Light travels across space and different media in the form of electromagnetic waves. The term electromagnetic means they contain both electric as well as magnetic fields. Akin to other waves, light waves are also characterized by a certain frequency and wavelength.
For example, light waves with frequencies in the range of 400 to 800 THz fall in the visible region and we can see them with the naked eye. Red color has the highest wavelength at around 600 nm and thus, the lowest frequency, whereas violet light has the highest frequency in the visible region.
In this tutorial, we will discuss a region of the electromagnetic spectrum known as Xrays. Before that, let us give a quick recap of what the electromagnetic spectrum is.
The word “spectrum” is used to refer to a range of values that can differ continuously, instead of being discrete and digital. For instance, in a water tank, the water level is not discrete. Depending on how much water is used up, the water level can vary from anything between 0 to 100.
Similarly, the electromagnetic spectrum is the spectrum or the range of continuous frequencies that electromagnetic waves can have. It ranges from less than 1 Hz to as much as $\mathrm{10^{25}}$ Hz. This is an enormous range and understandably, the properties of electromagnetic waves differ significantly in different parts of this spectrum. To make the study of electromagnetic waves easier, this spectrum is said to be divided into various bands. The frequencies in one single band have somewhat similar properties, and thus, can be studied together without too much loss of generality.
X-rays, discovered in 1895, are a form of electromagnetic radiation characterized by energies as high as 123 keV. Their frequencies fall between $\mathrm{30\times 10^{15}}$ Hz to $\mathrm{30\times 10^{18}}$ Hz. This energy range is high enough for X-rays to be able to penetrate through matter, which makes them suitable for a wide variety of applications. Contrary to common misconceptions, X-ray exposure under a certain limit is safe enough and thus, they are used medically for internal imaging purposes like detecting bone fractures, cancers, pneumonia, etc.
During the early days, the dangers of X-rays weren’t so well known, and thus, scientists played around too freely with X-rays, leading to bald spots, burns, and in worse cases, cancer. However, since then, advanced research has allowed us to understand X-rays and their safe limits better. Today, X-rays form an invaluable part of our medical and scientific processes.
The quickest way to generate X-rays is via electron bombardment. In this method, highenergy electrons are bombarded at metal targets. The target is usually made up of tungsten, though copper and molybdenum are also used.
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Fig: 1 Generation of X-ray
wikiRadiography, Xray anode and cathode, CC BY-SA 4.0
This apparatus consists of a vacuum tube inside which, electrons are accelerated via a high-voltage source. When they fall on the metal target, X-rays are generated. The energy and thus, the frequency of the X-rays generated depends on the energy of the incident electron.
X-rays have energies that can go up to 160 keV. This is massive compared to most other forms of radiation you might have come across. Gamma rays are the only radiation with energies greater than X-rays.
X-rays can penetrate through most matter quite easily. This makes them a danger if one is exposed to them for longer durations. Early attempts to study their effects led to burns, blisters, and in one case, even cancer.
X-rays carry enough energy to easily ionize atoms or molecules it interacts with. This makes it particularly harmful to living tissue if exposed in high doses. At the same time, X-rays can be used in cancer treatment.
X-rays have enormous applications in medical and scientific communities. Here, we discuss a few of them.
Due to their shorter wavelengths, X-rays are most suited for crystallographic studies. You will find it interesting to know that the reflection of X-rays from crystals in a solid is what allows us to study and characterize them.
X-rays are penetrating radiation and can pass through most objects. However, since our bone density and tissue density differ significantly from each other, doctors can use an X-ray image to study fractures, cancers, and pneumonia in patients. X-rays can also be used to kill cancer cells.
This branch of astronomy uses the X-rays emitted by celestial objects to study them. Airport security scanners use X-rays to detect security threats, as do border patrols.
X-rays, due to their ionizing nature, are harmful to living tissue. It can cause burns and blisters in small amounts. But what makes X-rays so dangerous is that they increase the risk of cancer in the long term.
You must understand that X-rays shouldn’t be taken lightly. They can prove significantly harmful if not handled with care. Indeed, it is estimated that X-ray exposure can increase risk by up to 3%. X-rays are more dangerous to fetuses and small children and thus, it is medically advisable to avoid X-rays and CT scans where children are concerned.
A chest CT scan exposes the patient to as much radiation as they would receive in about 2-3 years. On the contrary, a simple dental scan causes as much exposure as a person would receive in 10 days. Thus, overuse of X-rays should be controlled.
Spectrum refers to the continuous range of values that a quantity can take. Unlike digital steps, values in a spectrum aren’t discrete or quantized. Thus, the electromagnetic spectrum refers to the range of frequencies that electromagnetic waves can have. It goes from about a Hertz to as much as $\mathrm{10^{26}}$ Hz.
The electromagnetic spectrum is divided into various bands of which, the secondhighest energy band between 30E15 and 30E18 Hz falls in the X-ray region. This frequency range corresponds to energies as high as 124 keV. X-rays were discovered in 1895. They are characterized by penetrating and ionizing nature and thus, harmful to living tissue. To generate X-rays, electron bombardment of suitable targets like tungsten, molybdenum, or copper is done via voltage-based acceleration.
X-rays have vast uses, including medical applications wherein, they are used to image fractures, pneumonia, and cancer cells. They are also used in crystallography to locate atoms inside crystals or to detect impurities. Aside from that, they also have been used in astronomy and other areas of science.
Q1. Why are X-rays used in medicine despite the associated dangers?
Ans. The benefits of X-ray imaging far outweigh the tiny danger they pose in a short exposure time. Regardless of that, medical professionals are advised not to prescribe Xrays or CT scans without reason.
Q2. Are X-rays visible?
Ans. Not normally, no. X-rays lie far beyond the visible region. However, when produced in vast amounts, they can produce a faint bluish glow in the eye. The mechanism behind this is not investigated since the amount a person is exposed to in such experiments is too high.
Q3. How is X-ray exposure measured?
Ans. In SI units, we measure exposure in terms of Coulomb/kilogram (C/kg). It is the amount of radiation required to create a charge of 1 Coulomb in 1 kg of matter.
Q4. Why are X-rays named “X-rays”?
Ans. Wilhelm Conrad Röntgen, who first discovered X-rays, named them so since they were previously unknown. The X corresponds to the unknown part.
Q5. Is there a correct scientific spelling for X-ray?
Ans. Variations like X-ray, x-ray, or X-ray exist. Most commonly, people prefer the hyphenated variant, i.e., “X-ray”.
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