Yes and no. Yes, the explosion would keep expanding and any particles in said expansion would keep going out in a sphere until they interacted with something else with mass. However, it would not continue to be a "sphere of death" because as it continued to expand, the particles would be spread over larger and larger distances in a sphere around the original point of explosion. The energy imparted on the particles would dissipate through radiation but the particles themselves would get further and further apart.