Non-Ionizing
Radiation
Electromagnetic
Radiation
Electromagnetic radiation, also known as
non-ionizing radiation, is transmitted by many devices that are used in
everyday life. Radio, television, microwave oven are examples for such devices
that make use of electromagnetic waves. Radio waves, microwaves, visible light,
and x rays are all examples of electromagnetic waves that differ from each
other in wavelength. Wavelengths range from long (3 x 10 8 m) and
very low frequency (1 Hz) to short (2 x 10-15 m) and very high
frequency (10 23 Hz). There are many sources of electromagnetic
radiation energy. Sun and fires are natural sources, others, like microwaves,
radio transmission, lamps and lasers are manufactured sources.
Figure 1.
Electromagnetic waves.
(a) Longer
wavelength; (b) shorter wavelength.
Figure 2.
Frequency and the wavelength
Electromagnetic waves are produced by the
motion of electrically charged particles. These waves are also called
"electromagnetic radiation" because they radiate from the
electrically charged particles. They travel through empty space as well as
through air and other substances. Scientists have observed that electromagnetic
radiation has a dual "personality." Besides acting like waves, it
acts like a stream of particles (called "photons") that have no mass.
The photons with the highest energy correspond to the shortest
wavelengths.
The full range of wavelengths and photon
energies is called the "electromagnetic spectrum." The spectrum is
divided into several bands; gamma rays, x-rays, ultraviolet, visible, infrared,
microwave, television and radio waves, induction heating and power waves.
Electromagnetic
Spectrum; Non-Ionizing and Ionizing Radiation Wavelengths and Frequencies
The electromagnetic spectrum covers a wide
range of wavelengths and photon energies. Light used to "see" an
object must have a wavelength about the same size as or smaller than the
object. Look at the picture of the electromagnetic spectrum. See if you can
find answers to these questions:
1.What kind of
electromagnetic radiation has the shortest wavelength? The
longest?
2.What kind of
electromagnetic radiation could be used to "see" molecules? A cold virus?
3.Why can't you
use visible light to "see" molecules?
Figure 3. Electromagnetic spectrum
Some sources of radiant energy such as ionizing
radiation have energy levels high enough to ionize atoms or molecules or break
the bond of molecular elements. Gamma and x-ray are examples for the type of
electromagnetic radiation where the frequency of the electromagnetic radiation
is high enough to break these bonds and change the atomic and molecular
structure of the materials. Photon energies of electromagnetic radiation are
proportional to radiation frequency and inversely proportional to wavelength.
On the electromagnetic spectrum X-ray and gamma ray represent the highest
frequencies and the lowest wavelengths and also the highest photon energy which
is needed to change the molecular or atomic structure of a material that is
exposed to this type of radiation. (As the electromagnetic wave frequency
increases, the energy level of the photons also increases).
At low frequencies the energy level of the
photons becomes very low. Infrared, microwaves, radio waves are the examples
for this type of radiation. Because of very low level of photon energy it is
not possible to change the atomic or molecular structure of the materials that
are exposed to this type of radiation, which is known as non-ionizing
radiation.
Some effects of electromagnetic waves that are
dependent on frequency include visibility and penetration and heating of
materials and tissue. Some properties apply across the spectrum, for example,
energy from radiation source diminishes as a function of distance squared.
Although energy levels for non-ionizing
radiation do not affect molecular structure, non-ionizing radiation can affect
biological tissue molecules, often producing heat. Heat most easily effects certain tissue, like that of the eye because the eye
has little blood circulation and little ability to remove heat through blood
movement. Tissue absorbs some wavelengths, but for other wavelengths, tissue is
essentially transparent. The depth of penetration for absorbed wavelengths
varies as well. Figure 3 shows the general absorption properties of the eye for
electromagnetic radiation.
Figure
4. General absorption properties of the eye for
electromagnetic radiation.
Non-Ionizing
Radiation Characteristics:
Electromagnetic radiation
Does not ionize atoms
Does not break down the
molecules into their elements
Even though the energy
level of non-ionizing radiation photons does not affect the molecular structure,
it can harm biological tissue by producing high levels of heat.
Major target organs are eyes
and skin
Sources and industrial
applications are communication systems, medical equipment, microwave ovens,
electrical heating elements, radiative heat ovens,
lasers, visual display terminals, low frequency electric and magnetic fields,
sun (ultraviolet radiation), heliarc welding, xenon
lamps...
Electromagnetic waves travel through vacuum
with a speed of 300,000 km/sec . Visible light has a
wavelength of 4x10-7 m to 7x10-7m.
C = Speed of
visible light (m/sec)
l =Wavelength (m)
f = frequency
and the speed
is equal to:
c =l x f
Using this equation we get f:
f = c / l
for the speed
of light , c=300,000,000 m/sec and the wavelength (l ) of 4x10-7 m to 7x10-7m,
we can find the upper and lower level of frequencies (f) that the visible light
travels.
For l
=4x10-7 m the frequency is f=7.5 x1014 (Hz) and for l =7x10-7m, the frequency is
f=4.3x1014 (Hz)
More reading materials can be found at the
following sites:
How Is
Seeing Related to Wavelength? Click here for the answer.
Last update: January
9, 2007
By: Serdar Z. Elgun