benchmark was located later a tie-in could be determined. It was not necessary to clear lanes in both directions of a square grid; a baseline could be cleared, then access lanes cleared, perpendicular to the baseline, and at appropriate intervals. In cases where the island shape was not amenable to construction of one suitable baseline, a more complex pattern of lane clearing was utilized. (For example, see Figure 6-6 ofIsland Belle.) Lane clearing on islands scheduled for the in situ gamma scan was accomplished between September 1977 and March 1978. This period included action on many concurrent tasks by DOE and elements of the JTG; consequently, communication between DOE and JTG regarding layout of the island grids fell short of the intentions of the DOE/ERSP element. Military surveyors, left to their concocted 10 different grid numbering systems while surveying and staking 20 islands. of the situation led to the conclusion that the confusion that would result from changing all island grids to a uniform numbering system would be greater than the making do with the numbering systems as developed. own devices, An appraisal retroactively confusion of Stake locations are recorded on magnetic media along with all soil sample and in situ gamma data and are in the same format as these locations appear on the maps in Chapter 7. 6.3 TRANSURANICS IN THE ENEWETAK ATOLL ENVIRONMENT (by Richard Hoff, Lawrence Livermore National Laboratory, and John Stewart, DOE/NV) The following information demonstrates which of the alpha emitting transuranie elements, from nuclear weapons debris, have been determined to be of significance and were included in the total soil transuranic (TRU) caleulations during cleanup at Enewetak Atoll In addition, this information will be used to help explain the wide range of TRU-to-americium ratios measured during the soil cleanup operations. During the period 1948-1958, a total of 43 nuclear tests were conducted at Enewetak Atoll. The radioactive debris from nearly all of these nuclear explosions was sampled, usually by drawing air and particulate matter that were present in or very near the mushroom-shaped cloud, through a filter which was mounted on a jet-propelled aircraft. These so-called "prompt" samples, which were collected within a few hours after the explosion, were analyzed for their radioactive content. Some of the samples were analyzed as soon as possible in laboratories located at Enewetak; other samples were returned to the laboratories at Livermore, California, and Los Alamos, New Mexico, where more extensive analyses were performed. Fission products were identified by their beta- and gamma-decay characteristics. Alpha-emitting nuclides were measured directly; mass spectrometric techniques were utilized to determine the isotopic content of chemically-purified uranium (U) and plutonium (Pu) fractions in the samples. Interpretation of these data included the use of the bomb-fraction tracer concept. When one knows the exact amountoffissile fuel (e.g., 235U and/or 289Pu) incorporated into a given nuclear device, postshot samples can be related to the entire device through measurementof residual amounts of the fissile fuel nuclides, making appropriate corrections for destruction as deduced from the fission products observed in the sample. Thus, small samples, taken randomly from various parts of an often huge mushroom cloud, could be used to calculate the entire inventory of observed radioactive species for a single event at various times following the explosion. The results of these analyses have been documented in classified reports. Given these experimental observations, one ean predict which long-lived radioactive species will be found in debris samples collected at Enewetak during a period 15-30 years after the cessation of nuclear testing activities at that atolL On the other hand, prior to the survey of the Enewetak Atoll for radioactivity performed in 1972-73, knowledge of the definition of radioactive fallout within the atoll's land areas and lagoon sediments, and of concentrations of radionuclides in the vegetation, marine life, and sea water of the atoll, was limited. Given-the high energy yields of many of these devices, much of the debris was driven high into the atmosphere (and stratosphere) by the violent force of the explosion. No calculational models were expected to be accurate for prediction of close-in fallout within the atoll region. 154