Operation Hardtack, Project 2.8 - Aircraft and Rocket Fallout (Deleted)

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AIRCRAFT AND ROCKET FALLOUT U.S. Naval Radiological Defense Laboratory San Francisco 24, California

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The primary objective of the project was to estimate the partition of range nuclear detonations over land and water surfaces. A secondary objective was to determine the spatial distribution of radioactivity (and particles) in the nuclear clouds a few minutes after stabilization. It was planned to achieve these objectives by radiochemical analyses and particle size measurements on the following types of samples: 1. Samples of the particles and radioactive gases present in the upper portions of the clouds to be collected by high flying aircraft. 2. Samples of the particulate matter in the clouds to be collected along nearly vertical flight paths , at several different distances from the cloud axis, by rocket-propelled sampling devices. 3. Samples of the fallout to be collected at an altitude of 1,000 feet The project participated in a megaton shot (Koa) fired over a coral island ~~~~~ shot (Walnut) fired from a barge in deep water, and a 9-MT shot (Oak) fired over a coral reef in shallow water. The air craft sampling progranrwas generally successful, and fairly complete sets of both cloud and fallout samples were collected on each shot. The rocket program was unsuccessful due to a variety of equipment malfunctions. ~~ p~~o

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Th& gas samples were analyzed for radioactive krypton and the cloud and fallout samples were each analyzed for Srg”, CSI137 and several other nuclides selected to give information on fractionation. Fall rate and size distribution measurements were made on the particle samples from the land surface shot. The combined analytical data was used to estimate the distribution of Sr9° and Cs 137 between the local and long-range fallout. The results indicate that for water shots, around one -half of the Sr 90’ and two-thirds of the Cs formed will be dispersed over distances greater than 4, 000 miles. Corresponding figures for a coral land surface are onenounced in the land surface shot. The local fallout was depleted in both Sr90 and CS137 and the upper portions of the clouds were enriched. Frac - tionation was much less for the water shot. There are no results to be reported on the spatial distribution of radioactivity in the clouds since this part of the project was dependent the rocket samples. It is recommended that a similar project, with particular emphasis on land detonations, be included as part of the program if future weapons tests are scheduled. Such a project could provide a valuable check on the HARDTACK data and would be relatively inexpensive if only the long-lived nuclides

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In the formulation of this project, three distinct parts were established: rocket fallout sampling, aircraft fallout sampling and sample analysis, data interpretation and report preparation. Responsibility y for the conduct of rocket sampling was assigned to the University of California Radiation Laboratory (UCRL); responsibility for the conduct of the aircraft sampling was assigned to the Los Alamos Scientific Laboratory (LAS L); and re - sponsibility for the conduct of sample analysis, report writing, etc. , was assigned to the U. S. Naval Radiological Defense Laboratory (NRDL). The Project Officer was supplied from the NRDL technical staff. H. F. Plank, as technical advisor to the project officer, was responsible for the conduct of the LASL portion, E. H. Fleming acted in a similar capacity for the UCRL portion and N. E. Ballou and T. Triffet are responsible for the

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The authors wish to acknowledge the vital contributions made to the Project, in both the field and the laboratory, by members of the Los oratory, and the U. S. Naval Radiological Persons c lntributing invaluable aid aad H. Plank from the Los Alamos Scientific Laboratory; R. Batzel, R. Stevenson, and K. Street from the University of California Lawrence Radiological Defense Laboratory.

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TABLE OF CONTENTS Procedures for the Determination of Fallout Partition ., Prior Estimates of Local Fallout .......ll l’ World Wide Fallout ................ Fractionation Effects (1): Observations at other Tests . Fractionation Effects (II): Relations among the R-Values for Several Radionuclides ............. 1. 3.1 Outline of the Program. ............. 1. 3.2 Rocket Sampling of Clouds ............ 1. 3.3 Aircraft Sampling of Clouds .......l..l. 1. 3.4 Aircrtit Sampling of Fallout ......lll.ll 1. 3.5 Selection of Radionuclides ......l.ll “ l

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2. 2.3 Discussion of Some Errors 3.3 Comparison with Results of Previous Tests .....lslll 3.4 Effectiveness of Instrumentation ............... CHAPTER 4. CONCLUSIONS AND RECOMMENDATIONS ........

