Fallout Location and Delineation by Aerial Surveys (U) (Operation Redwing - (Project 2.64) (Nyo Program) (Deleted)

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FALLOUTLOCATION Od DELINEATION by AERIAL SURVEYS (U) New York Operations Office Atomic Energy Commission New York, New York 326 US. ATOMIC ENERGY - I

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This report presents the final results of one of the projects participating in the military-effect programs of Operation Redwing. Overall information about this and the other military -effect projects can be obtained from WT- 1344, the “ Summary Report of the Commander, Tasi@nit 3.” This technical summary includes: (1) tables listing each detonation with its yield, type, environment, meteorological conditions, etc.; (2) maps showing shot locations; (3) discussions of results by programs; (4) summaries of objectives, procedures, results, etc., for all projects; and (5) a listing of project reports for the military-effect programs.

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The objectives were to: (1) survey the gamma radiation from fallout-contaminated ocean areas by means of aerial detectors and (2) from the aerial detectors make air-absorption measurements so that the data might be related to the dose rates at 3 feet above the sea. Radiation detectors were mounted in P2V-5 aircraft that surveyed the ocean areas of expected fallout after Shots Cherokee, Zuni, Flathead, Navajo, Mohawk, and Tewa. A control center coordinated all air and surface radiation-survey activities to insure complete coverage of the fallout area. The contamination densities in the delineated areas were related to the percentage of the total yield that prodaced fission products. Gamma -isodose plots were prepared from data obtained during Shots Zuni, Flathead, Navajo, and Tewa. NO fallout could be located following Shot Cherokee and only on atoll islands after Shot Mohawk. Zuni, a land-surface shot, contaminated 13,400 naut miz of ocean with 48 percent of its fissionNavajo, a water-surface shot, contaminated 10,500 naut miz with 50 percent of the fissionproduct yield. After Flathead, another water -surfac? shot, the outer boundary could not#! determined because of contamination of project amcraft on D + 1 day by airborne radioacti~;e material that resuLted in a high background. However, extrapolated values indicate 29 percent of its fission-product yield was present as fallout in the local area. The fallout from the watersurface shots was concentrated primarily in the more remote areas, and a relatively small amount fell close to ground zero. Tewa, a reef shot, contaminated 43,500 naut miz of ocean with 28 percent of the fissionHelicopters and P2V-5 aircraft were used to gather data for air-absorption measurements. The aerial-survey technique may be used directly for radiological surveys over land. O~er the sea, the depth of mixing of the fallout in the water volume must be determined before the survey resu~ts may be converted to equivalent land-fallout contours and contamination-density distributions. Data on depth of mixing was obtained from samp~es of sea water collected by the U.S. Naval Radiological Defense Laboratory and the Scripps Institute of Oceanography. Repeated aerial surveys provided information on the stability of the contaminated volume.

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Patrol Squadron ONE, U. S. Navy, operated the aircraft used for the aerial surveys. The author gratefully acknowledges the diligence and high professional competence which contributed so much to the project’s operations. Commander Kelly, USN, was the Air Officer on the staff of Commander, Task Grou &$.3. His efforts were responsible for the fulfillment of the project’s aircraft requirements. Members of the Health and Safety Laboratory, U.S. Atomic Energy Commission, who participated in the field operations, and whose contributions are gratefully acknowledged are I. Whitney, G. Hamada, S. Tarras and T. French of the Analytical Branch, H. Sadowski and F. Wilson of the Instruments Branch and K. O’ Brien of the Radiation Branch.

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1.3.1 Fallout Contamination of a Water Volume -------------- ---------- 12 1.3.2 Fallout Contan~ination ofa Land Surface ------------------------ 13 2.4.1 Distribution of Contamination in the Sea --------------------- ---23 2.4.3 Stability of Contaminated Area -------------------- -----------23 3.4.1 Gamma Radiationasa Functionof Beta Activity -------------------45

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4,3 Distribution of Contamination in the Sea -------------------- --------56 CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS -------------------- 60 APPENDIX A DERIVATION OF ALTITUDE ABSORPTION APPENDIX C ALTITUDE ABSORPTION MEASUREMENTS DURING -. APPENDIX D ANALYTICAL DATA FROM SAMPLES OF SEA WATER ----------69 Coordinate system of gamma radiation from a water volume -------------- 13 Determination of estimated outer boundary -------------------- ------ 15 Communication routing, Project 2.64 air control -------------------- -- 18 Energy dependence of dose rate response, Top Hat plastic Angular response of Top Hat radiation detector --------------- Summary of 37 pre- and postflight calibrations of Top Hat ~OE-ARalVES

