Conversation so far:
What is the Manhattan Project?
atomic bomb project.
When did this project begin?
In February 1944.
Did he work on this with other people?
Rotblat joined the Los Alamos Laboratory as part of Chadwick's British Mission to the Manhattan Project.
What kind of things did they do on this project?
investigating whether high-energy gamma rays produced by nuclear fission would interfere with the nuclear chain reaction process.
Are there any other interesting aspects about this article?
By the end of 1944 it was also apparent that Germany had abandoned the development of its own bomb and Rotblat asked to leave the project.

Question: What did he do after he left?
Self-contained rewrite: What did Joseph Rotblat do after he left?