Hello, I am working on theoretical research for what is turning into somewhat complicated nuclear physics. I am not a nuclear physicists, so I would appreciate help with finding the information I need. First and foremost piece of information I need to solve my system of equations is the critical density of Uranium 235.
I cannot find this information directly in books or the internet. However, online articles suggested statistics from bare spheres. It was suggested by Wikipedia that the critical conditions for an unspecified grade of Uranium 235 at an unspecific temperature (but I am assuming room temperature) and an unspecific pressure (but I am assuming 1 atmosphere) was 52000 grams in a sphere 17 centimeters large. But to me, this information seems inaccurate.
I calculated the natural density of pure Uranium 235 to be approximately 18.075g/cm^3. The density of elemental Uranium with mixes of different isotopes is 18.95-19.01 g/cm^3 with Uranium 238 being the most common isotope. So, it makes sense that the natural density of pure U235 is around 18g/cm^3.
With that said, it seems illogical that the critical density solid Uranium is 52000g/(4/3*pi*(17cm)^3)=2.526g/cm^3. The bare spheres were not in environments of exceedingly high temperatures in a vacuum, so I cannot figure out how the density of solid Uranium in spherical shape could be that dramatically lower in only that specific experiment.
Does anyone know of credible resources where I can find the information I am looking for and explain this discrepancy?