free-air ionization chamber
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free-air ionization chamber[¦frē ¦er ‚i·ə·nə′zā·shən ‚chām·bər]
An ionization chamber in which the ionizing radiation is limited by a diaphragm, so that ionization is detected in a region of accurately known volume, away from the electrodes and other internal parts of the equipment.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.