Pub. 5 2015 Issue 3

18 AT THE CENTER OF UTAH INDUSTRY Metals and Mineral Products Used to Make X-ray Machines W hen you think about x-rays, you may not think about it as a kind of light, but that is exactly what it is. Light is a form of electromagnetic energy, and it has different wavelengths. All the wave- lengths together are called the electromagnetic spectrum. Short wavelengths have high energy; x-rays fit this descrip- tion. Long wavelengths have lower energy and are what we call radio waves. Visible light, which is what you see when you look at a sunset or around your office, is in the middle. The invention of the technology behind the x-ray ma- chine was a complete accident. Wilhem Roentgen, a German physicist, was experimenting with a gas discharge tube and electron beams in 1895. The gas discharge tube had heavy black cardboard around it. There was a fluorescent screen in the lab, and it started to glow when he turned on the electron beam. This surprised him, because he thought the cardboard would have blocked the electron beam. He started putting ob- jects between the tube and the screen, but the objects didn’t block the electron beam, either. Finally he put his hand in front of the beam and he saw an x-ray of the bones of his hand. X-ray machines are built as follows: • There is a lead case. Lead is used because it is extremely dense and has a positively charged nucleus. As a result, lead can absorb a great deal of energy. It is also cheaper than gold or silver, is less toxic and easier to work with than bismuth or thallium, and is readily available. • Inside the case is a vacuum tube with a cathode and an anode made of tungsten in the shape of a flat disc. The cathode is a heated filament. The anode is a flat disc. • The vacuum tube is surrounded by an oil bath. The oil bath is for insulation, and it absorbs heat from the high voltage. • If you were able to look inside the box when the x-ray is on, you would see an electron beam between the anode and the cathode. • The tungsten anode has a motor underneath it. • A filter is located where the x-ray beam exits the box. In medical radiography, the filter is usually made of alumi- num and is used to produce a cleaner x-ray image. This is done by absorbing x-ray photons that have lower energy and are more likely to scatter.