That's true , but radioactive is actually the base of nuclear bomb's .

I suggested thulium because that's the only radioactive source that goes in metal or other solid electricity elements . It doesn't explodes actually , if you know what i mean :)

Thulium is a little the same as Plutonium .

Think about it :

Nuclear Plutonium Bomb :

Metal plus Plutonium is an explosion !

If you do pauze , then you can do everything !

But now there is no pauze !

So it is :

Thulium plus Metal and this time add Neutron and Plutonium :)

After a few seconds the explosion comes because Thulium is also ( scientists say this ) a diamond sort .

The formula is now this :

The Thulium needs to melt , the hot pressure activates the metal  so it begins to spark because the metal is this time  charged by the heat  !  The spark activates the Plutonium . It begins to burn slowly and the Neutron blinds the area  . After you know it , it explodes :)

Okay then , now you know why i have chosen Thulium :)