levels to infer the operational history of nuclear facilities.
Similar types of analyses have been performed on interdicted
nuclear materials for nuclear forensic purposes, e.g., Kristo
4
and Moody et al.
5
The IAEA Department of Safeguards has
identified “age determination of U and Pu relevant to the
origin of nuclear materials” to be a “top priority R&D need”.
6
For decades, bulk analytical techniques have been used to
determine dates for the purification or manufacture of nuclear
material using the decay of radioisotopes, such as U and its
decay products, e.g.,
234
U–
230
Th–
226
Ra and
235
U–
231
Pa–
227
Ac.
Model ages can be constructed by comparing the ratio of
decay products to parent radioisotopes using their character-
istic decay rates, under the assumption that the chronometers
were initially “reset” from material processing, i.e., only parent
isotopes were present at the time of material production.
Incomplete purification of decay products would bias these
analyses, resulting in artificially older model ages. Recently,
the National Institute of Standards and Technology (NIST)
extended the application of age dating using the
234
U–
230
Th
chronometer (t
1/2
= 245.6 ka) to the regime of individual U
microparticles using Large-Geometry Secondary Ion Mass
Spectrometry (LG-SIMS).
7
Challenges associated with the ana-
lyses of trace isotopes in atom-limited microparticles have
long been acknowledged, highlighting the need for continued
metrology and reference material development.
7–15
Several important factors impact the accuracy and precision
of U particle age dating analyses by LG-SIMS.
7,10
One set of
factors regards intrinsic sample attributes, such as the enrich-
ment level, particle mass, and material age. Generally, the
higher the
234
U enrichment (which is often correlated with
235
U enrichment), the larger the sample mass, and the older
the material, the more
234
U and
230
Th atoms will be available
to analyze, which increases the relative precision of a measure-
ment. Other factors are instrumentation and analysis protocol-
related, including the ion yield and instrument transmission,
detector background rate, measurement duty cycle per isotope,
† Electronic supplementary information (ESI) available. See DOI: https://doi.org/
10.1039/d5an00249d
a
Materials Measurement Science Division, National Institute of Standards and
Technology, Gaithersburg, MD, 20899, USA. E-mail: evan.groopman@nist.gov
b
Pacific Northwest National Laboratory, Richland, WA, 99354, USA
c
Savannah River National Laboratory, Aiken, SC, 29808, USA
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