Age determination of plutonium material in nuclear forensics by thermal ionisation mass spectrometry

Abstract

Age is a key parameter when deducing the history of plutonium material, i.e. the plutonium produced in the nuclear reactors. This is of vital importance, when a smuggled plutonium sample has been seized and the origin has to be determined. A methodology is described which allows accurately to determine the age of plutonium material by thermal ionisation mass spectrometry using independent parent/daughter relations. This has been demonstrated for Reference Materials of known ages as well as for real samples. The already established method using gamma spectrometry is compared to this.

Nuclear Forensic Science: Analysis of Nuclear Material Out of Regulatory Control

“…If concordant model ages are determined with multiple radiochronometers, then the model age may be interpreted as the production age of the material with a high degree of confidence. Concordant model ages are observed in many uranium and plutonium reference materials that are commonly analyzed for validation of analytical methods (Wallenius & Mayer 2000, Nygren et al 2007, Shinonaga et al 2009, Eppich et al 2013, Sturm et al 2014). However, reference materials are produced with great care in controlled environments; real world samples produced in industrial facilities may not necessarily be expected to exhibit such ideal behavior.…”

“…The model age is best utilized as a predictive signature for nuclear materials that are highly purified, such as U or Pu metals and oxides (e.g., Wallenius & Mayer 2000, Wallenius et al 2002, Williams & Gaffney 2011. For materials that are less pure, such as UOCs, or samples for which the source material was purified much earlier than the sample production date, the model age is expected to be slightly to significantly older than the production age (Hanlen 2011.…”

“…Gamma spectrometry requires large sample masses, however, and is best suited for high-activity samples; the method generally is less precise than mass spectrometry or alpha spectrometry methods. Gamma spectrometry can be used with bulk uranium materials (Moorthy & Kato 1997;Nguyen 2005;Nguyen & Zsigrai 2006a,b;Ramebäck et al 2008) as well as bulk plutonium materials (West & Sherwood 1981, Wallenius & Mayer 2000, Keegan & Gehrke 2003, Nguyen 2006. Alpha spectrometry is a destructive analytical method that requires chemical purification prior to analysis and can be used to measure most U-series and Pu-series nuclides (Moorthy & Kato 1997, Wallenius et al 2002, Chen et al 2009), although it is most commonly used for analysis of highspecific-activity nuclides that are present at low concentrations in bulk uranium and plutonium materials.…”

“…These methods are capable of the highest-precision analyses for most uranium and plutonium radiochronometry systems. Because of their higher sensitivity relative to counting methods for most radionuclides, mass spectrometry methods can be used to analyze samples that are comparatively much smaller or younger and therefore have very low total amounts of decay products (e.g., Wallenius & Mayer 2000, Wallenius et al 2002, Eppich et al 2013, Gaffney et al 2015, Kayzar & Williams 2016, Varga et al 2015. Isotope dilution methods are used for quantification of parent and progeny isotope abundances by TIMS or ICP-MS. For ICP-MS and TIMS, the analyte must be purified from sample matrix, whereas SIMS analysis utilizes bulk sample.…”

REIMEP-22 inter-laboratory comparison: “U Age Dating – determination of the production date of a uranium certified test sample”

“…The "age" of a nuclear material refers to its production date, i.e. the time elapsed since the last chemical separation of the daughter nuclides from the parent U or Pu radionuclides [3,4]. During its production, the nuclear material is chemically purified from impurities including radioactive decay products.…”