Detection systems for the low-level radiochemical analysis of iodine-131, iodine-129, and natural iodine in environmental samples

A procedure based on chemicsl separation techniques and activation anslysis was developed for the sequential analysis of low levels of /sup 131/I, / Sup 129/I, and natural iodine in environmental samples. The iodine is first separated from the samples by oxidation. The separated iodine is then counted by low-level, beta-gated gamma spectrometry for the measurement of /sup 131/I. The chemical yield for the separation is measured by means of /sup 125/I tracer. Activation analysis is used for measurement of the separated natural iodine (/sup 127/I) and /sup 129/I. The natural iodine is estimated from either the /sup 126/ I or /sup 128/I activity produced in the sample; the induced /sup 130/I is used to estimate the /sup 129/I concentration. The measurement of /sup 130/I at low levels requires specialized counting methods. Interfering activities that may be present in the irradiated sample include /sup 125/I, /sup 126/I, short-lived fission-product iodine activities produced by activation of uranium impurities, and /sup 82/Br from bromine impurities. Since /sup 130/I decays with several coincident gamma rays, multiple gamma coincidence counting techniques can be used to reduce background and discriminate against interfering activities. Severail three- and four-segmented NaI(Tl) detectors were used for these measurements and compared with other detector systems. The sensitivities for different coincidence counting modes were compared for several of the detector systems. Detection sensitivities achieved for /sup 131/I and /sup 129/I are 0.02 dpm and 10/sup -6/ dpm, respectively. Meaeurements have been made of iodine radioactivity in the environment at concentrations below the limits established for radiation protection purposes. (auth) Twelve papers were presented at the symposium and separate abstracts have been prepared for seven of them. Five of the papers were previously abstracted for NSA and appeared as 26: 25164