X-ray

An X-ray is a form of high-energy electromagnetic radiation. It has a wavelength shorter than ultraviolet rays and longer than gamma rays. X-rays can pass through many solid objects, including human bodies and building materials. This makes them useful in many areas.

X-rays were discovered in 1895 by the German scientist Wilhelm Conrad Röntgen. He called them X-radiation because their properties were not known at the time. X-ray radiography is now an important tool in medical diagnostics. Doctors use X-rays to see inside the body without surgery. For example, X-rays help doctors find broken bones or check for issues in the chest.

X-rays are a type of ionizing radiation. This means they can damage cells if a person is exposed to too much. Because of this, the use of X-rays is carefully controlled to keep exposure at safe levels.

History

X-rays were first noticed as a kind of unknown radiation coming from special glass tubes used in experiments. These tubes, called Crookes tubes, could create beams of electrons. Early scientists saw strange effects from these beams, which later turned out to be X-rays.

The discovery of X-rays is credited to Wilhelm Conrad Röntgen in 1895. While experimenting with Crookes tubes wrapped in black paper, Röntgen noticed a glow on a nearby screen. He found that invisible rays were passing through the paper and could affect photographic plates. Röntgen shared his findings in a paper, calling these rays “X” to show they were unknown. His work helped X-ray technology spread quickly for medical imaging and other uses.

Energy ranges

X-rays with higher energy, called hard X-rays, are used to see inside objects, like in hospitals and airports. They also help scientists study the structure of crystals. X-rays with lower energy, called soft X-rays, are easily absorbed by air.

There is some confusion about the difference between X-rays and gamma rays. One way to tell them apart is by where they come from: X-rays come from electrons, while gamma rays come from the centers of atoms. Sometimes it can be hard to tell them apart because they can have similar energies.

Properties

X-rays are a kind of high-energy light that can go through solid things. We use them to see inside objects that are hard to see, like in hospitals or at airports. Doctors use X-rays carefully to help people without causing too much harm.

Because X-rays have very short waves, they can show very tiny details. This helps scientists study the tiny parts of materials and even see how atoms are arranged in crystals.

Interaction with matter

X-rays interact with matter in three main ways: photoabsorption, Compton scattering, and Rayleigh scattering. These interactions depend mostly on the energy of the X-rays and the types of atoms in the material.

Photoabsorption happens more with lower energy X-rays and atoms that have higher atomic numbers, like those in bones. Compton scattering is more common with higher energy X-rays and soft tissue. Rayleigh scattering is an elastic scattering that mostly keeps the X-ray’s energy the same.

Production

X-rays are made when particles like electrons hit a material. One common way to make X-rays is by using an X-ray tube. This tube uses electricity to speed up electrons from a hot part called a hot cathode. These fast electrons then crash into a metal target, called the anode, and X-rays are produced.

The X-rays can be created in two main ways during this crash. First, if an electron knocks out another electron from inside the atom, X-rays are released. Second, X-rays are also made when electrons are pulled by the atom’s center. Both of these ways create X-rays that doctors and scientists use for their work.

Detectors

X-ray detectors come in different shapes and sizes for different uses. In the past, detectors for taking pictures of bones or other body parts used special photographic plates and film. Today, most of these detectors are digital, like image plates and flat panel detectors.

To keep people safe from too much X-ray exposure, special tools called ionization chambers and dosimeters are used. These help measure how much radiation a person has been exposed to. For studying the details of X-rays, scientists use devices called spectrometers, and for looking at the structure of tiny things like crystals, they often use hybrid photon counting detectors.

Medical uses

Since Wilhelm Conrad Röntgen discovered that X-rays could show bone structures, they have been widely used in medical imaging.

Projectional radiography creates flat, two-dimensional pictures using X-rays. Because bones contain a lot of calcium, they block X-rays well and appear clearly on the image. This helps doctors see problems in the skeletal system and some issues in softer parts of the body, like the lungs. Common tests include chest X-rays to look for lung diseases and abdominal X-rays to find blockages or fluid in the belly.

Other medical uses of X-rays include computed tomography (CT scans), which create detailed slices of the body, and fluoroscopy, which shows moving images of internal structures. X-rays are also used in radiation therapy to treat cancers by targeting them with controlled radiation beams.

Adverse effects

X-rays are a type of ionizing radiation and can be harmful if not used properly. They can increase the chance of getting cancer, especially if you have many X-rays or high-dose ones like CT scans.

The risk depends on the type of X-ray and the part of the body being imaged. For example, a simple chest X-ray has a very low risk, similar to a short period of natural background radiation. But a CT scan uses much more radiation.

Pregnant women should avoid X-rays when possible, as radiation can affect the developing baby. Doctors often use ultrasound instead for pregnant patients because it does not use radiation. It is important to use X-rays only when necessary to keep health risks low.

Other uses

X-rays have many important uses beyond medical imaging. For example, X-ray crystallography helps scientists study the tiny structures inside crystals, and X-ray astronomy lets us observe high-energy light from stars and other objects in space.

Other uses include checking the quality of products in factories with industrial radiography and automated X-ray inspection, scanning luggage at airports for safety with airport security, and even creating art with fine art photography. These examples show how useful X-rays can be in many different fields.

Visibility

X-rays are usually invisible because our eyes can't see them. But in very dark places, near very strong X-ray machines, some people have seen a faint blue-gray glow. Scientists believe this glow might be from a special kind of light called Cherenkov radiation.

Even though X-rays can't be seen, very strong X-ray beams can make the air glow. This happens when the X-rays hit air molecules hard enough to make them shine.

Units of measure and exposure

X-rays can affect materials by putting in energy, and scientists measure this in different ways. The SI system uses the gray (Gy) to measure the energy absorbed, where 1 Gy means one joule of energy in one kilogram of material. There is also an older unit called the rad, where 100 rad equals 1 gray.

Another important measure is the equivalent dose, which shows how radiation affects human tissue. For X-rays, this is the same as the absorbed dose. The sievert (Sv) is the SI unit for this, and for X-rays, 1 Sv equals 1 Gy.