How does an X-ray machine make an image？ An X-ray makes an image because some parts of the body absorb X-ray radiation and some parts of the body don’t. Bones absorb the majority of it and appear white.
X-rays are a type of electromagnetic radiation with a wavelength between 10 nanometers and 10 picometers. There are 1000 picometers in a nanometer. To give you an idea of how small that is, a human hair is about 80,000 nanometers, so the wavelength of X-rays is minuscule. Electromagnetic radiation is a band of radiation with wavelengths that range from radio waves with wavelengths of many kilometers to Gamma rays that have wavelengths of less than 10 picometers. Energy is inversely proportional to wavelength, so the shorter the wavelength of an electromagnetic wave, the more energy it has. Gamma rays have the most energy, and radio waves have the least. The sun is the biggest source of electromagnetic waves in our vicinity, which is where our light comes from. Luckily, we have a thick atmosphere that blocks gamma rays and X-rays from coming down to the surface, because they are very dangerous and could do a lot of damage.
The X-rays in an X-ray machine are produced here on Earth and very carefully controlled. They are made by firing electrons at a metal plate at a very high speed. The X-ray machine consists of several parts. The X-ray generator is on one side, and the photographic plate is on the other, with a gap between them for the person to stand in. The X-ray generator has a glass tube with a filament inside it. Most of the air has been taken out of the glass tube, so it is a partial vacuum. When the X-ray machine is turned on, an electric current heats the filament. This makes the electrons boil off the filament, similar to steam coming off boiling water. The glass tube points towards a metal plate, usually tungsten, that is in a straight line with the photographic plate across the gap. When the X-ray machine is triggered, a powerful electric current runs between the filament and the tungsten metal plate. The filament instantly becomes negative, and the metal plate instantly becomes positive. The electrons get a huge amount of energy from the electric current, and they are immediately attracted to the positively charged metal plate. They hit it at enormous speeds, stopping instantly, and some of the energy they are carrying is converted into an X-ray photon that carries straight on. A lot of the energy is absorbed by the metal plate and becomes heat, but enough of the energy becomes X-rays to enable the hospital to take an image. The X-rays cross the gap, go through whatever is being X-rayed, and hit the photographic plate. Although these days, they are usually digital, so it is some other kind of X-ray sensitive material.
If you get between the X-ray generator and the photographic plate, the X-rays will go straight through most of you. The less dense the material in your body is, the more X-rays will go through. X-rays easily pass through flesh, organs, and the softer parts of our bodies. The more dense regions, such as our bones, block the X-rays. That means far fewer X-rays pass through our bones and hit the photographic plate. The more X-rays hit the plate, the darker the image is. Bones block a lot of the X-rays, so they appear white, while the other parts of the body appear darker, depending on how dense they are. When I say that the bones block the X-rays, they actually absorb them. They scatter some, but the majority are absorbed.
When X-rays and the ability to take photos of the inside of the body were first discovered by Wilhelm Conrad Rontgen in 1895, nobody knew that they could actually be dangerous. These days, we know of the dangers of radiation. There are two types of radiation: non-ionizing and ionizing radiation. Non-ionizing radiation doesn’t have as much energy and can’t get through our skin. It is harmless in small amounts. Ionizing radiation has more energy and can go straight through us. X-rays and gamma rays are ionizing radiation. They have enough energy to tear the electrons off the atoms in our bodies, which can cause irreparable damage. To this end, X-ray sessions are extremely fast and use the lowest number of X-rays possible. More at risk is the radiologist, so they must always ensure that they are shielded or not in the room when the X-ray is taken. And this is what I learned today.
Sources
https://en.wikipedia.org/wiki/X-ray
https://en.wikipedia.org/wiki/Electromagnetic_radiation
https://my.clevelandclinic.org/health/diagnostics/21818-x-ray
https://www.nhs.uk/tests-and-treatments/x-ray
https://www.radiologycafe.com/frcr-physics-notes/x-ray-imaging/production-of-x-rays
https://www.nrc.gov/reading-rm/basic-ref/students/science-101/what-are-different-types-of-radiation
Photo by cottonbro studio: https://www.pexels.com/photo/x-ray-of-the-hands-5723885/