All known isotopes of curium are radioactive and have a small critical mass for a sustained nuclear chain reaction.

A nuclear chain reaction was proposed by Leó Szilárd in 1933, shortly after the neutron was discovered, but more than five years before nuclear fission was discovered.

Szilárd knew of chemical chain reactions, and he had been reading about an energy-producing nuclear reaction involving high-energy protons bombarding lithium, demonstrated by John Cockcroft and Ernest Walton, in 1932.

Thus was born the practical nuclear chain reaction by the mechanism of neutron-induced nuclear fission.

Demonstration of a self-sustaining nuclear chain reaction was accomplished by Enrico Fermi and others, in the successful operation of Chicago Pile-1, the first artificial nuclear reactor, in late 1942.

* 1942 – Manhattan Project: A team led by Enrico Fermi initiates the first self-sustaining nuclear chain reaction.

When the first self-sustained nuclear chain reaction was achieved, one of the physicists, Arthur Compton, made a coded phone call to James Conant, chairman of the National Defense Research Committee.

In 1932, the physicist and conceiver of nuclear chain reaction Leó Szilárd read The World Set Free, a book which he said made a great impression on him.

For example, an explosion is the result of a chain reaction that transforms potential energy stored in chemical, mechanical, or nuclear form into kinetic energy, acoustic energy, and electromagnetic radiation.

This makes possible a self-sustaining nuclear chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon.

Nuclear fission differs importantly from other types of nuclear reactions, in that it can be amplified and sometimes controlled via a nuclear chain reaction.

The chemical element isotopes that can sustain a fission chain reaction are called nuclear fuels, and are said to be fissile.

Most nuclear fuels undergo spontaneous fission only very slowly, decaying instead mainly via an alpha / beta decay chain over periods of millennia to eons.

As noted above, the subgroup of fissionable elements that may be fissioned efficiently with their own fission neutrons ( thus potentially causing a nuclear chain reaction in relatively small amounts of the pure material ) are termed " fissile.

A schematic nuclear fission chain reaction.

A few particularly fissile and readily obtainable isotopes ( notably < sup > 235 </ sup > U and < sup > 239 </ sup > Pu ) are called nuclear fuels because they can sustain a chain reaction and can be obtained in large enough quantities to be useful.

If enough nuclear fuel is assembled in one place, or if the escaping neutrons are sufficiently contained, then these freshly emitted neutrons outnumber the neutrons that escape from the assembly, and a sustained nuclear chain reaction will take place.

An assembly that supports a sustained nuclear chain reaction is called a critical assembly or, if the assembly is almost entirely made of a nuclear fuel, a critical mass.

This nuclear reaction is:

Neutrons are liberated when beryllium nuclei are struck by energetic alpha particles producing the nuclear reaction

Thus, natural beryllium bombarded either by alphas or gammas from a suitable radioisotope is a key component of most radioisotope-powered nuclear reaction neutron sources for the laboratory production of free neutrons.

Recently, the team at the Institute of Modern Physics ( IMP ), Lanzhou, have studied the nuclear reaction between americium-243 and magnesium-26 ions in order to synthesise the new isotope < sup > 265 </ sup > Bh

The number of atoms on the left and the right in the equation for a chemical transformation is equal ( when unequal, the transformation by definition is not chemical, but rather a nuclear reaction or radioactive decay ).

The remaining 7 transient elements ( technetium, promethium, neptunium, americium, curium, berkelium, and californium ) occur only rarely, as products of rare nuclear reaction processes from uranium or other heavy elements.

The general concept of a chemical reaction has been extended to non-chemical reactions between entities smaller than atoms, including nuclear reactions, radioactive decays, and reactions between elementary particles as described by quantum field theory.

On December 2, 1942, physicist Enrico Fermi conducted the world's first controlled nuclear reaction at the University of Chicago as part of the top-secret Manhattan Project.

