Report to the Scientific Director - Nature, Intensity, and Distribution of Fall-Out from Mike Shot, Project 5.4A, November 1952 (Ivy Operation)

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Report to the Scientific Director NATURE, INTENSITY, AND DISTRIBUTION OF FALL-OIJT FROM MIKE SHOT U. 9. Naval Radiologlcrrl Defense Laboratory San Francisco, California This document rictecldata 81)dew of it8 contenta in any mamer to aa tmauthorized per8on is pro-

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The physical and chemical properties of the particulate matter deposited following Mike shot, Operation Ivy, together with its distribution in time and area, were investigated. Total fall-out and differential fall-out collectors were installed on islands, anchored lagoon floats, and free-floating sea stations about the detonation point. All collected samples were analyzed at the U. S. Naval Radiological Defense Laboratory. All the samples of primary fall-out collected were in a cross-wind direction from the detonation point; secondary fall-out samples were collected to distances of 600 miles from this point. Radiation levels as high as 800 r/hr at 2 hr were found 3 miles from the detonation point. No positive evidence of the occurrence of a base surge was found. The primary fall-out. was a dry or semidry particulate of compounds of calcium with entrapped fission products. This particulate underwent a chemical change when in a sea-water environment, causing it to become very firmly attached to any surface it touched. Particles were found ranging in dia.meter from less than 10 p to more than 5000 V. There was no indication of size fractionation of the particles with distance and only meager evidence of size fractionation with time. The quantity of primary fall-out varied from more than 20 g/sq ft at 4 miles cross wind to 0 g:/sq ft at 15 miles from the shot point. The time of arrival along the cross-wind direction was completely independent of the distance from the shot point. The secondary fall-out originating in the stratosphere was less than 25 y in diameter and arrived 2 to 5 days after shot time. None of the stations where secondary fall-out was collected reported a gamma dose rate greater than 10 mr/hr.

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3.1.2 Mechanical and Electrical Restrictions . 3.1.3 Pressure and Thermal Effects Expected from the Design of Stations .... 3.10.8 RCeumi of the Operationof the Inetrumente .

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4.2.2 Chemical Composition of the Particulate . . 4.2.3 Leaching of Activity ...... 4.2.4 Decay of Activity ....... 4.4.1 Particle-size Distribution as a Function of Time . 4.4.2 Particle-size Distribution as a Function of Distance 4.5 Time of Arrival of Particulate .... 4.5.3 Distribution of Activity with Time . . 5.2 Levels of Radioactivity ..... CHAPTER 6 METEOROLOGICAL CONSIDERATIONS AND 6.4 The Effect of Vertical Mixing .... Analysis of the Differential Fall-out Samples . Radiochemical Analysis of Selected Samples .

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APPENDIXB TABULATED DATA ...... B.3 Summary of Data Collected on the Free-floating Sea Stations APPENDIX D OPERATIONAL ORDERS AND PERSONNEL D.2.1 Design of Instruments and Equipment D.2.2 Laboratory Work on Samples. 2.2 Outer Island Stations .... Incremental Liquid Fall-out Collector Recording Rain Gage .... A Typical Land Station ... A Typical Lagoon Station ... 4.1 Fall-out Gamma Pattern at 2 Hr as Would Be Experienced 4.2 Particles Collected by a Differential Fall-out Collector .

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Plan View of a. Typical Fall-out Particle Deposited on Inverted View of Typical Particles Removed from Beta and Gamma Decay Curve from 15 to 90 Days After Shot Variation of Cross-wind Fall-out with Distance from Size Distributign of Radioactive Particles as a Function of Time and Distance. ....... 5.2 Periods of Secondary Fall-out at the Outer Island Stations CHAPTER 6 METEOROLOGICAL CONSIDERATIONS AND 6.1 Predicted Ama of Primary Fall-out ..... APPENDIX C ELECTRONIC TRIGGER MECHANISM C.l Schematic Diagram of the Electronic Trigger Mechanism. 3.1 Instrumentation at Land and Lagoon Stations at Eniwetok Atoll . 4.1 Spectrographic Analysis of the Radioactive Particles Removed from 4.2 X-ray-diffraction Analysis of Radioactive Particles Removed from APPENDIX B TABULATED DATA B.l Weight and Activity of Solid Fraction of Collected Material . . B.2 Volume and Activity of Liquid Fraction of Collected

