This image from 1945 shows Manhattan Project physicist Harold Agnew smiling and holding the plutonium core of one of the world's most devastating weapons. Weighing 14 pounds and responsible for ...

In 1946, a P-239 plutonium core scheduled for detonation-by-nuclear-bomb was harmlessly melted down and reintegrated into the United States’ nuclear stockpile. That was the end of a 14-pound ...