Question 1.11 Neptunium. In the fall of 2002, scientists at Los Alamos National Laboratory determined that the critical mass of Neptunium-237 is about 60 kg. The critical mass of a fissionable material is the mini-mum amount that must be brought together to start a nuclear chain reaction. Neptunium-237 has a density of 19.5 g/cm3. What would be the radius of a sphere in this material that has a critical mass?
This video is a bit long because it is meant to teach students physics not assist with doing homework. Please jump to the end of the video if you just want the answer.
Source University Physics with Modern Physics by Hugh D. Young and Roger A. Freedman, 14th Edition.