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The gamma-radiation hazard associated with radioactive debris from nuclear explosions constitutes an important capability of atomic weapons. The degree to which this capability can be exploited depends upon the magnitude of the militarily significant gamma-radiation fields produced and upon the ability to predict the location and extent of these fields. The phenomenon, commonly referred to as fall-out, varies with weapon yield and conditions of detonation. The present work proposes to extend the knowledge of such variations by investigating the fall-out material from Mike shot, Operation Ivy. The information derived will be useful for both offensive and defensive planning. Fall-out from surface and subsurface nuclear detonations has been documented at previous test programs. The phenomenon was first observed after the detonation of the Alamogordo device in 1945.’ Since that time it has become well established that the gamma hazard resulting from fall-out must be seriously considered as a problem of military significance for all types of detonations except the air burst. * Fall-out was first fully documented at Operation Jangle, but limited data we.re obtained at Operations Crossroads and Greenhouse. The fall-out study conducted at Operation Greenhouse revealed significant residual contamination from the Dog and Easy tower shots. This investigation was the first comprehensive study of fall-out forecastirqg.2 These forecasting techniques, together with the work of J. 0. Hirschfelder,s are the basis for the theories presented in the discussion of the fall-out at 1.1.2 At Operation Jangle The surface shot at Operation Jangle more nearly represented a miniature Mike shot than any previous detonation. Fall-out studies were made at this operation, and complete data were obtained to a distance of several miles from ground zero.’ The results were used in planning for Operation Ivy, and certain data to be found herein were extrapolated from information gained from the fall-out studies of Operation Jangle. *An air burst is defined for the purposes of this report as an explosion detonated at an elevation of such height thatt the resulting fireball at no time touches the surface of the earth.

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The gathering of fall-out data from Mike shot was a logical extension of previous fall-out documentation. The nature of Mike shot, Operation Ivy, made the study of fall-out extremely important. The yield from this shot was expected to exceed by many times that from any previous detonation, and consequently the cloud and associated debris were expected to rise to much greater heights. The additional fact that the shot was to be a surface explosion indicated the possibility of serious fall-out over large areas. The present work (Project 5.4a) was designed to accomplish the following specific ob1. To measure the amount, distribution, and particle size of radioactive fall-out following Mike shot at Operation Ivy. 2. To determine at a limited number of close stations the rate of arrival of inert liquid or solid materials and asa~ociated radioactive materials. 3. To determine the particle-size fractionation of the radioactive fall-out with time and 4. To analyze the base surge, if formed, for activity and to correlate this information with the fall-out data. 5. To correlate the fall-out pattern obtained with that predicted from a knowledge of the meteorological conditions and atomic cloud behavior. 6. To calculate from the intensities of radiation from fall-out the radiation field levels which would have been observed if the fall-out had occurred over extended land areas. Government Printing Gffice, Washington, 1950. Charles E. Adams, Fall-out Phenomenology, Greenhouse Report, Annex 6.4, WT-4, August Government Printing Office, Washington, 1950. *Full attainment of the objectives of this project was not possible because of operational restrictions imposed at a late date. See Appendix D, Tab A (revised) to Appendix I to Annex V.

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Preliminary estimates of the extent and intensity of fall-out expected from Mike shot varied by as much as an order of magnitude. Since no one estimate could be assigned a high degree of confidence, plans were bae’ed on the maximum prediction. Providing instrumentation for extensive areas, many of which were over open water, presented a difficult logistic problem. Since it was not practical to locate stations at great distances over 360’, a forecast was made of the most probable wind pattern expected at shot time, and this was used as a basis for laying out the collecting station array. Atoll island stations, anchored lagoon stations, distant island stations, and an array of free-floating sea stations oriented in the quadrant having the highest probability of receiving fall-out were used. An examination of the geographical location of Eniwetok Atoll, and in particular Elugelab Island, on which the shot occurred, shows that the number of land masses available for fallout studies was extremely limited (Fig. 2.1). Beyond Eniwetok Atoll, the following were the only logistically acceptable locations for these studies: Guam, about 1000 miles to the west; Wake, about 600 miles to the northeast; Bikini, about 190 miles to the east; Kwajalein and Majuro, to the southeast about 300 and 600 miles, respectively; Ku&e, about 400 miles to the south; and Ujelang and Ponape, to the southwest about 150 and 300 miles. Stations were established on the following islands of Eniwetok Atoll: Bogallua (Alice), . Stations were also located on Bikini, Kwajalein, Majuro, Ponape, and Kusaie (Fig. 2.2). A detailed description of equipment used at each of these points is given in Chap. 3. Emplacements for the land stations on Eniwetok Atoll were constructed by Holmes and Narver from specifications furnished by project personnel. Stations outside the Atoll required no special installations. On Majuro, Ponape, and Kusaie, task force weather units assumed responsibility for the operation of the stations. Since the. equipment on Bikini and Kwajalein was more extensive, these stations were operated by project personnel. A station on Wake had been planned, but it was abandoned because of typhoon damage. No station was planned for Guam since it was assumed that the possibility of fall-out there was very remote. The island of Ujelang to the southwest is the nearest island to Eniwetok. Although it was not possible to locate a station there, one was installed aboard a Navy LST which was . standing off the island to evacuate island personnel if such action was necessary. Transportation of equipment and personnel to each of the islands was made by periodically

