Coulomb force determines the motion of electrons in an atom. By now, we already know that the binding energy per nucleon is around 8 MeV, for average mass nuclei. This is much larger than the binding energy in atoms. Hence, the nuclear force required to bind a nucleus together must be very strong and of a different type. It should overcome the repulsion between like-charged protons and should bind the protons and neutrons into a really small nuclear volume. In this article, we will look at the features of this force, also called the nuclear binding force.
The nucleus of all atoms (except hydrogen) contain more than one proton. Also, protons carry a positive charge. And, like charges repel each other. Then why or how do these nucleons stay together in a nucleus? They should repel each other, right? This is where the strong nuclear force comes into play.
Features of Nuclear Force
Between 1930 and 1950, many experiments were conducted to understand nuclear force. Some key observations and/ or features are listed below:
- The nuclear force acts between the charges and functions as the gravitational force between masses. This is much stronger than the Coulomb force. This is because the nuclear force needs to overpower the Coulomb repulsive force between the like-charged protons inside the nucleus. Hence, the nuclear force > the Coulomb force. Also, the gravitational force much weaker than the Coulomb force.
- The distance between two nucleons is measured in femtometers (1fm = 10–15m). The nuclear force is really attractive when the distance between two nucleons is around 1fm. As the distance increases beyond 2.5fm, this attractive force starts decreasing rapidly. Hence, for a medium to a large-sized nucleus, the forces get saturated leading to the constancy of the binding energy per nucleon. Also, if the distance falls below 0.7fm, then this force becomes repulsive. A rough plot of the potential energy between two nucleons as a function of distance is shown below.
- Finally, the nuclear force between two neutrons, two protons and a neutron and a proton is nearly the same. It is important to note that the nuclear force is independent of the electric charge of the neurons. Further, unlike Coulomb’s Law or Newton’s Law of Gravitation, Nuclear force does not have a simple mathematical form.
There are four basic forces in nature:
- Gravitational Force
- Electromagnetic Force
- Strong Nuclear Force
- Weak Nuclear Force
The strong nuclear force is what keeps the nucleons together despite having a similar charge.
Solved Examples for You
Assertion: More energy is released in fusion than fission.
Reason: More number of nucleons take part in fission.
- Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
- Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
- Assertion is correct but Reason is incorrect.
- Both Assertion and Reason are incorrect.
Solution: Option B. Since energy released per mass is more in fusion as compared to fission, more energy is released in it. More number of neutrons are released in fission as compared to fusion and hence, more nucleons take part in fission.
Question: In nuclear reaction: 4Be9+2He4→6C12+X, X will be:
No. of protons is already balanced with C.
∴ X carries no charge.
and 9+4 > 12 by 1 unit mass.
∴ X carries one unit mass.
It’s a neutron.