They went to the US government shortly after the first nuke was set off and asked them what was going on because they had very clear evidence that something had happened, and if they could tell because it showed up on their film (that they were selling to the C_A for their spy planes) and other film manufacturers would also be able to tell as the fallout spread.!
The film was then later used to identify the spread of fallout, how much, where and when. Literal patterns (wind) shown for detonation after detonation (for decades not just 1945) via Kodak film.!!! Two impressive stories in one...
As for whether any of their scientists worked ON the Manhattan Project before this event I do not know, I am not an expert in this field, but know of the above Kodak incidents (it was on QI (Quite Interesting) many years ago) and it's not something I would forget unless I had dementia.