Isotopes of calcium
has 26 known isotopes, ranging from Ca to Ca. There are five stable isotopes, plus one isotope with such a long half-life that it is for all practical purposes stable. The most abundant isotope, Ca, as well as the rare Ca, are theoretically unstable on energetic grounds, but their decay has not been observed. Calcium also has a cosmogenic isotope, Ca, with half-life 99,400 years. Unlike cosmogenic isotopes produced in the air, Ca is produced by neutron activation of solid Ca 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 Ca with half-life 162.61 days and Ca with half-life 4.536 days. All other calcium isotopes have half-lives of minutes or less.
Ca comprises about 97% of natural calcium and is mainly created by nucleosynthesis in stars. Like Ar, however, some Ca is radiogenic, created by radioactive decay of K. While K–Ar dating has been used extensively in the geological sciences, the prevalence of Ca 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 and Collision-Cell Multi-Collector Inductively-coupled plasma mass spectrometry techniques, however, have been used for successful K–Ca dating similar in method to Rb-Sr dating, as well as determining K losses from the lower continental crust and for source-tracing calcium contributions from various geologic reservoirs.
Stable isotope variations of calcium are also widely used across the natural sciences for a number of applications, ranging from early determination of osteoporosis to quantifying volcanic eruption timescales. Other applications include: quantifying carbon sequestration efficiency in CO2 injection sites and understanding ocean acidification, exploring both ubiquitous and rare magmatic processes, such as formation of granites and carbonatites, tracing modern and ancient trophic webs including in dinosaurs, assessing weaning practices in ancient humans, and a plethora of other emerging applications.
List of isotopes
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 5.6×10 years, though single beta decay is also theoretically possible. This decay can analyzed with the sd nuclear shell model, and it is more energetic than any other double beta decay. It is used as a precursor for neutron-rich and superheavy isotopes.Calcium-60
Calcium-60 is the heaviest known isotope as of 2020. First observed in 2018 at Riken alongside Ca and seven isotopes of other elements, its existence suggests that there are additional even-N isotopes of calcium up to at least Ca, while Ca is probably the last bound isotope with odd N. Earlier predictions had estimated the heaviest even isotope to be at Ca, and Ca unbound.In the neutron-rich region, N = 40 becomes a magic number, so 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.