can be distinguished from the background caused by Comptons of higher energy radionuclides. In Figure 1 is presented a spectrum of iodine, separated from an irradiated blood sample, which demonstrates the high degree of decontamination achieved by this method. Isolation of lZ8Ifrom urine samples is equally evident from spectral data. This fulfills onc prcrrquis:te for R sensitive method. In addition this procedure has a radiochemical yield of >99% and can be performed in less than 5 minutes. Therefore, this technique appears to offer the maximum sensitivity that can be achieved through use of activation analysis and gamma spectrometry for l P 8 I . The spectrum in Figure 1 was obtained during the analysis of a sainple of serum that contained 58 ng of iodine. As little as 4 ng of iodine, irradiated and measured under the same conditions, would have been sufficient to yield lZsI activity equal to that of the background which is essentially due to 38Clcontamination. The high decontamination that is attained by this procedure also permits accurate measurements of iodine at normal concentrations in biological fluids with a single-channel analyzer, thereby reducing equipment cost and facilitating data reduc-
tion. The background, primarily W l Compton, is prohibitively large only when the concentration of iodine is
