3 levels down to those represented approximately by Case IV.) An average reduction of a factor of 3 was computea from HASL transport calculations (Beck and de Planque, 1968; Beck, 197) based on the apparenth-5 cm relaxation lengths for the present activity. This additional modification results in the doses shown in row 3 for each case which are in general less than the external doses which the U.S. population would receive for comparable time periods. 6. Table V gives the fraction of the 30 year unmodified dose received by each age group for case Ia to indicate the large fraction of the dose resulting in this case from travel to outer "hot" islands. The dose breakdown by population group is also shown to indicate the relative insensitivity to population distribution. Similar insensitivity to age was obtained for the other cases. Te The calculated doses are believed to be conservative estimates of the mean doses to the population group as a whole. Because some of the ‘northern islands have dose rates ih some areas several times those chosen for our model. Some individuals could (although it is probably unlikely) receive doses perhaps 2 or 3 times those calculated if they happened to build houses in an immodified area on an island with . larger gamma-ray levels. yo i 8. ‘ e Beta Dose - As a general guideline, fer sources distributed in the soil with a 3-5’cm relaxation length we estimate the 7sr-?y beta free air dose will be about four times that due to 137¢5 y exposure.