How are excess neutrons formed to create isotopes? I know that one method is through the use of a cyclotron which accelerates a proton and causing a collision with a "target". This would increase the atomic number, Z and create an isotope with 1 less neutron. But how does this method produce an isotope with an excess of neutrons ? For instance Technetium-99 is formed from Mo-99, but how is Mo-99 formed?