<P> In nuclear physics , beta decay ( β - decay ) is a type of radioactive decay in which a beta ray ( fast energetic electron or positron ) and a neutrino are emitted from an atomic nucleus . For example , beta decay of a neutron transforms it into a proton by the emission of an electron , or conversely a proton is converted into a neutron by the emission of a positron ( positron emission ) , thus changing the nuclide type . Neither the beta particle nor its associated neutrino exist within the nucleus prior to beta decay , but are created in the decay process . By this process , unstable atoms obtain a more stable ratio of protons to neutrons . The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy . The binding energies of all existing nuclides form what is called the nuclear band or valley of stability . For either electron or positron emission to be energetically possible , the energy release ( see below ) or Q value must be positive . </P>
this type of nuclear decay effectively turns a proton into a neutron
beta decay