by Ron Kurtus (30 January 2008)
X-rays have waveform characteristics similar to other electromagnetic waves. Namely, they have velocity, wavelength, frequency and amplitude. When x-rays encounter matter, their characteristics are determined by the short wavelength of the radiation. Many materials are transparent to x-rays, while lead and other dense materials will not transmit the radiation.
X-rays can be detected with photographic film, similar to visible light. Another effect x-rays have on matter is that they can ionize atoms, which can cause radiation damage to living tissue.
(Note: For information on how much radiation is safe, see X-ray Health Risks)
Questions you may have include :
- What are the waveform characteristics of x-rays?
- How do x-rays interact with matter?
- How do x-rays affect matter?
This lesson will answer those questions. Useful tool: Units Conversion
Like every waveform, x-rays have velocity, wavelength, frequency and amplitude.
Since x-rays are electromagnetic radiation, their velocity in a vacuum is the same as visible light: 186,000 miles/second or 300,000 kilometers/sec. Its velocity through transparent matter is less, according to the index of refraction for that material at that wavelength.
X-rays have a very short wavelength compared to other electromagnetic waves.
|Approx. 1.5 kilometer or 1 mile = 1.5 x 105cm|
|1/1000 centimeter = 10-3cm|
|1/1000000 centimeter = 10-6cm|
Only gamma rays coming from atomic explosions have a shorter wavelength than x-rays.
The frequency of x-rays is its velocity divided by wavelength:
Frequency = Velocity / Wavelength
The amplitude of an x-ray is equivalent to its intensity or brightness. Just like a bright visible sunlight can cause a burn, so too can an intense x-ray burn the skin.
Interactions with matter
The way the various types of electromagnetic radiation interact with matter is determined by their wavelength. Since x-rays have a very short wavelength, they have different characteristics than visible light. The most interesting characteristic of x-rays is their ability to pass through many materials, as well as how the radiation is stopped by materials like lead.
Passes through things
They easily pass through soft body tissues, but they are somewhat blocked by hard material like bones.
X-ray of a person's head
Stopped by lead
X-rays are absorbed by dense materials such as lead and uranium, such that they can penetrate only a short distance into the material. This is why lead shielding is used to protect people from excessive exposure to x-rays.
The thickness of the shielding is determined by the voltages used to generate the x-rays, which in turn determines the amplitude and wavelength of the radiation. For x-rays generated by peak voltages of 75 kilovolts (kV), a thickness of only 1 millimeter (mm) or 0.039 inches of lead shielding is sufficient to stop the x-rays. But for x-rays generated with 900 kV, a thickness of 51 mm or 2 inches of lead shielding is required.
Effect on matter
The effect x-rays have on matter initiating chemical effects, such as exposing photographic film, and ionizing atoms that can cause harm to living tissue.
An important characteristic of x-rays is that they will expose photographic film, even if it is in a container. That is why you do not want to put a camera with film through an airport x-ray machine.
Thus, if a beam of x-rays passes through your body and exposes some film, a faint outline of your soft tissues will be seen, but your bones will show up distinctly. If a sheet of lead was put between the source of the x-rays and the film, it would not be exposed.
A dental x-ray requires holding a piece of film behind the teeth
Medical and dental x-ray technicians often wear a badge that contains photographic film to monitor how much stray x-ray radiation they receive in their jobs. The film in the badge is checked periodically to see how much exposure was received.
X-rays can also be detected electronically, with a detector similar to that used in a digital camera to record visible light.
Since x-rays have so much energy because of their short wavelength, they can ionize atoms they strike. In many situations, that does little or no harm. But when atoms in living cells are ionized, it can kill the cell or cause mutations. For this reason, exposure to x-rays should be controlled so as to keep it at a safe level.
X-rays have waveform characteristics of velocity, wavelength, frequency and amplitude. Many materials are transparent to x-rays, while lead and other dense materials will not transmit the radiation. X-rays can be detected with photographic film, similar to visible light. Another effect x-rays have on matter is that they can radiation damage to living tissue by ionizing atoms.
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