When an atom undergoes radioactive decay, what is actually split or affected the most?

When an atom undergoes radioactive decay which is where it spontaneously emit matter and energy from its nucleus, the part of the atom that is affected is the nucleus as it is known to breakdown due to the instability it possesses because of the neutron to proton ratio. This matter and energy is released as the atom hopes to attain stability - transmutes from one element to the next, and will continue emission until it does attain stability.