Neutron migration was a process that could occur within stellar cores.
Doctor Timicin's attempt to revitalize Beta Praxillus in 2367 failed due to neutron migration within the inner core, as evidenced by two sudden increases in hydrogen-alpha emissions. The neutron migration caused convection boundary uncoupling and unexpectedly high gas turbulence, eventually leading to the star going nova. Though Lieutenant Commander Data noted there was no method of controlling neutron migration, Timicin was optimistic that it could be accomplished with a new computer model of the star's energy dynamics. (TNG: "Half a Life")