In 1929, Robert Atkinson of Rutgers University in the U.S. and Friedrich Houtermans of the Georg-August University of Gottingen in Germany were working on a theory of nuclear fusion as the basis for stellar energy production. They applied George Gamow’s theory of quantum tunneling and Albert Einstein’s famous equation E = MC2 to combining or fusing nuclei of light elements to form heavier elements. Their work showed that such a process could release enormous energy that would explain the energy output of starts. Their theory was not accepted when it was first proposed because it required that stars be mostly hydrogen which was not believed to be the case at the time.
In 1932, Marcus Oliphant, an Australian scientist, was working at the Cavendish Laboratory of Cambridge University. He used their particle accelerator to fire nuclei of heavy hydrogen which contained a neutron in addition to a proton at targets of different elements. He discovered hydrogen 3 which contains two neutrons in the nucleus along with the proton and helium 3 which contained a single neutron in its nucleus along with the two protons. When helium 3 nuclei collided with hydrogen 3, the particles that were produced had much more energy than the two parent particles. He had demonstrated nuclear fusion in his laboratory.
In 1938, Hans Bethe, a German/American nuclear physicist at Cornell University in the U.S., attended a conference in stellar energy generation, a subject that he had not been interested in prior to the conference. George Gamow and Carl Friedrich von Weizacker had propose a simple fusion process for the energy generated by stars in a 1937 paper but it could not account for the observation of helium in stars. In their process, two hydrogen nuclei fused to become hydrogen 2. Bethe became interested in the problem and he came up with a much more complex process that involved the fusing of hydrogen 2, Helium 3, Helium 4, Beryllium 7, Lithium 7 and helium 4. This did explain the helium in stars but not the heavier elements observed in stars. Following the conference, Bethe continued to work on the problem and found what is referred to as the Carbon-oxygen-nitrogen cycle. In this process, carbon 12 fuses with a single hydrogen proton which is then followed by further fusion of nitrogen 14, carbon 13, oxygen 15, nitrogen 15 and protons which ultimately produces a carbon 12 nuclei and a helium 4 nuclei. Ultimately, Bethe won the Nobel Prize for his work.
In 1941, Enrico Fermi, an Italian physicist, was working on the project that resulted in the first nuclear reactor called the Chicago Pile-1 at the University of Chicago. He proposed the idea of using a fission bomb to initiate a fusion reaction in a mass of hydrogen to Edward Teller who was also working on the Manhattan Project to create the first nuclear fission bomb. Although he had proposed the idea, he eventually lobbied against the creation of a hydrogen bomb.
The Carbon-Nitrogen-Oxygen fusion cycles in stars:
