A tale of lost WW2 uranium cubes shows why Germany’s nuclear program failed

All the daughter products are in secular equilibrium and so are also "rate limited".

When you split uranium nuclei in nuclear chain reactors, many of the resulting "half-uranium" fission products are neutron rich, and have very short half-lives. They quickly decay towards stability and along the way shoot out lots of radiation very quickly. This is high-level nuclear material and is dangerous.

Heisenberg, the distinguished senior scientist who was basically running the whole affair to the extent that was true, was a great theoretician, "the first quantum mechanical mind" per Jeremy Bernstein, author of Hitler's Uranium Club: The Secret Recordings at Farm Hall of 10 German scientists captured by Project Alsos, but was awful with numbers, let alone experiments (Fermi was the only top mind of the period great at both). It's in fact a very good thing his reactor didn't go critical, because for some reason he though the reaction would be self-regulating....

Whereas on the other side the concept of an atom bomb of modest size through fast neutron fissioning was realized very early by Otto Frisch and Rudolf Peierls, authors of the critical document on the topic published in March 1940 (https://en.wikipedia.org/wiki/Frisch%E2%80%93Peierls_memoran...). While they underestimated the amount of pure U235 needed, they were in the right ballpark, something that took the Germans at Farm Hall several rounds after Hiroshima to start approaching.

Another critical scientific error was not trying hard enough with graphite, which required purification way beyond the industrial state of the art to get rid of enough neutron poisons. Resulting on a total dependence on heavy water, which the Allies were able to thoroughly sabotage.

Organizationally, I think it was Rhodes who observed that it was not probable that wartime Germany would develop a bomb, or peacetime America. And if you're interested in that, read up on Lieutenant General Leslie Groves, without the extraordinarily good leadership he provided the Manhattan Project wouldn't have finished by the time we'd conquered Japan with liberal use of chemical weapons.

It seems to be a universal problem.