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How does calcium-41 form naturally on Earth?

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A labeled diagram of the periodic table entry for calcium, showing its atomic number 20, symbol Ca, atomic weight 40.078, electron configuration, and classification as an alkaline-earth metal. Icons indicate calcium is a solid with a face-centered cubic crystal structure and strongly basic oxides at room temperature. — calcium The chemical element calcium is the most abundant metallic element in the human body.

On Earth, the radioactive isotope calcium-41 occurs in trace quantities as a result of the natural bombardment of calcium-40 by neutrons found in cosmic rays.1