Introduction
The study of the nucleus and radioactivity forms an important part of modern physics and plays a crucial role in understanding the fundamental structure of matter. The nucleus, discovered in the early 20th century, is the dense central core of an atom containing protons and neutrons, collectively called nucleons. Despite its extremely small size, the nucleus holds almost the entire mass of the atom and is responsible for nuclear phenomena such as radioactive decay, nuclear reactions, fission, and fusion.
Radioactivity is a natural phenomenon in which unstable atomic nuclei spontaneously emit radiation in the form of alpha (α), beta (β), and gamma (γ) rays to attain stability. This discovery revolutionized physics and led to applications in energy generation, medicine, industry, and defence technology. Understanding nuclear forces, mass defect, binding energy, and decay laws is essential to explain nuclear stability and transformations.
Core Concepts Covered
- Structure and composition of the nucleus
- Nuclear forces and their properties
- Mass defect and binding energy
- Radioactive decay and decay law
- Half-life and mean life
- Types and properties of nuclear radiations
- Nuclear reactions, fission, and fusion (basic idea)
These concepts explain why some nuclei are stable while others undergo radioactive decay.
Relevance for NDA–CDS 1 2026 Examination
For NDA and CDS examinations, this chapter is highly scoring and frequently asked. Questions are mainly concept-based and numerical, especially from:
- Radioactive decay law
- Half-life calculations
- Binding energy and mass–energy relation (E = mc²)
- Identification and properties of α, β, and γ radiations
A clear understanding of formulas, units, and physical interpretation is essential. This topic also strengthens conceptual clarity needed for defence-related applications, such as nuclear energy and radiation safety.
Conclusion
The chapter “Nucleus and Radioactivity” provides a deep insight into the atomic nucleus and the processes that govern nuclear stability and transformations. It bridges classical physics with modern nuclear science and highlights the immense energy stored within the nucleus. Mastery of this topic not only helps in scoring well in NDA–CDS 1 2026 Physics but also builds a strong foundation for advanced studies in nuclear physics and its applications in national defence, power generation, and medical science. A systematic approach with regular numerical practice ensures success in competitive examinations.
