: ~ ee ee eee tt oRaee ee ee S22een REmemetre CHAPTER 10 RADIOLOGICAL-SURVEY RESULTS EHECALES CT AEM EETIESIPAS TRS yr ys oe 10.1 MIKE SHOT Location: Elugelab Island (Flora), Eniwetok Atoll. Height of burst: Ground surface. Yield: 6 to 12 Mt. Timefired: 0715, Nov. 1, 1952. 10.1.1 Cloud Disposition Twenty-four-, forty-eight-, and seventy-hour trajectories indicated a column of alr 3 miles in height, from 40,000 to 55,000 ft, moving generally east under the tropopause. Below this altitude the cloud column was forecast to move generally west-northwest, whereas, above the tropopause, cloud parcels were forecast to move west. The final observed wind pattern placed all fall-out north of ground zero. Air radex gave an exclusion area bearing clockwise 280° true to 090° true. At H + 70 min the atomie cloud had reached an altitude greater than 120,000 ft and, in ita rapid climb, was forced to billow out at the tropopause level, although continuing to rise to a still greater height. This billowing-out effect reached a distance of 30 miles in diameter in regenTy a] proximately 40 min and resulted in fall-out as far south as a line between Runit and Ripill iaa‘nda (10 milea). The wind pattern for this shot wae nearly ideal from the Rad-Safe standpoint. 10.1.2 Ground Contamination An initial aerial-survey helicopter became contaminated from radioactive “rain-out™ at Nae r/hr. Similar readings above the blockhouse at Bogallua at an aititude of 1500 ft were 2.5 r/hr. A complete atoll survey was accomplished by helicopter at H + 24 hr and indicated contamination of all northern and weatern islands. The islands of Chinieero, Aniyaanii, Chinimi, Japtan, Parry, and Eniwetok were found free of contamination. These helicopter readings at 25 ft, when multiplied by a factor of 3, gave an approximation of ground readings. The relation between the 25-ft and the ground readings varied between 2 and 4; therefore this factor could not be considered absolute (Fig. 10.1). Self-decontamination of the islands was accomplished by radioactive decay and weathering (Tables 10.1 to 10.25). Weathering effects were most apparent during the first four to five . 37 (Text continues on page 65.) 2 eS FRR a emant H+ 40 min in the vicinity of Dilraa! Island. This rain-out was distinctly muddy in appearance and left a residual contamination of 2 r/hr at H+ 1 hr on the aircraft. meee " A damage survey at H+ 4 hr revealed some approximate intensities at Engebt, Bogon, and Bogallua. Readings on an AN/PDR-TIB meter in a helicopter 150 ft above the center of Engebi were greater than 50 r/hr. Similar readings 500 ft above the blockhouse on Bogon were 10