# The Electromagnetic Spectrum by year 12 physics students

X-rays

Rahul Kotha 12R and Abbas Mohsen 12 G

Introduction

This report is about X-Rays. It will give an outline of the history of the discovery of the wave and the man who discovered it, Wilhelm Röntgen. It will explain how X-Rays are formed and it will look at the properties such as wavelength and frequency in comparison to some other waves of the Electromagnetic Spectrum. It will also include information about some uses for the waves and also the dangers.

What is an X-Ray?

X-Rays are waves that are a part of the electromagnetic spectrum, and are found on the Violet side of the spectrum. They have the second highest frequency range, above that of Ultraviolet (UV) rays and below that of Gamma rays, in the range of 30 petahertz (3×10^16 Hz) and 30 exahertz (3×10^19 HZ). They also have the second shortest wavelengths, again between Ultraviolet rays and Gamma rays, in the range of 10 nm to 0.01 nm. Their energies are in the range of 100 eV (electron volts) to 100 KeV. They first got their name from the man who discovered them, Wilhelm Röntgen, who called them “X” rays, meaning the mathematical term “X” which usually means an unknown.

The picture above shows that X-rays are part of the electromagnetic spectrum, with wavelengths shorter than visible light. The diagram below shows that different applications use different parts of the X-ray spectrum.

http://en.wikipedia.org/wiki/X-ray

http://en.wikipedia.org/wiki/X-ray#Discovery

Discovery

The man who discovered X-Rays in 1895 was Wilhelm Röntgen, a German Physicist. The discovery made him famous and he received the first Nobel Prize in physics for it.

Röntgen accidently produced X-Rays when investigating cathode rays using a Crookes tube. He found that when the tube accelerated electrons to a high enough speed they could produce mysterious rays once they hit the anode target. These rays caused fogging of photographic film.

The low-voltage power supply heated a ﬁlament called a cathode, causing electrons to “boil off”—a process known as thermionic emission. The 100 kV supply accelerated the electrons towards the metal target, known as the anode.

These high-voltage electrons hit the target, causing electrons in the metal atoms to emit the X-rays.

He also found through later experiments that these strange invisible rays could pass through most objects. He wrote a paper on his findings and submitted it to the Würzburg Physical- Medical society, in which he named this new found radiation as “X-Rays”, since they were unknown. Once he sent his paper, he ran some experiments with his wife, where he took the first ever X-Ray photograph of the human body, with his wife’s hand.

Wilhelm Conrad Röntgen (German: 27 March 1845 – 10 February 1923)

http://en.wikipedia.org/wiki/Wilhelm_R%C3%B6ntgen

http://spie.org/samples/PM205.pdf

High speed electrons colliding with a metal target, is still used to produce very high energy X-rays. When these electrons slow down or decelerate rapidly, they give off energy as X-rays. (Source: Edexcel AS Physics – Student’s book)

Properties

X-ray photons carry enough energy to ionize atoms and disrupt molecular bonds. This is harmful to living tissue as it is a type of ionizing radiation. A low dose of radiation can increase the risk of cancer and a high dose can cause radiation sickness.

http://en.wikipedia.org/wiki/X-ray#Properties

Uses

X-Rays are extremely helpful in the medical world. Their amazing ability to look through certain objects has had a massive impact in how doctors today are able to treat patients, especially when it comes to surgical needs. X-Ray machines are able to emit X-Rays directly through a person and a detector records the X-Rays that have passed through. With the use of computers an image can be produced very quickly. This technology helps doctors to see any breaks or fractures in the skeleton of a person or to see where, for example, a swallowed pin may be.

The picture on the left is showing an X-ray image of a person with a broken elbow. The picture on the right shows Mrs. Hare’s plated broken wrist.

www.darvill.clara.net/emag/emagxray.htm

X-Rays are also used in airports for security purposes. They are used to take photos of the contents of bags and other objects, such as shoes, where illegal items such as weapons, explosives or drugs can be stashed. This minimises the danger and threats to the passengers. Portable X-Ray machines can be used by security services wherever there is a threat of danger.

Source: Discover magazine – Andrew Moseman – November 17th 2010

Astronauts and astronomers also use X-Rays in special telescopes that are able to pick up X-Ray radiation emitted by objects in space. These telescopes are able to display the X-Ray radiation to produce images of the different stars and planets at a much higher quality to those of standard visible light telescopes. This is mainly due to the fact that X-Rays are more energetic than visible light and are able to travel through objects in space which ultimately means they are able to travel much farther to give us better, high quality images.

http://en.wikipedia.org/wiki/X-ray_computed_tomography

X-ray computed tomography (X-ray CT) is a technology that uses computer-processed x-rays to produce tomographic images (virtual ‘slices’) of specific areas of the scanned object, allowing the user to see what is inside it without cutting it open.

The above picture shows a computed tomography of a human brain, from base of the skull to top.

http://en.wikipedia.org/wiki/X-ray_crystallography

X-ray crystallography is a tool used for determining the atomic and molecular structure of a crystal, in which the crystalline atoms cause a beam of X-rays to diffract into many specific directions. By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their disorder and various other information. One of most famous examples of this analysis was the determination of the structure of DNA.

Risks

Although X-Rays seem to be amazing through their ability to look through objects they can be extremely dangerous. They have the ability to mutate or destroy living cells. They can lead to severe burns, cancer or leukaemia due to their penetrating abilities. Also, due to the waves being able to kill cells, it is possible that the white blood cells can be destroyed and so weaken the immune system. Another problem is that the mutations may occur in the reproductive cells, which could possibly reduce the chances of having a child or could cause the child to be born with a disease or illness.

The exposure to X-Rays is also cumulative, which means that multiple minor exposures to the waves would be the same as one major exposure. In order for these effects to be minimised when X-Rays are used to look through a specific part of a person’s body, the rest is usually covered or shielded with lead infused materials, which have the ability to stop the waves from passing through into unwanted areas. Only the area of injury is exposed and nowhere else.

The risk of cancer increases significantly if you’re being exposed to ionizing radiation very regularly. This is why radiographers in hospitals stand behind a shield when they are taking an x-ray of their patient.

Pregnant women are usually discouraged from having X-rays, unless in an emergency, as there is a slight chance that it may affect the baby. Young children are also X-rayed very rarely due to the fact that their rapidly growing cells could be negatively affected.

www.nps.org.au/medical-imaging/for-induviduals/types-of-imaging/x-rays/for-induviduals/risks-and-benefits