Given the half-lives of the 14.4-year beta emitting 241Pu and its 433-year daughter, 241Am, and assuming only small amounts of americium present at time zero (time of nuclear explosion), one can ealculate that any sample of plutonium (containing some 241 Pu) will contain a maximum absolute amount of 241Am activity at 75 years after time zero, assuming no chemical fractionation between parent and daughter. One eanalso derive the fact that the maximum 241 Am content at 75 yearsis 50% greater than that observed at 20 years after time zero, i.e., at the approximate time of the 1972-73 survey. This information is reflected in the values given in Table 6-4. Thus, for any given activity ratio, total TRU /241Am observedin survey samples, the projected minimum in this ratio will be 69% of the observed value. Minimum values of the ratio for median values will be in the range, 2.3-6.9. Thereafter, this ratio will increase until the 241 py parent has been depleted sufficiently that 241 py beta decay produces 241am more slowly than 241 am is lost due to alpha decay. In the preceding discussion, it has been shown that the predominant radioactivity and, presumably, predominant source of biological dose from the transuranic elements present in the Enewetak gyyironment at this time can be ascribed to four alpha-emitting species: Pu, Pu, Am, and Pu. This concept was predicted prior to the extensive survey of the Enewetak environment in 1972-73 and is borne out by the experimental data collected during analysis of the Enewetak survey samples. It has also been shown that the observed 24lam is the product of 241 pu beta decay and in many circumstances the 241 am will occur with the Pu isotopes in predictable amounts. The absolute amount of 24lam radioactivity will reach a maximum in about the year 2028, i.e., 75 years after the time of nuclear detonation. For samples exhibiting the median value of the activity ratio, total TRU /24l!Am , ona given island, the maximum 24. am activity will range from 17% to 77% of the total Pu alpha activity. Uranium, although deposited on the Enewetak Atoll in comparable or even somewhat greater amounts than plutonium, is not an important source of radioactive contamination because of the much longer half-lives of the principally-occurring 235 and 238 isotopes. Other transuranie species, e.g., isotopes of Np, Am, or Cm, have been shown to be much less abundant (in terms of alpha radioactivity) than the major four nuclides listed in Table 6-2 and, thus, of negligible interest with respect to potential biological dose. Based upon the above information it was determined that during the Enewetak Atoll cleanup only the transuranie (TRU) nuclides 239py, 240py, 24lam and 238Pu would be measured and reported in the TRU data base. Experience during cleanup has shown soil ratios of TRU/“4lam to vary with about the same ranges as calculated from the original weapons systems data and measured during the 1972-73 survey. In general the pattern has been that islands with surface ground zeros (SGZ) of lower yield devices show a range of ratios for TRU to 241Am from about 5 to 10 near the GZ, which should reflect mostly fallout from that test. At further distances from SGZ and on islands without SGZ the ratios ranged from about 2.5 to 4.0, reflecting a mixture of fallout from many tests, and suggesting the majority of transuranic fallout comes from the high yield tests, such as Mike. The Island Pearl is a good example of the above. The measured ratios of TRU/24)Am in soil were 9.1 + 1.1 within 150 meters (m) of the INCA GZ, 7.80 + 2.2 for samples taken between 150 and 350 m Although a detailed review of the data has not been presented here, the range in ratios of TRU/24lAm that were measured on the various islands is consistent with the expectations from the source terms. a from SGZ, and 4.1 + 1.28 for samples taken beyond 350 m from SGZ. 6.4 ISLAND JANET(by Madaline Barnes, DRI) 6.4.1 IMP Start Up and Preliminary Surveys as various other experiments and sampling efforts. Janet was therefore the natural choice for developing and evaluating procedures for the IMP system, as well as initial IMP measurements. 159 rw: As the largest of the northern islands of Enewetak Atoll, Janet (Marshallese: Enjebi) has great cultural and political importance for the driEnjebi (Enjebi people). Because of this importance, Janet is also the site of studies of radionuclides in groundwater and plants (see Section 6.11), as well