Germany made many of the key discoveries in physics that made nuclear weapons possible, leading to fear in the U.S. that the Germans would build an atomic bomb.

• Henri Becquerel discovered radioactivity as a property of uranium in 1896, Marie Curie discovered other radioactive elements

  Lise Meitner

• Otto Hahn , Lise Meitner, and O.R. Frisch worked in the 1930s to understand the results of bombarding uranium with neutrons--realized that the uranium fissioned.
• by 1939 it was obvious and widely know that a chain reaction might be possible because each atom that fissioned released neutrons that could hit other atoms and cause them to fission
• Refugee scientists in the U.S. feared a German bomb. Leo Szilard composed two letters for Einstein to sign warning President Roosevelt of the dangers of a German atomic bomb, one in August 1939 and the other in April 1940.  Fear was widespread enough that U.S. and British journals volunarily censored related scientific papers.
• Germans were indeed working on a bomb, but got stuck in a dead end.  Supporters of Werner Heisenberg say he did this on purpose.

• First organized under National Defense Research Committee (approval for project Oct. 1941) then turned over to the army in June 1942.  The army put General Leslie Groves in charge.

The first thing to do was prove a chain reaction was possible.  That effort was led by Enrico Fermi , first at Columbia then at the University of Chicago.  The first successful chain reaction took place Dec. 2, 1942 in a small reactor built in a squash court at the Univ. of Chicago.
• Providing fuel for the bomb was a tremendous technical challenge--must separate uranium-235, which is less than 1% of the uranium mined and differs in weight by only .13%.  Two methods of separation: a cyclotron and gaseous diffusion of uranium hexaflouride (the only gaseous compound, but one that is both poisonous and corrosive) were set up at Oak Ridge , Tenn., using  TVA power.  The other alternative is to make plutonium by chain reactions--reactors to do this were built in Hanford, Washington.

 K-25 gaseous diffusion plant at Oak Ridge

• Robert Oppenheimer led the effort to design the bomb and said he needed to bring scientists together at a single laboratory.  Los Alamos opened in March 1943.  Developed two bomb designs, one using uranium and one using plutonium.  The plutonium design was tested in the Trinity test near Alamogordo NM on July 16, 1945.  Exploded with the force of 20,000 tons of TNT.

 Bombs used in Japan

The decision to drop the bomb
( good links on the decision )

• Germany was clearly defeated and the Japanese were retreating--was it necessary to use the bomb?
• Could there have been a demonstration and warning instead?  Would it have been used in Europe or was racism a factor?
• After spending $2 billion would the goverment have been accused of wasting money if it wasn't used?
• when Roosevelt died on April 12, 1945, the bomb project was so secret that Vice President Harry Truman didn't even know about it.  The bomb was used because having built it everyone assumed that having built it they would use it.
• three B-29 bombers set out for Hiroshima , Japan on Aug. 6, 1945.  The Japanese sounded the all-clear when they saw only 3 planes.  The Enola Gay dropped the 5 ton bomb and it exploded with the force of 15,000 tons of TNT.  130,000 people died within 3 months, 68% of the buildings of the city were destroyed.
• A plutonium bomb was dropped on Nagasaki on Aug. 9, 1945.  Exploded with the force of 22,000 tons of TNT.

 bomb damage in Hiroshima

 The scientists tried to prevent an arms race from developing.  Why did they feel so strongly, and did they have any hope of success?