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PARTICLE DATA AND CHARACTERISTICS, SHOT KOA . METEOROLOGICAL DATA TABLES ......... Battery of Rockets Ready for Firing ........ “ l “ l Filter Foil Installed on Top of B-50 .....lll “ l l Plan View Wind Velocity Hodograph, Shot Koa ........ Plan View Wind Velocity Hodograph, Shot Walnut ....... Plan View Wind Velocity Hodograph, Shot Oak ....Glll Particle-Gas Fission Ratios as a Function of Time for Samples from the Light and Variable Wind Layer ......llll Fraction of Total Sr90 Formed Which Remains Aloft at Various Fraction “of”T&~l Cs 137 Formed Which Remains Aloft at Various Diagram to Illustrate Rocket Programming ......... Schematic View of Rocket Nose Section .......... Particle Fall Rate Distribution Curves for Height Line Samples, Particle Fall Rate Distribution and Specific Activity Curves for Particle Fall Rate Distribution and Specific Activity Curves for Height Line Samples, Shot Koa: Wilson Special Sample . . .

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Particle Fall Rate Distribution and Specific Activity P&rticle Fall Rate Distribution and Specific Activity Curves for Cloud Samples, Shot Koa: Sample 502, Fine . l l l Particle Fall Rate Distribution and Specific Actitity Curves for Cloud Samples, Shot Koa: Sample 500, Coarse . c . Particle Fall Rate Distribution and Specific Activity Particle Fall Rate Distribution and Specific Activity Curves for Cloud Samples, Shot Koa: Sample 977, Coarse l Q l Particle Fall Rate Distribution and Specific Activity Particle Size Distribution Curves for Height Line Samples, Particle Size Distribution Curves for Cloud Samples, Shot Particle Size Distribution Curves for Cloud Samples, Shot Particle Size Distribution Curves for Cloud Samples ~ Shot Koa: Samples 977, Coarse, and 972 Fine .........0 “* l Particle-Gas Fission Ratios and R-Values for Samples from Light and Variable Wind Layer ................ Fractions of Nuclides Left in Cloud after One Day ....... Radiochemical Data, Koa Particulate Samples ......lll 1io Radiochemical Data, Walnut Particulate Samples .......l 112 Radiochemical Data, Walnut Gas Samples ........lll 113 Radiochemical Data, Oak Particulate Samples ......... 114 Radiochemical Data, Oak Gas Samples ............ 115

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List of Samples Measured, Shot Koa ............. 116 Winds Aloft Data, Shot Koa. ................ 129 Winds Aloft Data, Shot Walnut ............... 130 Winds Aloft Data, Shot Oak ................ 131 Atmospheric Temperature Data, Shot Koa .......... 132 Atmospheric Temperature Data, Shot Walnut ......... 133 Atmospheric Temperature Data, Shot oak .......... 134

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The general objective of the project was to estimate, from analytical on cloud samples, the relative distribution of certain radionuclides between the local and world-wide fallout formed by megaton-range detmations en land and water surfaces. Specific objectives were to: (1) obtain air~orne particle and gas samples by rocket and aircraft sampling techniques; (2) determine the distribution of two groups of particles which differed from one another in their falling rates in air and which could be considered representative of local and world wide fallout; (3) attempt to determine an early-time distribution of radionuclides and particles between the upper and lower halves of the cloud and radially outward from the cloud axis; (4) estimate ~he extent of separation of fallout from gaseous fission products by fission deterrnina - tdons on gas and particle samples collected coincidentally rmar the top of the cloud at various times following the shots, 1.2 BACKGROUND AND THEORY Data on the geographical distribution of fallout are particularly needed to assess the global hazards associated with the testing of nuclear weapons,

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but they-are also important for an appraisal of the effects of nuclear weapons used in warfare. It has been recognized since the earliest weapons tests that a substantial portion of the radionwclides formed in a nuclear detonation are deposited throughout the world, thereby becoming avaiLable for general biological as similatiom The total fallout is usually considered as being divided into two classes, designated as local and world-wide fallout. In. a general way, local fallout is thotaght of as consisting of relatively large particles, which reach the earth~s surface in a few hours, whereas world wide fallout is compofied of finely-divided material which may remain SU,Spended in the atmosphere for months or years and be deposited at long distances from the source. A more precise differentiation is needed for specific situations, one of the most importsmt considerations ‘being the location of the detonation site in relation to world centers of population. For explosions at the Pacific Proving Grounds~ the boundary between the two classes has been chosen at a particle falling velocity of 3 inches per second; material settling out more @lowly than this is likely to be transported beyond the cwean areas and deposited in inhabited regions, SAN 1311csu The ratio of local to world-wide fallout is governed by the size distribution of the particles in the nuclear cloud which act as collectors for the radioactive fis siomproduct atoms. If many large particles with fast falling

