Ayako Okubo

Round-robin 230Th–234U age dating of bulk uranium for nuclear forensics

In an inter-laboratory measurement comparison study, four laboratories determined 230Th–234U model ages of uranium certified reference material NBL U050 using isotope dilution mass spectrometry. The model dates determined by the participating laboratories range from 9 March 1956 to 19 October 1957, and are indistinguishable given the associated measurement uncertainties. These model ages are concordant with to slightly older than the known production age of NBL U050.

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.

Rapid collection of iron hydroxide for determination of Th isotopes in seawater

This work introduces a novel method of recovery of iron hydroxide using a DIAION CR-20 chelating resin column to determine Th isotopes in seawater with a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). Thorium isotopes in seawater were co-precipitated with iron hydroxide, and this precipitate was sent to chelating resin column. Ferric ions in the iron hydroxide were bonded to functional groups of the chelating resin directly, resulting in a pH increase of the effluent by release of hydroxide ion from the iron hydroxide. The co-precipitated thorium isotopes were quantitatively collected within the column, which indicated that thorium was retained on the iron hydroxide remaining on the chelating column. The chelating column quantitatively collected (232)Th with iron hydroxide in seawater at flow rates of 20-25 mL min(-1). Based on this flow rate, a 5 L sample was processed within 3-4 h. The >20 h aging of iron hydroxide tends to reduce the recovery of (232)Th. The rapid collection method was successfully applied to the determination of (230)Th and (232)Th in open-ocean seawater samples.

Uranium age-dating using in-situ isotope ratios by thermal ionization mass spectrometry for nuclear forensics

The model dates of two enriched uranium materials were determined using a new method for nuclear forensics investigation. In this method, without spike addition, the 230Th/234U ratio was calculated from the measured ratios of 230Th/234Th and 234U/238U and from calculated 234Th/238U ratio in secular equilibrium. The model date obtained for the low-enriched uranium material was in agreement with the known production date. For the highly enriched uranium material, a more recent model date than the known production date was obtained. The 234U interference on 234Th counting in thermal ionization mass spectrometer measurement was suspected as a potential cause.