where the nucleus loses two neutrons and two protons in the form of an alpha particle. Thus the atomic number and the number of neutrons each decrease by 2 (Z: 92 -> 90, N: 146 -> 144), so that the mass number decreases by 4 (A = 238 -> 234); the result is an atom of thorium-234 and an alpha particle :
:

On the other hand, carbon-14 decays by beta decay, whereby one neutron is transmuted