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<br /> thereby display a net negative charge. Such elec- As mentioned above,ionization of atoms in DNA
<br /> rrically unbalanced atoms are called ions.They molecules can have profound consequences.That
<br /> usually try to return to an electrically neutral state, is why ultraviolet rays,X-rays,and gamma rays
<br /> if possible.This makes them highly reactive chem- can be so dangerous.
<br /> ically,and ions can behave in ways that 4. Absorption and Reflection
<br /> neutral atoms do not.
<br /> Often,two or more atoms enter into electron- When a radio wave strikes a material,how the
<br /> wave interacts with that material depends on the
<br /> sharing arrangements for mutual benefit.This
<br /> material's electromagnetic characteristics.For
<br /> binds the atoms into a molecule.Two hydrogen
<br /> acorns and one oxygen atom sharing electrons form example, if the material is not a good conductor
<br /> of electricity,the material will be essentially trans
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<br /> a water molecule.More complicated organic
<br /> parent to the radio wave.The wave will pass
<br /> molecules,comprising atoms of carbon,hydrogen, through it largely unimpeded,and will not affect
<br /> and certain other elements,are the stuff of life. the material.If the material is a very good
<br /> 2. Cells conductor of electricity,the material will reflect
<br /> the radio wave with little loss of signal power.If
<br /> Each human being is a collection of millions of
<br /> living cells,many of which group together as an the material is somewhat conductive,some signal
<br /> organ to perform an essential function.Each living power will be reflected,some will be absorbed by
<br /> cell, in turn, is a large collection of organic mole- the material,and the rest will pass through the
<br /> cules.A cell membrane or cell wall forms the materia(.
<br /> boundary between a cell and its surroundings.. 5. Thermal and Athermal Nonionizing Exposures
<br /> Inside the cell wall is a viscous material called Nonionizing photons (radio,infrared,and visible
<br /> cytoplasm.Unlike nonliving collections of mole- light waves)cannot upset the electrical balance of
<br /> cules, a living cell can reproduce itself. It does so atoms,but they can affect atoms,hence molecules, •
<br /> through a splitting process called fission.A cell and hence living tissue in some ways.We learned
<br /> reproducing itself uses a blueprint stored in genetic
<br /> material in the cell's nucleus.The genetic material above that electric fields can attract or repel elec-
<br /> material
<br /> encoded as a very long sequence of a handful of trically charged particles,and that magnetic fields
<br /> can deflect them.We also learned that electrically
<br /> different organic molecules that bind togetherelectrically
<br /> DNA.So long as the encoded cell plans are not charged electrons orbit the nucleus at varying
<br /> corrupted, the daughter cell will be identical to the distances.
<br /> parent. However,if one or more constituent atoms A radio wave's electric and magnetic fields,which
<br /> in an organic molecule becomes ionized,it can alter switch polarity at the radio wave's frequency,can
<br /> that molecule's behavior. Ionization of atoms in cyclically affect electrons in orbit about the nucleus.
<br /> DNA molecules can cause profound consequences. The fields can pull the electrons first one way and
<br /> The structure of the DNA can change,and when then the other,but not strongly enough to liberate
<br /> the cell tries to reproduce,a mutation occurs. them from their orbits around the nucleus.
<br /> Through such effects on electrons,as the fields
<br /> 3. Nonionizing and Ionizing Energy
<br /> cycle through their polarity reversals,those fields
<br /> Electromagnetic energy behaves in some ways like can alternately twist and untwist a molecule's
<br /> waves,and in others like particles.As a group of shape,or cause molecules to line up first one way,
<br /> particles,electromagnetic energy travels in units and then another.
<br /> called photons.The amount of energy packed in a Strong nonionizing fields(that is,those from high
<br /> photon depends on the wave's frequency.The radio-wave power flux densities,much higher
<br /> higher the frequency,the greater the energy.A than those to which the public is exposed from
<br /> nonionizing photon is not energetic enough to cellular base stations)can cause water molecules
<br /> knock electrons away from parent atoms.Radio
<br /> in
<br /> waves, infrared,and visible-light waves are non- a measuring cup(or in living cells) CO gyrate
<br /> ionizing.An ionizing photon(an ultraviolet,X,or vigorously and rub against each other Such fields
<br /> gamma ray),which has a much higher frequency can also cause ions to move.The result is a ther410
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<br /> than a nonionizing photon,contains enough energymal effect,a warming of the water in the cup or of
<br /> the cells in living tissue.6 Intense nonionizing
<br /> to strip one or more electrons away from the atom. fields—far stronger than those to which the pub-
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