tems ee Padded o colloidal form. However, at 48 hours particulate radioactive material accounted for two-fifths of the total radioactivity. A major part of this activity was concentrated at the upper edge of the thermocline. Fig. 3 shows the percentage of radioactivity in the sea water in the particulate form at different depths with increasing time after detonation. In the two samples collected within the ‘mixed layer (0 m and 50 m) the percentage of particulate radioactivity in the water decreased between 6 and 28 hours androseslightly at 48 hours. However, in the upper edge of the thermocline (100 m) and inside the thermocline (300 m) the percentage of particulate activity rose at an increasing rate during the interval 6—48 hours post-detonation. The percentage of radioactivity in the particulate form at 300m rose at an exponential rate from a value of approximately 1% at 6 hours to 37% at 48 hours. During the interval 6—28 hours the leading edges of the particulate radioactivity moved downward approximately 50 m, and thoseof the soluble-colloidal activity approximately 60 m. During the time 28-48 hours the leading edges of both the particulate and the soluble activity in the mixed layer descended approximately 50m. Thus the activity in the mixed layer during the entire period of sampling descended at a rate of approximately 2.5 m per hour. Below the mixed layer, however, the radioactivity in the particulate form appeared to descend much faster than that in the mixed Jayer. During the period 28—40 hours the peak of radioactivity moved down at least 200 m, 1.5 WALTON SURVEY (JUNE It- 21, 1956) 1.4] 1.3 4.28 4 DAYS TO 23 GAYS AFTER CONTAMINATION otieMARSH SURVEY { SEPT. 1-20, 1956) G WEEKS AFTER END OF TEST SERIES ----- COLLETT SURVEY {AUG.8-14, 1958) AT END OF TEST SERIES ee SILVERSTEIN SURVEY (SEPT. 3-13, 1958) 4.44 J WEEKS AFTER ENC OF TEST SERIES 1.0F 245 C45 aT 8 FP 0 2550 RANGE OF UPPER E£0GE OF THERMOCLINE THERMOCLINE 100 i“ ra * 300 4ao DEPTH IN METRES Fig. 4 Ratio of activity in particulate fraction to that in soluble plus colloidal fraction in all water samples from four oceanic surveys made during 1956 and 1958 between the Eniwetok Test Site and Guam 112 on ~i”