4 that trips to islands in the South or North are equally likely for either group. The choice of fractional times for the various population groups are based on J. Tobin (this report) and the comments of the Eniwetok Magistrate at the May meeting. ‘Case qb differs from case I, in that more time is allotted to temporary occupation of islands other than Engebi while less time is spent in the Engebi village area. Case Ih probably leads to ‘upper limit doses for a sizable fraction of the population. represents the least exposed population group. Case Iv No attempt was made to break down the time spent on other islands into specific areas, Such a breakdown would appear to over complicate the calculations unnecessarily. The estimated mean exposure rates at the present time for each of the locales treated, and Le each major source, are given in Table IT. The average 137 os ana 69¢o exposure rates for each island were taken from the eet nie a meee EG&G summary table given in their section of this report. A mean for all the northern islands (excluding Yvonne) was obtained by weighting’ the individual island averages by their land area. The estimates for specific regions of Janet were obtained by examination of the EG&G 137cs and 60¢6