half-life
Time needed for one-half of the nuclei in a radioisotope to emit its radiation. Each radioisotope has a characteristic half-life, which may range from a few millionths of a second to several billion years. See radioisotope.
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Chapter 3 - Science, Systems, Matter & Energy
genes
Coded units of information about specific traits that are passed on from parents to offspring during reproduction. They consist of segments of DNA molecules found in chromosomes.
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gamma rays
Form of ionizing electromagnetic radiation with a high energy content emitted by some radioisotopes. They readily penetrate body tissues. See also alpha particle, beta particle.
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frontier science
Preliminary scientific data, hypotheses, and models that have not been widely tested and accepted. Compare consensus science.
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Freons
See chlorofluorocarbons.
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flows
See throughputs.
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fissionable isotope
Isotope that can split apart when hit by a neutron at the right speed and thus undergo nuclear fission. Examples are uranium-235 and plutonium-239. See nuclear fission.
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first law of thermodynamics
In any physical or chemical change, no detectable amount of energy is created or destroyed, but in these processes energy can be changed from one form to another; you cannot get more energy out of something than you put in; in terms of energy quantity, you cannot get something for nothing (there is no free lunch). This law does not apply to nuclear changes, in which energy can be produced from small amounts of matter. See also Second law of thermodynamics.
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first law of energy
See first law of thermodynamics.
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feedback loop
Circuit of sensing, evaluating, and reacting to changes in environmental as a result of information fed back into a system; it occurs when one change leads to some other change, which eventually reinforces or slows the original change. See negative feedback loop, positive feedback loop.
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