1.1 POT FALLOUT COLLECTIONS The Health and Safety Laboratory (HASL), AEC, has set up a network of fallout collection stations using stainless-steel pots with an open area of approximately 1 sq ft. The sampling period is one month, and the pot residues are collected and are analyzed for Sr®. The original collecting station in New York has been in operation since the beginning of 1954, and other stations have been added where laboratory facilities are available for transfer and shipment of the samples. This operation is carried out through the cooperation of scientists at the indi- vidual stations. The present network consists of 13 stations in the continental United States and 17 stations outside the continental United States. The data for New York City are shown in Table 1 and Fig. 1. The data for other United States stations are given in Table 2. Data for stations outside the continental United States are given in Table 3. (Not all the 30 stations mentioned have submitted samples in time for this report.) Fallout Monitoring by Other Countries, A number of other countries are reporting radiochemical analyses on pot type samples in submissions to the United Nations Scientific Committee on the Effects of Atomic Radiation. Although several countries are now producing reliable results, the only country, other than the United States, that has released any large number of Sr?” analyses is the United Kingdom. Their results are reprinted in Part 4 of this report. 1.2 PRECIPITATION COLLECTIONS FOR RADIOSTRONTIUM AND RADIOBARIUM The collection and analysis of individual rainfalls was begun at the University of Chicago andlater at the laboratories of Nuclear Science Corporation, Pittsburgh, Pa. The latter collection, the most complete set of individual collections, was begun in February 1955. These collections are carried out in duplicate with open vessels having an area of about 2.6 sq ft. They are exposed continuously, and, if a period of one week occurs without rainfall, the vessels are washed out and the residue is analyzed. The cumulative value, therefore, represents the total fallout since the beginning of the collection period. In addition to Sr™ measurements samples taken since the end of August 1957 have also been analyzed for Sr®™ and Ba’. These analyses can indicate the relative age of fallout debris in a qualitative way. The ratios of the three isotopes are subject to some variation from fractionization and do not follow the theoretical ratios obtained from thermal neutron fission suf- ficiently well to give exact ages of the radioactive material. This situation is complicated even more by the fact that current fallout is a composite material resulting from many indi- vidual weapons tests. The ratios, however, do give a reasonable indication as to whether a particularly high fallout value is probably fresh tropospheric material or older stratospheric material. The data for both types of analyses are given for Pittsburgh in Table 4 and areplotted in Fig. 2. The earlier Chicago rainfall samples are recorded in Table 5. 1.3 Sr® IN SOIL Strontium-90 analyses of soils have been made for several years to study geographical distribution and the amountof isotope available for uptake by plant systems. In both cases the measurements can be considered to be for monitoring purposes. In the geographical studies it is desirable to.measure all the sr* present in the soil per unit area regardless of the depth of penetration or the composition of the soil. Such measure- ments have been made in this country on soils from the United States and on samples collected in other countries. With the exception of the United Kingdom, other countries are just beginning soil analysis programs; hence foreign samples analyzed in the United States have been for the purpose of documentation until the various countries obtain their own data. For uptake studies it ig desirable to measure the Sr®* that is available to the plant and, in addition, to relate this to the available calcium in the soil. Comparative studies have shown that the results from the two techniques are not interchangeable, and the data reported here are exclusively those designed for revealing geographical distribution. 6