five titrations. The effect of trace amounts of oxygen is clearly shown by this lower result.This procedure has been used for the determination of plutonium in high purity plutonium metal samples, alloys with noninterfering metals such as iron, and nitric or hydrochloric acid solutions. About 15 determinations may easily be performed per day. Using an automatic heating-cycle controller for the two evaporations with perchloric acid, the operator time per determination should be greatly reduced. After the 31, 1138 (1959).
88C1third order approximation curve are used. The shape of the peak fractions is checked with normalized Gaussian curves.The peak fraction method was chosen, because it permits work without a catalog of standard spectra and gives better results than spectrum stripping in the lower energy region of composite spectra.Curve smoothing can show up peaks in statistically poor spectra and smaller peaks in the vicinity of large ones.Comparison with normalized Gaussian curves eliminates statistical fluctuations and Compton edges, but not Gaussianshaped peaks like backscatter peaks.Results have been found to be better than those obtained by the application of Covell's method with similar width of the calibrated peak fraction. However, it should be noted that the width is fixed by the proposed method, while Covell's method leaves the choice of the most suitable width open. The method is applied in this department for the simultaneous determination of trace elements in biological material and the program (Algol 60) is available on request.
ACKNOWLEDGMENTThe authors thank Professor Gilbert Forbes for his support and encouragement during the course of this study. They also thank the Scottish Research Reactor Centre and the Computing Department of Glasgow University for the use of equipment and facilities.
b Iodine-131, as iodide ion, is separated from other milk constituents by ion exchange on a silver chloride column. After elution as iodic acid from the column by acidified chlorine water, the eluate can b e directly analyzed by gamma counting. The time required to analyze a 1-liter sample by this method is approximately 30 minutes (exclusive of counting time). If beta counting or increased sensitivity is required, the iodine is subjected to two oxidation-reduction solvent-extraction cycles and finally precipitated as silver iodide prior to counting. Chemical and radiochemical yields for both added and metabolized iodide are identical, and are 90 to 95% for homogenized milk and 85 to 95% for raw milk.Total time for the complete procedure (exclusive of counting time) is approximately 2 hours for a single sample. Less than 2 picocuries of total iodine-131 can b e detected in 1 liter of milk, using the complete procedure. The application of the procedure to other materials is discussed.O D I N E -~~~ is an important radio-
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