Operation Redwing - Project 2.1, Gamma Exposure Versus Distance (Deleted)

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Gamma Exposure Versus Distance .‘L__’ This is an extract of WT-1310, Operation REDWING, which remains classified SECRET/RESTRICTED DATA as of this date. Extract version prepared for: DEFENSE NUCLEAR AGENCY Approved for public release;

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Gamma Exposure Versus Distance P. Brown et al Headquarters Field Command Defense Atomic Support Agency Sandia Base, Albuquerque, New Mexico Approved for public release; unlimited distribution. BEFORE COMPLETING FORY 6. TYPE Of ifPORT 6 PERIOD COVERE 6. PERFORYIktG ORG. REPORT NUYBER AREA 6 WORK UHtT UUUBERS This report has had the classified information removed and has been republished in unclassified form for public release. This work was performed by Kaman Tempo under :ontract DNAOOl-79-CT0455 with the close cooperation of the Classification Management Division of the Defense Nuclear Agency.

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This report has had classified material removed in order to make the information available on an unclassified, open publication basis, to any interested parties. This effort to declassify this report has been accomplished specifically to support the Department of Defense Nuclear Test Personnel Review (NTPR) Program. The objective is to facilitate studies of the low levels of radiation received by some individuals during the atmospheric nuclear test program by making as much information as possible available to all interested parties. The material which has been deleted is all currently classified as Restricted Data or Formerly Restricted Data under the provision of the Atomic Energy Act of 1954, (as amended) or is National Security Information. This report has been reproduced directly from available copies of the original material.. The locations from which material has been deleted is generally obvious by the spacings and "holes" in the text. Thus the context of the material deleted is identified to assist the reader in the determination of whether the deleted information is germane to his study. It is the belief of the individuals who have participated in preparing this report by deleting the classified material and of the Defense Nuclear Agency that the report accurately portrays the contents of the original and that the deleted material is of little or no significance to studies into the amounts or types of radiation received by any individuals during the atmospheric nuclear test program.

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The objective of Project 2.1 was to determine gamma expostires versus distance from the point of detonation of various high-yield devices. The following types of dosimeters were used as gamma-radiation detectors: photographic, quartz-fiber, chemical, and phosphate-glass. Correction factors were applied to compensate for the nonlinear speetral response of the dosimeters, when necessary, and for station shielding. All detectors were calibrated with Co6’ sources. Photographic dosimeter readings were accepted as the most reliable on a statistical basis and were used as bases for most of the curves plotted. Photographic dosimeter film-badge service and Co6’ calibration facilities were provided to other projects as, requested. Initial-gamma radiation was measured at a series of stations Iocated at about 1 to 4 miIes from ground zero. Mechanisms were installed at some of these stations to shield the detectors from residual radiation. An analysis of the data indicates that the initial-gamma exposure at 3 miles from Cherokee, Zuni, and Navajo was about 1 r. Consequently, initial-gamma radiation was of little military significance to exposed personnel as compared to thermal and blast damage resulting from high-yield devices. The curves in this report vary from those published in TM 23-200 (Reference 1). The field data falls below predictions at longer ranges and is greater than predicted at shorter ranges. This difference between predicted and field data increases with increasing yield. For fallout residual-gamma radiation measurements, instrument stations were located on aImost every island of Bikini Atoll at distances where neutron-induced activity was entirely negligible. The amount of residual-radiation exposure was a function of the fission yield. Residual-gamma radiation data points are mapped in this report for Shots Zuni, Flathead, Navajo, and Tewa.

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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, Task Unit 3. ” This technical summary includes: (1) tables listing each detonation with its yield, type, environment, meteorological conditions, etc.; (2) maps showing shot locations; (3) discussion 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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Acknowledgement is made to Captains Edwin York and Roger Boyd who attended this operation as Project.2.1 personnel through the cooperation of the Air Forces Special Weapons Center (AFSWC). Their assistance and suggestions contributed to the success of this project. Appreciation is expressed for the cooperation and participation of the Department of Radiobiology, School of Aviation Medicine, USAF, and particularly for the chemical dosimeter data, evaluated in the field and laboratory, of 1st Lt. Sanford C. Sigoloff, who also contributed the material for the discussion of chemical dosimeters in Section 2.2.3. Acknowledgment is also made to: Doctors Dunham, Corsbie, and Buterhoff, for making available the AEC dosimeter systems described herein; Doctors Taplin and Cassen, University of California, for their production and evaluation of the AEC dosimeter systems; S. C. Rainey, fiber dosimeters; C.N. Kingery, of Froject 1.1, for making available the use of the 113 series of stations on Sites Charlie and Dog for Shots Cherokee and Tewa; and Majors Roy Weidler and Thomas Connolly, of Headquarters, Armed Forces Special Weapons Project (AFSWP), for technical suggestions and advice.

