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File:Dusičnan vápenatý.JPG|Calcium nitrate
File:Dusičnan vápenatý.JPG|Calcium nitrate
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===Isotopes===
Calcium has 6 naturally occuring isotopes (<sup>40</sup>Ca, <sup>42</sup>Ca, <sup>43</sup>Ca, <sup>44</sup>Ca, <sup>46</sup>Ca and <sup>48</sup>Ca), of which <sup>48</sup>Ca is very slightly radioactive with a [[half-life]] about 6.4×10<sup>19</sup> years.<ref name=Arnold2016>{{Cite journal
|last1=Arnold |first1=R.
|display-authors=etal
|year=2016
|collaboration=[[NEMO-3 Collaboration]]
|title= Measurement of the double-beta decay half-life and search for the neutrinoless double-beta decay of <sup>48</sup>Ca with the NEMO-3 detector
|journal=[[Physical Review D]]
|volume=93 |issue=11
|pages=112008
|doi= 10.1103/PhysRevD.93.112008
|arxiv=1604.01710|bibcode=2016PhRvD..93k2008A}}</ref> Traces of <sup>41</sup>Ca, <sup>45</sup>Ca and <sup>47</sup>Ca are made by cosmic rays striking atoms, and are called [[cosmogenic nuclide]]s. <sup>41</sup>Ca is made by the neutron activation of <sup>40</sup>Ca in the upper layers of the Earth's crust and has a half-life of 102,000 years. Since it decays to potassium-41, it is a critical indicator of [[solar system]] anomalies.
Calcium-40 is the most abundant isotope (96% of all natural calcium), since it comes from radiogenic <sup>40</sup>K, which has a half-life of 1.25 billion years. However, along with calcium-46, it is theoretically unstable but with a half-life so long it has never been observed to decay.
==Occurrence==
==Occurrence==