Medical uses

X rays are valuable in the field of medicine because of their ability to penetrate matter. They are used to produce images of bones, tissues, and teeth. Doctors use these images to detect diseases such as cancer, to find foreign objects trapped in the body, to examine teeth for cavities, and to study damaged or broken bones.

A photographic plate that can capture X rays is placed behind the part of a person's body to be X rayed. A device that produces X rays is placed in front. The X rays are strong enough to pass through the soft tissues but are stopped by bones and dense tissues. The photographic plate that captured the X rays is then developed into a picture. In the developed plate, bones and dense tissues show up as light or white regions. Tissues that are easily penetrated by X rays appear dark.

X-ray techniques such as these have one major drawback. Organs that lie in front of the area that is to be X rayed may block the view of the area in question. For this reason, a new form of X-ray process called computed tomography, or CT, was developed. In this process the patient is placed inside an X-ray machine and a narrow beam of X rays sweeps across an area of the body. A computer analyzes and combines the resulting series of X-ray images. CT scanners are important tools in the diagnosis of brain diseases and head injuries.

Considerable care must be taken with X rays, since they can harm the cells of the body. All areas of the patient's body outside the area to be imaged must be shielded from the X rays. X-ray doses should be kept to a minimum.

However, the damaging effects of X rays may be put to medical use. Radiation affects rapidly dividing cells more than it affects slowly developing cells. Because cancer cells divide rapidly, doctors sometimes use X rays to kill cancerous growths.

Scientific uses

Because of their great penetrating power, X rays can be used to study the structure of living organisms and of nonliving matter. They can also be used to identify unknown materials. When an object is bombarded with X rays, its atoms absorb the energy and then release it. By analyzing the released X rays, scientists can determine the elements that make up the material.

Since the 1970s X rays have been used to study distant objects in outer space. X-ray telescopes are designed for this purpose. Very hot bodies of gas in space give off energy mainly in the form of X rays. Because these X rays are absorbed by the Earth's atmosphere they cannot be easily collected and observed by equipment on Earth. Therefore X-ray telescopes are mounted on board satellites that orbit far above the Earth. X-ray astronomy has revealed the presence of many X-ray sources in space, including stars.

Other uses

Manufacturers use X rays to find hidden flaws in their products. Since X rays can penetrate even the thickest material, small cracks in rockets or other large machines can be detected.

X rays have been widely employed for security purposes. Millions of travelers have had their baggage X rayed at airport or customs inspection stations.

Art historians and museum curators have discovered many problem pieces of art with the aid of X rays. For example, X-ray photographs of metal sculptures supposed to be from ancient Greece or Egypt may show internal structures of a type used only in modern times. Similarly, X rays can reveal old paintings that have been covered up by layers of paint.