enium was determined in separate aliquots vy the standard perchloric acid distillation method and by subsequent reduction to ruthenium metal by magnesium powder. Chemical yield factors were determined and applied to the results of all analyses except barium and strontium-calcium. Spiked samples prepared by mixing appropriate carriers and cor- responding radioisotopes were pun concurrently with samples. The results are shown in Table 18 as percent of total recovered activity. Total activity recovered varied from 60 to 100 per- cent of total activity in the aliquot of sample solution used, as determined by plating and counting triplicate one ml-aliquots of the solution. Absorption curves were made of each fraction separated from the Rojoa dredged sand and in each case showed the energy characteristic of the particular isotope separated. The curve of calcium-strontium shows that about three fourths of the activity has the energy corresponding to calctum45. one fourth may be sr90 | ¥9° and sr89, The remaining These mass absorption curves and decay curves for the same fractions are presented in Pigures 15 and 16. 4.9 Absorbed and Surface Contamination In a discussion of results, the path of the radioactive materials to the tissue and the source from which they are taken into the organism are important considerations. the individual organism is being considered, - B82 - If injury to the proximity of