The atomic bomb was invented by who in the 1950s?

The atomic bomb was invented in 1933 (by Leo Szilard) and finally built in 1945 (by the US Manhattan Project, which involved hundreds of thousands of people). It was duplicated in 1949 (by the USSR, assisted by information from spies in the US project).

It was already in "mass production" by both the US and USSR by the early 1950s , thus not invented by anyone in the 1950s.