How did Rutherford split the atom?

The Nuclear physics is the branch of physics that deals with the structure and behavior of atomic nuclei.

High-energy physics and elementary particle physics developed out of nuclear physics and were therefore included in it earlier; the actual nuclear physics was then sometimes called to differentiate Low energy- Nuclear Physics.

The technologies based on nuclear fission for generating energy (see also nuclear energy) and for weapons purposes have developed from certain research results in nuclear physics. But it is misleading to call this technical-economic-political area "the nuclear physics".


Nuclear physics is carried out both theoretically and experimentally. Your most important theoretical tool is quantum mechanics; the special theory of relativity is also required. Experimental tools are e.g. B. particle detectors and radiation detectors, particle accelerators and vacuum technology.

The task of "pure" nuclear physics in the sense of basic research is the elucidation of the nucleusstructure, so the details of the structure of the atomic nucleus. For this purpose, for example, spontaneous transformations of the nuclei (radioactivity), scattering processes on nuclei and reactions with nuclei are investigated.

From the investigation of these phenomena, many have also emerged Applications developed, for example

  • Energy generation from nuclear reactions using nuclear reactors and nuclear fusion reactors,
  • medical diagnosis and therapy procedures (such as magnetic resonance imaging, scintigraphy, brachytherapy),
  • Process for preventive damage detection in pipelines using gamma radiation,
  • Production of material surfaces with special properties by means of ion implantation,
  • Auxiliary methods for other research areas such as radiocarbon dating in archeology or cosmochemistry.

Typical orders of magnitude in the area of ​​atomic nuclei and nuclear processes are

  • Lengths: 1 fermi = 1 fm = 10-15 m
  • Energy: 100 keV to 100 MeV

The building blocks of the nuclei are the nucleons: neutrons and protons. The number Z the number of protons in a nucleus is equal to the number of electrons in a neutral atom. Z determines the chemical properties of the atoms and is therefore called the atomic number (or, based on the atomic nucleus, also the atomic number). The mass of the atomic nucleus is given by the number A. of all nucleons and is therefore also called mass number. As you can see is the neutron number N = A. - Z. Atoms with the same atomic number but different mass numbers are called isotopes. The physical properties of the nucleus depend on both the atomic number and the neutron number, the chemical properties (almost) only on the atomic number.

When describing nuclear reactions and scattering processes, the concept of the cross-section is important. The cross section is a measure of the probability of an interaction.

For more details see the main article atomic nucleus


Antoine Henri Becquerel, Pierre Curie and Marie Curie received the 1903 Nobel Prize in Physics for their experiments on radioactivity, which could be described as the historic beginning of modern nuclear research.

Radioactivity is always associated with the transformation of one chemical element into another. This was discovered by Ernest Rutherford, for which he received the Nobel Prize in Chemistry in 1908.

The Rutherford scattering experiment, in which alpha particles are scattered on gold foil, by Geiger, Marsden and Rutherford in 1909 marks a turning point in the idea of ​​the structure of atoms. Rutherford's interpretation of the results led to the idea of ​​the atomic nucleus. Almost the entire mass of the atom is united in the nucleus, but it only takes up a very small proportion of the volume of the atom.

In 1919, Rutherford achieved the first artificial element conversion by bombarding nitrogen with alpha radiation: oxygen was created. It was the nuclear reaction14N (α, p)17O.

The understanding of the binding energy of atomic nuclei, first expressed semi-empirically in 1935 in the Bethe-Weizsäcker formula, represented a decisive advance. The basis for the formula was the droplet model of the atomic nucleus (Bohr 1936). With the help of the Bethe-Weizsäcker formula it could be shown that energy is released in certain nuclear fusions as well as in certain nuclear fission. The droplet model can, for example, explain nuclear fission well.

A quantum mechanical description of the core structure, which can explain the stability of the nuclei, which changes systematically with atomic and mass numbers, was only found later with the shell model (Wigner, Goeppert-Mayer and Jensen 1949).

Nuclear fission

Otto Hahn and Lise Meitner discovered in 1938 that irradiation with neutrons cleaves uranium nuclei (induced nuclear fission). It was later demonstrated that a large amount of energy and further neutrons are released during this process, so that a fission chain reaction and thus the release of technically usable amounts of energy is possible in a short time, i.e. at high power. Research into the use of this energy for civil or military purposes then began, roughly at the same time as World War II. In Germany, among others, Carl Friedrich von Weizsäcker and Werner Heisenberg worked on the development of a nuclear reactor; the possibility of a nuclear weapon was seen but not seriously pursued because the foreseeable development period seemed too long for the ruling war. In Los Alamos, the physicists Enrico Fermi, Hans Bethe, Richard Feynman, Edward Teller, Felix Bloch and others conducted research in the Manhattan Project under the direction of Robert Oppenheimer. Although this project served the development of weapons from the beginning, its findings also led to the construction of the first nuclear reactors used for energy generation.

Public discussion

Hardly any other area of ​​physics has fueled public discussion more because of its ambivalence between peaceful and destructive use: for critics of progress, nuclear physics was a Pandora's box, and for those who believe in progress, it was one of the most useful discoveries of the 20th century. Nuclear fission technology was the trigger for a new ethics of science (Hans Jonas, Carl Friedrich von Weizsäcker). The political debate about the sensible and responsible use of nuclear energy continues to this day in the debate about Germany's exit from nuclear energy.

See also

Category: nuclear physics