Isotopes of calcium

<a href="/facts/Calcium/hf252CC0">Calcium</a> (20Ca) has 26 known isotopes, ranging from 35Ca to 60Ca. There are five <a href="/facts/Stable_isotope/vgcdxgjA">stable isotopes</a> (40Ca, 42Ca, 43Ca, 44Ca and 46Ca), plus one isotope (<a href="/facts/Calcium-48/cqqfNkMY">48Ca</a>) with such a long <a href="/facts/Half-life/kGVH8BAB">half-life</a> 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 <a href="/facts/Cosmogenic_isotope/TlJwc4wV">cosmogenic isotope</a>, 41Ca, with <a href="/facts/Half-life/kGVH8BAB">half-life</a> 99,400 years. Unlike <a href="/facts/Cosmogenic_isotope/TlJwc4wV">cosmogenic isotopes</a> that are produced in the <a href="/facts/Earth%27s_atmosphere/FV97Am25">air</a>, 41Ca is produced by <a href="/facts/Neutron_activation/FXwq3HUs">neutron activation</a> of 40Ca. Most of its production is in the upper metre of the soil column, where the cosmogenic neutron flux is still strong enough. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar system anomalies. The most stable artificial isotopes are 45Ca with half-life 163 days and 47Ca with half-life 4.5 days. All other calcium isotopes have half-lives of minutes or less.
Stable 40Ca comprises about 97% of natural calcium and is mainly created by nucleosynthesis in large stars. Similarly to 40Ar, however, some atoms of 40Ca are radiogenic, created through the radioactive decay of 40K. While <a href="/facts/K%E2%80%93Ar_dating/JQdWfdIB">K–Ar dating</a> has been used extensively in the <a href="/facts/Geology/WGvVRIYF">geological</a> 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 (<a href="/facts/Thermal_ionization_mass_spectrometry/11PUrL2T">TIMS</a>) and Collision-Cell Multi-Collector Inductively-coupled plasma <a href="/facts/Mass_spectrometry/RH5WBHJ2">mass spectrometry</a> (<a href="/facts/Inductively_coupled_plasma_mass_spectrometry/jtr1dzfg">CC-MC-ICP-MS</a>) techniques, however, have been used for successful <a href="/facts/K%E2%80%93Ca_dating/EaG0NEjV">K–Ca age dating</a>, as well as determining K losses from the lower continental crust and for source-tracing calcium contributions from various geologic reservoirs similar to <a href="/facts/Rb-Sr_dating/F1NA2T58">Rb-Sr</a>.
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 <a href="/facts/Osteoporosis/xa1W00Tj">osteoporosis</a> to quantifying <a href="/facts/Types_of_volcanic_eruptions/AwqpzdaG">volcanic eruption</a> timescales. Other applications include: quantifying <a href="/facts/Carbon_sequestration/WDBvr9eU">carbon sequestration</a> efficiency in CO2 injection sites and understanding <a href="/facts/Ocean_acidification/GE7MrSPj">ocean acidification</a>, exploring both ubiquitous and rare magmatic processes, such as formation of <a href="/facts/Granite/G2evuVKo">granites</a> and <a href="/facts/Carbonatite/FQXo0Td3">carbonatites</a>, tracing modern and ancient <a href="/facts/Trophic_web/YaakLo08">trophic webs</a> including in dinosaurs, assessing <a href="/facts/Weaning/Xm2LLpFn">weaning</a> practices in ancient humans, and a plethora of other emerging applications.

Isotopes of calcium open-in-new

Isotopes of calcium