What is nuclear interaction?

Subatomic particles made everything that we see today. After the birth of the universe, the nuclear interactions paved the way for nucleons, atoms, molecules, elements, and substance form.

In a nuclear interaction, two nuclei interact, or an external subatomic particle collides with a nucleus to produce new nuclides, and the subatomic particles release an enormous amount of energy. Thus, with each nuclear interaction, there is a transformation of one or more subatomic particles or nuclides. When a nucleus interacts with other nuclei, and there is no change in the parent nuclide, that interaction refers to nuclear scattering but not the nuclear reaction.

In general, two nuclides or subatomic particles or both interact to produce two or more products. But, it has been observed that, like the triple-alpha process, three nuclei meet at the same time and in the same place to produce products. However, the probability of such nuclear reactions is extremely rare. In nuclear physics, it has been observed that most of the reactions are caused due to nuclear force, but there are instances when heavy radioactive nuclei burst out due to huge instability, which is a spontaneous change. Such observations are detected in low-energy physics.

What are different types of interaction?

In nature, there are certain rules and standards for an interaction. These interactions are universally accepted. There are four types of interactions:

  • Strong interaction
  • Electromagnetic interaction
  • Weak interaction
  • Gravitational interaction

These are four fundamental interactions in decreasing order of strength. Their measurements are detected using low-energy and high-energy physics. Let us talk about them individually.

Strong interaction

Strong interactions are found in the smallest region of space, i.e., in the nucleus of an atom. The range of particles affected by the strong interaction include quarks and hadrons, using the exchange of gluons and mesons, respectively. This interaction results in the strong force field energy. A comparable radius of a nucleus is 10-15 m. Particles affected by the strong interaction are quarks and hadrons, using the exchange of gluons and mesons, respectively. Here, gluons carry interactions between the quarks, which construct nucleons, which leads to the formation of atomic nuclei. Most of the mass of an atom comprises the nucleus, where proton and neutron reside. This interaction results in the strong force field energy.

An image shows an interaction between two positively charged particles binds in nuclear forces.
Strong interaction

Electromagnetic interaction

Electromagnetic interactions are the results of various interactions in electricity, magnetism, or both. Electromagnetic interactions are caused by the charged particles. They have a range of , and their effect sustains to the same range. It is the second most affected interaction found so far in the universe. Photons are the carriers of electromagnetic forces.

Whenever there is an interaction between the charged particles like protons, electrons, and neutrons, the energy is emitted in the form of photons that leads to the creation of light. Those photons are the carrier of energy in the entire universe with illumination. Charged particles in the electromagnetic interaction are responsible for the structure of atoms, molecules, and various forms of matter. They have relative strength of 10-2.

Weak interaction

Weak interactions are the third most effective nuclear interaction. These are also termed as weak force or weak nuclear force. Quarks and leptons are the particles associated with the interaction of weak nuclear force, whose range is 10-18 m. Weak interactions are responsible for radioactive decay in the atoms, for example, the reactions in nuclear fission.

The more illustrative approach of weak forces is interactions of flavors of quarks and the theory Quantum Flavourdynamics (QFD). QFD is also known as electroweak theory (EWT). The relative strength of the associated particles is 10-5. Force carriers for the weak interactions are W+, W-, Zbosons. Weak interactions mediate the transformation of quarks and leptons. They also help in the composition of atomic nuclei via participating in various decay processes.

Gravitational interaction

Even though the range of the gravitational interaction is infinity, it is the weakest force present in the universe. All the elementary and former particles formed with the sub-atomic elementary particles lie in the region of the gravitational field. However, this force is not effective to the sub-atomic particles, but their impact is severe to the classical particles or bodies.

Gravitons are those virtual particles, which are responsible for such interactions. Their relative strength is 10-39. The constituents matter integrates to form planets, stars, and even galaxies. Gravitational interactions of gravitational forces might be the weakest form of force. But, it shows the strongest impact on heavier celestial bodies as it holds planets together to form a solar system.

Elementary Particles

Elementary particles or sub-atomic particles are the ones that are responsible for the above-said interactions. A specific particle or set of particles governs each interaction. They are divided into two categories: Leptons and hadrons.


Leptons are the lightest particles, which are affected by electromagnetic, weak, and gravitational interactions, but never participate in strong interactions. Leptons comprise charged particles, i.e., electrons, muons, tauons, and their respective neutrinos, i.e., electron-neutrino, muon-neutrino, and tau-neutrino. Neutrinos are neutral leptons.

This theory is derived by Paul A. M. Dirac in the year 1928. Leptons follow Fermi-Dirac distribution since they act as a fermion. They have a half-integral spin, and each particle has its associated anti-particles. Electrons are relatively stable and found more common in nuclear interactions. However, muons and tauons can only be found in cosmic ray incidents, i.e., high-energy collisions.

