Szilard's eureka moment

Leo Szilard, a Hungarian-born Jew, fled Germany for the UK two months after Adolf Hitler became chancellor.

At the time, James Chadwick just discovered the neutron. Not long after, Cambridge physicists split the atom by bombarding a lithium nucleus with protons. In this, they confirmed Albert Einstein's idea that mass and energy are different forms of the same thing.

In 1933, Szilard thought that if you could find an atom that was split by neutrons, and in the process, release two or more neutrons, then the mass would emit a huge amount of energy.