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# What is Nuclear Force? – Definition, Properties, Examples

• Last Updated : 20 Oct, 2021

Nuclear forces are very complex in nature, unlike coulomb’s Law or Newton’s law of gravitation, there is no simple mathematical form of nuclear force. Nuclear forces are non-Central forces. Now we know that for average mass nuclei the binding energy per nucleon is approximately 8 MeV much larger than the binding energy in atoms. Therefore to bind a nucleus together there must be strong nuclear forces of attraction that hold together the nucleons in the tiny nucleus of an atom, to overcome the repulsion between the protons.

Many facts about nuclear binding forces are obtained from a variety of experiments carried out from 1930 to 1950. Coulomb’s electrostatic force or gravitational force can not keep the nucleons inside the nucleus of very small size (∼10-15) m. Then to account for the stability of A nucleus, the concept of a new force called nuclear force was given by a Japanese physicist Yukawa.

This nuclear force was assumed to be a strong attractive force of magnitude greater than Coulomb’s repulsive force. Yukawa predicted that nuclear forces arise due to the exchange of particles known as π -mesons between the nucleons. Since these forces are highly Complex in nature and there is no simple way to demonstrate how the exchange of meson particles between nucleons lead to attractive forces so the process can be understood with the help of the following simple analogy:

Imagine two interacting nucleons as two dogs and a meson particle as a piece of bone. Each of the two dogs tries to snatch the piece of bone from the other. The bone is rabidly exchanged between the two dogs as neither of them can part with it. Thus, the rapidly exchanging bone keep the two dogs bound together. Similarly, the exchange of π mesons keeps the two nucleons bound together in the nucleus.

### What are Nuclear Forces?

The nuclear force is a force that exists between atoms’ protons and neutrons. The nuclear force is the force that holds protons and neutrons together in a nucleus.

This force can exist between protons, neutrons, and protons. It can also exist between neutrons and neutrons. This force is responsible for the nucleus’s stability. All atoms (excluding hydrogen) have more than one proton in their nucleus. Protons are also positively charged. In addition, similar charges repel each other. So, what keeps these nucleons together in a nucleus? Shouldn’t they repel each other? This is where a strong nuclear force may help.

Following Coulomb’s law, the charge of protons, which is +1e, tends to push them away from each other with a strong electric field repulsive force. However, nuclear force is powerful enough to hold them together and overcome that barrier at close range.

### Properties of Nuclear forces

• Nuclear force is a strong fundamental force in nature: The magnitude of the nuclear force between two protons is  100 times Coulomb’s electrostatic repulsive force and 1036 times the gravitational attractive force. The nuclear force is most stronger than Coulomb’s repulsive force is able to keep the protons bound in a very small nucleus.
• Nuclear force is mainly an attractive force: The variation of potential energy with the distance (r) between the nucleons is roughly shown in figure as, The graph in the figure reveals as under, Potential energy is released at distance r0 (≈ 0.8 fm). When the distance between two nucleons is >r0, the nuclear forces attractive. As the distance between them decreases and is < r0 this force becomes repulsive and becomes minimum (≈ 0.8 fm) and increases rapidly which avoids the collapsing of the nucleus.

• Nuclear force is charge independent: The interaction between two nucleons is independent of whether one or both nucleons have a charge on them. In other words, the nuclear force between Proton-Proton (p-p)proton-neutron (p-n)and neutron -neutron (n-n)is the same, so these forces are charge independent.
• Nuclear force is short-range force: The nuclear forces between two nucleons exist only when the distance between nucleons is comparable to the size of the nucleus i.e. of the order of 10-15. These forces cease to act as the distance between two nucleons exceeds 10-15. Moreover, a nucleon can interact with only its neighbouring nucleons just as an atom in solid form bonds only with the surrounding atoms. Thus, these forces are short-range forces.
• Nuclear force is a saturated force: Nuclear force becomes quickly zero when the distance between two nuclei is just about 3 fm. Thus a nucleon can attract only the nearest neighbours and has no influence on other nucleons. Nuclear force becomes saturated in a medium or big nucleus itself.
• Nuclear force is an exchange force: Nuclear forces are due to the exchange of π mesons between the nucleons, so they are called exchange forces.
• Nuclear force is non-central force: The force between two nucleons does not act along the line joining their centres and is therefore called non-Central force.
• Nuclear force is spin-dependent: It has been observed that the nuclear force between nucleons having parallel spins is greater than the force between nucleons having anti-parallel spins. Thus they are spin-dependent.

### Examples of Nuclear Forces

As previously mentioned, the most obvious example of Nuclear Force is the binding of protons, which are naturally repulsive due to their positive charge.

1. On a broad scale, this force is responsible for nuclear weapons’ enormous destructive potential. Strong nuclear forces cause the release of energy when a nuclear weapon is detonated. It is also used in nuclear power plants to create heat in order to generate energy, such as electricity.
2. A weaker nuclear force can convert a neutron to a proton, and a proton to a neutron. These forces are present in a variety of processes, including radioactive decay, sunburn, radiocarbon dating, and so on.

### Nuclear instability

Inside a nucleus, three forms of force interact with one another.

1. The main interaction in the nucleus is Strong interaction, which guarantees nucleus cohesiveness by pushing the different nucleons together, and is also responsible for the generation of alpha radiation.
2. Second, there is Electromagnetic repulsion between like-charged protons, but it is far less than the strong force.
3. The third of these nuclear interactions is the ‘weak‘ force, which works inside individual nucleons and can occasionally result in the change of a neutron into a proton (or vice versa), accompanied by the production of beta radiation.

### Sample Question

Question 1: What is Dog-Bone Analogy?

The foregoing interactions may be illustrated using the dog bone analogy, in which we imagine the two interacting nucleons to be two dogs with a shared bone tightly clamped between their jaws. Because each of these dogs wants to grab the bone, they can’t be separated easily. They appear to be connected together by a powerful attracting force (the bone), despite the fact that the dogs are fierce adversaries. The meson serves the same function as the common bone connecting two nucleons.

Question 2: How does nuclear force arise?

Yukawa predicted that nuclear forces arise due to the exchange of particles known as π -mesons between the nucleons. Also, these forces are highly complex in nature.

Question 3: Is Nuclear force charge independent?

The interaction between two nucleons is independent of whether one or both nucleons have a charge on them. In other words, the nuclear force between Proton-Proton (p-p)proton-neutron (p-n) and neutron-neutron (n-n) is the same, so these forces are charge independent.

Question 4: What is the range of Nuclear force?