Notes

NUCLEAR FISSION (PHYSICS)

nuclear - of or relating to the nucleus of an atom
fission - the action of dividing or splitting something into two or more parts
- a reaction when the nucleus of an atom , having captured a neutron, splits into two or more nuclei, and in so doing, releases a significant amount of energy as well as more neutrons. These neutrons go on to split more nuclei and a chain reaction takes place
fusion - a process where nuclei collide and join together to form a heavier atom. Large amount of energy gets released at extremely high temperatures


Nuclear fission - the subdivision of a heavy atomic nucleus (uranium or plutonium), and the release of a large amount of energy
- the process whereby the nucleus of a particular heavy element splits into two nuclei of lighter elements, with the release of substantial amounts of energy

Nuclear Fission is the main process of generating nuclear energy

-The nucleus of an atom breaks up into two lighter nuclei
-in the fission process, a large amount of energy is released, radioactive products are formed, and some neutrons are produced
-the neutrons that are produced can cause fission in nearby nuclei and release more neutrons that can repeat the sequence - causing a chain reaction

chain reaction - a large number of nuclei undergo fission and an enormous amount of energy is released
-a series of nuclear fissions, which is accompanied by an enormous release of nuclear energy

-The energy that is released can be either controlled in a nuclear reactor, or it can lead to a large explosion a.k.a. atomic bomb

1. A neutron strikes the nucleus of a uranium atom and causes it to split into two fragments - each fragment consists of a nucleus with half the neutrons and protons of the original nucleus
2. releases a large amount of energy in heat, radiation and Gamma rays
- releases neutrons - called "free" neutrons, now can split other uranium nuclei; and those release neutrons, which can split more nuclei

Uranium-235 Fission
- a slow neutron can be captured by a uranium-235 nucleus, rendering it unstable toward nuclear fission
- a fast neutron cannot be captured

Uranium Fuel
-uranium found as uranium oxide - rich yellow color "yellowcake" - goes through isotope enrichment process




History
-discovery of nuclear fission after discovery of neutron by Chadwick. Enrico Fermi (Italy) 1934, observed radioactive species from uranium with slow neutrons (irradiated uranium with neutrons) - believed to be "transuranium elements" of atomic numbers 93,94 and higher
-Otto Hahn and Fritz Strassman - (bombarding nuclei with neutrons) "transuranic elements" were radioisotopes of barium, lanthanum, etc.
-split uranium atom by bombarding it with neutrons - showed that barium and krypton were formed

-term "fission" used by German physicists Lise Meitner and Otto Frisch 1939

-"fission" to describe the disintegration of a heavy nucleus into two lighter nuclei of approximately equal size


1939 Frederic Joliot-Curie, Hnas von Halban, Lew Kowarski - found neutrons produced in fission of uranium 235 - discovery of possible chain reaction