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Ship pattern derived froni data received from Project 2.62 --------------- 41 Effective depth of mixing for fallout in the sea ------------------ ----- 52 4.1 Distribution of falLout contamination, Shots Flathead and Navajo- ----------- 58 4.2 Distribution of fallout contamination, Shots Zuni and Tewa --------------- 58 B.2 Energy dependence of dose-rate response, plastic and D.1 Gamma dose rate at 3 feet related to surface beta activity ------------- J--74 D.2 Depth of mixing from sea. water samples, Shots Flathead and Navajo -------- 75 D.3 Depth of mixing from sea water samples, Shot Tewa ------------------- 75 Altitude Radiation Data over land (Eniwetok Atoll) -------------------- - 26 Sunlmary of Fallout Distribution, Zuni --------------------- -------31 Summary of Fallout Distribution, Navajo ---------------- -----------45 Summary of Depth Samples of Sea Jvater --------------------- ------53 Altitude Absorption Measurements over Land, Old Fission Altitude Absorption Measurements over Land, Fresh Fission Sea Water Sanlples, Shot Flathead -----------------------71 Depth Sampies of Sea M’ater, Shots Flathead and Navajo --------- 73

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The objectives were to: (1) survey the gamma radiation from fallout-contaminated ocean areas using an airborne detector and (Z) make air-absorption measurements so that the data from the airborne detector might be related to [he dose rates at 3 feet above the sea. During Operation Ivy, the USAEC Health and Safety Laboratory (HASL) carried out a program of aerial surveys of the islands outside the Eniwetok Proving Ground (Reference 1). No major fallout occurred on any of these land surfaces. Traces of contamination were clearly discernible from the air, indicating the feasibil~ty of aerial surveys. However, with the meager basic>ata then available, it was not possible to determine whether the contamination from a multi megat~ri shot, namely, Shot h!lke, was primarily deposited as local fallout or remained in the upper leveis of the atmosphere. A similar program of aerial surveys was organized for Operation Castle (Reference 2). It was expanded to include monitoring installations at certain selected islands outside the Eniwetok Proving Ground. Shot 1 deposited appreciable fa~iout on the monitoring installation at wl~gerik. Although heavy fallout was thus documented from, a multimegaton shot, no estimate of the total quantities of contamination in local fallout could be formed. Succeeding shots in this series deposited little contamination on any of the islands. Just before Shot 5 during Operation Castle, it was found that fallout materia! remained suspended in the sea. Radiation detectors were hurriedly mounted in aircraft, and the ocean was surveyed following Shots 5 and 6. The work was necessarily limited by the lack of special radiation detectors, sufficient personnel, and aircraft. Because only one aircraft was avaiLab~e, the survey was confined to the area between 20 and 100 miles from ground zero. However, the rough estimates based on this survey data indicate that each of these shots contaminated about 4,000 miz with somewhat less than half of the~r total fission yield (Reference 3). DOE ARCFII\’ES The experience during Operation Castle indicated special problems that would arise in aerial surveys, particularly in surveys over tile ocean, Navigational correlation would be dlff~cul: to achieve over the open sea on long flights. One aircraft co~ld not cover the widespread areas contaminated after megaton-range shots. Isodose data could not be reduced in the aircraft, although required immediately during the flight period to control the aircraft’s flight pattern. Barometric altimeters are not accurate enough to provide the c!ose altitude control necessary for relating readings of radiat~on to an equivalent surface level. And lastly, the radiation detec - need a fast speed of response, shielding to rnlnimize the contribution of aircraft contarnlnatlon to the reaalngs, and independence fron] the aircraft supply of power for any critical section of the detector. The voltage from the aircraft generators varies over wide limits, and regulation must be &dded separately. Also, it would be highly desirable for the detector to have a lcgzri:h-

