When radioactive decay occurs, the original nucleus splits into daughter nuclei and the resulting nucleus is more stable than the original nucleus. The nucleus can be of a different element than the original.
Unstable nuclei often undergo radioactive decay. In a radioactive decay, the unstable nucleus is broken up into other nuclei. Usually, the nuclei formed during radioactive decay are smaller in mass compared to the original nucleus.
Also, the resulting nucleus is more stable than the original nucleus. The nucleus can be of a different element than the original.