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: 2nd Term
Week: 20
Grade code: 2.4.1.LI.1
Strand code: 4
Sub-strand code: 2
Content standard code: 2.4.1.CS.1
Indicator code: 2.4.1.LI.1
Theme: ATOMIC AND NUCLEAR PHYSICS
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 profound real-world applications right here in Ghana. From generating electricity and preserving our food crops like yams and mangoes, to diagnosing and treating diseases in hospitals like Korle Bu and Komfo Anokye, the principles of nuclear physics are vital to modern life. Understanding radioactivity helps us appreciate both its immense benefits and the need for its safe handling.
A. The Atomic Nucleus and Nuclear Stability
Recall that an atom consists of a tiny, dense nucleus surrounded by electrons. The nucleus contains protons and neutrons, collectively known as nucleons. Atomic Number (Z): The number of protons in a nucleus. It defines the element. Mass Number (A): The total number of protons and neutrons in a nucleus (A = Z + N, where N is the neutron number). Nuclide Notation: We represent a specific nucleus (a nuclide) as: `ᴬ_Z X` Where X is the chemical symbol, A is the mass number, and Z is the atomic number. Example: Carbon-14 is written as `¹⁴_6 C`. It has 6 protons and (14 - 6) = 8 neutrons.
Why are some nuclei unstable? The nucleus is held together by the strong nuclear force, which is a powerful but short-range force acting between all nucleons. This force must overcome the electrostatic repulsion between the positively charged protons. For a nucleus to be stable, it needs a suitable balance of neutrons and protons. For light elements (Z 20), more neutrons are needed to provide extra "glue" (strong force) to counteract the increasing proton-proton repulsion. The stable ratio of N/Z gradually increases to about 1.5.
If a nucleus has too many or too few neutrons for its number of protons, it becomes unstable. This instability leads to radioactivity. B. Radioactivity and Types of Radiation