Leptons have mass, spin, and charge associated with each particle except neutrinos, unlike hadrons, carry isospin, hypercharge, and strangeness number. Another property associated with leptons is chirality or commonly known as helicity. Helicity is related to the spin and momentum of the particle. If the momentum of a particle is in the same direction as its spin, then it is said to be right-handed, or else left-handed. This is detected using chiral Effective Field Theory (EFT).


Hadrons are massive particles consists of mesons and baryons. Mesons and baryons differ in their spin. Mesons are spin-less particles, and baryons have half-integral spin. Only omega particle carries three half-integral spins. Both participate in all four interactions. Hadrons decay to the leptons using various interactions.

Mesons are made up of one quark and an anti-quark. They are spin-less particles; however, they carry mass and charge. Mesons are distributed in three categories; pion, kaon, and eta particles. They can be studied using cosmic rays experiments and particle accelerator experiments. They are categorized in the scalar and pseudoscalar mesons according to their parity.

Pions have three particles as the charge positive, negative, and neutral. Kaons are positive and neutral particles, and eta particle is neutral. Also, each particle has its associated anti-particle. Mesons follow Bose-Einstein condensation since they are bosonic particles. Kaons are strange particles with positive strangeness numbers.

Baryons consist of three quarks; they can be all quarks, all anti-quarks, and mixed quarks, including quarks and anti-quarks. They carry spin and massive particles. Hadrons decay into leptons using multiple interactions. Baryons follow Pauli's exclusion principle since they act as fermions.

Hadrons consist of nucleons and strange baryon particles. Nucleons are the elementary particles that reside in the nucleus of an atom, i.e., proton and neutron. Strange particles are Lambda, Sigma, and Omega. They are massive and unstable particles with negative strangeness numbers. The only proton is the stable particle even outside the nucleus. However, the neutron is a neutral particle.

Hadrons carry isospin, hypercharge, strangeness number, and parity too. Hadrons participate mostly in the strong interactions, which decay until leptons are formed.

Meson exchange theory

It has been a mystery that how nuclear force binds nucleon with another nucleon. Later on, in 1935, Japanese physicist Hideki Yukawa proposed that particles intermediate in mass between electrons and nucleons are responsible for nuclear forces. Today these particles are called pions. Pions may be charged π+π- or neutral π0 and are members of a class of elementary mesons particles. The word pion is a contraction of the original name π meson.

According to Yukawa’s theory, every nucleon continuously emits and reabsorbs pions. If a nucleon is nearby, an emitted pion shifts across to it instead of returning to its parent nucleon. The associated transfer of momentum is equivalent to the action of force. Nuclear forces are repulsive at short range and attractive at greater nucleon-nucleon distances; otherwise, the nucleons in a nucleus would mesh together.

The emission of a pion by a nucleon, which does not change in mass, is a clear violation of the law of conservation of energy. It is possible if the nucleon reabsorbs it or absorbs another pion emitted by a neighboring nucleon so soon afterward that even in principle, it is impossible to determine whether or not any mass change has been involved.

Common Mistakes

Most students get confused about positron emission and electron capture. Both are nuclear reactions for positive beta decay. In both reactions, the proton decays or changes into a neutron. Positron emission takes place by releasing positron, and proton changes into neutrons. However, electron capture happens by absorbing electrons from nearby orbit and then creating neutrons.

Context and Applications

This topic is significant for professional exams for undergraduate and postgraduate courses, especially

Bachelor of Science in Physics

Bachelor of Science in Chemistry

Bachelor of Science in Biotechnology

Master of Science in Physics

Master of Science in Chemistry

Related concepts under nuclear interactions are as follows:

Quantum chromodynamics (QCD)

Quantum flavor dynamics (QFD) deuteron theory

Perturbation theory

Chiral effective field theory (EFT)

Quarks, gluons, and color quarks

Practice Problems

Q1: The splitting of a large nucleus into smaller nuclei is

  1. Fusion
  2. Fission
  3. Gamma radiation
  4. Both fission and fusion

Correct option: (b)

Q2: The moderator used in a nuclear reactor is

  1. Graphite
  2. Thorium
  3. Plutonium
  4. Uranium

Correct option: (a)

Q3: Which of the following is the only natural fissionable fuel occurring in nature?

  1. Thorium
  2. Plutonium
  3. Polonium
  4. Uranium

Correct option: (d)

Q4: Which atomic particle has the least mass energy?

  1. Deuteron
  2. Neutron
  3. Electron
  4. Proton

Correct option: (c)

Q5: The energy released during an atomic explosion is due to the

  1. Conversion of mechanical energy to nuclear energy
  2. Conversion of chemical energy to nuclear energy
  3. Conversion of mass to energy
  4. Conversion of protons to neutrons

Correct option: (c)

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