Rhodes writes about the significant concern far too much information leaked from Manhattan into "the Los Alamos primer" document that provided confirmation of "how to do it" -people got accused of leaking state secrets until the authorities realised it had been publicly released and approved for security downgrade.<p>He also writes about Kurchatov confirming soviet theory moving to praxis from a document kept on premises in a safe, presumably things Fuchs and others supplied: they had to "do the maths" to validate their engineering but Kurchatov had a check.