Isobar - Nuclear Physics

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What are Isobars?

In the year 1918, a British Chemist and a part-time novelist suggested the term isobars (originally isobares) for different atoms having a similar number of nucleons.

Isobars are atoms or nuclides of different elements that contain the same number of nucleons. For example, nuclides of Argon and Calcium bear the same number of nucleons. 

In nuclear Physics, the atoms having the same number of nucleons carry a varying number of protons and neutrons. 

In this article, we will learn about isobar nuclear Physics and isobar isotone in detail. 

What Is Nuclear Physics?

Nuclear physics is one of the well-known branches of Physics that deals with the structure of the atomic nucleus and the radiation emitted from the unstable nuclei. Around 10,000 times smaller than the atom, the constituent particles of the nucleus, protons, and neutrons, attract one another so strongly by the nuclear forces that nuclear energies are approximately 1,000,000 times larger than the normal atomic energies. We need to be thorough with Quantum theory for understanding nuclear structure.

For a subject like nuclear Physics, we have two terms involved in this case, and they are isobars and isotones. In this article, we will understand these two.

Isobar Nuclear Physics

If we talk about elements like Chlorine and Argon; these two elements have the same number of nucleons but they vary in the number of neutrons and protons.

However, if we bring our focus on isobar isotone, isobar varies with isotone because isobar talks of a set of elements having different neutrons, and isotone is the set of elements that have the same number of neutrons.

So, isobar isotone carries a huge difference in their meanings and significance.

Most Stable Nuclide of an Isobar

If A is the mass number of an element and Z is its atomic number, then we have:

 M (A, Z) = Z mP + (A - Z) mN - \[\frac{Eb(A,Z)}{C^{2}}\]

At first, for any mass number ‘A’, the most stable nuclide of the isobar is the one with the least mass. However, it should be the one with a proton number Z. Then:

              ∂M(A, Z) / ∂Z = 0


                  mP - mN - \[\frac{1}{C^{2}}\left ( \frac{\delta Eb(A,Z)}{\delta Z} \right )=0\]

After searching for the most stable isobar, it was found that isobars have the greatest binding energy, meaning only that Z satisfies and the equation for this statement is as follows:

                            \[\left ( \frac{\delta Eb(A,Z)}{\delta Z} \right )=0\]

So, our test failed here. This may be because the difference is just a (small) constant, i.e., Z and A. Let us assume that Zm is the value Zm the one obtained by minimizing M and Z is obtained by maximizing E, the graph plotted for the same is as follows:

[Image will be uploaded soon]

Here, Z begins to separate for large  A. For example, for 

A = 209

Zm (209) =  3.36 ≈ 83, and

ZE (209) = 82.22 ≈ 82


Isotone is a term used in nuclear Physics. When two or more species of nuclei or atoms have exactly the same number of neutrons, the two atoms are isotones.

For example, chlorine-37 and potassium-39 are isotones, because the nucleus of chlorine contains 17 protons and 20 neutrons, whereas the nucleus potassium contains 19 protons and 20 neutrons.

So, we conclude that two nuclides are isotones if they have the same number of neutrons but different proton numbers, i.e., Z.

Another example, the nuclei of both Boron-12, and Carbon-13 contain 7 neutrons, and so they are isotones.

Nuclear Physics and Atomic Physics

  • A basic difference between nuclear and atomic physics is that nuclear physics deals with the nucleus whereas atomic physics deals with an entire atom.

  • Atomic physics deals with all the properties of atoms, mainly due to their electronic configuration.

  • On the other end, nuclear Physics deals mainly with nuclei, their properties, structure, reactions, and interactions. In nuclear Physics, atoms make up all the matter in the universe.

  • After understanding the concepts of quarks and gluons, we can easily understand the forces related to nuclear physics. 

  • We find the application of nuclear physics largely in the field of power generation using nuclear energy. Once the force holding the nucleus is understood, we start performing splitting and fusing neutrons.

  • The energy evolved during the process can be used in the splitting of the nucleus to generate energy in Nuclear Fission and fusing two neutrons to produce energy is Nuclear Fusion.

Do You Know?

In Meteorology, an isobar is a curve drawn via points of equal pressure. For instance, it can be considered a line joining states of equal pressure in a graph representing all the thermodynamic processes. The term isobar is commonly used in meteorology where an isobar is a curve joining points of equal atmospheric pressure on a given reference surface, for instance, a sea level.


We can see that the atoms having the same number of protons is isotope, while atoms having the same number of neutrons are isotones. It’s just a variation of the alphabet. This is actually the stretching performed by the German physicist K. Guggenheimer.

FAQ (Frequently Asked Questions)

1. What are the Uses of Nuclear Physics?

Ans: The two uses of nuclear Physics are as follows:

  • Nuclear physics has helped us discover nuclear medicine, nuclear weapons, geology, and archaeology in terms of carbon dating.

  • An atom is composed of a dense nucleus carrying neutrons and protons at the core surrounded by orbiting around electrons as per the configuration. The center, i.e., a nucleus is positively charged and the surrounding cloud of electrons has a negative charge. On the whole, the atoms in consideration can both neutral and carry a charge (we also call atoms as ions).

2. Describe the Nature of Nuclear Forces.

Ans: The nature of forces we study under nuclear Physics is the nuclear force. Below is the nature of nuclear forces:

  • Nuclear forces are attractive, i.e, protons attract electrons and vice versa.

  • Nuclear forces are independent of charges.

  • The range of nuclear forces is short, i.e., if electrons are in the outermost shell, there are fewer chances of getting attracted by protons.

  • As the distance between two nucleons decreases, the nuclear force between atoms weakens. We see the atoms having a big ring of electron shells have less electronegativity (in Chemistry).

  • The nuclear force depends on the spinning of electrons.