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Calcium (Ca) has four stable isotopes (40Ca and 42Ca through 44Ca), plus two more isotopes (46Ca and 48Ca) that have such long half-lives that for all practical purposes they can be considered stable. It also has a cosmogenic isotope, radioactive 41Ca, which has a half-life of 103,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre or so of the soil column where the cosmogenic neutron flux is still sufficiently strong. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar-system anomalies.
97% of naturally occurring calcium is in the form of 40Ca. 40Ca is one of the daughter products of 40K decay, along with 40Ar. While K-Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca 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.
Standard atomic mass: 40.078(4) u
Table
nuclide
symbol |
Z(p) |
N(n) |
isotopic mass (u)
|
half-life |
nuclear
spin |
representative
isotopic
composition
(mole fraction) |
range of natural
variation
(mole fraction) |
| excitation energy |
| 34Ca |
20 |
14 |
34.01412(32)# |
<35 ns |
0+ |
|
|
| 35Ca |
20 |
15 |
35.00494(21)# |
25.7(2) ms |
1/2+# |
|
|
| 36Ca |
20 |
16 |
35.99309(4) |
102(2) ms |
0+ |
|
|
| 37Ca |
20 |
17 |
36.985870(24) |
181.1(10) ms |
(3/2+) |
|
|
| 38Ca |
20 |
18 |
37.976318(5) |
440(8) ms |
0+ |
|
|
| 39Ca |
20 |
19 |
38.9707197(20) |
859.6(14) ms |
3/2+ |
|
|
| 40Ca |
20 |
20 |
39.96259098(22) |
STABLE [>5.9E+21 a] |
0+ |
0.96941(156) |
0.96933-0.96947 |
| 41Ca |
20 |
21 |
40.96227806(26) |
1.02(7)E+5 a |
7/2- |
|
|
| 42Ca |
20 |
22 |
41.95861801(27) |
STABLE |
0+ |
0.00647(23) |
0.00646-0.00648 |
| 43Ca |
20 |
23 |
42.9587666(3) |
STABLE |
7/2- |
0.00135(10) |
0.00135-0.00135 |
| 44Ca |
20 |
24 |
43.9554818(4) |
STABLE |
0+ |
0.02086(110) |
0.02082-0.02092 |
| 45Ca |
20 |
25 |
44.9561866(4) |
162.67(25) d |
7/2- |
|
|
| 46Ca |
20 |
26 |
45.9536926(24) |
STABLE [>100E+15 a] |
0+ |
0.00004(3) |
0.00004-0.00004 |
| 47Ca |
20 |
27 |
46.9545460(24) |
4.536(3) d |
7/2- |
|
|
| 48Ca |
20 |
28 |
47.952534(4) |
43(38)E+18 a |
0+ |
0.00187(21) |
0.00186-0.00188 |
| 49Ca |
20 |
29 |
48.955674(4) |
8.718(6) min |
3/2- |
|
|
| 50Ca |
20 |
30 |
49.957519(10) |
13.9(6) s |
0+ |
|
|
| 51Ca |
20 |
31 |
50.9615(1) |
10.0(8) s |
(3/2-)# |
|
|
| 52Ca |
20 |
32 |
51.96510(75) |
4.6(3) s |
0+ |
|
|
| 53Ca |
20 |
33 |
52.97005(54)# |
90(15) ms |
3/2-# |
|
|
| 54Ca |
20 |
34 |
53.97435(75)# |
50# ms [>300 ns] |
0+ |
|
|
| 55Ca |
20 |
35 |
54.98055(75)# |
30# ms [>300 ns] |
5/2-# |
|
|
| 56Ca |
20 |
36 |
55.98557(97)# |
10# ms [>300 ns] |
0+ |
|
|
| 57Ca |
20 |
37 |
56.99236(107)# |
5# ms |
5/2-# |
|
|
Notes
- Evaluated isotopic composition is for most but not all commercial samples.
- The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
- Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
- Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
- Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.
References
- Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
- Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
- Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
- Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
- National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
- David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.
External links
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