Answer the following question given this paragraph: 

Alpha decay occurs when an unstable nucleus emits an alpha particle and energy. The diagram in Figure below represents alpha decay. An alpha particle contains two protons and two neutrons, giving it a charge of +2. A helium nucleus has two protons and two neutrons, so an alpha particle is represented in nuclear equations by the symbol . The superscript 4 is the mass number (2 protons + 2 neutrons). The subscript 2 is the charge of the particle as well as the number of protons.


Q: What occurs when an unstable nucleus emits an alpha particle and energy?


A:
alpha decay