Fission: Mass Conversion to Energy

any heavy elements...uranium, thorium, radium
       decay into simpler elements

  Uranium's mass =238.0508 atomic mass units (amu).  
  • decays into thorium (234.0436 amu) plus alpha                particle (4.0026 amu)
    Uranium's mass minus mass of decay products 

                   .0046 amu

Where did this "missing" mass go? 

Einstein said:

lot of energy stored in strong force holding  
       uranium atom together...binding energy 

potential energy stores as mass released  
       as kinetic energy (energy of motion)