Neptunium has a density of 19.5 . What would be the radius of a sphere made of this material that has a critical mass? (Recall that density is mass divided by volume.)
In the fall of 2002, a group of scientists at Los Alamos National Laboratory determined that the critical mass of neptunium-237 is about 60.0 . (The critical mass of a fissionable material is the minimum amount that must be brought together to start a nuclear chain reaction.)