Nucleon - Definition, Nucleon Number, Binding Energy, Types, Properties, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 04:59 PM IST

We can define nucleon as a collective term for the subatomic particle that is either the proton or the neutron contained in the atomic nuclei. Protons are the positively charged subatomic particles and neutrons are the uncharged particles. The neutrons behave identically under the influence of the short range of the nuclear force. These subatomic particles are tightly bound in atomic nuclei and are scattered by each other. In this article, we will discuss what nucleons are, what nucleons are in physics, the binding energy per nucleon, the types of nucleons, and the properties of nucleons.

Nucleon - Definition, Nucleon Number, Binding Energy, Types, Properties, FAQs

What are Nucleons?

We can define nucleon as one of the particles of the atomic nucleus. Every atomic nucleus has one or more Nucleons in it. These Nucleons are surrounded by one or more electrons. They occupy a small space inside the nucleus. Every atom is made up of nucleons and can be further divided into smaller particles such as electrons, protons, and neutrons and they move around the nucleus. We can consider an atom like a mini solar system, where the electrons orbit a central star which is the nucleus and is composed of nucleons.

The strong interaction between these particles is independent of the electric charge. Also, we find that the unstable subatomic particles are heavier than nucleons. These are hyperons and baryon resonances. These comprise a nucleon among their final decay products. We can consider the nucleon as in the baryon ground state. Also, we know that every particle has its antiparticle. The antinucleons are of two types i.e. the antiproton and the antineutron.

What are Nucleons in Physics?

We study the Nucleons both in chemistry and in physics and a nucleon can be either a proton or a neutron. By finding the number of nucleons in a nucleus, we can easily find the mass number of the isotopes. We can consider Nucleons as composite particles made up of three quarks that are bonded together by a strong intermolecular force. This strong interaction between two or more nucleons is known as inter-nucleon interaction or nuclear force. We know this fact that protons and neutrons are the components of an atomic nucleus.

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Binding Energy Per Nucleon

Even though the nucleus consists of neutrons and protons, we find that the mass of the nucleus is much less than the sum of the individual masses of the protons and neutrons. The difference is in the measurement of the binding energy per nucleon that keeps the nucleons together. This binding energy possessed by the nucleons can be determined by using the Einstein relationship:

Nuclear binding energy, $E=\Delta m \cdot c^2$

$\Delta m=0.0304 u$ for the alpha particles and gives a binding energy of 28.3 MeV.

Types of Nucleons

As we have already discussed, there are two types of nucleons i.e. protons and neutrons. A proton has a positive electric charge on it whereas; a neutron has no electric charge on it. These two particles are inside the nucleus of the atom and generate a positive charge as the neutron has no charge at all.

Proton

Positively charged particles in the nucleus
The charge of the proton is $+1 e$
The mass of the proton is $1.007 \mathrm{ u}$
It determines the atomic number of an element

Neutron

The particle in the nucleus which has no charge
The charge of the neutron is $0 \mathrm{e}$
The mass of the neutron is approximately $1.008 \mathrm{u}$
Reduces the electrostatic repulsion between the protons hence stabilising the nucleus.

Related Topics,

Properties of Nucleons

The neutron is not stable on its own. Generally, it can be found in nuclear reactions and is used in scientific analysis.
Both the proton and neutron have three quarks. The proton contains two up quarks (which is the lightest of all quarks and is a major constituent of matter also a type of elementary particle) and one down quark (which is the second lightest of all quarks). On the contrary, a neutron contains one up quark and two down quarks.
Nucleons are an integral part of the atomic nucleus as they cannot exist as independent nucleons.
The nucleons are held with a strong force by the atomic nucleus. When this strong force gets broken, it produces a lot of power, and this power is known as nuclear energy which is similar to what is used in nuclear bombs.
The Nucleons present in radioactive substances such as uranium can be very harmful as they can spread alpha radiation in a fraction of second.

Other properties are:

Composition of Nucleus: Generally, the nucleus is composed of protons and neutrons and is collectively known as the nucleons.
Nuclear charge: It is the total positive charge of the nucleus of an atom.

$$
\text { Nuclear Charge }=Z \cdot e
$$

Nuclear mass: The nuclear mass is the total mass of protons and neutrons inside the nucleus.
Nuclear Size and Shape: The shape of the nucleus is generally considered to be spherical and the size of the nucleus depends on the number of nucleons.

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Frequently Asked Questions (FAQs)

1. What are nucleons?

We can define a nucleon as one of the particles of the atomic nucleus. The nucleus is composed of protons and neutrons and is collectively known as the nucleons.

