Senseless, the deep dilemma of atoms,
   Unknowable clouds, whims of existence,
   Spinning shards of condensed light,
   Tripping stones for understanding:
They behave but they are not.       --Aliens!    

Dying to self is not fatal.
. . . . . . . . . . . . . . . . . . . . . . . . .
Nuclear fission is the splitting of a wobbly overweight atomic nucleus like uranium into two unequal  pieces.  It can happen spontaneously or as a result of a collision with a neutron.    The fission event, essentially instantaneous,  is accompanied by a large release of energy and a small number of fast-neutrons.  The physical details of nuclear fission are singularly curious and not fully understood.