Measurement of 55Fe in reactor samples by an intrinsic Germanium detector

Abstract

Determination of 55Fe in reactor samples requires some care because of the low-energy x-rays emitted following decay by electron capture and the presence of 59Fe and other possible γ-ray emitting contaminants in radiochemical separations. This problem was dealt with by radiochemical separation of Fe followed by use of an intrinsic germanium detector operated at high amplifier gain to count the low-energy x-ray emissions to quantitate 55Fe. Separation of this important nuclide in reactor samples was by solvent extraction using triisooctylamine in xylene. Low-energy photon counting was done with a high gain setting and a 3 μs shaping time, which provided accurate quantitation without interference of 59Fe and other potential contaminants, which were either removed by separation or discriminated against by the counting procedure. Iron-59, either present in the sample or added as a spike, was used as a tracer for determining radiochemical yield, which was about 70%. The lower limit of detection was found to be 80 pCi/g based on a 10 g sample and a 5 min counting time.