1. Structure of nucleus

The nucleus is the small, dense region consisting of protons and neutrons at the center of an atom. The atomic nucleus was discovered in 1911 by Ernest Rutherford based on the 1909 Geiger–Marsden gold foil experiment.

Law of radioactive decay

Law of radioactive decay - physical law which describes dependence of the intensity the radioactive decay from time and number of radioactive atoms. Open Frederick Soddy and Ernest Rutherford.

Kinds of radiation

Early researchers found that an electric or magnetic field could split radioactive emissions into three types of beams. The rays were given the names alpha, beta, and gamma, in order of their ability to penetrate matter. While alpha decay was seen only in heavier elements of atomic number 52 (tellurium) and greater, the other two types of decay were produced by all of the elements.

Alpha radiation is called the flow of positively charged particles, consisting of protons and neutrons. This flow occurs after the collapse of a heavy atom element. Alpha particles can scatter within 50 mm from the starting point of radiation.

B eta radiation is called the flow of electrons. These particles smaller than alpha particles, but have the ability to penetrate any body at 2cm.

Gamma radiation is called a photon stream which, when collisions with atoms, loses some energy. Gamma radiation extends to great distances, however, the greater the distance from the epicenter of the radiation, the less energy remains in photons

2. History of nuclear fission

The discovery of nuclear fission occurred in 1938 in the buildings of Kaiser Wilhelm Society for Chemistry, today part of the Free University of Berlin. In 1911, Ernest Rutherford proposed a model of the atom in which a very small, dense and positively charged nucleus of protons (the neutron had not yet been discovered) was surrounded by orbiting, negatively charged electrons (the Rutherford model). Niels Bohr improved upon this in 1913 by reconciling the quantum behavior of electrons (the Bohr model). Work by Henri Becquerel, Marie Curie, Pierre Curie, and Rutherford further elaborated that the nucleus, though tightly bound, could undergo different forms of radioactive decay, and thereby transmute into other elements. (For example, by alpha decay: the emission of an alpha particle—two protons and two neutrons bound together into a particle identical to a helium nucleus.)

Some work in nuclear transmutation had been done. In 1917, Rutherford was able to accomplish transmutation of nitrogen into oxygen, using alpha particles directed at nitrogen 14N + α → 17O + p. This was the first observation of a nuclear reaction, that is, a reaction in which particles from one decay are used to transform another atomic nucleus. Eventually, in 1932, a fully artificial nuclear reaction and nuclear transmutation was achieved by Rutherford's colleagues Ernest Walton and John Cockcroft, who used artificially accelerated protons against lithium-7, to split this nucleus into two alpha particles. The feat was popularly known as "splitting the atom", although it was not the modern nuclear fission reaction later discovered in heavy elements. The first artificial fusion reaction had been achieved by Mark Oliphant in 1932, using two accelerated deuterium nuclei (each consisting of a single proton bound to a single neutron) to create a helium nucleus.

After English physicist James Chadwick discovered the neutron in 1932

The experimental apparatus with which Otto Hahn and Fritz Strassmann discovered nuclear fission in 1938

Hahn was awarded the Nobel Prize for Chemistry in 1944 "for his discovery of the fission of heavy nuclei".

Joliot-Curie in April 1939 his team in Paris, including Hans von Halban and Lew Kowarski, reported in the journal Nature that the number of neutrons emitted with nuclear fission of 235U was then reported at 3.5 per fission. (They later corrected this to 2.6 per fission.) Simultaneous work by Szilard and Walter Zinn confirmed these results. The results suggested the possibility of building nuclear reactors (first called "neutronic reactors" by Szilard and Fermi) and even nuclear bombs. However, much was still unknown about fission and chain reaction systems.