26 V. Sr90 Content of Foreign Soils The results of sr?0 analyses for all foreign soil samples assayed since the publication of Chicago Sunshine Bulletin Ne. 11, December 1, 1955, are summarized in Table 6, Results for earlier foreign soil measurements, which include most of the data for soils collected during and prior to tne Spring of 195h, have been reported by W. F, Libby. The results reflect the substantial increase in the world-wide distributicor of Sr? fallout following the CASTIE tests, The increase is particularly striling for the southern hemisphere samples which show about an order of magni- tude increase in the Sr90 soil content for the period from Svring 195 to January 1956, . Two of the South American samples (Beltsville #5656 from Lima, Peru and #5647 from Antofagasta, Chile) are representative of areas of very low rainfall, Comparing their results with those for the Sao Paulo, Brazil and Anto- fagasta, Chile soils indicates a striking dependence of the fallout on rainfal’. The result for the Brawley, California soil (CL 1127, reported on page hh, this renort), which shows €0,8 Sunshine Units, corresvonding to $1.2 millicuries of gr 90 per square mile, is equally convincing in this resnect, It would apvear that, except within several thousand miles dovmwind of test areas where large particles of dry debris may fall out directly for a short period following a test shot, orecipitation must be the only important mechanism of fallout. This Cerendence can be further tested by relating the_Sr90 soil level to rainfall infornation for areas remote from test sites. The latitude dowtonce of fallov.. pointed out by '. F, Libby, 3 should be taken into account wien such a correlation is attemoted, 57