2. Write the difference between nucleus and nucleons.

The nucleus is the basically the positively charged core of an atom and is surrounded by a cloud of negatively charged particles known as the electrons. On the contrary the nucleons are the particles that the core of an atom consists of i.e. the positively charged protons and the neutral neutrons. In other words we can say that the nucleus is made up of nucleons.

3. What is the nucleon number?

The sum of the total number of protons and neutrons in an atom is known as mass number (A) or nucleon number.

4. What does a nucleus consist of?

Generally, the nucleus is composed of protons and neutrons and is collectively known as the nucleons.

5. Define nucleons.

Nucleon can be of the subatomic particles i.e. either the proton or the neutron contained in the atomic nuclei. We can define protons as the positively charged subatomic particles and neutrons as the uncharged particles. The neutrons behave identically under the influence of the short-range of the nuclear force. These subatomic particles are tightly bound in atomic nuclei and are scattered by each other.

6. How does the nucleon number relate to the mass number of an atom?

The nucleon number is identical to the mass number of an atom. It represents the total number of protons and neutrons in the nucleus. For example, if an atom has 6 protons and 6 neutrons, its nucleon number (and mass number) would be 12.

7. How does the strong nuclear force affect nucleons?

The strong nuclear force is the fundamental force that holds nucleons together in the nucleus. It is attractive between nucleons at short distances (about the size of a nucleus) but becomes negligible at larger distances, explaining why it only affects particles within the nucleus.

8. How does the size of a nucleus change with increasing nucleon number?

As the nucleon number increases, the size of the nucleus generally increases. The radius of a nucleus is approximately proportional to the cube root of the mass number (R ∝ A^(1/3)), where A is the nucleon number.

9. Why are protons and neutrons both considered nucleons despite their different charges?

Protons and neutrons are both considered nucleons because they have similar masses and occupy the nucleus of an atom. Their classification as nucleons is based on their location and role in the nucleus, rather than their electrical charge.

10. What is the difference between atomic number and nucleon number?

The atomic number represents the number of protons in an atom's nucleus, while the nucleon number (or mass number) represents the total number of protons and neutrons. For example, carbon-12 has an atomic number of 6 (6 protons) and a nucleon number of 12 (6 protons + 6 neutrons).

11. How do isotopes relate to nucleon numbers?

Isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons. This means isotopes have the same atomic number but different nucleon numbers. For example, carbon-12 and carbon-14 are isotopes with nucleon numbers 12 and 14, respectively.

12. How do protons and neutrons differ in their properties?

Protons have a positive electric charge, while neutrons are electrically neutral. Protons are slightly lighter than neutrons. Both have approximately the same mass and are affected by the strong nuclear force, but only protons experience electromagnetic forces.

13. What is the binding energy of a nucleus?

The binding energy of a nucleus is the minimum energy required to break apart a nucleus into its constituent protons and neutrons. It represents the energy that holds the nucleons together in the nucleus and is a measure of nuclear stability.

14. Why does the binding energy per nucleon vary for different elements?

The binding energy per nucleon varies due to the balance between the strong nuclear force (which attracts nucleons) and the electromagnetic repulsion between protons. This balance changes with the number of protons and neutrons, leading to different binding energies for different elements.

15. What is the shell model of the nucleus?

The shell model is a theoretical model that describes the structure of the nucleus in terms of energy levels or "shells" for nucleons, similar to electron shells in atoms. It helps explain the stability of certain "magic number" nuclei and nuclear spin properties.

16. What is a nucleon?

A nucleon is a subatomic particle found in the nucleus of an atom. It refers to either a proton or a neutron. Protons and neutrons are collectively called nucleons because they are the primary constituents of atomic nuclei.

17. How does the concept of nucleons help explain nuclear reactions?

Understanding nucleons is crucial for explaining nuclear reactions. In these reactions, nuclei can exchange nucleons, emit them, or absorb them. The conservation of nucleon number (baryon number) is a fundamental principle in nuclear physics, helping to balance nuclear equations.

18. How does the concept of nucleons relate to the idea of quarks?

Nucleons (protons and neutrons) are composed of quarks. Specifically, protons consist of two up quarks and one down quark, while neutrons consist of one up quark and two down quarks. This quark model explains the properties of nucleons at a more fundamental level.

19. How does the concept of nucleons help in understanding nuclear fission?

In nuclear fission, a heavy nucleus splits into lighter nuclei. Understanding nucleons helps explain why certain nuclei are more prone to fission, how the products are formed, and why energy is released. The distribution of nucleons in the fission products is crucial for explaining the process.

20. How is the binding energy per nucleon calculated?

The binding energy per nucleon is calculated by dividing the total binding energy of a nucleus by the number of nucleons in that nucleus. This value gives an indication of how tightly bound the nucleons are within the nucleus.

