Examlex
Describe Eratosthenes' most important astronomical achievement.
Stable Isotopes
Variants of elements that have the same number of protons but different numbers of neutrons, and do not undergo radioactive decay.
Radioactive Isotopes
Radioactive isotopes, or radioisotopes, are variants of chemical elements that emit radiation due to an unstable nucleus and undergo radioactive decay.
Atomic Number
The number of protons in the nucleus of an atom, unique to each element.
Naturally Occurring
Refers to substances, materials, or phenomena that exist in nature without human intervention.
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