Radiation and the Human Body


Interaction of radiation with matter

Electromagnetic spectrum

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Transparency

You can see for many miles through clear air and a clear piece of glass obviously is transparent to the wavelengths of visible light. The air is fortunately not transparent to the ultraviolet rays from the sun, though increasing transparency from ozone depletion is a concern. The clear piece of glass is transparent to visible light because the available electrons in the material which could absorb the visible photons have no available energy levels above them in the range of the quantum energies of visible photons. The glass atoms do have vibrational energy modes which can absorb infrared photons, so the glass is not transparent in the infrared. This leads to the greenhouse effect. The quantum energies of the incident photons must match available energy level gaps to be absorbed.

Interaction of radiation with matter

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Ionizing Radiation

Ionization is the ejection of one or more electrons from an atom or molecule to produce a fragment with a net positive charge (positive ion). The classification of radiation as "ionizing" is essentially a statement that it has enough quantum energy to eject an electron. This is a crucial distinction, since "ionizing radiation" can produce a number of physiological effects, such as those associated with risk of mutation or cancer, which non-ionizing radiation cannot directly produce at any intensity.

Although the precise ionization energy differs with the atom or molecule involved, a general statement is any radiation with quantum energy above a few electron volts is considered to be ionizing radiation. The threshold for ionization lies somewhere in the ultraviolet region of the electromagnetic spectrum, so all x-rays and gamma-rays are ionizing radiation. All forms of nuclear radiation are also ionizing radiation because of their extremely high energies.


Interaction of radiation with matterNuclear radiation as ionizing radiation
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