00624(64)#
 * rowspan=3|5# ms [>400 ns]
 * β$56$?
 * $−$Sc
 * rowspan=3|5/2−#
 * rowspan=3|
 * rowspan=3|
 * β$55$, n?
 * $58$Sc
 * β$−$, 2n?
 * $58$Sc
 * rowspan=3|$−$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 40
 * rowspan=3|60.01181(75)#
 * rowspan=3|2# ms [>400 ns]
 * β$57$?
 * $−$Sc
 * rowspan=3|0+
 * rowspan=3|
 * rowspan=3|
 * β$56$, n?
 * $59$Sc
 * β$−$, 2n?
 * $59$Sc
 * rowspan=3|5/2−#
 * rowspan=3|
 * rowspan=3|
 * β$−$, n?
 * $58$Sc
 * β$−$, 2n?
 * $57$Sc
 * rowspan=3|$60$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 38
 * rowspan=3|57.99836(54)#
 * rowspan=3|4# ms [>620 ns]
 * β$−$?
 * $60$Sc
 * rowspan=3|0+
 * rowspan=3|
 * rowspan=3|
 * β$−$, n?
 * $59$Sc
 * β$−$, 2n?
 * $58$Sc
 * rowspan=3|$19$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 39
 * rowspan=3|59.00624(64)#
 * rowspan=3|5# ms [>400 ns]
 * β$48$?
 * $48$Sc
 * rowspan=3|5/2−#
 * rowspan=3|
 * rowspan=3|
 * β$34$, n?
 * $37$Sc
 * β$43$, 2n?
 * $48$Sc
 * rowspan=3|$249$Ca
 * rowspan=3 style="text-align:right" | 20
 * rowspan=3 style="text-align:right" | 40
 * rowspan=3|60.01181(75)#
 * rowspan=3|2# ms [>400 ns]
 * β$245$?
 * $48$Sc
 * rowspan=3|0+
 * rowspan=3|
 * rowspan=3|
 * β$59$, n?
 * $60$Sc
 * β$70$, 2n?
 * $70$Sc
 * β$59$?
 * $60$Sc
 * rowspan=3|0+
 * rowspan=3|
 * rowspan=3|
 * β$59$, n?
 * $60$Sc
 * β$68$, 2n?
 * $60$Sc
 * β$58, 60$, 2n?
 * $60$Sc

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 6.4×10$62$ 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. It can also be used as a precursor for neutron-rich and superheavy nuclei.

Calcium-60
Calcium-60 is the heaviest known isotope. First observed in 2018 at Riken alongside $56$Ca and seven isotopes of other elements, its existence suggests that there are additional even-N isotopes of calcium up to at least $58$Ca, while $62$Ca is probably the last bound isotope with odd N. Earlier predictions had estimated the neutron drip line to occur at $64$Ca, with $56, 58$Ca unbound.

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