viewing overall activity distribution, but it is tedious and imprecise for quantifying hole counts and sizes. Microscopic examination of the film with transmitted green light causes the holes which have completely etched through the red film to appear as brilliant spots of light, readily visible at magnifications of 70-125x. Incompletely etched tracks are also visible, but in the interests of speed and simplicity, it was decided to count only those which had etched completely through. If this is done, there is little advantage to be gained from higher magnification. Films were also scanned with the Quantimet analysis system. Although it is no faster than manual counting and requires access to sophisticated instrumentation, this technique permits acquisition and storage in computer-compatible form of quantitative distribution and track dimension information. Agreement between manual and automated counting techniques could be brought to within about 5% if careful attention were paid to setting analyzer detection thresholds to agree with the microscopist's track acceptance criteria; without such effort, differences of about 15% were typical. Representative data are presented in Table 1 and discussed below. Standard source exposures: Table 1 summarizes the results obtained from exposures of films under various conditions to a Pu-plated planchet with 616 dpm 2399240py and 314 dpm 238pu in an active plated area with a diameter of 1.8 cm. All films had both an area exposed to the source (normally through a 12.8 um Mylar energy degrader, although exposures with no degrader and with 1.8 cm of air were also made) and a similar area reserved for blank determination. All completely etched tracks in an area 500-600 mm? contain-~ ing the exposed portion were counted, and a similar count was made in an equivalent blank area. This total count approach was taken to avoid problems with nonuniformity of source distribution; counts made by microscope are coded "M," while those obtained from the image analyzer system are coded "IA." Figures 1-3 are image analyzer plots of the distributions of track diameters (or the diameter of a sphere of equivalent projected area for asymmetric tracks) for representative samples. Figure 1 is the blank of film XXX, Figure 2 is for source exposure XXIX (see Table 1), where Ea ranged from 0 to 3.7 MeV, and Figure 3 is for source exposure XXXV, with an Eo range of 2.05 to 3.70 MeV. Environmental sample exposures: Samples of previously analyzed soils and sediments were used to investigate film sensitivities and exposure techniques for environmental samples. Table 2 gives the results obtained from relatively long exposure of the films to dried but otherwise unprocessed sediments from Bravo Crater in Bikini Atoll lagoon. The film pieces, mounted on slides, were gently covered with sediment (either in direct contact or with an intervening Mylar energy degrader), left for three weeks, and then rinsed off and etched. Portions of each film were selected at random, measured, and the tracks counted. For one measurement, a gridded slide was used and the tracks in each square millimeter 596