Alpha Decay

Uranium-238 decomposes by the loss of an α particle:

$^{238}_{92}\text{U}\rightarrow ^{234}_{90}\text{Th}+^{4}_{2}\text{He}$

From this decay, it should be noted that:

1. The sum of the mass numbers on the left and right of the equation is the same.
2. The sum of the atomic number on the left and right is the same.

Thus, the reaction does not create or destroys neither protons nor neutrons. Another example of α-decay is as follows:

$^{210}_{84}\text{Po}\rightarrow ^{206}_{82}\text{Pb}+^{4}_{2}\text{He}$

Source: Andrew R. Barron, http://www.vias.org/genchem/nuclear_chem_31328_04_02.html
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