Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Define hard and soft x-rays and their characteristics.
• Distinguish between hard and soft x-rays.
• Identify practical uses for both types of x-rays.
• Challenge stereotypes in the field of radiation physics.

Lesson summary

This lesson introduces X-rays, a fascinating and powerful form of electromagnetic radiation. We will explore how they are produced, their unique properties, and how they are classified. X-rays are a vital tool in our daily lives in Ghana, from the hospital in your district capital diagnosing a bone fracture to the security scanners at Kotoka International Airport ensuring our safety. Understanding the physics behind them is crucial for appreciating their benefits and handling them safely. This lesson will also encourage us to see that science, particularly fields like radiation physics, is open to everyone, regardless of their gender or physical abilities.

Lesson notes

2.1 What are X-rays? X-rays are high-energy, short-wavelength electromagnetic waves. They are invisible to the human eye. Their position in the electromagnetic spectrum is between ultraviolet (UV) light and gamma rays. Wavelength Range: Typically from 10⁻⁸ m to 10⁻¹³ m. Frequency Range: Typically from 3 × 10¹⁶ Hz to 3 × 10²¹ Hz. 2.2 Production of X-rays: The Coolidge Tube X-rays are produced when fast-moving electrons are suddenly stopped or decelerated by a metal target. The device used for this is called an X-ray tube or Coolidge tube.

Diagram of a Coolidge Tube: ``` High Voltage P.D. (V) +--------------------- - | | +--|--+ +--|--+ | Anode (+) | Cathode (-) | (Tungsten Target) | (Filament) | /| | | / | | -------> Low Voltage | / | e⁻ beam | Supply (for heating) | / |------------>| | / | | | / | | | / | | +--------+-------------+ Cooling Fins | | X-rays v

```

Key Components and their Functions: Heated Cathode (Filament): A tungsten filament is heated by a low-voltage supply. This causes it to emit electrons through a process called thermionic emission. The number of electrons emitted (and thus the intensity of the X-rays) is controlled by the filament current. High Potential Difference (P.D.): A very high voltage (tens of thousands of volts, kV) is applied between the cathode (-) and the anode (+). This strong electric field accelerates the emitted electrons to very high speeds and kinetic energies. Anode (Target): This is a block of metal with a high melting point, typically tungsten. When the high-speed electrons strike the target, they decelerate rapidly. Their kinetic energy is converted into other forms: ~99% is converted to Heat. This is why the anode is often made of copper (a good conductor of heat) with cooling fins or a rotating mechanism to dissipate the intense heat. ~1% is converted to X-ray photons. Evacuated Glass Tube: The entire setup is enclosed in a strong glass tube from which air has been removed (a vacuum). This prevents the accelerated electrons from colliding with air molecules, which would slow them down and cause energy loss.

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