Is the major process by which nuclei lose excess energy without a change in atomic number — Atomic Structure Chemistry Question

STEPS:

1. Identify the Core Constraint: The question asks for a process where a nucleus loses excess energy but the atomic number (the number of protons) remains exactly the same.
2. Understand the Concept of Nuclear Excitation: Just like electrons, a nucleus can exist in an "excited" state with surplus energy. To reach a more stable, lower-energy state, it must release this energy.
3. Evaluate Gamma^-Ray Emission: Gamma radiation ($\gamma$) consists of high-energy photons (electromagnetic radiation). Because photons have no mass and no electrical charge, their emission does not alter the number of protons or neutrons in the nucleus.
4. Confirm the Atomic Number Stability: Since the proton count remains constant during gamma emission, the identity of the element (the atomic number) does not change. This makes it the only process among the choices that solely releases energy without transforming the atom into a different element.

WHY_OTHERS_WRONG:

• Alpha-particle emission (A): The nucleus ejects a helium nucleus ($^4_2\text{He}$), which decreases the atomic number by 2 and the mass number by 4.
• Beta-particle emission (B): A neutron is converted into a proton (releasing an electron), which increases the atomic number by 1.
• Electron capture (C): The nucleus captures an inner-shell electron, converting a proton into a neutron, which decreases the atomic number by 1.
• Nuclear fission (E): A heavy nucleus splits into two or more smaller nuclei, resulting in a significant change in the atomic numbers of the products.