Discovery

• James Chadwick discovered the neutron in 1932. Leo Szilard was the first to theorize about the possibility of a nuclear bomb. He considered if the multiplying effect of a fission reaction could be harnessed, then a bomb could be manufactured. Szilard received a patent for his idea in 1934. In January 1939, Otto Frisch observed the first fission reaction. Neils Bohr determined U-235 and U-238 react differently to neutrons, which accounted for only the observation of slow reactions. Fermi and Anderson calculated that there are two neutrons produced for every neutron used in a reaction.
  
  

Manhattan Project

• World War II exploded at the same time the discoveries above were taking place. Scientists of the Manhattan Project were organized in January 1942, but languished without a direct purpose until September that year when Col. Leslie Groves was appointed to the project. He quickly brought things under control and purchased the materials to get started, including 52,000 acres for Oak Ridge, the site of a massive uranium enrichment laboratory in Tennessee that housed major experiments pertinent to the project. In October, Groves recruited Dr. J. Robert Oppenheimer to head the new laboratory. In 1944, work was underway in three important areas: weapon development, fissile material development and combat delivery preparations. April 1945, Oppenheimer finally reported an optimal implosion performance.
  
  

Significant Events

• After the death of President Roosevelt, President Truman learned of the existence of the atomic bomb on April 13, 1945. Three months later, on July 16, the first 100-ton test was successfully conducted and the atomic bomb was born. The first two bombs were Little Boy and Fat Man. Little Boy was detonated over Hiroshima, Japan on August 6, 1945, at 8:15 a.m., with 15 kilotons of force and Fat Man was dropped on August 9 at 11:02 a.m. with 22 kilotons of force on Nagasaki, Japan.
  
  

Cold War

• The end of World War II ushered in the beginning of the Cold War between the United States and the Soviet Union. Each country made significant leaps in technology and stockpiled a high number of weapons. The proliferation of nuclear weapons was quick and treaties were put in place to stop the spread. Both countries developed and tested hydrogen bombs by 1954, which were significantly more powerful than the atomic bomb. In 1961, the Soviet Union tested a 50 megaton bomb that was 1,000 times more powerful than the original.
  
  

Types

• There are two types of nuclear bomb. The first type uses a fission reaction only, which includes the atomic bomb. The second type developed uses a combination of fission and fusion to generate enormous power. This bomb type is known as thermonuclear. The power of thermonuclear weapons is unlimited and starts with X-rays and gammas to initiate the reaction.