Iodine analysis of biological samples by neutron activation of 127I, with scintillation counting of cerenkov radiation

The naturally occurring isotope, 127I, has been measured by neutron activation, postirradiation extraction of 128I plus 127I (added carrier), and timed scintillation counting of aqueous solution utilizing Cerenkov radiation. With extrapolation of the counts to zero time (end of irradiation) and measurement of chemical recovery by weighing of precipitated AgI, there are about 300 cpm above background per nanogram of I, in the range of 0–30 ng. The precision for samples of NH4I is ±2.6% coefficient of variation. The accuracy is good when standards, rat liver mitochondria, or thyroxine solutions are measured both by activation analysis and by a chemical method. The use of Cerenkov radiation simplifies sample preparation, eliminates the need for a γ- or β-spectrometer, and acts as an energy band-pass.