2e2 High Altitude Sampling A series of high altitude samples have been taken for radio- chemical analysis starting late in 1956. The samples are carried to altitude by balloons and an attempt is made to obtain total volumes of approximately 1,000 standard cubic feet. Four sampling sites are used: Minneapolis, Minnesota (changed to Sioux City, Iowa in August 1958); San Angelo, Texas; the Panama Canal Zone; and Sao Paulo, Brazil. An attempt is made at each location to obtain a sample monthly at each of four nominal altitudes. In addition to the difficulty of controlling sample flights at altitude for the required length of time, a mmber of samples are not recoverable or are otherwise lost. than 16 samples per month are usually available. Therefore, fewer The detailed data on completed samples taken from November 1956 through June 1958 are given in Table 9. All the completed data are presented in this report since several corrections and recalculations have been made due to interelaboratory calibrations. Therefore the C837, cel and Cs137/sr90 ratio will not correspond to previously published data. - 57 -