Just before the First World War two German scientists, James Franck and Gustav Hertz carried out experiments where they bombarded mercury atoms with electrons and traced the energy changes that resulted from the collisions. Their experiments helped to substantiate they theory put forward by Nils Bohr that an atom can absorb internal energy only in precise and definite amounts.
In the 1930s they became interested in the research being carried out by Enrico Fermi and Emilio Segre at the University of Rome. This included experiments where elements such as uranium were bombarded with neutrons. By 1935 the two men had discovered slow neutrons, which have properties important to the operation of nuclear reactors.
Otto Hahn and Lise Meitner were now joined by Fritz Strassmann and discovered that uranium nuclei split when bombarded with neutrons. In 1938 Meitner, like other Jews in Nazi Germany, was dismissed from her university post. She moved to Sweden and later that year she wrote a paper on nuclear fission with her nephew, Otto Frisch, where they argued that by splitting the atom it was possible to use a few pounds of uranium to create the explosive and destructive power of many thousands of pounds of dynamite.
In January, 1939 a Physics Conference took place in Washington in the United States. A great deal of discussion concerned the possibility of producing an atomic bomb. Some scientists argued that the technical problems involved in producing such a bomb were too difficult to overcome, but the one thing they were agreed upon was that if such a weapon was developed, it would give the country that possessed it the power to blackmail the rest of the world. Several scientists at the conference took the view that it was vitally important that all information on atomic power should be readily available to all nations to stop this happening.
On 2nd August, 1939, three Jewish scientists who had fled to the United States from Europe, Albert Einstein, Leo Szilard and Eugene Wigner, wrote a joint letter to President Franklin D. Roosevelt, about the developments that had been taking place in nuclear physics. They warned Roosevelt that scientists in Germany were working on the possibility of using uranium to produce nuclear weapons.
Roosevelt responded by setting up a scientific advisory committee to investigate the matter. He also had talks with the British government about ways of sabotaging the German efforts to produce nuclear weapons.
In May, 1940, Germany invaded Denmark, the home of Niels Bohr, the world's leading expert on atomic research. It was feared that he would be forced to work for Nazi Germany. With the help of the British Secret Service he escaped to Sweden before being moving to the United States.
In 1942 the Manhattan Engineer Project was set up in the United States under the command of Brigadier General Leslie Groves. Scientists recruited to produce an atom bomb included Robert Oppenheimer (USA), David Bohm (USA), Leo Szilard (Hungary), Eugene Wigner (Hungary), Rudolf Peierls (Germany), Otto Frisch (Germany), Felix Bloch (Switzerland), Niels Bohr (Denmark), James Franck (Germany), James Chadwick (Britain), Emilio Segre (Italy), Enrico Fermi (Italy), Klaus Fuchs (Germany) and Edward Teller (Hungary).
Winston Churchill and Franklin D. Roosevelt were deeply concerned about the possibility that Germany would produce the atom bomb before the allies. At a conference held in Quebec in August, 1943, it was decided to try and disrupt the German nuclear programme.
In February 1943, SOE saboteurs successfully planted a bomb in the Rjukan nitrates factory in Norway. As soon as it was rebuilt it was destroyed by 150 US bombers in November, 1943. Two months later the Norwegian resistance managed to sink a German boat carrying vital supplies for its nuclear programme.
Meanwhile the scientists working on the Manhattan Project were developing atom bombs using uranium and plutonium. The first three completed bombs were successfully tested at Alamogordo, New Mexico on 16th July, 1945.
By the time the atom bomb was ready to be used Germany had surrendered. Leo Szilard and James Franck circulated a petition among the scientists opposing the use of the bomb on moral grounds. However, the advice was ignored by Harry S. Truman, the USA's new president, and he decided to use the bomb on Japan.
On 6th August 1945, a B29 bomber dropped an atom bomb on Hiroshima. It has been estimated that over the years around 200,000 people have died as a result of this bomb being dropped. Japan did not surrender immediately and a second bomb was dropped on Nagasaki three days later. On 10th August the Japanese surrendered. The Second World War was over.