Cold fusion is a proposed type of nuclear reaction that would occur at, or near, room temperature, compared with temperatures in the millions of degrees that is required for " hot " fusion.

As a new type of nuclear reaction, it was proposed to explain reports by experimenters of anomalously high energy generation under certain specific laboratory conditions.

He did not envision nuclear fission as one of these neutron-producing reactions, since this reaction was not known at the time.

Later, after nuclear fission was discovered in 1938, Szilárd immediately realized the possibility of using neutron-induced fission as the particular nuclear reaction needed for a chain-reaction, so long as fission also produced neutrons.

In a full-size nuclear power plant, the heat of a nuclear reaction is used to run a heat engine.

Some engines convert heat from noncombustive processes into mechanical work, for example a nuclear power plant uses the heat from the nuclear reaction to produce steam and drive a steam engine, or a gas turbine in a rocket engine may be driven by decomposing hydrogen peroxide.

* 1986 – A nuclear reactor accident occurs at the Chernobyl Nuclear Power Plant in the Soviet Union ( now Ukraine ), creating the world's worst nuclear disaster.

While most elements are generally viewed as stable, a small amount of natural transformation of one element to another also occurs in the present time, through decay of radioactive elements as well as other natural nuclear processes.

* 2007 – An earthquake of magnitude 6. 8 and 6. 6 aftershock occurs off the Niigata coast of Japan killing eight people, injuring at least 800 and damaging a nuclear power plant.

The dependence of the hydrogen fusion rate on temperature and pressure means that it is only when it is compressed and heated at the surface of the white dwarf to a temperature of some 20 million kelvin that a nuclear fusion reaction occurs ; at these temperatures, hydrogen burns via the CNO cycle.

In engineered nuclear devices, essentially all nuclear fission occurs as a " nuclear reaction " — a bombardment-driven process that results from the collision of two subatomic particles.

A similar process occurs in fissionable isotopes ( such as uranium-238 ), but in order to fission, these isotopes require additional energy provided by fast neutrons ( such as produced by nuclear fusion in thermonuclear weapons ).

A common source of neutron radiation occurs inside a nuclear reactor, where meters-thick water layer is used as effective shielding.

The first salvo of the Soviet nuclear attack on the central United States ( as shown from the point of view of the residents of Kansas and western Missouri ) occurs at 3: 38 p. m. Central Daylight Time when a large-yield nuclear weapon is air burst at a high altitude over Kansas City, Missouri, in order to generate an electromagnetic pulse and disable any defensive weapons covering the nearby Minuteman III missile silos of Whiteman AFB.

If too many of these neutrons are absorbed by other uranium-235 nuclei, a nuclear chain reaction occurs that results in a burst of heat or ( in special circumstances ) an explosion.

* April 6 – A nuclear accident occurs at Tomsk 7 in Russia.

* September 29 – Kyshtym disaster occurs at a nuclear fuel reprocessing plant in Russia.

Beta decay commonly occurs among the neutron-rich fission byproducts produced in nuclear reactors.

This parameter corresponds to the temperature and density of the early universe and allows one to determine the conditions under which nuclear fusion occurs.

* Metro 2033 ( 2010 ): A nuclear war occurs in this year.

This supernova nucleosynthesis occurs in explosive environments in supernovae, in which the elements between silicon and nickel are synthesized by a quasiequilibrium established during fast fusion that attaches by reciprocating balanced nuclear reactions to < sup > 28 </ sup > Si.

The late Eugene Shoemaker of the U. S. Geological Survey came up with an estimate of the rate of Earth impacts, and suggested that an event about the size of the nuclear weapon that destroyed Hiroshima occurs about once a year.

" Second Variety " occurs in the aftermath of an extensive nuclear war between the Soviet Union ( sometimes referred to as Russia ) and the United Nations.

* Ixeris type: Meiosis I fails to complete ; three rounds of nuclear division occur without cell-wall formation ; wall formation then occurs.