What is meant by nuclear physics?

Nuclear physics is the branch of physics and nuclear science that analyses atomic nuclei and their structure, along with the study of other types of nuclear matter. Nuclear physics must not be misunderstood with atomic physics, which studies the atomic element as a whole, inclusive of the electrons.

Nuclear physics inventions gave rise to its applications like nuclear power and weapons, nuclear pharmaceutical products, material engineering, radioactive carbon dating, archaeology, geology, resonance imaging, and so on. Particle physics is a field of nuclear physics and both of them are usually taught parallelly. The major application of nuclear physics known as nuclear astrophysics is vital in studying the interior works of stars and the emergence of chemical elements.


Discovery of the nucleus by Rutherford

With Rutherford's research of the information in 1911, the discovery led to the Rutherford model of the atom, in which the atom comprised of a tiny and very dense nucleus and having heavy positively charged particles with implanted electrons for balancing out the charge (due to the non-existence of neutron). For example, in this ancient model, nitrogen (14) contained a nucleus with 14 protons and 7 electrons (21 in total) and the nucleus had 7 more adjoining orbiting electrons.

Between 1911–1912 Rutherford presented before the Royal Society to describe the experiments and put forward the new theory of the atomic nucleus.

Discovery of the neutron by James Chadwick

In 1932, Chadwick noticed that the radiation that had been seen was actually because of a neutral particle of about a similar mass as the proton, which he called the neutron. In the same year, Dmitri Ivanenko said only the proton and neutron particles are present with no electrons in reality. The neutron spin quickly gave a solution to the nitrogen-14 issue since a single unpaired proton and a single unpaired neutron each gave a spin of 0.5 in the same direction, thus producing a final total spin of 1.

By comparing the nuclear mass with that of the protons and neutrons which composed it, researchers and scientists could now determine what fraction of binding energy each nucleus had.

Meson of Yukawa that acts as a binder to the nuclei

In 1935, Yukawa proposed the first important theory of the strong force to explain how the nucleus is held together. A meson (virtual particle), conveyed a force among all nucleons, including protons and neutrons. Later, the pi meson discovery showed it to have similar properties with that of Yukawa's particle. Yukawa's research helped to accomplish the modern atomic model.

The study of the strong and weak nuclear forces led the nuclear physicists to manage the collision of nuclei and electrons at ever higher energies. This research became particle physics or particle science under the standard model of particle physics.

Particle Physics

The most crucial branch of contemporary nuclear physics deals with the fundamental subatomic elementary particles of matter and the high-energy physics developed experimental areas of nuclear and cosmic-ray physics. After World War ll, researchers slowly started using the high-energy particle accelerator to provide subatomic particles for study.

However, low-energy nuclear physics research is understanding the element and steadiness of the nuclei in the atoms. Bosons (gluons, mesons, and photons) have integral spins and give direction to the fundamental forces of physics. Baryon and meson together called hadrons have been originated from indivisible elements called quarks which were never isolated. A lot of specific future predictions of QCD have been tested by performing experiments and found true.

Nowadays, the high-energy particle accelerator can be large kilometers in length, cost hundreds of millions of dollars, and accelerate particles to abundant energies. The strong force called quantum chromodynamics (QCD) or Quark Matter, 8 quanta (gluons) secure quarks (quark-gluon plasma) for baryon formation and also tie antiquarks to create mesons. A lot of specific future predictions of QCD have been experimentally tested and found correct.

Relativistic mechanics

The theory of relativity, Albert Einstein's discovery was developed in 1905. The Relativistic Heavy Ion Collider (RHIC) is the foremost and one of the two functioning heavy-ion colliders along with the only spin-polarized proton collider ever constructed.

The methodology of nuclear physics

The experimental teams discovered the W+, W- and the Z quanta at the European Laboratory for Particle Physics in Geneva. A number of visual and electronic techniques were used to segregate the vast amounts of data produced by their efforts, and particle-physics laboratories are the prime users of the superconductive magnets or supercomputers.

Modern (state-of-the-art) nuclear physics

Certain methods try to deduce the solution to the nuclear many-body problems from the ground up, starting from the nucleons and their interactions.

