correction factor. The altitude error at the 300-foot level has a maximum value of 15 feet based on the APN-1 specification. The altitude correction-factor error will be less than 4 percent. The absolute value assigned to an isodose depends on the calibration of the radiation detector and altimeter, and on the altitude-correction factor. The major assumption of an average gamma-emission energy of 500 kev in evaluating the altitude absorption derivation is supported by the gamma-spectrometer results (Section 3.1.2), and the ratio of the radiation readings of an energy-dependent detector and the Top Hat detector during a survey over the Eniwetok Atoll (Section 3.2). Examination of the radiation dose-rate relations between various altitudes over land and water during Operation Redwing (Section 3.2), during previous operations (Appendix C), and during Operation Plumbbob (Reference 12) indicate the validity of the assumptions and the accuracy of the calculated altitude-correction values. 4.2.2 Contamination-Density Determinations. As indicated in Section 1.3.4, fallout on a land surface is expected to produce, at 3 feet from the surface, a gamma dose rate about 1,100 times higher than the dose rate resulting from the same fallout density in the sea. Agreement of data with the theoretical derivation primarily depends on the accuracy of three factors: (1) the depth of vertical mixing, because material belowthe surface of the sea will not contribute to the gamma field, (2) the average gamma-emission energy, which determines the thickness of the surface layer that does contribute tothe gamma fie!d, and (3) the air absorption, which determines the surface area viewed by the radiation detector. The equivalent depth of mixing was estimated as 60 meters (Section 3.4.2). This is in essential agreement with measurements made during Operation Castle. The experimental work was based on only a fewstations and did not necessarily represent the conditions throughout the fallout area. However, variation in mixing will introducesefriations in the area enclosed by an isodose contour; this is discussed in Section 4.3.1. The average gam- ma energy and the altitude absorption characteristics assumptions are supported by several measurements as discussed in Section 4.2.1. There is one direct comparison of the land and water equivalence based on the fallout following Tewa (Figure 3.23). The isodose pattern encloses Parry Island, Eniwetok Atoll. This island is located between the 25 and 250 mr/hr land-equivalent isodose lines (0.025 and 0.25 mr/hr water isodose). Radsafe measurements indicate a gamma dose rate between 100 and 125 mr/hr on Parry at 24 hours following Shot Tewa. The contamination density calculations are based on the factors discussed above, and on the relationship between beta and gamma curies. A direct comparison of the conversion between gamma dose rate and beta specific activity is discussed in Appendix D. The measurements are not conclusive. However, the general trend of this data does agree with the theoretical calcuiations (Section 1.3.1). The fallout estimates based on the aerial-survey charts showa definite relation to the fission yield. However, the distribution of this material is not related to the total energy yield, because the conditions of the shot— water, land, or air—affect the fallout. also play a major part in determining the area of contamination. Meteorological conditions DOE ARCii: 4.3.1 Stability of Contaminated Area. Fallout deposited in the sea is acted upon by the ocean currents, producing a horizontal translation of the location of the material, and a vertical displacement based on the mixing of the material in the sea volume. To obtain a measure of the stability over a period covered by the aerial surveys, measurements were repeated from dayto day. All gamma radiation measurements were referred to 3 feet from the surface and to H+24 hours so that a common comparison could be made for any particular isodese area. The horizontal translation is clearly indicated by the positional shift of the isodose pattern. The vertical mixing is indicated by the amount of area enclosed within the described pattern. ee de teat chants a! ct jasahnnihabat : aledaiteaailsiti 4.3 DISTRIBUTION OF CONTAMINATION IN THE SEA 56 a , 53 w