Ca48

Ca-48 is a calcium isotope with 20 protons and 28 neutrons, giving a mass number of 48. It is notable for its doubly magic character, arising from closed proton and neutron shells (Z = 20 and N = 28). This closed-shell structure leads to relatively high binding energy per nucleon and a near-spherical shape. The ground-state spin is 0+.

Ca-48 is not absolutely stable; it is a long-lived radioactive nuclide. It decays via two-neutrino double beta decay to titanium-48 (Ti-48). The observed half-life for this process is extremely long, on the order of 4 × 10^19 years. Ca-48 is also a target in searches for neutrinoless double beta decay, a hypothetical process with implications for the nature of neutrinos, but 0νββ has not been observed in Ca-48 to date.

Natural abundance and production are relevant for experiments. Ca-48 occurs in very small but measurable amounts in terrestrial calcium, with a natural abundance around 0.1–0.2%. In research contexts, Ca-48 can be enriched to increase its fraction in a sample, aiding the study of double beta decay and related nuclear phenomena. Its relatively simple shell structure and the presence of a closed neutron shell make it a valuable isotope for testing nuclear models and for calibrating detectors in low-background experiments.

In summary, Ca-48 is a long-lived, doubly magic calcium isotope (Z = 20, N = 28) that decays via double beta processes, is present in trace natural abundance, and plays a significant role in experimental studies of nuclear structure and neutrino physics.