Ni-59 determination by measurement of annihilation energy

Abstract

Radioactive waste is subject to regulations regarding its inventory, transportation and final deposition. Such standards require the knowledge of the tailing contents in a way that is possible to accommodate them in a repository capable of containing their radiation completely. In this study a methodology was established for determining the concentration of 59Ni using the annihilation energy (0.511 MeV) between a positron from its + emission, and an electron that is widely present in matter. To ensure the reliability of the methodology, the area of the annihilation peak was compared to 59Ni Kα and Kβ x-ray peaks. To make this method viable the separations of Ni from the other components of the sample was necessary. This was done by using dimethylglyoxime (DMG) for Ni precipitation. Of all the Ni radioisotopes only 59Ni have a half-life longer than a few days, so that 59Ni can be determined without radioisotopical interferences. After precipitation with DMG, the substrate was vacuum filtered on filter paper, using an apparatus to preserve the geometry of the precipitate in different samples. The 59Ni precipitate was then counted in an extended range gamma spectrometer and the 511 keV peak compared to the Ni x-rays in order to verify the reliability of the method.