CHAPTER 18: X-RAYS

How do doctors see inside the human body without surgery? How do airport scanners see through luggage? What are the invisible rays that can both heal and harm? The answer is X-rays—a form of high-energy electromagnetic radiation discovered by Wilhelm Röntgen in 1895. This chapter explores how X-rays are produced in a Coolidge tube, the difference between hard and soft X-rays, their properties, and the crucial safety measures required when working with them.

18.1 DISCOVERY OF X-RAYS

In 1895, German physicist Wilhelm Conrad Röntgen was experimenting with cathode rays (electron beams) in a vacuum tube. He noticed that a fluorescent screen in his laboratory glowed even when the tube was covered with black cardboard. He realized that the tube was emitting an unknown type of radiation that could pass through opaque materials. He named them X-rays (X for unknown).

For this discovery, Röntgen received the first Nobel Prize in Physics in 1901.

18.2 PRODUCTION OF X-RAYS: THE COOLIDGE TUBE

Modern X-ray tubes are based on the design developed by William Coolidge in 1913. The Coolidge tube is an evacuated glass tube containing two main electrodes: a cathode and an anode.

18.2.1 Construction of the Coolidge Tube

The Cathode (Filament):

• A tungsten filament (coiled wire) that serves as the source of electrons.
• It is heated by a low-voltage current (typically 6-12 V) to produce electrons by thermionic emission.
• The filament is surrounded by a focus