Strontium-90 in dairy milk 1975

The present report is the tenth in a series of periodical reports dealing with the measruement of strontium-90 in dairy milk in Sweden. The measuring programme includes nine dairies so chosen that they are representative of both the milk production and the geographical distribution. When calculating the averages presented in Table 2 and Figure 1 the small mountain dairy Taernaby was excluded. Investigations in 1969 and in 1970 showed that the arithmetic mean of the remaining eight dairies is in good agreement with an average for the whole country weighted for the analysis performed during 1975. A milk volume of about 700 ml is dried and ashed. The ash is dissolved in 1M HCl and yttrium is extracted from the solution with 5 percent HDEHP in toluene. The yttrium is backextracted into 3M HNO3 and precipitated as oxalate. The low-β counter used for the measurements has a background of 0.57+-0.05 cpm and a counting efficiency of 40 - 45 percent depending upon the sample thickness. The overall analytical error is less than 10 percent (1 sigma). (author)