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: 19
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, moving beyond the electron shells to the very heart of the atom—the nucleus. We will explore the phenomena of radioactivity and nuclear reactions. For Ghana, understanding nuclear physics is not just an academic exercise. It is directly linked to national development, from the medical treatments at Korle Bu Teaching Hospital and Komfo Anokye Teaching Hospital, to agricultural research at the Ghana Atomic Energy Commission (GAEC) that helps our farmers, and even to our nation's future energy plans to ensure a stable power supply.
This section breaks down the essential knowledge needed to understand the applications of nuclear physics. A. The Basics of the Nucleus and Radioactivity The Nucleus: The tiny, dense centre of an atom containing protons (positive charge) and neutrons (no charge). These particles are collectively called nucleons. Isotopes: Atoms of the same element that have the same number of protons but a different number of neutrons. For example, Carbon-12 (6 protons, 6 neutrons) is stable, but Carbon-14 (6 protons, 8 neutrons) is unstable. Radioactivity: Some isotopes have unstable nuclei. To become stable, they spontaneously break down or "decay", releasing energy in the form of particles or waves. This process is called radioactivity, and such isotopes are called radioisotopes. Types of Radiation: Alpha (α) particles: A Helium nucleus (2 protons, 2 neutrons). They are heavy, slow, and have low penetrating power (stopped by a sheet of paper or skin). Beta (β) particles: A high-speed electron. They are lighter and faster than alpha particles, with medium penetrating power (stopped by a thin sheet of aluminium). Gamma (γ) rays: High-energy electromagnetic waves (like X-rays, but more energetic). They have no mass or charge and have very high penetrating power (requiring thick lead or concrete to be stopped). B. Half-Life (T½)
The half-life of a radioisotope is the time it takes for half of the unstable nuclei in a sample to decay. It is a constant value for each specific isotope. Concept: Imagine you have 800 atoms of a radioisotope with a half-life of 10 days. After 10 days (1 half-life), 400 atoms will have decayed, and 400 will remain. After another 10 days (20 days total), half of the remaining 400 will decay, leaving 200 atoms. After another 10 days (30 days total), half of the remaining 200 will decay, leaving 100 atoms. Formula: The amount of substance remaining (N) can be calculated using the formula: `N = N₀ * (1/2)ⁿ` where: `N` is the final amount remaining. `N₀` is the initial amount. `n` is the number of half-lives that have passed (`n = t / T½`, where `t` is the total time and `T½` is the half-life).