Sang Ho Lim

Combinatory use of time-of-flight secondary ion mass spectrometry (SIMS) and sector-field SIMS for estimating elemental and isotopic compositions of nuclear forensic samples

This paper describes an alternative approach to nuclear forensic analysis by employing time-of-flight (TOF) SIMS and sector-field (SF) SIMS collaboratively. A set of synthetic samples consisting of UO2 and other metal (Gd, Mo or Zr) oxide was analyzed by the both instruments. With TOF–SIMS, qualitative elemental analysis was possible in U-dominant or low-U samples. TOF–SIMS was also useful for investigating potential isobars for U isotopes induced by the other metals. To avoid the isobaric interferences, particle search and major U isotope analysis using SF–SIMS were performed by measuring UO2+ instead of U+, and thus the effects of interference were reduced.

Validation of Bulk Analysis with Simulated Swipe Samples Containing Ultra-Trace Amounts of Uranium and Plutonium Using MC-ICP-MS

Suitable analytical procedures for the bulk analysis of ultra-trace amounts of uranium and plutonium have been developed using multi-collector inductively coupled mass spectrometry (MC–ICP–MS). The quantification and determination of the isotopic ratios of uranium and plutonium in three simulated swipe samples, a swipe blank, and a process blank were performed to validate the analytical performance. The analytical results for the simulated swipe samples were in good agreement with the certified values, based on the measurement quality goals for the analysis of bulk environmental samples recommended by the International Atomic Energy Agency (IAEA)

The application of radiochronometry during the 4th collaborative materials exercise of the nuclear forensics international technical working group (ITWG)

In a recent international exercise, 10 international nuclear forensics laboratories successfully performed radiochronometry on three low enriched uranium oxide samples, providing 12 analytical results using three different parent-daughter pairs serving as independent chronometers. The vast majority of the results were consistent with one another and consistent with the known processing history of the materials. In general, for these particular samples, mass spectrometry gave more accurate and more precise analytical results than decay counting measurements. In addition, the concordance of the 235U–231Pa and 234U–230Th chronometers confirmed the validity of the age dating assumptions, increasing confidence in the resulting conclusions.

Overall approaches and experiences of first-time participants in the Nuclear Forensics International Technical Working Group’s Fourth Collaborative Material Exercise (CMX-4)

The Fourth Collaborative Material Exercise (CMX-4) of the Nuclear Forensics International Technical Working Group (ITWG) registered the largest participation for this exercise in nuclear forensics, with seven of the 17 laboratories participating for the first time. Each of the laboratories had their strategic role to play in its respective country, analyzing real-world samples using their in-house resources. The scenario was fictitious but was thoughtfully crafted to engage participants in nuclear forensic investigations. In this paper, participants from five of the first-time laboratories shared their individual experience in this exercise, from preparation to analysis of samples.

Improvement in the chemical separation and determination of uncertainties for bulk analysis of Pu isotopes at ultra-trace levels by using MC-ICP-MS

Improved bulk analysis based on extraction chromatography and systematic evaluations of uncertainties of plutonium isotopes at ultra-trace levels in environmental swipe samples are presented. In the modified method based on a single column system using UTEVA resin for MC-ICP-MS, hydrogen peroxide was introduced to obtain pure plutonium isotopes from chemical separation by removing excess organic-based reducing reagents. We confirmed that hydrogen peroxide effectively decomposed the reducing reagents characterized by UV–Vis absorption spectroscopy and the peak fluctuations were significantly reduced. To examine the reliability of analytical performance, we systematically evaluated the combined uncertainties during the overall chemical procedures using simulated samples containing Pu reference materials.

A simple correction method for isobaric interferences induced by lead during uranium isotope analysis using secondary ion mass spectrometry

Isobaric interference is a major limitation of secondary ion mass spectrometry. We developed a simple correction method for polyatomic mass interferences from lead in isotope ratio measurements of uranium. Lead-generated isobars were measured to determine their formation rates relative to lead isotopes. The rates were used to mathematically subtract the isobar contributions from the signal intensities in the uranium mass range. The correction method was successfully verified using mixed uranium-lead samples (oxide powder and solution-dried residue).

Improvement of bulk analysis technique for uranium in environmental samples with high thorium contents

Multi-channel inductively coupled plasma mass spectrometry and multi-collector ICPMS were used for effective bulk analysis techniques of environmental samples with high thorium contents. A desolvating nebulizer system was adopted to reduce the 232ThH/232Th formation rate, which was evaluated using U/Th mixture solution. A UTEVA-based chemical separation method, with adjustment of the separation parameters for uranium and thorium, allowed for effective separation of uranium. The separation yields for uranium and thorium were estimated from the elution profiles of various U/Th mixture solutions. Bulk analysis of uranium in simulated samples with high thorium contents was performed to validate the improved analytical procedures.