Lesson Notes By Weeks and Term v4 - SHS 2
NUCLEAR PHYSICS
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NUCLEAR PHYSICS
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Subject: Physics
Class: SHS 2
Term: 1st Term
Week: 1
Grade code: 1.4.2.LI.1
Strand code: 4
Sub-strand code: 2
Content standard code: 1.4.2.CS.1
Indicator code: 1.4.2.LI.1
Theme: ATOMIC AND NUCLEAR PH YSICS
Subtheme: NUCLEAR PHYSICS
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This lesson introduces the fascinating world of nuclear physics, focusing on the phenomenon of radioactivity. We will explore why some atomic nuclei are unstable and how they release energy and particles to become stable. This process is not just an abstract concept; it has powerful real-world applications right here in Ghana, from treating cancer at Korle Bu Teaching Hospital to preserving our agricultural produce like yams and tomatoes, and even generating electricity in other parts of the world. Understanding radioactivity is key to appreciating both the power held within the atom and the scientific advancements that harness it for humanity's benefit.
A. The Unstable Nucleus: The Root of Radioactivity
Recall that an atom consists of a central nucleus (containing protons and neutrons) and electrons orbiting it. Atomic Number (Z): The number of protons. It defines the element. Mass Number (A): The total number of protons and neutrons (A = Z + N). Notation: We represent a specific nucleus (or nuclide) as: `^A_Z X` Example: Carbon-14 is written as `¹⁴₆C` (A=14, Z=6, so it has 6 protons and 14 - 6 = 8 neutrons).
The nucleus is held together by the strong nuclear force, which is a powerful attractive force between nucleons (protons and neutrons). However, protons, being positively charged, repel each other due to the electrostatic force.
Why are some nuclei unstable? The stability of a nucleus depends on the balance between the attractive strong nuclear force and the repulsive electrostatic force. This balance is determined by the neutron-to-proton ratio (N:Z). For light elements (Z 20), more neutrons are needed to provide extra "glue" (strong force) to overcome the increasing repulsion between the many protons. The stable ratio becomes closer to 1.5:1 (e.g., `²⁰⁶₈₂Pb` has 82 protons and 124 neutrons; ratio ≈ 1.51).