In one second nucleus with the diameter of thousands kilometres changes to the small ball with the diameter only 10 or 15 kilometres. Than upper layers will fall down to the nucleus and the implosion will change to explosion and whole material of the star will fly out to the space. We understand this like the explosion of supernova.
For the creation of the neutron star the star has to have some materiality, we can say 10 times more, than our Sun. The stars with lower materiality can˘t change to the neutron star, because the pressure of the upper layers to their nucleus is insufficient and from their nucleus can be only white dwarf. For example from our Sun can never be supernova or neutron star. .