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The most stable artificial isotopes are 45 Ca with half-life 163 days and 47 Ca with half-life 4.5 days. All other calcium isotopes have half-lives of minutes or less. [4] Stable 40 Ca comprises about 97% of natural calcium and is mainly created by
Radioactive isotope table "lists ALL radioactive nuclei with a half-life greater than 1000 years", incorporated in the list above. The NUBASE2020 evaluation of nuclear physics properties F.G. Kondev et al. 2021 Chinese Phys. C 45 030001. The PDF of this article lists the half-lives of all known radioactives nuclides.
Natural calcium is a mixture of five stable isotopes (40 Ca, 42 Ca, 43 Ca, 44 Ca, and 46 Ca) and one isotope with a half-life so long that it is for all practical purposes stable (48 Ca, with a half-life of about 4.3 × 10 19 years). Calcium is the first (lightest) element to have six naturally occurring isotopes. [14]
This is the longest half-life directly measured for any unstable isotope; [4] only the half-life of tellurium-128 is longer. [ citation needed ] Of the chemical elements, only 1 element ( tin ) has 10 such stable isotopes, 5 have 7 stable isotopes, 7 have 6 stable isotopes, 11 have 5 stable isotopes, 9 have 4 stable isotopes, 5 have 3 stable ...
At least 3,300 nuclides have been experimentally characterized [1] (see List of radioactive nuclides by half-life for the nuclides with decay half-lives less than one hour). A nuclide is defined conventionally as an experimentally examined bound collection of protons and neutrons that either is stable or has an observed decay mode .
Naturally occurring scandium (21 Sc) is composed of one stable isotope, 45 Sc. Twenty-seven radioisotopes have been characterized, with the most stable being 46 Sc with a half-life of 83.8 days, 47 Sc with a half-life of 3.35 days, and 48 Sc with a half-life of 43.7 hours and 44 Sc with a half-life of 3.97 hours.
Scandium-44 (44 Sc) is a radioactive isotope of scandium that decays by positron emission to stable 44 Ca with a half-life of 4.042 hours.. 44 Sc can be obtained as a daughter radionuclide of long-lived 44 Ti (t 1/2 60.4 a) from 44 Ti / 44 Sc generator or can be produced by nuclear reaction 44 Ca ( p, n) 44 Sc in small cyclotrons.
In this situation it is generally uncommon to talk about half-life in the first place, but sometimes people will describe the decay in terms of its "first half-life", "second half-life", etc., where the first half-life is defined as the time required for decay from the initial value to 50%, the second half-life is from 50% to 25%, and so on.