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rates are present, as is the case for surface or underground shots where the fireball contacts the ground, the local fallout will be large. Local fallout can be expected to decrease as the detonation height increases and become a negligible quantity for an air burst high above the ground. Numerous estimates of local fallout have been prepared at previous Operation9, mainly from analyses of radiation intensity data obtained in aerial and surface monitoring surveys. However, the uncertainties in converting from dose rate measurements to fission products deposited per unit area are so great that the results cannot be regarded with a great deal of confidence. More reliable values are evidently needed and in planning for Operation HARDTACK, the AEC lxamined possible ways of obtaining- s’uch information (Reference 1). After consideration of the difficulties inherent in additional refinement of surface measurement techniques, this approach was abandoned. An alternative program based on further development of existing cloud sampling procedures was formulated (Reference 2) and this culminated in Project 2.8. A knowledge of fallout partition and how it is influenced by shot environment may contribute to reduction in world-wide fallout at future tests and to a better understanding of the military implications of local fallout. It will also assist in extrapolation to previously untried shot con-

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1.2.1 Formation and Nature of Fallout Particles. When a surface is detonated, great quantities of the adjacent environment are swept mixed with the incandescent air in the fireball. There is sufficient thermal energy in the hot gas to completely vaporize all the material in the immediate vicinity, but the flow of heat into a massive object, such as l shot tower, shield or coral rock, will be comparatively slow even with a high temperature gradient. Consequently, the interior portions of large structures in the neighborhood may not receive enough heat to evaporate and will be melted only. Later, when the fireball has risen lbove the surface, the material carried into it by the vertical air currents around ground zero will not be heated to the melting point. As a results the fireball in its later stages will contain the environmental components as a mixture of solid particles, molten drops and vapor. The extraneous material in the Pacific shots will consist of coral and ocean water salts plus the components of the device, shield, and tower or barge. The preponderance of oxygen and of the environmental material in the fireball is of outstanding importance in the formation of the fallout particles. As the hot air cools through the range 3500-1000 K“, , it becomes saturated with respect to the vaporized constituents lnd they condense out as an aggregate of liquid drop ~ most of which are very small (References 4 and 5). These are mixed with the larger drops formed by

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fusion a=d with solid particles. The radionuclide atoms present will collide frequently with oxygen atoms or molecules and, since the majority of them are electron donors, metallic oxide molecules will be formed which become thermodynamically stable as the temperature falls. The oxide molecules, or free radionuclide atoms~ also have frequent collisions with the liquid drops of environmental mater ial [silica, alumina$ iron oxide or calcium oxide) and these will be held by be inelastic since in some cases the incoming molecules strong attractive forces. The radioactive oxide molecules which condense at the liquid surface will spread into the interior of th ,S drops and become more or less uniformly distributed throughout. Later, after the liquid drops have frozen, the incoming radionuclide molecules may be held by surface forces. Another way in which the radionuclide molecules may become asso - ciated with the environmental material is by participation in the structure of the cluster embryos which are the precursors of the liquid drops (RefDue to the very low concentrations of the radionuclide oxide molecules, collisions with one another will be relatively infrequent and it appears that the aggregation of enough molecules of this type to form a drop or crystal will be a rare event, if it occurs at all. S4LV13RUI~ ~C

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T-he isobaric radionuclide chains formed in the explosion are known distributed on a mass scale in a way generally similar to the proof asymmetric fission of U235 by thermal neutrons, but with some important differ ences. The experimental yield curve for slow neutron fission has a broad minimum for mass n~bers approximately one-half that of the original nucleus and maxima on either in the neighborhood of 95 and 139 (Reference 7)0 side at mass numbers Comparing the chain yields for megaton-range detonations with this curve, it is noted that there is a small drop in the peak yields accompanied by an increase in the symmetric fission probability. The same nuclide distribution might be ex- ., petted in the fallout material and this is found to be roughly true under certain conditions. In other cases, the chains formed initially separate from one another so that samples of fallout may differ in composition among themselves and also from the distribution curve characteristic Fractionation is a term which has been applied to this phenomenon and it is used to signify an alteration in nuclide composition of some portion of the debris which renders it non-representative of the bomb products as a whole. The R-values, which are commonly used for reporting radiochemi - cal data on cloud and fallout samples g are useful indites of fractionation. The R-value for any nuclide is defined as the ratio of the number of atoms

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of this nuclide to the number of atoms of a reference substance (usually M099) in the ‘sample divided by the same ratio for the products of thermal neutron fission. Atoms which do not stance have R-values appropriate for richment or depletion are manifested the characteristic curve. separate from the reference subthe type of detonation, while en- “ by positive or negative deviations f r oxn Knowledge of the causes and mechanism of …