Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Distinguish between hard and soft X-rays.
• Describe the properties and uses of X-rays.
• Challenge stereotypes in radiation physics.
• Understand safety measures when using X-rays.

Lesson summary

This lesson delves into the fascinating world of X-rays, a crucial part of atomic physics. X-rays are invisible, high-energy waves that have transformed modern life, especially in medicine. Many of us in Ghana have seen or heard of X-ray images used in hospitals like Korle Bu Teaching Hospital or Komfo Anokye Teaching Hospital to see broken bones. Understanding how they are produced, their properties, and their different types is essential not only for passing examinations but also for appreciating their role in healthcare, industry, and security, as well as the safety precautions needed when working with them.

Lesson notes

A. What are X-rays?

X-rays are a form of electromagnetic radiation, just like visible light, radio waves, and microwaves. However, they are much more energetic. Position on the EM Spectrum: X-rays are found between ultraviolet (UV) rays and gamma rays. They have a very short wavelength (typically 10⁻⁸ m to 10⁻¹² m) and a very high frequency. Energy: Because of their high frequency, X-ray photons carry a large amount of energy, which allows them to pass through many materials that are opaque to visible light. B. Production of X-rays: The Coolidge Tube

X-rays are produced when fast-moving electrons are suddenly stopped or decelerated. This is achieved in a device called an X-ray tube or Coolidge tube.

The process involves four main steps: Thermionic Emission: A filament (cathode) made of tungsten is heated by a low-voltage supply. When the filament gets very hot, it releases electrons. This process is called thermionic emission. Acceleration: A very high potential difference (the accelerating voltage, typically tens of thousands of volts) is applied between the cathode (-) and a metal target (anode, +). This strong electric field accelerates the free electrons from the cathode towards the anode at very high speeds. Deceleration/Collision: The high-speed electrons collide with the target, which is usually a heavy metal like tungsten embedded in a copper block. The copper helps to conduct heat away, as over 99% of the electrons' kinetic energy is converted into heat. X-ray Production: Less than 1% of the electrons' kinetic energy is converted into X-rays. This happens in two ways: Bremsstrahlung (Braking Radiation): As the fast-moving electrons pass close to the nuclei of the target atoms, they are deflected and slowed down (decelerated) by the strong electrostatic attraction. This loss in kinetic energy is emitted as an X-ray photon. This process produces a continuous spectrum of X-ray energies. Characteristic X-rays: If an incoming electron has enough energy, it can knock out an electron from an inner shell (e.g., the K-shell) of a target atom. This leaves a vacancy. An electron from a higher energy shell (e.g., L or M shell) then drops down to fill this vacancy, emitting an X-ray photon with a specific energy difference between the two shells. This energy is a "characteristic" of the target material, producing sharp peaks in the X-ray spectrum. C. Distinguishing Between Hard and Soft X-rays

Evaluation guide

• Distinguish between hard x -rays and soft x -rays
• Experiential learning: From the video learners must also come out with the characteristics
• and uses of x -rays.
• conceptual