On August 13, 1945, there was a nuclear bomb known as the "demon core" that was ready to be used against Japan. A week earlier, two other nuclear bombs, "Little Boy" and "Fat Man," had already been used in Hiroshima and Nagasaki, respectively, and caused significant destruction and loss of life. However, Japan surrendered on August 15 after the attack on Nagasaki, with Emperor Hirohito acknowledging the demands of the Allies. These were the only nuclear bombs ever used in warfare and resulted in the deaths of approximately 200,000 people. If circumstances had been different, there may have been a third nuclear strike.
The surrender of Japan on August 15, 1945, also had significant implications for the scientists at the Los Alamos Laboratory in New Mexico who were working on a third nuclear bomb, which had a 6.2-kilogram plutonium and gallium core known as "Rufus." If the war had continued, this core would have been used in a second "Fat Man" bomb and detonated over another Japanese city just four days later. However, with the end of the conflict, the core was retained at the laboratory for further testing. It was during these tests that the device earned the nickname "demon core." This was the first time that the Japanese public had heard the voice of one of their emperors.
The nuclear experiment, which was planned for launch but ultimately didn't happen, resulted in a core called the "demon core" being left at Los Alamos. The scientists at Los Alamos were aware of the dangers of working with the core, as they were conducting experiments to determine the point at which the plutonium would reach a critical mass and cause a nuclear chain reaction, releasing harmful radiation.
On the night of August 21, 1945, Los Alamos physicist Harry Daghlian was working alone in the lab (contrary to safety protocols) with only a security guard present. He was attempting to conduct a "tickling the dragon's tail" experiment, in which he placed bricks made of tungsten carbide around a plutonium sphere to bring it closer to criticality. As he continued to add bricks, the neutron-monitoring equipment indicated that the plutonium was almost at the point of becoming supercritical. As he reached to remove one of the bricks, he accidentally dropped it onto the top of the sphere, causing it to reach super criticality and emit a blue light and a burst of heat.
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