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GATE 2025 PH – Question 20

Nuclear and Particle Physics · nuclear force and two nucleon problem · 1 mark · Multiple choice

The nuclear energy levels of mirror nuclei are similar. Using this empirical fact alone, the nuclear force can be said to be independent of which one of the following properties of the nucleons?

  1. Mass
  2. Spin
  3. Charge
  4. Parity

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Correct answer: (C) Charge

Explanation

**Mirror nuclei** are pairs of nuclei in which the numbers of protons and neutrons are interchanged (for example tritium and helium-3, or nitrogen-15 and oxygen-15).

If the nuclear force were different for protons and neutrons, the energy levels of the two nuclei would be different (apart from the Coulomb energy). The observation that their nuclear energy levels are **similar** shows that the nuclear force between two protons is the same as that between two neutrons (and between a proton and a neutron). This property is called **charge independence** of the nuclear force.

The nuclear force is therefore independent of the **charge** of the nucleon (option C). This one empirical fact says nothing about mass, spin or parity.