How Do X-rays Work?
Hope F
2011
You probably know that X-rays save millions of lives in many ways. But do you know how do they do this challenging task? The best place to start would be with Wilhelm Roentgen and the discovery of X-rays.
The Discovery of X-rays
On a late dark night in November 1895, Wilhelm Roentgen, a physical scientist, discovered something that would make him internationally famous and change the course of science forever. Roentgen was experimenting with cathode rays when he discovered X-rays. He had almost all the air in a glass tube pumped out, creating a vacuum. Two wires connected to a generator were stuck into the glass tube. One was a negative pole, a cathode, and the other a positive pole, an anode. When the generator was turned on, a stream of charged electric particles (electrons) would flow from the cathode to the anode, creating an invisible ray called cathode rays. Well, Roentgen decided that he should take the experiment a step further than other scientists. He wanted to see if cathode rays could travel through glass. Scientists already knew that when cathode rays could pass through thin metal, like tin foil. When cathode rays touch oxygen, they let off a colorful glow. Roentgen wrapped the glass tube in black cardboard, and concluded that if cathode rays could travel beyond the airless tube, then he could see it glow outside of the black cardboard. The results were quite disappointing. There was no colorful glow, so cathode rays couldn’t pass through glass. Roentgen was going to clean up, when he noticed something glowing on another side of his workshop. A sheet of paper coated in a fluorescent material called barium platinocyanide was glowing! Roentgen brought the sheet of paper closer to the glass tube. It appeared to be that the stronger the electric current, the brighter the paper would glow! Whatever Roentgen put in front of the paper, it still glowed. He noticed that a shadow of his skeleton was visible when he placed his hand between the paper and the vacuum tube. The only thing that really prevented the paper from glowing was lead. Roentgen wondered if film would work in the same way, and it did! The rays coming from the glass tube would turn the film dark, and some opaque materials, like lead and zinc, would be white on the film. Finally Roentgen had a way to save his images and show the world that he had discovered a ray that could travel through almost anything. Roentgen named these mysterious rays X-rays, after the mathematical symbol X, which stands for the unknown.

Roentgen's_wife's_hand_x-ray.jpg
This is an x-ray of Roentgen’s wife’s hand. The large circle is her wedding Ring. This is the first x-ray of a human ever taken.









The Uses of X-rays
X-rays are used in many fields, but the most known one is probably medical purposes. X-rays have located many symptoms that we wouldn’t be able to find without them. The most common and obvious use is to see the inside of the human body. This works because bones and teeth can absorb the X-rays, while soft tissue cannot. As you already know, the spots were x-rays can pass through will appear black on a film, while the spots where they cannot appear white. Bones are opaque, and soft tissues are translucent. Some harder tissues, like cancer cells, will appear on an X-ray. But what if doctors want to see soft tissues? Doctors will make patients drink an opaque liquid, something that absorbs an X-ray, to make your gastro intestines (stomach) to appear on the X-ray, for example. This method works wonderfully well for identifying broken bones, but the problem is, inside us, all of our organs are layered on top of each other, and this form of X-ray only shows the top layer, even when opaque liquids are taken. That is why CT scans are very helpful. CT stands for Computerized Tomography. It’s a special X-ray machine that has X-rays pulse over the target (for ex., a person) multiple times at different angles. A computer puts all the images together to make a 3D image of the inside of the target. CT scans can detect the slightest change in tissue, and have found cancer cells frequently. Though you may not think of it, the X-rays themselves can heal. In cancer treatment, X-rays can slow down rapidly dividing cells, and save the cells around it from the same fate. Keep in mind, X-rays are actually very dangerous, and will ionize cells (to break apart the molecules in cells, can kill the cells). Anyone in exposure to X-rays should be covered with something that can absorb them.
Medicine isn’t the only place that X-rays are used. Interestingly enough, X-rays are used in astronomy. Some really dense objects and extremely hot bodies of gas will radiate of energy in X-rays. Telescopes with deeply concaved mirrors will capture these X-rays and bring them in to focus in detectors that will locate where they came from.
X-rays are also used for security purposes. In airports and important buildings, X-ray machines will check bags and do body scans for the safety of the people. In manufacturing, X-rays can find the tiniest flaws in products, and can find small cracks in really heavy material that would be hard to find manually. X-rays can actually be used to detect art forgeries. They can see through layers of paint and find newer metal structures in supposedly ancient sculptures.




Titian_Venus_with_a_mirror_x-ray.jpg
This image is an X-ray of a painting called Venus with a Mirror by a painter named Titian. Can you see all the different stages where he changed the orientation of the image?












How X-rays Work
Now we get to the question that will explain everything. How do X-rays work? We know what they are used for and who discovered them, but the big question is HOW. Well, it actually isn’t as complicated as you might think.
An X-ray is formed when electrons are accelerated and they hit target electrode, a heavy metal foil target. An electrode is a conductor, something that can carry electricity. An electron is a negatively charged electric particle. A cathode ray is a stream of electrons coming from the electrode, the cathode, the negative pole. The heavy metal foil target is an electrode, because it too can conduct electricity. Accelerate means to change speed or direction. This probably didn’t make much sense, so here are the same words in a diagram:

Science_Diagram.jpg
This diagram is a nice example of how the modern X-ray machine works.

This graph clears up a lot. The outer lines of the diagram represent the vacuum tube that this would be in. As you can see, the electrode, the cathode, is letting off electrons, negatively charged electric particles. When the electrons hit the target electrode, they become accelerated electrons, where they change speed or direction, and they go to high energy levels. When these energy levels go back to normal, the electrons emit X-rays!
Though Wilhelm Roentgen didn’t exactly know it, his discovery of X-rays would leave a mark on the world forever. He had done something way beyond the science of his time. Today, we are still finding new ways to use the invisible ray. Thanks for learning about the X-ray!












Glossary
Accelerate- To change speed or direction. When cathode rays accelerate and hit the target electrode, the emit X-rays.
Barium Platinocyanide- A chemical that reacts to X-rays by glowing. The sheet of paper that glowed when Roentgen was experimenting with the vacuum tube was coated with Barium Platinocyanide.
Cathode- the negative pole. Also known as an electrode, a conductor.
Computerized Tomography- a 3 dimensional X-ray created when waves of X-rays are pulsed over a target at different angles, creating multiple images. A computer then puts these images to create the 3D X-ray.
Electrode- Something that can carry electricity, in other words, a conductor. The cathode is an electrode because it is carries streams of electrons.
Electron- a single particle of either negative or positive electricity. A cathode carries negative particles.
Opaque- A material that can absorb X-rays. Our bones are opaque because they absorb the X-ray before the film does, so they appear white on the film where the film is left alone.
Translucent- Something that X-rays can pass through. Our soft tissues can’t absorb X-rays, so the X-rays go through them and make the film behind it black
X-ray- An invisible ray that’s made when cathode rays (negative charged electric particles) accelerate (change speed or direction) and hit a target electrode (a conductor of electricity, in our case, it’s a piece of metal).




Citations:
Books
Garcia, Kimberly. Wilhelm Roentgen and the discovery of x rays. Bear, Del.: Mitchell Lane Publishers, 2003. Print.

McClafferty, Carla K. The head bone's connected to the neck bone: the weird, wacky, and wonderful x-ray. New York: Farrar, Straus and Giroux, 2001. Print.

Databases
"X ray." Compton's by Britannica. Encyclopædia Britannica Online School Edition. Encyclopædia Britannica, Inc., 2011. Web. 15 Sept. 2011. <http://school.eb.com/comptons/article-9277823>.