Oxygen Isotopic Measurements by Secondary Ion Mass Spectrometry in Uranium Oxide Microparticles:  A Nuclear Forensic Diagnostic

Abstract

To exploit oxygen isotopic measurement by SIMS as a diagnostic tool in nuclear forensics, the magnitude and reproducibility of 0-isotope instrumental mass discrimination for O-isotope standards in the SIMS laboratory at the Institute for Transuranium Elements has been evaluated. Tests for matrix-dependent discrimination effects on three different O-isotope standards with substantially different matrix compositions have been performed. The results were checked by an interlaboratory comparison of O-isotope discrimination with those obtained in the SIMS laboratory at the Lawrence Livermore National Laboratory on two standards. The results from the two laboratories are in very good agreement, indicating statistically indistinguishable instrumental mass discrimination factors for 180/160 ratios on the Cameca 6f and 3f, when the analyses are performed under the experimental conditions described. The 2sigma(mean) uncertainties of these factors are in the range of 0.3-0.9%. In accordance with the tested methodology, 0-isotope compositions were measured in three particulate uranium oxide samples of nuclear forensics interest.

Isotope ratio measurements by secondary ion mass spectrometry (SIMS) and glow discharge mass spectrometry (GDMS)

“…Once localised, the particles of interest were then individually analysed with a focused ion beam scanned over an area of 3 m × 3 m. Use of optical encoders circumvented the poor reproducibility of the commercial sample stage and positioned the beam within 1 m of a predefined point. The statistical error on 28 Si and 29 Si using the peak-jumping mode was 2.6 and 2.7‰, respectively, while the intrinsic uncertainty remained within 3‰/amu for Si isotopic ratios. The automated analysis typically processed 300 particles per day, depending on the number of grains per area and their size.…”

“…Experiments on crystal growth and silicon isotopic ratio of the silicon crystal have been precisely determined using a SIMS with multicollectors IMS-1270 SIMS [23,24]. The 30 Si/ 28 Si ratios have been determined and isotopic variations in the range of 1‰ were observed along the growth direction of the crystal. A defocused Cs + primary beam was restricted to 40 m in diameter by a circular aperture to obtain a homogeneous primary beam of about 3 nA.…”

“…Negative secondary ions of silicon were detected after being uniformly sputtered by a primary beam with a total impact energy of 20 kV. The secondary 28 Si, 29 Si and 30 Si ions were simultaneously detected without energy filtering and using three Faraday cups (FC) of the multicollection system. The internal precision and accuracy in the 30 Si/ 28 Si ratios (2σ) were better than 0.1 and 0.2‰, respectively.…”

“…As for Pu, the isotopic ratio 239/240 was determined and resulted in agreement with the results from thermal ionisation mass spectrometry. The same authors have measured 18 O/ 16 O isotope ratio by SIMS in uranium oxide microparticles [28] for nuclear forensic diagnostic. The same group [51] has exploited SIMS, in combination with other instrumental analytical techniques, for the characterisation of soil particles bearing depleted uranium (DU).…”

Tracing the Origin of Diverted or Stolen Nuclear Material through Nuclear Forensic Investigations

“…An intensive study was performed using three mass spectrometric techniques, TIMS, SIMS and GDMS. In particular the TIMS and SIMS results reveal significant differences between UO 2 pellets produced in different locations [31,32,33].…”