a. Seventeen Sites Within the Continental United States (1955-1957). Yearly collections of soil have been made at 17 sites within the continental United States since 1955. The sites were selected at airports where continuous gummed film sampling has been carried out since 1952. The analyses were intended for comparison with Sr*® estimates from gummed film measurements, but they have also provided direct data for fallout within the United States. The sites were selected without consultation with soil scientists, and it is believed that a few of the airports may not be ideal sampling locations because of soil grading and packing. These sites will be reviewed before collection of future samples. b. Measurements made at Lamont Geological Observatory, Columbia University, Palisades, N. Y. The Lamont Geological Observatory has been carrying out soil analyses for several years. Like other laboratories a considerable portion of their early data was obtained by am- monium acetate leaching of the soil. This is of interest in studies of availability for uptake, but it is of dubious value in studying geographical distribution, since there is considerable variation from soil to soil in the efficiency of the acetate leaching process. Therefore, the data reported here are chiefly limited to samples leached with hydrochloric acid. c. Sr” in Soils Collected Outside the United States. Collections of soil samples have been made in several countries outside the United States for determination of accumulated Sr® fallout, These samples were taken to obtain results for the countries concerned and for comparison with other fallout sampling techniques. In general, the countries sampled were not making their own sr*® measurements at the time, and, even at present, soil analyses are being carried out in very few laboratories. Soil sampling represents our best method of obtaining cumulative fallout measurements, but the sampling is extremely difficult and is subject to many possible errors. It is sometimes impossible to obtain representative samples because of soil drainage or packing conditions. The samples reported in Table 9 are limited largely to those collected for determination of Sr® fallout per unit area, in which the measurement was made by leaching the soil with hydrochloric acid. A number of early samples were analyzed by leaching with ammonium acetate. Although this may have value in uptake studies, the results are not valid for fallout measurements. These samples have been omitted for the tabulation. It is expected that the number of samples from other countries will be reduced as the particular countries begin their own programsof soil and other fallout analyses. , d. Sr* in Soil Collected and Analyzed in the United Kingdom. Annual samplesof soil from several sites in the United Kingdom have been collected and analyzed for several years. A description of these sites and the results of the analyses are included in Part 4 of this report. 1.4 SUMMARY OF GUMMED FILM FALLOUT MEASUREMENTS THROUGH JUNE 1957 A primary technique in studying long-range fallout is the measurementof the rateof deposition and the cumulative deposit per unit area. For this purpose, three types of samples are currently used: soil, pot or funnel, and gummedfilm. There can be no absolute sampling procedure for fallout deposition because the deposition in a given situation will be influenced by the type of surface. However, the collection performance of the gummedfilm has been studied in relation to collections by pots to permit some basis of comparison. In earlier reports it has been shown that the gummedfilm, under conditions of moderate rainfall in a temperate climate, yields fallout samples with an over-all efficiency of about 63 per cent compared with the values from high-walled pots. In regions where muchof the fallout occurs with snow, the gummed film method may grossly underestimate the true fallout values. Despite this objection the gummedfilm technique has proved desirable because of the simplicity with which daily samples can be accumulated from a large number of widely scattered locations. Since late 1954 the computation of Sr® from the total beta activity of the gummed film samples has becomeincreasingly difficult because the computed values are sensitive to the assumed age of the debris. The accumulation of long-lived fission products in the stratosphere and the greater frequency of weapons tests has greatly complicated the problem of assigning 8