Isotopes of calcium
Encyclopedia
Calcium
(Ca) has a total of 24 isotopes, from 34Ca to 57Ca. There are five observationally stable isotope
s (40Ca, 42Ca through 44Ca and 46Ca), plus one isotope (48Ca) with such a long half-life
that for all practical purposes it can be considered 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, radioactive 41Ca, which has a half-life
of 102,000 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.
All other isotopes have half-lives of 163 days or less, most under a minute. The least stable is 34Ca with a half-life shorter than 35 nanoseconds.
40Ca comprises about 97% of naturally occurring calcium. 40Ca is also 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
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
(Ca) has a total of 24 isotopes, from 34Ca to 57Ca. There are five observationally stable isotope
Stable isotope
Stable isotopes are chemical isotopes that may or may not be radioactive, but if radioactive, have half-lives too long to be measured.Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory...
s (40Ca, 42Ca through 44Ca and 46Ca), plus one isotope (48Ca) with such a long half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
that for all practical purposes it can be considered 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, radioactive 41Ca, which has a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 102,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
, 41Ca is produced by neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
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.
All other isotopes have half-lives of 163 days or less, most under a minute. The least stable is 34Ca with a half-life shorter than 35 nanoseconds.
40Ca comprises about 97% of naturally occurring calcium. 40Ca is also one of the daughter products of 40K decay, along with 40Ar. While K-Ar dating has been used extensively in the geological
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
sciences, the prevalence of 40Ca in nature has impeded its use in dating. Techniques using mass spectrometry
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
and a double spike isotope dilution have been used for K
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
-Ca age dating.
Standard atomic mass: 40.078(4) u
Table
| nuclide symbol |
Z(p Proton The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number.... ) |
N(n Neutron The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of... ) |
isotopic mass (u) |
half-lifeBold for isotopes with half-lives longer than the age of the universe (nearly stable) | decay mode(s)Abbreviations: EC: Electron capture Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... |
daughter isotope(s)Bold for stable isotopes |
nuclear spin |
representative isotopic composition (mole fraction) |
range of natural variation (mole fraction) |
|---|---|---|---|---|---|---|---|---|---|
| 34Ca | 20 | 14 | 34.01412(32)# | <35 ns | p Proton emission Proton emission is a type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case the process is known as beta-delayed proton emission, or can occur from the ground state of very... |
33K | 0+ | ||
| 35Ca | 20 | 15 | 35.00494(21)# | 25.7(2) ms | β+ Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... (>99.9%) |
35K | 1/2+# | ||
| β+, p (<.1%) | 34Ar | ||||||||
| 36Ca | 20 | 16 | 35.99309(4) | 102(2) ms | β+, p (56.8%) | 35Ar | 0+ | ||
| β+ (43.2%) | 36K | ||||||||
| 37Ca | 20 | 17 | 36.985870(24) | 181.1(10) ms | β+, p (74.5%) | 36Ar | (3/2+) | ||
| β+ (25.5%) | 36K | ||||||||
| 38Ca | 20 | 18 | 37.976318(5) | 440(8) ms | β+ | 38K | 0+ | ||
| 39Ca | 20 | 19 | 38.9707197(20) | 859.6(14) ms | β+ | 39K | 3/2+ | ||
| 40CaHeaviest nuclide with equal numbers of protons and neutrons with no observed decay | 20 | 20 | 39.96259098(22) | Observationally StableBelieved to undergo β+β+ decay to 40Ar with a half-life no less than 5.9×1021 a | 0+ | 0.96941(156) | 0.96933-0.96947 | ||
| 41Ca | 20 | 21 | 40.96227806(26) | 1.02(7)×105 a | EC Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... |
41K | 7/2- | TraceCosmogenic nuclide Cosmogenic nuclide See also Environmental radioactivity#NaturalCosmogenic nuclides are rare isotopes created when a high-energy cosmic ray interacts with the nucleus of an in situ solar system atom, causing cosmic ray spallation... |
|
| 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 | β- | 45Sc | 7/2- | ||
| 46Ca | 20 | 26 | 45.9536926(24) | Observationally StableBelieved to undergo β-β- decay to 46Ti with a half-life not less than 100×1015 a | 0+ | 4(3)×10−5 | 4×10−5-4×10−5 | ||
| 47Ca | 20 | 27 | 46.9545460(24) | 4.536(3) d | β- | 47Sc | 7/2- | ||
| 48Ca Calcium-48 Calcium-48 is a rare isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, the only radioactive decay pathway open to it is the extremely rare process of double beta decay... Primordial Primordial nuclide In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known... radionuclide Radionuclide A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma... |
20 | 28 | 47.952534(4) | 43(38)×1018 a | β-β-Lightest nuclide known to undergo double beta decay Double beta decay Double beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted... |
48Ti | 0+ | 0.00187(21) | 0.00186-0.00188 |
| 49Ca | 20 | 29 | 48.955674(4) | 8.718(6) min | β- | 49Sc | 3/2- | ||
| 50Ca | 20 | 30 | 49.957519(10) | 13.9(6) s | β- | 50Sc | 0+ | ||
| 51Ca | 20 | 31 | 50.9615(1) | 10.0(8) s | β- (>99.9%) | 51Sc | (3/2-)# | ||
| β-, n Neutron emission Neutron emission is a type of radioactive decay of atoms containing excess neutrons, in which a neutron is simply ejected from the nucleus. Two examples of isotopes which emit neutrons are helium-5 and beryllium-13... (<.1%) |
50Sc | ||||||||
| 52Ca | 20 | 32 | 51.96510(75) | 4.6(3) s | β- (98%) | 52Sc | 0+ | ||
| β-, n (2%) | 51Sc | ||||||||
| 53Ca | 20 | 33 | 52.97005(54)# | 90(15) ms | β- (70%) | 53Sc | 3/2-# | ||
| β-, n (30%) | 52Sc | ||||||||
| 54Ca | 20 | 34 | 53.97435(75)# | 50# ms [>300 ns] | β-, n | 53Sc | 0+ | ||
| β- | 54Sc | ||||||||
| 55Ca | 20 | 35 | 54.98055(75)# | 30# ms [>300 ns] | β- | 55Sc | 5/2-# | ||
| 56Ca | 20 | 36 | 55.98557(97)# | 10# ms [>300 ns] | β- | 56Sc | 0+ | ||
| 57Ca | 20 | 37 | 56.99236(107)# | 5# ms | β- | 57Sc | 5/2-# | ||
| β-, n | 56Sc | ||||||||
Further reading
- C.Michael Hogan. 2010. Calcium. ed. A.Jorgenson and C.Cleveland. Encyclopedia of Earth, National Council for Science and the Environment, Washington DC