You've done some good thinking about your paper! I do wonder, though, if you're not getting somewhat off-topic by getting into the later bomb developments and their effects on the world. If that's all right, based on your assignment instructions, then, no problem. But if your paper is supposed to stay focused "on the Atomic bomb - and how the jewish refugees helped the United States create the first nuclear weapon" you might want to concentrate more on the events which led up to the bomb's creation. You could probably find a lot of information on the development of the science (without getting too technical), and the political atmosphere that created the need for the scientists who became refugees to leave Germany. I think perhaps the reason you are having trouble putting your present outline into one cohesive thesis statement is because it's really two different topics.
Give this some thought, and if you still want to go in that direction, I'll see what I can do to help you come up with your thesis. I do think you can get 10 pages out of the original thesis if you concentrate on the events preceding WWII.
Let me know what you think!