UNCLASSIFICD "As a result of this data, plans were made to take measurements on the NECTOR shot. A flight was made a N # 13 hours. Because darkness had set in, it was considered inadvisable to fly below 800 feet above sea level. The major part of the flight was taken at 1000 fect in the sector predicted for fall-out. Even The flight was completed at N +17 hours. at 1000 feet the general trajectory of the fall-out could be determined. By dropping down to 800 feet, the measurement could be identified with sea water since the reading increased. "at D+ 1, two flights were sent out. The information was sent by radio to CTG 7.3, where the information was plotted. The path jocated the previous night was again measured, and precise data were secured from the air. Simultaneous surface sea-water samples were taken by sea-going tugs which were placed in the anticipated fall-out zone, "There was no indication of fall-out beyond 150 miles from ground zero. On completion of the runs in the sector of major interest, the aree around ground zero wes swept by a series of chords within circles 25, 50, 100, and 150 miles in diameter. Two more lobes were located, of which one was of reasonably high intensity and pointing towards the west (possibly activity from the stem) and the second faced to the southwest and was of fairly low intensity. All the readings were no _ greater than 2 mr/hr above a background of 1 mr/hr in the planes. A single plane was sent out on D + 2, and the major lobe (NNE) was again located. The activity level had now dropped to 0.1 mr/hr above a background of 1 mr/hr in e plane. The area had spread somewhat, but the zone was clearly indicated. The westerly lobe had practically disappeared except for a small segment 40 miles from the atoll. "One hundred twenty water samples have been brought to the NYOO Health and Sefety Laboretory for enelysis. Weter semples relating to surface end depth were secured by NRDL for the YANKEE shot. The path located by a sea-going tug end the aerial survey ere related; the water samples approximately match the spots where the airplane was flown. "The dete are being enalysed and should be reedy shortly for initiel presentation. "StretosphericAir Dust Sampler - Stratospheric dust samples were obteined on approximately a weekly baSis during the month of April. The sample for April 15 indicated e sharp rise in activity, having a peak reading of approximately 1 a/m/M3. This is approximately 200 times lerger then the normal background readings. This activity decreased to about 50% of maximum value on April 22 and approximetely down to 20% on April 27. It is believed thet this activity was from the March 1 detonation and picked up on its second traverse around the earth. An analysis of the radioactive meteriel indicates that it is approximately 35% strontium-39 and the remainder substantially strontium- UNCLASSIFIED Cae