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Shot Navajo Residual Exposure _________________________________ 37 2.10 Quartz fiber dosimeter energy dependence curve normalized Initial-gamma exposure versus distance for Shots Cherokee Initial-gamma exposure versus distance for Shots Flathead, Comparison of data from Ridwing and previous operations,

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The objective of Project 2.1 was to determine gamma exposures versus distance from the point of detonation of various high-yield devices. A secondary objective was to determine the gamma exposures received in several discrete time intervals between time of arrival of the thermal pulse and 1 minute after time of detonation. Initial-gamma radiation may be considered as that emitted during the first 30 seconds after detonation. The initial-ga.mma radiation output for nuclear devices with yields up to 250 kt has been well documented in previous test operations Gamma-radiation measurements from high-yield nuclear devices d ing Operation Ivy showed that the initialgamma radiation did not follow the same scaling laws that had been established for smaller devicesj. 1 This was attributed in part to the hydrodynamic effect, which results in an enwent of the gamma radiation. This effect is caused by the passage of the shock front through the detector station, resulting in a reduced air density between detector and radiating source. Section 1.3.4 gives a simplified treatment of the hydrodynamic effect. Measurements were made during Operation Castle by the U.S. Army Signal Engineering Laboratories to determine the empirical relation between yield and hydrodynamic enhancement : Some high-yield Operation Castle devices provided data points; however, it was ‘felt that additional data were needed at a number of suitably spaced points for various yields and types of nuclear devices to determine more valid scaling laws. The present scaling laws for initial-gamma radiation from high-yield thermonuclear devices were based on data from relatively low-yield fission devices (1 to 500 kt), a few data points from Operation Ivy, and the sparse data from Operation Castle. Initial-gamma radiation appeared to be of little significance compared to damage caused by blast and thermal effects. Residual-gamma radiation is here defined as that which reaches the detector 30 seconds or more after time of detonation. Residual-gamma exposure measurements have been made by various organizations at previous test operations (References 2, 3, 5, and 6). During Operation Buster-Jangle, the Signal Corps, in conjunction with the National Bureau of Standards (NBS), made residual-gamma exposure measurements of a l-kt surface blast and a 1-M device detonated at a depth of 17 feet (Reference 7). During Operation Teapot the U.S. Army Signal Engineering Laboratories made measurements of residual-gamma exposure resulting from an underground blast of a low-yield device (Reference 3). The advent of high-yield thermonuclear devices has :resulted in a manifold increase in the radiological hazard, and gamma radiation from fallout has become of greater military significance. Operation Castle demonstrated that large quantities of radioactive material could be deposited by high-yield devices over areas of several thousand square miles. This led to a military requirement for fallout data for devices of various types and yields. Project 2.1 was charged with documenting the residual-gamma radiation exposures from the fallout at land Stations at Bikini Atoll during Operation Redwing.

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ual radiation from fallout will follow approximately the expressions: Where: It = exposure rate at time t 1, = exposure rate at unit time r = exposure between times t, and t,, where t 2 10 seconds. It is expected that the decay of the residual radiation will vary with device design. For example, the-presence of Npz3’ would tend to decrease the absolute value of the decay exponent for a period of time. CAPTURE TO FISSION RATIO*05 Figure 1.1 Gamma exposure for 1 kt surface burst. 1.3.3 Absorption in Air. The absorption of unscattered gamma radiation in air is exponential with distance. From a point source of mono-energetic radiation, the variation of intensity with distance is expressed as:

