He hoped that the U.S. government would not use nuclear weapons because of their potential for use against civilian populations. Szilárd hoped that the mere threat of such weapons would force Germany and/or Japan to surrender. He drafted the Szilárd petition advocating demonstration of the atomic bomb. However with the European war concluded and the U.S. suffering many casualties in the Pacific Ocean region, the new U.S. President Harry Truman agreed with advisers and chose to use atomic bombs against Hiroshima and Nagasaki over the protestations of Szilárd and other scientists.
[edit]After the war



Szilard and Norman Hilberry at the site of CP-1, at the University of Chicago, some years after the war
During 1947, Szilárd switched topics of study because of his horror of atomic weapons, changing from physics to molecular biology, working extensively with Aaron Novick. In February 1950 Szilárd proposed a cobalt bomb, a new kind of nuclear weapon using cobalt as a tamper, which he said might destroy all life on the planet.

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actually you can pick a salting time and then pick an element that does that.