21. What is the significance of the binding energy curve?

The binding energy curve shows how the binding energy per nucleon changes with the mass number of nuclei. It helps explain nuclear stability, fusion, and fission processes. Elements with higher binding energy per nucleon are more stable.

22. What is the liquid drop model of the nucleus?

The liquid drop model is a theory that compares the nucleus to a drop of incompressible liquid. It helps explain various nuclear properties and phenomena, such as binding energy, nuclear fission, and the spherical shape of most nuclei.

23. How do nucleons contribute to nuclear compressibility?

Nuclear compressibility describes how resistant a nucleus is to compression. It depends on the interactions between nucleons and affects various nuclear properties. Understanding nucleon behavior under compression is crucial for studying dense nuclear matter and neutron stars.

24. What is nuclear saturation?

Nuclear saturation refers to the observation that the density of nucleons in a nucleus remains roughly constant, regardless of the size of the nucleus. This is due to the short-range nature of the strong nuclear force, which only affects nearby nucleons.

25. How does the neutron-to-proton ratio change as atoms get heavier?

As atoms get heavier, the neutron-to-proton ratio generally increases. This is because additional neutrons help counteract the increasing electromagnetic repulsion between protons, maintaining nuclear stability in larger nuclei.

26. What is meant by the "valley of stability" in nuclear physics?

The "valley of stability" refers to the region on a chart of nuclides where the most stable isotopes of each element are found. These nuclei have the optimal neutron-to-proton ratio for stability. Nuclei outside this valley are generally radioactive and decay towards it.

27. What is the significance of the "magic numbers" in nuclear physics?

Magic numbers (2, 8, 20, 28, 50, 82, and 126) represent the number of protons or neutrons that result in exceptionally stable nuclei. Nuclei with these numbers of protons or neutrons are more tightly bound and abundant in nature, analogous to noble gases in atomic physics.

28. How do nucleons contribute to nuclear spin?

The nuclear spin is determined by the combined spins of its nucleons. Each nucleon (proton or neutron) has an intrinsic spin of 1/2. The total nuclear spin depends on how these individual spins combine, following quantum mechanical rules.

29. What is nucleon decay, and why is it significant?

Nucleon decay is a hypothetical form of radioactive decay where a proton or neutron decays into lighter particles. It's significant because if observed, it would violate the conservation of baryon number, a fundamental principle in particle physics. So far, no evidence of nucleon decay has been found.

30. What is the role of virtual mesons in nucleon interactions?

Virtual mesons, particularly pions, are thought to mediate the strong force between nucleons in the nucleus. This concept, part of the meson theory of nuclear forces, helps explain how nucleons interact and stay bound within the nucleus.

31. How does the mass of a nucleus compare to the sum of its nucleon masses?

The mass of a nucleus is always slightly less than the sum of its individual nucleon masses. This mass difference, known as the mass defect, is converted to binding energy according to Einstein's equation E = mc². This explains why nuclei are bound systems.

32. What is meant by the "drip line" in nuclear physics?

The drip line represents the limit of nuclear stability for a given element. Beyond this line, nuclei are so unstable that they immediately emit nucleons (protons or neutrons "drip out"). There are separate proton and neutron drip lines, marking the limits of proton and neutron excess, respectively.

33. How do nucleon interactions change in neutron stars?

In neutron stars, the extreme density causes most protons and electrons to combine into neutrons. The nucleon interactions are fundamentally altered under these conditions, with the strong nuclear force playing a crucial role in supporting the star against gravitational collapse.

34. What is the nucleon-nucleon potential?

The nucleon-nucleon potential describes the force between two nucleons as a function of their separation. It's typically attractive at medium range, strongly repulsive at very short range (explaining why nuclei don't collapse), and approaches zero at large distances.

35. How does the Pauli exclusion principle apply to nucleons?

The Pauli exclusion principle states that no two identical fermions (particles with half-integer spin) can occupy the same quantum state. This applies to nucleons within the nucleus, influencing nuclear structure and stability by preventing all nucleons from occupying the lowest energy state.

36. What is isospin and how does it relate to nucleons?

Isospin is a quantum number used to describe the strong interaction between nucleons. Protons and neutrons are treated as two states of the same particle (the nucleon) with different isospin values. This concept helps explain certain symmetries in nuclear physics.

37. How do nucleons contribute to nuclear magnetic moments?

Nuclear magnetic moments arise from the intrinsic magnetic moments of nucleons and their orbital motion. Protons, being charged, contribute more significantly than neutrons. The arrangement and coupling of nucleon spins determine the overall magnetic moment of a nucleus.

38. What is the EMC effect and how does it relate to nucleons?

The EMC (European Muon Collaboration) effect refers to the unexpected observation that the distribution of quarks in nucleons bound in a nucleus differs from that in free nucleons. This suggests that nucleon properties can be modified by the nuclear environment.