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intensity at distance D linear absorption coefficient (this varies with gamma energy, and is generally lower for higher energies). The absorption coefficient p in Equation 1.2 is applicable for narrow-beam geometry, and a correction should be made for field cgnditions where the detector is approximately a 271sensing element. This is done by adding a buildup factor B to Equation 1.2, to account for the scattered radiation that will be detected. Buildup factors for different energies and distances have been calculated (Reference ll), and some values are shown in Table 1.2. For omni-directional detectors, the expression is: 1.3.4 Hydrodynamic Effect. AS shown in Section 1.3.3, the attenuation of gamma radiation is highly dependent on the amount of absorber between the source and the detector. For devices of TABLE 1.2 CALCULATED BUILDUP FACTORS puted by Nuclear Development Associates for AFSWP (Reference 9). Mev 1,000 yds 1,500 yds 3,000 yds less than lOO-kt yield, essentially all the initial-gamma radiation is emitted before :the shock front can produce an appreciable change in the effective absorption of the air between source and detector. For high-yield devices, the velocity of the shock front is sufficiently high to produce a strong enhancement of a large percentage of the initial-gamma radiation (Reference 10). The higher the yield, the larger is this percentage. A simplified treatment of the hydrodynamic efAssume a sphere that has a volume V, and radius R, and is filled with a gas of density p. and Let the gas be compressed into a shell with thickness A R (R remaining constant).. The new gas volume is expressed as Vi with a density of pi (V, = 4 KR2 A R). The mass has not changed;

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Equation 1.6 indicates that a ray originatin, u in the center of the sphere would traverse only ‘/3 of the mass in the shell model that it would in the homogeneous model. The result would be an enhancement of radiation. Once the shell of material in the shock front passes the detector, an even greater enhancement results. As previously stated, the Ni4 (n, y) N15 component of initial radiation is essentially emitted within 0.2 second. Since it takes at least 1 second for the shock front to reach a detector at a distance of 7,000 feet (even for devices in the order of 6 Mt), the N’” (n, y) N” component is not significantly enhanced. The fission-product gammas continue to contribute for the first 30 seconds. Therefore, this radiation is strongly enhanced by the shock wave.

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Project 2.1 participated in Shots Cherokee, Zuni, Flathead, Dakota (limited), Navajo, and Tewa. For every shot except Dakota, all possible stations were instrumented with every available type of detector of appropriate range. For Shot Dakota, stations were loaded ,with photographic-type dosimeters just prior to shot time, and these were recovered at the instrumentation time for Shot ,Navajo. Stations were instrumented as late as possible prior to shot time and recovered as soon as rad-safe conditions permitted. 2.2.1 Photographic Dosimeter. The primary detector consisted of film exposed in the NBStype film holder. This consisted of a bakelite container with an 8.25-mm wall thickness covered with a 1.07-mm layer of tin and a 0.3-mm layer of lead. The lead and tin acted as filters to suppress the lower energies sufficiently to keep the response linear above 115 kev. Below 115 kev, the gamma radiation was attenuated excessively, and exposure caused by gammas below 115 kev was small compared to that above 115 kev (Reference 12). The thickness of bakellte was determined experimentally on the assumption that the spectrum from a lo-Mev betatron was similar to the initial radiation of the device (Reference 13). The electron equilibrium layer presented a source of electrons that might have been scattered into the emulsion to replace those electrons produced by gamma radiation absorbed near the surface of the film and lost without being detected. In the energy range from 1.15 kev to 10 Mev, the dosimeter was considered accurate to within *20 percent with the film types used on this operation (References 14 and 15). For Shot Cherokee, film was exposed both with and without NBS holders to obtain an indication of the presence of low gamma-energy components in initial radiation, since bare films showed maximum sensitivity to gamma energies at about 60 kev. Two dental-size film packets, each containing from one to three different film emulsions, could be placed in the holder. A lead strip of 0.78-mm thickness was wrapped around the outer edge of the holder to cover the seam. The holder was placed in a sealed plastic can to protect the film from weather while in the field. The primary film packets used were Du Pont 553 containing Emulsions 502, 510, and 606, and coat film. These packets were individually sealed in polyethylene bags. In addition, Eastman Table 2.1 lists the ranges of the films, and Figures 2.1, 2.2, and 2.3 show examples of the caliThe films were stored in a refrigerator at Site Elmer and withdrawn as needed. Sets of calibration films were exposed to the Co6’ calibration source from 30 minutes to 12 hours after each detonation. Films were processed about a week after each event, thereby minimizing possible errors caused by latent image fading. Variations caused by temperature, aging, and processing technique were compensated for by the calibration film. Factors that caused variation in density from event to event were the latent image fading of Eastman 548-O film and the small variation in the temperature of the developer solution. In Shots Dakota, Navajo, and Tewa, an increase in the background density equivalent to about 200 mr was noted on the DuPont Emulsion 502. The use of calibration film in each of these events compensated for this background

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The photographic transmission density was read on an Ansco-McBeth Model 12 densitometer, with a calibrated photographic density …