Nuclear Waste
In our first example of fissioning, we had:
92U238 50Sn129 + 42Mo106 + 30n1 + energy
The stable isotopes of 50Sn are Sn-112,114, 115,116,117,118,119,120,122,124. The stable isotopes of 42Mo are 92,94,95,96,97,98,100.
In both cases, we have an excess of about 5 neutrons in the decay products which makes them radioactive.