A book I was looking at referred to an example of a mooted potential law
of nature, the “uranium so-called law (all spheres of uranium are less
than 100 metres in diameter)" and then went on to suggest that “the
prohibited sphere of uranium does become stable at an extremely low
temperature. Thus, if the history of the Earth were such that the
temperature never rose above that low level, then the so-called uranium
law would not be true. Since the evolution of the Earth does include a
higher temperature, uranium spheres with diameters of 100 meters are not
stable.”
Now a sphere of uranium of 100 metres in diameter is vastly bigger than
the critical mass (by an order of a hundred million?) which would seem
to seriously undermine the argument, but, /leaving that aside/, I
wondered why temperature made a difference. I could not immediately see
anything to explain this in a websearch. Nuclear processes are
independent of temperature, but does an extremely low temperature
somehow change the ‘moderating’ properties of the metal as neutrons move
about the material?