Nuclear chemists also determine the types and energies of radiation emitted by the nuclide. Early Experiments R adioactivity was discovered in uranium salts by the French physicist Henri Becquerel in 1896. Naturally occurring isotopes of these elements are stable. The German nuclear chemists Otto Hahn and Fritz Strassmann discovered nuclear fission in 1938. When uranium is irradiated with neutrons, some uranium nuclei split into two nuclei of about half the atomic number of uranium.
Fission releases enormous energy and is used in nuclear fission weapons and reactors .
Nuclear fission is one of three types of nuclear reactions that release substantial amounts of energy, the other two being radioactive decay and nuclear fusion . Nuclei can also react with each other, but being positively charged, they repel each other with great force. The projectile nucleus must have a high energy to overcome the repulsion and to react with target nuclei. A lpha particles, most of which are emitted by elements with atomic numbers above 83, have discrete energies characteristic of the emitting nuclide. Thus, -emitters can be identified by measuring the energies of the particles.