Nuclear fission

Nuclear fission

Karla Reyes 534 A

December 1938

1932

1939

1944

December 1938

1934

1938

Narration of how the discovery was made

Nuclear fission

The neutron was discovered in 1932. In 1934 Enrico Fermi bombarded uranium with neutrons, producing what he thought were the first elements heavier than uranium. Following Fermi’s work, Meitner and Hahn, along with chemist Fritz Strassmann, also began bombarding elements with neutrons and identifying the series of decay products. Meitner, who had Jewish ancestry, worked at the KWI until July 1938, when she was forced to flee from the Nazis with just two small suitcases. In December 1938, Hahn and Strassmann, continuing their experiments, found what appeared to be isotopes of barium among the decay products. They couldn’t explain it, since it was thought that a tiny neutron couldn't possibly cause the nucleus to crack in two to produce much lighter elements. Hahn sent a letter to Meitner describing the puzzling finding.

Over the Christmas holiday, Meitner had a visit from her nephew, Otto Frisch, a physicist who worked in Copenhagen at Niels Bohr's institute. Meitner shared Hahn's letter with Frisch. They knew that Hahn was a good chemist and had not made a mistake, but the results didn't make sense. They went for a walk in the snow to talk about the matter. Meitner suggested they view the nucleus like a liquid drop, following a model that had been proposed earlier by the Russian physicist George Gamow. Frisch drew diagrams showing how after being hit with a neutron, the uranium nucleus might, like a water drop, become elongated, then start to pinch in the middle, and finally split into two drops. After the split, the two drops would be driven apart by their mutual electric repulsion at high energy, about 200 MeV, Frisch and Meitner figured. Meitner determined that the two daughter nuclei together would be less massive than the original uranium nucleus by about one-fifth the mass of a proton, which, when plugged into Einstein’s famous formula, E=mc2, works out to 200 MeV. Everything fit.

Meitner and Frisch sent their paper to Nature in January. Frisch named the new nuclear process "fission" after learning that the term "binary fission" was used by biologists to describe cell division. Hahn and Strassmann published their finding separately, and did not acknowledge Meitner’s role in the discovery. Scientists quickly recognized that if the fission reaction also emitted enough secondary neutrons, a chain reaction could potentially occur, releasing enormous amounts of energy. Many scientists joined the efforts to produce an atomic bomb, but Meitner didn't want to be part of that work, and was later greatly saddened by the fact that her discovery had led to such destructive weapons. She did continue her research on nuclear reactions, and contributed to the construction of Sweden's first nuclear reactor. Hahn won the Nobel Prize in chemistry in 1944, but Meitner was never recognized for her important role in the discovery of fission.

relevance oF

the discovery

Nuclear fission "led directly to nuclear energy reactors - which power much of the world - and the nuclear bomb - which forever changed warfare and geopolitics".

Fission to Electricity

During the fission of 235U, three neutrons are released in addition to the two daughter atoms. If these released neutrons collide with nearby 235U nuclei, they can stimulate the fission of these atoms and start a self-sustaining nuclear chain reaction. The heat released during this reaction is harvested and used to generate electrical energy. A nuclear power plant uses less fuel than a comparable fossil fuel plant does. A rough estimate is that it takes 17,000 kg of coal to produce the same amount of electricity as 1 kg of nuclear uranium fuel.

Nuclear bomb

Nuclear fission produces the atomic bomb, a weapon of mass destruction that uses power released by the splitting of atomic nuclei. Atomic bombs were exploded in war in Hiroshima and Nagasaki at the end of World War II.

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Why did I choose this discovery?

I chose this one because I'am impressed about how this discovery (and others) can be used for good and bad actions. It is supposed that the science works for the social good but there are people that only think about themselves and their intereses. Also I think that the Meitner's lack of recognizing was wrong, because she helped to do that discovery and and she didn't accept to use the nuclear fission for make a nuclear bomb. The women's lack of recognizing is a fight that we until have and it's time to be considered as important as men.