When Uranium-238 (^{238}{92}U) undergoes alpha decay, it forms Thorium-234 (^{234}{90}Th) and an alpha particle (^{4}_{2}He). The alpha particle is essentially a helium nucleus, containing 2 protons and 2 neutrons1. So, the nuclear equation for this decay process is:

^{238}_{92}U ā†’ ^{234}_{90}Th + ^{4}_{2}He.