Nuclear decay

In nuclear or gamma decay, a nucleus decays from an excited state into a relatively lower energy state, by emission of a gamma-ray.

Nuclear fusion

The two low-mass nuclei come very close to each other with each other to fuse them together by a strong force. It requires a large amount of energy for the nuclear forces to get over the electrical repulsion between the nuclei to get them together, thus nuclear fusion can only occur at very elevated temperatures or pressures. When nuclei fuse, a very large amount of energy is released and the combined nucleus usually has a lower energy level. The binding energy per nucleon increases with the mass number up to nickel (62). In the Sun, four protons change into a helium nucleus, two neutrinos, and two positrons by the process of fusion.

Since the 1920s, cloud chambers played an important role of particle detectors and eventually lead to the discovery of positron, muon and kaon
CC BY-SA 4.0 | Image Credits: https://en.wikipedia.org | Nuledo s.r.o

Nuclear fission

Nuclear fission is the exact reverse process of nuclear fusion. For the nuclei that are heavier than nickel, the binding energy per nucleon reduces with the mass number. Heavy nuclei such as uranium and thorium also experience spontaneous fission but are more likely to go through alpha decay. In nuclear physics, a heavy-ion is a particle with more than one unit of electric charge and a mass more than that of the helium nucleus (alpha particle).

Nuclear collision

These experiments use beams of high-energy particles, including unstable particles called mesons produced by primary nuclear collisions in the accelerator or meson factories. 


Nuclear astrophysics is a branch of both nuclear physics and astrophysics, which associates close partnership between researchers in different sub-fields. The work has led to the invention of neutrino oscillation (pointing out a non-zero mass for the neutrino absent Standard model of physics) was inspired by a solar neutrino flux that is about thrice lower than expected from theories.

Nucleosynthesis which is an interdisciplinary part of nuclear physics is the process that makes new atomic nuclei from the former existing nucleons and nuclei. With reference to current studies, the first nuclei were formed a few minutes after the Big Bang through nuclear reactions in a process called Big Bang Nucleosynthesis. The entire universe swelled and cooled after 20 minutes at which these high-energy collisions among nucleons came to closure, so only the swift and easiest reactions occurred, leaving the whole universe with 75% hydrogen and 24% helium by mass.

Major types of nucleosyntheses in nuclear physics:

  1. Big Bang
  2. Stellar
  3. Explosive
  4. The neutron stars collision
  5. Blackhole accretion disk
  6. Cosmic ray spallation

Context and Application

This topic is taught in courses related to:

  • Bachelor of Technology (Civil Engineering)
  • Masters in Science (Nuclear Science and Engineering)
  • Masters in Science (Nuclear Energy and Thermo physics)

Practice Problems

Q1. Which of the following is a part of nuclear physics?

  1. Particle physics
  2. Nuclear fusion
  3. Nuclear astrophysics
  4. All of these

Correct Option: (d)

Explanation: Particle physics, nuclear fusion and nuclear astrophysics are all part of nuclear physics.

Q2. Who discovered neutron?

  1. Ernest Rutherford
  2. James Chadwick
  3. Hideki Yukawa
  4. Joseph Priestly

Correct Option: (b)

Explanation: James Chadwick discovered the neutron.

Q3. Baryon and meson together are called as?

  1. Hydrons
  2. Bosons
  3. Gluons
  4. Photons

Correct Option: (a)

Explanation: Baryon and meson together are called hydrons.

Q4. The European Laboratory of Particle Physics is located in?

  1. France
  2. Japan
  3. Geneva
  4. The USA

Correct Option: (c)

Explanation: The European Laboratory of Particle Physics is located in Geneva.

Q5. By what percent of hydrogen helium by mass the universe had left after the Big Bang?

  1. 75% of hydrogen and 24% of helium
  2. 25% of hydrogen and 75% of helium
  3. 60% of hydrogen and 39% of helium
  4. None of these

Correct Option: (a)

Explanation: After the Big Bang, the universe was left with 75% of hydrogen and 24% of helium by mass.

  • Synchrotron particle accelerator
  • Brookhaven National Laboratory
  • The nuclear physics program
  • The fundamental electromagnetic force

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