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mic response, ... that a wide range of radiation intensity .ld be recorded without a change of The Top Hat aerial radiation detector was developed by HASL to overcome these problems. Units were installed m three AD-5N aircraft and field-tested at the Nevada Test Site (NTS) during Operation Teapot. The AD-5N aircraft used during Operation Teapot were transferred to an aircraft carrier for surveys following the undersea test during Operation Wigwam (Reference 4). A wide range of radiation intensities were encountered in this operat~on. The first pass over surface zero was shortly after H + 11 minutes, and measurements were made which extrapolated to approximately’ 400 r/hr at the surface. At the other extreme, surveys were made at D + 4 days to delineate the edges of the contaminated area, where the dose rates were approximately 0.1 mr/hr. The Top Hat system was modified for Operation Redwing, and additional units were constructed. ~ No changes were made in the basic detecting elements; however, the hermetic sealing was improved in anticipation of the humidity at the Eniwetok Proving Ground. The heat resulting from an atomic explosion vaporizes the products of the explosion and the bomb casing. Soil and water in the vicinity of ground zero are also vaporized and picked up by the updraft produced by the rise of the ball of incandescent gases. On cooiing, the material in the fireball condenses into particles that include the radioisotopes resulting from the fission process and from neu[ron activation of inert rnateriak. The energy released in the explosion will influence not only the quantity of particulate material but also its altitude distribution in the vicinity of ground zero. The portion oi the yield related to the fission process is represented by the amount of radioactive contamination carried by the particles. Once the particles are formed, they fall and, influenced by the winds, will reach the surface displaced from gg@md zero. The radioactive fallout from megaton shots may contaminate thousands of square” miles The shot conditions influence the form and quantity of the fallout. When a shot is exploded on land, a large amount of soil is picked up and much of it is vaporized by the intense heat. This material condenses in a wide range of particle sizes. Some of the radioactive products are condensed around large particles that were picked up in the updraft but not vaporized. These larger particles fall rapidly and reach the surface relatively close to ground zero. When a shot takes place at the surface of deep water, vaporized water can carry some of the activity away from the site. The large particulate fallout encountered in the land shot will be missing, and this will be reflected in the distribution of fallout on the surface. An air shot is one in which the fireball does not touch the surface, so that compared with surface shots relatively Little foreign material is vaporized. Because there are no available particulate on which the fission products can condense, most of the active material remains in the upper atmosphere and little fallout is likely to be detected in the vicinity of the shot site. I 1.3.1 Fallout Contamination of a Water Volume. When the contamination falls into the sea, dispersion and dilution carry much of the material below the surface (Reference 3). The intervening water acts as a shieid between the surface and much of the gamma activity. Thus, the radiation dose rates measured above the surface are reduced many orders of magnitude; however, sensitive detectors can be used to delineate the area of contamination. Also, if samples are taken at various depths, the quantity of radioactivity present can be integrated to Lhe maximum depth of mixing, and in this manner, it is possible to secure isodose distributions of the fallout as they would appear on an equivalent land surface. The location of detector and source voiunie on a coordinate system is shown in Because of the absorption of the gamma rays by the water, radiation detected above the surface comes from the top 10 to 20 cm of the sea. The following equation describes the variation of

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curies per cubic meter a polynomial, dependent on the altitude of the aircraft, h; and half angle, @ which subtends the diameter at the surface contamination. The gamma rays from the fission products are assumed to have an effective gamma energy of 0.5 hlev when 1 to 6 days old (Reference 5). This reference states quantitatively that gamma curies and beta curies are nearly equivalent in this period. Estimates based on this assumption indicate that contamination with a beta activity of 4.43 ~ 10 G(dis/min)/liter at the surface should produce a 1 mr/hr gamma flux at 3 feet from the surface, when the diameter of the contamination is large enough to appear infinite (6 = 90 deg). Fig~re 1.1 Coordinate system of gamma radiation from a water volume. Fallout of 0.404 megacurie per naut miz deposited’ in the sea, uniformly mixed to a depth of 60 meters (Reference 3 and Section 3.4.2), would produce a 1 mr/hr gamma field at 3 feet above The gamma dose rate at any a~titude fa, related to the 3-foot value is expressed by the ratio of the polynomials L(h, 90 deg). The altitude absorption I/fa is plotted in Figure 1.2. 1.3.2 Fallout Contamination of a Land Surface. Wlen fallout is deposited on land, the contaminated area appears as a large plane source. At any point in the radiation fle Ld, the gamma intensity will include contribution from a circle whose radius :s determined by the absorption of the gamma photons in air. The ciose rate ( ) above such a plane is ~iven by the followlng equaWhere: C = curies per square meter J(h, 6) = a polynomial similar in construction to that in Section 1.3.1, ~Q~ ARCHIVE With the same assumptions as for the water case (Eo = 0.5 Mev and the ratio of beta and gamma curies equal to 1), 2.1 x 107(dis/min)/ft2 of beta activity will result in a 1 mr/hr gamma field at 3 feet from the surface, when the source ammeter is proportional to 6 = 90 deg. A

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gamma fiel: 1,000 mr/hr will correspond to a conta ation of 0.356 megacurie per naut mi~. The altitww absorption factor, over land, is shown in Figure 1.2. 1,3.3 %dioactive Decay. Mixed fission products have been assumed to have a radioactive decay proportional to t-j”: (Reference 6), to reduce the aerial-survey measurements to a common time, t is the time since the detonat~on. Large amounts of Np23g may be found in the fallout fro~, thermonuclear shots. It is p~ssible calculate the expected increase in the total activity, over thatresulting solely from flsslon Figure 1.2 Radiation attenuation referred to h = 3 feet. products, from the capture-to-fission ratio of the device. The decay characteristics of the fallout activity will be modified by the Np23g contribution. The Np23g can be present …