S appear to remain in the surface inal site of contamination over an and vertical turbulence tend to » obscuring effects of these factors i masses. terials introduced into the sea was wetok Atoll. Measurements were an one hour after the detonation, > depths to 300 m were taken over radioactive material in the water particulate fraction greater than is than 0.45 u. The distribution of times is shown in Fig. |. During dioactivity was in the top 25 m. hat through the upper edge of the me-eighth that at the surface. At — 6 HouRS tenn 28 HOURS seseeeaes 4&8 HOURS want 28 hours the radioactivity was distributed throughout the upper half of the mixed layer, and dropped in value rapidly between the depths of 50 m and the upper edge of the thermocline at 100 m. At 48 hours the major part of the total radioactivity was concentrated at the upper edge of the thermocline (100 m); the activity fell to a low value at approximately 150m and then rose gradually to a level approximately one-half that at 100m. Thus the radioactivity was distributed throughout the mixed layer between 28 and 48 hours. Probably at no time, however, was it evenly distributed throughout the mixed layer. The distribution of activity with depth for the particulate fraction and the soluble-colloidal fraction at the three times following contamination is shown in Fig. 2. During the first 6 hours approximately one-fourth of the radioactivity was in the particulate fraction and was located in the top 25 m. The radioactivity associated with particles at this time was highest in the top 15m of water, and a lower level of activity (approximately one-third of the radioactivity at the surface) was at approximately 50 m depth. At 28 hours only one-eighth of the total radioactivity was associated with the particulate fraction, and the major part of the total activity was located in the top 60m of water. The two peaks of activity noted in the particulate fraction at 6 hours had migrated downward a distance of approximately 50 m each during the 22-hour period, and the deeper peak of activity coincided with the lower edge of the mixed layer. At 48 hours a major part of the radioactivity in both fractions was concentrated at a depth of 100 m (at the upper edge of the thermocline). At 300 m the radioactivity in both the particulate and the soluble-colloidal fractions rose to a value of about one-half that at 100 m. At 48 hours the particulate activity accounted for approximately twofifths of the total. During the period 6—28 hours following detonation, the activity associated with particulate matter dropped from one-fourth to one-eighth of thatin the soluble$0 50 m 40 fF — 6 Hours ---- 28 Hours ACTIVITY see tea HOURS ASSOCIATED WITH PARTICLES 48 % oF 30 20 + 5 100m 10 renee! ent dd HourRSsS -colloidal activity with depth at 6, 2rwater detonation AFTER DETONATION Fig. 3 Percentage of radioactivity in sea-water in the particulate form at different depths with increasing time lll a7 oR pote ae