Re: what changes come in radioactive elements when they become stable?

All radioactive isotopes eventually become stable after emitting 
radiations.  The nuclear quantum state changes as various particles or 
photons are emitted, eventually arriving at a stable (non-radioactive) 
state.  The isotope will remain in this state indefinitely.  While it is 
possible to change the quantum state externally, it is unlikely, and 
barring such an event, the isotope will remain in its stable state forever.