Developments toward the measurement of I-129 in lignite

The concentration of the long-lived radioisotope 129I was determined in two Austrian lignite samples through 129I/127I isotopic ratio measurement by AMS, and through a measurement of the total iodine content with an ion-selective electrode. In addition, the uranium concentration of the samples was measured by α-spectrometry. From the mean values of the uranium concentrations the steady-state concentration of 129I in lignite was calculated; the 129I concentrations derived from the measured 129I/127I ratio and the total iodine content, however, were much higher than expected, clearly indicating that lignite does not represent a closed system for 129I. The observed high ratio in the sample from the surface mine suggests the presence of anthropogenic 129I, while the source for the high 129I concentrations in the subsurface lignite is the addition of fissiogenic 129I either from the lignite itself (from layers with much higher U content than in the samples investigated) or from nearby geological formations rich in uranium.