One thing more though is this. Add protons too. And have neutrons (when their "life") runs out, not actually disappear.Instead have them decay to a proton+electron pair. Also have a direct colision between any electron and proton generate a neutron who's "life" is equal to the sum of the "life" numbers of the electron and proton that collided. An electron colliding with a neutron should NOT cancel out the neutron, but instead the 2 should bounce off each other based on the angle of incidence of the collision. Also inherited speed of each particle should be based on an elastic collision (ie they transfer kinetic energy).