How does alpha decay work?

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Answer 1 · 2016-07-29T23:55:48

Alpha decay is a process that some unstable nuclei use to become more stable.

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During alpha decay, a nucleus emits a particle that consists of two protons and two neutrons — an alpha (α) particle, which is also a helium nucleus.

Since the atom loses two protons, it changes to a different element.

Its atomic number ( $Z$ $Z$ ) decreases by two units.

The atom loses two nucleons (protons and neutrons), so its mass number ( $A$ $A$ ) decreases by four units.

For example, an atom of uranium-238 (with 92 protons) becomes an atom of thorium-234 (with 90 protons) when it undergoes alpha decay.

$_{92}^{238} U \to l_{90}^{234} Th + l_{2}^{4} He$ $""_92^238"U" →color(white)(l) _90^234"Th" +color(white)(l) _2^4"He"$