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By the end of this section, you will be able to:
  • Describe the biological impact of ionizing radiation
  • Define units for measuring radiation exposure
  • Explain the operation of common tools for detecting radioactivity
  • List common sources of radiation exposure in the US

The increased use of radioisotopes has led to increased concerns over the effects of these materials on biological systems (such as humans). All radioactive nuclides emit high-energy particles or electromagnetic waves. When this radiation encounters living cells, it can cause heating, break chemical bonds, or ionize molecules. The most serious biological damage results when these radioactive emissions fragment or ionize molecules. For example, alpha and beta particles emitted from nuclear decay reactions possess much higher energies than ordinary chemical bond energies. When these particles strike and penetrate matter, they produce ions and molecular fragments that are extremely reactive. The damage this does to biomolecules in living organisms can cause serious malfunctions in normal cell processes, taxing the organism’s repair mechanisms and possibly causing illness or even death ( [link] ).

A diagram is shown which has a white sphere followed by a right-facing arrow and a large sphere composed of many smaller white and green spheres. The single sphere has impacted the larger sphere. A right-facing arrow leads from the larger sphere to a pair of smaller spheres which are collections of the same white and green spheres. A starburst pattern lies between these two spheres and has three right-facing arrows leading from it to two white spheres and a circle full of ten smaller, peach-colored circles with purple dots in their centers. An arrow leads downward from this circle to a box that contains a helical shape with a starburst near its top left side and is labeled “D N A damage.” A right-facing arrow leads from this circle to a second circle, with nine smaller, peach-colored circles with purple dots in their centers and one fully purple small circle labeled “Cancer cell.” A right-facing arrow leads to a final circle, this time full of the purple cells, that is labeled “Tumor.”
Radiation can harm biological systems by damaging the DNA of cells. If this damage is not properly repaired, the cells may divide in an uncontrolled manner and cause cancer.

Ionizing and nonionizing radiation

There is a large difference in the magnitude of the biological effects of nonionizing radiation    (for example, light and microwaves) and ionizing radiation    , emissions energetic enough to knock electrons out of molecules (for example, α and β particles, γ rays, X-rays, and high-energy ultraviolet radiation) ( [link] ).

A diagram has two vertical sections. The upper section has two right-facing, horizontal arrows labeled “Increasing energy, E” and “Increasing frequency, rho symbol,” respectively. A left-facing, horizontal arrow lies below the first two and is labeled “Increasing wavelength, lambda symbol.” Beginning on the left side of the diagram, a horizontal, sinusoidal line begins and moves across the diagram to the far right, becoming increasingly more compact. The lower section of the diagram has a double ended, horizontal arrow along its top, with the left end drawn in red and labeled “Non-ionizing” and the right end drawn in green and labeled “Ionizing.” Below this is a set of terms, read from left to right as “Broadcast and wireless radio,” “Microwave,” “Terahertz,” “Infrared,” “Visible light,” “Ultraviolet,” “X dash ray,” and “Gamma.” Four columns lie below this row of terms. The first contains the phrases “Non-thermal” and “Induces low currents” while the second reads “Thermal” and “Induces high currents, Heating.” The third contains the phrases “Optical” and “Excites electrons, Photo, dash, chemical effects” while the fourth reads “Broken bonds” and “Damages D N A.” A series of terms lie below these columns are read, from left to right, “Static field,” “Power line,” “A M radio,” “F M radio,” “Microwave oven,” “Heat lamp,” “Tanning booth” and “Medical x, dash rays.”
Lower frequency, lower-energy electromagnetic radiation is nonionizing, and higher frequency, higher-energy electromagnetic radiation is ionizing.

Energy absorbed from nonionizing radiation speeds up the movement of atoms and molecules, which is equivalent to heating the sample. Although biological systems are sensitive to heat (as we might know from touching a hot stove or spending a day at the beach in the sun), a large amount of nonionizing radiation is necessary before dangerous levels are reached. Ionizing radiation, however, may cause much more severe damage by breaking bonds or removing electrons in biological molecules, disrupting their structure and function. The damage can also be done indirectly, by first ionizing H 2 O (the most abundant molecule in living organisms), which forms a H 2 O + ion that reacts with water, forming a hydronium ion and a hydroxyl radical:

This image shows a reaction. It starts with H subscript 2 O plus radiation. There is a right-facing arrow which points to H subscript 2 O superscript positive sign plus H subscript 2 O. From the arrow, there is another arrow that curves upward and points to an e superscript negative sign. After the second H subscript 2 O there is another right-facing arrow which points to H subscript 3 O superscript positive sign plus O H superscript negative sign.

Because the hydroxyl radical has an unpaired electron, it is highly reactive. (This is true of any substance with unpaired electrons, known as a free radical.) This hydroxyl radical can react with all kinds of biological molecules (DNA, proteins, enzymes, and so on), causing damage to the molecules and disrupting physiological processes. Examples of direct and indirect damage are shown in [link] .

Two pairs of images are shown and labeled “a” and “b.” In the first pair, a helical structure on the left with a starburst on it middle right side is connected by a right-facing arrow to a sphere composed of smaller green and white spheres. A squiggly arrow points toward the sphere from the upper left and a downward-facing arrow leads away from the sphere to a small circle with a negative sign. In the second pair of images, a squiggly arrow lead to a water molecule while a downward-facing arrow leads away from it to a small circle with a negative charge written on it. A helical shape with a starburst on it middle right side is drawn to the far right and an upward-facing arrow leads to it from the following equation “H, subscript 2, O, plus sign, radiation, yield arrow, H, subscript 2, O, superscript plus sign, plus sign, e, superscript negative sign, down-facing arrow, H, subscript 2, O, superscript plus sign, plus sign, H, subscript 2, O, right-facing arrow, H, subscript 3, O, superscript plus sign, plus sign, O H, superscript negative sign. Below this equation is the phrase “Indirect effect.”
Ionizing radiation can (a) directly damage a biomolecule by ionizing it or breaking its bonds, or (b) create an H 2 O + ion, which reacts with H 2 O to form a hydroxyl radical, which in turn reacts with the biomolecule, causing damage indirectly.

Questions & Answers

what us atomic of molecule
Imhologhomhe Reply
chemical formula for water
Muhammad Reply
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Maryam Reply
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How can water be turned to gas
what's a periodic table
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how does carbon catenate?
obuke Reply
condition in cracking from Diesel to petrol
Brient Reply
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i also
I also
condition for cracking diesel to form kerosene
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what is periodic law
rotimi Reply
periodic law state that the physical and chemical properties of an element is the periodic function of their atomic number
how is valency calculated
Ashley Reply
How is velency calculated
Hi am Isaac, The number of electrons within the outer shell of the element determine its valency . To calculate the valency of an element(or molecule, for that matter), there are multiple methods. ... The valency of an atom is equal to the number of electrons in the outer shell if that number is fou
what is the oxidation number of this compound fecl2,fecl3,fe2o3
Asmau Reply
bonds formed in an endothermic reaction are weaker than the reactants but y r these compound stable at higher temperatures
zille Reply
what is a disproportionation reaction
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folarin Reply
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Richard Reply
chemistry is one of the three main branches of pure science the other two being physics and biology. chemistry deals with the composition properties and uses of matter. it probes into the principle governing the changes that matter undergo.
Chemistry is a branch of science that deals with atom & constitution of substances & d changes they undergo
chemistry is a group of science deals with mater
Hy! I'm Abdul gafar chemistry is a branch of science dat deals with an atom and change they undergo as a result of alterations in d constitution of there molecules
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quame Reply

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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