Overview

The chapter Nuclei is a vital topic in NEET Physics that focuses on the structure, stability, and properties of atomic nuclei. It explains concepts such as mass defect, nuclear binding energy, radioactivity, decay laws, and nuclear reactions. This chapter is crucial for understanding how energy is released in nuclear processes, as well as calculating half-life, decay constant, and binding energy per nucleon. NEET questions often include numerical problems, conceptual questions, and real-life applications such as nuclear power and radiation. Mastery of the key formulas and concepts in this chapter is essential for exam success.

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Structure of Nucleus

• A nucleus consists of protons (Z) and neutrons (N)

• Mass number (A) = Z + N

• Charge of nucleus = Z e, where e = electronic charge

Key points for NEET:

• Protons determine the atomic number

• Neutrons provide nuclear stability

• Nucleus is very small compared to the atom but contains almost all the mass

Mass Defect and Binding Energy

• Mass defect (Δm): Δm = Z m_p + N m_n - m_nucleus

  • m_p = mass of proton, m_n = mass of neutron, m_nucleus = mass of nucleus

• Binding energy (BE): BE = Δm c²

  • c = speed of light

• Binding energy per nucleon: BE/A = total BE / A

Key points for NEET:

• Explains nuclear stability

• Higher BE/A → more stable nucleus

• Mass defect accounts for the energy released in nuclear reactions

Radioactive Decay

• Decay law: dN/dt = -λ N

• Number of nuclei after time t: N = N₀ e^(-λ t)

• Activity (A): A = λ N

• Half-life (T₁/₂): T₁/₂ = 0.693 / λ

• Mean life (τ): τ = 1 / λ

Key points for NEET:

• Activity measures the rate of decay

• Half-life is independent of the initial number of nuclei

• Useful in solving numerical problems on radioactive decay

Types of Nuclear Radiation

1. Alpha decay (α): Emission of He²⁺ nucleus

   • X → Y + α

   • Reduces atomic number by 2, mass number by 4

2. Beta decay (β): Emission of electron or positron

   • β⁻: n → p + e⁻ + ν̄_e

   • β⁺: p → n + e⁺ + ν_e

   • Mass number remains constant, atomic number changes by ±1

3. Gamma decay (γ): Emission of high-energy photons

   • Usually follows α or β decay

   • Mass and atomic numbers remain unchanged

Key points for NEET:

• Alpha: heavy, slow, least penetrating

• Beta: light, faster, moderately penetrating

• Gamma: no mass, highly penetrating

Nuclear Reactions and Energy

• Nuclear reaction general form: A + a → B + b

• Energy released (Q-value): Q = (mass_initial - mass_final) c²

Applications:

• Energy production in nuclear reactors

• Fusion and fission reactions

• Explains energy release in stars

Important Formulas to Remember for NEET

1. Mass number: A = Z + N

2. Mass defect: Δm = Z m_p + N m_n - m_nucleus

3. Binding energy: BE = Δm c²

4. Binding energy per nucleon: BE/A = BE / A

5. Radioactive decay law: N = N₀ e^(-λ t)

6. Activity: A = λ N

7. Half-life: T₁/₂ = 0.693 / λ

8. Mean life: τ = 1 / λ

9. Q-value of nuclear reaction: Q = (mass_initial - mass_final) c²

Memorizing these formulas ensures accuracy in solving NEET problems on nuclear physics.

Practical Applications

The concepts in Nuclei are widely applied in:

• Nuclear power plants for electricity generation

• Medical imaging and cancer therapy using radioactive isotopes

• Carbon dating using half-life of isotopes

• Nuclear weapons and energy release calculations

• Research in nuclear physics and astrophysics

Understanding practical applications helps students relate theoretical formulas to real-world phenomena, improving retention and conceptual clarity.

Preparation Tips for NEET Nuclei

1. Understand Conceptually – Focus on nuclear structure, mass defect, binding energy, and decay laws.

2. Create a Formula Sheet – Include mass defect, binding energy, half-life, decay constant, and Q-value formulas.

3. Use Diagrams – Draw decay processes, nuclear reactions, and energy level transitions.

4. Regular Revision – Solve numerical and conceptual problems frequently.

5. Connect with Real Life – Relate nuclear concepts to reactors, medical isotopes, and energy applications.

Conclusion

Nuclei is a high-yield chapter for NEET Physics that connects atomic structure, nuclear stability, radioactivity, and nuclear reactions. Mastering mass defect, binding energy, decay laws, half-life, and nuclear reaction formulas allows students to solve both numerical and conceptual problems efficiently. Understanding the physical significance of each formula, visualizing decay processes, and revising regularly enhances confidence, accuracy, and speed. This guide provides NEET aspirants with a structured approach to learn, revise, and master the chapter Nuclei effectively, making it an essential resource for exam success.