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‘Twenty stations within the Eniwetok Lagoon (Fig. 2 .l) were mounted on standard Navy 60-man life floats fastened to moorings provided by Holmes and Narver. The anchor for each mooring was a 4000-lb concrete block to which a discarded oil drum was attached as a float. A l-in. wire cable, which was one-third greater in length than the depth of the water, was shackled to the ancho:r and made fast to the float by passing it through two pad eyes welded to the drum and then secured by clamping on itself. An LSU with a crane aboard placed the anchors. Engineers stationed on two of the Atoll islands maintained radio contact with the LSU and directed it to the proper positions. All instruments were installed aboard the life floats at Parry Island. These floats were then loaded aboard an LSU and taken to the designated mooring. Once at the mooring a crane placed the floats in the water. An LCM then towed the float to the mooring, where it was secured to the pad eye on the top of the drum with 100 ft of 3-m. manila line. This phase of the operation was completed by M-15 day. Two teams using LCM’s visited each location approximately one week after the initial installation and again on either M-3 or M-2 day for final adjustment of the equipment aboard the floats. A dinghy, which had been towed to the location, was used to board the floats to avoid any possible damage to the equipment should the LCM and the float bump together. Of a total of 20 Ube floats, two were discovered to be missing at the end of one week. In each instance, both the float itself and the oil drum to which it was fastened were missing. It is assumed that the failure occurred where the cable was clamped on itself after passing through the pad eyes on the drum or at the anchor. During a storm on the night of M-4 day and also on M-3 day, four life floats broke loose. Although a 3-m. manila line was used, it was chafed apart about 3.5 ft from the shackle. It is believed that, as the float swung, the line became wedged in the V created by the clamping of the wire underneath the drum. Gn M-2 day a short section of wire was added to the mooring lines to eliminate further difficulties of this kind. Two of the four floats which broke loose lodged on the reef only about one-quarter mile off their original position, and samples were recovered from them after the shot. Because of the depth of the water surrounding Eniwetok Atoll, it was not operationally feasible to place any number of moored floats outside the lagoon. The 500-fathom curve runs approximately 1 mile from the edge of the reef. By 5 miles the depth increases to about 1000 fathoms and beyond that rapidly approaches depths between 2000 and 3000 fathoms. The use of ships in the area and a type of free-floating station were the obvious solutions for extending the collecting area. Fall-out stations were installed on 10 task force ships [see Appendix D for Appendix I, Tack Group 132.1 (TIG132.1) Operation Order]. A description of the collectors used on shipboard will be found in Chap. 3. Mounting the collectors aboard the ships was relatively easy. Operational movements of the vessels in a few instances required close coordination between ship and project personnel in placing the equipment aboard, instructing ship personnel in operation of the equipment, and the recovery of the samples for air shipment to the United States. The additional variable introduced in the measurements by the movement of the collector was virtually elilminated by keeping a careful record of the ship’s position at stated infer-

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vals, Since all task force ships were equipped with a washdown system, some difficulty was encountered in mounting the collectors at a position which was above the spray from this system. However, location on the highest platform on the mainmast was satisfactory. One reason for approving this phase of the project was to ascertain the operational feasibility of a system of free-floating stations (Fig. 2.3). A system of free-floating stations to measure fall-out over sea areas was first proposed during the early planning for Operation windstorm, but these tests were subsequently moved to Nevada, and the scheme was never tried. From the start it was realized that such an undertaking presented many problems. As first conceived, the pllan called for the use of a raft which would be large enough to support the collection devices and provide a working platform for personnel to make instrument adjustments after the ratft was in the water. As the time approached for establishing definite instrument requirements, information on the number and types of ships which would positively be available for the project was almost entirely absent. Therefore plans were modified to provide for a float smaller than a raft and one which …