39. What is the role of nucleons in stellar nucleosynthesis?

Stellar nucleosynthesis involves the creation of heavier elements from lighter ones in stars. Understanding nucleon binding energies and stability helps explain which nuclear reactions are possible and energetically favorable, determining the pathways of element formation in stars.

40. How do nucleon interactions change in high-energy collisions?

In high-energy collisions, such as those in particle accelerators, nucleons can break apart into their constituent quarks and gluons. This reveals the internal structure of nucleons and allows scientists to study the fundamental properties of quarks and the strong force.

41. What is the significance of the nucleon axial coupling constant?

The nucleon axial coupling constant is a fundamental parameter in weak interactions involving nucleons, such as beta decay. It describes the strength of the axial-vector weak interaction of nucleons and is important for understanding various processes in nuclear and particle physics.

42. How does the concept of effective mass apply to nucleons in a nucleus?

The effective mass of a nucleon in a nucleus can differ from its free mass due to interactions with other nucleons. This concept helps explain various nuclear properties and reactions by accounting for the complex environment within the nucleus.

43. What is the nucleon form factor?

The nucleon form factor describes how nucleons respond to electromagnetic probes. It provides information about the internal structure and charge distribution of nucleons. Form factors are crucial for understanding nucleon structure and interpreting scattering experiments.

44. How do nucleons contribute to nuclear deformation?

Nuclear deformation occurs when nuclei deviate from a spherical shape. The arrangement and interactions of nucleons, particularly in certain "magic number" configurations, can lead to stable deformed shapes. This affects nuclear properties and decay modes.

45. What is the role of nucleons in understanding the nuclear force?

Studying nucleon interactions has been crucial in developing models of the nuclear force. The complex behavior of nucleons in nuclei has led to sophisticated theories, from the simple meson exchange model to more advanced approaches based on quantum chromodynamics.

46. How does the spin-orbit coupling affect nucleons in a nucleus?

Spin-orbit coupling in nuclei refers to the interaction between a nucleon's intrinsic spin and its orbital angular momentum. This effect is important for explaining the magic numbers and shell structure in nuclei, influencing nuclear stability and properties.

47. What is nucleon transfer reaction?

A nucleon transfer reaction is a type of nuclear reaction where one or more nucleons are transferred from one nucleus to another. These reactions are important tools for studying nuclear structure and properties, as they can probe specific nuclear states.

48. How do nucleons contribute to nuclear collective excitations?

Nuclear collective excitations, such as vibrations or rotations of the nucleus, arise from the coordinated motion of many nucleons. Understanding how nucleons behave collectively is crucial for explaining various nuclear phenomena and spectroscopic observations.

49. What is the nucleon-nucleon scattering length?

The nucleon-nucleon scattering length is a parameter that characterizes the low-energy interaction between two nucleons. It's important for understanding nuclear forces and plays a role in various areas of nuclear physics, including the study of few-body systems and nuclear matter.

50. How does the concept of nucleons relate to the nuclear symmetry energy?

The nuclear symmetry energy describes how the binding energy of a nucleus changes as we move away from equal numbers of protons and neutrons. It's crucial for understanding the stability of neutron-rich nuclei, neutron star properties, and the limits of nuclear existence.

51. What is the nucleon-nucleus optical potential?

The nucleon-nucleus optical potential is a complex potential used to describe the interaction of a nucleon with an entire nucleus. It's a simplified model that accounts for various complex interactions and is useful for analyzing nucleon-nucleus scattering and reactions.

52. What is the role of nucleons in understanding nuclear pairing?

Nuclear pairing refers to the tendency of nucleons to form pairs with opposite spins. This pairing effect, analogous to electron pairing in superconductors, influences nuclear stability, energy levels, and various nuclear properties, and is key to understanding nuclear structure.

53. How does the concept of nucleons help explain the nuclear skin and halo?

Nuclear skin refers to an excess of neutrons at the surface of neutron-rich nuclei, while a nuclear halo is an extreme case where one or more nucleons orbit far from the nuclear core. These phenomena are understood through the behavior of loosely bound nucleons and their wavefunctions.

54. What is the significance of nucleon polarizability in nuclear physics?

Nucleon polarizability describes how easily the charge distribution of a nucleon can be distorted by an external electric field. It provides insights into the internal structure of nucleons and plays a role in precision measurements of nuclear properties.

55. How do nucleons contribute to our understanding of the nuclear equation of state?

The nuclear equation of state describes how the energy of nuclear matter changes with density and composition. Understanding nucleon interactions and behavior under various conditions is crucial for developing this equation, which is important for nuclear physics, astrophysics, and the study of neutron stars.