Nuclear fission is a process largely used in nuclear chemistry and physics. In this article, we are going to define nuclear fission and explain this process in detail. Finally, we will also offer some breakthrough examples for a better understanding.

Nuclear Fission Definition

Nuclear fission is an energy-releasing process through which an atom is divided into two or more nuclei that are smaller than the initial atom. They are called fission products.

Most fissions that take place are binary ones. This means that they produce 2 charged fragments. More rarely, in 2 to 4 cases in 1000 events, there is a ternary fission that takes place, with three fragments that have positive charges.

In the case of ternary fission, the smallest fragment can vary in size from the dimensions of a proton to that of an argon nucleus. In general, the fission products have a mass that represents half of the original one. Besides, there are also two or three neutrons that are emitted.

What Is Fission?

Now that we know what is nuclear fission, we should also clarify what fission entails. Besides the nuclear fission definition included above, the term ‘fission’ can also refer to another process. It can also mean a spontaneous form of natural radioactive decay.

The main difference here is the fact that nuclear fission is harnessed and exploited by humans. Meanwhile, the radioactive decay occurs naturally. Also called spontaneous fission, this process appears only with very heavy chemical elements.

Spontaneous fission happens when the nuclear binding energy of certain heavy elements reaches the maximum atomic mass number, namely 58. At this point, a spontaneous breakdown takes place. The elements are then divided into smaller nuclei, as well as some isolated particles.

Nuclear Fission Process

Now that we covered the nuclear fission definition, we will explain the process in detail. There are indeed nuclei that can support spontaneous fission, as explained above. However, the nuclear fission process can only be sustained by certain nuclei, such as plutonium-239, uranium-233, and uranium-235.

Out of all the elements, only these three can go through a fission chain reaction to produce energy. This happens because when they are broken apart, they release neutrons, which can, in turn, induce fission of other nuclei. The free neutrons released by each of the fissions are very important since they trigger the reaction.

Nuclear Binding Energy

The nuclear binding energy is the type of energy necessary to break down the nucleus of an atom. The result consists in its components: protons and neutrons. These two components are being held together inside the atom by nuclear forces. The mass of a nucleus totals to less than the sum of the masses of its own protons and neutrons after they are separated. The difference is, in fact, a measure of the nuclear binding energy.

What Happens During the Fission?

During the nuclear splitting, a part of the nucleus mass gets converted into energy. As such, the mass is then removed from the total amount of mass belonging to the original particles. In this case, the nuclear binding energies reach impressive levels, even millions of times larger than the binding energies keeping the electrons together in the atom.

Critical Energy

Theoretically, any nucleus can be split, if it is in a highly excited state. The minimum excitation energy for fission to occur is called critical energy or threshold energy. The amount of this energy depends greatly on the nuclear structure. In the case of spontaneous fission, the heavy nuclei don’t need any excitation energy added externally. As such, they can trigger fission even in the ground state.

Energy Release

Nuclear fission usually gives away huge quantities of energy. However, the amount of energy depends on the nucleus that is fissioned. One important step in the process is calculating the power of the reactor used. Scientists need to know the exact individual components, namely the total energy that is going to be released, as well as the energy that they can recover in the reactor.

Fission Fragments

The fission fragments are the parts that are left after a nuclear fission takes place. Usually, when the uranium 235 nucleus suffers fission, it splits into two other nuclei which are smaller. Besides, it also releases a few neutrons, as well the energy in the form of heat, plus gamma rays.

Usually, it breaks up into various unequal fragments. A large part of the fission fragments is very unstable and suffer further radioactive decays. This is part of their attempt to stabilize themselves. They interact with other atoms or molecules found nearby, which makes them ionized.

Chain Reaction

The nuclear chain reaction can only happen if certain conditions are met. One requirement is to have a proper multiplication environment. In the case that one neutron will trigger two other fissions, the number of neutrons found in the multiplication system will increase and so will the reactor power. For scientists to stabilize the multiplication environment, they should increase the absorption of non-fission neutrons into the system.

Here you have a clip illustrating the entire nuclear fission process:

Breakthrough Examples of Nuclear Fission

Just as the nuclear fission definition states, this process yields a huge amount of energy. This energy can be used for various purposes. Naturally, the most famous example is the Manhattan Project. Initiated in 1939, the infamous experiment led to the creation of the first fission (atomic) bomb in the world.

However, nuclear energy is valuable in times of peace as well. One of the most appreciated uses of the process are the power plants. They rely on the energy to heat water. With the resulting steam, the power turbines, as well as other electrical generators. Nowadays, many countries rely on power plants to provide the necessary electricity. However, it is still a controversial source of energy.


Even though it may sound like nuclear physics, the nuclear fission process is simple to understand. The complicated part comes after when people must decide whether they will use this knowledge to power electrical generators or construct nuclear warheads.

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