Non-ionizing radiation includes electromagnetic radiation such as radio waves, microwaves, infrared, visible light, and ultraviolet radiation. This radiation does not have enough energy to ionize atoms or molecules, but can still be absorbed, causing excitation of electrons or increasing molecular motion and vibration. Ionizing radiation like X-rays and gamma rays have high enough energies to remove electrons from atoms, causing ionization which can damage biological tissues. The distinction between ionizing and non-ionizing radiation is important as ionizing radiation can directly cause mutation or cancer.

1. Non-ionizing
radiation
Dr. Hiba ZBIB
2015-2016
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2. Non-Ionizing Vs Ionizing radiation
• Radiation that has enough energy
to move atoms to vibrate, but not
enough energy to remove
electrons.
• The process by which a neutral
atom acquires a positive or a
negative charge is know as
Ionization.
• Removal of an orbital electron
leaves the atom positively
charged, resulting in an ion pair.
– Molecule with a net positive charge.
– Free electron with a negative charge.
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3. Nonionizing radiation (NIR)
• The classification of radiation as ionizing is essentially
a statement that it has enough energy to eject an
electron.
• This is crucial distinction, since ionizing radiation can
produce a number of physiological effects, such
mutation or cancer , which non-ionizing radiation
cannot directly produce at any intensity.
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4. Non-ionizing radiation
• Radiation in the visible or longer wavelength range does not
have sufficient energy to ionize an atom, so we classify it as
non-ionizing radiation.
• The threshold for ionization occurs somewhere in the
ultraviolet range, with the specific threshold depending upon
the type of atom or molecule.
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5. Interaction of radiation with matter
• If there are no available quantized energy levels matching the quantum energy
of the incident radiation, then the material will be transparent to that radiation
Wavelength
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6. Interaction of radiation with matter
• The different parts of the electromagnetic spectrum have very different effects upon
interaction with matter.
• Low frequency radio waves: the human body is quite transparent.
• Microwaves and infrared to visible light: you absorb more and more strongly.
• Ultraviolet range: all the UV from the sun is absorbed in a thin outer layer of your skin.
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7. Interaction of radiation with matter
• X-ray: you become transparent again. You then absorb only a small fraction of the radiation, but that
absorption involves the more violent ionization events.
• Each portion of the electromagnetic spectrum has quantum energies appropriate for the excitation
of certain types of physical processes.
• If electromagnetic energy is absorbed, but cannot eject electrons from the atoms of the material,
then it is classified as non-ionizing radiation, and will typically just heat the material.
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8. Molecular absorption processes
• Electronic transitions
• UV and visible wavelengths
• Molecular vibrations
• Thermal infrared wavelengths
• Molecular rotations
• Microwave and far-IR wavelengths
• Each of these processes is quantized
Increasing energy
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9. Microwave interactions
• Quantum energy of microwave photons (0.00001-0.001 eV)
matches the ranges of energies separating quantum states of
molecular rotations.
• Note that rotational motion of molecules is quantized, like
electronic and vibrational transitions.
• Absorption of microwave radiation causes heating due to
increased molecular rotational activity.
•Since the quantum energies are a million times lower than those of
x-rays, they cannot produce ionization.
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10. Infrared Interactions
• The term "infrared" refers to a broad range of frequencies, beginning at
the top end of the microwaves and extending up to the low frequency
(red) end of the visible spectrum.
• The range adjacent to the visible spectrum is called the "near infrared"
and the longer wavelength part is called "far infrared".
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11. Infrared Interactions
• Infrared is absorbed more strongly than microwaves,
but less strongly than visible light.
• The result of infrared absorption is heating of the
tissue since it increases molecular vibrational activity.
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12. Infrared (IR) interactions
•Quantum energy of IR photons (0.001-1.7 eV) matches the ranges of
energies separating quantum states of molecular vibrations.
• Vibrations arise as molecular bonds are not rigid but behave like springs.
•A single molecule can vibrate in various ways; each of these different
motions is called a vibration "mode".
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13. Visible Light Interactions
• The primary mechanism for the absorption of visible light
photons is the elevation of electrons to higher energy levels.
• There are many available states, so visible light is absorbed
strongly.
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14. Ultraviolet interactions
• Near UV radiation (just shorter than visible wavelengths) is absorbed very
strongly in the surface layer of the skin by electron transitions.
• At higher energies, ionization energies for many molecules are reached and
the more dangerous photoionization processes occur.
• Sunburn is primarily an effect of UV radiation, and ionization produces the
risk of skin cancer.

15. Ultraviolet Interactions
• The ozone layer is important
for human health because it
absorbs most of the harmful
ultraviolet radiation from the
sun before it reaches the
surface.
• The higher frequencies in the
ultraviolet are ionizing
radiation and can produce
harmful physiological effects
ranging from sunburn to skin
cancer.
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16. UV LIGHT
• Light with wavelengths between 100 nm and 400 nm.
• The UV spectrum is divided into three regions:
– UVA, 320–400 nm;
– UVB, 280–320 nm;
– and UVC, 100–280 nm.
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17. Sources of UV radiation
• The sun is the largest source of UV radiation; the
sunlight that reaches the earth’s surface consists
mainly of UVA radiation, with a smaller
component of UVB.
• All of the UVC is filtered by the ozone layer, and
thus no UVC reaches the earth’s surface.
• Man-made sources of UV radiation: black light
lamps
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18. X-ray interactions (IR)
• Quantum energies of x-ray photons are too high to be absorbed by electronic
transitions in most atoms - only possible result is complete removal of an electron
from an atom
• Hence all x-rays are ionizing radiation
• If all the x-ray energy is given to an electron, it is called photoionization
• If part of the energy is given to an electron and the remainder to a lower energy
photon, it is called Compton scattering

19. Absorption of radiation by molecules
• Atoms and molecules can absorb
electromagnetic radiation, but only at
certain energies (wavelengths).
• The three groups of lines correspond
to different electronic configurations.
• Certain energies in the visible and UV
regions of the spectrum can cause
electrons to be excited into higher
energy orbitals;
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20. Absorption of radiation by molecules
• Photons in the infrared region of the
spectrum can excite vibrations in
molecules.
• There are many possible vibrational
levels within each electronic state.
• Transitions between the vibrational
levels are indicated by the vertical
arrows on the left side of the
diagram.
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