Donald G. Graczyk

Application of mass spectrometric isotope dilution methodology for 90Sr age-dating with measurements by thermal-ionization and inductively coupled-plasma mass spectrometry

Application of an isotope-dilution method for determining 90Zr and 90Sr in a 90Sr source material spiked with 86Sr and 92Zr is described. A miniature gas pressurized extraction chromatography (GPEC) system with a column containing Eichrom Sr Resin™ was used for separating the elements so isobaric isotopes could be measured by mass spectrometry. Zirconium was rinsed through the column with 3 M HNO3/trace HF and strontium was eluted with 1% acetic acid. Two mass spectrometric techniques, inductively coupled plasma mass spectrometry (ICP-MS) and thermal ionization mass spectrometry (TIMS), were used for measuring isotope ratios. Data were obtained with 90Sr from a blood-irradiator source. Results from the TIMS measurements gave a decay time of 45.16 ± 0.26 years, and those from the ICP-MS gave 45.24 ± 0.20 years (uncertainties are expanded uncertainty, k = 2). Quadrupole ICP-MS is preferable to TIMS in this application if the ICP-MS data are suitably corrected for non-linearity and mass discrimination.

A nuclear forensic method for determining the age of radioactive cobalt sources

An analytical procedure for determining the relative amounts of 60Co and its 60Ni daughter in a radioactive cobalt source by means of chromatographic separation and radiometric and mass spectrometric detection was developed, optimized and assessed through two round robin exercises for nuclear forensic investigations. Solid phase extraction (EXC) using Ni resin (Eichrom) and ion exchange (IEC) using Dowex-1X8 (Acros Organics) chromatographic approaches were considered for separating Co and Ni. Decontamination factors of 25 and 2.8 × 106 were measured for EXC and IEC, respectively. Based on those results, only the IEC option was pursued. The effects of particle size, mass of resin, and degree of cross-linkage for decontamination performance were assessed, and the loading/eluting conditions were optimized. Canadian (CNSC, RPB, UL, RMC, AECL) and American (ANL) laboratories participated in two round robin exercises designed by the National Research Council of Canada to determine the suitability and limitations of the proposed methods. Age determination for freshly irradiated sources (<1 a) and for sources with high Ni content was challenging for the laboratories. Nevertheless, age estimates were obtained with sufficient accuracy for nuclear forensic purposes.

Age-dating methodology for 137Cs ceramic sources

Age-dating of 137Cs ceramic sources is shown to be a viable technology for nuclear forensics investigations. The 137Cs age-dating method in general, however, could be substantially improved by using radiometric rather than ICP-MS measurement of the 137Cs isotope and by refining the Cs/Ba separation process. With these improvements, uncertainty in the age of a 60-year-old source decreases from 1.35 to 0.68 y.

An alternative separation procedure for 90 Sr age dating using DGA Resin

The likelihood of an attack by a terrorist organization using a radiological dispersal device (RDD) is much higher than that of an attack with an improvised nuclear device or true nuclear weapon, as much less technical expertise is required to build an RDD. Consequently, there has been an effort to develop methods for age-dating radiological sealed sources in recent years. One such procedure, described by Steeb et al., is used for determining the age of 90Sr sources. That procedure utilized a rather expensive extraction chromatography resin and was based on an uncommon apparatus with limited sample capacity for the separation step. The procedure also left the Zr fraction contaminated with the radioactive 90Y daughter nuclide. The present work investigates using an alternative separation scheme that utilizes a less costly resin in a widely available column configuration and results in the isolation of 90Sr’s stable granddaughter, 90Zr, without 90Y contamination. This allows the zirconium quantification to be done with a mass spectrometer outside the radiological environment and increases the number of instruments capable of making the measurement, which could allow measurements to be made more quickly.