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Machine-read from the scan, so expect some errors. Lines that couldn’t be read are left out.
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Energy Measwe~ents Group . Las Vegas Operations 6ao E SUNSEWOAD. LAS VEGAS, NV l TEL (702) 739-0461 l MAIL BOX 1912. LAS VEGAS NV 89101 Office of Health and United States Department of Energy Enclosed are the data summary tables for*Bikini, Rongelap and Rongerik Atolqs which we discussed last week. The data given represent average values rather t than maximum levels which were given in previous summaries. Values are given for the total terrestrial exposure rate as well as the individual contributions due to 137CS and ‘°Co. Average values were obtained by numerically averaging the individual second-by-second data points obtained over a given island. Islands lying close together were treated as a single island. In using the aerial data, it is important to remember that each one second data point represents an average value over an area several thousand times greater than the area which would be measured with an instrument placed at one meter. For very small islands, the aerial data will indicate a lower value than that measured from the ground, since part of the area being measured lies over water. Data obtained over lar9er islands, however, should agree in general with that measured on the ground. For RonqelaP and Ronqerik, exposure rate values are only given for those-islands lar~e enough to ~rovide reasonable agreement between airborne and ground based Cesium and cobalt exposure rate values were obtained from photopeak count rate data. Procedures used to extract the photopeak counts and obtain exposure rate values were similar to those presented in NVO-140 for the 1972 Enewetak aerial survey. The total terrestrial exposure rate values were obtained from gross count data after subtracting a water background. Subtracting the water background renwves contributions to the spectrum from internal sources within the aircraft and from cosmic rays, resulting in a net count due to terrestrial activity. It can be seen that the sum of the 1S7CS and ‘“co contributions, on the average, agree quite well with that obtained from the total gross counts. This supports previous data which indicates that there is little or no naturally occurring terrestrial radioactivity within these coral atolls. For some of the atolls surveyed, the terrestrial activity levels were too low to determine the individual contributions due to 137CS or ‘°Co using the photopeak extraction technique. Exposure rate values in these cases can only be obtained from the total gross
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In addition to Bikini, Rongelap and Rongerik, average terrestrial exposure rate levels were also determined for Ujelang and Utirik Atolls. For both of these atolls, the levels observed were essentially constant over the entire atoll. The gross count data gave an average exposure rate of 0.15 VR/h at Ujelang and 0.6 pR/h at Uterik. The primary source of activity at Uterik was due to 137CS. Levels were too low on Ujelang to positively identify any specific isotopes. In order to obtain the total external exposure rate, it is necessary to include cosmic ray contributions. A value of 3.3 uR/h has been assumed for this component. Where comparisons can be made, the resulting total external exposure rate values from the aerial survey agree quite well with those measured during 1976 and 1977 by Brookhaven National Laboratory using a“pressurized ion chamber (BNL 50797). The island numbering system and the Marshallese island names were based on rather old atoll maps. The island names in some cases may reflect the influences of the Japanese. If you have any information on updated Marshallese spelling, please let me know. I hooe to com~lete this ty~e of analysis for the remaininq atolls within the next few weeks. Please let me-know if th;re data might prove useful to you for your Section Head IV is tiny atoll in p~rticular where this
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Northern Marshall Islands Aerial Radiation Survey Preliminary Data Summary Average Terrestrial Exposure Island Frame Marshallese Total 1 37c~ 60(.0 Number Number Name Gross Count Component Component Extrapolated from aerial data obtained at an altitude of 38 meters (125 feet). An additional 3.3 P R/h due to cosmic ray contributions must be added to obtain the total external exposure rate.
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Northern Marshall Islands Aerial Radiation Survey Preliminary Data Summary Average Terrestrial Exposure Island Frame Marshallese Total 137(-s 6 Oco Number Number ~ Name Gross Count Component Component * Extrapolated from aerial data obtained at an altitude of 38 meters (125 feet). An additional 3.3 p R/h due to cosmic ray contribution must be added to obtain the total external exposure rate.
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Northern Marshall Islands Aerial Radiation Survey Preliminary Data Summary Average Terrestrial Exposure Island Frame Marshallese Gross Count Component Component Number Number Name * Extrapolated from aerial data obtained at an altitude of 38 meters (125 feet) An additional 3.3 p R/h due to cosmic ray contributions must be added to obtain the total external exposure rate.
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Northern Marshall Islands Aerial Radiation Survey —— Preliminary Data Surmnary Average Terrestrial Exposure island Frame Marshallese Total 1 37(=s 60(-0 Number Number Name Gross Counts Component Component * Extrapolated from aerial data obtained at an altitude of 38rn (125 feet). An additional 3.3 u R/h due to cosmic ray contributions must be added to obtain the total external exposure rate.