1) Transmutation.
A transmutation occurs when an element is changed into another by radioactive decay.
2) Alpha decay.
In this type of radiation, the nucleus expels an alpha particle. An alpha particle has two neutrons and two protons.
The transmutation occurs because the number of protons changes.
3) Beta decay.
In this type of radiation, a neutron turns into a proton and a beta particle. That last one is expelled from the nucleus.
Since a neutron turns into a proton, the atomic number changes.
4) Positron emission.
In this type of radiation, a proton turns into a neutron and a positron. That last one is expelled from the nucleus.
Since a neutron turns into a proton, the atomic number changes.
In the three cases, transmutation occurs because the number of protons (atomic number) changes.