Part of the mission for the microplot study was to determine whether a good correlation existed between FIDLER measurements and data obtained from radiochemical determinations and to determine whether FIDLER data could be used to calculate inventories. Plutonium radiochemical analytical results typical of the area near the microplot were compared with their respective determinations made in situ by the FIDLER, and made by Ge(Li) spectrometry. Table 1 presents a comparison of those data obtained from the survey. The points to be noted relate to compari- sons of activities in isopleth 2 with those in isopleth 6 and the ratios listed in the last two columns. Activities determined by radiochemistry were used as a basis for comparison. There is an apparent general increase in radioactivity among samples as determined by the FIDLER and Ge(Li) spectromety, which is not necessarily true for the case of radiochemical analysis. If the FIDLER and Ge(Li) spectrometer were detecting the same source of radioactivity, their ratios to radiochemistry should be relatively constant. That condition is more nearly approached in the case of the Ge(Li) and radiochemistry determi- nations for higher activity samples. The lack of consistent agreement between FIDLER results and results from radiochemical analysis performed on the soil samples is partially due to the fact that the FIDLER senses radioactivity from an area about 1 m dia and about 1 cm deep, whereas Ge(Li) spectrometry and radiochemical analyses are performed on a limited sized sample. In order for the FIDLER to serve as an instrument for the determination of inventory, the following requirements would have to be met: 1. The radioactivity must be located in a very thin layer at the surface or 2. the radioactivity must be evenly distributed locally, 3. Americium-241 and plutonium must be equally distributed horizontally and vertically, 4. the ratio of 24lam to plutonium must be known if 24!Am concentrations are 5. vegetation present in the area of measurement must have no influence on the radioactivity-detector geometry, and 6. the measurement area must not have quantities of radionuclides which would interfere with the 60 keV 2*!Am gamma emission. at a known, and constant, depth, to be used to estimate plutonium concentrations, All of the above conditions are rarely met in practice. The FIDLER could serve as a survey instrument to define isopleths but would not provide acceptable data for the determination of inventories of surfacedeposited materials at the safety shot site areas. The FIDLER also can be used in some instances to indicate differences in activities of importance in grouping samples for analysis. The Ge(Li) spectrometer can be used to estimate plutonium where a specific sample to be analyzed is small, contains no interfering radioisotopes, has sufficiently high levels of **1Am, and the ratio of 24lam to plutonium is known; under many conditions, Ge(Li) spectrometry has been used successfully for the determination of 24lam on samples from the safety shot sites. 20