Thank you I've been trying to remember the details of who was involved in that incident for ages. As to Heisenberg its still a toss up as to whether he simply made a mistake or whether he was genuinely trying to keep Hitler from developing the bomb.
I think both, as in he didn't want Hitler to chase the 1 ton HEU bomb, not because he was a good bloke but because it wasn't practical in wartime. I think that if he had figured out the real amount of HEU needed he wouldn't have been so reticent.