X-Rays and Gamma Rays: Rays That Changed the World of Science


By Robert Hazen, Ph.D.George Mason University

X-rays and gamma rays are the highest energy radiation that can be utilized and produced by technology. The ionizing x-ray waves range from about 0.1-100 billionths of an inch, while gamma rays are wavelengths smaller than a hundred trillionths of a meter. The longer the wavelength, the lower the energy, and vice versa.

An illustration of an X-ray tube.
X-rays are produced by electrical charges in an electromagnetic field. (Image: Fouad A. Saad/Shutterstock)

How Are X-rays Produced?

X-rays were discovered in 1895 by Wilhelm Conrad Roentgen, who lived from 1845 to 1923. X-rays, like all other kinds of electromagnetic radiation, are produced by the acceleration of electrical charges. An x-ray tube produces a beam of X-rays in a very simple way, and the way it works is very similar to a light bulb, with one important difference. 

In an X-ray tube, a very high negative voltage is applied to the filament and a high positive voltage to a copper or molybdenum or other metal plates. When that high voltage is applied, sometimes 50,000 volts, electrons boil off the filament that’s glowing hot, and they come crashing down, smashing into the plate. 

Because they’ve accelerated at such a high velocity, those electrons— which are charged particles—decelerate so quickly that they have to emit electromagnetic radiation. Because, after all, electromagnetic radiation is just the acceleration or the deceleration, the wiggling of charged particles. 

These electrons wiggle by smashing into the plate and stopping, and that produces a stream of X-rays. The X-rays then come out of a port in more or less a straight beam that can be used in various kinds of scientific or technological experiments.

This is a transcript from the video series The Joy of ScienceWatch it now, on Wondrium.

X-rays in Medical Science

The great penetrating power of these rays, combined with the fact that they were absorbed by some kinds of photographic plates, made them ideal for looking into hidden structures in the body. 

X-ray room in a hospital.
X-rays are widely used in medical science. (Image: Roman Zaiets/Shutterstock)

Medical X-rays work because parts of the tissues are transparent to them, more or less, but bones absorb more of the X-rays, and, therefore, the doctor gets contrast on the film and starts seeing inner structures of the body.

And that’s how a dental x-ray works. X-rays pass through the cheek and gum, through the teeth, onto the film. Then the dentist can see whether or not there are cavities, because, of course, the cavity doesn’t absorb X-rays, but teeth do.

Gamma Rays

And then we come to gamma rays, the highest-energy electromagnetic waves. Remember, all electromagnetic rays are produced by the wiggling, the vibration of electric charges. And this is true for gamma rays, but this occurs not with electrons, but with protons in the nucleus of the atom. 

A nucleus is a place of tremendously high energy, and when the protons in a nucleus are accelerated, gamma rays come streaming out. 

There are government laboratories, such as Oakridge National Laboratory in Tennessee, that produce small amounts of gamma ray-emitting materials, radioactive chemicals that can be used in medicine, and various sorts of research applications. 

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Gamma Rays: Uses and Applications 

Gamma rays are used for medical diagnosis, where the doctor takes small amounts of a gamma ray-producing chemical that then migrates to a specific part of the body, and he can see how that body part is working because the chemical gets absorbed into tissues or into a particular organ. 

An image of a CT-scan room in a hospital.
Doctors use gamma rays to see how the inner parts of the body work. (Image: Blue Planet Earth/Shutterstock)

For example, the doctor can take a gamma ray-emitting phosphorous compound, inject it into the patient’s blood, and that phosphorous compound will congregate in places where bones are healing, where a fracture may be re-mending itself, and so doctors can monitor the process of the healing bone just by looking at the gamma ray-emitting chemical.

Physicists use gamma rays to study the structure of atoms, and astronomers are really interested in gamma rays because there are objects in the distant heavens that produce bursts of gamma rays. 

ELF: Extremely Low-frequency Waves

It’s clear that the shorter wavelengths are more dangerous, they have more energy. But recently, a controversy has swirled around the longest wavelengths, the lowest energy end of the spectrum, on beyond radio waves at the long-wavelength end. These are called ELF, or extremely low-frequency waves. 

Waves at about 60 cycles per second, the kind that is used when power is produced in a power plant. They have no real technological applications, but they’re constantly produced in the environment by various apparatus that people use. There is also another range of ELF from about 15,000 to 30,000 cycles per second; those are produced by video display terminals.

Recently, a number of government reports that have come out that look into this question of extremely low-frequency radiation. Most people’s exposure is not very large. Nevertheless, there are high exposures associated with certain kinds of employment. Power line workers or people who sit in front of a video display for many, many hours, they may be exposed to higher than average levels of some of this radiation.

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Are X-rays and Gamma Rays Dangerous?

So far there’s no convincing evidence of risk. There was a study of 36,000 power line workers in California. They found no increased cancer risk amongst those workers. Then, there was a study of 138,000 utility workers in North Carolina. There seemed to be no increased risk of leukemia, but there was perhaps a slightly elevated risk of brain cancer. 

So, it’s not really clear if there’s a link there. And then there was a study of 223,000 utility workers in Canada and France. And that found a slight increase in risk of leukemia, but no increase in risk for other types of cancer, and so people are dealing with statistics here. A lot more research is needed.

Common Questions about X-Rays and Gamma Rays

Q: What is the difference between X-rays and gamma rays?

X-rays and gamma rays are both electromagnetic rays generated by vibration in an electromagnetic field. The difference between the two is in their wavelength. Gamma rays have shorter wavelengths than X-rays.

Q: How are X-rays and gamma rays utilized? 

X-rays and gamma rays are widely used in the medical industry. They are used to diagnose internal diseases and for observing the internal condition of the body.

Q: Are X-rays and gamma rays dangerous?

Many studies have been conducted on the dangers of X-rays and gamma rays, and so far no definitive proof that they are dangerous has been uncovered.

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