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Visual science, half (7/40) Halves can be very useful indeed, let's look at an example. Elements can be made of different isotopes, isotopes are the atoms that have the same number of electrons and protons but a different number of neutrons. Sometimes isotopes can be stable and happy these elements are the one's we see in nature, sometimes isotopes are unstable, they are called radioactive isotopes. The half-life of an isotope is the time on average that is taken for half of the atoms to decay. Very precise dating of objects can be calculated given the known half-life for that element.