What is Nuclear Fission? | Definition, Concept and Parts of an Fission

What is Nuclear Fission?

Nuclear fission is a reaction in which a heavy nucleus, when bombarded with neutrons, becomes unstable and decomposes into two nuclei, whose sizes are of the same order of magnitude, with great energy release and the emission of two or three neutrons.

These neutrons, in turn, can cause more fission by interacting with new fissile nuclei that will emit new neutrons and so on.Nuclear Fission

This multiplier effect is known as the chain reaction. In a small fraction of a second, the number of nuclei that have fissioned releases an energy one million times greater than that obtained by burning a block of coal or exploding a block of dynamite of the same mass.

Because of the speed at which a nuclear reaction takes place, energy is released much more rapidly than in a chemical reaction.

If only one of the neutrons released is able to produce subsequent fission, the number of fission events that take place per second is constant and the reaction is controlled.

This is the operating principle on which nuclear reactors, which are controllable nuclear fission power sources, are based.

Other Definition of Nuclear Fission

Nuclear fission is the disintegration of the force that holds the nucleus of the atom together, creating two different but lighter nuclei.

In nuclear fission, the aim is to break the force of attraction or nuclear force that unites protons and neutrons that form the nucleus of an atom.

Non-electrically charged neutrons are used against the nucleus of the atom to produce enough excitation energy to deform the nucleus into two halves.

The nuclei obtained from nuclear fission are different and lighter than the initial nucleus. The excess energy that is released from nuclear fission is what is known as nuclear energy.

Stars are a clear example of the release of heat caused by nuclear fusion. Nuclear weapons also use this principle, as is the hydrogen bomb.

In stars this phenomenon occurs thanks to the high temperature and the union of small atoms to create larger atoms, releasing enormous amounts of heat and radiation.

Basic notions of nuclear fission

Nuclear fission is a physical phenomenon that occurs at subatomic scales by dividing an atomic nucleus in two by a collision with a quantum particle, in order to take advantage of the energy that held them together before the impact and which is called link energy and is precisely the energy E=mc2.

When a neutron collides with the uranium 235 nucleus, its mass and energy are added to it, increasing it into a heavier and more unstable nucleus: uranium 236.

This begins to oscillate and, in fractions of a second, it splits into two stable nuclei, releasing the energy that held them together, plus the emission of two to three neutrons, which in turn serve to divide new nuclei that release energy in addition to the emission of three other neutrons that hit more nuclei, and… so on, in an uncontrolled reaction of rapid growth.

Meaning of Nuclear

What is Nuclear:

Nuclear means what is at the core, at the center of something, what is main, what is most important or something.

Thus, in chemistry and physics, nuclear is a characteristic or a feature of the nucleus of a cell, for example, the nuclear membrane, or of an atom, for example, nuclear energy.

Also in art, there is the nuclear, nuclear painting was a pictorial trend that developed in Italy in the 1950s. From 1952, this trend focused its interest on informal art and science fiction.

What is the difference between fission and nuclear fusion?

Both nuclear fission and nuclear fusion are nuclear reactions that release the energy stored in the nucleus of an atom. But there are important differences between the two.

Nuclear fission is the separation of a heavy core into smaller nuclei, while nuclear fusion is the combination of light nuclei to create a larger, heavier one.

Fission

Nuclear fission is a reaction in which a heavy nucleus, when bombarded with neutrons, becomes unstable and decomposes into two nuclei, whose masses are of the same order of magnitude, and whose sum is slightly less than the mass of the heavy nucleus, resulting in a large release of energy and the emission of two or three neutrons.

These neutrons, in turn, can cause more fission by interacting with other fissile nuclei that will emit new neutrons, and so on. This multiplier effect is known as the chain reaction.

In a small fraction of the time, the fissioned nuclei release an energy one million times greater than that obtained, for example, in the combustion reaction of a fossil fuel.

If only one of the neutrons released is able to produce subsequent fission, the number of fission events that take place per unit time is constant and the reaction is controlled.

Fusion

Nuclear fusion is a reaction in which two very light nuclei are joined together to form a heavier stable nucleus, with a mass slightly less than the sum of the masses of the initial nuclei.

This defect in mass results in a large release of energy. The energy produced by the Sun has this origin.

For fusion to take place, positively charged nuclei must be brought closer together by overcoming electrostatic repulsive forces.

On Earth, where the high pressure inside the Sun cannot be reached, the energy needed for the nuclei to react to overcome interactions can be supplied in the form of thermal energy or by using a particle accelerator.

A typical nuclear fusion reaction consists of the combination of two isotopes of hydrogen, deuterium, and tritium, to form a helium plus neutron atom.

An example of natural fusion is the energy produced inside the Sun. Hydrogen atoms, subjected to enormous gravitational pressures, collide with each other and fuse at very high temperatures (around 15 million°C). Every second, 600 million tons of hydrogen fuses into helium.

At present, there are no commercial fusion reactors yet, as it is a technology for the time being experimental. One example is the ITER fusion experimental reactor under construction at Cadarache (France).

This is a scientific research and international cooperation project aimed at determining the technological and economic feasibility of nuclear fusion by magnetic confinement.

Controlled nuclear fission

To maintain sustained nuclear reaction control, for every 2 or 3 neutrons released, only one must be allowed to hit another uranium core.

If this ratio is lower than one then the reaction will die, and if it is larger it will grow out of control (an atomic explosion). To control the amount of free neutrons in the reaction space a neutron absorption element must be present.

Most reactors are controlled by means of control rods made of neutrons of a strong absorbent material, such as boron or cadmium.

In addition to the need to capture neutrons, neutrons often have a lot of kinetic energy (they move at high speed). These fast neutrons are reduced through the use of a moderator, such as heavy water and tap water.

Some reactors use graphite as a moderator, but this design has several problems. Once the fast neutrons have slowed down, they are more likely to produce more nuclear fission or be absorbed by the control rods.

Spontaneous nuclear fission

In this type of reaction, it is not necessary to absorb an external neutron. In certain isotopes of uranium, and especially plutonium, they have such an unstable atomic structure that they fuse spontaneously.

The rate of spontaneous nuclear fission is the probability per second that a given atom will spontaneously fission – that is, without any external intervention. Plutonium-239 has a very high spontaneous fission rate compared to the spontaneous fission rate of uranium-235.

Uses of nuclear fission

Nuclear fission can be used both for military purposes in the construction of atomic bombs and for pacifist purposes in the construction of reactors for the production of electrical energy.

An example of the application of nuclear fission is present in atomic bombs.

  1. Nuclear Energy
  2. Nuclear weapons
  3. Creation of radioisotopes
  4. Thermonuclear generators

The applications of fusion are currently oriented exclusively towards the production of electricity. But for now what exists are experimental research reactors such as ITER, which is being built in Cadarache, France.

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