in which no reflected energy illuminates the target, only that radiated by the source. Under actual conditions where microwave radiations at fairly high densities are encountered by human beings, for example, aboard ships, in or about aircraft, or near ground-based radars, there are nearly always reflective surfaces that could reflect additional en- ergy on a biological target. Unfortunately, addi- tional concentrations of reflected energy may not be detected by densitometers because of their high directional sensitivity. A radio-frequency field that measures low in density may actually contain significant levels of energy. Such was the finding in a collaborative investigative venture by the engineer Arthur Guy and psychologist Susan Korbel. Guy and Korbel (Note 3) radiated models of rats in a 500-MHz microwave field that, as care- fully measured by several densitometers, appeared to have an incident density near 1 mW/cm2 Activity levels of radiated rats had earlier been found to differ reliably from levels of controls after exposures at this low density (cf. Korbel, 1970; Korbel-Eakin & Thompson, 1965). Guy and Korbel were aware that the exposures had taken place in an electrically shielded enclosure. Since the shielding created the possibility of un- detected reflections and concentrations of energy within the enclosure, thermographic studies were performed on radiated models. Extremely high concentrations of thermalized energy were found, some of sufficient density that they would result in focal burns in the heads and extremities of live animals. The hot spots observed in the models would be less severe in a live animal because of partial thermal equilibration by the circulatory system; of major interest is that the total amount of energy absorbed by the models was often much higher than what would be predicted from the mea- sured density of the microwave field. Guy and subjects. The quantity of microwave energy ab- sorbed by an animal in such a cavity can be closely metered and controlled (Justesen, Pendleton, & Porter, 1961; Justesen & Pendleton, Note 4). Justesen, Levinson, Clarke, and King (1971) trans- formed the cavity (a Tappan microwave oven) • -Oven door ^Photooperondum . Figure 3. Plexiglas conditioning chamber lo- cated in a multimode cavity. (Microwave energy enters the cavity from the wave guide and is mixed by a slowly rotating mode stirrer so that it im- pinges on the animal in the chamber from all angles. A photodetector of the licking response, a liquid feeder, and a special grid for presenting electrical shocks to the feet provide for operant and/or respondent conditioning of an animal during radiation. A steady stream of cooled air flows from an air duct into the cavity and the chamber and out of small holes in the door of the cavity. Temperature in the chamber is monitored via an electrically shielded thermistor.) AMERICAN PSYCHOLOGIST • MARCH 1975 • 39.7 into an operaht and respondent conditioning cham- ber that permits radiation during behavioral test- gram (J/g) serve as the dosing unit of total ab- sorbed energy. Since the joule per second is the
Posted on: Tue, 15 Oct 2013 03:04:35 +0000
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