Atomo de Helio-4

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The helium-4 is a non-radioactive and light isotope of helium. It's far and away the most abundant of the two naturally occurring isotopes of helium, making up approximately 99.99986 percent of helium on Earth. Its nucleus is an alpha particle that contains two protons and two neutrons. Since alpha decay is a common mode of decomposition for many radioactive isotopes, this could explain its abundance. In fact, the alpha decay of heavy elements is the natural source of helium-4 presence on Earth.