Nuclear, not so much. At least, in some cases. A former colleague had a ukrainian wife who under the soviet regime designed triggers for 'instant sun' devices. Now she's unable to work in that field because only a handful of countries are in a position to do research in that area, and she's trusted by none of them. Or at least, not needed enough that they'd make it work. The countries who do research in thermo nuclear weapons have enough scientists of better repute.